Study to Predict the Electromagnetic Interference for a typical house in 2010

By Anita Woogara  (Bristol University)  in co-operation with the Smith Group at Guildford.

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Contents

1. Introduction

1.1 General
1.2 Objectives
1.3 Content of the report

2.1 Background
2.2 Susceptibility/ immunity
2.3 Regulations and standards
2.4 Testing for electromagnetic compatibility
2.5 Solutions
2.6 General public awareness

3.1 Natural interference sources
3.2 Power supply irregularities
3.3 Electrostatic discharge
3.4 Household wiring
3.5 Domestic appliances
3.6 Baby monitoring
3.7 Electronic wheelchairs
3.8 Hearing aids
3.9 Mobile phones
3.10 Hobby radio
3.11 Automobiles
3.12 Aircraft
3.13 Railway systems
3.14 Trams
3.15 Nuclear electromagnetic pulse

4.1 General
4.2 Teleworkers
4.3 Computing environment
4.4 Home networking
4.5 Phones
4.6 Entertainment
4.7 Kitchen appliances
4.8 Garden equipment
4.9 Health
4.10 Transport
4.11 Change in environment
4.12 Alternative ideas

5.1 Summary of today’s problems
5.2 Future trends – Change in culture
5.3 Change in electronic equipment
5.4 Change in communication between devices
5.5 Lack of communication between manufacturers and users
5.6 Old environment
5.7 Lack of communication between installers and manufacturers
5.8 Suitability of regulations and testing procedures
5.9 Actions to be taken to reduce future problems
5.10 Further work

A.1 Digital versus analogue
A.2 Sharing frequencies
A.3 Models for separate devices

Top

1. Introduction

1.1 General

This report has been prepared by Anita Woogara, a vacation student on a placement with The Smith Group, on behalf of the Radiocommunications Agency.

The main objectives for this project consist of predicting the Electromagnetic interference (EMI) situation in a typical household in 2010 with the aim of seeing if there is anything that can be implemented now which would reduce or prevent problems later.

For the purposes of this project a typical house means a two floor semi-detached house in the suburbs of a major city. So this house has to deal with a fair amount of traffic from the roads, airports and possibly from underground trains. The following items among others are considered:

medical devices such as hearing aids, pacemakers, electronic wheelchairs, etc;
automobiles as they are started near the house;
traffic as discussed above;
garden equipment;
overhead lighting;
electronic toys;
security systems;
electronic tagging.

This report is organised as follows:

Section 2 (Electromagnetic compatibility (EMC) ) introduces the concepts of electromagnetic compatibility and interference, why they need to be considered and how interference manifests itself. The present regulations are looked at and any exceptions to these are noted. The ways, in which companies test for EMC are examined, especially the options open to smaller companies. Typical solutions to EMI are also examined, those available to the customer and techniques used by the manufacturer.

Section 3 (Electromagnetic interference in a typical house today) discusses the ways in which EMI can occur. Then a closer look is taken to sources of emissions such as: natural interference, manmade interference, nuclear electromagnetic pulses and electrostatic discharge. Susceptibility and immunity of objects is examined such as the immunity to power supply irregularities.

Section 4 (Future developments) describes future technologies and assesses the impact on EMC. As part of this task, manufacturers and other relevant organisations have been contacted. The answers provided by these companies are examined. A mention of the wilder ideas is also given and then an informed analysis follows. Finally, alternative ideas of transferring information, other than electronically, are discussed here.

Section 5 (Conclusions) presents the conclusions of the report: the implications raised and some of the actions that can be taken now to reduce problems in the future are discussed.

2. Electromagnetic Compatibility

2.1 Background

Radio waves are generally considered to be the frequencies between 9kHz and 105GHz. Magnetic fields are generated by wires carrying current. In order for this current to flow, there needs to be a potential difference and hence there is an electric field. These fields can exist in any substance including a vacuum. If these fields are strong enough they are able to affect other electrical devices. When this interaction is unwanted it is called electromagnetic interference (EMI).

EMI can manifest itself in several ways; it can range from simple annoyance to more serious problems. Some examples are shown below:

a radio broadcast transmitter audible on a telephone line;
television screens being interfered with by an electric hair dryer;
a computer screen turning blue and corrupting text due to magnetic fields from an underground train.

Interference can occur not only between unrelated devices but also between the subsystems of the same piece of equipment, for example, the monitor and the Central Processing Unit (CPU) of a PC could interfere with each other. If, as in this case, two systems have to operate together, the susceptibility of the one has to be at such a level that it is not affected by the interference created by the other; they can then be said to be electromagnetically compatible (EMC). Therefore, in order to minimise EMI it is necessary to reduce emissions and increase immunity of devices.

When assessing whether equipment can withstand a certain amount of interference it is important to define the point at which interference can be tolerated, for example, should it:

be just discernible, but tolerable;
cause a data error to occur;
cause a program error to occur;
be just short of component burn out?

The second and third options can be, to some extent, manual or self-correcting if the programmer has taken the possibility of EMI into account. The general public is unlikely to tolerate anything past this level of severity.

Continuous interference is less likely to be tolerated than short bursts of interference, because infrequent interference can be dismissed, especially if it does not last long.

The International Special Committee on Radio Interference (CISPR), a sub-committee of the International Electrotechnical Commission Council, meet and set out standards. These recommendations do not become law until the individual countries decide to implement them, this leads to incompatibilities between countries. In an attempt to unify EMC standards, the European commission introduced the European Community Directive.

Radiated electromagnetic interference can affect equipment other than that owned by the person with the interfering device. The interfering device may work perfectly while rendering someone else’s equipment completely useless. Regulations seek to minimise the risk of EMI. However, they seem to be mainly involved with protecting particular frequencies and services associated with them, rather than being concerned with increasing electromagnetic compatibility as a whole.

There are two classes for equipment to fall in:

Commercial equipment
Equipment marketed for home use

In this report we will be concentrating on class B. Below is a table showing some of the emission limits covered by the CISPR 22.

Table -1: Emission limits for Class A and Class B equipment

This table shows that the emission limits increase slightly as the frequency increases and that the emission limits placed on equipment classified for home use is more stringent than that for commercial equipment.

The European EMC Directive, 89/336/EEC, states that the apparatus shall be constructed so that:

the electromagnetic disturbance it generates does not exceed a level allowing radio and telecommunications equipment and other apparatus to operate as intended;

the apparatus has an adequate level of intrinsic immunity to electromagnetic disturbance to enable it to operate as intended.

The following relevant devices are exempt from the directive

self built amateur radio apparatus (but not Citizen Band (CB) equipment);
medical devices and active implantable medical devices (all phenomena) (now covered by the Medical Devices Directive);
electricity meters (immunity);
motor vehicle ignition systems (emissions pending the Automotive EMC Directive).

These regulations are self-certifying and the Trading Standards Committee only investigates complaints. Products found to be producing excess emissions are removed from the market.

It is expensive for small companies to have large test houses so there are a variety of options:

Join a group of similar companies in the same situation so that a test house can be financed jointly.
Use an independent test house for all EMC requirements
Use in house testing equipment.

The first option has not been well established in the UK yet. With the last two options there are problems with measurement uncertainty as there is no guarantee that a test at one facility will give the same results as an apparently similar test at another. In house testing is not always done in a controlled environment and the equipment can still be quite expensive. Staff training is also required and there is a need to keep up to date with the changing EMC requirements. Companies often combine in house testing with independent test houses in order to compare with their own standards.

Devices are only tested just before being placed on the market. Later they may emit more as the products age due to the capacitors in the filters drying out or poorly fitting microwave doors. Also if they are repaired badly.

EMI can be reduced by:

having an EMC engineer work with the designer during product design, to solve problems effectively during manufacture and to make sure that EMC problems are taken into account;

reduce interference on printed circuit boards (PCBs), as EMI can be affected by the position of the electronics;

increasing awareness in the general public and manufacturers. (An understanding of EMC will encourage the public to enquire about interference before buying electronic items. If manufacturers are educated then many problems can be solved before products are placed on the market);

reducing bandwidth. If the bandwidth is large then the probability of interference is higher.

The materials used to protect electronic equipment need to be considered very carefully, as a substance that protects at low frequencies may be useless at higher ones. Shielding can not only be effective at protecting internal equipment from external radiated emissions but also at preventing inside emissions escaping. Both these functions are important in order for products to meet EMC requirements.

When choosing what material to use for shielding, it is important to remember there are two components of electromagnetic waves: electric and magnetic. Metals need to be electrically conducting and magnetically permeable (high permeability means the metal is highly conductive to lines of magnetic force). If metal is not going to be used to shield the product and the design calls for plastic instead, it is possible to coat the plastic with metal giving a similar effect to the metal casing. The use of plastics could become more popular since the colourful iMac has been such a success. It is simple to effectively shield a closed box, although in practice this will be entirely useless, as most electronic equipment needs to be accessed in some way.

As the electromagnetic current will take the path of least resistance it will run around the outside of a seamless box but at any joint it will move to the inside surface instead and affect the electronics. The amount a hole compromises the shielding depends on the frequency of the radiation it is attempting to block. Radiation with low frequencies and long wavelengths are not affected much by small holes, however, these same holes in shielding for high frequency waves would severely affect its performance. The use of apertures for ventilation is excluded if significant attenuation of high frequency signals is required. Where there is a need for joints and seams, gaskets are often used to reduce the loss of shielding integrity.

Ventilation

Equipment running at high speeds often needs ventilation and this involves a hole in the shielding. Honeycomb vents can be used, which allow airflow and reduce Radio Frequency Interference (RFI) to a certain extent. Dust filters can also be used these perform the same task and reduce the amount of dust allowed into the device.

Viewing apertures

The need for displays compromises shielding integrity. Wire mesh can be laminated between two layers of glass or acrylic, providing an anti-reflective surface that can be used to display information and also give some continuation to the EMI shield.

Flexible shields

It is possible to produce textile EMI shields that can then be made into items such as curtains in offices or houses, which will provide an EMI shield compromised slightly by the windows.

Photonic band gaps

This technology is being researched in America but could be available in ten years. Materials are being developed which will absorb frequencies of a certain range and will be transparent to other frequencies. This could be used as effective shielding for electronic products.

Disadvantages

The disadvantages with shielding are that: It makes the product heavier; more expensive and could restrict the appearance of the device.

Interference sources within the equipment circuit or its power supply are coupled onto the power cable. Interference can also be coupled from another cable to the power cable. The resulting interference may appear as differential mode (between live and neutral, or between signal wires) or as common mode (between live/neutral/signal and earth) or as a mixture of both. Filters are used to reduce this type of interference.

It is possible to fit filters to electronic devices so that they become less susceptible to emissions and reduce unwanted radiation. Examples of filters are:

High pass filters, which can be used in the line between the television set and the antenna to prevent unwanted signals from entering the tuner. An ideal high pass filter would pass all frequencies above a certain point and nothing below it. This would prevent strong signals interfering with the reception of the television.

Low pass filters, which are used in the cable between an Amateur Radio transmitter and station antenna to suppress unwanted signals above a certain frequency.

Power-line filters, which are fitted between the AC line cord and outlet an ideal filter would pass energy at the frequency used on the power line and nothing above it.

The disadvantage of relying on filters is that they rarely cut off unwanted signals sharply and so cannot be depended upon alone.

It is possible, using error correction mechanisms, to programme software to check that it is receiving the correct information from the expected source. This is called defensive programming and would reduce the probability of the device acting on an unrelated signal. This method is used for military applications where it is important that electronic devices operate in a wide range of situations and the consequences of interference are more serious than in the domestic environment. Microsoft is presently investigating defensive tools that could be used by the consumer if problems occurred due to EMI frequently.

The disadvantage with using defensive programming is that it will require more planning during production and could reduce response times.

Although the public are aware that objects can interfere with each other, such as mobile phones and television sets, this does not seem to influence the products they buy. This is because people’s attitude towards products is heavily influenced by the media and so EMC may become a greater issue after the ‘Millennium bug’ scares have died down and consumers might ask more questions before buying electronic products.

In the future, users of mobile phones could be suing the manufacturers for causing health problems. Companies are aware that they could be accused of covering up any health problems and are very eager to provide information. It is the job of the National Radiological Protection Board (NRPB) to respond to matters that relate electromagnetic fields to health problems.

Present research is inconclusive on the effects mobile phones could have on health, however, the mobile phone companies themselves are funding most of this research and very little independent study is being done. Some research suggests that users of ‘hands free’ equipment, where the phone is clipped to the belt, causes problems for the liver and kidneys. This is likely to be because phones at waist height need to use more power to produce a reasonable signal than those near the head.

3. Electromagnetic interference in a typical house today

It is important to examine the electromagnetic interference problems that exist today and what the sources are, as these problems are unlikely to have disappeared in ten years.

Lightning can be a natural source of electrical interference. Lightning is caused when there is a build up of static charges on the clouds; this discharges in the form of a spark when a sufficient potential is reached with respect to the ground.

The current of a lightning strike can be between 3 – 200 kA, about 1% are over 100kA. This current is dissipated over the area around the strike and, due to the soil resistance, differences in potential can develop. If two systems are grounded in different areas and connected to each other for communication purposes, this would cause a lightning-induced interference signal to be injected into the system. Electromagnetic fields from lightning discharges can also induce currents in conducting material in the vicinity.

Remote lightning and electrical storms create electromagnetic fields, which cover a wide frequency spectrum. The strength of these fields varies depending on the time of year and geographical location. Phenomena, such as sunspots can cause a low-level noise over a wide frequency spectrum, rising to a maximum every 11 years.

Impact on domestic environment

In the domestic environment lighting can cause problems on the power and telephone lines, particularly where overhead distribution is used. Apart from this it does not have that much effect other than causing interference in TV reception.

There is nothing that can be done to prevent natural interference, such as lightning from occurring. The only way to reduce the effect on electronic equipment is to increase protection. Lightning is unlikely to have disappeared in ten years time, in fact, the effect of lightning is likely to get worse due to modern telephones being earthed in the home, thus providing a path for the induced charge.

Although manufacturers are unlikely to try to protect against a direct hit, some attempt is made to protect against lightning electromagnetic pulses. Telephone companies should place protectors in people’s houses, at telephone exchanges and repeater stations to reduce the effect on the customer. The bandwidth of broadcast receivers is relatively narrow and so is unlikely to be affected adversely apart from some interference with the picture and a crackling noise.

Mains powered equipment in the UK is expected to work within ± 10V. Even DC supplies can fluctuate due to load changes. Battery operated devices need to be able to work when fully and partially charged.

This is important because electronic items will be expected to perform to the same standards whatever their power situation is. If items become more susceptible when only partially charged then this is a concern.

ElectroStatic Discharge (ESD) is due to objects sliding over each other and the resulting displacement of charges. Discharge is affected by the humidity; in the UK where it is relatively humid a potential of about 15,000V is to be expected. Below is a table of some typical ESD potentials, it considers two bands of relative humidity (RH). It can be seen that as the humidity increases the electrostatic voltages are reduced by the leaking of the built up charges.

Table 3-2: Some typical ESD potentials

Almost all ESD problems result in digital upset. This is mostly due to the fact that ESD produces wideband interference and most digital devices concentrate on being immune to narrow band interference. The ESD process rarely affects analogue devices, as the extremely brief transient is too short to affect most analogue circuits. The most common problems are reset, lockup and data errors.

Materials can be categorised by their surface resistivity. Items with a low resistivity discharge quickly and can cause some damage, compared to items with antistatic and insulative properties which discharge more slowly and are, therefore, safer. Earthing equipment is also an important way of reducing ESD. Due to more digital devices being available, ESD is likely to become more of a problem in the future.

The methods used to wire houses have changed very little in the past 25 years. Traditionally, electricians take no precautions against EMI when wiring a standard house. Competition in the market is great and as a result the emphasis is on price rather than reducing any EMC problems. It can therefore be said that this competitiveness is holding back many of the advancements that could be made in this field. In houses where EMC is a requirement, such as those similar to ‘Smart homes’, particular attention is paid to reducing EMI from household wiring and making sure that the wiring can cope with the amount of electronic equipment being used. Electricians must comply with the BS 7671: 1992 Requirements for Electrical Installation (The Institute of Electrical Engineers (IEE) Wiring Regulations).

Power cables should not have any radio frequency (RF) on them. However, power line telecommunications (PLT) have been investigated and unless designed carefully has a tendency to interfere. Signal cables, however, may have to carry RF currents. If the cable is carrying a current that returns via a nearby conductor on the same cable then it is known as a differential-mode current. The fields are proportional to the current loop; thus if the cable is small so is the radiation. Currents that only flow in one direction, common-mode currents, are more troublesome and at the point where they enter the shield the interference behaves as if the noise source is located at the hole.

As cables are used by most electronic items and every house has wires running through the walls there is a potential for interference from these sources everywhere. In the future, problems will continue to arise due to the density of some housing estates. There has been an increasing interest in pre-fabricated houses, where the lack of ducts in the walls will provide little or no shielding of EM fields from the wiring.

Devices such as television sets are quite susceptible to electrical interference; this is usually seen as sparkly lines across the screen. If digital signals are interfered with by wideband interference it is usually more noticeable than if it were an analogue transmission, as it corresponds to the total loss of signal (e.g. no picture on TV) instead of a degraded signal with analogue (e.g. sparkly lines across the screen). Digital TV uses a positive pulse to mark the start of a new image on the screen, unfortunately car ignitions emit a similar pulse and this could confuse the TV ruining the image. As there is a move towards digital transmissions and a larger bandwidth, shielding of domestic appliances needs to be increased.

Many parents use an electronic baby monitoring device, which consists of a transmitter set up near the child and a receiver placed in the parent’s room or carried with them. However, these products are prone to interference especially in urban areas, from cordless phones other baby monitors or echoes from concrete walls. To reduce interference it is recommended that devices with a small bandwidth are purchased.

Technology for wheelchairs has increased dramatically in the last 15 years. It is now possible to move the chair using a joystick, which is appropriate for elderly people who may not have enough strength in their arms to move the chair manually. Although only a minority of people use these wheelchairs, the susceptibility of these devices will become more of an issue, as the ageing population increases and the cost of sophisticated wheelchairs decreases.

There are many diagnostic circuits incorporated in devices such as wheelchairs to ensure that if there is an electronic failure, possibly due to EMI, this does not result in injury. In the future wheelchairs could become much more sophisticated, catering for the more disabled by analysing eye movements. So care has to continue to be taken so that problems are not caused by electromagnetic interference.

Hearing aids operate between 200 – 4000 Hz. Manufacturers have to comply with the Medical Devices Directive and the IEC118-13 ‘Immunity of hearing aids from interference with cellular phones’. However, due to the interference experienced, it is not felt that these standards are adequate for those users who also wish to use items such as mobile phones, although Nokia provides accessories for hearing aid users so they can use the induction loop with their mobile phones.

The amount of people obtaining hearing aids from the NHS is not increasing, this may be due to the stigma attached to them, especially as the NHS only issue large visible ones. People could be obtaining ever-increasing numbers from private sources.

The technology for hearing aids has allowed them to become smaller and more discrete this involves placing the electronics even closer together, and so the problems will get worse especially as people with hearing aids will want to use all electronic equipment.

The layout of a mobile phone network is based on a set of cells. Each cell has a separate channel and they are arranged in such a way that no two cells with the same channel touch. This usually takes the form of seven different cells forming a cluster.

As mobile phone usage increases, people are going to expect a better service from their phone suppliers and in particular the continuation of the signal when moving into a building. It is important to consider this as it could lead to interference and more transmitters being built to reduce the problem. The amount of signal lost depends on factors such as the amount of glass on the outside wall and the way in which the floors are divided. The amount of signal received also depends on how far from the ground the phone is; the ground just outside the building will be obscured from the base station and will suffer from diffraction effects from the building next to it. As the building is ascended, the signal may become clearer as there is less diffraction loss. One way to reduce signal loss in buildings is to use a ‘leaky feeder ‘ (a type of coaxial cable with a leaky outer screen so that energy is radiated from it along its length) to distribute the signals around the building. This improves the signal but could cause more problems with electromagnetic interference, as the signal is now stronger near other electronic equipment.

Since mobile phones contact the base station when moving from one cell to another, this signal can interfere with other electronic equipment such as the TV, computer or radio.

Hobby radio has been around for a long time and, since it started, enthusiasts have been very wary of any interference they may cause to other people innocently watching their TV or using their phone. They take many precautions to prevent spurious emissions and to increase immunity of their own equipment. However, although their equipment is getting more advanced, they may find their bands being swamped by commercial users as they try to find less heavily used frequencies to operate on.

This has become a worry in America where there has been a call to buy the frequencies from the Federal Communications Commission (FCC), to ensure that they are only used by amateurs. In ten years time there is likely to be the same amount of interest in Hobby radio as there is now. Attention should continue to be given to these users so that they are able to continue using the spectrum without interference.

Cars and other vehicles now contain many electronic systems. These range from electronic engine management systems to achieve maximum efficiency to electronically operated airbags to protect the driver in the event of a crash. Unfortunately this leaves cars more vulnerable to electromagnetic interference. Mobile phones and passing taxi radios have been known to interfere with Anti-skid Braking Systems (ABS) and airbags, causing drivers to lose control of the car. Car ignition has been changed recently to a short high voltage spark, although better for exhaust emissions this causes wideband interference. As the car industry is very competitive, cutbacks are often made on the wiring, which increases the risk of susceptibility.

The inclusion of computers in cars for navigation purposes will also increase the susceptibility.

Automobiles are covered in the Automotive Directive; this excludes them from the EMC Directive on sub-assemblies and devices that may be sold separately from the vehicles. All of the systems in the car have to be able to work simultaneously without interference from each other; ignition interference and external radiated interference. However, interference from objects brought into the car, such as mobile phones and laptops, may have been missed out. Additionally, household electronics can be affected by cars outside, in the street or garage, which is especially relevant in houses with small front gardens.

Aircraft rely heavily on radio systems for navigation and are therefore susceptible to EMI. Some of the frequencies used for communication and navigation are as follows:

Table 3-3: Frequencies involved for communication and navigation of aircraft

Radar is used at airports for air traffic control; it consists of a strong pulsed signal that can interfere with electrical equipment in the surrounding area. Aircraft could also create problems. However, EMI from the aeronautical industry represent an issue only where the house is situated near an airport.

Both over and underground railway systems use electrically powered locomotives (25,000 Volts). The EMI can be produced by the sparking from the pick-up shoes on overhead lines, ground currents, or induction from the power lines themselves. Sparking from the pick-up shoes can be minimised by reducing the power demand, either automatically or manually, by the driver before discontinuities are reached in the catenaries.

Railways cover most of the country and as the demand for housing increases, they can pass quite close to residential buildings and hence affect equipment inside them. Additional immunity constraints are placed on the users of information technology equipment in the near vicinity. However, it is unclear how suppliers know that their users will be situated near railway systems.

Trams have the potential to cause more problems in the domestic environment than railways, as they can pass as close as 5 meters from houses. Tramlines are also more likely to be placed near crowded council estates due to the lower house prices. The building of tramline networks in cities such as Croydon also mean the use of CCTV cameras and electronic information terminals at tram stops. As well as the overhead cables carrying electricity the drivers will be in contact via radio with the co-ordinators.

Both types of railway have a corridor that extends 10 meters from the centre of the track, within this EM emissions are completely unregulated up to the boundary. Due to housing pressures, many houses fall inside this corridor, and are therefore subjected to a lot of interference. This fixed width corridor should be changed for a more flexible one that does not allow households to fall inside an unregulated area.

This would occur during wartime or during the testing of nuclear bombs. The gamma rays from these bombs can seriously affect electrical equipment. If an explosion occurred 500km above the North Sea, it could damage sites as far as the south of Spain and the north of Norway. In the future, it is likely that wars will be fought in this way and much defensive equipment is designed specifically to be less susceptible and shielded rooms are also created. This report will not analyse this situation in detail as more important problems than domestic electromagnetic issues are likely to require attention.

4. Future Developments

4.1 General

In the next ten years there are likely to be many new items brought into the market that are accessible to the average person, such as, advances in TVs, audio equipment and communication. This will lead to the purchase of many more electrical items which will not necessarily replace those previously bought and so there will be a mix of old and new technology working in close proximity. Many houses have a TV in every bedroom; there will often be more than one computer and numerous radios.

On the other hand, there will be a convergence of products, the most obvious example being the TV and computer. With the introduction of interactive digital TV it will be possible to browse the net, check e-mails and watch a program on TV simultaneously. As well as being able to listen to the radio using a computer, graphics have advanced to allow TV programmes to be watched. Other items converging will include mobile phones with access to the Internet. As manufacturers of devices seek to incorporate more technologies in smaller and smaller units, EMC is going to become more of an issue, both in terms of immunity and emissions.

A teleworker is someone who works remotely from their employer or client and uses technology to link to them. Most predictions are that teleworking will increase significantly in the coming decade. This, however, depends on a number of factors. Teleworking is not suitable to all professions or all individuals. Many people may feel a sense of isolation from working at home, while others see it as a way of cutting down on commuter time and an effective way of working inside school hours. In order to be successful, teleworkers need a separate room in the house to work in. This provides a clear division between work and home and should allow the worker to switch from one to the other.

As regards EMC, if teleworking does become more popular then the amount of electronics being used in the home will increase as well as the amount of networking. Teleworkers will require equipment used in offices such as fax machines, scanners, a fast Internet connection and possibly video conferencing. This could mean that these houses should be given more protection from natural interference sources as well as better wiring of homes. Some teleworkers convert part of the garage into an office, since they require planning permission for this. Advice on solving EMC problems could be given at this time.

PCs are already an essential part of the majority of households, in ten years time there are likely to be more computers, the majority of which will have a connection to the Internet. The speed of computers is likely to increase dramatically, as well as the storage space available. Advancements like these mean that interference from computers will increase as more electronics are placed inside

As well as this, there will be technology normally associated with computers placed in other devices, such as hard disc drives in video recorders, which will increase potential EMI effects.

Computer memory

A university in Britain has already developed a 3-D memory system that acts just like a hard disk. It can store nearly three-and-a-half terabytes, which is hundreds of times bigger than those available presently. Because of its small size and cheap price this technology is likely to be fitted into items such as watches enabling them to become more sophisticated and will encourage more electronics to be placed inside, thus increasing the susceptibility to interference.

The most popular type of display used at present is the Cathode Ray Tube (CRT). This display causes a fair amount of interference in the near vicinity with radio receivers. It is likely to be used increasingly before it is replaced, by the new technologies currently being developed. Some of these are detailed below:

Continuous grain silicon

Continuous Grain Silicon (CGS) is being developed by Sharp. This allows ‘paper thin’ screens to be produced leading to the production of wrist videophones, and maybe wrist Internet browsing.

Light emitting plastics

Cambridge Display Technology is researching light emitting plastics (LEPs). The plastics emit light in response to the electric field created around them. The advantage of this technology over silicon based screens is that it can be more easily scaled to larger sizes. This technology could, therefore, lead to having screens hanging on walls looking like wallpaper until activated. Presently they are being suggested for use as backlights for the automotive and telecom industries.

Virtual reality

At the moment this is expensive and is only really used seriously for military applications. Research is being done so that the images are directed straight into the eye and a headset does not need to be worn in order to experience the virtual world. If this succeeds virtual reality could become a commonly used piece of equipment, possibly used for browsing the web.

EMI problems

It has been difficult to find information about the EMI impact these new types of displays will have, this is due to the fact that these technologies are still in the design stage and also because EMC is possibly not the main concern. We can, however, assume that Light emitting plastics may be a problem, as they require an electric field around them to work.

There has always been some interest in building a device that can think like a human being. This began by requesting the computer to search through a list of rules and apply the appropriate one; this is the method used to make ‘Deep Blue’ the computer that beat the world chess champion. Research has now turned to making machines that are like children and can learn from their environment. It is unlikely that there will be walking robots in households, however, household objects could become more ‘intelligent’. The television could learn what type of programmes members of the household liked to watch and inform them when they were on. All this will require more microchips inside items and hence electromagnetic interference could be more of a concern.

Lucent technologies have made a colour video camera the size of a coin, with a video quality similar to a camcorder. This could lead to small cameras in laptops, computer monitors, and doorbells and thus to more electronics being placed in small devices and so their susceptibility to interference will increase.

As many homes now have a computer and research has shown that an increasing number have more than one, home networking becomes an issue. This could also expand to include televisions, VCR’s and CD players along with kitchen equipment such as refrigerators and microwaves. This technology needs to become easier to use as consumers consistently fail to adopt new technologies that are difficult to set up and use.

As it is often cost prohibitive for consumers to rewire portions of their houses to support a home network, technologies that use existing wiring and also wireless technologies are likely to be more successful.

Ethernet

Ethernet is fast and reliable but it is necessary to install new cables in order to use. This type of networking is notoriously complicated so while it will remain a vital component of corporate networking, home users are not expected to adopt this in large numbers.

AC power lines

It is possible to control household appliances via AC power lines. The most popular piece of equipment to use for this purpose is known as X10. This consists of a controller/ transmitter, which is plugged into a standard electrical outlet. Then each appliance to be controlled is plugged into a X10 module, which in turn is plugged into a standard electrical outlet. Each device can be programmed, via the module, and controlled individually.

The advantages of this type of networking are that it is simple and uses existing wiring. However, the data integrity is a concern especially in old houses and data security between houses and apartments is not sufficiently protected. Efforts to standardise home networking over AC power cables have lagged behind wireless/ RF and home phone line technologies, and as such is unlikely to become the prevailing technology.

Wireless technologies

Wireless technologies use radio frequencies to communicate rather than wires. At the moment most of this technology is too expensive for the average home user, although Apple has recently introduced an iBook, a portable version of the iMac. This is now available in America and can connect wirelessly to the Internet by communicating with a small base-station, which can cover an area of 150 feet radius.

Bluetooth and Home RF Working Group are also trying to produce affordable wireless technologies.

Bluetooth

Bluetooth was first set up by a small number of companies but now has over 600 members. Bluetooth aims to link several different electronic items together. The gadgets will communicate with each other via short-range radio waves. Bluetooth is designed to work in an electromagnetically ‘loud’ environment. It locates a frequency and then synchronises all the devices in the same group to jump from one frequency to another (up to 1,600 hops per second) this reduces any interference caused and also any susceptibility from any other objects.

Bluetooth hopes to ultimately enable:

household items to contact repairmen when broken;
refrigerators, freezers and bathroom cabinets to report when items are running low;
instant photos and video clips to be sent from any location by cordlessly connecting the camera to a mobile phone;
information to be shared cordlessly with other people in a meeting;
laptops to be used to access the Internet whether they are wirelessly connected or otherwise.

Home RF Working Group

The Home RF Working Group was established in March 1998 and is a subset of the International Telecommunication Union. It currently provides for wireless Ethernet transmission for as far as 40 meters and four personal communication services including quality voice channels for cordless telephones. They are also developing a Shared Wireless Access Protocol (SWAP) which operates in the 2.4 GHz range and can perform up to 50 hops per sec. It is expected to support 127 devices per network, up to 50 meters apart.

The objective of the Home RF Working Group is to develop wireless technologies that have the potential to work with minimal interference. This shows that EMI would be reduced if devices were properly designed.

Hybrid networks

It is unlikely that one method of networking will be used exclusively in a household, especially considering that equipment will be utilised both at work and home. This will result in a hybrid network, consisting of a resident PC operating as the gateway, which is ‘always on’ i.e. it maintains a broadband connection with the Internet access service. Other PCs are plugged into existing phone sockets and can use the Internet without having to ‘dial in’. Lights and audio equipment can be controlled via AC power lines and portable laptops and mobile phones could be connect to the network via wireless technologies such as Bluetooth.

Electronics like this could ultimately lead to owners being greeted by their houses, which then turn the lights on when they walk through the door. Saying goodbye would cause the lights to turn off and the answer phone to be switched on.

This will mean, however, that all these different types of networking need to be able to work together so any EMI problems will need to be solved.

4.5 Phones

Popularity

Since December last year there has been a dramatic increase in the number of people using mobile phones, this is because prices have decreased and ‘pay as you talk’ phones have been introduced. Mobile phones are now seen as being affordable to everyone. As the market is unlikely to be saturated in the near future the number of people owning a mobile phone will increase.

Mobile phones are becoming so popular that in America it is difficult for people to have a phone call without being cut off due to the interference. This is leading to people suing mobile phone companies for not providing the advertised service.

Third generation mobile phones

It is planned to implement the third generation of mobile phones late 2001/2002, which will utilise wireless information and interactive services for personal and location-based use. This will enable virtual work teams, even when on the move, to focus on common tasks and projects. By incorporating multimedia capabilities, data and images can be shared simultaneously with users, who are connected with a voice or video connection.

Communicator

Nokia have already brought out a phone called the Communicator, which opens up to reveal a small keypad, allowing e-mails to be checked and faxes to be sent. Some companies are starting to offer a phone email service for normal mobiles via the text messaging facility. The Wireless Application Protocol (WAP) being developed by Nokia will provide the facility, among others, to access the Internet. This has already been used successfully to access details of the Edinburgh festival.

One phone

BT is presently advertising the use of one phone. This will mean that, while the owner is in the house it will act as a cordless phone using the Digitally Enhanced Cordless Telephony (DECT) system, transferring to the Global System for Mobiles (GSM) when it moves further away. When the phone enters a house it will send a signal to ask whether it has permission to use the DECT system, this signal is likely to interfere with other equipment but it should be brief. This transition from a mobile system to a home system should prevent the use of ‘leaky feeders’. See section 3.9 for more details on this issue.

Pagers versus mobile phones

Since mobile phones can now be used for two-way text messaging, pagers seem to have lost importance. However, pagers may still survive if they continue to offer other services such as better coverage, information such as football scores and remain cheaper. Pagers may, in the future, be used more by network engineers so they can be informed if something goes wrong.

Conclusion

Mobile phones will continue to be a popular method of communication, due to their convenience. However, if companies are not careful they could suffer from their own success and people could receive a reduced service, similar to America.

4.6 Entertainment

Analogue services withdrawn

It has yet to be announced when analogue television services will be terminated, when this does occur everyone will be using digital televisions.

Interactive television

This has been considered a lot as something for the future. In order for interactive TV to be realised, a broader bandwidth will be required. It could, for example, change the way our government is run, as voters could be polled electronically for referendums. Television may take on a new role with people actively taking part in programs to such an extent that they can download their own personal videos for viewing by others. Technology to this extent is unlikely to be launched before 2010 but some form of interactive TV might be available earlier.

Electronic books

In the future it may be possible to buy just one book that will look like a hardback book, with turnable pages, but will have a control panel on the spine, which enables the reader to choose which book to read. This involves the use of very thin and cheap displays and so is unlikely to be very widely used in ten years time. What is more likely is that it will be possible to download the books to be read onto a device which is handheld, or a CD or minidisk can be inserted from which the information can be gained.

Speakers

It is already possible to buy speakers which are so thin they can be made to look like picture frames, and hung on the wall. This would mean that it would be possible to have speakers in every room of the house and if the appliances were networked it could be programmed so that the music followed a person as they moved from room to room.

Toys

At the moment most toys do not contain a large amount of sophisticated circuitry and are therefore not very susceptible to emissions, nor do they tend to emit much. The regulations for toys are lower than for other household items. This should be considered carefully since the sophistication of toys is increasing due to technology becoming cheaper and many toys will continue to mimic real life items such as mobile phones and laptops.

EMI problems

Home entertainment is a growing market for technology, so there are always going to be interference problems, especially if lots of electrical equipment is packed closely into a room.

Broadcasting Food

A new idea, being investigated by Motorola, is to remove barcodes and replace them with a microchip, which has enough memory to store 110 characters and has its own built in radio antenna. This will enable information to be picked up by a trolley, which can calculate how much is owed and also deliver the information to the food manufacturers telling them that their products have been bought. The problem with these products is that the tags will continue to broadcast while they are sitting in the fridge and cupboards and there could be a potential for interference.

Products could instead be made to emit at the supermarket by firing a high frequency beam at them, however microwave ovens would have the same effect and would therefore cause the tags to emit in the home, causing interference with other electronic items.

Surfing Microwaves

It may soon be possible to access the Internet using the microwave. It will allow recipes to be found and can also inform food manufacturers what is eaten. This will again require a larger bandwidth, and therefore be more susceptible to EMI problems.

Nowadays electronic equipment is not just kept in the house, the garden too can be automated. When electromagnetic interference occurs from sources such as lightning, it can lead to equipment, which is controlled remotely, starting apparently of its own accord. It is important that potentially dangerous devices, such as power tools, are designed to avoid this problem.

Robomo

An automatic lawnmower has been invented. Once a perimeter wire has been placed around the lawn the mower can automatically sense the edges and avoid the flowerbeds. The wire carries 4.5 V and is therefore unlikely to be an interference problem. The same manufacturers are now turning their thoughts to a similar type of machine that would hoover a house. This would cause more problems than the lawnmower because of the possible interference with other domestic appliances.

Medical devices

Currently, very few electronic devices are implanted into the human body and only a small number of the population use hearing aids. It is, however, very important that items such as pacemakers are not interfered with as this could have dire consequences. BT is doing some research into a ‘wired man’, which is an investigation into how people’s internal and external electronics will interact. They feel that in the future people will have more medical devices implanted into the body, and perhaps some non-medical implants, which enable external electronics to be operated by thought.

Cochlea implants, small electronic devices placed under the skin to assist hearing, are already available. Unfortunately, they are prone to interference with objects, such as the security checks at shop entrances and airline security, which can damage an implant. People with cochlea implants have also been told not to use mobile phones.

Electronic wheelchairs

An increasing number of people are using these to move around their house and to get to places a short distance away. Advances could be made so that a track of some sort could be laid in the home and the wheelchair would electronically follow it. See section 3.7 for more details.

Monitoring

As medical equipment becomes cheaper it is conceivable that monitoring systems may be installed in homes. These could be used to monitor heart rates of people who are susceptible to heart attacks or have had previous heart conditions. This type of technology is likely to be introduced in America first and then Britain, but probably not in a major way for another 15 years or so.

The 1997 ‘A vision for transport 2020’ published by the Civil Engineers on behalf of the Engineering Council mentions the need for concern over global warming but not for EMC. Many ideas are put forward to improve transport, most of which involve more electronics inside the cars and on the road for speed control etc. All of these items will be next to houses and, if not properly shielded, could cause interference. Handheld navigation systems were also considered, these would be carried into people’s houses and used next to mobile phones.

The government is trying to encourage people to use public transport, as congestion is becoming a major problem. An incentive to use public transport would be punctuality. BT is investigating an idea, which would enable the time of arrival of the bus to be checked by using either the web a mobile phone or a pager. The bus would be fitted with a GPS tracker, so that its position could be monitored. This technology would be useful but in large cities such as London, GPS on buses may not be that reliable, due to the interference.

Alternative fuel vehicles

With concern rising over decreasing amounts of fossil fuels and air pollution, electric cars may be seen as an emission free alternative. However, depending on how the electricity is generated it could just move the pollution from exhaust pipes to the power stations. Other problems with electric cars are that the battery does not last for a very long time. Also although they are more energy efficient, electric cars are unlikely to achieve the range and performance of cars running on petrol. Electric cars may cause interference with other electronics inside the car, but these problems would have to be solved before these cars are marketed.

A hybrid car, which runs off the battery until it is exhausted and then switches over to petrol is a more likely alternative. However, this will only be phased in gradually and only a small percentage will be around by 2010. Solar power is unlikely to be an option for much of Britain due to the lack of sunshine. Cars that run on ethanol are possibly a better solution. This fuel can be home grown in the form of corn and is a cleaner fuel. It is also a more obvious solution in light of dwindling oil supplies.

Satellite radio receivers in cars

Ford has announced that they will start producing cars in America with satellite radio receivers as early as 2001. This results from a deal made with CD Radio. These receivers will be used very close to the house and could interfere with automatic garage controls. See section 3.11.

4.11 Change in environment

Smart cards

Many companies, including Motorola, are researching smart cards. The ultimate idea is that the ‘Smart Card’ can be used to pay for items such as plane tickets, bus fare etc. The card will hold personal details, such as medical details, personal preferences (e.g. non-smoking and bank details). Although these cards themselves obviously do not produce any emissions or are susceptible in any way, the idea does show that society is moving towards integrated technology. This means that more devices will perform more than one task and it will be expected that one type of technology is compatible with another. There may be an introduction of laptops that accept the card in a slot, which then can send the information to an airport to buy the plane tickets. Although it is unlikely that these cards will be used to this extent, however, an identity card of some sort will be introduced.

Customisability

Increasingly, electronic items are being made more customisable, for example mobile phones have a number of settings, it is possible to tailor voice mail or to decide whether international calls are to be received. This all requires an increase in bandwidth, making it more susceptible to outside EMI and increasing the interaction with other items.

Electronic tagging

Electronic tagging takes the form of a small bracelet worn around the wrist or ankle. Presently the Home Office is the main user of electronic tagging, keeping track of prisoners in the community. The use of this will increase, as problems increase, due to lack of space in prisons.

Tagging could have other uses, such as helping to increase the security of children on their way to school. Children could be fitted with the bracelet before setting off and, if linked with GPS, parents could be notified if the child wanders off the route via mobile phone or pager. This will have the added benefit of reducing traffic as more children will be able to walk to school safely.

The problem with this would be, when the GPS signal was interfered with and incorrectly showed that the child was off the route. This interference is likely to take place in cities where children walk to school. These problems already occur with prisoner tagging.

Optoelectronics

The Optoelectronics Research Centre (ORC) is researching the method of using photons rather than electrons to transmit, store and process information at Southampton University. Using photons means that the information is transmitted at the speed of light making it a lot faster than anything built using electrons so far. The research has also led to the development of optical fibres that amplify light, eliminating the need for electronic repeaters, hence reducing EMI problems. Optical fibres are already available and are used in some places to transmit information, this continued research should increase its use.

Quantum computing

This could be the next big step for computers; it will directly employ the principles of quantum mathematics to perform calculations that are infeasible on today’s computers. Although there is a lot of research being done, mostly in universities around the country, it is mostly theoretical at the moment. This type of technology will not be around within ten years and is therefore out of the scope of this report.

Electromagnetic powercoupling

Electromagnetic powercoupling could mean that a wireless lamp could be placed on a desk, where it would detect the lamp and supply the correct amount of power to it. This could be established possibly by modulating the impedance through the desktop. This type of technology may be around in 14 years.

It is unknown exactly what kind of EMI problems this may produce, obviously it would be important to supply the power carefully and only to those devices that required it. On the positive side, it should remove the need for power leads.

Sulphur lamps

The introduction of sulphur lamps could revolutionise home lighting. The lamp is the size of a golf ball and emits a bright and efficient light when energised by microwaves (2.5 GHz). A hollow pipe distributes the light from the sulphur lamp evenly throughout the building providing a softer light. The main problem with this idea is that it utilises microwaves that could cause problems if not properly shielded. This form of lighting could conceivably be used in the home in 10 years.

5. Conclusions

Many changes are taking place in the electronics industry, some of these are causing EMC problems. The increase alone in the number of items containing electronics means that almost anything can be susceptible to emissions. Most of these items are not self contained and usually send and/or receive information either via cables or radio waves. This move towards communication, coupled with the devices becoming more portable, means that these products are used everywhere, often in close proximity to other electrical appliances. As digital signals become more popular, their susceptibility to broadband emissions, such as car ignition, becomes more serious.

New Technology

When trying to predict what sort of technology may be around in our homes in 2010, it is important to take account of public reaction to new inventions and radically new ideas. If the general population does not accept these technologies, then they will never be adopted in a large way.

Health

There will continue to be concerns about the effects of electronic equipment on health, especially due to the number of people using mobile phones, possibly leading to worries about other electronic items. This would result in the public demanding reduced emissions and possibly safety warnings to be placed on mobile phones. This scenario is likely to reduce emissions a lot faster than any public concern over interference. On the other hand there could be very little concern, as companies will have carried out their research and acted quickly on their findings. However, I find the latter to be less likely.

Concerns such as these could also lead to people adding objects to devices, for example, covers for mobile phone aerials, to reduce the effect on their health. Unfortunately, such items cause the phone to increase the power of its signal as it has difficulty contacting the base station with a cover over the aerial. Thus, the cover causes the electromagnetic field around the phone to be more intense.

Quantity

Not only will there be an increase in the amount of electronic equipment owned by a household, there will also be an increase in the sophistication, which will leave these objects more susceptible to EMI. For example, thermostats used to be made from bimetallic strips. Now they are made using computer chips, which are susceptible to EMI.

Add-ons

When new services become available that require new equipment to receive or utilise, such as digital TV or Sky, there will always be items, such as set-top boxes, that have to be produced to persuade customers to use the service for a minimum cost. This will encourage people to buy more electronics to use with their older items which were not designed to run with other electronic devices, and so interference may occur.

Low voltage items

Items that are powered by low voltages are more susceptible to electromagnetic interference. This is because they detect a smaller signal to noise ratio. Low voltage items are likely to become more popular, especially in portable devices.

Quantity

The main items which cause the most EMI problems are those which communicate with others. Mobile phones interfere with other devices when they are contacting base stations; television sets are most susceptible to interference via the leads connecting it to other items such as a power source and the aerial. When items do not need to communicate with anything else and have their own internal power supply, they tend to interfere less with other objects, although they may still be susceptible to emissions from others.

Technology seems to be moving towards more items communicating with each other, giving the user control over many devices through one medium. So interference along cables will increase unless the communication is wireless, although this could create its own problems. As concerns increase over declining fossil fuels and therefore the availability of petrol for transport, there could be an even more concentrated effort to improve communications in the form of video conferencing or something similar.

Bandwidth

Most of the future items talked about involved a connection with the Internet in some way. This would involve an increase in bandwidth. Asynchronous Digital Subscriber Line (ADSL) technology could be used to provide broadband Internet access as it will allow a superfast connection which is ‘always on’. As it is unlikely that only one company will install these lines, there is an increased potential for interference between mismatched cables running through underground ducts. There is some worry that Internet connections through ordinary phone lines will be endangered by electromagnetic interference if many companies offer this service. However, it is conceded that competition is required to prevent one company, such as BT, from maintaining a monopoly.

Wireless

Bluetooth and other similar projects are unlikely to produce devices that will interfere with other electronic items due to the continuous switching of frequencies. The only place interference is likely to occur is between the electronic objects themselves. As this is an aspect the designers have to overcome before the devices will operate as specified, this too is unlikely to be much of a problem after a while. Bluetooth has a lot of potential and, if handled well, it will contribute to the growing convergence of technologies.

Some manufacturers seem to produce electronic equipment with the idea that it will be used in an office environment, where the buildings are more likely to be newer and may even have some degree of shielding to EMI. As opposed to a domestic environment where there are many different electronic items which will be placed much closer together. This lack of communication between manufacturers and users could therefore increase EMC problems.

One of the problems is going to be that many people will be using new equipment in old houses, where the wiring is probably not brilliant or adequate for the amount of electrical devices. People living in newer houses, where the wiring has been carried out taking into account the electrical equipment, will not be as susceptible to interference. People could rewire their houses but this is expensive and the majority of people will not and are unlikely to see the need to.

In an attempt to conserve Green Field sites, houses are being built closer together as demand for housing continues to rise. This would mean that the probability of objects in one house interfering with devices from another would increase. In blocks of flats interference could occur from devices in the apartments above and below, as well as those from the sides.

EMC problems can occur if there are communication problems between the people handling the products. It is possible that two devices can comply with the current regulations when used separately but it is when they are used in conjunction with each other that the problems arise. The problem might not be fixed quickly, as the companies will spend time trying to place the responsibility on the other. Communication can also break down between the manufacturer and the organisation installing the product, especially if clear instructions about earthing are not given.

In order to decide whether the EMC environment will get worse in the future, the regulations in force at present need to be examined and then assumed that all electronic devices are obeying these. If they are not, then this should be obvious to the Trading Standards Authority who then take appropriate action. If all devices are working within specifications and there are still problems - there seem to be - then perhaps these standards need to be changed. However, this will not happen unless there is a large amount of scientific evidence to show that this is necessary.

Maybe the answer is subtler than that; the standards set at the moment, such as CISPR concentrate on keeping particular frequencies clear, for example broadcasting. It may be better to change the approach and seek to reduce the interaction of electronic items. Regulations and standards seem to be around for most electronic equipment but there are no tests for the buildings that house them. This may not be feasible as there is still a question of who will be responsible for funding the changes needed if the home failed any given test.

Products such as automobiles and medical devices have their own regulations, which exempts them from the EMC directive, so problems arise due to lack of unification of regulations. For example, interference may occur between medical devices and security equipment in shops, although both products are conforming to their respective regulations.

When testing for EMC, most manufacturers wish to do everything possible to reduce emissions and increase immunity, as any major problems could damage their reputation. Some importers, however, just want to satisfy the minimum requirements so that they can put their product on the market.

There is often a long gap between changes in technology and changes in regulations. This is because changes in regulations involve many people coming together and discussing the relevant topics. Possibly a smaller group should meet more often and their decisions could be reviewed at the next major meeting.

Awareness

From talking to manufacturers, it is clear that the main problem is awareness of EMC and greater co-operation between companies needs to be sought. If the public were made aware of EMC problems and how it is possible for electronic items to work together rather than interfere with each other, there would be a demand, for products certified by organisations such as Bluetooth. Therefore due to customer demand companies would have to become more concerned with EMC, and so the situation would get better.

Due to the rapid increase of electronic items used in the majority of households, it is important that manufacturers and regulation bodies keep informed of new developments and areas for concern. Surveys could be carried out to give a better idea of the density of electronic items in homes.

There also needs to be more awareness of EMC problems by manufacturers. This needs to start at the ground level with more universities offering courses on the subject. This will mean that more electrical engineers understand how important EMC issues are and how best to tackle them. Companies require at least one informed person who co-ordinates the projects with respect to EMC. Lack of knowledge in this field can lead to badly designed products.

Regulations

Devices often operate quite well in a ‘normal’ EM environment, it is only when a new technology is introduced, which operates in a band or in a way that was not expected, that there are problems. Immunity regulations should be written with a view to the future.

Regulations often state a limit on the emissions, a certain distance from the source. This distance is usually 3 meters, however, in a domestic environment electronic items are often put closer together than 3 meters, perhaps the regulations should be changed to reflect this.

New buildings

Any new buildings that are built need to consider EMC protection from natural interference and power cable coupling. Floors such as the study and lounge, where typically the TV, hi-fi and computer are placed, should be anti-static.

New buildings should also be wired to take account of the quantity of electronic items people use; this will reduce the need for adapters and external wiring. More than one phone socket is required and it should be accepted that more than one computer would be accessing the Internet at a time. This is especially true in student residences.

Feedback

There is no direct method for consumers to inform regulatory bodies of problems with the electronic equipment they have purchased. This would be a useful way of highlighting any problem areas missed.

This report has generally covered EMC problems encountered in the home, it could be extended to include the office environment. This would be different because although offices generally have equipment such as computers set up closer together, the buildings can be purpose built to reduce the effects of EMI. Alternatively, a single area such as ‘communications’ could be concentrated on in more detail.

New advances in technology are being made constantly and so it would be advisable to review this topic in 12 years time to see how the EM environment and people’s attitude has changed.

Occasionally, it was difficult to find information on how certain electronics are affected by EM emissions, or whether they are producing any interference which affects other devices. This was because some technologies are still in the design stages, or EMC was not the main concern of the developers. In the latter case it shows the lack of concern shown by manufacturers about EMC.

Practical research needs to be done so that a model of EMI between equipment can be drawn up to quantify the problem, this will then lead to better regulations.

A Appendix 1

Information is transmitted either in an analogue or digital form. The first radio communication was in the former, although more recent trends have tended towards the latter.

Analogue is any form of transmission where the signals information-bearing characteristic (usually amplitude or frequency) is in direct proportion to the intensity of the sound or brightness of the picture.

Digital transmissions are in the form of trains of pulses rather than a continuous signal as for analogue.

The advantages of digital over analogue are that a digital signal is more robust than an analogue one, although if it is interfered with the consequences are worse. The carrier to interference ratio of a digital signal is higher than that of an analogue one. This means that the spacing of cochannel cells for mobile phones can be closer without increased degradation to the system performance. Using a digital signal also allows security through encryption and can easily be made compatible with the Integrated System Digital Network (ISDN), which can support data as well as voice transmission. However, digital signals normally require a larger bandwidth.

Due to the growing use of the radio spectrum very few frequencies are allocated exclusively to one service. Nowadays up to 6 different services can use the same frequency. Sharing frequencies is a useful way of letting more services use the radio spectrum and effectively reuses it. However, sharing frequencies can cause problems such as sharing constraints and co-ordination between same frequency users.

Most electric and magnetic field sources behave as combinations of dipoles. This means that the field intensity near a static electric or magnetic dipole decreases in proportion to the inverse cube of the distance. Thus the field becomes insignificant at moderate distances. However, it is possible for electric and magnetic fields to interact with each other so that their intensity varies inversely with the distance. This is often called radiated coupling.

Looking at the solution for a source consisting of a small electric dipole or current loop. It can be seen that:

The region for which r >> is known as the far-field region. And the region nearer to the source, where r << , is called the near–field region.

Where:

r = distance between the source and measuring point

l = Wavelength of signal

For a signal of frequency 400MHz (the speed of a typical PC) the value of is = 0.12m (2 significant figures). So in most cases it is safe to say that other electronic devices will be in the far-field. This means that the intensity will decrease inversely with the distance r from the electric field source. Therefore other electronic objects can easily be affected by the emissions from the source.

B References

Ellis N, Electrical interference handbook, Reed Educational and Professional Publishing Ltd, 1998

Hutchinson C, Radio Frequency Interference, How to Identify and Cure It, The American Radio Relay League, Inc, 1987

Kenward M, Photonic clusters promise bright future, Physics World, Vol. 12 No 6, June 1999

Mills J, Electromagnetic Interference, Reduction in Electronic Systems, PTR Prentice-Hall, Inc., 1993

Molyneux-Child J, EMC Shielding Materials A Designer’s Guide, Reed Educational and Professional Publishing Ltd, 1997

Radiocommunications agency, UK Spectrum Strategy, 1997

Williams T, EMC for Product Designers, Reed Educational and Professional Publishing Ltd, 1996

C List of Companies Contacted

A table showing which companies were contacted and asked for information, concerning this report.

Table 5-4: Table to show which companies were contacted.

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