EMR Health Alliance of BC

In certain cases electromagnetic interference causes an irritating noise on the radio. In other cases it could be harmful to life, such as the effects a signal from a mobile phone could have on the electronic safety systems in a car. It then becomes increas ingly important to make computations of electro magnetic fields. Such computations are Jan Carlsson’s specialist field and they can be used in several applications at SP, the Swedish Testing and Research Institute in Borås, where he is employed. Electro­magnetic Compatibility, EMC, is the ability of a product to function without interference and is one of his principal areas of interest.

“The automotive industry is extremely interested in our work. Now we are involved in a third project, where we are co-operating with all the vehicle manufacturers in Sweden. What is interesting is that, together with Chalmers, we have produced a so-called hybrid code, which offers enormous potential. We can receive cad files from the vehicle manufacturer and calculate directly the electromagnetic fields generated – in a car by the current in the cables – and at the same time test alternative locations. For the manufacturers, being able to simulate this on a computer is invaluable.”

With the aid of software, the electromagnetic fields formed by electric cables and other components can be simulated. Modern cars also have an increasing number of antennas, such as GPS, mobile phones, bluetooth and crash radar. It is a matter of finding the best locations for these and ensuring that everything works optimally together, i.e. that they are compatible.

“In the vehicle simulations it is also possible to put a driver behind the wheel. Then it can be demonstrated clearly how electromagnetic fields enter the body and how they affect the antenna diagrams. Recently we looked at a car where the driver was also speaking on a mobile phone and we tested it using different numbers of passengers.”

Jan Carlsson has already worked a great deal with Chalmers. He was employed at SP and did his thesis in emc as an industrial doctoral student at Chalmers in 1998. This was the first thesis on this subject.

“We have been aware of the phenomenon of electromagnetic interference since the 1920s, when it was first noticed that electrical apparatuses could interfere with the radio. During the Vietnam War there was a more drastic example of the effect of interference when the radar on an American aircraft carrier caused a loose cable to set off a rocket from an aircraft on deck, killing and injuring many of the people on board.”

It is of course possible to protect the equipment in different ways, such as using metal covers and screens. But in cars we are chasing grams in weight reduction and it would be inconceivable to cover all the cables in metal. The design and positioning of electrical and electronic units is therefore crucial.

Now that safety systems in society are controlled to such a large extent by electronics, EMC is very much at the forefront. With the EU issuing peremptory directives in 1996, whereby all apparatuses should be EMC-approved, many believed that the need for testing would increase dramatically. Although several test labs were set up the upturn was not as great as expected and certain laboratories were forced to make cutbacks. SP, however, is going against the flow and expanding in order to, among other things, offer customers calibration of test antennas for EMC, an area where there is considerable interest. There is also collaboration with Ericsson in Mölndal on their new measurement range, where the aim is to offer other customers accredited antenna measurements with a high degree of accuracy.

A model of a car including the driver and three passengers with the driver speaking on a mobile phone. The picture shows the electric field in a cross section through the car at the frequency 875 MHz.

Recently, Jan Carlsson has co-operated a great deal with the antenna group at Chalmers and studied so-called patch antennas, which are found at base stations. They have also tested antennas on mobile telephones.

“We use a reverberation chamber which is not new in itself although it is new with regard to testing mobile telephone antennas. The chamber is around one and a half cubic metres in volume and much simpler to work with than a large echo-free room. We can also place a model of the human head inside the chamber and see directly to what extent the output decreases, i.e. how much disappears into the head. We can also measure the effect of placing telephones and antennas in different positions.”

Personally, Jan Carlsson is not particularly afraid of the radiation emitted by mobile tele phones.

”I don’t use a mobile phone very much. Despite everything, up to 80 per cent of the output disappears into the head. A great deal needs to be done with regard to antenna design and this is something I would like to continue with. We already have an industrial doctoral student who will investigate how we can direct and adapt the different electromagnetic fields.”