Managing radiated EM field hazards in vehicles

Edited by the Engineeringtalk editorial team Jun 15, 2001

Vehicle electronic systems must demonstrate an adequate immunity to high intensity radiated fields to operate safely, according to a paper to be presented at the Vehicle Electronics Conference

"Vehicle electronic systems such as collision avoidance, adaptive cruise control, electric steering and braking must demonstrate an adequate immunity to high intensity radiated fields (HIRF) to operate safely at all times otherwise there could be tragic consequences", warns Erik Stevens, Head of Electromagnetic (EM) Measurements at ERA Technology, in his paper to be presented at the Vehicle Electronics Conference on 27-28 June 2001.

"In modern vehicles the critical control functions, which are provided by vehicle electronic systems, must not malfunction or deviate from their defined performance characteristics, when exposed to the defined HIRF environment", explains Stevens.

"Within the automotive industry there are now stringent performance and safety requirements specified for these automotive critical electronic control systems.

These requirements include assessments of the immunity of those systems in the EM environments in which the vehicle may be expected to operate, since all electronic systems are susceptible to radiated EM fields, provided the fields are of sufficient amplitude." Vehicles and their electronic systems are exposed to a variety of EM environments, from sources which are both remote from the vehicle and also onboard the vehicle.

External HIRF sources include high power broadcast transmitters for radio and TV, high power aeronautical and marine radars, communication systems and transmitters onboard adjacent vehicles.

The various onboard sources may include radio transmitters such as private mobile radio (PMR), citizen band (CB), amateur radio and mobile telephones.

Vehicles will be exposed to many different HIRF environments depending on the use of the vehicle.

"Vehicles driven to normal public areas of airports may experience radar interference breakthrough on the car radio", explains Stevens, "however, if the vehicle is taken into the airfield then field strength levels may increase significantly and could cause interference problems which are more critical.

Similarly a vehicle which is used close to ships or ferries may be exposed to extreme HIRF levels from the marine radars." The susceptibility effects of HIRF on automotive electronic systems will depend on the functional criticality of that system.

Stevens explains that interference to a vehicle's audio/visual entertainment system will not hazard the safe operation of the vehicle, whereas uncommanded deviations in the speed of a vehicle may lead to disaster.

Critical control systems must fail safe if they are susceptible to interference.

Stevens' paper provides an overview of the HIRF threat environments to vehicles and HIRF coupling mechanisms to vehicle electronic equipment, and discusses HIRF transfer function measurements and HIRF immunity test techniques which may be applied to verify the EM performance of these vehicle electronic systems.

Also the paper discusses the applications of low level transfer function measurements, to whole vehicles, to determine HIRF susceptibility test limits for vehicle electronic systems, together with bulk current injection and other onboard vehicle immunity tests.

Stevens explains that many of these methods have been successfully applied to aircraft for many years and lessons learned can be transferred to the automotive industry especially when assessing systems in large vehicles.

"These techniques have many advantages for large vehicle constructors.

They can provide a cost-effective way of assessing system performance where tests have been constrained due to the limited size of the test chamber, or where a vehicle is assembled relying on the bench tested performance of ESAs.

In both cases the techniques described in this paper can provide additional confidence for vehicle manufacturers, particularly if safety critical systems are involved." Steven's paper will be presented at the conference 'Vehicle Electronic Systems', organised by ERA Technology Ltd on 27-28 June 2001 at Coventry, UK.

Taking a pragmatic approach this intensive two-day conference will examine in detail technology applications that will provide real benefit on tomorrow's vehicles.

The event will appeal to those working in vehicle manufacturing and design, or component supply.