Magnetic fields are common in automobiles. Even cars with gasoline engines can have high levels, depending on the wiring configurations and the locations of the tires and other moving engine parts relative to the passengers. Electric or hybrid vehicles can have very high levels due to the high current demand and re-charging mechanisms. Every vehicle will have multiple sources of magnetic field, some of which may be in areas that are difficult to access for shielding. With persistence, a satisfactory reduction of field levels is usually achievable. But don’t expect the levels to drop to zero.

Begin by diagnosing the fields in your vehicle. Use a 3-axis gaussmeter with a range of at least 200 mG, and flat frequency response.

– A 3-axis meter “looks” in all directions simultaneously, so you won’t risk missing important data because you were holding the meter at the wrong angle.

– If the range of the meter is too small (10 mG for example), you may only see “over range” on the meter everywhere. This will not help you determine the “hot spots” and therefore the location of the offending sources of the field.

– If you use a meter which is frequency weighted (instead of flat frequency response), you will get artificially high readings due to the mixture of frequencies present, which can be very misleading.

The Datalogging 3-Axis Gaussmeter is a good choice for this work.

Select a location away from powerlines and other sources of background magnetic fields. Notice the background level with the car not running. You will subtract this number from all further meter readings. Park the car, but leave the engine running. Slowly move the gaussmeter in the passenger areas. Check all areas that will be occupied by passenger bodies, including the seat, head, and floor areas. If you have an electric or hybrid vehicle, you should have an assistant drive the vehicle while you make meter readings. Check during the various modes of power: electric only, gas only, accelerating, cruising, braking, etc. Identify areas which have high levels (above 3mG).

Next, for each “hot spot”, sweep around that immediate area looking for the source of the high field. Naturally, the true source may be hidden under the floor, behind a panel, or on the other side of the firewall. But identify the accessible area closest to the source. This will be the surface with the highest readings. Remember to check under the dash as well!

Starting with the area with the highest field, place the meter in a location which you can find again after shielding is installed. You may need to measure its position relative to landmarks in the car, such as bolts, wires, etc. It is important that the meter position be repeated in exactly the same position (before and after shielding), as changing the meter position will change the readings.

Now lay a piece of shielding in the area of the hot spot. Magnetic Shielding Foil was used in this example. Giron is also a good choice. (Caution! The edges are sharp!) Use the largest piece of shielding that will fit. You can always trim edges or corners to work around odd shapes. If your largest piece of shielding is not wide enough, you can place pieces next to each other, with 1-2 inches of overlap where they meet.

Later, you will lock these pieces in position and cover them with protective carpeting. It is imperative that they do not come loose and create a driving hazard!

Complicated shapes and multiple barriers in a vehicle may not permit the placement of shielding in all locations that need it. You have to accept some level of compromise because of these limitations.

Now, place the meter back in the same position and take a reading. The level should be lower. Sweep around the shielded area to identify the remaining “hot spots”. You may need to add more shielding to the edge of the shield. Or try another layer of shielding. Or you may need to shield an area opposite the shield (In this example, we shielded the driver’s foot area, and needed to add shielding to the underside of the dash.)

Keep adding shielding until either you are satisfied with the results, or you find that adding more shielding does not yield any further decrease in readings.

Refine the shapes of the shielding pieces by trimming and bending. You can number them with a marker or tape to help you remember where they go. Take up carpeting if possible and lay the shielding in its final position. Fasten it securely. Use screws, pop rivets, tape, glue or any other mechanism you can think of to keep the shielding material in place. In this case, we were able to achieve an 84% reduction (1.47-0.25 / 7.61-0.25 = 16% field remaining).

Tape any seams with a sturdy, water resistant tape. You can also roll tape over sharp edges to keep the carpet and passengers safe.

Please the carpeting back over the shielded area (or add new carpeting as needed).
At this point, that area is done. You can move on to the next worst area and repeat the process.

Tips:

1- Make written notes as you go. Trust me, after a few meter readings, you won’t remember what the second reading was, or the exact position of the meter
2- Use caution when handling the shielding. It has sharp edges!
3- Use a tin snips to cut the shielding material
4- Tape cut edges with a study and water proof tape to protect people and prevent corrosion to the shield
5- Lock the shielding material in place so it cannot become a hazard to people and pets, nor create a driving hazard. One option is to cover floor shielding with custom fitted floor mats

Tape any seams with a sturdy, water resistant tape. You can also roll tape over sharp edges to keep the carpet and passengers safe. Please the carpeting back over the shielded area (or add new carpeting as needed). At this point, that area is done. You can move on to the next worst area and repeat the process. Tips: 1- Make written notes as you go. Trust me, after a few meter readings, you won’t remember what the second reading was, or the exact position of the meter 2- Use caution when handling the shielding. It has sharp edges! 3- Use a tin snips to cut the shielding material 4- Tape cut edges with a study and water proof tape to protect people and prevent corrosion to the shield 5- Lock the shielding material in place so it cannot become a hazard to people and pets, nor create a driving hazard. One option is to cover floor shielding with custom fitted floor mats