California Air Resources Board Releases Results of Electronic Signal Testing on Reflective Glass
November 16, 2009

As part of its work toward enacting auto glass regulations in the state of California, the California Air Resources Board (CARB) has released information on testing it has conducted on the reflective glass that could be required by the legislation and its impact on electronic frequencies and signals. The recent testing was completed "to determine the relative impact of reflective windows on some portable electronics devices," and the three electronic items tested were GPS monitoring ankle bracelets, GPS navigation devices (Garmin, specifically) and cell phones. The group found that reflective glass causes no interference for ankle bracelets or cell phones, but could impact the use of GPS units in certain cases.

The vehicles used in the testing were a Mercedes S Class vehicle, which has reflective glass on all windows and the windshield, and the BMW 7, which has reflective glass in the windshield, according to information from CARB. A BMW 5, which is not equipped with reflective glass, was used as a control vehicle-and testers alternated between using it as is and adding reflective film to its windshield and windows.

The vehicles were driven from El Monte, Calif., to Los Angeles and back-approximately 26 miles in total-for each of the three devices tested.

During the drive, the ankle bracelets were placed in the front footwell and rear footwell (at various times) of the vehicles, and were tested in a BMW 5 with no film, BMW 5 with reflective film on the windshield, BMW 5 with reflective film all-around, and the two vehicles equipped with reflective glass-the BMW 7 and Mercedes S.

The researchers found that there was a high degree of variability in the signal strength, "with GPS drops occurring in all vehicles." However, they determined that the drops that did occur did so in "urban canyon[s]" and that the drops were common. CARB notes that it has presented this information to the state's Department of Corrections, which "reviewed the ankle bracelet monitoring and stated that none of the test track data would raise any concerns."

For the cell phone portion of the testing, three calls were made with each cell phone tested along the route at pre-determined points. Each call was two minutes in length and was recorded for quality purposes. CARB reports that in all cases, the use of reflective glass did not affect the cell phone signal; no calls were dropped and the call quality was not affected, according to the study.

Finally, the group tested GPS units both with and without antennas and placed them in the vehicles' "deletion windows"-areas of the glass not equipped with the reflective film or coating-and non-deletion areas. In these cases, CARB found that the electromagnet signals endured "few effects when only the windshield has [the] reflective coating." They found the largest impacts were seen in the vehicles with all-around reflective glazing, and that both the use of an antenna and deletion window were effective in "mitigating the effect of the reflective glazing."

"Our overall findings were that the devices would continue to work successfully if the device or its antenna is placed in a deletion window or if an external antenna is used," says Dr. Marijke Bekken, the CARB representative overseeing the development of the regulations. "This was the case even for all-around solar reflective glazing tested, which is one of the ways manufacturers could choose to comply with the 2016MY requirements. For 2012, of course, only the windshield would use glazing that might have electronic interference issues. If the manufacturer is able to select a non-metallic approach (ceramic or polymeric reflective films, for example), the issue does not arise, of course."

The California regulations will require that glass on new cars sold in the state, beginning in 2012, only transmit certain amounts of sunlight in an effort to reduce the load on the cars' air conditioners-and thereby cutting down on the state's carbon emissions. (CLICK HERE for related story.) The final numbers and details of the legislation have not been released, but are scheduled to be released this fall for public comment.

"There has been a slight delay in the release of the 15-day due to the need to work out the equivalency option," adds Bekken. "We hope to finalize that tomorrow, and should be able to release the draft soon thereafter.

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