New Radio Antennas May Cool Car Interiors, Defrost Car Windows

The marriage of these two technologies may lead to invisible radio antennas that not only receive AM and FM signals, but also defrost windshields and help keep car interiors cooler.

Eric K. Walton, senior research scientist and adjunct professor of electrical engineering, said that this work is a response to the auto industry’s desire to build more antennas into new cars.

“We’ll soon see car antennas not just for radios, but for radar, cellular phones, and global positioning systems,” said Walton. “That’s why we’re developing multi-purpose antennas that fit unobtrusively into the windshields of cars.”

Walton explained that traditional antennas aren’t very aerodynamic and break easily, while visible wire antennas embedded within windows often have to be hidden behind a strip of black paint around the periphery of the glass.

The two new designs take advantage of materials already present in car windows so the antennas don’t protrude from the body of the car or need to be hidden behind paint. The researchers have received patents on the two antennas, and work relating to the first design appeared in a recent issue of the journal IEEE Transactions on Vehicular Technology.

The first antenna relies on a transparent metal film imbedded between the layers of window glass. Some new car windows already contain this film, which deflects the heat from sunlight and keeps a car’s interior cooler.

The drivers of these new cars use their air conditioners less, and save energy. Moreover, automakers can install air conditioners in these cars that are more environmentally-friendly.

Walton and his students designed coupling techniques that allow this film to receive AM/FM radio signals.

To test the design, the researchers installed a film antenna in the windshield of a late model Cadillac, connected it to a computer-interfaced, digitally-tuned radio, and took the car for test drives around Columbus. They drove within the city, on the freeway, and through suburban areas.

For AM radio stations, the early design of the film antenna performed 5 decibels better than a traditional antenna. For FM radio stations, the received signal was 5 decibels weaker in the early design.

Walton stressed that, although neither difference changes the overall quality of the sound to the human ear, since running those initial tests he and his students have improved the film antenna’s FM reception considerably.

“Of course, as researchers we’re interested in the details,” said Walton. “But the person who buys a car with this kind of antenna and listens to the radio isn’t going to notice the small differences that we’re measuring here.”

The second design makes a radio antenna out of the wire heating elements already embedded in many rear windows.

Normally, the wires that power these heating elements would short a radio antenna. Walton and his students built an isolation transformer system that allows AM/FM reception while permitting heating power to pass through. The device is inside the body of the car beneath the rear window.

“The heating elements are already there, and they are insulated from the body of the car, so they already have many of the characteristics of an antenna,” said Walton. “The equipment to manufacture them already exists, so we knew this would be a very inexpensive way to add an antenna to an automobile.”

Walton said that the reception of the heating elements is comparable to a standard antenna. Those results have yet to be published, but Ohio State received a patent on the technology in July 1998.

In 1999, the researchers will work to combine the two technologies into a heated metal film antenna. Sponsor PPG Industries of Pittsburgh, PA, will continue to provide funding and prototype windshields.

“If we put both these patents together, we could produce a front windshield that can help cool a car in summer, defrost itself in winter, and receive AM/FM signals -- but still remain completely transparent,” said Walton.

He added that the same technology could be used in windows for ships and aircraft, and he’s hoping to pursue those avenues in the future.