Infrared headset nixes radiation

By Chhavi Sachdev, Technology Research News

Hands-free headsets may help you keep your eyes on the road and hands on the wheel, but the devices may also be exposing you to electromagnetic stress by amplifying the phone’s radiation.

A headset connects to the phone by an electrical wire. Research has shown that the wire can act as a conduit for microwave radiation, which has been tagged as a possible health risk. The earpiece of traditional cell phones also contains an electromagnetic coil that turns electrical signals into audible signals but in doing so gives off electromagnetic radiation.

Borrowing from the field of optical communications, a researcher at the University of Warwick in England has devised a hands-free cell phone that sidesteps the problem by eliminating the headset wire and the earpiece electromagnetic coil.

The device replaces the headset wire with a five-millimeter plastic pipe that carries infrared, or heatwave, signals. There is no radiation, because there is no conductive link through wire, said Roger J. Green, a professor of electronic communication systems at the University of Warwick.

The device converts electrical signals to infrared signals, sends the signals through the pipe, detects the infrared signals and converts them back to electrical signals. “We use light-emitting diodes to convert electrical signals into infrared [and] photodetectors to convert light back into electrical signals,” Green said.

Infrared radiation falls between visible lightwaves and microwaves on the electromagnetic spectrum. Visible light has higher frequencies and shorter wavelengths than infrared light, which has higher frequencies and shorter wavelengths than microwaves.

A communication using Green's device involves two sets of infrared beams: one for the microphone-to-phone link, and the other for the phone-earphone link. Green's device also uses a piezoelectric crystal instead of an electromagnetic coil.

When a person speaks into a cell phone, the sound waves of speech hit a tiny diaphragm in a microphone, causing vibrations that are converted to electrical signals.

In conventional headsets, electrical signals from the remote caller are converted back to sound by reversing the process: an electromagnetic coil moves a tiny diaphragm in sync with the electrical signals. The motion of the diaphragm varies according to the electrical signal, and so “reproduces the sound wave by compressing and decompressing the air just above it at a rapid rate,” said Green.

The electromagnetic coil, however, produces electromagnetic radiation. “A headset with a coil in the earpiece has an antenna which can pick up electromagnetic radiation," he said. "This could radiate into the head."

Replacing the earpiece electromagnetic coil with a piezoelectric crystal eliminates the electromagnetic radiation altogether. "There is no antenna effect in the earpiece,” said Green. “There is no radiation at the earphone due to any radio frequency (RF) energy.”

Piezoelectric materials, such as the crystals used in watches do not conduct electricity, but instead expand and contract in the presence of an alternating electric charge; these physical vibrations generate high-frequency sound waves.

Though no medical evidence correlating brain tumors and cell phone usage is of long-term significance yet, replacing the questionable components of cell phones is an obvious way to stay on the safe side, said Green.

The trick to designing a headset that does not conduct or emit electromagnetic radiation was making the connection between the two subject areas of optical and radio communications, said Green. Once both fields are involved, "the problem is solved cheaply and effectively,” he added.

The headset could be used with any mobile phone on the market today, according to Green. "It is ready for commercialization," he said. The headset component cost is slightly higher than that of traditional headset phones, but the end-product should be only slightly more expensive, said Green.

This technique of converting radio frequency into infrared could also be used in other types of electronics in order to shield users from electromagnetic radiation, said Green.

The research was funded by the University of Warwick and Warwick Ventures.

Timeline:   Now
Funding:   University; Corporate
TRN Categories:   Engineering and Optical Computing; Optoelectronics and Photonics
Story Type:   News
Related Elements:   None


April 9/16, 2003

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