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Electronics Production | February 27, 2006

New magnetic sensors eases the use of hearing aids

A new magnetic sensor makes it possible to use a cellphone while using a hearing aid without switching off the hearing aid.
With many hearing aids users have to switch the hearing aid manually when they want to use a device such as a phone. With the advent of cellphones this problem has become more acute. It's one thing to be sitting at home or in your office when you need to do this, quite another when you are standing on a crowded, and possibly moving, train.

A new magnetic sensor manufactured by NVE corporation using GMR technology ( giant magnetoresistance ) allows the hearing aid to switched automatically to the different sound source without the user having to do anything other than lift the phone to his or her ear. This makes using the hearing aid as natural as possible.

Some advanced hearing aids do have automatic switching facility built into them , but the results are often inconsistent and the sensor employed is often very large compared to the other components used making it more difficult to manufacture as discreet a device as possible.

GMR ( giant magnetoresistance ) is the effect observed in multilayer structures of magnetic and non magnetic alloys , where changes in the applied magnetic field cause a large change in resistance. This technology has been widely employed by pneumatic cylinder manufacturers for accurate detection of piston position, and is now being used frequently in medical applications.

With most hearing aid designs size is one of the most important criteria. The NVE GMR sensor is significantly smaller than other magnetic sensing devices used for this application. Measuring only 1.6 mm2 in die form the sensor will allow the US manufacturer Starkey Laboratories Inc. to build much smaller hearing aids than before.

Hearing impaired user and Starkey Laboratories quality engineer Dale Lizakowski explained the GMR sensors advantage: “I have personally worn the GMR sensor technology as well as tested it via our industry-leading quality control standards and it performs well above and beyond any product I have tested or used in our market place for switching sensitivity, reliability and size. Our hearing aids can now be built much smaller and perform significantly better.”

Most current applications for GMR sensors are in industrial control markets such as pneumatic cylinder and gear tooth sensing, but due to their precision and small size they are increasingly used as a sensor in medical devices.

One such application is the use of these sensors in pacemakers and implantable defibrillators. The GMR devices allow non-invasive high speed communication between a practitioner and the implanted device. Data can be downloaded from or uploaded to the device without having to remove it from the body.

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