Magnetic Sensors Enable Noninvasive Communication With Pacemakers

February 1, 2007

NVE Corporation of Eden Prairie, MN develops and sells devices using "spintronics," a nanotechnology that uses electron spin rather than electron charge to acquire, store, and transmit information. Spintronic products include sensors and couplers used in applications in industrial controls and medical devices. The products use one of two patented spintronic nanoscale structures: spin-dependent tunnel junctions, and giant magnetoresistors (GMRs). Both produce a large change in electrical resistance, depending on the predominant spin of electrons in a thin metal layer. In this way, electron spin can be converted to an electrical signal compatible with conventional electronics.

Beginning in 1992, and continuing through 2003, the Missile Defense Agency (MDA) funded NVE to develop GMR materials and processing technology. Using GMR materials, NVE developed solid-state magnetic biosensors with extremely high sensitivity that found a spinoff use in replacing reed switches in implantable pacemakers.

How it Works

In medical applications, spintronic sensors are used as replacements for electromechanical magnetic switches such as microelectromechanical system (MEMS) reed switches. Reed switches enable doctors to tune the operation of pacemakers from outside the body. The spintronic GMR sensors are an order of magnitude more sensitive than the reed and are solid-state devices, unlike the mechanical reed. Spintronic sensors are not damaged by large magnetic fields, and they are compatible with semiconductor processing techniques.

Giant magnetoresistors get their name due to the large change in resistance when the devices are subjected to a magnetic field, compared with other magnetic sensors. GMR sensors are used in hard drives to sense magnetic fields and read information, but the NVE sensors are designed for short-distance wireless magnetic communication. The components use small coils as transmitters and GMR sensors as receivers, making them ideal for the pacemaker application.

The Cardiac Rhythm Management Division of St. Jude Medical, a pacemaker manufacturer in St. Paul, MN, has been manufacturing pacemakers using NVE's GMR sensors since 2001. Pacemakers need to be tuned to the specific needs of each person's body, and doctors use magnetics to perform that tuning outside the patient's body. NVE's sensors are replacing the reed switches in St. Jude Medical's pacemakers to provide noninvasive, high-speed communication with the implanted pacemaker.

Where it Stands

Other customers for NVE's GMR sensors include Agilent Technologies, Motorola, Cyprus Semiconductor Corp., Digi-Key Corp., and Honeywell. Other companies are using the sensors for vehicle traffic sensors embedded in roadways to detect cars, trigger traffic lights, and record traffic volume.

New hearing aids developed by Starkey Laboratories use NVE's GMR-based components to automatically detect whether a telephone headset or headphones are being used. Conventional hearing aids must be switched manually or incorporate a bulky mechanical coil sensor so they can amplify sounds produced by the telephone or speaker. Now, Starkey produces small hearing aids that automatically adjust — something that was not possible without the GMR sensor.

NVE is developing a nanoscale biological sensor that uses GMR sensors to detect and track molecules, such as DNA and proteins that have been attached to nanosized magnetic beads.

Since mechanical devices have a known failure mechanism, they may take longer to clear the U.S. Food and Drug Administration (FDA) requirements. GMR sensors have no known failure mechanism, allowing quicker FDA approval.

More Information

For more information on GMR sensor products available from NVE Corporation, visit http://info.hotims.com/10962-844  .

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