Wireless system for biological signal recording with Gallium Arsenide high electron mobility transistors as sensing elements

• We propose a fully-passive tag device for sensing of human body vital signs.
• The tag consists of a high-electron mobility transistor connected to a loop antenna.
• We obtain amplitude modulated signals from a HEMTs array tested in liquid environment.
• Two loop antennas operating at 30 MHz are fabricated and tested as an inductive link.
• Electrical characterization of the inductive link connected to the HEMTs array is reported.

We propose the realization of a compact fully-passive biotelemetry tag composed of a high-electron mobility transistor (HEMT) connected to a wireless link. The Gallium Arsenide based gateless HEMT serves both as the environmental sensing element and as the amplitude modulator of the carrier signal received by the antenna. A prototype demonstrator operating in the MHz range has been developed: it consists of an array of transistors with different gate geometries and two spiral loop resonators implementing the wireless link. More specifically, one resonator (Tag-resonator) is connected to the array of transistors, while the other one (Reader-resonator) is connected to a power generator/reader device; the wireless link uses the magnetic coupling between the two resonators. Experimental results demonstrate that the reader-resonator exhibits an intensity modulation of the resonance dip depending on the voltage applied to the HEMT gate. These results will be used as a guideline for the realization of biocompatible sub-millimeter tags operating in the Gigahertz frequency range.

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