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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