The present application describes embodiments of a zero-power radio-frequency identification (RFID) sensor chip based on a combination of a surface acoustic wave (SAW) transducer and two-dimensional electron gas (2DEG) or two-dimensional holegas (2DHG) conducting structure, and its use as an ultrasensitive microphone for material and structure sensing. The SAW RFID sensor contains a piezoelectric substrate, on which a multilayer heterojunction structure is deposited. The heterojunction structure comprises at least two layers, a buffer layer and a barrier layer, wherein both layers are grown from III-V single-crystalline or polycrystalline semiconductor materials, such as Ga N/Al Ga N. Interdigitated transducers (IDTs) transducing SAWs are installed on top of the barrier layer. A conducting channel comprising a two-dimensional electron gas (2DEG), in case of two-layers configuration, or a two-dimensional hole gas (2DHG), in case of three-layers configuration, is formed at the interface between the buffer and barrier layers and provides electron or hole current in the system between the non-ohmic (capacitively-coupled) source and drain contacts connected to the formed channel.

A method of interrogating an acoustic wave sensor comprises transmitting, by an interrogator, an interrogation radiofrequency signal to the acoustic wave sensor by way of a transmission antenna, receiving, by the interrogator, a response radiofrequency signal from the acoustic wave sensor by way of a reception antenna, and processing by a processing means of the interrogator the received response radiofrequency signal to obtain in-phase and quadrature components both in the time domain and the frequency domain, determining by the processing means perturbations of the obtained in-phase and quadrature components both in the time domain and the frequency domain and determining by the processing means a value of a measurand based on the detected perturbations.

A sensor device that includes an integrated sensor assembly having a surface acoustic wave (SAW) sensor disposed on a piezoelectric substrate. The SAW sensor is adapted to measure an environmental condition of an environment in response to an RF signal. The SAW sensor includes an interdigitated transducer (IDT) formed on a substrate having at least a layer of a piezoelectric material. The SAW sensor includes either one or more SAW reflectors of a second IDT formed on the piezoelectric material. The SAW sensor further includes an RF antenna formed on the piezoelectric material. The SAW sensor and the RF antenna are integrated with one another on the piezoelectric material.

Subharmonic tags for passive far-field sensing are provided having at least one antenna configured to receive an interrogation signal having a plurality of interrogation frequencies, a passive LTI network in electrical communication with the at least one antenna, and two or more resonators, each resonator having a different resonant frequency and a corresponding trigger frequency different than the resonant frequency, wherein the passive LTI network is configured such that the tag only produces a response signal for trigger frequencies that are different from any of the resonant frequencies of the resonators, each resonator of the subharmonic tag configured to produce a response signal having a different frequency than the trigger frequency, the subharmonic tag configured to produce an output signal responding to the interrogation signal, the output signal including one or more of the response signals.

Devices (e.g., resonators) comprising a single-crystalline material, and related systems and methods, are generally described.

Subharmonic tags for passive far-field sensing are provided having at least one antenna configured to receive an interrogation signal having a plurality of interrogation frequencies, a passive LTI network in electrical communication with the at least one antenna, and two or more resonators, each resonator having a different resonant frequency and a corresponding trigger frequency different than the resonant frequency, wherein the passive LTI network is configured such that the tag only produces a response signal for trigger frequencies that are different from any of the resonant frequencies of the resonators, each resonator of the subharmonic tag configured to produce a response signal having a different frequency than the trigger frequency, the subharmonic tag configured to produce an output signal responding to the interrogation signal, the output signal including one or more of the response signals.