Passive acoustic sensor circuit and related wireless sensing system
A passive acoustic sensor circuit and related wireless sensing system are provided. The passive acoustic sensor circuit is configured to induce an electrical current in response to receiving a radio frequency signal. The passive acoustic sensor circuit includes a sensor circuit, which can detect a sensory event (e.g., a touch or key press) and cause a variation in the electrical current in response to the sensory event. In contrast, the sensor circuit will not cause the variation in the electrical current in absence of the sensory event. In this regard, the presence or absence of the current variation, which can be detected remotely and wirelessly, will serve as an indication of the sensory event. By detecting the current variation remotely and wirelessly, it is possible to reduce physical wiring in an electronic device (e.g., smartphone, smartwatch, etc.) to help reduce design and manufacturing complexity of the electronic device.
1 . A wireless sensing system comprising:
a passive acoustic sensor circuit comprising:
a conductive structure configured to induce an electrical current between an input node and an output node in response to receiving a radio frequency (RF) signal;
an acoustic resonator configured to:
resonate at a serial resonance frequency to pass the electrical current between the input node and the output node; and
block the electrical current between the input node and the output node at a parallel resonance frequency different from the serial resonance frequency; and
a sensor circuit configured to cause a variation of the electrical current at the parallel resonance frequency in response to detecting a sensory event.
2 . The wireless sensing system of claim 1 , further comprising a transceiver circuit configured to:
transmit the RF signal toward the passive acoustic sensor circuit and receive an echo of the transmitted RF signal reflected by the passive acoustic sensor circuit; and
determine the variation of the electrical current in the passive acoustic sensor circuit based on the transmitted RF signal and the echo of the transmitted RF signal to thereby detect the sensory event.
3 . The wireless sensing system of claim 2 , wherein:
the conductive structure comprises a linear antenna; and
the transceiver circuit is further configured to transmit the RF signal at the parallel resonance frequency.
4 . The wireless sensing system of claim 3 , wherein the transceiver circuit is further configured to detect the variation of the electrical current in response to a voltage standing wave ratio (VSWR) measured based on the transmitted RF signal and the echo of the transmitted RF signal being above a predefined threshold.
5 . The wireless sensing system of claim 3 , wherein the transceiver circuit is further configured to detect the variation of the electrical current based on one or more harmonics associated with the echo of the transmitted RF signal.
6 . The wireless sensing system of claim 2 , wherein:
the conductive structure comprises a nonlinear antenna; and
the transceiver circuit is further configured to transmit the RF signal concurrently in the serial resonance frequency and the parallel resonance frequency.
7 . The wireless sensing system of claim 6 , wherein the transceiver circuit is further configured to detect the variation of the electrical current based on one or more intermodulation products associated with the echo of the transmitted RF signal.
8 . The wireless sensing system of claim 1 , wherein:
the acoustic resonator is configured to cause a first capacitance between the input node and the output node at the parallel resonance frequency; and
the sensor circuit is configured to:
cause a second capacitance that is equal to four times the first capacitance between the input node and the output node in absence of the sensory event; and
cause the second capacitance that is not equal to four times the first capacitance between the input node and the output node in a presence of the sensory event.
9 . The wireless sensing system of claim 1 , wherein the sensor circuit comprises an acoustic structure coupled between the input node and the output node, and a sensor coupled to the acoustic structure.
10 . The wireless sensing system of claim 1 , wherein the sensor circuit comprises an acoustic structure and a sensor each coupled between the input node and the output node.
11 . A passive acoustic sensor circuit comprising:
a conductive structure configured to induce an electrical current between an input node and an output node in response to receiving a radio frequency (RF) signal from a transceiver circuit;
an acoustic resonator configured to:
resonate at a serial resonance frequency to pass the electrical current between the input node and the output node; and
block the electrical current between the input node and the output node at a parallel resonance frequency different from the serial resonance frequency; and
a sensor circuit configured to cause a variation of the electrical current at the parallel resonance frequency in response to detecting a sensory event.
12 . The passive acoustic sensor circuit of claim 11 , wherein the transceiver circuit is configured to determine the variation of the electrical current in the passive acoustic sensor circuit based on the transmitted RF signal and the echo of the transmitted RF signal to thereby detect the sensory event.
13 . The passive acoustic sensor circuit of claim 12 , wherein the transceiver circuit is further configured to detect the variation of the electrical current in response to a voltage standing wave ratio (VSWR) measured based on the transmitted RF signal and the echo of the transmitted RF signal being above a predefined threshold.
14 . The passive acoustic sensor circuit of claim 12 , wherein the transceiver circuit is further configured to detect the variation of the electrical current based on one or more harmonics associated with the echo of the transmitted RF signal.
15 . The passive acoustic sensor circuit of claim 11 , wherein the conductive structure comprises a linear antenna configured to receive the RF signal at the parallel resonance frequency.
16 . The passive acoustic sensor circuit of claim 11 , wherein the conductive structure comprises a nonlinear antenna configured to receive the RF signal concurrently in the serial resonance frequency and the parallel resonance frequency.
17 . The passive acoustic sensor circuit of claim 16 , wherein the transceiver circuit is further configured to detect the variation of the electrical current based on one or more intermodulation products associated with the echo of the transmitted RF signal.
18 . The passive acoustic sensor circuit of claim 11 , wherein:
the acoustic resonator is configured to cause a first capacitance between the input node and the output node at the parallel resonance frequency; and
the sensor circuit is configured to:
cause a second capacitance that is equal to four times the first capacitance between the input node and the output node in absence of the sensory event; and
cause the second capacitance that is not equal to four times the first capacitance between the input node and the output node in a presence of the sensory event.
19 . The passive acoustic sensor circuit of claim 11 , wherein the sensor circuit comprises an acoustic structure coupled between the input node and the output node, and a sensor coupled to the acoustic structure.
20 . The passive acoustic sensor circuit of claim 11 , wherein the sensor circuit comprises an acoustic structure and a sensor each coupled between the input node and the output node.