Multi-Parameters Detection Implemented by LC Sensors With Branching Inductors

Inductor-capacitor (LC) sensors utilize magnetic coupling to transfer signals to the readout coil, realizing a passive wireless working pattern. They are of high use in situations where wired connections are impossible to be established. An increasing number of demands, arising from the emerging applications in the Internet of Things and portable devices, require a simultaneous monitoring in sensors. This paper proposes a branching inductor to implement multiple resonances in a single inductor. Each branch of the inductor forms a secondary inductance, which is connected with a sensitive capacitor to work as an LC sensor. The multiple resonances in the branching inductor work in a multi-mode coupling pattern. The coupling, comprising inductive coupling, and capacitive coupling is analyzed and detected. In experiments, a double branching inductor is fabricated on PET substrate. Two sensitive capacitors for humidity and pressure, respectively, are connected to the inductor, resulting in two resonant peaks to monitor the ambient humidity and pressure level. The experimental results are decoupled to obtain final outcomes: the humidity sensor can respond from 15%RH ~ 90%RH with a sensitivity of -45.3 kHz/%RH; and the pressure sensor can work from 750 mmHg ~1000 mmHg with a sensitivity of -811.2 kHz/mmHg.