This paper presents the LC-type passive wireless sensing system for the simultaneous and independent detection of triple parameters, featuring three different capacitive sensors controlled by two mechanical switches. The sensor coil was connected with three different capacitors in parallel and two mechanical switches were in series between every two capacitors, which made the whole system have three resonant frequencies. The readout coil was magnetically coupled with the sensor coil to interrogate the sensor wirelessly. The circuit was simulated advanced design system (ADS) software, and the LC sensor system was mathematically analyzed by MATLAB. Results showed that the proposed LC sensing system could test three different capacitive sensors by detecting three different resonant frequencies. The sensitivity of sensors could be determined by the capacitance calculated from the detected resonant frequencies, and the resolution of capacitance was 0.1 PF and 0.2 PF when using the proposed sensor system in practical applications. To validate the proposed scheme, a PCB inductor and three variable capacitors were constructed with two mechanical switches to realize the desired system. Experimental results closely verified the simulation outputs.

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This article proposes a SnO 2 -based lowpower quadrilateral gas sensor, which can realize different responses by self-temperature modulation using a singlelayer electrode. Four detection channels are located on four edges and are integrated with a quadrilateral microheater to constitute the completed sensor. Under the premise of ensuring good electrical insulation, the heater and the detection electrodes are designed in parallel on the same layer, eliminating the need for the isolation layer and subsequent dry etching steps to expose the pad. This scheme can greatly simplify the fabrication process and save manufacturing costs. On top of that, temperature modulation is realized by designing the gradational width of the microheater metal line on the four edges to achieve different responses to gases. Six types of food-related gases (trimethylamine, ethanol, hydrogen sulfide, ammonia, ethyl acetate, and formaldehyde) were tested, and the four channels of the sensor show different performances to these stimuli, which can be utilized for gas identification. Moreover, six food species were also tested, showing that the sensor can efficiently differentiate the fruit, vegetables, and meats.