Voltage standing wave ratio reading circuit design for inductance capacitance wireless passive ammonia sensors

It is not easy to conduct wired tests on sensors in harsh environments, and network analyzers are large, heavy, and inconvenient to carry. At the same time, the price of network analyzers is usually very high, which greatly limits their application. In this study, a voltage standing wave ratio reading circuit is designed to test inductively coupled (LC) wireless passive sensors. By introducing the theory of the standing wave ratio, the design concept and function of each module are analyzed from each specific module. The resonant frequency reading circuit of the sensor is designed and fabricated, and its sweep frequency range covers the frequency range of the commonly used LC wireless sensor, which widens the bandwidth measurement range. The main control chip adopts STM32 series, which makes the circuit and sensor module simple in structure and low in cost. This circuit can accurately obtain the resonant frequency of the sensor through the standing wave ratio and can measure the dynamic change in the sensor standing wave ratio. The output frequency range and output precision of the linear sweep source of the signal reading circuit were tested, and the dynamic testing ability of the circuit to the changing frequency was verified and improved the measurement accuracy.