The design of the rain sensor using a coaxial cavity resonator

Abstract

This article is a study of design of the rain sensor using a coaxial cavity resonator. We made some ranges of resonant frequencies by controlling the input voltage of the oscillator which will be mainly resonated in the coaxial cavity resonator. First, we made the coaxial cavity resonator by simulating the resonator structure with the proposed size and we expect the resonant frequency with the simulation and then we decide the voltage control oscillator (VCO) by the result. Second, we made the coaxial cavity resonator with the simulation result and water droplets detecting sensor circuit which is composed of voltage controlled oscillator, radio frequency (RF) Detector, and microcontroller unit (MCU). VCO makes the frequency which is resonated in the resonator, and RF Detector gets the RF signal and informs it to the analog voltage, and MCU gets the analog voltage and then changes it to the digital signal. We decided the size of the resonator with inner conductor 5 mm, outer conductor 14 mm, the height of the resonator 9.5 mm, and the height of the glass 6 mm from the simulated result. The simulated resonant frequencies is 3.09 [GHz], and we made the VCO frequency has ranges from 2.56–3.2 [GHz]. The measured resonant frequency is 2.97 [GHz] and the return loss is under −8.4 dB at the center frequency. When the water dropped on the glass of the resonator, the voltage has changed from 690 to 145 mV. It shows the proposed water sensor can detect the water variation by the variation of the resonant frequency of the resonator. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:128–133, 2016