Comparative characterization of long-range capacitive sensor frontends

At present,indoor positioning technology has a key impact on people’s daily production and life. Sensors are one of the keys to this technological breakthrough, and sensors based on different technologies have become the focus of attention of researchers. For instance,imaging techniques (camera, lidar), capacitive sensing, microwave (RFID, WIFI, ultrasound), inertial sensors dead reckoning (gyroscope and accelerometer). However, different sensors have their own unavoidable advantages and limitations. This thesis will focus on capacitive sensors to reveal their long-range front-end characteristics. The reason for choosing a capacitive sensor is its low cost, low power consumption, and effective sensing. And currently, more research is focused on short-distance applications of capacitive sensors. The purpose of this research is to characterize its long-range characteristics. This research is based on the 555 timer IC that produces a very stable 555 oscillator circuit in astable mode, which is used to generate high-precision free-running waveform. The output frequency can be adjusted by an externally connected RC resonant circuit consisting of only two resistors and one capacitor. In my case, the capacitor in the 555 oscillator circuit is replaced by the coupling capacitance generated by a metal plate and the human body. Changing the distance between the human body and the metal plate, the coupling capacitor will change accordingly, and its output frequency will change, thereby establishing the relative relationship between the distance and the frequency. Analyzing this relationship can get the distance characteristic of the capacitive sensor. Since the coupling capacitor is very susceptible to interference from the environment and reference objects (such as the size of the plate, the human body and large metal objects). During the test, I compared the results of different sizes of metal plates and different environments to draw more accurate conclusions. Under indoor conditions, the 45 cm x 16 cm metal plate has good stability within 2 m, and ii the sensitivity can exceed 5m. Under outdoor conditions, using a 45 cm x 50 cm metal plate with the human body as the reference object, the sensitivity can reach 20 m, but due to the limitations of the environment and equipment, the sampling stability is poor. For large reference objects like a car. Follow-up research can improve the environment and device to achieve better performance.