The interference of metal working surfaces on the electric field can lead to performance variations between the flush mounting and non-flush mounting of capacitive proximity sensors in industrial applications. Traditional active shielding circuit designs are complex, while grounding shields not only reduce the sensor sensitivity but are also unsuitable for grounded sensors. To address this issue, this paper proposes an innovative near-ground (NG) shielding structure. This structure effectively concentrates the electric field between the sensing electrode and ground by adding a common ground electrode around the sensing electrode, thereby reducing the electrical coupling between the metal working surface and the sensing electrode and achieving the desired shielding effect. Through finite element analysis and experimental verification, this study performed an in-depth investigation of the capacitance difference $C_d$ and the rate of change of capacitance with the target distance of sensors under the two mounting methods. The proposed structure achieved a performance comparable with active shielding (17 fF $C_d$) while operating passively, which addressed a critical cost–adaptability trade-off in industrial CPS designs. The results show that although the performance of the NG shielding was slightly inferior to active shielding, it was significantly better than traditional grounding shielding, and its structure was simple and low cost, showing great potential in practical applications.

Enhancing the sensitivity and resolution of the readout circuit is a pivotal technological approach to extending the detection range of capacitive proximity sensors (CPS). This paper introduces a novel high-sensitivity readout circuit that leverages the resonant amplification effect of the LC network in an oscillator to generate high-voltage excitation signals. By incorporating a feedback diode rectifier circuit, the circuit achieves a significant boost in sensitivity and resolution. Experimental results demonstrate an ultra-high sensitivity of 55.8 V/pF and a resolution of 0.45 fF, far surpassing conventional methods. In various detection scenarios with different electrode sizes, the proposed circuit exhibits a superior detection distance compared to commercial CDC chips and capacitive proximity switches. Furthermore, the paper systematically investigates the influence of circuit parameters on its performance. With its simple structure, low cost, and exceptional performance, this circuit is well-suited for applications in capacitive proximity switches and smart environmental monitoring.