Capacitive proximity sensor uses electric fields to detect contactless objects like human body. Owing to its simplicity and low cost, it is an attractive choice for the application of human-computer interaction. For existing capacitive proximity sensors systems, their detection ranges are less than 20 cm that cannot meet the requirements of the applications for long distance sensing. This motivates us to develop a new capacitive proximity sensor system for human-computer interaction in this work. A capacitive sensor array, which consists of 4 × 4 sensor units with comb shapes, is first designed. The dimensions of the whole array and a single unit are respectively 30 cm × 30 cm and 4 cm × 4 cm, which are comprehensively considered with hand swing distance in natural state and the sensing distance. More specifically, a outer guard with a lattice-like structure encloses sensor cells is designed to reduce the crosstalk from its neighboring cells, and a simple capacitance measuring circuit is presented. Comparing to the charge/discharge, AC-based and CDC-chip-based capacitance measuring circuit, the proposed measuring circuit offers plain design, highest sensitivity (3.53 V/pF) and fastest speed (4 μs). The experimental results show that the system can capture hand motion up to 45 cm and get hand motion trajectory using the hand position tracking algorithm. These features indicate the proposed system is very suitable for human-computer interaction applications in the future, such as rehabilitation training and somatosensory game.

In this brief, a high sensitivity measuring system for capacitive sensor to detect moving target is presented. It mainly consists of a capacitance measuring circuit and a dc-blocking circuit. The capacitance measuring circuit is used to convert a capacitance to a dc voltage and the dc-blocking circuit is employed to extract the voltage variation. The experimental results show that when the measured capacitor is between 1 pF to 7.5 pF, the sensitivity is 3.53 V/pF, the linearity error is 6.13%, the SNR increases from 26.6 dB to 57.7 dB, the resolution is 3.1 fF and the time delay is about 4 μs. Comparing to five other common capacitance measuring circuits, the proposed one offers plain design, high sensitivity, and fast speed. Simulation results show that the proposed dc-blocking circuit has short time delay and unattenuated output. Moreover, as demonstrated by system tests, the proposed measuring system is qualified for capacitive sensor for detection of moving target with different speeds.

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.