Application Cases

Experiment Name: Research on Indoor Human Localization Based on Electrostatic Sensors

Test Purpose: A type of electrostatic sensor capable of detecting human motion has been designed and fabricated. The electrostatic sensor consists of a sensing electrode and a signal conditioning circuit, which includes a charge amplifier, a voltage amplifier, a low-pass filter with a cut-off frequency of 30Hz, and a notch filter with a notch frequency of 50Hz. Human motion causes disturbances in the electric field in space. According to the principle of electrostatic induction, the charge on the surface of the electrode is redistributed, generating a varying induced charge signal. The charge amplifier converts the charge signal into a voltage signal, which is proportional to the induced charge quantity. The signal is then amplified and filtered to obtain a low-noise electrostatic signal of human motion, which can be used to acquire information about human motion.

Testing Equipment: Voltage amplifier, charge amplifier, filter, acquisition card, etc.

Figure 1: Schematic Diagram of the Electrostatic Sensor Structure

Experiment Process:

The structure of the electrostatic sensor is shown in Figure 1, consisting of a sensing electrode, a conditioning circuit board, and a metal shielding case. The sensing electrode circuit board is connected to the conditioning circuit board with a pin header and placed inside an aluminum metal shielding case.

The output charge signal from the sensing electrode is very weak and susceptible to interference from environmental noise. To extract useful information from the signal and prevent signal characteristics from being lost during transmission and processing, it is necessary to amplify and filter the weak charge signal. Figure 2 shows the block diagram of the electrostatic sensor signal conditioning circuit, which includes four parts: a charge amplifier, a voltage amplifier, a low-pass filter, and a dual-T notch filter. The conditioning circuit is powered by a direct current voltage of ±2.5V.

The acquisition card used in the signal acquisition device has 8 input channels, a sampling rate of 48kS/s, and a resolution of 14 bits. It can perform analog-to-digital conversion of the output signals from multiple electrostatic sensors and adjust the sampling frequency as needed for analysis and processing by computer software.

Figure 2: Block Diagram of the Signal Conditioning Circuit

Experimental Results:

The design of the electrostatic sensor, the selection of the signal acquisition device, and the design of the system localization software are detailed. The designed electrostatic sensor electrode is a circular electrode that obtains varying induced charge signals through electrostatic induction and inputs them into the conditioning circuit board. The signal conditioning circuit includes a charge amplifier, a voltage amplifier, a low-pass filter with a cut-off frequency of 30Hz, and a dual-T notch filter with a notch frequency of 50Hz. The conditioning circuit converts the weak induced charge signal into a voltage signal, which is then amplified and filtered before being output. The acquisition card collects the electrostatic signal output from the conditioning circuit, converts the analog signal into a digital signal, and uploads it to the system localization software. Through the localization software, real-time analysis of the electrostatic signal and real-time calculation of human position can be performed.

Voltage Amplifier Recommendation: ATA-214

Figure: Specification Parameters of the ATA-214 High-Voltage Amplifier

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