Application Cases

Experiment Name: Sensor Acoustic Characteristic Testing

Research Direction:
This chapter designs an ultrasonic sensor for audio directional technology, conducts simulation analysis of the working parameters of the designed sensor, and verifies the rationality of the design. A prototype of the capacitive ultrasonic sensor is fabricated. The mechanical characteristics of the sensor are tested using a laser Doppler vibrometer system, and the electrical input impedance of the sensor is measured with an impedance analyzer. An experimental system for testing the acoustic characteristics of the sensor is constructed. The developed capacitive ultrasonic sensor is used to transmit ultrasonic waves, and a commercial ultrasonic sensor is employed as the receiver for validation experiments.

Test Equipment:
Voltage amplifier, Function generator, Ultrasonic sensor, Oscilloscope, Sensor, etc.

Experimental Process:

Figure 1: Sensor Acoustic Characteristic Testing System

Figure 1 shows the acoustic characteristic testing system for the miniature ultrasonic sensor. The DC bias and AC excitation voltage output by the function generator are amplified by the voltage amplifier and applied to the capacitive ultrasonic sensor, causing it to emit ultrasonic waves. An ultrasonic sensor is used as the receiver, placed opposite the capacitive ultrasonic sensor in a transmit-receive configuration. The ultrasonic signal received by the ultrasonic sensor is output to the oscilloscope after amplification.

Figure 2: Waveform Received by the Ultrasonic Sensor

A sinusoidal AC excitation with a frequency of 30 kHz, 20 Vp-p, and 10 cycles is applied to a sensor with a diameter of 2.5 mm, with a DC bias voltage of 100 V. The transmit and receive sensors are placed 5 mm apart, and the original waveform of the signal received by the sensor is shown in Figure 2.

Experimental Results:

Figure 3: Waveforms Received at Transmit-Receive Sensor Distances of 5 mm, 3 mm, and 2 mm

Figure 3 shows the filtered results of the signals received by the sensor when the transmit and receive sensors are placed at distances of 5 mm, 3 mm, and 2 mm, respectively. The peak-to-peak values of the received signals are approximately 0.071 V, 0.122 V, and 0.129 V. Since the signals received by the sensor in the test circuit are amplified before output to the oscilloscope, the actual peak-to-peak values of the received signals are approximately 0.35 mV, 0.61 mV, and 0.64 mV.

Figure 4: Waveforms of Signals Transmitted by 40 kHz Flat and Non-Flat Membrane Sensors

The 40 kHz flat and non-flat membrane sensors are used as transmitters, and the sensor is used as the receiver, with the two sensors placed 5 mm apart. A sinusoidal AC excitation with a frequency of 40 kHz, 20 Vp-p, and 10 cycles is applied to the sensors. The bias voltage for the flat membrane sensor is 100 V, and for the non-flat membrane sensor, it is 200 V. Figure 4 shows the waveforms of the received signals, with the upper graph showing the signal transmitted by the flat membrane sensor and the lower graph showing the signal transmitted by the non-flat membrane sensor. The peak-to-peak values of the received signals are approximately 0.074 V and 0.088 V, and the actual peak-to-peak values of the received signals are approximately 0.37 mV and 0.44 mV. The test results indicate that the output sound pressure of the non-flat membrane sensor is higher than that of the flat membrane sensor. Due to the small bias voltage applied to the sensors, the amplitude of the received signals is relatively small.

Figure 5: Waveforms of Acoustic Waves Transmitted by Flat and Non-Flat Membrane Sensors

Transmission experiments are conducted using fabricated flat and non-flat membrane sensors of the same frequency. The applied bias voltages are 100 V and 200 V, respectively, and the AC excitation is a 40 kHz, 25 Vp-p, 1-cycle sinusoidal signal. The original waveforms of the signals received by the sensor are shown in Figure 5. The amplitude of the acoustic wave signal transmitted by the flat membrane sensor is approximately 0.082 V, and the amplitude of the acoustic wave signal transmitted by the non-flat membrane sensor is approximately 0.113 V.

Figure 6: Filtered Waveform and Spectrum of the Flat Membrane Sensor

Figure 6 shows the filtered waveform and spectrum analysis results of the signal transmitted by the flat membrane sensor. The center frequency of the sensor is approximately 35 kHz, with a bandwidth of about 90%. Figure 7 shows the filtered waveform and spectrum analysis results of the signal transmitted by the non-flat membrane sensor. The center frequency is approximately 34 kHz, with a bandwidth of about 100%. The acoustic characteristic test results of the sensors indicate that the transmission capability of the non-flat membrane sensor is higher than that of the flat membrane sensor, and the bandwidth of the non-flat membrane sensor is greater than that of the flat membrane sensor, which is consistent with the simulation analysis results.

Figure 7: Filtered Waveform and Spectrum of the Non-Flat Membrane Sensor

Voltage Amplifier Recommendation: ATA-2042

Figure: ATA-2042 High-Voltage Amplifier Specifications

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