Application Cases

Experiment Name: Experimental Testing of Transparent Directional Sound Transducers

Experimental Principle:
The transparent directional sound transducer studied in this experiment is a novel type of transducer. The purpose of audible sound pressure level testing and frequency response testing is to determine the first-order resonant frequency of the transducer and the far-field sound pressure level at this frequency. Since environmental noise may interfere with the testing, the entire system must be placed in an anechoic chamber. A signal generator is used to emit a sweep signal within the ultrasonic frequency range, and a microphone is placed at a far-field distance along the transducer's acoustic axis to collect sound pressure level data. The frequency response curve of the test sample is then plotted. The objective of directivity testing is to determine the acoustic field distribution when the transducer operates at its first-order resonant frequency, verifying whether the main lobe of the sound beam is concentrated and whether side lobe signals are effectively suppressed. A turntable is required to control rotation, allowing for the measurement of the acoustic field distribution in the plane containing the transducer's central acoustic axis. A two-dimensional directivity diagram is then plotted. The audio directional transducer testing system is illustrated in Figure 1.

Testing Equipment: Signal generator, ATA-4011B high-voltage power amplifier, signal acquisition device, transducer, microphone, oscilloscope

Figure 1: Audio Directional Transducer Testing System

Experimental Procedure:
The measurement of the transducer's ultrasonic sound pressure level and frequency response is the primary focus of the testing. The system block diagram is shown in Figure 2.

Figure 2: Frequency Testing System Block Diagram

First, calibrate the microphone used in the test with a standard sound source calibrator to obtain the conversion relationship between the microphone's measured voltage value and the sound pressure level under real-time conditions. Next, use a signal generator to produce a signal with an amplitude of 10 Vpp and a frequency range of 1 kHz to 100 kHz. The output signal is amplified by the ATA-4011 power amplifier by a factor of 10 and serves as the driving signal for the test sample and the input signal for the oscilloscope. After the sample vibrates and emits sound, the microphone receives the signal at a fixed distance from the sample and inputs it into a dynamic analyzer. After confirming the validity of the sample's input signal via the oscilloscope waveform, record the peak value of the dynamic analyzer waveform as raw frequency response data. Finally, calibrate the test data based on the pre-test calibration results to obtain frequency versus sound pressure level data and plot an intuitive frequency response curve. The testing environment must be in an anechoic chamber or using an anechoic box, with the default distance between the microphone and transducer set to 10 cm. If special testing is required, adjust the distance accordingly.

The transparent directional sound transducer can utilize ultrasonic characteristics to produce highly directional audible sound signals. Therefore, directivity testing is necessary to evaluate the performance of the designed transducer in suppressing side lobe signals effectively.

Figure 3: Directivity Testing System Block Diagram

First, place the entire transparent directional sound transducer system in an anechoic chamber, fix the transducer on a turntable capable of 360° rotation, and position the microphone directly in front of the transducer's central axis. Calibrate the microphone used in the test with a standard sound source calibrator to obtain the conversion relationship between the microphone's measured voltage value and the sound pressure level under real-time conditions. Next, determine the resonant frequency of the sample through frequency response testing. Use a signal amplifier to generate a signal with an amplitude of 10 Vpp and a frequency of 5 kHz. The output signal is amplified by the ATA-4011 power amplifier by a factor of 10 and serves as the driving signal for the test sample and the input signal for the oscilloscope.

After the sample vibrates and emits sound, the microphone receives the signal at a distance of 10 cm from the sample and inputs it into a dynamic analyzer. After confirming the validity of the sample's input signal via the oscilloscope waveform, record the peak value of the dynamic analyzer waveform as raw frequency response data. The angular range for testing the sample is ±90°, with a step size of 5°. Repeat this step after each angular change, recording data after each rotation of the turntable to obtain the sound pressure level in the plane containing the transducer's central acoustic axis at various angles. Finally, calibrate the test data based on the pre-test calibration results to obtain frequency, angle, and sound pressure level data, and plot an intuitive directivity diagram. The frequency range, angular variation range, and step size are reference values and can be adjusted according to actual conditions. The testing schematic is shown in Figure 4.

Figure 4: Directivity Testing Schematic

Experimental Results:
The final manufactured sample is shown in Figure 5, consisting of 54 array elements. Due to limitations in manufacturing precision, the samples exhibit low accuracy, resulting in invalid test results for multiple sample sets. To address this, samples were carefully screened to improve testing efficiency. Using several transducers with good precision as examples, the test results validated the correctness of the simulation results and the feasibility of the designed transducer.

Figure 5: Manufactured Sample

The samples were placed in an anechoic chamber for testing of the first-order resonant frequency, sound pressure level, and directivity. After testing a series of samples and eliminating uncontrollable factors and irregularities caused by manufacturing, two sets of favorable test data were obtained. The frequency response curve obtained from the test is shown in Figure 6(a), and the directivity pattern is shown in Figure 6(b).

Figure 6: Sample Test Results

Based on theoretical calculations and simulation results, the sound pressure level of a 54-element array at 10 cm should be 14.6 dB higher than that of a single element at 1 cm. The measured first-order resonant frequency and sound pressure level were generally consistent with the simulation results.

Figure: ATA-4011C High-Voltage Power Amplifier Specifications

The experimental materials in this article were compiled and published by Xi'an Aigtek Electronics. Aigtek has become a large-scale instrument and equipment supplier with an extensive product line in the industry. All demonstration units support free trials.