Application Cases

Experiment Name: Application of High-Voltage Power Amplifier in Acoustic Pressure Measurement of Ultrasonic Standing Wave Field Using Acoustic Sensor

Research Direction: 3D Printing

Test Objective: Utilizing an acoustic sensor for sound field measurement involves collecting  acoustic pressure, followed by CPB analysis and FFT analysis to derive the sound pressure at the  involved  point. Since the signal acquired by the acoustic sensor is in the time domain, while time-domain signals allow intuitive  observation of the signal shape, this characteristic relies on observation over extremely short time periods. Moreover, limited parameters  cannot uniquely describe the signal, making analysis difficult; no matter how dense  the sampling  period , the original  signal cannot be uniquely reconstructed. In contrast, frequency-domain signal processing can decompose complex signals into multiple simple signals, such as sinusoidal signals, enabling constructive analysis of the acquired signal. The method for frequency-domain analysis utilizes FFT to transform the time-domain signal into its corresponding frequency-domain representation, identifying spectral  within the frequency domain to extract signal features. CPB analysis, a common technique for analyzing vibration signals, finds  wide application  in acoustics, structural response, vibration analysis, and other fields.

Testing Equipment: ATA-4052 High-Voltage Power Amplifier, Signal Generator, Oscilloscope for Monitoring Input Signals, Microphone, Acoustic Test Analyzer, Preamplifier, Transducer, Chiller, Computer.

Figure: Acoustic Sensor Measurement System for Ultrasonic Standing Wave Field

Experimental Procedure: The measurement system is designed to generate a sound field via transducer vibration. A signal generator drives the transducer, and an Aigtek ATA-4052 power amplifier regulates the power. An oscilloscope monitors the signal to adjust the resonant frequency point. Since heat generated during transducer operation affects performance, a chiller provides constant-temperature, constant-flow, constant-pressure cooling water for heat dissipation of the operating transducer. The presence of interfering objects, such as sensors, within the sound field can impact its inherent characteristics, altering the high-frequency sound field at the interfering object's location and resulting in inaccurate sound pressure measurements. Therefore, a 1/4-inch pre-polarized free-field measurement microphone is used to sense  the sound field, avoiding this issue. The microphone's frequency response is adjusted to compensate for errors in high-frequency sound pressure caused by  involvement  the sound field, enabling measurement of undistorted  true  sound pressure. A 1/4-inch microphone preamplifier connects the microphone to the data analysis device and calibrates the charge injection and the entire measurement system. The data analysis device, an acoustic test analyzer, acquires and records sound pressure at extraction points, performing post-processing using FE spectrum analysis (including FFT frequency band extraction) and standard 1/3 octave filter analysis for CPB analysis. Ensuring the acoustic sensor and the horn axis are aligned, the acoustic sensor is moved stepwise from far to near using a mobile platform, measuring and recording sound pressure at test points and the distance between the test point and the transducer end face. The transducer power is varied, multiple data sets are measured, and statistical data are collected for further analysis.

Experimental Results: Sound field measurements were conducted using the aforementioned acoustic sensor sound pressure measurement experimental system. Due to the microphone's directionality, the influence of acoustic sensor directionality on sound field measurement was first  investigated. The acoustic sensor was placed both transversely and longitudinally; the results are shown in Figure 1. When placed transversely, fluctuations were and the sound pressure amplitude was significantly smaller than when placed longitudinally. Therefore, the microphone's directionality significantly impacts the measured sound field, and longitudinal placement was chosen for measurements.

Figure 1: Experimental Results of Acoustic Sensor Directionality

The axial sound pressure distribution from measurement results is shown in Figure 2-a, and the axial sound pressure distribution curves at different radial positions are shown in Figure 2-b. Based on the sound field measurement results, a 3D sound pressure distribution diagram was plotted using MATLAB. The mesh command was used for programming, and 3D point interpolation (griddata) was applied to smooth the surface plot  for  plotting  the 3D sound field sound pressure distribution.

Figure 2: Axial Position Distribution Diagram of Measurement Results

From the distribution curve in Figure 2-a, fluctuations exist in the sound pressure measurement results. This is because the measured sound field is generated with relatively small amplitude and power, leading to energy fluctuations in low sound pressure sound fields. However, the fluctuation range size  is related to the wavelength, serving as one criterion for judging simulation correctness. Figure 2-a also shows that the maximum energy node is located near 22 mm. When the sound field sound pressure distribution  is consistent, the maximum energy node position remains the same, serving as another criterion for judging simulation correctness. Figure 2-b indicates that the axial sound pressure amplitude is significantly larger than at other radial positions, with sound pressure decreasing farther from the axis.

Figure 3: Sound Pressure Distribution Curves at Different Powers

The transducer output power was adjusted, and axial sound pressure distributions for different output powers were measured. The curves from experimental results are shown in Figure 3. Higher output power results in greater sound field sound pressure, with similar sound pressure distribution, but high-output power sound fields exhibit fewer fluctuations.

Figure: ATA-4052C High-Voltage Power Amplifier Specifications and Parameters