Application Cases

Experiment Name: Sound Pressure Measurement of Ultrasonic Standing Wave Field Using an Acoustic Probe

Objective:
This experiment employs an acoustic probe to measure the sound field by collecting sound pressure data and processing it using CPB analysis and FFT analysis to determine the sound pressure at specific points.

Equipment:
Power amplifier, signal generator, oscilloscope, microphone, amplifier, data acquisition card, computer, acoustic probe, chiller, ultrasonic transducer.

Experimental Procedure:
The measurement system is designed to generate an acoustic field using transducer vibrations. A signal generator drives the transducer, with the power regulated by an ATA-4052 power amplifier. An oscilloscope is used to observe and adjust the resonant frequency. Since the transducer generates heat during operation, which can affect its performance, a chiller provides constant-temperature, constant-flow, and constant-pressure cooling water to dissipate heat. The presence of sensors or other objects in the acoustic field may alter the characteristics of the high-frequency acoustic field, leading to inaccurate sound pressure measurements. To avoid this, a 1/4-inch prepolarized free-field measurement microphone is used to perceive the acoustic field. The microphone's frequency response is adjusted to compensate for errors in high-frequency sound pressure caused by its presence, enabling the measurement of undistorted true sound pressure. A 1/4-inch microphone preamplifier connects the microphone and the data analysis device, calibrating charge injection and the entire measurement system. The data analysis device is an acoustic test analyzer, which collects and records sound pressure at specific points and performs post-processing using FFT spectrum analysis (including FFT band extraction) and CPB analysis (with a standard 1/3 octave filter). Ensuring the acoustic probe and the amplitude transformer axis are aligned, the acoustic probe is moved from far to near using a translation stage to test and record the sound pressure at each point and its distance from the transducer surface. The transducer power is varied to collect multiple sets of data, which are then statistically analyzed.

Figure 1-1: Block Diagram of the Acoustic Probe Sound Field Measurement System

Results:
When the acoustic probe is placed horizontally, fluctuations are significantly more pronounced, and the sound pressure amplitude is notably smaller compared to when placed vertically. This indicates that microphone directivity has a substantial impact on sound field measurements. Therefore, the vertical placement is chosen for measurements. Fluctuations are observed in the sound pressure measurement results, which arise because the measured sound is generated with small amplitude and low power, leading to energy fluctuations in low-pressure sound fields. The fluctuation range is related to the wavelength and serves as one of the criteria for validating the simulation.

Figure 1-2: Experimental Results of Acoustic Probe Directivity

Recommended Power Amplifier: ATA-4052C

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

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