Determination of acoustic field parameters for high-frequency focusing ultrasonic transducers up to 100 MHz

High-frequency focused ultrasonic technology offers distinct advantages in microstructural inspection and high-resolution imaging owing to its short wavelength and superior acoustic field-focusing capability. Accurate determination of focused acoustic field characteristics is essential for reliable defect evaluation and image quality. This study proposes a precise method for calibrating the effective radius of high-frequency focusing ultrasonic transducer and −6 dB beamwidth of its acoustic field – two key parameters that directly affect the spatial resolution and focusing accuracy. A theoretical acoustic field model was established based on the Rayleigh integral, and the computational efficiency was enhanced using the Fresnel approximation. A hydrophone-based experiment was designed: the iterative method was employed to invert the geometric focal length and effective radius by analyzing the extrema (maximum and minimum values) of the on-axis acoustic pressure distribution, while the −6 dB beamwidth was determined by incorporating a spatial averaging correction into the analysis of the focal plane pressure profile. The experimental results demonstrate that the determined beamwidths agree with the measured values to within 3% across a frequency range of up to 100 MHz, thereby confirming the accuracy, robustness and practical applicability of the proposed calibration approach.