Research on the Performance of Lens-Focused Ultrasonic Transducers for Ultrahigh- Frequency Applications

Ultrahigh frequency (UHF) ultrasonic transducers are widely used in the fields of biomedical microscopy and nondestructive testing. However, the operating frequency and electro-acoustic conversion efficiency of UHF transducers have potential for further improvement. This work presents design, simulation, and fabrication of focused 300 MHz ultrahigh frequency (UHF) ultrasonic transducers. The UHF ultrasonic transducers were designed and simulated by equivalent circuit model and finite element analysis. Furthermore, the effect of lens aperture and ultrasonic frequency on the distribution of sound field were studied. To improve their performance, the UHF ultrasonic transducers were fabricated by using lithium niobate piezoelectric material and quartz glass focal lens. As a result, The pulse-echo measurements show the center frequency of the echoes were 238.7 MHz, 119.8 MHz and 73.1 MHz from the lens, near field and the focal point, respectively. According to the axial sound pressure distribution of the focusing transducer and the echoes, the ultrasound attenuation in water was calculated of 1.74 (± 0.16) × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> × <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (dB/cm). In addition, the image of 10 μm tungsten wire target illustrated the lateral and axial resolutions of the UHF ultrasonic transducers were 28.9 μm and 31.4 μm, respectively. This study highlights strategies for optimizing transducer performance and improving imaging resolution in Scanning Acoustic Microscopy (SAM) systems.