In order to improve the fabrication efficiency and performance of an ultrasonic transducer (UT), a particle swarm optimization (PSO) algorithm-based design method was established and combined with an electrically equivalent circuit model. The relationship between the design and performance parameters of the UT is described by an electrically equivalent circuit model. Optimality criteria were established according to the desired performance; then, the design parameters were iteratively optimized using a PSO algorithm. The Pb(Zr_xTi_1−x)O₃ (PZT) ceramic UT was designed by the proposed method to verify its effectiveness. A center frequency of 6 MHz and a bandwidth of −6 dB (70%) were the desired performance characteristics. The optimized thicknesses of the piezoelectric and matching layers were 255 μm and 102 μm. The experimental results agree with those determined by the equivalent circuit model, and the center frequency and −6 dB bandwidth of the fabricated UT were 6.3 MHz and 68.25%, respectively, which verifies the effectiveness of the developed optimization design method.

Acoustic microscopes and acoustic tweezers have great value in the application of microparticle manipulation, biomedical research and non-destructive testing. Ultrahigh frequency (UHF) ultrasonic transducers act as the key component in acoustic microscopes, and acoustic tweezers and acoustic lenses are essential parts of UHF ultrasonic transducers. Therefore, the preparation of acoustic lenses is crucial. Silicon is a suitable material for preparing acoustic lenses because of its high acoustic velocity, low acoustic attenuation and excellent machinability. In previous research, silicon lenses were mainly prepared by etching. However, etching has some drawbacks. The etching of large sizes is complex, time-consuming and expensive. Furthermore, vertical etching is preferred to spherical etching. Thus, a new method of ultra-precision machining was introduced to prepare silicon lenses. In this paper, silicon lenses with an aperture of 892 μm and a depth of 252 μm were prepared. Then, UHF ultrasonic transducers with a center frequency of 157 MHz and a −6-dB bandwidth of 52% were successfully prepared based on silicon lenses. The focal distance of the transducers was 736 μm and the F-number was about 0.82. The transducers had a lateral resolution of 11 μm and could distinguish the 13 μm slots on silicon wafers clearly.

Focused ultrasound featuring non-destructive and high sensitivity has attracted widespread attention in biomedical and industrial evaluation. However, most traditional focusing techniques focus on the design and improvement of single-point focusing, neglecting the need to carry more dimensions of multifocal beams. Here we propose an automatic multifocal beamforming method, which is implemented using a four-step phase metasurface. The metasurface composed of four-step phases improves the transmission efficiency of acoustic waves as a matching layer and enhances the focusing efficiency at the target focal position. The change in the number of focused beams does not affect the full width at half maximum (FWHM), revealing the flexibility of the arbitrary multifocal beamforming method. Phase-optimized hybrid lenses reduce the sidelobe amplitude, and excellent agreement is observed between the simulation and experiments for triple-focusing beamforming metasurface lenses. The particle trapping experiment further validates the profile of the triple-focusing beam. The proposed hybrid lens can achieve flexible focusing in three dimensions (3D) and arbitrary multipoint, which may have potential prospects for biomedical imaging, acoustic tweezers, and brain neural modulation.

Lead-free piezoelectric material-based ultrasonic transducers have been researched for several years, but the inefficient properties and design difficulties have troubled lead-free ultrasonic transducers for a long time. To improve the performance and design efficiency of lead-free ultrasonic transducers, in this work, an equivalent circuit model and intelligent optimization algorithm were combined for use in a transducer design. Firstly, 0.94(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃(BNT-6BT) lead-free piezoelectric ceramics were prepared and characterized. Then, BNT-6BT ceramics were used to fabricate the ultrasonic transducers. An equivalent circuit model-based software, PiezoCAD, and a genetic algorithm-based back-propagation neural network were used to optimize the design of the transducers. A 3.03 MHz center frequency and 60.3% −6 dB bandwidth of the optimized transducers were achieved, which were consistent with the neural networks optimization results. To verify the application potential of the lead-free transducers, tungsten rods phantom imaging and polystyrene spheres with 300 μm diameter manipulation were completed by the transducers, and the experiment results indicate that the BNT-6BT lead-free transducers have great potential in further biological and biomedical applications.

High-frequency ultrasonic transducers are pivotal for detecting minute defects, offering distinct advantages in terms of non-destructive evaluation, non-invasiveness, and superior spatial resolution. However, achieving effective focusing and efficient acoustic transmission for ultra-high-frequency ultrasonic transducers is a significant challenge. To address this challenge, a mass–spring acoustic matching layer is designed for a transducer based on a half-concave LiNbO₃ piezoelectric element at 100 MHz. The proposed mass–spring stack, comprising a 0.25 μm Au layer and a 2.5 μm Parylene-C layer, operates within a deposition-friendly thickness range ideal for curved substrates, while a conventional quarter-wavelength Parylene-C layer would necessitate a thickness of 6.0 μm at this frequency. The transducer is modeled in COMSOL Multiphysics 6.1, coupling solid mechanics, electrostatics with piezoelectric effects, and pressure acoustics for the water load. Using a fixed concave geometry (curvature radius is 1 mm, which means the focal length is also 1 mm), a frequency sweep from 50 MHz to 150 MHz is conducted to evaluate performance. Analysis of the pressure distribution in the focal plane reveals that the focal length and the −6 dB beamwidth are predominantly governed by aperture diffraction and exhibit minimal variation upon incorporation of a matching layer. The focal length is approximately 1.02 mm within the excitation frequency range of 70 MHz–150 MHz, and the beamwidth decreases markedly with increasing frequency. At 100 MHz, the measured −6 dB beamwidth is approximately 31.6 μm without a matching layer, 32.3 μm with a quarter-wavelength matching layer, and 31.0 μm with a mass–spring matching layer. Crucially, quantitative comparisons reveal that this design yields a systematically higher focal pressure; near the 100 MHz design frequency, the acoustic pressure amplitude achieved with the mass–spring configuration is 1.5 times greater than that obtained using the quarter-wavelength reference. These research results provide a theoretical basis for the application of ultra-high-frequency ultrasound in the detection of tiny defects.