Ultrawide Bandwidth High-Frequency Ultrasonic Transducers With Gradient Acoustic Impedance Matching Layer for Biomedical Imaging

An Emerging Era: Conformable Ultrasound Electronics

Conformable electronics are regarded as the next generation of personal healthcare monitoring and remote diagnosis devices. In recent years, piezoelectric-based conformable ultrasound electronics (cUSE) have been intensively studied due to their unique capabilities, including nonradiative monitoring, soft tissue imaging, deep signal decoding, wireless power transfer, portability, and compatibility. This review provides a comprehensive understanding of cUSE for use in biomedical and healthcare monitoring systems and a summary of their recent advancements. Following an introduction to the fundamentals of piezoelectrics and ultrasound transducers, the critical parameters for transducer design are discussed. Next, five types of cUSE with their advantages and limitations are highlighted, and the fabrication of cUSE using advanced technologies is discussed. In addition, the working function, acoustic performance, and accomplishments in various applications are thoroughly summarized. It is noted that application considerations must be given to the tradeoffs between material selection, manufacturing processes, acoustic performance, mechanical integrity, and the entire integrated system. Finally, current challenges and directions for the development of cUSE are highlighted, and research flow is provided as the roadmap for future research. In conclusion, these advances in the fields of piezoelectric materials, ultrasound transducers, and conformable electronics spark an emerging era of biomedicine and personal healthcare.

Ultra-High Frequency Self-Focusing Ultrasonic Sensors With Half-Concave Geometry for Visualization of Mouse Brain Atrophy

Ultra-high frequency (>100 MHz) acoustic waves feature biocompatibility and high sensitivity and allow biomedical imaging and acoustic tweezers. Primarily, excellent spatial resolution and broad bandwidth at ultra-high frequency is the goal for pathological research and cell selection at the cellular level. Here, we propose an efficient approach to visualize mouse brain atrophy by self-focused ultrasonic sensors at ultra-high frequency with ultra-broad bandwidth. The numerical models of geometry and theoretically predicted acoustic parameters for half-concave piezoelectric elements are calculated by the differential method, which agrees with measured results (lateral resolution: 24 μm, and bandwidth: 115% at -6 dB). Compared with the brain slices of 2-month-old mouse, the atrophy visualization of the 6-month-old mouse brain was realized by C-mode imaging with an acoustic microscopy system, which is a potential prospect for diagnosis and treatment of Alzheimer's disease (AD) combined with neuroscience. Meanwhile, the acoustic properties of the brain slices were quantitatively measured by the acoustic microscopy. These encouraging results demonstrate the promising application for high-resolution imaging in vitro biological tissue with ultra-high frequency self-focusing ultrasonic sensors.

Intelligent Optimization Design of a Phononic Crystal Air-Coupled Ultrasound Transducer

To further improve the operational performance of a phononic crystal air-coupled ultrasonic transducer while reducing the number of simulations, an intelligent optimization design strategy is proposed by combining finite element simulation analysis and artificial intelligence (AI) methods. In the proposed strategy, the structural design parameters of 1-3 piezoelectric composites and acoustic impedance gradient matching layer are sampled using the optimal Latin hypercube sampling (OLHS) method. Moreover, the COMSOL software is utilized to calculate the performance parameters of the transducer. Based on the simulation data, a radial basis function neural network (RBFNN) model is trained to establish the relationship between the design parameters and the performance parameters. The accuracy of the approximation model is verified through linear regression plots and statistical methods. Finally, the NSGA-II algorithm is used to determine the design parameters of the transducer. After optimization, the band gap widths of the piezoelectric composites and acoustic impedance gradient matching layer are increased by 16 kHz and 13.5 kHz, respectively. Additionally, the -6 dB bandwidth of the transducer is expanded by 11.5%. The simulation results and experimental results are consistent with the design objectives, which confirms the effectiveness of the design strategy. This work provides a feasible strategy for the design of high-performance air-coupled ultrasonic transducers, which is of great significance for the development of non-destructive testing technology.