Recent Advances in Flexible Ultrasonic Transducers: From Materials Optimization to Imaging Applications

Abstract

Ultrasonic (US) transducers have been widely used in the field of ultrasonic and photoacoustic imaging system in recent years, to convert acoustic and electrical signals into each other. As the core part of imaging systems, US transducers have been extensively studied and achieved remarkable progress recently. Imaging systems employing conventional rigid US transducers impose certain constraints, such as not being able to conform to complex surfaces and comfortably come into contact with skin and the sample, and meet the applications of continuous monitoring and diagnosis. To overcome these drawbacks, significant effort has been made in transforming the rigid US transducers to become flexible and wearable. Flexible US transducers ensure self-alignment to complex surfaces and maximize the transferred US energy, resulting in high quality detection performance. The advancement in flexible US transducers has further extended the application range of imaging systems. This review is intended to summarize the most recent advances in flexible US transducers, including advanced functional materials optimization, representative US transducers designs and practical applications in imaging systems. Additionally, the potential challenges and future directions of the development of flexible US transducers are also discussed.

Towards ultrasound wearable technology for cardiovascular monitoring: from device development to clinical validation

“…Moreover, the creation of couplings based on hydrogel encapsulated by elastomer membranes and coated by thin bioadhesive layers makes possible robust adherence of rigid probes to the curvature of the skin [55]. Three-dimensional printing, photolithography, and laser techniques promote the fabrication of flexible and 3D freeform surfaces that offer promising conformability to the skin [55,123,124].…”

The Biomechanics of Musculoskeletal Tissues during Activities of Daily Living: Dynamic Assessment Using Quantitative Transmission-Mode Ultrasound Techniques

“…Sequential scanning approaches, such as those used in synthetic transmit aperture (STA) imaging [368], represent a natural extension of current bi-directional transmission approaches [270] and may be a useful adjuvant to aid multiparameter imaging. Simultaneous developments in wearable ultrasonic arrays are likely to yield viable low-cost methods for extended, serial, and multi-parameter transmission measurements of musculoskeletal tissues that can be acquired at rest during activities of daily living and in settings outside the hospital or the laboratory [369]. Current wearable devices provide 48 h or more of continuous ultrasound scanning to depths of 30-40 mm, with contrast and axial/lateral resolutions in the order of ≈3 dB and 0.25/1.0 mm [370].…”

Conformable ultrasound breast patch for deep tissue scanning and imaging

“…To achieve insights and decoding into the deep tissue, piezoelectric-based ultrasound transducer technology has attracted substantial attention because of its advantages over computed tomography, a more costly and less accessible method that uses ionizing radiation, and magnetic resonance imaging ( 7 , 8 ). Although ultrasound bypasses radiation concerns, this technology faces fundamental challenges, limiting its ubiquitous integration with wearable technologies ( 9 , 10 ). In particular, it is not feasible for current ultrasound transducers to conform to curved body surfaces ( 11 ).…”