Emerging biomedical ultrasound tech: Flexible micromachined ultrasound transducers

A new review article unveils the world of flexible micromachined ultrasound transducers (MUTs), an emerging technology at the intersection of wearables, ultrasound, and MEMS. These cutting-edge devices, which include both piezoelectric (PMUT) and capacitive (CMUT) variants, can offer flexibility and user-friendly health care solutions. Capable of conforming to the body’s contours, flexible MUTs can enable continuous monitoring and targeted stimulation. The study dives deep into the fabrication methods, performance benchmarks, and potential applications of these revolutionary devices.

Ultrasound technology is a cornerstone of medical imaging, commonly using rigid probes that rely on piezoelectric vibration in their thickness mode. While effective, these probes have limitations due to their fabrication methods, such as mechanical dicing.

To overcome these challenges, micromachined alternatives like PMUTs and CMUTs have been developed. These devices offer advantages such as smaller size, lower power consumption, compatibility with CMOS electronics, and efficient batch manufacturing.

Parallelly, a new era of user-friendly alternatives is emerging with the advent of flexible sensor technology. Flexible ultrasound transducers take the MEMS advancements further by introducing the ability to conform to curved surfaces like the human body. Consistent skin contact can reduce diagnostic errors and enhance the quality of results. This technology could obviate the need for experienced operators and operator-dependent variability, a requirement of traditional rigid probes used in traditional clinical settings.

However, key hurdles remain in achieving high-performance materials-stack design, developing reliable manufacturing processes, and ensuring seamless integration with existing medical systems. Overcoming these challenges is crucial for the widespread adoption of flexible micromachined ultrasound transducers (MUTs) in the biomedical field.

On January 16, 2025, a research team from KU Leuven published an in-depth review in Microsystems & Nanoengineering, focusing on the development of flexible micromachined ultrasound transducers. The review offers a comprehensive exploration of flexible micromachined ultrasound transducers, an emerging technology in biomedical diagnostics.

The review paper discusses the need for flexibility in ultrasound transducers, highlighting potential applications and explores the potential of flexible PMUTs and CMUTs in meeting the evolving demands of biomedical research. The authors then examine fabrication techniques for both piezoelectric (PMUT) and capacitive (CMUT) variants, detailing the innovative approaches that enable flexibility without much compromise on performance.

The study compares key performance parameters such as resonance frequency, sensitivity, and flexibility, revealing the unique advantages of each type. For example, PMUTs are known for their low-voltage operation, while CMUTs stand out for their ultra-high bandwidth capabilities.

The research highlights the critical role of material selection and design optimization in achieving the desired performance characteristics. The article also addresses challenges in integrating these flexible devices with electronic systems, proposing solutions to overcome these obstacles.

This comprehensive analysis not only summarizes the current state of the field but also outlines future research directions needed to unlock the full potential of flexible MUTs in biomedical applications, providing valuable insights for researchers, engineers, and health care professionals.

Sanjog Vilas Joshi, one of the lead authors of the study, commented, “The emergence of flexible micromachined ultrasound transducers opens up interesting possibilities in biomedical ultrasound, for instance, the integration of flexible MUTs into everyday health care in the form of smart patches for remote patient monitoring. However, achieving such pioneering goals requires addressing technical limitations, such as those outlined in the review.

“To achieve this, further investment in R&D on flexible MUT-based technologies is required. In the recent research domain of flexible ultrasound, bulk piezoelectric transducers have shown great promise with various demonstrated applications including wearable ultrasound imaging and continuous monitoring.

“On the other hand, flexible CMUTs are emerging demonstrating proof of concept for imaging. Flexible PMUTs remain the most recent one with significant optimization challenges. Nevertheless, with sustained research, flexible MUTs have the potential to close the gap with other mature ultrasound modalities and unlock new opportunities in wearable ultrasound to aid diagnostics and disease prevention. “