05.12.2025

A research team at KAIST has developed a flexible ultrasound sensor with adjustable curvature that delivers stable, high-output performance for noninvasive therapeutic use. The device transitions between rigid and flexible states, enabling precise focusing on target tissues. The approach supports future wearable systems for imaging and ultrasound-based treatments.

Image: The image shows three people; Copyright: KAIST

Wearable ultrasound systems may benefit from flexible sensors that adjust curvature to deliver stable imaging and noninvasive therapeutic ultrasound energy.

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KAIST reports the development of a flexible ultrasound sensor designed to overcome performance limitations found in conventional wearable ultrasound devices. Traditional systems often struggle with low acoustic output and limited stability, restricting their use in high-resolution imaging or therapeutic ultrasound applications.

Transition between flexibility and rigidity

The research team, led by Professor Hyunjoo Jenny Lee from the School of Electrical Engineering, created a “flex-to-rigid (FTR)” capacitive micromachined ultrasonic transducer (CMUT). Using semiconductor wafer processing, the device can shift dynamically between flexible and rigid states, enabling reliable body-conforming operation.

The FTR system incorporates a low-melting-point alloy (LMPA). When electrical current is applied, the metal softens, allowing the sensor to bend. After cooling, it solidifies to maintain the selected curvature.

Addressing limitations of polymer-based CMUTs

Polymer-membrane CMUTs typically provide insufficient acoustic energy due
to low elastic modulus and cannot adjust curvature for targeted focusing.
Professor Lee’s group designed a hybrid structure that combines a rigid silicon
substrate with a flexible elastomer bridge. This allows:

stable acoustic performance
dynamic shape adjustment
improved focusing without external beamforming

The LMPA element enables repeated bending without loss of electrical or
mechanical stability.

Potential for therapeutic ultrasound

The device provides acoustic output reaching low-intensity focused ultrasound (LIFU) levels. LIFU can gently stimulate tissues without harming surrounding structures. In preclinical studies on animal models, noninvasive spleen stimulation reduced inflammation and improved mobility in arthritis models.
Experiments confirmed that the FTR sensor can automatically direct ultrasound energy to a defined region based on its curvature and maintain accuracy across multiple deformation cycles.

Outlook: Toward wearable ultrasound systems

The research team plans to extend the technology toward a two-dimensional (2D) sensor array, enabling simultaneous imaging and therapy. Such an array could allow clinicians and nurses to perform real-time monitoring while delivering focused ultrasound treatment.
Since the technology aligns with semiconductor manufacturing processes, it is suitable for scaling, offering potential for:

wearable therapeutic devices
home-use ultrasound systems
integrated smart medical platforms

This development may support broader adoption of ultrasound-based therapies by making systems more adaptable and accessible.

COMPAMED-tradefair.com; Source: KAIST (Korea Advanced Institute of Science and Technology)

More about the KAIST at: www.kaist.ac.kr/en