Innovation. A flexible ultrasound sensor that opens new possibilities for wearable devices

Korea Advanced Institute of Science and Technology (KAIST) researchers have developed a flexible ultrasound sensor with statically adjustable curvature.

This breakthrough opens new possibilities for wearable medical devices that can capture precise, body-conforming images and perform noninvasive treatments using ultrasound energy.

`Flex-to-rigid’ (FTR) capacitive micromachined ultrasonic transducer (CMUT) is capable of transitioning freely between flexibility and rigidity using a semiconductor wafer process (MEMS).

The team incorporated a low-melting-point alloy (LMPA) inside the device. When an electric current is applied, the metal melts, allowing the structure to deform freely; upon cooling, it solidifies again, fixing the sensor into the desired curved shape.

Conventional polymer-membrane-based CMUTs have suffered from a low elastic modulus, resulting in insufficient acoustic power and blurred focal points during vibration. They have also lacked curvature control, limiting precise focusing on target regions.

FTR structure combines a rigid silicon substrate with a flexible elastomer bridge, achieving both high output performance and mechanical flexibility. The embedded LMPA enables dynamic adjustment and fixation of the transducer’s shape by toggling between solid and liquid states through electrical control.

As a result, the new sensor can automatically focus ultrasound on a specific region according to its curvature – without requiring separate beamforming electronics – and maintains stable electrical and acoustic performance even after repeated bending.

The device’s acoustic output reaches the level of low-intensity focused ultrasound (LIFU), which can gently stimulate tissues to induce therapeutic effects without causing damage. Experiments on animal models demonstrated that noninvasive spleen stimulation reduced inflammation and improved mobility in arthritis models.

Since the technology is compatible with semiconductor fabrication processes, it can be mass-produced and adapted for wearable and home-use ultrasound systems.
MB Bureau