Flexible ultrasonic sensor offers accurate, cuff-free blood pressure readings

A new technology has been developed that enables cuffless non-invasive blood pressure monitoring by using ultrasonic to track real-time changes in vascular diameter-without the need for a traditional cuff. The technology is expected to serve as a core component in future wearable healthcare devices and smart medical monitoring platforms.

A research team led by Dr. Shin Hur at the Korea Institute of Machinery and Materials (KIMM, President Seog-Hyeon Ryu), including Syed Turab Haider Zaidi, a student researcher from the UST–KIMM School at KIMM, in collaboration with Dr. Byung-Chul Lee's team at the Korea Institute of Science and Technology (KIST), has developed the world's first skin-attachable, noninvasive blood pressure sensor using PMN-PT single-crystal piezoelectric composites integrated through a low-temperature soldering process.

*PMN-PT (Lead Magnesium Niobate–Lead Titanate) is a single-crystal piezoelectric material known for its exceptionally high electromechanical properties.

The team applied a dual-side SnBi (tin–bismuth) low-temperature solder bonding technique to integrate high-performance piezoelectric devices onto a flexible substrate without depolarization. They designed and fabricated a 5×4 array structure ultrasonic transducer array (UTA). The ultrasonic beam from this sensor penetrates the skin, detects signals reflected from the vessel walls, and measures changes in vessel diameter. Using this principle, it measures the real-time changes in blood vessel diameter corresponding to systolic and diastolic blood pressure and calculates blood pressure values. Built on a flexible polyimide (PI) substrate with a Parylene-C encapsulation layer, the sensor adheres securely to human skin and maintains a total thickness under 0.5 mm and a weight below 1 g, ensuring long-term wearability.

The sensor operates by transmitting ultrasound generated by PMN-PT single-crystal 1–3 composites into blood vessels, analyzing the reflected echoes to measure the vascular diameter and calculating blood pressure. To optimize acoustic propagation and reflection characteristics, the team conducted multi-physics simulations using COMSOL. The dual-side low-temperature soldering method (below 150 °C) prevents thermal depolarization commonly observed in lead-based piezoelectric devices, ensuring high signal-to-noise ratio (SNR) and strong electrical bonding reliability without requiring high-temperature processing.

Existing optical cuffless blood pressure measurement technology is susceptible to external environmental factors such as skin color, movement, and lighting. It also has limitations in that it can only measure blood vessels close to the skin surface, making it unable to measure blood pressure in deep blood vessels. In contrast, ultrasound-based blood pressure measurement technology can directly measure actual diameter changes in deep blood vessels beneath the skin. Traditional ultrasonic sensors made with rigid PZT materials also suffer from poor wearability, whereas the PMN-PT composite combined with low-temperature soldering enables conformal attachment to curved skin surfaces without performance loss. The simplified structure maintains excellent SNR without acoustic matching or backing layers, improving manufacturing efficiency. The sensor achieves high accuracy (within ±4 mmHg), flexible and skin-attachable performance, offering clear advantages over existing technologies.

The team validated the sensor using an artificial-skin vascular phantom. The measured systolic and diastolic blood pressures showed errors of ±4 mmHg and ±2.3 mmHg, respectively-meeting the AAMI clinical standard of ±5 mmHg. This represents one of the highest accuracy levels reported for noninvasive ultrasonic blood pressure monitoring.

This technology is the first to demonstrate continuous, cuff-free blood pressure monitoring using a skin-attachable ultrasonic sensor. Combined with AI-based blood pressure analysis, it will evolve into a core platform for personalized cardiovascular disease prediction and smart healthcare."

Dr. Shin Hur, Korea Institute of Machinery and Materials

The development of this non-invasive blood pressure sensor was carried out with support from the Ministry of Trade, Industry and Resources' Materials and Components Technology Development Program (project: Development of Multi-Sensory Sensors for Service Robots). This research was published in January 2026 under the title "Skin-Conformal PMN-PT Ultrasonic Sensor for Cuffless Blood Pressure Sensing via Eutectic Solder Integration" in Microsystem & Nanoengineering, which ranks first in the Instruments & Instrumentation category (JCR 0.6%, Impact Factor 9.9, as of 2024).