Lead-Free Potassium Sodium Niobate-Based Wearable Ultrasonic Patches for Blood Pressure Detection

Abstract

Ultrasound is one of the most promising methods for blood pressure monitoring due to its harmless, non-invasive, and high-precision characteristics. To further enhance the biocompatibility of ultrasound blood pressure monitors, this work reports wearable ultrasonic patches for blood pressure monitoring based on lead-free KNN (potassium sodium niobate)-based materials. The patches are designed and fabricated with a center frequency of 5 MHz and dimensions of 2.8 mm × 2.8 mm, optimized for both electrical impedance matching and vascular detection. Moreover, biocompatible silicone rubber is used for the packaging. The wearable ultrasonic patches are demonstrated to effectively transmit and receive signals. The diameter of artificial blood vessels is measured to validate the vascular diameter detection capability of the patches. The relationship between blood pressure and vascular diameter is then calculated. A radial artery vascular system platform is built to simulate changes in human blood pressure. Finally, the patches are shown to successfully measure the variation in vessel diameters on this platform. These patches exhibit sufficient detection ability, good biocompatibility, and can adhere tightly to human skin without coupling agents, providing the possibility for safe, sustainable, comfortable, and wearable long-term blood pressure monitoring.

Keywords: KNN; blood pressure detection; lead-free; ultrasonic transducers; wearable.

Figure 1

(a) Photograph of ultrasonic wearable patch adhering to skin for measuring the artery; (b) ultrasonic wearable patch structure; and (c) simulated sound field of patch at 5 MHz.

Figure 2

(a) Impedance phase results for the wearable patch. (b) Diagram of the pulse-echo testing environment. (c) Pulse-echo results for the wearable patch.

Figure 3

The diagram of the principle of blood pressure monitoring.

Figure 4

(a) Diagram of ultrasonic wearable patch measurement of biomimetic blood vessels. (b) Biomimetic vascular experimental patches. (c) Echo signals of biomimetic blood vessels.

Figure 5

(a) Photograph of bionic vascular system. (b) Principle of blood vessel diameter testing.

Figure 6

(a) Echo signals from simulated vascular phantoms with different aperture sizes tested using wearable patches. (b) Measured results (red dots) and the blood pressure–diameter relationship (black line).