Piezo Capsule: Ultrasonic Way of Wireless Pressure Measurement

Abstract

Heart failure (HF) rates elevate worldwide with the aging population. Miniaturized and wireless implants with real-time data transfer capability can alleviate the surgical complexities of cardiac pressure monitoring. Despite recent developments of mm-size implants with complex circuitries and self-powering units, a simple, passive, and effective implant design for the real-time pressure reading is missing. Here, the piezo capsule, a simple, cost-effective, and miniaturized passive ultrasound pressure sensing system, is introduced. The capsule design consists of a 1 mm-cube-sized lead zirconate titanate (PZT) transducer and a T-shaped mechanical pin. The impedance changes of an interrogating ultrasound probe, which is ultrasonically coupled to the receiver implant, correlate to the electrical/mechanical loading of the piezo capsule. The ultrasonic sensing properties of the proposed device are characterized across a hard-solid medium (e.g., plexiglass) and soft tissue-like media (e.g., polydimethylsiloxane (PDMS) and chicken breast tissue) and verified the impedance changes using finite element simulations. Last, dynamic wireless pressure readings of an artificial vessel for varying fluid flow pulse-frequency and volumetric rate are demonstrated. The sensitivity of 0.375 Ω kPa−1 is achieved as the pressure changed from 14 to 86 kPa and pulse frequency from 0 to 100 bpm with a fixed flow rate of 8 mL min−1.