Electronics-Free Deep-Tissue Sensing via Passive Ultrasonic Backscatter
Affiliation Type:
Academia
Keywords:
Backscatter, Implant, Demodulation, Antiresonance
Abstract:
Monitoring physiological signals in deep tissue is limited by implant size, power constraints, and poor wireless signal penetration. Traditional implantable sensors depend on active electronics and electromagnetic transmission, which hinder miniaturization and reduce long-term reliability. A fully passive ultrasonic sensing method addresses these limitations by encoding capacitive sensor states as antiresonance shifts in the backscattered signal of a piezoelectric transducer. This study experimentally validates the approach by demonstrating that shifts observed in the backscatter signal closely match resonance changes directly measured at the implant. In an acoustic tank setup using 2 MHz piezoceramic elements, a 10×10 mm implant loaded with 0–681 pF capacitors exhibited antiresonance shifts up to ~11.02 kHz in backscatter and ~3.01 kHz in resonance. Lower capacitance values (0–204 pF) enhanced sensitivity, while both methods showed consistent shifts at higher ranges. The strong agreement between backscatter and implant responses confirms that the observed changes stem from passive capacitive modulation, highlighting the potential of this method for scalable, long-term deep-tissue biosensing.
