Pressure Sensor Embedded Inductive Coil Toward a Wireless Pressure Sensing Stent

Abstract

This paper reports the development of a wireless pressure sensing coil system by embedding a capacitive micro sensor onto a wire. The coil system, consisting of an inductor (coil itself) and multiple capacitors (sensors), formed a passive LC telemetry configuration for wireless sensing. The capacitive sensor, utilizing the movements of a liquid in a sealed chamber for hydraulic amplification, enabled high capacitance changes and amplified signal outputs. The capacitive sensor also produced digitized signal outputs as the liquid movement crossed a finite number of the interdigitated electrodes. Such characteristics were modeled and confirmed by establishing an equivalent fluidic circuit. The capacitive sensor was fabricated by grafting and polishing a copper wire piece on a silicon wafer, then performing standard microfabrication on the polished wire surface and filling a liquid into a sensor chamber. The fabricated pressure sensing coil system demonstrated a pressure sensitivity of 11.8 kHz/mmHg under a clinical pressure range of 0~206.9 mmHg in an ex vivo test with a water flowing tube, meeting the requirements for wireless detection of vessel restenosis. The sensitivity corresponded to the capacitance changes of 0.052 fF/mmHg and liquid displacement of 0.39 μm/mmHg. The fabricated coil system held a dimension of 2.5 mm in diameter and 7.2 mm in length in the form of a wound wire (copper, 260 μm in diameter). The embedded capacitive sensor consisted of a hydraulic chamber of 400×100×1 2 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and a microchannel of 500×20×1 2 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . [2020-0364]