Micromachined antenna stents and cuffs for monitoring intraluminal pressure and flow

This paper describes two stainless steel microstructures that are microelectrodischarge machined from 50-[micro]m-thick planar foil for intraluminal measurements of pressure and flow (with potential for applications ranging from blood vessels to bile ducts). The first structure is an inductive antenna stent (stentenna) with 20-mm length and 3.5-mm expanded diameter. It is coupled with capacitive elements to form resonant LC tanks that can be telemetrically queried. The resulting LC tanks are deployed inside silicone mock arteries using standard angioplasty balloons and used in a passive telemetry scheme to sense changes in pressure and flow. Using water as the test fluid, the resonant peaks shift from about 215 to 208 MHz as the flow is increased from 0 to 370 mL/min. The second structure is a ring-shaped intraluminal cuff with two 400 x 750-[micro][m.sup.2] electrodes that are used to provide a direct transduction of flow velocity in the presence of a magnetic field. It is fabricated in a manner similar to the stentenna, but with an insulating segment. The voltage has a linear dependence on flow rate, changing by 3.1-4.3 [micro]V per cm/s of flow (of saline) over a 180 cm/s dynamic range, with a magnetic field of about 0.25 T. [1733] Index Terms--Bloodflow, cardiac, microelectrodischarge machining, sensor network, wireless.