Wetness sensor using RF circuit with frangible link

摘要

A wetness sensor includes a substrate that carries a tuned RF circuit. The circuit includes a conductive pattern applied to the substrate, a capacitor, and a jumper all disposed on a same side of the substrate. The conductive pattern includes an inductive coil, and an inner and outer terminus. The jumper electrically couples the inner terminus to the outer terminus. The jumper also includes a frangible link which, when contacted by a target fluid, produces a drastic change in the operation of the RF circuit. The drastic change can be interpreted by a remote reader as a “wet” condition. Contact of the frangible link by the target fluid may change the impedance or resistance of the RF circuit by at least a factor of 5, 10, 100, or more, and/or may cause the frangible link to disintegrate to produce an open circuit, and/or may substantially render the RF circuit inoperative.

主权项

1. A sensor, comprising:
a first substrate; and a tuned RF circuit carried by the first substrate, the RF circuit including a first conductive pattern, a first capacitor, and a jumper all disposed on a same side of the first substrate, the RF circuit being characterized by an impedance or resistance; wherein the first conductive pattern includes a coil, an inner terminus, and an outer terminus; wherein the jumper electrically couples the inner terminus to the outer terminus; and wherein the jumper includes a frangible link, and the impedance or resistance of the RF circuit changes by at least a factor of 5 when the frangible link is contacted by a target fluid.