Wetness sensor using RF circuit with frangible link

US8978452B2 · kind B2 · utility

Assignee

• 3M INNOVATIVE PROPERTIES COMPANY · US

Inventors

• Justin M. Johnson · Hudson, US
• Lori-Ann S. Prioleau · Windom, US
• Brinda B. Badri · Woodbury, US
• James C. Vanous · Roseville, US
• Robert D. Lorentz · Saint Paul, US
• Jacob D. Chatterton · Windom, US
• Steven J. Perron · Windom, US
• Donald R. Battles · Arden Hills, US

Key dates

• Filing date: Aug 11, 2011
• Grant date: Mar 17, 2015
• Expiry date: Nov 9, 2032

Classification

• Technology area (CPC A): Human Necessities
• CPC primary: A61F2013/424
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

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.