US 11,815,644 B2
Foreign object detection circuit using mutual impedance sensing
Hans Peter Widmer, Wohlenschwil (CH); and Lukas Sieber, Olten (CH)
Assigned to WiTricity Corporation, Watertown, MA (US)
Filed by WiTricity Corporation, Watertown, MA (US)
Filed on Nov. 28, 2022, as Appl. No. 18/059,280.
Application 18/059,280 is a continuation of application No. 17/232,868, filed on Apr. 16, 2021, granted, now 11,513,251.
Application 17/232,868 is a continuation of application No. 16/358,534, filed on Mar. 19, 2019, granted, now 11,002,874, issued on May 11, 2021.
Claims priority of provisional application 62/783,488, filed on Dec. 21, 2018.
Prior Publication US 2023/0099095 A1, Mar. 30, 2023
This patent is subject to a terminal disclaimer.
Int. Cl. G01V 3/10 (2006.01); H02J 50/12 (2016.01); H02J 50/60 (2016.01)
CPC G01V 3/104 (2013.01) [H02J 50/12 (2016.02); H02J 50/60 (2016.02)] 18 Claims
OG exemplary drawing
 
1. An apparatus for detecting an object, the apparatus comprising:
a plurality of sense circuits, each of the plurality of sense circuits comprising:
a primary sense coil and a secondary sense coil configured to inductively sense the object and to have a mutual reactance at an operating frequency; and
a capacitor having a reactance at the operating frequency;
a driver circuit configured to selectively drive a current at the operating frequency in the primary sense coil and the capacitor of each of the plurality of sense circuits; and
a measurement circuit configured to selectively measure a voltage across the secondary sense coil and the capacitor of each of the plurality of sense circuits in response to the current in the primary sense coil and the capacitor;
wherein each of the plurality of sense circuits is configured to:
cause the reactance of the capacitor to substantially compensate for the mutual reactance of the primary and secondary sense coils at the operating frequency; and
cause a transimpedance, defined by the ratio of the voltage and the current, to be substantially resistive at the operating frequency.