Systems, methods, and apparatus for detection of metal objects in a predetermined space

A method for detecting a presence of an object, the method comprising:

• applying a signal to a plurality of resonant sense circuits, each having a resonant frequency, each resonant sense circuit coupled to a multiplexer and comprising a respective first electrically conductive structure and a coupling circuit configured to determine resonance and an amount of coupling, the first electrically conductive structures comprising a plurality of first loops collectively defining a first plane, and wherein the plurality of resonant sense circuits and the multiplexer are coupled with at least one capacitor therebetween;
• wirelessly transmitting power via a second electrically conductive structure different from the first electrically conductive structures, the power transmitted via a magnetic field at a sufficient level to power or charge a load, the second electrically conductive structure comprising a second loop defining a second plane substantially parallel with the first plane, the plurality of first loops at least overlapping an area enclosed by the second loop;
• and
• detecting the presence of the object via a detection circuit coupled to the multiplexer in response to detecting a difference between a measured characteristic that depends on a frequency at which the resonant sense circuit is resonating and a corresponding characteristic that depends on the resonant frequency of the resonant sense circuit.

An apparatus for detecting a presence of an object, the apparatus comprising:

• a plurality of means for resonating at a plurality of resonant frequencies, the plurality of resonating means positioned in a multi-dimensional array;
• means for determining resonance and an amount of coupling;
• means for multiplexing coupled to the plurality of resonating means with at least one capacitor therebetween
• means for wirelessly transmitting power via a magnetic field at a level sufficient to power or charge a load;
• and
• means for detecting the presence of the object in response to detecting a difference between a measured characteristic that depends on frequencies at which each of the plurality of resonating means is resonating and a corresponding characteristic that depends on the resonant frequencies of each the plurality of resonating means.

An apparatus for detecting a presence of an object, the apparatus comprising:

• a plurality of sense circuits comprising respective electrically conductive structures, the plurality of sense circuits including at least a first sense circuit and a second sense circuit, the first sense circuit comprising a first electrically conductive structure and forming a first resonant circuit having a first resonant frequency, and the second sense circuit comprising a second electrically conductive structure and forming a second resonant circuit having a second resonant frequency different than the first resonant frequency;
• wherein the respective electrically conductive structures each form respective loops, the loops positioned in a multi-dimensional array defining a first plane;
• a detection circuit coupled to the first and second sense circuits, the detection circuit configured to detect the presence of the object in response to detecting:
• a difference between a first measured characteristic that depends on a frequency at which the first resonant circuit is resonating and a first corresponding characteristic that depends on the first resonant frequency, or
• a difference between a second measured characteristic that depends on a frequency at which the second resonant circuit is resonating and a second corresponding characteristic that depends on the second resonant frequency;
• and
• a coupling circuit coupled between the first and second sense circuits and the detection circuit, the coupling circuit configured to reduce variation of the first and second resonant frequencies by the detection circuit in the absence of the object,
• wherein the first and second sense circuits further comprise a first and second capacitor, respectively, the first and second capacitors each having values tuned to determine the first and second resonant frequencies, respectively, wherein the coupling circuit comprises a third capacitor coupled between the detection circuit and the first and second sense circuits, at least the third capacitor and the first capacitor forming a capacitive voltage divider.

An apparatus for detecting a presence of an object, the apparatus comprising:

• a plurality of resonant sense circuits, each having a resonant frequency, each resonant sense circuit comprising an electrically conductive structure and a coupling circuit configured to determine resonance and an amount of coupling, the electrically conductive structure comprising a loop positioned within a multidimensional loop array;
• a multiplexer coupled to the plurality of resonant sense circuits;
• and
• a detection circuit coupled to the multiplexer, the detection circuit configured to detect the presence of the object in response to detecting a difference between a measured characteristic that depends on a frequency at which a resonant sense circuit of the plurality of resonant sense circuits is resonating and a corresponding characteristic that depends on the resonant frequency of the resonant sense circuit at least one capacitor coupled between the multiplexer and the detection circuit.