Systems, methods, and apparatus for detecting ferromagnetic foreign objects in a predetermined space
One aspect of the disclosure provides apparatus for detecting an object. The apparatus comprises a sense coil. The apparatus comprises a processor configured to determine an amount of change in a reactance of the sense coil from a previous reactance value for the sense coil. The processor is configured to determine an amount of change in a resistance of the sense coil from a previous resistance value for the sense coil. The processor is configured to determine a presence of the object based on a relationship between the amount of change in the reactance of the sense coil and the amount of change in the resistance of the sense coil. The processor performs an inverse tangent operation on a quotient of the amount of change in the reactance of the sense coil divided by the amount of change in the resistance of the sense coil.
1. An apparatus for detecting an object, comprising:
a sense coil configured to receive a voltage signal from a signal generator; and
a processor configured to:
determine an amount of change in a reactance measured at a sense frequency f s , of the sense coil from a previous reactance value previously measured at the sense frequency f s for the sense coil,
determine an amount of change in a resistance of the sense coil from a previous resistance value for the sense coil,
perform a trigonometric operation on a ratio of the amount of change in the reactance of the sense coil to the amount of change in the resistance of the sense coil,
determine a type of the object based on a result of the trigonometric operation falling within a predetermined range of values corresponding to the type of the object and determine a presence of the object based on the trigonometric operation.
2. The apparatus of claim 1 , wherein the processor is further configured to receive a signal from the sense coil, and wherein the reactance of the sense coil and the resistance of the sense coil are determinable from the received signal.
3. The apparatus of claim 2 , wherein the processor is further configured to high pass filter the received signal from the sense coil.
4. The apparatus of claim 1 , wherein the processor is further configured to determine the presence of a living object when the amount of change in the reactance of the sense coil is positive and the amount of change in the resistance of the sense coil is positive.
5. The apparatus of claim 1 , wherein the processor is further configured to determine the presence of a metallic object when the amount of change in the reactance of the sense coil is negative and the amount of change in the resistance of the sense coil is positive.
6. The apparatus of claim 1 , wherein the processor is configured to determine the type of the object as a metallic object or a living object based on the result of the trigonometric operation falling within a predetermined range of values corresponding to metallic objects or a predetermined range of values corresponding to living objects.
7. The apparatus of claim 1 , wherein the processor is further configured to trigger a positive object detection event when the trigonometric operation satisfies a triggering criteria for a predetermined amount of time.
8. The apparatus of claim 1 , wherein the previous reactance value for the sense coil is a reactance of the sense coil when no object is present and the previous resistance value for the sense coil is the resistance of the sense coil when no object is present.
9. An apparatus for detecting an object, comprising:
means for sensing an object configured to receive a voltage signal from a signal generator;
means for determining an amount of change in a reactance measured at a sense frequency f s of the means for sensing the object from a previous reactance value previously measured at the sense frequency f s for the means for sensing the object,
means for determining an amount of change in a resistance of the means for sensing the object from a previous resistance value for the means for sensing the object,
means for performing a trigonometric operation on a ratio of the amount of change in the reactance of the means for sensing the object to the amount of change in the resistance of the means for sensing the object;
means for determining a type of the object based on a result of the trigonometric operation falling within a predetermined range of values corresponding to the type of the object; and
means for determining a presence of the object based the trigonometric operation.
10. The apparatus of claim 9 , further comprising means for determining the presence of a living object when the amount of change in the reactance of the means for sensing the object is positive and the amount of change in the resistance of the means for sensing the object is positive.
11. The apparatus of claim 9 , further comprising means for determining the presence of a metallic object when the amount of change in the reactance of the means for sensing the object is negative and the amount of change in the resistance of the means for sensing the object is positive.
12. The apparatus of claim 9 , further comprising means for determining the type of the object as a metallic object or a living object based on the result of the trigonometric operation coinciding with a predetermined range of values corresponding to metallic objects or a predetermined range of values corresponding to living objects.