Material-discerning proximity sensing

1. A material-discerning proximity sensing device, comprising:

an antenna that is arranged to radiate a radio-frequency signal;

a capacitive sensor that is arranged to detect a change in capacitance of the capacitive sensor and that is arranged to receive the radio-frequency signal; and

an electrical quantity sensor that is arranged to detect a change of the received radio-frequency signal;

wherein the electrical quantity sensor comprises an analog to digital converter arranged to quantify the detected change of the received radio-frequency signal using a sampling rate that is less-than-or-equal-to twice the frequency of a carrier wave of the radio-frequency signal.

2. The device of claim 1 , wherein the analog to digital converter is arranged to quantify the detected change of the capacitance of the capacitive sensor.

3. The device of claim 2 , wherein the analog to digital converter is arranged to output time-multiplexed readings of the received radio-frequency signal and the capacitance of the capacitive sensor.

4. The device of claim 1 , wherein the capacitive sensor is conductive material arranged having a surface.

5. The device of claim 4 , wherein the surface of the capacitive sensor is planar.

6. The device of claim 4 , wherein the antenna is arranged as a coil that, when energized, has an electrical core that extends through a portion of the surface of the capacitive sensor.

7. The device of claim 4 , wherein the antenna is arranged as a series of conductive traces on a substrate that surround an inner portion of the capacitive sensor when viewed as a two-dimensional projection using an axis of projection that is not parallel to a portion of the surface of the capacitive sensor.

8. The device of claim 4 , wherein the antenna is arranged as a coil that, when energized, generates an electrical and magnetic field having an upper lobe and a lower lobe, the upper lobe and lower lobe defining an axis that extends through a portion of the surface of the capacitive sensor.

9. The device of claim 8 , wherein the antenna is arranged to radiate a radio-frequency signal using a transmit output power below the FCC threshold requiring certification.

10. A method for material-discerning proximity sensing, comprising:

radiating a radio-frequency signal using an antenna;

detecting a proximity of an object by detecting a change in capacitance of a capacitive sensor;

receiving the radio-frequency signal using the capacitive sensor;

detecting a change of the received radio-frequency signal;

converting the change of the received radio-frequency to a digital signal, wherein a sampling rate of converting the change of the received radio-frequency to a digital signal is less-than-or-equal-to twice the frequency of a carrier wave of the radio-frequency signal;

monitoring detected changes of the digital signal;

detecting a characteristic of a material of the object based on the detected changes of the digital signal; and

outputting a detection signal in response to detecting the proximity of the object and detecting the characteristic of the material of the object.

11. The method of claim 10 , wherein the characteristic of the material of the object is a conductivity of the material of the object.