Foreign object detection using infared sensing
View Patent ↗Certain aspects of the present disclosure provide methods and apparatuses for detecting foreign objects via infrared sensing. One example apparatus generally includes at least one infrared (IR) sensor configured to output a thermal signal indicative of a temperature of an area. The apparatus further includes at least one time differentiator coupled to the at least one IR sensor, the at least one time-differentiator being configured to generate a time-differentiated thermal signal based on the thermal signal. The apparatus further includes at least one correlation unit configured to correlate the time-differentiated thermal signal to a varying exposure level magnetic field. The apparatus further includes a determining unit configured to determine whether an object is present in the area based on the correlation of the time-differentiated thermal signal to the varying exposure level magnetic field.
1. An apparatus for detecting an object, the apparatus comprising:
at least one infrared (IR) sensor configured to output a thermal signal indicative of a temperature of an area;
at least one time differentiator coupled to the at least one IR sensor, the at least one time-differentiator being configured to generate a time-differentiated thermal signal based on the thermal signal;
at least one correlation unit configured to correlate the time-differentiated thermal signal to a varying exposure level magnetic field; and
a determining unit configured to determine whether the object is present in the area based on the correlation of the time-differentiated thermal signal to the varying exposure level magnetic field.
2. The apparatus of claim 1 , wherein the time-differentiated thermal signal is indicative of a change of the temperature in the area from a first time to a second time.
3. The apparatus of claim 1 , wherein the at least one IR sensor comprises a plurality of IR sensors, and wherein the determining unit is configured to determine whether the object is present in the area based on whether any of a plurality of time-differentiated thermal signals corresponding to the plurality of IR sensors correlates to the varying exposure level magnetic field.
4. The apparatus of claim 1 , further comprising a limiter configured to limit the time-differentiated thermal signal to an upper and lower limit.
5. The apparatus of claim 1 , further comprising a circuit configured to generate a non-linearity in the time-differentiated thermal signal prior to input of the time-differentiated thermal signal to the at least one correlation unit.
6. The apparatus of claim 1 , wherein the correlation unit is configured to perform the correlation in the time domain by generating an output indicative of whether a first value of the time-differentiated thermal signal at a first time correlates with a first level of the varying exposure level magnetic field at the first time and a second value of the time-differentiated thermal signal at a second time correlates with a second level of the varying exposure level magnetic field at the second time, the second level higher than the first level, such that the second value is greater than the first value.
7. The apparatus of claim 1 , wherein the correlation unit is configured to perform the correlation in the frequency domain by generating an output indicative of whether a frequency of the time-differentiated thermal signal correlates to a frequency of change in exposure level of the varying exposure level magnetic field.
8. The apparatus of claim 1 , wherein the correlation unit comprises a narrow band filter.
9. The apparatus of claim 1 , wherein an exposure level of the varying exposure level magnetic field varies periodically.
10. The apparatus of claim 1 , wherein the correlation unit is further configured to apply a time shift to one of the time-differentiated thermal signal and a signal indicative of the varying exposure level magnetic field before performing the correlation.
11. The apparatus of claim 1 , wherein the time differentiator comprises at least one of: a delay line filter configured to substantially cancel out a DC component of the thermal signal or a high pass filter having a cut-off frequency lower than a frequency of variation of the varying exposure level magnetic field.
12. The apparatus of claim 1 , further comprising a transmitter configured to output the varying exposure level magnetic field.
13. The apparatus of claim 1 , wherein the varying exposure level magnetic field comprises a wireless power field for coupling by a wireless power receiver to transfer power from a transmitter to the wireless power receiver.
14. The apparatus of claim 1 , wherein the apparatus further comprises a wireless power receive element configured to inductively couple power via the varying exposure level magnetic field.
15. A method for detecting an object, the method comprising:
generating a time-differentiated thermal signal based on a thermal signal indicative of a temperature of an area;
correlating the time-differentiated thermal signal to a varying exposure level magnetic field; and
determining whether the object is present in the area based on the correlation of the time-differentiated thermal signal to the varying exposure level magnetic field.
16. The method of claim 15 , wherein the time-differentiated thermal signal is indicative of a change of the temperature in the area from a first time to a second time.
17. The method of claim 15 , wherein the thermal signal corresponds to an output of at least one infrared (IR) sensor.
18. The method of claim 15 , further comprising limiting the time-differentiated signal to an upper and lower limit prior to the correlation.
19. The method of claim 15 , further comprising generating a non-linearity in the time-differentiated thermal signal prior to input of the time-differentiated thermal signal to the at least one correlation unit.
20. The method of claim 15 , wherein correlating the time-differentiated thermal signal to the varying exposure level magnetic field comprises generating an output indicative of whether a first value of the time-differentiated thermal signal at a first time correlates with a first level of the varying exposure level magnetic field at the first time and a second value of the time-differentiated thermal signal at a second time correlates with a second level of the varying exposure level magnetic field at the second time, the second level higher than the first level, such that the second value is greater than the first value.
21. The method of claim 15 , wherein correlating the time-differentiated thermal signal to the varying exposure level magnetic field comprises performing the correlation in the frequency domain by generating an output indicative of whether a frequency of the time-differentiated thermal signal correlates to a frequency of change in exposure level of the varying exposure level magnetic field.
22. The method of claim 15 , wherein an exposure level of the varying exposure level magnetic field varies periodically.
23. The method of claim 15 , wherein correlating the time-differentiated thermal signal to the varying exposure level magnetic field comprises applying a time shift to one of the time-differentiated thermal signal and a signal indicative of the varying exposure level magnetic field before performing the correlation.
24. The method of claim 15 , wherein generating the time-differentiated thermal signal comprises at least one of: substantially cancelling out a DC component of the thermal signal or cutting-off frequencies in the thermal signal lower than a frequency of variation of the varying exposure level magnetic field.
25. The method of claim 15 , further comprising outputting the varying exposure level magnetic field.
26. The method of claim 25 , wherein the varying exposure level magnetic field comprises a wireless power field for coupling by a wireless power receiver to transfer power from a transmitter to the wireless power receiver.
27. An apparatus for detecting an object, the apparatus comprising:
means for generating a time-differentiated thermal signal based on a thermal signal indicative of a temperature of an area;
means for correlating the time-differentiated thermal signal to a varying exposure level magnetic field; and
means for determining whether an object is present in the area based on the correlation of the time-differentiated thermal signal to the varying exposure level magnetic field.
28. The apparatus of claim 27 , further comprising means for limiting the time-differentiated signal to an upper and lower limit prior to the correlation.
29. The apparatus of claim 27 , wherein means for correlating the time-differentiated thermal signal to the varying exposure level magnetic field comprises means for generating an output indicative of whether a first value of the time-differentiated thermal signal at a first time correlates with a first level of the varying exposure level magnetic field at the first time and a second value of the time-differentiated thermal signal at a second time correlates with a second level of the varying exposure level magnetic field at the second time, the second level higher than the first level, such that the second value is greater than the first value.
30. A computer readable storage medium comprising instructions that when executed by a processing device cause the processing device to perform a method for detecting an object, the method comprising:
generating a time-differentiated thermal signal based on a thermal signal indicative of a temperature of an area;
correlating the time-differentiated thermal signal to a varying exposure level magnetic field; and
determining whether the object is present in the area based on the correlation of the time-differentiated thermal signal to the varying exposure level magnetic field.