Wireless charging system and associated methods
A wireless charging system concurrently charges several wireless devices within a shielded chamber acting as a hollow electromagnetic waveguide. Electrically conductive walls of the chamber create transverse modes that support longitudinal propagation of the electromagnetic field along the waveguide with no diminution of the energy flux density due to the inverse-square law. A transmitting antenna located inside the chamber emits an electromagnetic field that excites one or more transverse modes of the waveguide. An absorptive lid absorbs the electromagnetic field to minimize reflections that could excite longitudinal modes. Each wireless device includes a whisker antenna that receives part of the electromagnetic field for charging a battery. Due to the spatial uniformity of the electromagnetic field, the wireless devices charge with high efficiency regardless of their positions, ensuring they all charge at a similar rate.
1. A wireless charging system, comprising:
a hollow electromagnetic waveguide;
an input coupler located near a first longitudinal end of the hollow electromagnetic waveguide, the input coupler being operable to excite a propagation mode of the hollow electromagnetic waveguide;
an absorptive material located near a second longitudinal end of the hollow electromagnetic waveguide; and
a platform within the hollow electromagnetic waveguide such that at least one wireless device positioned on the platform converts electromagnetic energy from the propagation mode into electrical energy;
wherein the absorptive material is configured to absorb electromagnetic energy from the propagation mode that is not converted into electrical energy by the at least one wireless device.
2. The wireless charging system of claim 1 , the second longitudinal end further comprising an openable lid.
3. The wireless charging system of claim 2 , the absorptive material being affixed to the openable lid such that the absorptive material terminates the hollow electromagnetic waveguide when the openable lid is closed.
4. The wireless charging system of claim 1 , the first longitudinal end of the hollow electromagnetic waveguide having an electrically conductive layer facing inside the hollow electromagnetic waveguide.
5. The wireless charging system of claim 1 ,
the hollow electromagnetic waveguide having transverse dimensions such that the input coupler only excites a transverse electric TE 10 mode.
6. The wireless charging system of claim 1 , the platform being configured to position the at least one wireless device away from the input coupler such that the at least one wireless device does not couple with a near field that is generated by the input coupler when the input coupler is electrically driven.
7. The wireless charging system of claim 1 , further comprising a driver configured to electrically drive the input coupler.
8. The wireless charging system of claim 4 , wherein the electrically conductive layer is grounded to form a counterpoise for the input coupler.
9. The wireless charging system of claim 1 , further comprising a sense antenna located inside the hollow electromagnetic waveguide.
10. The wireless charging system of claim 1 , the hollow electromagnetic waveguide having either a square cross section or a rectangular cross section.
11. A wireless power transfer (WPT) method, comprising:
positioning one or more wireless devices inside a hollow electromagnetic waveguide; and
exciting, near a first longitudinal end of the hollow electromagnetic waveguide, a propagation mode of the hollow electromagnetic waveguide;
converting, with each wireless device of the one or more wireless devices, electromagnetic energy from the propagation mode into electrical energy; and
absorbing, with an absorptive material located near a second longitudinal end of the hollow electromagnetic waveguide, electromagnetic energy from the propagation mode that is not converted into electrical energy by the one or more wireless devices.
12. The WPT method of claim 11 , further comprising charging a battery of said each wireless device with the electrical energy.
13. The WPT method of claim 11 , wherein:
the second longitudinal end comprises a lid; and
the method further comprises:
opening the lid prior to said positioning; and
closing the lid after said positioning.
14. The WPT method of claim 11 , further comprising wirelessly communicating, prior to said exciting, with each wireless device, of the one or more wireless devices, to determine an identity of said each wireless device.
15. The WPT method of claim 11 , wherein said exciting includes electrically driving an input coupler positioned near the first longitudinal end of the hollow electromagnetic waveguide.
16. The WPT method of claim 15 , wherein said positioning includes positioning the one or more wireless devices away from the input coupler so that the one or more wireless devices do not couple with a near field generated by the input coupler.
17. The WPT method of claim 15 , where said electrically driving includes feeding an oscillatory drive signal from a power amplifier to the input coupler.
18. The WPT method of claim 17 , further comprising:
monitoring a standing-wave ratio of the oscillatory drive signal; and
disabling the power amplifier when the standing-wave ratio exceeds a threshold.
19. The WPT method of claim 12 , further comprising:
pausing, at intervals, said exciting the hollow electromagnetic waveguide;
transmitting an interrogation signal within the hollow electromagnetic waveguide;
receiving, from at least one wireless device, of the one or more wireless devices, a status message indicating a battery level of the battery of the at least one wireless device; and
resuming said exciting the hollow electromagnetic waveguide if the battery level is below a threshold.
20. The wireless charging system of claim 1 , the input coupler comprising one of a probe coupler and a magnetic loop coupler.