AUTOMATICALLY TUNING A TRANSMITTER TO A RESONANCE FREQUENCY OF A RECEIVER

• US 20120311356A1
• Filed: 04/20/2012
• Published: 12/06/2012
• Est. Priority Date: 05/31/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: TAN, Li-Quan
• Granted Patent: US 8,796,886 B2
• Time in Patent Office: Days
• US Class Current: 713/310
• CPC Class Codes: H01F 38/14 Inductive couplings for wireless supply or distribution of electric power using inductive coupling H02J50/10
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/40 using two or more transmitting or receiving devices H02J50/50 takes precedence
• CPC Class Codes: H02J 7/0042 characterised by the mechanical construction
• CPC Class Codes: H04B 5/26 using coils
• CPC Class Codes: H04B 5/263 Multiple coils at either side
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer

Abstract

Various embodiments of a wirelessly powered local computing environment are described. The wireless powered local computing environment includes at least a near field magnetic resonance (NFMR) power supply arranged to wirelessly provide power to any of a number of suitably configured devices. In the described embodiments, the devices arranged to receive power wirelessly from the NFMR power supply must be located in a region known as the near field that extends no further than a distance of a few times a characteristic size of the NFMR power supply transmission device. Typically, the distance can be on the order of 1 meter or so. The NFMR power supply is used to tune a transmitter in order to maintain a high Q factor.

Claims

1. A wireless power transmission unit comprising:

a varying frequency excitation source arranged to provide a variable circuit excitation at frequency f; and

a first resonator structure coupled to the varying frequency f power supply, the first resonator structure having a resonant frequency ω

₁, a first Q factor Q₁, and a characteristic size L₁ wherein non-radiative energy transfer between the first resonator structure and at a second resonator structure positioned apart from the transmission unit, the second resonator structure having a resonant frequency ω

₂, a second Q factor Q₂, and a characteristic size L₂ is mediated through a magnetic resonant coupling associated with evanescent tails between the first resonator structure and the second resonator structure when the first resonator structure and the second resonator structure are in a tuned state when the first resonant frequency ω

₁ and the second resonant frequency ω

₂ are within the narrower of first resonance width Γ

₁ or second resonance width Γ

₂ such that the first resonant frequency ω

₁ and the resonant frequency ω

₂ are separated by a bandwidth of no more than 3 db, wherein the first resonator structure maintains the first resonator structure and the second resonator structure in the tuned state by varying the first resonant frequency ω

₁ such that the first resonant frequency ω

₁ and the resonant frequency ω

₂ are separated by the bandwidth of no more than 3 db or are within the narrower of first resonance width Γ

₁ or second resonance width Γ

₂ in accordance with any changes in the second resonant frequency ω

₂.

2. The wireless power transmission unit as recited in claim 1, wherein the varying frequency excitation source is a varying voltage supply arranged to provide frequency dependent voltage V_f.

3. The wireless power transmission unit as recited in claim 2, wherein the first resonator structure comprises:

a transmitter coil coupled to the varying frequency f power supply, wherein in the tuned state, the transmitter coil wirelessly provides real power P_real at the first resonant frequency ω

₁ to the second resonator structure by magnetic resonant inductive coupling, the transmitter coil having a representative transmitter coil resistance R_coil.

4. The wireless power transmission unit as recited in claim 3, wherein the transmitter coil further comprising:

a variable impedance element coupled in series with the transmitter coil resistance R_coil.

5. The wireless power transmission unit as recited in claim 4, further comprising an average current (I_ave) indicator connected in series to the varying voltage supply, the transmitter coil resistance R_coil and the variable impedance element, the I_ave indicator arranged to provide an indication of an average current I_ave in real time in the wireless power transmission unit;

a parasitic resistance R_p connected in series with the variable impedance element and the coil resistance R_coil; and

a receiver load R_p corresponding to a receiver load representing a load on the wireless power transmission unit caused by the coupling of the first resonator structure and the second resonator structure

6. The wireless power transmission unit as recited in claim 5, wherein the wireless power transmission unit has an effective circuit impedance Z_circuit at resonance in accordance with Z_circuit=R_s+R_coil+R_p+R_r.

7. The wireless power transmission unit as recited in claim 6, further comprising:

a processor coupled with the varying frequency voltage supply and with the average current I_ave indicator arranged to calculate a real power (P_real) value corresponding to an amount of real power P_real wirelessly transmitted by the first resonator structure to the second resonator structure in real time in the tuned state.

8. The wireless power transmission unit as recited in claim 7, wherein the processor calculates the amount of real power P_real wirelessly transmitted by the first resonator structure to the second resonator structure in accordance with P_Real=(I_ave)²Z_circuit.

9. The wireless power transmission unit as recited in claim 8, wherein the processor automatically determines second resonant frequency ω

₂ by;

setting the frequency f of the variable voltage supply to a current frequency f_current;

performing a frequency sweep by incrementing the current frequency f_current in a range of frequencies having a low frequency f_low and a high frequency f_high;

adjusting the variable impedance element to maintain the wireless power transmission unit in resonance at the current frequency f_current;

instructing the I_ave indicator to periodically measure the I_ave as a current I_ave at the current frequency f_current;

calculating a current real power P_real at the current frequency f_current;

comparing the current real power P_real with a previously calculated real power P_real;

if the current real power P_real is less than the previously calculated real power P_real by at least a pre-determined amount, then setting the frequency f of the variable voltage supply to the current frequency f_current, otherwise,

adjusting the current frequency f_current within the range of frequency low f_low to frequency high f_high.

10. The wireless power transmission unit as recited in claim 9, comprising:

a variable capacitance element having a variable capacitance value C, the variable capacitance element coupled to the processor, wherein the processor maintains the wireless power transmission unit in resonance during the frequency sweep by adjusting the variable capacitance value C such that the overall impedance of the wireless power transmission unit is essentially zero.

11. The wireless power transmission unit as recited in claim 9, comprising:

a variable inductance element having a variable inductance value L, the variable inductance element coupled to the processor, wherein the processor maintains the wireless power transmission unit in resonance during the frequency sweep by adjusting the variable inductance value L such that the overall impedance of the wireless power transmission unit is essentially zero.

12. A wirelessly powered local computing environment, comprising:

a variable frequency power supply arranged to provide power at a frequency;

an resonance frequency adjustable near field magnetic resonance (NFMR) wireless transmitter coupled to the power supply and arranged to create a resonance channel used to transfer useable energy from the power supply to a receiver within a near field distance d; and

a central processing unit, the central processing unit providing processing resources to the variable frequency power supply and the resonance frequency adjustable NFMR transmitter, wherein when the NFMR transmitter establishes a resonance coupling with the receiver, the central processing unit maintains at least a minimum system Q factor Q_system by adjusting only the resonance frequency of the NFMR transmitter.

13. The wirelessly powered local computing environment as recited in claim 12, further comprising:

a power detector connected in series with the variable frequency power supply arranged to monitor a current in the NFMR wireless transmitter and provide a corresponding current value.

14. The wirelessly powered local computing environment claim 12, wherein during a frequency sweep operation, the central processing unit adjusts the frequency of the variable frequency power supply from a low frequency value to a high frequency value and the instructs the power detector to concurrently monitor the power in the NFMR transmitter.

15. The wirelessly powered local computing environment as recited in claim 14, further comprising:

an adjustable reactive element connected in series with variable frequency power supply forming an RLC equivalent circuit corresponding to the NFMR transmitter, wherein during the frequency sweep operation the central processing unit adjusts the adjustable reactive element in order to maintain the NFMR transmitter in resonance.

16. The wirelessly powered local computing environment as recited in claim 15, wherein the adjustable reactive element is an adjustable capacitor having an adjustable capacitance C or adjustable inductance L.

17. The wirelessly powered local computing environment as recited in claim 16, wherein when the monitored power in the NFMR transmitter at a current frequency is less than an average power value by a pre-determined amount, then the frequency of the adjustable power supply is set to the current frequency.

18. A method performed by a wireless power transmission unit for automatically tuning a wireless power transmission system, comprising:

wherein the wireless power transmission unit includes at least a first resonator structure coupled to a varying frequency f voltage supply,

in a tuned state, establishing a magnetic resonant inductive coupling between the first resonator structure to a second resonator structure positioned apart from the wireless power transmission unit;

non-radiatively transferring useable power from the first resonator structure to the second resonator structure using the magnetic resonant inductive coupling between the first resonator structure and the second resonator structure, wherein in the tuned state, a first resonant frequency ω

₁ of the first resonator structure and the second resonant frequency ω

₂ of the second resonator structure are separated by a bandwidth of no more than 3 db;

wherein the first resonator structure maintains the first resonator structure and the second resonator structure in the tuned state by varying a first resonant frequency ω

₁ of the first resonant structure in order to maintain the first resonant frequency ω

₁ and a second resonant frequency ω

₂ are separated by the bandwidth of no more than 3 db in accordance with any change in the second resonant frequency ω

₂.

19. The method as recited in claim 18, wherein the varying frequency excitation source is a varying voltage supply arranged to provide frequency dependent voltage V_f.

20. The method as recited in claim 19, wherein the first resonator structure comprises:

a transmitter coil coupled to the varying frequency f power supply, wherein in the tuned state, the transmitter coil wirelessly provides real power P_real at the first resonant frequency ω

₁ to the second resonator structure by magnetic resonant inductive coupling, the transmitter coil having a representative transmitter coil resistance R_coil.

21. The method as recited in claim 20, the transmitter coil further comprising:

a variable impedance element coupled in series with the transmitter coil resistance R_coil.

22. The method as recited in claim 21, the wireless power transmission unit further comprising:

an average current (I_ave) indicator connected in series to the varying voltage supply, the transmitter coil resistance R_coil and the variable impedance element, the I_ave indicator arranged to provide an indication of an average current I_ave in real time in the wireless power transmission unit;

a parasitic resistance R_p connected in series with the variable impedance element and the coil resistance R_coil; and

a receiver load R_r corresponding to a receiver load representing a load on the wireless power transmission unit caused by the coupling of the first resonator structure and the second resonator structure

23. The method as recited in claim 22, wherein the wireless power transmission unit has an effective circuit impedance Z_circuit at resonance in accordance with Z_circuit=R_s+R_coil+R_p+R_r.

24. The method as recited in claim 23, wireless power transmission unit further comprising:

a processor coupled with the varying frequency voltage supply and with the average current I_ave indicator arranged to calculate a real power (P_real) value corresponding to an amount of real power P_real wirelessly transmitted by the first resonator structure to the second resonator structure in real time in the tuned state.

25. The method as recited in claim 24, wherein the processor calculates the amount of real power P_real wirelessly transmitted by the first resonator structure to the second resonator structure in accordance with P_Real=(I_ave)²Z_circuit.

26. The method as recited in claim 25, wherein the processor automatically determines the second resonant frequency ω

₂ by;

setting the frequency f of the variable voltage supply to a current frequency f_current;

performing a frequency sweep by incrementing the current frequency f_current in a range of frequencies having a low frequency f_low and a high frequency f_high;

adjusting the variable impedance element to maintain the wireless power transmission unit in resonance at the current frequency f_current;

instructing the I_ave indicator to periodically measure the I_ave as a current I_ave at the current frequency f_current;

calculating a current real power P_real at the current frequency f_current;

comparing the current real power P_real with a previously calculated real power P_real,

if the current real power P_real is less than the previously calculated real power P_real by at least a pre-determined amount, then setting the frequency f of the variable voltage supply to the current frequency f_current, otherwise,

adjusting the current frequency f_current within the range of frequency low f_low to frequency high f_high.

27. The method as recited in claim 26, wireless power transmission unit further comprising:

a variable capacitance element having a variable capacitance value C, the variable capacitance element coupled to the processor, wherein the processor maintains the wireless power transmission unit in resonance during the frequency sweep by adjusting the variable capacitance value C such that the overall impedance of the wireless power transmission unit is essentially zero.

28. The method as recited in claim 27, wireless power transmission unit further comprising:

a variable inductance element having a variable inductance value L, the variable inductance element coupled to the processor, wherein the processor maintains the wireless power transmission unit in resonance during the frequency sweep by adjusting the variable inductance value L such that the overall impedance of the wireless power transmission unit is essentially zero.