Electromagnetic interference mitigation

Abstract

A primary unit for transmitting power and/or data wirelessly by electromagnetic induction to a secondary unit separable from the primary unit, the primary unit comprising: a coil; and driving means operable to drive a fluctuating current through the coil, wherein both ends of the coil are decoupled from the driving means so that in use a voltage level at each end of the coil fluctuates with time.

1 . A primary unit for transmitting wireless power by electromagnetic induction to a secondary unit in proximity to said primary unit, the secondary unit being separable from said primary unit, said primary unit comprising:
 drive circuitry operable to output a fluctuating current at an operating frequency;   a driven transmitter operably connected to said drive circuitry, said driven transmitter configured to directly transmit wireless power to the secondary unit, said driven transmitter configured to generate a first field in response to being driven by said fluctuating current output from said drive circuitry; and   a passive transmitter disposed within said first field and operable to transmit wireless power to the secondary unit, said passive transmitter configured to generate a second field in response to coupling with the first field generated by said driven transmitter, wherein said passive transmitter is undriven by said drive circuitry;   wherein driven transmitter and said passive transmitter are arranged such that the secondary unit couples with said primary unit to receive wireless power.   
     
     
         2 . The primary unit as claimed in  claim 1 , further comprising a housing containing said driven transmitter and said passive transmitter. 
     
     
         3 . The primary unit as claimed in  claim 1 , wherein each of said driven transmitter and said passive transmitter is capable of transmitting wireless power to the secondary unit by electromagnetic induction. 
     
     
         4 . The primary unit as claimed in  claim 3 , wherein said driven transmitter and said passive transmitter cooperatively and simultaneously transmit wireless power to the secondary unit. 
     
     
         5 . The primary unit as claimed in  claim 1 , further comprising a coil, wherein said driven transmitter and said passive transmitter respectively comprise first and second coil portions of said coil. 
     
     
         6 . The primary unit as claimed in  claim 5 , wherein each end of the coil is connected to the drive circuitry via a respective capacitor. 
     
     
         7 . The primary unit as claimed in  claim 5 , wherein both ends of the coil are decoupled from any DC source voltage present in the primary unit other than along the length of the coil. 
     
     
         8 . The primary unit as claimed in  claim 5 , wherein the driven transmitter and the passive transmitter are configured such that fluctuations in voltage level at one end of the coil are substantially 180 degrees out of phase with fluctuations in voltage level at the other end of the coil. 
     
     
         9 . The primary unit as claimed in  claim 5 , wherein the driven transmitter and the passive transmitter are configured such that, when a voltage level at one end of the coil fluctuates positively away from a ground voltage, a corresponding negative voltage fluctuation is experienced at the other end of the coil. 
     
     
         10 . The primary unit as claimed in  claim 5 , wherein:
 the first coil portion has a first end and a second end and the second coil portion has a third end and a fourth end, the second and third ends being connected together at a reference such that the first and fourth ends form the ends of the coil; and   the first and second coil portions are configured such that they are magnetically coupled to one another.   
     
     
         11 . The primary unit as claimed in  claim 10 , wherein the first and second coil portions are configured such that coupling takes place from the first portion, in the direction from the first end to the second end, to the second portion, in the direction from the third end to the fourth end. 
     
     
         12 . The primary unit as claimed in  claim 10 , wherein the coil is configured such that windings of one of said portions overlap or run alongside windings of the other one of said portions. 
     
     
         13 . The primary unit as claimed in  claim 10 , wherein a manner of winding of the first portion, from the first end to the second end, is the same as a manner of winding of the second portion, from the third end to the fourth end. 
     
     
         14 . The primary unit as claimed in  claim 10 , wherein a DC source voltage is applied to the coil between said first and second coil portions. 
     
     
         15 . The primary unit as claimed in  claim 14 , wherein the DC source voltage is a ground source voltage applied to the coil between the first and second coil portions. 
     
     
         16 . The primary unit as claimed in  claim 1 , wherein the driven transmitter and the passive transmitter are configured such that the driven transmitter has a voltage that is substantially equal to and the opposite of the voltage of the passive transmitter, whereby a net charge induced by capacitive coupling of the driven transmitter and the passive transmitter with a proximate object would be substantially zero. 
     
     
         17 . The primary unit as claimed in  claim 1 , wherein:
 the drive circuitry is an alternating voltage source having first and second terminals; and   the voltage source is connected at one said terminal to a ground source voltage such that it operates as a single-polarity voltage source.   
     
     
         18 . The primary unit as claimed in  claim 1 , wherein a coupling coefficient between the driven transmitter and the passive transmitter is greater than 0.5 and preferably within the range 0.9 to 1. 
     
     
         19 . The primary unit as claimed in  claim 1 , wherein properties of the driven transmitter and properties of the passive transmitter are substantially the same. 
     
     
         20 . The primary unit as claimed in  claim 1 , wherein the coupling between said driven transmitter and said passive transmitter is magnetic coupling, and wherein the first field and the second field are magnetic fields. 
     
     
         21 . A wireless power transfer system, comprising a primary unit as claimed in  claim 1  and at least one said secondary unit configured to receive power wirelessly from the primary unit. 
     
     
         22 . A primary unit for transmitting wireless power to a secondary unit in proximity to said primary unit, the secondary unit being separable from said primary unit, said primary unit comprising:
 a first coil and a second coil, each of said first coil and said second coil being configured to couple with a secondary unit to transmit power wirelessly; and   a drive circuit configured to supply fluctuating current to said first coil, said first coil configured to generated a first field in response to said fluctuating current, wherein said second coil is undriven by said drive circuit;   wherein said second coil is disposed within and driven by said first field to generate a second field.   
     
     
         23 . The primary unit as claimed in  claim 22 , wherein said first coil and said second coil are configured to cooperatively and simultaneously supply wireless power to the secondary unit. 
     
     
         24 . The primary unit as claimed in  claim 22 , wherein:
 the first coil has a first end and a second end and the second coil has a third end and a fourth end, the second and third ends being connected together at a reference; and   the first and second coil portions are configured such that they are magnetically coupled to one another.   
     
     
         25 . The primary unit as claimed in  claim 24 , wherein the first end is connected to a first capacitor and the fourth end is connected to a second capacitor, wherein the drive circuitry is connected to said first capacitor and said second capacitor. 
     
     
         26 . The primary unit as claimed in  claim 25 , wherein a circuit node defined by the connection between the second capacitor and the drive circuitry is connected to said reference. 
     
     
         27 . The primary unit as claimed in  claim 24 , wherein said reference is a ground source voltage. 
     
     
         28 . The primary unit as claimed in  claim 24 , wherein said first coil and said second coil are physically arranged so that said first field and said second field are substantially coextensive and cooperatively induce power in the secondary unit. 
     
     
         29 . A method of transmitting wireless power from a primary unit to a secondary unit by electromagnetic, the secondary unit being separable from the primary unit, the primary unit having a first coil and a second coil, the method comprising:
 supplying a fluctuating current at an operating frequency to the first coil;   generating a first field from the first coil in response to said supplying the fluctuating current, wherein the first field is generated to supply wireless power by electromagnetic induction;   generating a second field from the second coil in response to said generating the first field, wherein the second coil is disposed within and driven by said first field, wherein the second field is generated to supply wireless power by electromagnetic induction; and   transmitting wireless power to the secondary unit by electromagnetic induction.   
     
     
         30 . The method of  claim 29  further wherein said transmitting wireless power includes cooperatively and simultaneously transmitting wireless power from the first coil and the second coil.