Wireless energy transfer using variable size resonators and system monitoring

A wireless power transfer system with an adjustable effective size magnetic resonator comprising:

• a source with an adjustable effective size resonator including a plurality of differently sized source magnetic resonators and at least one power and control circuit configured to selectively connect to at least one of the plurality of differently sized source magnetic resonators;
• a device separated from the source, the device having at least one device magnetic resonator;
• and
• measurement circuitry to measure at least one parameter of a wireless power transfer between the source and the device, wherein one or more connections between the plurality of differently sized source magnetic resonators and the at least one power and control circuit are configured to change an effective size of the adjustable effective size resonator according to the at least one parameter measured by the measurement circuitry.

An adjustable effective size resonator for wireless power transfer comprising:

• a magnetic resonator including a plurality of differently sized inductive elements;
• at least one power and control circuit configured to selectively connect to and energize at least one of the plurality of differently sized inductive elements;
• and
• measurement circuitry to measure at least one electrical parameter of the magnetic resonator, wherein one or more connections between the plurality of differently sized inductive elements and the at least one power and control circuit are configured according to the at least one electrical parameter.