Antenna configuration

Apparatus comprising:

• a medical implant, the medical implant comprising:
• a receiving coil;
• and
• a plurality of electrodes;
• a transmitting coil, having wire disposed at all rotational locations about a central longitudinal axis of the transmitting coil, oriented such that:
• (a) the central longitudinal axis of the transmitting coil is substantially perpendicular to a central longitudinal axis of the receiving coil,
• (b) at one of the rotational locations, a line from the wire and substantially parallel to the central longitudinal axis of the transmitting coil intersects the receiving coil, and at 180 degrees from the rotational location a line from the wire and substantially parallel to the central longitudinal axis of the transmitting coil does not intersect the receiving coil,
• (c) a first, distance from the central longitudinal axis of the transmitting coil to a longitudinal center of the receiving coil, is greater than a second distance from the central longitudinal axis of the transmitting coil to an inner edge of the transmitting coil at the one of the rotational locations, and
• (d) the first distance is less than a third distance from the central longitudinal axis of the transmitting coil to an outer edge of the transmitting coil at the one of the rotational locations;
• and
• control circuitry configured to transmit power to the medical implant by driving a current through the transmitting coil that induces an induced current in the receiving coil.

Apparatus for use with a medical implant that comprises a receiving coil, the apparatus comprising:

• a flexible housing configured to be placed against skin of a subject;
• a flexible transmitting coil disposed in the housing;
• control circuitry configured to transmit power to the medical implant by driving a current through the transmitting coil that induces an induced current in the receiving coil;
• a sensor coupled to the control circuitry, the sensor configured to determine an extent of divergence of (a) a resonance frequency of the transmitting coil when the transmitting coil is flexed from (b) a nominal resonance frequency of the transmitting coil, occurring in the absence of any forces applied to the transmitting coil, and configured to output a signal according to the determination;
• and
• one or more electrical components, coupled to the control circuitry and configured to tune the resonance frequency of the transmitting coil in response to the determination of the sensor.