Devices and methods for non-invasive implant length sensing

A method of sensing the length of an implantable medical device having first and second portions moveable relative to one another comprising:

• providing a resistive pathway on one of the first and second portions of the implantable medical device;
• providing a contact disposed on the other of the first and second portions, the contact being in sliding contact with the resistive pathway upon relative movement between the first and second portion;
• measuring the electrical resistance along a path including a variable length region of the resistive pathway and the contact;
• and
• converting the measured electrical resistance to a length.

A device comprising:

• an implantable medical device having first and second portions moveable relative to one another;
• a primary drive coil surrounding a segment of the implantable medical device containing both the first and second portions;
• at least one secondary coil surrounding a segment of the implantable medical device containing both the first and second portions;
• and
• a first circuit configured to apply a drive voltage to the primary drive coil and measure signals in the at least one secondary coil and output a signal indicative to the length of the implantable medical device.

A method of sensing the length of an implantable medical device having first and second portions moveable relative to one another comprising:

• applying a driving voltage to a primary drive coil surrounding a segment of the implantable medical device containing both the first and second portions;
• measuring signals in at least one secondary coil surrounding a segment of the implantable medical device containing both the first and second portions;
• and
• converting the measured signals in the at least one secondary coil to a length.

A device comprising:

• an implantable medical device having first and second portions moveable relative to one another, wherein the first and second portions are separated from one another by a dielectric material;
• an implantable resonant coil coupled to the first and second portions;
• an externally located drive coil operatively coupled to a signal generator;
• and
• a frequency analyzer operatively coupled to the drive coil configured to detect the resonant frequency of the implantable medical device, wherein said resonant frequency varies depending on the degree of relative orientation between the first and second portions.

A method of sensing the length of an implantable medical device having first and second portions moveable relative to one another comprising:

• providing an implantable medical device wherein the first and second portions are coupled to an implanted resonant coil;
• driving an external drive coil adjacent to the implanted resonant coil with a signal generator at different frequencies;
• detecting a resonant frequency of the implantable medical device;
• and
• converting the resonant frequency of the implantable medical device to a length.

A device comprising:

• an implantable medical device having first and second portions moveable relative to one another;
• an elongate member having first and second ends, the first end being secured to the first portion of the implantable medical device, the second end having secured thereto a magnet;
• a fulcrum on the second portion of the implantable medical device and in contact with various points along the elongate member in response to relative movement of the second member relative to the first member;
• and
• an externally located magnetic field source, the externally located magnetic field source configured to apply an oscillating magnetic field in proximity to the magnet secured to the elongate member.

A method of sensing the length of an implantable medical device comprising:

• providing an implantable medical device having first and second portions moveable relative to one another, an elongate member having first and second ends, the first end being secured to the first portion of the implantable medical device, the second end having secured thereto a magnet, and a fulcrum on the second portion of the implantable medical device and in contact with various points along the elongate member in response to relative movement of the second member relative to the first member;
• applying an oscillating magnetic field at different frequencies in proximity to the magnet with an externally located magnetic field source driven by a power source;
• monitoring the power source for the externally located magnetic field source;
• and
• determining the resonant frequency of the elongate member based at least in part on the current draw of the power source;
• and
• converting the resonant frequency of the elongate member to a length.