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Flexible Shield For Wearable and Stretchable Coil

IP.com Disclosure Number: IPCOM000028970D
Publication Date: 2004-Jun-09
Document File: 3 page(s) / 1M

Publishing Venue

The IP.com Prior Art Database


The present invention relates to electric field shields that can be placed on or over external wearable coils. The shields may be placed along the coil wires, but the shields should not complete a loop in the direction of current flow, so as to not attenuate the magnetic field produced by the coil in accordance with Faraday's Induction law. The shields may be made of metallic conductors such as those containing copper, aluminum, nickel, steel, etc. The shields may be made of a tape form of these metals. Alternatively, the shield material may be a conductive fabric that is flexible and comfortable to wear.

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Flexible Shield For Wearable and Stretchable Coil

Implantable medical devices have been used successfully to treat a wide variety of diseases and disorders.  Pacemakers and implantable cardiac defibrillators (ICDs) are used effectively to treat cardiac arrhythmias.  Spinal cord stimulation (SCS) systems are used to treat chronic pain syndromes.  Deep brain stimulation is being used to treat a variety of disorders such as epilepsy and movement disorders such as essential tremor. In recent investigations, peripheral nerve stimulation (PNS) has demonstrated efficacy in treating chronic pain syndromes and incontinence.


All of these implanted medical devices are powered by electricity.  Some of these devices are powered by primary battery cells.  In other cases, the implanted device does not contain a battery but draws power transcutaneously, i.e., through the skin.  For example, some cochlear implants continuously draw power from an external source of radio-frequency (RF) power to deliver stimulation to cochlear nerves.  Some implanted devices contain a rechargeable battery, which can be charged transcutaneously from an external power source.

Transcutaneous transfer of power through the skin can be achieved through electromagnetic induction.  At least two coils are required, a primary coil external to the skin and a secondary coil implanted within the patient.  The primary and secondary coils are positioned so that they are inductively coupled.  By energizing the primary coil with a time-varying current, a time-varying magnetic flux can be produced by the primary coil.  When the secondary coil is appropriately oriented and in proximity to the primary coil, a time-varying magnetic flux induces a time-varying current within the secondary coil, according to Faraday’s principle of electromagnetic induction.  Systems delivering energy or power in this fashion are called transcutaneous energy transfer or “TET” systems.

During the course of therapy, it is usually necessary to adjust the output parameters of the implant or communicate with the implant.  For example, with implantable neurostimulators, adjustments to stimulation parameters are usually made by sending radio-frequency signals to the implant, which radio-frequency signals are generated by external controllers.  These signals are sent and received via antennas, which are, in some cases, similar to or the same as the coils used for recharging or powering.  Using the same antenna, some implanted devices can send or receive energy and also transfer or receive data using a modulated magnetic field.

In most applications, the primary coil is placed on or beneath the surface of the skin.  The primary coil often remains in a given position with respect to the secondary coil for an extended period of time.  As such, it is important to produce coils that are comfortable for the patient to wear.  Since the coils are usually made from metal wires, they are typically stiff and ca...