Patent No. 6174276 Magnetic coil for pulsed electromagnetic field

 

Patent No. 6174276

Magnetic coil for pulsed electromagnetic field (Blackwell, Jan 16, 2001)

Abstract

A portable electronic PEMF apparatus comprises a PEMF coil, power supply, and electronic switching means contained therein. The power supply along with the switching means provide periodic electric power to the PEMF coil. The PEMF coil comprises multiple turns of a conductive wire around a core with an elongated cross section. The core comprises a magnetic shield layer of materials such as mu metal or soft iron. The power supply comprises a battery, a regulated voltage source and unregulated voltage source from the battery and electronic switching circuit, powered by the regulated voltage, for electrically connecting the unregulated voltage source to the coil. The electronic switching circuit is tuned to periodically provide power to the coil at a frequency to generate a non-inverting, varying electromagnetic field from the coil.

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SUMMARY OF THE INVENTION

It is an object of the present invention to overcome these and other drawbacks of the prior art.

It is another object of the invention to provide a PEMF apparatus that is relatively small, light and thin yet which generates a relatively strong magnetic flux per unit length.

It is another object of the present invention to provide a PEMF apparatus using a coil design that produces a single polarity magnetic field that is relatively homogenous and that maintains its field strength even at distances spaced from the coil.

It is another object of the present invention to provide a PEMF apparatus using a planar coil with a core comprising a magnetic shielding material.

It is another object of the present invention to provide a PEMF apparatus sized to allow PEMF treatment while a patient is mobile and engaged in physical activity.

It is another object of the present invention to provide a PEMF apparatus which can be incorporated as part of a cast or attached to the outside of a cast to augment the natural healing abilities of the body.

It is another object of the present invention to provide an efficient method to energize a coil to produce a single polarity PEMF that eliminates or minimizes ringing without the need for a shunt diode across the coil.

It is another object of the present invention to provide a coil for use in PEMF treatment which is deformable, flexible and pliant and easily adaptable for the application of an electromagnetic field to injuries at any location on a patient's body.

To accomplish these and other objects of the present invention, one preferred embodiment of the invention is directed to a PEMF apparatus having a coil wrapped around a core in a generally rectangular configuration with a magnetic shield located within the core. The coil comprises a plurality of turns of an electrical conductor, preferably with each turn having a length to width ratio of at least five. The apparatus may be deformable, flexible and pliant, and may be shaped to conform to portions of a patient's body. Advantageously, both the top and bottom surfaces of the apparatus will produce a substantially homogeneous, unipolar, non-inverting PEMF with little or no field dropout. The top and the bottom surface generate PEMF of opposite polarity. Preferably the surface generating the North (N) polarity of the magnetic field may be positioned proximal to the portion of the patient to be treated.

According to another preferred embodiment, the core comprises a first end portion and a second end portion of a spacer material such as wood, plastic, foam, or other material which defines a width, height and thickness. The first and second end portions may be separated by a space therebetween. A sheet of magnetic shielding material such as metal is wrapped around the first and second end portions to define a core with an inner surface and a top surface. A plurality of turns of an electrical conductor may be wound around the first end portion, the bottom surface, the second end portion and the top surface to form a coil. The components of the core may be attached to each other and to the coil by suitable adhesives. For example, epoxy may be used to attach the components.

According to another preferred embodiment, a PEMF treatment apparatus for PEMF treatment of a patient while the patient is engaged in active physical activity is disclosed. The PEMF treatment apparatus preferably comprises a coil wrapped around a flexible core, a power supply and a solid state switching circuit connected between the power supply and the coil to drive the coil with a current at a periodic pulsed frequency to generate a non-inverting PEMF. The power supply is preferably a battery.

According to another preferred embodiment, a PEMF coil is disclosed that is relatively small, thin and light yet generates a relatively strong magnetic flux per unit length. Preferably, a relatively small gauge wire is used to wind the coil. According to one embodiment, the PEMF coil is wrapped around a core which is of a relatively thin cross section. A core of relatively thin cross section may be achieved for certain embodiments of the invention by implementing layers of magnetic shielding material. The magnetic shielding material reduces the magnetic interference from opposing sides of the coil within the need for a relatively large spatial separation. Layers of magnetic shielding material are, preferably, interspaced between relatively thin layers of insulating material.

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Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The specification and examples should be considered exemplary only. The intended scope of the invention is only limited by the claims appended hereto.