WO1994028969A1

WO1994028969A1 - Focal inductor for use in electromagnetic field therapy

Info

Publication number: WO1994028969A1
Application number: PCT/IB1994/000216
Authority: WO
Inventors: Jeffrey D. Edwards
Original assignee: Australasian Medical Technology (Nz) Limited
Priority date: 1993-06-09
Filing date: 1994-06-07
Publication date: 1994-12-22

Abstract

Inductors for propagating electromagnetic fields are each comprised of a flexible planar coil (10) in the form of an annular ring having an inner perimeter (14), an outer perimeter (16) and a void central region, the dimensions of the inner perimeter (14) or void region and the outer perimeter (16) having a specified range of ratios to provide an inductor having high focal characteristics and producing minimal frequency distortion when energized by known driver circuits or waveform generators. The inductors produce a directionally oriented electromagnetic field, have a low physical mass and are flexible and conformable. The inductors are particularly suited for use in electromagnetic field therapy for the treatment of conditions involving tissue damage, inflammation, arthritis and other disorders.

Description

DESCRIPTION

FOCAL INDUCTOR FOR USE IN ELECTROMAGNETIC FIELD THERAPY

Technical Field

The present invention relates to the field of electromagnetic field therapy ("EMFT") and pulsed electromagnetic field therapy ("PEMFT") , and in particular to inductors and coils for propogating electromagnetic fields.

Background Art

It is generally known and accepted that the application of certain exogenous electromagnetic fields have the ability to modify certain cellular processes and cellular communication mechanisms in a beneficial manner. Such electromagnetic fields, when used therapeutically, are generally produced by applying a predetermined and pre-shaped electrical current to one or more inductor(s) or coil(s) in order to produce a desirable magnetic field with specified field characteristics.

The magnetic field and therefore the applied therapy is generally referred to as the "waveform". The characteristics of the waveform are dependent upon the applied electrical current and the magnetic and physical characteristics of the inductor(s) or coil(s). It has been proposed that the observed biological affects of such electromagnetic fields result from an athermal inductive response that leads to modification of certain electrical parameters within the target tissues. Many magnetic field parameters have been proposed in an effort to achieve effective treatment. See, for example, U.S. Patent Nos. 5,131,904, 5,100,373, 5,014,699, 4,911,686 and Australian Patent 52909/79. More recent research has indicated that more than one type of waveform may be required to influence biological,processes in the desired manner. It is quite probable that more than one type of waveform or frequency component will be required in order to achieve maximum efficacy in a number of disorders.

Since such developments would require apparatus capable of delivering a wide range of accurate frequencies, a single inductor capable of propagating a number of electromagnetic field frequencies with a minimum of distortion would be desirable. If such an inductor could be made available, while providing maximum control of the resulting flux gradients, then the inductor would indeed be beneficial.

Traditionally, multi-turn fixed radius coil inductors have been employed in the therapeutic application of pulsed electromagnetic field therapy ("PEMFT"). However, some solenoidal (U.S. Patent 4,757,804) and toroidal (U.S. Patent 5,131,904) configurations have been suggested. Such inductors, including the solenoidals and toroidals, are generally not designed specifically for the propagation of harmonic free, therapeutic, extremely low frequency ("ELF") electromagnetic fields for application at distances of less than λ/6 (1/6 wavelengths), i.e. in the "Near Field" as it is commonly known.

This is generally due to the large number of turns required to produce a field of specific magnetic flux. Conventional saddle or fixed radius inductors generate maximum flux gradients in close proximity to the current carrying conductors. As therapeutic applications require specific magnetic flux densities at the treatment site, which is usually central to the inductor, excessive numbers of turns are required to achieve central flux magnitude, which results in higher than optimum magnetic reluctance and introduces undesirable harmonics at field collapse points. This is also the case with toroidals. Solenoidals compound the problem due to the orientation of the collapsing fields. In addition, both solenoidals and toriodals are generally unsuited to integration into user applied orthotic devices, due to their physical geometry. Saddle inductors are more suitable, but their physical mass and lack of flexibility make them undesirable and uncomfortable in use.

It is generally thought that the optimum inductor for application of therapeutic pulsed electromagnetic field therapy should be of a type that would enable it to be readily integrated into a wearable orthotic device in order that correct field alignment and orientation is assured without the necessity for the user to be skilled in either electromagnetics or physiology.

In addition, traditional inductive coils, including solenoidals and toriodals, are required to be frequency and impedance matched with the driver circuitry in order to avoid generation of excessive and undesirable harmonic frequencies, especially during periods of field collapse. Additionally, such traditional inductive coils have significant magnetic reluctance properties. This reduces the overall rise times available through the application of such inductors, thus reducing their overall inductive capabilities.

When such traditional inductors are employed, even slight modifications to magnetic field requirements, physical fit or placement, or flux density output necessitates a complete redesign of both the driver electronics and the inductor, in order to avoid undesirable and potentially damaging side effects. As such redesign is effectively a new implementation, such modification necessitates the re-submission of such devices to the U.S. Food and Drug Administration ("USFDA") and other certification bodies prior to use. Such requirements would unnecessarily impose delays in release of the new or improved implementation and would introduce expenses that otherwise could legitimately be avoided.

It would therefore be desirable to make available a coil inductor of such design, construction, layout and specification as to provide a means of propagating a pure DC electromagnetic field, free of undesirable and unnecessary harmonics, and to provide such an inductor in a form that provides minimal magnetic reluctance in order to provide superior overall performance across a broad range of frequencies and driver current parameters. it would also be desirable if such an inductor could be provided in the form of a formable or flexible device of a type suitable for integration into wearable orthotic devices in order to provide accurate fit and positional stability when used by a user with little or no skills in electromagnetics or physiology.

With those requirement in mind, a search was undertaken to identify an inductor for the propagation of extremely low frequency (ELF) electromagnetic fields in the Near Field region for the purpose of modifying biological processes, in order that such an inductor could be used for the treatment of conditions involving tissue damage, inflammation and osteoarthritis.

Several designs and disclosures were investigated, including U.S. Patent No. 5,100,373, which discloses a single treatment head (inductor), a plurality of treatment heads greater than two, or a single solenoid. Also considered was McLeod and Rubin who, in U.S. Patent No. 4,993,413, disclose that the treatment coil is preferably in the form of a multi-conductor ribbon cable with appropriate male and female connectors. Such proposals and disclosures did not provide the benefits sought, as neither provided an inductor that offered minimal magnetic reluctance, broad frequency response and the ability to be readily integrated into a wearable orthotic. Various disclosures refer to alternative implementations of existing and well understood Farraday principles, which in general terms offer poor performance specifications in the propagation of magnetic fields in the Near Field, i.e., at distances of less that λ/6 (1/6 wavelengths). Bentall et al, in Australian Patent No. 52909/79, disclose a flexible inductor for the propagation of low power Radio Frequencies specifically for application in the Far Field region. Bentall's disclosure specifies an inductor that is an integral part of a high frequency oscillator, and by design, provides no benefit in overall frequency response or minimal magnetic reluctance. Bentall's disclosure is not capable of producing a range of distortion free frequencies resulting from the application of electrical current, nor is it designed to produce an

ELF therapeutic electromagnetic field of any particular shape, rise time or gradient.

The prior art has thus failed to identify any existing method, design or product suitable for the purposes above described.

It is therefore the object of the present invention to provide a method and device for the propagation of a range of therapeutic, distortion free, ELF time varying electromagnetic fields for use in the treatment and prevention of conditions involving tissue damage, inflammation, arthritis and the like, in a form capable of being readily integrated into an article of clothing or a wearable orthotic device. Disclosure of the Invention

The present invention provides a planar focal inductor, for use in association with various electrical current shaping means, for the purpose of propagating therapeutic Extremely Low Frequency (ELF) electromagnetic fields in the Near Field region with the aim of modifying biological processes in a beneficial manner.

The inductor of the invention, in a circular embodiment, comprises a single layer spirally wound coil of an electrically conductive material laid out in such manner as to provide a flexible or formable planar disk having a central void region of a diameter of from about 20% to about 40% of the total diameter of the coil. Such design and layout provides an inductor capable of focusing maximum magnetic flux density over the central void region, and provides an inductor having minimal self induction and minimal total magnetic reluctance. The planar focal inductor of the invention therefore provides a means for accurately propagating range of time varying DC electromagnetic fields with minimal undesirable harmonics and minimal magnetic reluctance. The inductor is designed to be used in association with various and differing current shaping means, such as are known to the art, and to act as the inductive means in association with such current shaping means in order to propagate a desirable therapeutic electromagnetic field without the need to custom design, develop and certify a unique and matched inductor for each such current shaping circuitry, as was heretofore the case.

To verify the efficacy of the present invention, and to assure the benefits sought will be delivered, the invention was implemented in a number of orthotic devices and tested in limited field trials. Two waveforms previously approved by the USFDA were employed. FDA 1 is referred to as being primarily Chondro-active and is a single pulse waveform. FDA 2 is generally considered Osteo-active and comprises repeated bursts, most of pulse packets.

Several physically sized planar focal inductors were employed, of a size appropriate for each disorder and body region to be treated. Entries are made only for disorders that achieved better than 80% improvement.

Condition Region Treated Waveform

Tennis Elbow Elbow FDA 1

Golfer Elbow Elbow FDA 1

Throwers Elbow Elbow FDA 1 Rotator Cuff Shoulder FDA 1

Supra Spinatus Shoulder FDA 1

Cervical Spine Pain Neck FDA 1 & 2

Anterior Knee Pain Knee FDA 1

Patella Femoral Knee FDA 1 Patella Tendon Disorder Knee FDA 2

Osteoarthritis Hand FDA 1 & 2

Osteoarthritis Fingers FDA 2

Wrist Strain Wrist/Hand FDA 1

Sinus Tarsi Foot FDA 1 Planar Fascitis Foot FDA 1

Lumbo Sacral Back FDA 1 & 2

Sherman's Back FDA 2

Groin Strain Groin FDA 1

While the size, scope and duration of the trials carried out cannot be considered numerically significant, the results obtained compare very favorably with previous studies that employed traditional fixed radius inductors. In fact, the present invention achieved efficacy in excess of 80% overall, where efficacies of 60% and less have been reported with traditional inductors.

The planar focal inductor of the invention may be employed in various medical, pharmaceutical and industrial situations where modification of biological processes are desirable or where the propagation of time varying DC electromagnetic fields are required.

These and other objects and advantages of the invention will become apparent from the following detailed description as considered in conjunction with the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a plan view of a first embodiment of the present invention, indicating the relationship between the central void diameter and the total inductor diameter.

Figure la is a perspectively extended fragmentary cross-section of the embodiment of the invention illustrated in Fig. 1. Figure 2 is a plan view of a second embodiment of the invention.

Figure 2a is perspectively extended fragmentary cross-section of the embodiment of the invention illustrated in Fig. 2. Figure 3 comprises graphic representations of the magnetic flux density peaks obtainable from the present invention (Fig. 3a), a traditional fixed radius inductor (Fig. 3b), and the present invention when formed into a semi-circular configuration (Fig. 3c). Figure 4 is a perspective representation of a third embodiment of the invention implemented as a composite of more than one individual coil unit.

Figure 5 is a schematic plan view of a fourth embodiment of the present invention as implemented in an oval or ellipitical configuration. Best Mode for Carrying Out the^' Invention

The following is a detailed description of several embodiments of the invention that are presently contemplated by the inventor to be the best mode of carrying out his invention.

Referring to Figures 1 and la, there is shown a planar focal inductor 10 comprising a single continuous filament 12 of conductive material, wound spirally into a flexible coil and having an inner perimeter or diameter 14, an outer perimeter or diameter 16, and a void central region 18. The inner perimeter or central void is of a diameter d(v) that is from about 20% to about 40% of the outer perimeter diameter, i.e., the total inductor diameter d(t). For many applications, a dimension d(v) equal to about 30% of the dimension d(t) is highly advantageous.

The conductive element 12, be it monofilament wire, multi-strand wire or etched copper track, is so disposed as to assure intimate horizontal contact with minimal vertical proximity. The inductor design and layout serve the purpose of propagating therapeutic time varying electromagnetic fields when energized by a suitable driver circuit, such as any of those known to the art. The type of driver circuit or waveform/ frequency generator is not esential to the invention. Any suitable waveform generator known to the art may conveniently be used with the inductor coil of the present invention, because the coil has the capability to propagate more than one frequency component. When used for purposes of propagating therapeutic electromagnetic fields into tissues under treatment, for example a shoulder, knee, elbow, neck, ankle, or leg, etc., the present invention provides centrally focused time varying magnetic fields with fast rise times and minimal harmonic ringing or distortion, especially during periods of magnetic field collapse. The inductor may be deployed either as a single coil inductor, or as a multiple coil inductor having the coils disposed in the Helmholtz configuration, which is well known in the art, or in an overlap manner, in order to produce a magnetic flux density more suitable to the treatment of a broader range of tissues and disorders. The invention provides such variants in utility while remaining less bulky and more comfortable than traditional inductive means. Moreover, due to its flexibility and formability, the induction means of the invention is adapted to be easily and conveniently integrated into wearable orthotics, for example.

Figures 2 and 2a graphically illustrate a planar focal inductor 20 comprised of a flexible planar dielectric substrate 21 bearing a thin layer of copper which has been etched to form a continuous conductive spiral coil or track 22. The coil or track has an inner perimeter or diameter 24, an outer perimeter or diameter 26 and a substantially void central region 28. The relationship between the diameter of the void central region and the outer diameter of the coil is the same as in the embodiment of Fig. 1. The inner perimeter, more specifically the terminal end of the inner winding of the coil, is provided with an electrical terminal 24a preferably positioned on the substrate 21 within the void region 28. Similarly, the outer perimeter, i.e., the terminal end of the outer winding of the coil, is provided with an electrical terminal 26a suitably located on a radial tabular extension of the substrate 21. A coil energizing source of power is thus readily connected to the inductor.

Instead of an etched copper track, the coil may be formed of other conductors appropriately bonded or adhered to the flexible substrate. The substrate may comprise any of the dielectric sheets and films conventional in the art, such as polyamide, polycarbonate, polyurethane or silicone rubber. The inductor of the invention is thus easy to apply to a patient and may readily be integrated into a wearable orthotic. The construction shown in Figure 2 provides the same benefits of minimum self-induction and focused magnetic densities as obtained with the construction of Figure 1.

Figure 3a is a graphical representation of maximum flux densities obtainable by energizing the inductor of the invention. The area indicated in Fig. 3a, i.e., the area enclosed by both arcs, shows the area of high density flux, which is obtained by energizing the inductor. As will be readily understood by the artisan, such area of high flux density is far superior to that obtainable through the use of traditional fixed radius inductors, which is illustrated in Fig. 3b. The benefit of greater flux area and less steep flux gradients provide particular therapeutic benefit when employed as a means of propagating therapeutic electromagnetic fields.

To achieve a performance similar to the present invention, traditional inductors would be required to generate higher overall magnetic fields, which may not only be therapeutically undesirable, but which introduce undesirable harmonics during field collapse and increase significantly overall magnetic reluctance, and therefore impact adversely on frequency response. Figure 3c is a graphical representation of the improved flux density patterns achieved by the present invention when the inductor is curved to a semi¬ circular configuration, as would be the case in many of the applications of the inductor to a patient. In such applications, the invention provides even greater benefit by further focusing of the resulting electromagnetic fields. In addition, the curvature produces complex field characteristics, especially at the peripheral regions of the inductor, which provides even greater benefit in the treatment of complex tissue disorders such as osteoarthritis, because the complex field gradients provide three dimensional magnetic potentials in all orientations.

Figure 4 shows a further embodiment of the invention comprised of an inductor 30 in which two coil units 32a, 32b of the invention are utilized. The coils may be of the same construction as described in conjunction with either Figure 1 or Figure 2. In the embodiment illustrated, the units 32a, 32b have been overlapped so that the outer perimeter of each coil is aligned with the inner perimeter of the other coil. This arrangement further enlarges the overall flux density regions obtainable. Any number of individual units may be overlapped to create a single implementation of the present invention, although non- overlapping or Helmholtz coil configurations may also provide similar benefits.

Figure 5 depicts a planar focal inductor 40 that is of generally oval or elliptical shape, but that will provide the same benefits as above described as long as the preferred relationship between void diameter and overall diameter is maintained in at least one dimension.

As illustrated schematically in Figure 5, a single layer of conductive material 42 is spirally wound in the configuration generally of a planar ellipse or oval coil having a long X axis and a short Y axis. The resulting coil has an inner perimeter 44, an outer perimeter 46 and a void central region 48. The dimensions of the inner and outer perimeters are such that along at least one of said axes, e.g., the short Y axis, the dimension d(v) of the inner perimeter 44 and the void 48 is from about 20% to about 40% of the dimension d(t) of the outer perimeter 46. With this relationship maintained, the inductor will produce the same advantageous propagation of electromagnetic fields as above described. Moreover, an inductor having oval or elliptical geometry may prove very desirable in some situations, such as may be the case with knees, shoulders and other complex and large body regions. For example, for treatment of osteoarthritis of an articulated joint such as the knee, the generally elliptical format of Fig. 5 is especially useful.

In a particular application of an elliptical inductor useful for treatment of an articulated joint such as the knee, the ratio of the dimension of the inner perimeter of the coil along the short or Y axis of the coil to the dimension of the inner perimeter of the coil along the long or X axis of the coil is preferably three units to four units, and the ratio of the dimension of the inner perimeter of the coil to the dimension of the outer perimeter of the coil along the short or Y axis is preferably three units to eight units. The thus dimensioned coil is curved about its short or Y axis to generally semi-circular form along a radius of curvature equal approximately to 3.5 units, thereby to conform the coil or inductor to the exterior of the joint. Units of measure are supplied in order to provide an understanding of the ratios involved and not actual physical dimensions, since the dimensions may be varied to produce inductors of different specified sizes. When energized by an electrical current of appropriate waveform and/or frequency, the curved inductor is especially beneficial. In this application, the ratio of void area to overall area and active width to curve radius are important to the overall benefits obtainable through the present invention. In view of the foregoing, it will be understood that the focal inductor of the invention may be formed into any number of shapes and sizes to provide better and more comfortable conformance to compound shaped body parts. In addition, because the inductor is thin, essentially planar, flexible and conformable, it is ideally suited to be incorporated into wearable orthotic devices, wearing apparel and even furniture such as beds and easy chairs, so as to facilitate EMF therapy by individuals who have little if any knowledge of electromagnetics or physiology. The size of the conductor and the number of turns in the coil may be varied to meet respective requirements. As long as the preferred void diameter ratio is maintained in at least one dimension, the inductor will serve to focus the propagated electromagnetic field and provide an increase in utility.

The objects and advantages of the invention have thus been shown to be attained in a convenient, economical, practical and facile manner.

While preferred embodiments of the invention have been herein illustrated and described, it is to be appreciated that various changes, rearrangements and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. A focal inductor for propagating electromagnetic fields comprising a single layer spiral coil of electrically conductive material in the form of an annular ring having an inner perimeter, an outer perimeter and a substantially void central region, the inner perimeter of said coil having a dimension equal to from about 20% to about 40% of the dimension of the outer perimeter of the coil along at least one dimension of the coil when the coil is laid flat.

2. An inductor as set forth in Claim 1 wherein the coil when flat comprises a circular annulus having an inner diameter and an outer diameter, the inner diameter being from about 20% to about 40% of the outer diameter.

3. An inductor as set forth in Claim 1 wherein said coil when flat comprises a generally elliptical annulus having a long axis and a short axis, the dimension of the inner perimeter of said annulus comprising from about 20% to about 40% of the dimension of the outer perimeter of said annulus along at least one of said axes.

4. An inductor as set forth in Claim 1 wherein said dimension of the inner perimeter is about 30% of said dimension of the outer perimeter.

5. An inductor as set forth in Claim 1 wherein the inner perimeter of the coil has an electrical terminal located within said void central region and the outer perimeter of the coil has an electrical terminal adjacent the periphery of said coil.

6. An inductor as set forth in Claim 1 wherein a plurality of said coils are disposed in partial overlapping relationship with the outer perimeter of one coil aligned with the inner perimeter of an adjacent coil.

7. An inductor as set forth in Claim 1 wherein a pair of said coils of the same size and the same shape are disposed in correspondingly oriented overlapping relationship with the outer perimeter of each of said coils aligned with the inner perimeter of the other coil.

8. A focal inductor for propagating low frequency electromagnetic fields in the near field region for use in electromagnetic field therapy comprising a thin, flexible, substantially planar dielectric substrate, a single layer spiral coil of electrically conductive material on said substrate, said coil comprising an annular ring having an inner perimeter, an outer perimeter and a substantially void central region, the inner perimeter of said coil having a dimension equal to from about 20% to about 40% of the dimension of the outer perimeter of said coil along at least one dimension of the coil in the plane of said substrate, said substrate and said coil being flexible and conformable to a body surface to facilitate electromagnetic field therapy.

9. An inductor as set forth in Claim 8 wherein said substrate and said coil are flexibly and conformably insertable in any one of an article of wearing apparel, an article of furniture and an orthotic device.

10. An inductor as set forth in Claim 8 wherein a plurality of said coils are provided on said substrate.

11. An inductor as set forth in Claim 8 wherein a plurality of said coils are disposed in partial overlapping relationship with the outer perimeter of one coil aligned with the inner perimeter of an adjacent coil.

12. An inductor as set forth in Claim 8 wherein a pair of said coils of the same size and the same shape are disposed on said substrate in correspondingly oriented overlapping relationship with the outer perimeter of each of said coils aligned with the inner perimeter of the other coil.

13. An inductor as set forth in Claim 8 wherein said substrate and said coil are curved into substantially semi-circular form for use in therapy of any one of the legs, arms, leg joints and arm joints of the body.

14. An inductor as set forth in Claim 8 for use in therapeutic treatment of an articulated joint of the body and wherein said coil comprises a generally elliptical annulus having a long axis and a short axis, the ratio of the dimension of the inner perimeter of said coil along the short axis to the dimension of the inner perimeter of said coil along the long axis being about 3 units to 4 units, the ratio of the dimension of the inner perimeter of said coil along the short axis to the dimension of the outer perimeter of said coil along the short axis being about 3 units to 8 units, said substrate and said coil being curved about said short axis into substantially semi-circular form along a radius of curvature, the radius of curvature in relation to the other units being about 3.5 units.

15. A method of applying electromagnetic field therapy to a portion of a body comprising the steps of applying to the exterior of the body proximate the portion to be treated an electromagnetic field propagating focal inductor which comprises a single layer spiral coil of electrically conductive material in the form of an annular ring having an inner perimeter, an outer perimeter and a substantially void central region, the inner perimeter of said coil having a dimension equal to from about 20% to about 40% of the dimension of the outer perimeter of the coil along at least one dimension of the coil, and energizing the coil by applying thereto an electrical current of predetermined waveform.

16. A method as set forth in Claim 15 including the steps of applying to the exterior of the body proximate to the portion to be treated a plurality of said focal inductors, and energizing each of said inductors.

17. A method as set forth in Claim 15 including the steps of applying to the exterior of the body proximate to the portion to be treated at least a pair of said focal inductors so disposed that one inductor overlaps the other inductor with the outer perimeter of the coil of one inductor substantially aligned with the inner perimeter of the coil of the other inductor, and energizing the coils.

18. A method as set forth in Claim 15 including the step of applying to the inductor a pulsed electrical current of predetermined frequency.