CA2036896A1 - Shielded electromagnetic transducer - Google Patents

Abstract

ABSTRACT

An electrical to electromagnetic transducer for applying electromagnetic energy to damaged potions of the living body, which provides high efficiency generation of electromagnetic fields for electromagnetic therapy by directing electro-magnetic energy to the damaged body part. Electromagnetic energy is initially generated by a dipole consisting of a bar of high permeability material wrapped with an electrically conductive coil. The dipole is placed between a conductive shield and the damaged body part. An electrical signal passes through the coil which causes a magnetic field to be generated through and around the high permeability material.
The field radiation pattern of the dipole is directed toward the damaged body part by a conductive shield. Magnetic fields which are generated away from the damaged body part intersect the conductive shield and establish eddy currents. These eddy currents in turn generate magnetic fields opposite and nearly equal to the magnetic fields generated by the electromagnetic source. These resultant redirected electromagnetic fields then reinforce the electromagnetic field directed towards the damaged body part and diminish the electromagnetic field directed away from the damaged body part.

Description

2~_ RAN8DUCBR
3FIELD OF T~E INVENTION
4The present invention relates to the field of transducers for converting electrical energy into electromagnetic fields.
6 Nore specifically, the present invention relates to the use 7 of transducers to provide electromagnetic fields to damaged 8 body components to promote healing.
g BACRG~OUND OF T~2 INVENTION
ll The use o~ electric or electromagnetic fields to promote 12 healing, particularly the healing of fractured bones, has been 13 investigated since the early l9th Century. See Spadaro, 14 "Bioelectric Stimulation of Bone Formation: Methods, Models and Mechanisms," ~. Bioelectr~city, 1, 1, 99-128 (1982).
16 Initially, direct current techniques were used by applying 17 electrodes to the skin or via the use of implanted electrodes 18 into the bone. More recently, mechanisms which encourage 19 growth have been investigated which involve the use of electromagnetic fields to induce voltage and current effects 21 within the tissue. These techniques have been particularly 22 useful in non-healing or "non-union" fractures by inducing 23 bones to heal which will not heal naturally.
24 An example of a technique for the use of electromagnetic radiation to promote bone growth is disclosed in U.S. Patent 26 No. 4,266,532. However, the techniques disclosed therein 27 required the u e of power applied ~rom a standard wall socket.
28 Electro~agnetic therapy i8 only useful so long as the patient 29 uses it. Being tethered to the wall is a sufficient annoyance such that many patients will not follow the electrotherapy 31 regimen prescribed by their doctors.
32 In view of this problem, a great deal of work has 33 occurred to try to develop mechanisms whereby portable ' ~
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2~36896 1 electrotherapy may be provided. Examples of such techniques 2 are shown in U.S. Patents Nos. 4,432,361; 4,574,809; and 3 4,587,957. The system shown in the first of these patents 4 requires the use of invasive electrical probes into the bone.
It is desirable to avoid invasive techniques if possible 6 because of the possibility of infection. The systems of the 7 other two patents use magnetic transducers and/or Helmholtz 8 coils designed to provide a uniform electromagnetic field 9 throughout the treatment area. The system of the third patent also included a polarized magnetic field. These types of 11 transducers establish electromagnetic fields outside of the 12 damaged body portion and waste a great deal of energy inside 13 the damaged body portion by radiating areas where stimulation 14 is unnecessary. For example, the tibia and scaphoid bones are very close to the surface of the skin. Use of the techniques 16 shown in the above references causes radiation to be generated 17 throughout the entire limb even though the damaged portion is 18 close to the surface of the skin. This problem is even more 19 striking in the case of bones in the trunk of the body such as vertebrae and ribs. Therefore, a technique for applying 21 electromagnetic fields in a manner which concentrates their 22 application on the desired area while minimi2ing wasted 23 electromagnetic energy would be desirable.
24 The benefits of electromzgnetic stimulation of damaged or diseased tissue are being further developed and are widely 26 accepted by today's scientific community. Examples of studies 27 which show the benefits of electromagnetic stimulation to soft 28 tissue as well as bone are Black, "Electrical Stimulation of 29 Hard and Soft Tissues in Animal Models," Clinics in Plastic Surgery, 12, 2 (April, 1985) and Frank et al., "A Review of 31 Electromagnetically Enhanced Soft Tissue Healing," IEEE
32 Eng~lneering ~n Medic~ne and B~ology, 27-32 (December, 1983).
33 In addition, diseased rather than broken bones may benefit ,, ~ ~ tGRIFzpAT.Al4]

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1 from electromagnetic therapy. For example, see U.S. Patent 2 No. 4,467,808, and Bassett et al., "Treatment of Osteonecrosis 3 of the Hip with Specific Pulsed Electromagnetic Fields 4 (PEMFs): A Preliminary Clinical Report," Bone Circulation, Ch.
56, pp. 343-354, Arlet et al., eds. (1984).

7 ~U~MARY OF ~B INVEN~ION
8 The present invention provides an electrical to 9 electromagnetic transducer fox applying electromagnetic energy lo to damaged portions of the living body, to stimulate healing 11 and help provide quicker recovery. The embodiments of the 12 present invention provide high efficiency generation of 13 electromagnetic waves for electromagnetic therapy by directing 14 electromagnetic radiation to the damaged body part. In one embodiment, the electromagnetic radiation is initially 16 generated by a dipole consisting of a bar of high permeability 17 material wrapped with an electrically conductive coil. An 18 electrical signal passes through the coil which causes a 19 magnetic field to be generated through the high permeability material. The field pattern of the dipole is directed towards 21 the dama~ed body part by a conductive shield. The electro-22 magnetic field generator i5 placed between the conductive 23 shield and the damaged body part. Magnet:lc fields which are 24 generated away from the damaged body part intersect with the conductive shield. The change in the magnetic ~ield 26 establishes eddy currents within the conductive shield. These 27 eddy currents generate magnetic fields opposite and nearly 28 equal to the magnetia fields generated by the electromagnetic 29 source. The magnetic fields generated by the eddy currents provide an electromagnetic field which reinforces fields 31 directed towards the body part and diminish electromagnetic 32 ~ields dire~ted away from the damaged body part.
33 In another embodiment of the invention, the electro-:
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2~3~896 1 magnetic generator is a bar type dipole, arcuate dipole or 2 compound (such as quadripole). Multiple separate electro-3 magnetic generators are employed in still other embodiments, 4 as well as variations on the spacing of the turns of the conductive coils.
6 In another embodiment of the present invention, a second 7 piece of high permeability ~aterial is placed adjacent to the 8 damaged body part but separated te.g. diametrically opposed) 9 from the shielded electromagne~ic transducer. The presence of the high permeability material creates high electromagnetic 11 flux lines directed towards the high permeability material.
12 The high permeability material behaves as a magnetic conductor ;~
13 much like an electrical conductor alters an electric field.
14 Thus, even more precise direction of the electromagnetic field may be achi~ved.
16 By directing the electromagnetic field only to the appro-17 priate damaged body part, large savings in power dissipation 18 are ac~ieved. In addition, the deleterious effects of 19 electromagnetic radiation on healthy tissue are minimized by precise direction of the electromagnetic field.

22 ~RIBF D~CRIP~ION OF THF DRA~IN~
23 Figure 1 i8 a schematic diagram showing the flux lines 24 emanating from a prior art dipole electromagnet;
Figure 2 is a schematic diagra~ showing the flux lines 26 generated by a dipole transducer in conjunction with a 27 conductive shield;
28 Figure 3 shows the application of shielded dipole 29 transducer 10 to provide electromagnetic therapy to a broken 30 tibia; ;~
31 Figure 4 is a perspective view of the shielded dipole 32 transducer shown in Figure 2;
33 Figure S is cross-sectio~al view of shielded dipole [GRIFZPAT.A14]

2~3~896 l transducer 10 taken along cross-section line 4 of Figure 4;
2 Figure 6 iæ another cross-sectional view of shielded 3 dipole lO taken along section lines 5 of Figure 4;
4 Figure 7 shows the flux lines generated within the patient's leg by electrical, signals applied to the shielded 6 dipole transducer;
7 Figure 8 is a diagram showing the wasted electromagnetic 8 energy generated by an oversized shielded dipole transducer;
9 Figure 9 is a computer generated diagram showing the flux line~ of a shielded dipole transducer as calculated by a 11 computer simulation;
12 Figures lOA and lOB are graphs of representative signals 13 applied to leads 17 of transducer 10;
14 Figure ll is a chart showing the stiffness ratios of healed rabbit bones versus the applied search coil voltage;
16 Figure 12A is a graph showing the relationship between 17 the intensity o~ the electromagnetic field and the stiffness 18 of the bone treated using electromagnetic therapy;
19 Figure 12B is a graph showing the intensity of the electromagnetic ~ield generated by a shielded dipole 21 transducer as determined from the computer simulation shown in 22 Figure 9;
23 Figure 13A is a schematic diagram showing an approximate 24 equivalent circuit for shielded dipole 10;
2S Figure 13B i8 a schematic diagra~ reducing the circuit 26 shown in Figure 13A to basic circuit elements;
27 Figure 14 is a side view diagram of another shielded 28 dipole transducer 100 showing the altered flux lines by the 29 ~odification of shielded dipole 100 as compared to shielded dipole lO;
31 Figure 15 is a side view diagram describing the 32 alteration and the flux lines caused by altering the turn 33 spacing of the coil of shielded dipole 110;

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1 Figure 16A is an end view diagram 6howing the positioning 2 of interlocking shielded dipole transducers around invasive 3 bone stabilization equipment (e.g. external fixators) for 4 providing electromagnetic therapy in conjunction with invasive S technologies to treat extremely severe broken bones;
6 Figure 16B is a top view showing the interlocking 7 shielding of the shielded dipole transistors 122 and 124 of 8 Figure 16A;
9 Figure 17A is an end view diagram showing the positioning of an arcuate shielded dipole transducer on a leg;
11 Figure 17B is a side view diagram showing arcuate 12 transducer 140 positioned on a leg;
13 Fiqure 18A is a top view diagram showing the positioning 14 of a partially arcuate shielded dipole transducer;
Figure 188 is a side view diagram of transducer 150 of 16 Figure 18A;
17 Figure 19 is a side view diagram showing a quadripole 18 shielded transducer; and 19 Figure 20 is an end view diagram showing the lines of flux for positioning a portion of high permeability material 21 in the vi~inity of the operation of shielded dipole 10.
22 .

24 Figure 1 is a chematic diagram showing a prior art :
dipole electromagnet 2. High permeability bar 4 is wrapped by 26 wire 6 a selected number of turns N. When current is passed 27 through windings 6, a magnetic field is generated symbolized 28 by flux lines 8. The intensity of the far magnetic field in 29 a direction R perpendicular to dipole 2 is given tsee Plonus, Applied Electroraa~net~cs, 328 (1978) ~ by the equation:
31 B = ~IA/4nR3 32 where B i8 the absolute value of the intensity Gf the 33 field, tGRIFZPAT.A14]
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2~3~6 l ~O is the permeability of air, 2 n is the number of turns of winding 6, 3 I is the current passing through winding 6, 4 A is the cross-sectional area of bar 4, and R is the distance from the geometric center of bar 4.
6 A primary goal of the present invention is to efficiently 7 apply electromagnetic energy to a damaged body portion. One 8 major source of waste in the generation of electromagnetic 9 fields is the generation of electromagnetic fields in areas where they are not useful. As can be seen from Figure 1, an 11 equal amount of the electromagnetic field is generated above 12 and below dipole 2. In fact, the electromagnetic lines of 13 flux forms a toroidal shape centered around the major axis of 14 bar 4.
Figure 2 is a side view diagram of one embodiment of the 16 present invention showing a shielded dipole arrangement 10.
17 Windings 16 are wrapped around high permeability bar 12 and 18 current i5 passed through winding 16 to generate a magnetic 19 f~eld represented by flux line~ 18. Dipole assembly 13 is positioned inside indentation 15 in conductive plate 14.
21 Plate 14 can be formed of a number of known conductive 22 materials. It iB advantageous that the material used to 23 construct conductive plate 14 i8 as flexible as possible and 24 i~ as conductive as possible. I anticipate that an ideal conductive plate 14 will be a superconductor material.
26 ~ When time varying current passes through winding 16, a 27 time varying magnetic flux is generated. The magnetic flux 28 which attempts to pass through conductive plate 14 induces 29 ~eddy ~current~. These eddy currents generate magnetic flux ~whi~ch tends to oppose the magnetic flux which caused the eddy 31 current~ in the first place. This principle is known as Lenz' 32 ~Law. If conductive plate 14 were a perfect conductor, the 33~ magne~tic flux generated by the eddy currents would be opposite [GRIFZPAT.A14]

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1 and equal to the magnetic flux which caused the eddy currents 2 in the first place. Thus, the magnetic flux on the upper side 3 of conductive plate 14 would be completely cancelled and the 4 magnetic flux on the lower side of conductive plate 14 would be reinforced. However, ohmic losses in conductive plate 14 6 reduce the efficiency so that a partial magnetic field is 7 generated above conductive plate 14. However, the eddy current 8 induced magnetic flux provides a focusing action directing the 9 magnetic field to one side and allows a concentration of the generated magnetic field into a selected body part to aid in 11 the healing pr~cessO
12 Figure 3 is a 6ide view diagram showing the placement of 13 shielded dipole transducer 10 on a person's leg 20 to promote 14 the healing of a broken tibia 22. Leads 17 indicate the connection to an electrical source for generating the magnetic 16 field. Experiments have shown that an electrical signal 17 comprised of a train of bursted symmetrical pulses having a 18 frequency of up to 1 ~Hz in burst intervals of 5 msec provides 19 optimal power efficiency with effective therapeutic benefit.
This signal i8 provided to leads 17.
21 Figure 4 i6 a perspective view showing the shape of 22 shielded dipole transducer 10.
23 Figure 5 i8 a cut-away portion along lines 5-S of Figure 24 4 showing the construction of shielded dipole transducer 10.
High per~eability bar 12 and winding 16 are placed in 26 indentation 15 and indentation 15 i~ filled with an epoxy 27 material to 19 securely affix bar 12 and winding 16 in 28 indentation 15. Leads 17 are brought out through the surface 29 of field 14 for connection to a power source. Figure 6 is a cut-away view of transducer 10 on lines 6-6 of Figure 4.
31 Figure 7 is a side view diagram showing how the 32 electro~gnet$c field focusing a~pects of shielded dipole 10 33 direct the electromagnetic field to the damaged body portion [GRIFZPAT.A14 ]

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g 1 and maximize the efficiency of the applied energy.
2 It is important that the size of the shielded dipole 3 transducer be appropriately selected for the depth of penetra-4 tion required to induce healing in the appropriate body part.
As illustrated in Figure 8, an oversized shielded dipole 6 will generate considerable electromagnetic radiation outside 7 of leg 20 thereby wasting energy. The determination of the 8 intensity of the electromagnetic field of a field generated by 9 a shielded dipole transducer is extremely complex.
Figure 9 i8 ~ drawing taken from a computer generated 11 diagram for synthesizing the electromagnetic field generated 12 by a shielded dipole such as transducer 10. In this model the 13 shield 14 is assumed by the computer to be an ideal conductor.
14 Three points, A, B and C (Figure 12B) are indicated on the diagram. A indicates the intensity of the electromagnetic 16 field directly beneath shielded dipole 10. B indicates the 17 level where the electromagnetic field corresponds ~o the 1~ minimum e~fective field for promoting healing. C i8 an 19 arbitrarily chosen far field point.
Portability is preferably realized by integrating or 21 associating the transducer with the cast around the fracture 22 site, and having the power (battery) source and signal 23 generator located a short distance away. For example, the 24 latter components might be attached to the user's waist belt and connected via leads to the transducer. Alternately, all 26 the components may be attached to or lntegrated into the cast.
27 The former situation may be favored when a patient needs 28 constant electrostimulation which ~ay necessitate frequent 29 replacement of batteries. On the other hand, for patients with simple or small geometry fractures, the time of appli-31 cation needed for maximum rate of healing may be considerably 32 reduced, and there may be no need to change batteries over the 33 required ætimulation period. Here it might be desirable, for CGRIFzpAT.Al4~

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1 the patient's convenience and aesthetic purposes, to integrate 2 the entire unit into the cast. Any apparatus installation 3 which minimizes patient involvement or apparatus obtrusive-4 ness, greatly enhances the likelihood of success through improved patient compliance.
6 It i8 anticipated that the power source and signal ~ -7 generator circuitry used to generate the therapeutic signal 8 will weigh less than 1 pound and be about the æize of a common g pocket camera. Typically the battery voltage will be on the order of 6-40 V and the unit will accommodate a battery having 11 a volume on the order of about 2-60 cm3. It has been deter-12 mined that higher voltages are more efficient than lower 13 voltages. However, 40 V is the generally accepted maximum 14 voltage that can be applied to humans without substantial injury. Present devices operate at 35 V to allow a 5 V margin 16 in case of accidental application of the driving voltage to 17 the patient.
18 The signal applied to leads 17 is illustrated in Figures 19 lOA and lOB. The therapeutic effects of the signal of Figures lOA and 10~ were established using an animal ~odel system. In 21 the signal shown in Figures lOA and lOB V~ is the search coil 22 voltaqe; ~tpW is pulse width; ~tBW $s burst width and fBp is 23 burst frequency. The search coil voltage is that voltage 24 which i8 generated by a time varying magnetic field through a single loop of conductor having an internal area of 1 cm2.
26 A ~trW in the range of 0.5-20 ~sec, preferably 2-10 ~sec, 27 is therapeutically effective, with 5 ~sec being particularly 28~ ~effective. While I do not wish to be bound to any specific 29 theory of operation, I believe that the effectiveness of this invention conforms to theoretical considerations. Activation 31 of the cellular machinery involved in bone repair ffl electro-32 magnetic radiation requires delivery of a signal to the 33 in~ured site having defined time constants for burst width and .
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1 burst frequency. In order to realize this, it is necessary 2 for the signal to be established in healthy tissue and to 3 reach the injured site without being significantly attenuated 4 by the tissue. This in turn suggests that the ti~e constants associated with the ~agnetic, electric, chemical and electro-6 diffusion effects caused by the signal exhibit particular time 7 constants. I believe that the magnetic "diffusion" equation 8 assures that below 100 MHz the magnetic field completely 9 penetrates through to the injured site. For electric "diffusion", penetration of the bone by the displacement 11 current density remains low until 1 MHz (equivalent to ~t~ =
12 0.5 ~sec). Further, the viscous flow of interstitial fluids 13 in the canaliculi can follow frequencies up to 1 MHz. In 14 contrast, however, mechanical stress frequency responses attenuate after SQ0 Hz. Based on this brief analysis, it is 16 apparent that signal current densities with pulses widths as 17 low as 0.5 ~sec would likely be established in the tissue, and 18 thus potentially produce therapeutically effective results.
19 I have found that the procedure is particularly effective when V~ is 74 mV, ~tFW i8 5 ~sec, fB is 15 Hz, ~t~w 21 i~ 5 msec and t~ i8 varied from 2-10 ~sec. Moreover, Figure 22 11 illustrates that the effectiveness of these parameters is 23 a function of the amplitude of the signal. A search-coil 24 voltage amplitude A of 25<A~200 mV is effective with 50-100 ~V
being particularly effective.
26 It will, of course, be appreciated that what has been 27 described i8 a method for treating certain types of bone 28 fractures and is believed applicable both to animals and to 29 humans, and to stimulation of healing of various types of bone fractures and damaged tissues, including fresh fractures, and 31 especially bone fractures that do not readily heal in the 32~ absence of treatment, such as delayed unions, non-unions and 33 failed fu-ion~.

~GRIFZPAT.A14]
, 203~8~6 1 Figure 12A is a graph depicting relative stiffness of 2 osteotomized rabbit bones corresponding to the search coil 3 current used to promote healing in the broken rabbit bones, 4 and shows that both the minimum search coil voltage typically necessary for significant healing enhancement, although a 6 broad range of search coil voltages provides effective 7 therapy. Thus, uniformity of the applied field is not 8 necessary for effective therapy and in fact, because the 9 optimal voltage for each type of cell may vary, a range of applied signals increases the probability that the optimal 11 voltage will stimulate these various cell types and thus 12 enhance the healing process over the prior art teaching of 13 uniform applied fields.
14 Figure 12B is a graph depicting the magnetic field 15 generated by the simulation of Figure 9 in terms of ~earch 16 coil voltage. As can be seen from the graph of Figure 12B, 17 point 8 i8 the ~arthest point from the ~hielded dipole which 18 will provide adeguate healing electromagnetic fields and that 19 closer points to the ~hield have a signal which will provide effective therapy. For optimal efficiency, the size of 21 shielded dipole 10 (Figure 7) should be cho~en so that point 22 B i~ just beyond the damaged body portion in which healing is 23 to be promoted. The Table below shows the size of bar 12 24 (Figure 2) and the corresponding depth of penetration (DOP) and optimal shield length and width (both in cm).
26 TAB~E

29 ENGTH (cm) ~NGTH WIDTH

As stated earlier, for maximum utility, the shield 14 3~6 should be flexible to allow the molding of the shield to GR}FZPAT.A14]

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2~3~896 1 conform to the damaged limb or other damaged body part.
2 However, a conflicting goal is the requirement of maximum 3 conductivity. An extremely thick plate is highly conductive 4 but very inflexible. On the other hand, a thin plate is highly flexible but not very conductive. To determine an 6 adequate compromise, the conductivity of the shield material 7 at operating frequency must be determined. In direct current 8 situations, the conductivity of the shield material is 9 determined by the cross-sectional area of the conductor perpendicular to the direction of current flow. However, for 11 efficient electromagnetic wave generations the higher the 12 frequency generated, the greater the transfer efficiency into 13 the electromagnetic field. Given a bursted rectangular 14 waveform applied to leads 17 having a pulse width of approxlmately 5 ~sec, the effective frequency F is 1/(2 x 16 5 ~s) = 100 kHz. To obtain the Lenz effect for the ninth 17 harmonic, and thus for approximately 90% of the ~ignal, a 18 thickness for the shield must be chosen so that the 6kin depth 19 at this frequency i6 about one third of the thickness of the shield. One third of the thickness i8 for one surface of the 21 shield,-another is for the other surface and the third i5 for 22 additional margin. The skin depth is determined by the 23 equation:
24 D = (FMS) - 0.5 where D i8 the skin depth, 26 F is the frequency of the signal, 27 M is the relative permeability, and 28 S is the shield material conductivity.
29 ~ ~ Solvlng these equations for copper and ~00 kHz yields D(Cu) z 0.06 mm and thus a shield thickness of 0.2 mm.
31 The conductive material is preferably a highly conductive 32 material such as copper or aluminum. Aluminum is also 33 advantageous because it is X-ray transmissive. Thus adequate [GRIFZPAT.A14~
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1 X-rays may be taken through the aluminum shield. Various 2 configurations of shield material have proven ef~icacious.
3 For example, a wire mesh and a metal foil affixed to a cloth 4 backing has been used. A particularly advantageous embodiment is foil mounted on a cloth backing where a regular pattern of 6 holes, such as diamond shaped holes, are formed in the foil.
7 The holes allow lateral compression of the foil which allows 8 excellent three dimensional conformability to the surface of g the injured body portion.
The electrical characteristics of transducer 10 can be 11 expressed as a loosely coupled transformer which is schema-12 tically represented by Figure 13A~ Using the T network model 13 for representation of transformers, an equivalent circuit can 14 be shown a in Figure 13B. R(L~) i6 the resistance and Ll i8 the inductance of coil 16. M is the transinductance or 16 coupling of the "transformer." R(~) is the resistance and 17 i8 the inductance of shield 14. Treating the dipole itself as 18 a separate inductor, and a~suming that the solenoid has a 19 length to diameter ratio of 1, the inductance is given by:
L (in ~H) = 6.8 s~2 21 where L-is the inductance;
22 S i8 the diameter of the solenoid; and 23 n is the number of turns.
24 Different 601enoid configurations require different analysis. Inductive analysis is well known in the art.
26 The ohmic energy losses are represented by the ohmic 27 losses passing through R(LI) and R(~). The resistance of the 28 solenoid R(L1) is determined by taking the unit length 29 resistance of the coil times the total length of the coiled wire. Because shield 14 is loosely coupled, M is nearly equal 31 to zero and R(~) has a nearly direct effect consumption of 32 energy. Therefore, it is very important that the conductivity 33 of shield 14 be maximized. Accurate mathematical models for :
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203~6 1 R(~) can only be determined empirically unless very sophis-2 ticated computer modeling techniques are used.
3 Figure 14 is a technique for enhancing the field 4 distribution of a single dipole shielded dipole transducer.
Shielded dipole transducer 100 includes angled end pieces on 6 high permeability bar 104. By angling the end portion away 7 from the shield and towards the surface of the body part under 8 therapy, the magnetic field generated through high perme-9 ability bar 104 is directed slightly towards the surface of the body part under therapy. This increases efficiency by 11 directly applying the magnetic field to the body part under 12 therapy and minimizing the field which must be redirected by 13 conductive shield 106.
14 Figure 15 is another embodiment of the present invention which tailors the magnetia field by separating the coil around 16 high permeability bar 116 into coils 112 and 114. This 17 creates a flux gap which allows the bulging of the ~lux field 18 in the center of the dipole. Thi~ is another method of 19 tailoring the field beneath shielded dipole 110.
In certain therapy regimens for severe non-union 21 problems, electromagnetic therapy may be used in conjunction 22 with invasive techniques for positioning bones in the proper 23 healing position. A shielded transducer particularly adapted 24 for use with such a therapy regi~en is shown in Figure ~6A.
Shielded dipole transducers 122 and 124 are positioned on 26 either side of pins 126. Proper positioning of the pins 126 27 precludes optimal positioning of a single shielded transducer 28 and thus two tran6ducers are used to allow proper application 29 of the electromagnetic ~ield. Pins 126 are usually composed of steel or other conductive material~ which alter the 31 electromagnetic fields in the region by the Lenz effect;
32 however, this effect is mini~al. Depending on the desired 33 orientation and resultant efficiency, the coils of shielded tGRIFZPAT.A14]
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1 dipole transducers 122 and 124 will be connected either in 2 series or parallel.
3 Figure 16B is a top view of the interleaved relationship 4 of shielded dipole transducers 122, 124 and pins 126. As shown in Figure 16A, the dipole transduceræ of shielded dipole 6 transducers 122 and 124 provide complimentary magnetic fields 7 as indicated by the N (north) and as S (south) indicators on 8 the dipoles. Alternatively, these dipoles may be wired to 9 generate opposing magnetic fields which may cause desired magnetic field characteristics in certain instances.
11 Figures 17A and 17B show another embodiment of the 12 present invention. Arcuate shielded dipole 140 includes an 13 arcuate dipole to conform to the body part to allow for 14 transverse application of the shielded dipole transducer 140.
In certain fractures, æuch as hairli~e fractures, the fracture 16 occurs along the major axis of the bone. Although the precise 17 mechanism for enhanced bone growth i8 not known, some 18 researchers have suggested that applying a field transverse to l9 the fracture generates the physical mechanism which promotes bone growth.
21 Figures 18A and 18B show another embodiment of the 22 present invention where the dipole itself is twisted and 23 curved around the body part to provide a perpendicular field 24 to an angled fracture.
Figure 19 is a quadripole shielded transducer including 26 an arcuate dipole 152 and a linear dipole 154, both shielded 27 by conductive shield 156. In certain instances, the complex 28 magnetic fields generated by two dipoles may prove beneficial.
29 Figure 20 shows another embodiment of the present ~invention wherein shielded dipole 10 is positioned near high 31 permeability piece 160. Hiqh permeability piece 160 may also 32 be positioned diametricalIy opposed to shielded dipole 10.
33 The positioning of high permeability piece 160 alters the : :
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1 magnetic flux like the presence of a conductor alters the 2 electrical flux in an electrical field. The field altering 3 characteristics of the positioning of high permeability piece 4 160 can aid in directing the magnetic field towards the desired body portion or modify the field distribution.
6 Although specific embodiments of the present invention 7 are herein disclosed, they are not to be construed as limiting 8 the scope of the invention. For example, although devices -9 shown for generating magnetic fields from electrical current 10 are coils surrounding high permeability materials any elect- -11 rical to electromagnetic transducer is useful in con~unction 12 with the present invention and is another embodiment of the 13 present invention. The scope of the invention is only limited 14 by the claims appended hereto. ~ -I claim:

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Claims (10)

1. A transducer for converting an electrical signal into an electromagnetic field for application of said electro-magnetic field to a damaged body part to promote healing of said body part, said transducer comprising:
a conductive coil, said coil having first and second terminals at opposite ends of said coil, said first and second terminals connected to receive said electrical signals said coil providing an electromagnetic field in response to said electrical signal and said coil providing said electromagnetic field to said damaged body part when placed proximal to said damaged body part; and a conductive plate adapted to be positioned adjacent to said conductive coil and opposite from said damaged body part, said plate having a major surface adapted to be positioned parallel to said damaged body part and said plate extending laterally beyond said conductive coil in the direction of said major surface.

2. A transducer for converting an electrical signal into an electromagnetic field for application of said electro-magnetic field to a damaged body part to promote healing of said body part, said transducer comprising:
a core piece comprising high permeability material;
a conductive coil wrapped around said core piece, said coil having first and second terminals at opposite ends of said coil, said first and second terminals connected to receive said electrical signal, said coil and said core piece providing an electromagnetic field in response to said electrical signal and said coil and core piece providing said electromagnetic field to said damaged body part when placed proximal to said damaged body part; and a conductive plate adapted to be positioned adjacent to said core piece and conductive coil and opposite from said damaged body part, said plate having a major surface adapted to be positioned parallel to said damaged body part and said plate extending laterally beyond said core piece and conductive coil in the direction of said major surface.

3. A transducer for converting an electrical signal into an electromagnetic field for application of said electro-magnetic field to a damaged body part to promote healing of said body part, said transducer comprising:
a plurality of core pieces comprising high permeability material;
a conductive coil wrapped around said core pieces, said coil having first and second terminals at opposite ends of said coil, said first and second terminals connected to receive said electrical signal, said coil and said core pieces providing an electromagnetic field in response to said electrical signal and said coil and core piece providing said electromagnetic field to said damaged body part when placed proximal to said damaged body part; and a plurality of conductive plates one for each of said core pieces adapted to be positioned adjacent to said core pieces and conductive coil and opposite from said damaged body part, said plates having a major surface adapted to be positioned parallel to said damaged body part and said plates extending beyond said core piece and conductive coil in the direction of said major surface.

4. A transducer for converting an electrical signal into an electromagnetic field for application of said electro-magnetic field to a damaged body part to promote healing of said body part, said transducer comprising:

first and second core pieces comprising high permeability material;
a conductive coil wrapped around said first and second core pieces, said coil having first and second terminals at opposite ends of said coil, said first and second terminals connected to receive said electrical signal, said coil and said first and second core pieces providing perpendicular electromagnetic fields in response to said electrical signal and said coil and core piece providing said electromagnetic field to said damaged body part when placed proximal to said damaged body part; and a conductive plate adapted to be positioned adjacent to said first and second core pieces and conductive coil, and opposite from said damaged body part, said plate having a major surface adapted to be positioned parallel to said damaged body part and said plate extending laterally beyond said first and second core pieces and conductive coil in the direction of said major surface.

5. A transducer for converting an electrical signal into an electromagnetic field for application of said electro-magnetic field to a damaged body part to promote healing of said body part, said transducer comprising:
a core piece comprising high permeability material said core piece being curved to conform to said damaged body part;
a conductive coil wrapped around said core piece, said coil having first and second terminals at opposite ends of said coil, said first and second terminals connected to receive said electrical signal, said coil and said core piece providing an electromagnetic field in response to said electrical signal and said coil and core piece providing said electromagnetic field to said damaged body part when placed proximal to said damaged body part; and a conductive plate adapted to be positioned adjacent to said core piece and conductive coil and opposite from said damaged body part, said plate having a major surface adapted to be positioned parallel to said damaged body part and said plate extending beyond said core piece and conductive coil in the direction of said major surface.

6. A transducer for converting an electrical signal into an electromagnetic field for application of said electro-magnetic field to a damaged body part to promote healing of said body part, said transducer comprising:
a core piece comprising high permeability material;
a conductive coil wrapped around said core piece, said coil having first and second terminals at opposite ends of said coil, said first and second terminals connected to receive said electrical signal, said coil and said core piece providing an electromagnetic field in response to said electrical signal and said coil and core piece providing said electromagnetic field to said damaged body part when placed proximal to said damaged body part;
a shunt piece of high permeability material placed adjacent to said damage body part; and a conductive plate adapted to be positioned adjacent to said core piece and conductive coil and opposite from said damaged body part, said plate having a major surface adapted to be positioned parallel to said damaged body part and said plate extending beyond said core piece and conductive coil in the direction of said major surface.

7. A transducer for converting an electrical signal into an electromagnetic field for application of said electro-magnetic field to a damaged body part to promote healing of said body part, said transducer comprising:

a core piece comprising high permeability material;
a plurality of electrically connected conductive coils wrapped around said core piece, said plurality of coils having first and second terminals at opposite ends of said plurality of coils, said first and second terminals connected to receive said electrical signal, said plurality of coils and said core piece providing an electromagnetic field in response to said electrical signal and said plurality of coils and core piece providing said electromagnetic field to said damaged body part when placed proximal to said damaged body part; and a conductive plate adapted to be positioned adjacent to said core piece and plurality of conductive coils and opposite from said damaged body part, said plate having a major surface adapted to be positioned parallel to said damaged body part and said plate extending beyond said core piece and plurality of conductive coils in the direction of said major surface.

8. A transducer as in any of Claims 1-7 wherein said plate includes an indentation adapted for said coil, said major surface of said plate being closer to said damaged body part in the area extending beyond said coil than the area of said major surface not extending beyond said conductive coil.

9. A transducer as in Claim 8 wherein said area of said major surface extending beyond said coil is substantially flush with the surface of said coil nearest said damaged body part.

10. A transducer as in any of Claims 1-7 where said conductive plate comprises a flexible mesh of conductive wire or a layer of conductive and malleable material affixed to a flexible backing, said layer having a regular pattern of holes formed therein.