CA2007439C - Transcutaneous energy transfer device - Google Patents

Transcutaneous energy transfer device

Info

Publication number
CA2007439C
CA2007439C CA 2007439 CA2007439A CA2007439C CA 2007439 C CA2007439 C CA 2007439C CA 2007439 CA2007439 CA 2007439 CA 2007439 A CA2007439 A CA 2007439A CA 2007439 C CA2007439 C CA 2007439C
Authority
CA
Canada
Prior art keywords
primary
fet
device
coil
tet
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
CA 2007439
Other languages
French (fr)
Other versions
CA2007439A1 (en
Inventor
John Miller
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
University of Ottawa
Original Assignee
University of Ottawa
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University of Ottawa filed Critical University of Ottawa
Priority to CA 2007439 priority Critical patent/CA2007439C/en
Publication of CA2007439A1 publication Critical patent/CA2007439A1/en
Application granted granted Critical
Publication of CA2007439C publication Critical patent/CA2007439C/en
Anticipated expiration legal-status Critical
Application status is Expired - Lifetime legal-status Critical

Links

Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61NELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00Electrotherapy; Circuits therefor
    • A61N1/18Applying electric currents by contact electrodes
    • A61N1/32Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/36Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
    • A61N1/372Arrangements in connection with the implantation of stimulators
    • A61N1/378Electrical supply
    • A61N1/3787Electrical supply from an external energy source
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61NELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00Electrotherapy; Circuits therefor
    • A61N1/18Applying electric currents by contact electrodes
    • A61N1/32Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/36Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
    • A61N1/372Arrangements in connection with the implantation of stimulators
    • A61N1/37211Means for communicating with stimulators
    • A61N1/37217Means for communicating with stimulators characterised by the communication link, e.g. acoustic or tactile
    • A61N1/37223Circuits for electromagnetic coupling

Abstract

An improved transcutaneous energy transfer (TET) device comprises a primary winding for placement on or near a skin surface, and a secondary winding for implantation under said skin surface. A field effect transistor (FET) is arranged to switch said primary coil across an external DC power supply. A tuning capacitor is linked to said primary coil whereby said primary coil, when said FET is turned off, will resonate at its natural frequency thereby compensating for drift in component values and reducing power transfer sensitivity to component drift.

Description

201074~
The present invention relate~ to the f ield of medical device~: .
In particular, the present invention relates to power supply systems for transcutalleous energy transfer (TET) devices. Even more particularly, the present invention relates to an improvement in TET devices which simplifies such devices and; ov~:s their 5 energy transfer efficiency.

A TET device is a device for providing electrical power to an implanted mechanical or electrical medical device, such as prosthetic hearts and ventricular assist devices, without having to breach the skin to lead conducting wires therethrough.

An example of a TET device is shown in U . S . Patent No .
4,665,896 (LaForge et al) dated May 19, 1987. That patent shows a blood pump system powered by a TET device having an external primary winding and an implanted secondary winding. It is design5~1 to be regulated to a precise deqree, the power delivered to zm 15 implanted medical device. ~owever, it is not concerned with power transfer efficiency across the skin.

U.S. Patent No. 4,408,607 (Maurier) dated October 11, 1983, on the other hand, describes a TET device which charges an implanted capacitor. Power is then drawn by an implanted medical 20 device from the capacitor. Maurier does not retluire particularly efficient TET efficiency, it will be understood, because it 20074~9 ' utilizes TET technology to provide an induced voltage to charge a capacitor. An efficient capacitor is, under Maurier's proposal, much more crucial than efficient TET.

In U.S. Patent No. 4,741,339 of May 3, 1988, Harrison et al 5 describe a TET with i ~ ~ v~d coupling between internal and external inductive coils. The means for achieving such improved coupling proposed by Harrison includes a circuit electrically coupled to the primary coil, tuned to increase the quality factor of the primary transmitter circuit which includes the primary coil.

The object of the present invention is to provide a simple means of increasing power transmission efficiency levels in a TET
device to over 80% - higher than in previous TET devices. The present invention accomplishes this result without the need for complex and expensive additional circuitry.

In a broad aspect, the present invention relates to an improved transcutaneous energy transfer (TET) device including: a primary winding for placement on or near a skin surface; a secr~ ry winding for implantation under said skin surface; a field effect transistor ~FET~ arranged to switch said primary coils 20 across an external DC power supply; and a tuning capacitor linked to said primary coil whereby said primary coil, when said FET is turned off, will resonate at its natural frequency thereby 20074~
.
c~ - - ting for drift in component values and reducing power transfer sensitivity to component drift.

In another broad aspect, the present invention relates to a transformer having a primary coil and a secondary coil, said 5 primary coil being substantially bell-shaped, and said secondary coil being 6uitably shaped and dimensioned whereby to allow for a substantial amount of variation in the relative positions of said primary and ~ n~9~ry coils while minimising the variation in coupling between said coils.

In drawings which illustrate the present invention by way of example:
Figure 1 is a schematic of a DC to AC converter u~ i 1 i 7 i n~ the pL~V~ ~ of the present invention;
Figure 2 is a detail of the circuit of the secondary winding 15 shown in Figure 1;
Figure 3 is a cross sectional schematic of the conf iguration of the primary and secondary coils according to the present invention .

Referring now to Figures 1 and 2, it will first be appreciated 20 that the present invention is designed to induce A. C . current in a subcutaneous winding, for transformation to DC to power of a medical device. AC current is in;uced in L2, the secon~ary winding .
which may be, for instance, a toruæ wound with a core of Litzendraht (Litz ) wire implanted just under the skin S with electrical leads connected to a medical device requiring electrical power. A similar primary winding Ll is located in alignment with 5 the secondary winding, on the skin surf ace .

Primary winding Ll is connected to a capacitor 11 that is conn~t~fl to the negative of a DC input bus. Winding Ill is also connected to a field effect transistor (FET) 10, as indicated in Figure 1.

Power transfer takes place in two phases, a storage phase and a resonant phase. During the storage phase, energy is stored in the primary coil using a field effect transistor (FET) to switch the coil directly across the DC input supply. The FET is selected for its very low "on" resistance to minimize the conduction losses 15 and operates as a "single-ended" power switch.

The ratio of duty time/cycle time for the system of the present invention is about 759~. Accordingly, the subcutaneous secondary circuit is, in the present invention, tuned to half the ~requency of the primary, forming a dual resonant design. This 20 causes the s~nnA~ry circuit to uncouple from the primary during the primary resonant phase, thereby reducing waveform distortion resulting from wide variations i load.

During the resonant phase, the FET is turned off allowing the TET transformer primary to resonate with a tuning capacitor 11, thus transferring energy into the secondary coil. Allowing the transformer to resonate at its natural frequency enables automatic 5 compensation for any drift in the comron~nt values in the primary circuit, thus reducing the power transfer sensitivity to component drift .

The resonant phase is terminated when the voltage across the FET reaches zero. At this point, the FET is again turned on to 10 begin a new energy storage phase. Since the FET is only turned on close to a zero voltage crossing, switching losses in the FET are minimized. This enables the TET operating frequency to be increased over previous designs. Operating at higher frequencies permits smaller capacitors to be used for energy storage and 15 smaller magnetic r ~ ~nts for the transformer .

In addition, the use of a single ended quasi-resonant drive for the primary coil enables this circuit to tolerate variations in the transformer coupling due to coil separation. In previous designs, the primary transformer current increased as coupling was 20 reduced, theoretically approaching infinity as the coupling reached zero. Thus it was necessary to include special circuitry to turn off the primary coil driver under such conditions. This additional Z0~743~
circuitry is not required in the present design since a constant maximum stored energy operating mode is employed.

This mode of operation also allows the TET to tolerate induction losses due to adjacent conducting masses. In previous 5 designs, the TET would shut down under such conditions, ceasing power transfer. The present design copes with this situation by reducing power transfer efficiency, shutting down only in extreme situations .

The use of the Litz wire contributes to the overall efficiency 10 of the TET, which is over 80% for a wide range of load conditions.
The Litz wire is composed of many individually insulated strands which are bunched in a particular way to reduce eddy current losses. There are fi~e bunches of five bunches of three bunches of 23 strands i~ the Litz wire giving a total of (5x5x3x23=) 1,725 15 strands. The increased surface area of the Litz wire contributes to the reduction in the losses in the coils.

As can be seen in Figure 2, the AC current induced in secondary winding L2 which resonates with capacitor 12. The AC is converted to DC by means of a simple circuit including a 20 complimentary resonant capacitor 14 to further enhance the transmission efficiency of the TET systems. Resonant capacitor 12 is split into two capacitors 13 and 14. Under heavy load - 2~307~39 '-conditions, L2 resonates with 13. Under light or no load conditions, L2 resonates with 13 and 14.

The inclusion of this load sensitive tuning tends to stabilize the voltage transf er ratio of the TET against load variations .
5 This is achieved by modifying the resonant frequency of the secondary circuit as the load varies. This improves load regulation, and permits operation of the secondary circuit without complex feedback regulation.

Turning to Figure 3, the conf iguration of the primary and lO secondary coils is illustrated. It will be understood in previous TET designs, the implanted secondary coil is substantially encircled by the torus-like primary coil which sits on the skin surface. This arrangement permits fairly accurate emplacement of the primary coil over the secondary, and means that there is very 15 little change in coupling co-efficient if the primary and ~econ~lAry coils are moved slightly, as can easily happen in normal use. The problem with this type of arrangement is that it is very sensitive to inductive influences, and the proximity of a large metal object will result in a complete shutdown of energy transfer.

The present invention however, provides a coil configuration that is relatively insensitive (about 12% power loss) to the presence of metallic ob jects. As can be seen from Figure 3, the Z007~3~
present transformer e~ploys ~ primary coil having a shallow bell shaped profile which covers the secondary coil. This results in a design which is relatively insensitive to inductive interference by adjacent c~n~llle~;n~ objects. The present method of electronic 5 power transfer is also more tolerant to inductive interference and thus the overall TET system enables the energy transfer to tolerate close contact with a metallic surface. When a large metallic plate is brought into close contact with the TET primary coil, ( limited only by the insulation thickness of said primary) energy transfer lO efficiency falls by only about 12%. A similar situation applied to the prior systems would result in a complete shutdown of energy trans f er .

The dome shaped construction of the secondary coil assists in coupling st~h; 1 i~4Ation and also mechanical alignment of the primary 15 coil. The internal space that this affords is utilised to house the internal AC-DC converter 13, which results in a number of significant advantages: (1) Power dissipation in the AC-DC
converter is better distributed by the large copper mass of the secondary coil . ~ 2 ) This power no longer contributes to the 20 increased temperature of the internal electronic controller . ( 3 ) High frequency, high voltage AC is kept within the secondary coil and away from other sensitive electronics. (4) The interconnecting wires from the secondary coil to the electronics and pump module carry DC and are not part of th- tune~ secondary circuit. This 2007~3~
.
reduces the effective resistance and thereby increases the efficiency of the tuned circuit and enables conventional smaller gauge stranded wire (not Litz~ to be used to carry the DC from the coil to the electronics.

In a typical embodiment, the primary coil will be about 90mm in diameter, with a depth of 23mm, and the secondary coil will be 66mm in diameter, with a depth of 24mm.

It is to be understood that the examples described above are not meant to limit the scope of the present invention. It is expected that numerous variants will be obvious to the person skilled in the TET art, without any departure from the spirit of the present invention. The appended claims, properly construed, form the only limitation upon the scope of the present invention.

Claims (5)

1. An improved transcutaneous energy transfer (TET) device comprising:

i) a primary winding for placement on or near a skin surface:

ii) a secondary winding for implantation under said skin surface;

iii) a field effect transistor (FET) arranged to switch said primary coil across an external DC power supply; and iv) a tuning capacitor linked to said primary coil whereby said primary coil, when said FET is turned off, will resonate at its natural frequency thereby compensating for drift in component values and reducing power transfer sensitivity to component drift.
2. A device as claimed in Claim 1, wherein said windings are made from Litzendraht (Litz) wire.
3. A device as claimed in Claim 2, wherein said FET is turned on when voltage across it reaches zero and said primary winding ceases resonating, whereby switching losses in the FET are minimised.
4. A device as claimed in Claim 1, 2 or 3, wherein a second tuning capacitor is provided, linked to said secondary coil, to stabilize the voltage transfer ratio from the primary to the secondary coil permitting operation without feedback regulation to control for output variations with load.
5. A device as claimed in Claim 1, 2 or 3, wherein said secondary coil is tuned to half the frequency of the first, resulting in dual resonance, and a duty cycle ratio of on time/cycle time of about .75.
CA 2007439 1990-01-09 1990-01-09 Transcutaneous energy transfer device Expired - Lifetime CA2007439C (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA 2007439 CA2007439C (en) 1990-01-09 1990-01-09 Transcutaneous energy transfer device

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CA 2007439 CA2007439C (en) 1990-01-09 1990-01-09 Transcutaneous energy transfer device
GB9009713A GB2239802B (en) 1990-01-09 1990-05-01 Transcutaneous energy transfer device

Publications (2)

Publication Number Publication Date
CA2007439A1 CA2007439A1 (en) 1991-07-09
CA2007439C true CA2007439C (en) 1996-08-13

Family

ID=4143975

Family Applications (1)

Application Number Title Priority Date Filing Date
CA 2007439 Expired - Lifetime CA2007439C (en) 1990-01-09 1990-01-09 Transcutaneous energy transfer device

Country Status (2)

Country Link
CA (1) CA2007439C (en)
GB (1) GB2239802B (en)

Families Citing this family (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995007109A1 (en) * 1993-09-10 1995-03-16 Ottawa Heart Institute Research Corporation Electrohydraulic ventricular assist device
US5591217A (en) * 1995-01-04 1997-01-07 Plexus, Inc. Implantable stimulator with replenishable, high value capacitive power source and method therefor
US5630836A (en) * 1995-01-19 1997-05-20 Vascor, Inc. Transcutaneous energy and information transmission apparatus
SE9603099D0 (en) * 1996-08-27 1996-08-27 Pacesetter Ab Medical implant
US6366815B1 (en) 1997-01-13 2002-04-02 Neurodan A /S Implantable nerve stimulator electrode
US6327504B1 (en) * 2000-05-10 2001-12-04 Thoratec Corporation Transcutaneous energy transfer with circuitry arranged to avoid overheating
GB2370509A (en) * 2000-08-29 2002-07-03 Don Edward Casey Subcutaneously implanted photovoltaic power supply
US20060009755A1 (en) * 2003-09-04 2006-01-12 Sra Jasbir S Method and system for ablation of atrial fibrillation and other cardiac arrhythmias
DE10353943B4 (en) 2003-11-18 2013-01-03 Deutsches Zentrum für Luft- und Raumfahrt e.V. Arrangement for the wireless transmission of energy to an implanted device
US7599743B2 (en) 2004-06-24 2009-10-06 Ethicon Endo-Surgery, Inc. Low frequency transcutaneous energy transfer to implanted medical device
US20050288740A1 (en) * 2004-06-24 2005-12-29 Ethicon Endo-Surgery, Inc. Low frequency transcutaneous telemetry to implanted medical device
US7599744B2 (en) 2004-06-24 2009-10-06 Ethicon Endo-Surgery, Inc. Transcutaneous energy transfer primary coil with a high aspect ferrite core
US20070005141A1 (en) * 2005-06-30 2007-01-04 Jason Sherman Apparatus, system, and method for transcutaneously transferring energy
US7780613B2 (en) 2005-06-30 2010-08-24 Depuy Products, Inc. Apparatus, system, and method for transcutaneously transferring energy
US8075627B2 (en) 2006-04-07 2011-12-13 Depuy Products, Inc. System and method for transmitting orthopaedic implant data
US8015024B2 (en) 2006-04-07 2011-09-06 Depuy Products, Inc. System and method for managing patient-related data
US7962211B2 (en) 2006-04-28 2011-06-14 Medtronic, Inc. Antenna for an external power source for an implantable medical device, system and method
WO2007126454A2 (en) 2006-04-28 2007-11-08 Medtronic, Inc. System for transcutaneous energy transfer to an implantable medical device with mating elements
US8632464B2 (en) 2006-09-11 2014-01-21 DePuy Synthes Products, LLC System and method for monitoring orthopaedic implant data
US8080064B2 (en) 2007-06-29 2011-12-20 Depuy Products, Inc. Tibial tray assembly having a wireless communication device

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4014346A (en) * 1975-06-26 1977-03-29 Research Corporation Hermetically sealed cardiac pacer system and recharging system therefor
JPS5634883B2 (en) * 1976-12-20 1981-08-13
US4389702A (en) * 1980-08-20 1983-06-21 International Rectifier Corporation Switching power supply circuit having constant output for a wide range of input voltage
US4408607A (en) * 1981-04-13 1983-10-11 Empi, Inc. Capacitive energy source and circuitry for powering medical apparatus

Also Published As

Publication number Publication date
GB2239802B (en) 1994-01-05
GB9009713D0 (en) 1990-06-20
CA2007439A1 (en) 1991-07-09
GB2239802A (en) 1991-07-17

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Legal Events

Date Code Title Description
EEER Examination request
MKLA Lapsed
MKEC Expiry (correction)

Effective date: 20121202