Abstract:
An implantable medical device, such as a bi-directional infuser device for hydraulically controlling an artificial sphincter (e.g., adjustable gastric band) benefits from being remotely powered by transcutaneous energy transfer (TET), obviating the need for batteries. In order for active components in the medical device to operate, a sinusoidal power signal received by a secondary coil is rectified and filtered. An amount of power transferred is modulated. In one version, a voltage comparison is made of a resulting power supply voltage as referenced to a threshold to control pulse width modulation (PWM) of the received sinusoidal power signal, achieving voltage regulation. Versions incorporate detuning or uncoupling of the secondary coil to achieve PWM control without causing excessive heating of the medical device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is related to four co-pending and commonly-owned applications filed on even date herewith, the disclosure of each being hereby incorporated by reference in their entirety, entitled respectively: 
        “TRANSCUTANEOUS ENERGY TRANSFER PRIMARY COIL WITH A HIGH ASPECT FERRITE CORE” to James Giordano, Daniel F. Dlugos, Jr. &amp; William L. Hassler, Jr., Ser. No. ______;     “MAGNETIC RESONANCE IMAGING (MRI) COMPATIBLE REMOTELY ADJUSTABLE GASTRIC BAND” to William L. Hassler, Jr. et al., Ser. No. ______;     “SPATIALLY DECOUPLED TWIN SECONDARY COILS FOR OPTIMIZING TRANSCUTANEOUS ENERGY TRANSFER (TET) POWER TRANSFER CHARACTERISTICS” to Resha H. Desai, William L. Hassler, Jr., Ser. No. ______;     “LOW FREQUENCY TRANSCUTANEOUS TELEMETRY TO IMPLANTED MEDICAL DEVICE” to William L. Hassler, Jr., Ser. No. ______; and     “LOW FREQUENCY TRANSCUTANEOUS ENERGY TRANSFER TO IMPLANTED MEDICAL DEVICE” to William L. Hassler, Jr., Daniel F. Dlugos, Jr., Ser. No. ______.       
 
     
    
     FIELD OF THE INVENTION  
       [0007]     The present invention relates, in general, to medically implantable devices that receive transcutaneous energy transfer (TET), and more particularly, such implant devices that regulate power transfer.  
       BACKGROUND OF THE INVENTION  
       [0008]     In a TET system, a power supply is electrically connected to a primary coil that is external to a physical boundary, such as the skin of the human body. A secondary coil is provided on the other side of the boundary, such as internal to the body. With a subcutaneous device, both the primary and secondary coils are generally placed proximate to the outer and inner layers of the skin. Energy is transferred from the primary coil to the secondary coil in the form of an alternating magnetic field. The secondary coil converts the transferred energy in the AC magnetic field to electrical power for the implant device, which acts as a load on the secondary coil.  
         [0009]     In a TET system, the primary and secondary coils are placed on separate sides of the boundary or skin. This separation typically results in variations in the relative distance and spatial orientation between the coils. Variations in the spacing can cause changes in the AC magnetic field strength reaching the secondary coil, in turn causing power fluctuations and surges in the implant device. Implant devices, such as those used in medical applications; usually rely upon a microcontroller to perform various functions. These microcontrollers require a consistent, reliable power source. Variations in the supplied power, such as sudden changes in voltage or current levels, may cause the device to perform erratically or fail to function at all. Accordingly, one issue associated with conventional TET systems is that the physical displacement of either the primary or secondary coils from an optimum coupling position may cause an unacceptable effect on the output power supplied to the implanted device. Additionally, the implant load on the secondary coil may vary as the device performs different functions. These load variations create different demands on the TET system, and lead to inconsistencies in the output power required to drive the load. Accordingly, it is desirable to have an accurate, reliable system for controlling the output power supplied to a load in a TET system. In particular, it is desirable to regulate the power induced in the secondary coil to provide an accurate, consistent load power despite variations in the load or displacement between the TET coils.  
         [0010]     In U.S. Pat. No. 6,442,434, an energy transfer system is described wherein stable power is maintained in an implanted secondary circuit by having the secondary circuit generate a detectable indication that is sensed by the primary circuit. For instance, a voltage comparator in the secondary circuit senses that too much TET power is being received and shorts the secondary coil by closing a switch. The shorted secondary coil causes a current surge that is observable in the primary coil. The primary circuit is then adjusted so that these surges have a very small duty cycle, thus achieving voltage regulation since this condition indicates that the voltage in the secondary circuit is cycling close to a reference voltage used by the voltage comparator.  
         [0011]     While apparently an effective approach to power regulation in a TET system, it is believed in some applications that this approach has drawbacks. For high impedance secondary coils, shorting the secondary circuit in this manner may create excessive heating, especially should the primary circuit continue to provide excessive power to the secondary circuit. Insofar as the &#39;434 patent addresses continuous TET power of an artificial heart and other high power applications, such heating is a significant concern, warranting significant emphasis on modulating the power emitted by the primary circuit.  
         [0012]     In U.S. Pat. No. 5,702,431, controlling current in a secondary circuit for battery charging is based upon switching capacitance into the secondary resonance circuit to change its efficiency. To that end, the AC resonance circuit is separated from the battery being charged by a rectifier. Current sensed passing through the battery is used to toggle two capacitors to vary the resonance characteristics of the secondary coil. The problem being addressed is providing a higher current during an initial stage of battery charging followed by a lower current to avoid damaging the battery due to overheating.  
         [0013]     While these approaches to modifying power transfer characteristics of TET to a medical implant have applications in certain instances, it would be desirable to address the power requirements of a bi-directional infuser device suitable for hydraulically controlling an artificial sphincter. In particular, the power consumed to pump fluid is significant, as compared to what would be required for only powering control circuitry, for example. Moreover, powering the active pumping components need only occur intermittently. Since reducing the size of the medical implant is desirable, it is thus appropriate to eliminate or significantly reduce the amount of power stored in the infuser device, such as eliminating batteries.  
         [0014]     Using TET to power the active pumping components, control circuitry and telemetry circuitry without the electrical isolation provided by a battery suggests that power regulation is desirable. In particular, most electronic components require a supply voltage that is relatively stable, even as the power demand changes. While having a primary circuit that is responsive to power transfer variability is helpful, such as alignment between primary and secondary coil, etc., it is still desirable that the implantable infuser device be relatively immune to changes in the power transferred. This becomes all the more desirable as rapidly changing power demands in the implanted medical device vary beyond the ability of the primary circuit to sense the change and respond.  
         [0015]     Consequently, a significant need exists for an implantable medical device having secondary circuitry that optimizes power transfer characteristics from received transcutaneous energy transfer to power active components.  
       SUMMARY OF THE INVENTION  
       [0016]     The invention overcomes the above-noted and other deficiencies of the prior art by providing an implantable medical device having receiving circuitry for transcutaneous energy transfer (TET) from primary circuitry external to a patient. In particular, the receiving circuitry performs voltage regulation sufficient to support active components, such as integrated circuitry, without resorting to batteries. Moreover, insofar as the receiving circuitry adjusts power transfer autonomously with regard to the primary circuitry, the implantable medical device is less susceptible to damage or inoperability due to variations in a power channel formed with the primary circuitry.  
         [0017]     In one aspect of the invention, an implantable medical device includes an active load that benefits from a stable electrical power supply with voltage remaining within a voltage range near a voltage reference even though the current demand may vary significantly. Receiving circuitry in the implantable medical device includes a secondary coil that is configured to be in resonance with a frequency of a power signal received from a primary coil of primary circuitry external to a patient. Sinusoidal received power is rectified to supply electrical power. Voltage regulation circuitry responds to a supply voltage of the supply electrical power delivered to the active load by switching detuning circuitry into and out of electrical communication with the secondary coil to manage an amount of power received. Thereby, a stable electrical power supply is provided to the active load.  
         [0018]     These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.  
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0019]     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and, together with the general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention.  
         [0020]      FIG. 1  is a block diagram illustrating an exemplary energy transfer system in accordance with the present invention;  
         [0021]      FIG. 2  is a block diagram illustrating a first embodiment for the power control system of the present invention;  
         [0022]      FIG. 3  is a graphical representation of the output power from the secondary resonant circuit as modulated by the power control system;  
         [0023]      FIG. 4  is a more detailed circuit diagram for the first embodiment of the power control system shown in  FIG. 2 ;  
         [0024]      FIG. 5A  is a simplified circuit diagram depicting a first exemplary switching scheme for the power control system in a series resonant circuit;  
         [0025]      FIG. 5B  is a simplified circuit diagram depicting a second exemplary switching scheme for the power control system in a series resonant circuit;  
         [0026]      FIG. 5C  is a simplified circuit diagram depicting a third exemplary switching scheme for the power control system in a series resonant circuit;  
         [0027]      FIG. 5D  is a simplified circuit diagram depicting a fourth exemplary switching scheme for the power control system in a parallel resonant circuit;  
         [0028]      FIG. 5E  is a simplified circuit diagram depicting a fifth exemplary switching scheme for the power control system in a parallel resonant circuit;  
         [0029]      FIG. 5F  is a simplified circuit diagram depicting a sixth exemplary switching scheme for the power control system in a parallel resonant circuit;  
         [0030]      FIG. 5G  is a simplified circuit diagram depicting a seventh exemplary switching scheme for the power control system in a series resonant circuit;  
         [0031]      FIG. 6  is a block diagram illustrating a second embodiment for the power control system of the present invention;  
         [0032]      FIG. 7  is a schematic diagram depicting in more detail the power control system of  FIG. 6 ;  
         [0033]      FIG. 8  is a block diagram illustrating a third embodiment for the power control system of the present invention; and  
         [0034]      FIG. 9  is a block diagram illustrating a fourth embodiment for the power control system of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     Referring now to the drawings in detail, wherein like numerals indicate the same elements throughout the views,  FIG. 1  illustrates a transcutaneous energy transfer (TET) system  20  for an implant device  22  in accordance with the present invention. TET system  20  includes a primary circuit  24  comprising a power supply  26  located external to a physical boundary  28 . Boundary  28  may be the skin of a human or animal body, such as in the case of a medical implant, or may be any other type of inanimate material or tissue depending upon the particular application of TET system  20 . Primary circuit  24  also includes a primary coil  30  and one or more capacitors  36 . Capacitor  36  is connected in parallel with primary coil  30  to form a primary resonant circuit  38 . Primary resonant circuit  38  is electrically coupled to power supply  26  to resonate at the desired power signal frequency. An alternating magnetic field  32  is generated in primary coil  30  in response to input power provided by power supply  26 .  
         [0036]     A secondary coil  34  is provided in a spaced relationship from primary coil  30 . Typically secondary coil  34  will be located on the opposite side of boundary  28  from primary coil  30 . In the discussion herein, secondary coil  34  is located within implant device  22 . Secondary coil  34  is electrically coupled to primary coil  30  via alternating magnetic field  32 , symbolically illustrated in the figures as arrows emanating from primary coil  30  and propagating towards secondary coil  34 . Secondary coil  34  is electrically connected in series with one or more tuning capacitors  40 . Tuning capacitor  40  is selected to enable coil  34  and tuning capacitor  40  to resonate at the same frequency as primary resonant circuit  38 . Accordingly, first and second coils  30 ,  34  and corresponding capacitors  36 , 40  form a pair of fixed power resonator circuits which transfer a maximum amount of energy between power supply  26  and implant  22  at the resonant frequency.  
         [0037]     As shown in  FIG. 1 , primary coil  30  and secondary coil  34  are usually positioned relative to each other such that the secondary coil intercepts at least a portion of alternating magnetic field  32 . While primary coil  30  and secondary coil  34  are magnetically coupled, the coils are typically not physically coupled. Accordingly, coils  30 ,  34  may be moved relative to each other, and the energy coupling between the coils may vary depending upon the relative displacement between the coils. The relative displacement between the coils  30 ,  34  may be in an axial direction as indicated by reference numeral  42 . Similarly, the displacement between coils  30 ,  34  may be in a lateral direction, essentially orthogonal to the axial displacement, as indicated by reference numeral  44 . The displacement between coils  30 ,  34  could also consist of a change in the angular orientation of one coil relative to the other coil, as indicated by reference numerals  46  and  48 . Each of these various displacements between coils  30 ,  34  can cause a change in the amount of alternating magnetic field  32  reaching the secondary coil  34 . The power induced in secondary coil  34  is inversely related to the displacement between coils  30 ,  34 . The greater the displacement between coils  30 ,  34 , the lower the amount of power induced in secondary coil  34 . As primary coil  30  moves relative to secondary coil  34  (such as when primary circuit  24  is manipulated by a medical practitioner in the case of a medical implant) the power induced in secondary coil  34  can swing from very high to very low voltage and/or current levels.  
         [0038]     Secondary coil  34  is electrically coupled to a load  50  and provides output power to the load from the received magnetic field  32 . Depending upon the particular application, load  50  may represent one or more of a variety of devices that use the output power provided by secondary coil  34  to perform different operations. Load  50  may be associated with some resistance or impedance that, in some applications, may vary from time to time during normal operation of the load depending, in part, on the particular function being performed. Accordingly, the output power required by load  50  may also vary between different extremes during operation of implant  22 .  
         [0039]     In order to respond to these inherent power variations and provide a stable power supply to load  50 , the present invention includes a power control circuit  52 . Power control circuit  52  interfaces with secondary coil  34  and tuning capacitor  40  to control the power transfer from the primary coil  30 . Power control circuit  52  measures the power signal from a secondary resonant circuit  54 , formed by the combination of the secondary coil  34  and the tuning capacitor  40 , and based upon the measured value, pulse width modulates the power signal to produce an output voltage at an acceptable level for implant load  50 .  
         [0040]     In a first embodiment shown in  FIG. 2 , power control circuit  52  comprises a switch  56  that internally modulates the power signal induced in secondary coil  34  to control the power output to load  50 . Switch  56  modulates the power signal by selectively detuning secondary resonant circuit  54  when the voltage output to load  50  exceeds a predetermined threshold level. A suitable switch  56  may include a solid state switch such as a triac or silicon controlled rectifier (SCR). The secondary resonant circuit  54  is detuned by placing switch  56  in the resonant circuit, and selectively closing the switch  56  to short-circuit either tuning capacitor  40  or secondary coil  34 . Short-circuiting either capacitor  40  or coil  34  causes secondary resonant circuit  54  to lose resonance, thereby preventing energy transfer through coil  34  to load  50 . When the load voltage drops below the voltage threshold, switch  56  is opened to again transfer power to load  50 . By repeatedly detuning and then retuning secondary resonant circuit  54 , to stop and start energy transfer through secondary coil  34 , power control circuit  52  modulates the output power from coil  34  into a series of power pulses.  
         [0041]     It should be appreciated by those skilled in the art that selectively detuning to manage power transfer may be in response to sensed load current in addition to, or as an alternative to, sensed load voltage.  
         [0042]      FIG. 3  depicts an exemplary series of power pulses corresponding to the selective tuning and detuning of resonant circuit  54 . As the distance between primary and secondary coils  30 ,  34  varies, the width of the power pulses (indicated as PW in  FIG. 3 ) will vary to adjust the output power to load  50 . The smaller the relative displacement between the coils  30 ,  34 , the shorter the power pulses necessary to generate the desired load power output. Conversely, the greater the displacement between primary and secondary coils  30 ,  34 , the greater the period of time switch  56  is opened in order to transfer sufficient power to drive load  50 . As the load power requirements vary, the pulse width PW will also vary. When load  50  requires an increased amount of power, such as to drive a motor or operate an element within implant  22 , the pulse width PW or switch open time will increase to allow more power to be applied to the load. A full-wave rectifier  62  rectifies the pulse width modulated power signal. In addition, one or more filter capacitors  64 , shown in  FIG. 4 , filter the power signal before it is applied to load  50 .  
         [0043]     To determine when the induced power signal exceeds the voltage threshold for load  50 , power control circuit  52  includes a comparator  66  shown in  FIG. 2 . Comparator  66  compares the output voltage for load  50  with a predetermined threshold voltage level  70 . The threshold voltage level  70  may be the maximum desired operating voltage for the implant load  50 . Comparator  66  outputs a signal  74  that varies continuously in proportion with the difference between its inputs, namely the output voltage from filter capacitors  64  and the reference voltage (i.e., voltage threshold  70 ). Comparator output  74  is coupled to switch  56  to activate the switch  56  based upon the comparison between the output load voltage and the threshold voltage  70 . When output signal  74  from comparator  66  reaches the activation point for switch  56 , indicating an increase in the voltage level beyond the acceptable operating range, switch  56  is activated to short circuit the resonant circuit  54 . Likewise, when the output voltage from capacitors  64  drops below an acceptable level for implant operation, such as when either the load demand, relative displacement between the coils  30 ,  34 , or both increase, then output signal  74  of comparator  66  triggers switch  56  to open, thereby enabling power to again be induced and transferred through secondary coil  34 .  
         [0044]      FIG. 4  provides a more detailed, exemplary schematic diagram for the first embodiment of the present invention. As shown in  FIG. 4  in the first embodiment, switch  56  is placed in parallel with tuning capacitor  40  in order to short-circuit the capacitor from resonant circuit  54  when the switch  56  is closed. Switch  56  is depicted as a solid-state relay that is flipped on or off when output signal  74  from comparator  66  reaches the set point. Also in this exemplary embodiment, voltage rectifier  62  is a full-wave bridge rectifier comprised of four Schottky diodes connected to rectify or demodulate the power signal from power circuit  52 . Capacitors  64  filter the rectified power signal before application to load  50 .  
         [0045]     As mentioned above,  FIG. 4  depicts switch  56  as a solid-state relay in parallel with capacitor  40  for pulse width modulating resonant circuit  54 . In addition to this switching configuration, numerous other embodiments may also be utilized for selectively decoupling secondary coil  34  from primary coil  30  to regulate power transfer to the implant. Any available circuit topology may be employed in the present invention that would achieve the selective decoupling of the TET coils  30 ,  34  in response to the variations in transfer power.  
         [0046]      FIGS. 5A through 5G  illustrate several exemplary circuit topologies that may be implemented to achieve power regulation in accordance with the invention.  FIG. 5 A  illustrates one embodiment for selectively short-circuiting secondary coil  34  when the coil and tuning capacitor  40  form a series resonant circuit. Switch  56  is selectively turned on by comparator output signal  74 , which is not shown in  FIGS. 5A-5G , when the voltage induced in secondary coil  34  exceeds voltage threshold  70 . When switch  56  is turned on, switch  56  forms a short circuit across secondary coil  34  to detune resonant circuit  54  and prevent energy transfer from the secondary coil. When switch  56  is turned off, the short circuit (or detuning) is removed and secondary circuit  54  returns to resonance.  
         [0047]      FIG. 5B  depicts another exemplary embodiment for selectively detuning secondary resonant circuit  54  when secondary coil  34  and capacitor  40  form a series resonant circuit. In this embodiment, switch  56  is placed in parallel with capacitor  40  to short-circuit the capacitor out of resonant circuit  54  when the switch  56  is turned on.  FIG. 5C  depicts a third exemplary embodiment for short-circuiting secondary resonant circuit  54  when secondary coil  34  and capacitor  40  are a series resonant circuit. In the  FIG. 5C  embodiment, switch  56  is placed in series with secondary coil  34  and capacitor  40  to short-circuit resonant circuit  54  and prevent energy transfer from the coil to load  50 . Switch  56  is controlled by an output signal from comparator  66  to pulse width modulate the energy transferred from secondary coil  34  to full-wave rectifier  62 .  
         [0048]      FIGS. 5D-5F  depict several embodiments for selectively detuning secondary resonant circuit  54  and, thus, regulating power transfer when secondary coil  34  and capacitor  40  are connected as a parallel resonant circuit. In  FIG. 5D , switch  56  is connected in parallel between secondary coil  34  and capacitor  40  to effectively short-circuit capacitor  40  out of the circuit when the switch  56  is turned on. In  FIG. 5E , switch  56  is placed in parallel with secondary coil  34  and capacitor  40  between secondary resonant circuit  54  and voltage rectifier  62 . This embodiment is similar to that provided in  FIG. 5C , in that when turned on, switch  56  short-circuits resonant circuit  54  and prevents energy transfer from secondary coil  34  to load  50 . In  FIG. 5F , switch  56  is placed in series with capacitor  40  to short-circuit the capacitor from resonant circuit  54  when switch  56  is turned on.  
         [0049]      FIG. 5G  depicts another exemplary circuit topology for detuning secondary resonant circuit  54  when secondary coil  34  is too large of a load to short circuit using one of the other embodiments described above. In this embodiment, secondary coil  34  is divided into two sections and one section is placed in an H-bridge  86 . Pairs of switches in the H-bridge are alternately closed and opened to effectively reverse one-half of secondary coil  34  in and out of the circuit. When the switches are closed, such that one-half of secondary coil  34  is reversed relative to the other half, the two coil halves electrically cancel each other, effectively turning secondary coil  34  off when the transfer power exceeds the threshold voltage.  
         [0050]      FIG. 6  depicts a second embodiment for the present invention, in which switch  56  is located between full-wave voltage rectifier  62  and filter capacitors  64  to modulate the rectified power signal. In the first embodiment described above, switch  56  short-circuits either secondary coil  34  or capacitor  40  to selectively decouple resonant circuit  54  and thereby regulate the transfer power. In the second embodiment shown in  FIG. 6 , switch  56  is positioned between voltage rectifier  62  and filter capacitors  64  to pulse width modulate the rectified power signal. When switch  56  is closed, power is drawn from secondary coil  34 , rectified, and transferred to load  50  through filter capacitors  64 . When switch  56  is opened, the power transfer circuit is open-circuited and power is not drawn from the secondary coil. While switch  56  is opened, filter capacitors  64  discharge and provide power to load  50 . After the load voltage drops below the threshold level, switch  56  is closed, and power transfer is resumed. Filter capacitors  64  recharge as power is transferred from coil  34  to load  50 .  
         [0051]      FIG. 7  provides a detailed schematic diagram illustrating the second embodiment of the invention. The schematic in  FIG. 7  is similar to the schematic in  FIG. 4  except for the relocation of switch  56 . As shown in  FIG. 7 , in this exemplary embodiment switch  56  comprises a solid-state relay between full-wave rectifier  62  and filter capacitors  64 . An output signal from comparator  66  turns the relay on and off, based upon the output power to load  50 . While switch  56  is depicted as a solid-state relay, numerous other types of switching devices could also be used to accomplish the present invention.  
         [0052]      FIG. 8  illustrates an alternative embodiment for the power control circuit  52  of the present invention. In the alternative embodiment, comparator  66  in the closed loop power control system is replaced with a Proportional, Integral, Derivative (PID) controller  90 . PID controller  90  activates switch  56  to pulse width modulate the power signal. PID controller  90  modulates the power signal by first calculating the error between the actual voltage in load output signal  72  and voltage threshold  70 . This error is multiplied by the proportional gain, then integrated with respect to time and multiplied by the integral gain. Finally, the error is differentiated with respect to time and multiplied by the differential gain of controller  90  to generate a control signal  74  for switch  56 . Control signal  74  will continually vary based upon the amplifier gains. Controller  90  operates at a fixed frequency and determines the amount of time to open and close switch  56  during each duty cycle, based upon the gains acting upon the error signal. By operating at fixed frequency intervals, the PID controller  90  responds quickly to changes in the power levels and provides increased control over the pulse width modulation of the power signal.  
         [0053]      FIG. 9  illustrates another alternative embodiment for the present invention, in which a microcontroller  100  is utilized to control the difference between the voltage of output signal  72  and a desired voltage level. From this difference, microprocessor  100  digitally controls switch  56  to modulate the power signal. Microprocessor  100  provides precision control over the selective detuning of secondary resonant circuit  54  and, thus, a stable load power. While  FIGS. 9 and 10  depict switch  56  in the first embodiment position, where the switch selectively detunes resonant circuit  54 , PID controller  90  and microprocessor  100  may also be used in the closed loop control of the second embodiment described above, in which switch  56  is positioned between voltage rectifier  62  and filter capacitors  64 .  
         [0054]     It should be appreciated that various loads  50  of an implant device  22  may benefit from regulating transferred power, to include both maintaining voltage within certain parameters and current within certain parameters. Thus, sensing current may be used as an alternative to, or in addition to, sensing voltage.  
         [0055]     While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications may readily appear to those skilled in the art.  
         [0056]     For example, implantable, bi-directional infusing devices that would benefit from enhanced TET powering and telemetry are disclosed in four co-pending and co-owned patent applications filed on May 28, 2004, the disclosures of which are hereby incorporated by reference in their entirety, entitled (1) “PIEZO ELECTRICALLY DRIVEN BELLOWS INFUSER FOR HYDRAULICALLY CONTROLLING AN ADJUSTABLE GASTRIC BAND” to William L. Hassler, Jr., Ser. No. 10/857,762; (2) “METAL BELLOWS POSITION FEED BACK FOR HYDRAULIC CONTROL OF AN ADJUSTABLE GASTRIC BAND” to William L. Hassler, Jr., Daniel F. Dlugos, Jr., Rocco Crivelli, Ser. No. 10/856,971; (3) “THERMODYNAMICALLY DRIVEN REVERSIBLE INFUSER PUMP FOR USE AS A REMOTELY CONTROLLED GASTRIC BAND” to William L. Hassler, Jr., Daniel F. Dlugos, Jr., Ser. No. 10/857,315; and (4) “BI-DIRECTIONAL INFUSER PUMP WITH VOLUME BRAKING FOR HYDRAULICALLY CONTROLLING AN ADJUSTABLE GASTRIC BAND” to William L. Hassler, Jr., Daniel F. Dlugos, Jr., Ser. No. 10/857,763.