News Column

Researchers Submit Patent Application, "Implantable Medical Device Charging", for Approval

March 6, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor JOSHI, Himanshu (Stillwater, OK), filed on October 17, 2013, was made available online on February 20, 2014.

The patent's assignee is Cyberonics, Inc.

News editors obtained the following quote from the background information supplied by the inventors: "Advances in technology have led to the development of miniature medical devices that can be implanted within a living organism, such as a human, to provide treatment or monitoring. Powering such implantable medical devices can be a concern. For example, some implantable medical devices use an onboard battery as a power source. However, since batteries store a finite amount of energy, an onboard battery may only be a temporary power source. Replacing batteries for implantable medical devices may be expensive and inconvenient. For example, depending on the specific nature of the implantable medical device, surgery may be needed to replace the device or to replace the battery.

"Due to these and other concerns, some implantable medical devices may use rechargeable batteries. However, recharging batteries that are located inside a device that is implanted in a patient presents other concerns. For example, when long charging times are required, patient compliance can be a problem. As another example, inefficient recharging may cause energy to be lost as heat. Such heat losses may dissipate into surrounding tissues, which may be harmful to the patient."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "A battery onboard an implantable medical device can be recharged using an inductively-coupled recharging system. For example, a recharging device that is external to a patient may include a power circuit coupled to a primary coil. The implantable medical device (internal to the patient) may include a recharging circuit coupled to a secondary coil. The primary and secondary coils may be inductively coupled to enable transfer of energy from the primary coil to the secondary coil. The recharging circuit may provide energy received by the secondary coil from the primary coil to a battery. Thus, the inductively-coupled recharging system enables the battery to be wirelessly recharged from a source external to the patient via the inductive coupling of the primary and secondary coils.

"Heat losses of the implantable medical device can be reduced by reducing resistive heating. Resistive losses in an RLC circuit, such as the power circuit and the recharging circuit, can be reduced by operating the RLC circuit at its resonant frequency. However, the resonant frequency of the inductively-coupled recharging system can be difficult to determine and can change dynamically. For example, minor variations in the circuits (e.g., from one implantable medical device to another implantable medical device) can change the resonant frequency. Other variations, such as position or orientation differences between the primary coil and the secondary coil, can also affect energy transfer efficiency.

"To address such concerns, an alignment relationship may be determined to determine whether the signal is provided at the resonant frequency of the power circuit. For example, the alignment relationship may be determined by evaluating voltage and current of a signal applied to the primary coil. The voltage and the current of the signal are aligned (e.g., in phase) when a frequency of the signal is at the resonant frequency of the inductively-coupled recharging system. Phase differences between the current and the voltage of the signal can be used to estimate the resonant frequency. For example, when the voltage is lagging the current, the resonant frequency of the inductively-coupled recharging system is higher than the frequency of the signal. Alternately, when the voltage leads the current, the resonant frequency of the inductively-coupled recharging system is lower than the frequency of the signal. Thus, in a particular embodiment, the inductively-coupled recharging system can be controlled to reduce heating and to improve recharging efficiency based on measurements of the phase difference between the voltage and the current of the signal provided to the primary coil.

"Further improvement of the efficiency of energy transfer may be achieved by monitoring parameters of the recharging circuit. For example, a voltage applied to the battery by the recharging circuit within the implantable medical device may be monitored. For a particular duty cycle of the signal applied to the primary coil, the voltage applied to the battery may be greatest when the signal is at the resonant frequency of the inductively-coupled recharging system. A frequency sweep may used to identify the resonant frequency. The frequency sweep may be performed by applying signals of different frequencies to the primary coil while measuring the voltage applied to the battery by the recharging circuit within the implantable medical device. A range of frequencies to be swept by the frequency sweep may be determined based on the phase difference between the current and the voltage at a particular frequency. For example, when a first signal is applied to the primary coil, the phase difference between the current and the voltage of the first signal may be determined. A frequency sweep range may be selected based on the phase difference. To illustrate, a direction to change the frequency relative to the first frequency may be determined based on a sign of the phase difference. In addition, a magnitude of a frequency change from the first signal to a particular portion of the frequency sweep (e.g. a midpoint of the frequency sweep range) may be selected based on a magnitude of the phase difference.

"After the resonant frequency has been determined (within a threshold), a recharging signal having the resonant frequency may be provided to the primary coil. Additionally, a duty cycle of the recharging signal may be increased to increase a rate of energy transfer to the implantable medical device. Thus, heating losses during battery recharging may be reduced, improving patient safety. The energy transfer rate also may be improved (by reducing losses and by increasing the duty cycle at the resonant frequency) which may improve patient compliance with recharging the battery since battery recharge time may be shortened.

"In a particular embodiment, a method of controlling power delivery to an implantable medical device includes providing a first signal to a primary coil that is inductively coupled to a secondary coil of an implantable medical device. The method also includes determining a first alignment difference between a voltage corresponding to the first signal and at least one of a current corresponding to the first signal and a component voltage at a component of a primary coil circuit. The method further includes determining a frequency sweep range based on the first alignment difference. The method also includes performing a frequency sweep over the frequency sweep range.

"In a particular embodiment, a device includes a primary coil coupled to a circuit and operable to inductively couple to a secondary coil within an implantable medical device to transfer energy to the secondary coil within the implantable medical device responsive to a signal of the circuit. The device also includes a sensing system coupled to the circuit. The sensing system is operable to detect an indication of an alignment relationship between a voltage corresponding to the signal and at least one of a current corresponding to the signal and a component voltage at a component of the circuit. The system also includes a control system responsive to the sensing system. The control system is operable to determine a frequency sweep range based on the alignment relationship and to cause the primary coil to receive a charging signal having a frequency within the frequency sweep range during the transfer of the energy.

"In a particular embodiment, an implantable medical device includes a secondary coil coupled to a circuit and operable to inductively couple to a primary coil to receive energy from the primary coil. The implantable medical device also includes a battery charging system coupled to the secondary coil and operable to receive a current from the secondary coil and to apply a charging voltage to a battery responsive to the current. The implantable medical device further includes a measurement system coupled to the circuit and operable to measure an electrical property of the circuit and to output information indicative of a value of the electrical property. The secondary coil is operable to receive a charging signal from the primary coil. A frequency of the charging signal is determined based on the information indicative of the value of the electrical property and based on a detected alignment relationship between a voltage corresponding to a signal applied to the primary coil and at least one of a current corresponding to the signal and a component voltage at a component associated with the primary coil.

"The features, functions, and advantages that have been described can be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which are disclosed with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a block diagram of a particular embodiment of an implantable medical device and a charging system;

"FIG. 2 is a simplified circuit diagram of a particular embodiment of an implantable medical device and a charging system;

"FIG. 3 is a chart of load voltage and frequency for two frequency sweeps that are simulated for a particular embodiment of a system to charge an implantable medical device;

"FIGS. 4-13 are diagrams illustrating particular embodiments of waveforms that may be used during charging of an implantable medical device; and

"FIG. 14 is flow chart of a particular embodiment of a method of charging an implantable medical device."

For additional information on this patent application, see: JOSHI, Himanshu. Implantable Medical Device Charging. Filed October 17, 2013 and posted February 20, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=1208&p=25&f=G&l=50&d=PG01&S1=20140213.PD.&OS=PD/20140213&RS=PD/20140213

Keywords for this news article include: Cyberonics Inc.

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Source: Politics & Government Week


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