RU2752139C1 - Device for percutaneous energy transfer using inductive coupling - Google Patents

Abstract

FIELD: medical equipment.

SUBSTANCE: invention relates to medical technology and can be used for energy supply of implantable medical devices (IMD). The objective of the invention is to increase the stability of percutaneous energy transmission using inductive coupling when changing the relative position of the transmitting and receiving modules. This is achieved by the fact that the proposed device for percutaneous energy transmission using inductive coupling contains a tuning module connected to the power supply module, containing a computing unit with a microcontroller and an executive unit with an alternating current generation circuit based on the design of a class E power amplifier, and the alternating current generation circuit contains two voltage-controlled variable capacitors (varicaps) connected in series and in parallel to the transmitting inductor coil, or two arrays of series-connected switchable capacitors connected in series and in parallel to the transmitting inductor coil, or two arrays of parallel-connected switchable capacitors connected in series and in parallel to the transmitting inductor coil. Changing the capacitances in the load circuit of a class E power amplifier is carried out in such a way as to compensate for changes in the reflected impedance when changing the relative position of the receiving and transmitting inductors coils and thus, ensure that the power is maintained at the load as close as possible to the nominal value.

EFFECT: increase in the stability of percutaneous energy transmission using inductive coupling when changing the relative position of the transmitting and receiving modules.

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Description

The invention relates to the field of medical technology and can be used to supply power to implantable medical devices (IMD). These devices include pacemakers, implantable cardioverters / defibrillators, neurostimulators, implantable infusion pumps, motorized telescopic distraction rods, cochlear implants, visual prostheses (artificial retina), mechanical circulatory support devices, etc. there is a need for wireless transmission of energy over short distances, for example, in the field of power supply of portable digital devices and electric vehicles.

At present, wireless transcutaneous energy transmission using inductive coupling is one of the main directions in the development of power supply for MPS. This technology is based on the use of the phenomenon of electromagnetic induction: an alternating magnetic field formed by an external (transmitting) inductor connected to a current source induces an induction current in the implanted (receiving) inductance coil, which is used to power the MFI.

Today, wireless percutaneous energy transmission using inductive coupling is used in low and medium power implants, for example, in cochlear implants [1-4], neurostimulators [5] and visual prostheses [6-7], and is considered as a promising technology for energy supply of others. UTI, primarily systems of mechanical support of blood circulation [8-9].

One of the main problems in the design of devices for transcutaneous energy transfer using inductive coupling to the MFI is the problem of minimizing the output power drops when changing the operating parameters of the device. The strongest influence on the change in parameters is exerted by the displacement of the transmitting and receiving inductors relative to the nominal position [10]. Moreover, the displacements themselves can be divided into three main types [10]:

- slow irregular, which are caused by a change in the state of the biological tissue at the site of implantation of the induction coils, for example, postoperative edema, inflammation or implant migration;

- fast irregular, which are caused by the patient's movements;

- fast regular, which are caused by walking breathing.

Geometrically, displacements can be divided into longitudinal (axial), lateral (lateral), angular and rotational [10].

A number of devices are known in which means of mechanical fixation of the position of the receiving and transmitting coils using a textile fastener of the VELCRO type or permanent magnets are used to compensate for displacements [11-13]. Mechanical positioning can reduce or even completely eliminate the effect of some types of offsets on the output power level. A significant disadvantage of this method is that it does not allow to eliminate or reduce the effect of longitudinal displacements (increase in the distance between the receiving and transmitting coils) of any of the three types described above. Additional disadvantages are the occurrence of undesirable consequences for the well-being and convenience of the patient, as well as restrictions on the use of magnetic resonance imaging.

A number of devices for wireless inductive power transmission are also known, in which a stable level of output power when changing the relative position of the transmitting and receiving coils is maintained by changing the operating frequency of the device [14, 15]. A significant disadvantage of this approach is the need to use operating frequencies of a wide range, which is not always allowed by existing regulatory documents and can lead to aggravation of possible problems of mutual interference from the device and other radio-emitting devices and systems.

A device for wireless transcutaneous power supply of implantable medical devices is known, in which the displacement of the receiving and transmitting coils is compensated by selectively connecting one or more conductors from a plurality in the transmitting and receiving coils [16]. Changing the intrinsic inductance and Q-factor of the inductors can reduce the power drop across the load. Significant disadvantages of this approach are the coarseness of adjusting the parameters of the system, due to the need to use relatively large conductors to change the inductance of the coils, and a significant decrease in the overall reliability of the device.

Known devices that use displacement detectors that record changes in the parameters of the electrical signal in the transmitting or receiving part of the system [17, 18]. A significant disadvantage of this method is that it uses indirect registration of the fact of displacement. This makes it possible to compensate for the effect of displacements only partially, since the available information is insufficient to determine the geometric characteristics of the displacement (linear and angular) and there is no possibility of compensating for displacements by moving the external (transmitting) coil.

The closest to the proposed device is a device for wireless transcutaneous power supply of implantable medical devices [19]. In this device, the problem of reducing the efficiency of transdermal energy transfer when the position of the transmitting module is changed relative to the receiving module is solved by using a module for determining the relative position of the transmitting and receiving modules using ultrasound. This solution allows you to adjust the position of the receiving and transmitting modules relative to each other to achieve maximum efficiency of energy transfer. Two significant disadvantages of the prototype can be distinguished: this device does not solve the problem of changing the axial distance between the transmitting and receiving modules, since such displacements cannot be eliminated manually; and the problem of eliminating the influence of rapid regular displacements caused by respiratory movements or arising from walking or running has not been solved [10].

The objective of the invention is to increase the stability of transcutaneous energy transfer using inductive coupling when changing the relative position of the transmitting and receiving modules.

This is achieved by the fact that the proposed device for transcutaneous energy transfer using inductive coupling additionally contains a trimmer module connected to the power module, containing a computing unit with a microcontroller and an executive unit with an alternating current generation circuit based on the design of a class E power amplifier, and the generation circuit alternating current contains two voltage-controlled variable capacitors (varicaps) connected in series and in parallel to the transmitting inductor, or two arrays of series-connected switched capacitors connected in series and in parallel to the transmitting inductor, or two arrays of parallel-connected switched capacitors connected in series and in parallel to the transmitting inductor. The change in capacitances in the load circuit of a class E power amplifier is carried out in such a way as to compensate for changes in the reflected impedance when the relative position of the receiving and transmitting inductors changes and, thus, to maintain the power at the load as close as possible to the nominal value.

The proposed device eliminates the most important disadvantage of the prototype: if the prototype cannot compensate for changes in axial displacements, since these changes cannot be eliminated by moving the transmitting module in relation to the receiving module, in the proposed device this problem is solved by adjusting the parameters of the alternating current generation circuit in the executive unit tuned module. In addition, in the proposed device, it is also possible to automatically compensate for the influence of rapid regular displacements caused by breathing or walking, which is also impossible in the prototype. At the same time, the proposed device retains all the basic capabilities of the prototype, including the ability to restore the relative position of the transmitting and receiving modules close to the nominal, based on the information received by the patient from the module for determining the relative position. Thus, in the proposed device, certain disadvantages of all the above devices are eliminated or smoothed, and at the same time, the device implements the possibility of compensating for all types of displacements (slow irregular, fast irregular, fast regular) for all four options (axial, lateral, angular, rotational ).

The executive unit as part of the tuned module is implemented using an alternating current generation circuit based on the design of a class E power amplifier [20, 21], with variable values of the capacitance of the shunt capacitor and / or series capacitor. Changing the capacitance of the shunt capacitor and / or series capacitor allows you to control the amount of power of the current supplied from the receiving module to the load (MPS) without changing the operating frequency of the system.

Changing the capacitance of the shunt and / or series capacitors in the AC generation loop based on a class E power amplifier in the execution unit of the tuned module is carried out using an array of switched capacitors to set the required values of the capacitance of the bypass capacitor and / or series capacitor. An array of switched capacitors can be controlled using electrical switching devices (keys) to close and / or open an electrical circuit connected to the input of each capacitor in the array. An implementation of an array of capacitors is to use n parallel-connected capacitors, the nominal capacitance of the former being 1 nF, and the nominal capacitance of the nth being 2 ^n-1 nF. Such a set of capacitors allows to set the required capacity in the range of 1 ... 2 ⁿ nF 1 nF with accuracy.

The implementation of changing the capacitance of the shunt and series capacitors in the alternating current generation circuit based on the design of a class E power amplifier in the executive unit as part of a tuned module is also the use of a voltage controlled variable capacitor (varicap). Due to the change in voltage at the input of the varicap, there is a dependent change in its capacitance. The voltage at the input of the varicap can be changed using a microcontroller with an output contact that implements pulse width modulation (PWM). On most microcontrollers, the PWM input allows you to smoothly change the voltage from 0 to 5 volts. This voltage satisfies the input voltage of most varicaps. It should be noted that the range of possible changes in the capacitance of existing varicaps is limited, and therefore, depending on the required output characteristics of the device, either a varicap or an array of switched capacitors described above can be used, which provides a significantly wider range of possible changes in capacitance.

The computing unit as a part of the adjusted module must contain at least one microcontroller, which makes it possible to determine the required value of the capacitance of the bypass capacitor and the series capacitor based on the data received from the module for determining the relative position of the data. The implementation of the method for determining the required capacitance values of the shunt capacitor and / or series capacitor by the computing unit is to write to the microcontroller memory a control data array of the form "axial displacement - shunt capacitor capacitance - series capacitor capacitance" and select a pair of required capacitance values based on the data on the axial displacement value received from the module for determining the relative position of the receiving and transmitting modules. The implementation of the method is also a preliminary recording into the microcontroller's memory of a data array containing pairs of the type "bypass capacitor capacity - series capacitor capacity - axial displacement - lateral displacement", or any other combinations of displacements.

FIG. 1 shows a block diagram of the proposed device for transcutaneous energy transfer using inductive coupling, where:

1 - transmitting module with transmitting inductance coil;

2 - receiving module with a receiving inductance coil;

3 - biological tissue;

4 - module for determining the relative position of the receiving and transmitting modules;

5 - adjusted module;

6 - computing unit as part of a tuned module;

7 - an executive block as part of a tuned module;

8 - power module (constant voltage source).

FIG. 2 shows an example of a change in the output power when the receiving and transmitting modules are axially displaced relative to each other.

FIG. 3 is an example showing the possible technical effect of the present invention.

Shown in FIG. 2, the calculation results were obtained for the following parameters: the operating frequency of the device is 1 MHz, the intrinsic inductance of the transmitting coil in the transmitting module is 10 μH, the intrinsic inductance of the receiving coil in the receiving module is 10 μH, the intrinsic inductance of the choke in the class E power amplifier for generating a direct current of 1000 μH, the amplitude an alternating signal generator 5 V, the voltage of the power supply module (constant voltage source) is 7 V, the load resistance (IMP) is 50 Ohm, the capacitance of the capacitor in the receiving module is 2.53 nF. The calculation was performed for a device that uses an AC generation loop based on a Class E power amplifier design. The power amplifier is tuned to provide a 1 W nominal output power near the center of the offset range, i.e. point corresponding to an offset of 12.5 mm. The above calculation shows that the change in the axial displacement is within the limits typical for the power supply of the IMP, i.e. from 10 to 15 mm, leads to a significant change in the output power of the device for transcutaneous energy transfer using inductive coupling, namely, the value of the output power is reduced from 1.2 to 0.8 mW. At a rated power of 1 W of the device, the difference is ± 20%.

) 13(

) 14 (

) 15 (•) мм. Каждый вариант отличается от другого величиной емкости последовательного и шунтирующего конденсаторов в составе контура генерации переменного тока на основе конструкции усилителя мощности класса Е. Видно, что изменение величины емкости последовательного и шунтирующего конденсаторов при изменении осевого расстояния позволяет удерживать выходную мощность вблизи номинального значения в 1 Вт. Величина перепада определяется точностью изменения величины емкости последовательного и шунтирующего конденсаторов. Так, при осевом смещении в 12 мм величина выходной мощности составляет 1,02 Вт при условии, что величина емкостей последовательного и шунтирующего конденсаторов меняется таким образом, что соответствует настройке на осевое смещение в 12 мм. Теоретически, изменение величины емкостей позволяет обеспечить непрерывный переход от кривой, соответствующей настройке на осевое смещение в 10 мм, к кривой, соответствующей осевому смещению в 15 мм и тем самым свести отклонения от номинальной мощности к пренебрежимо малым.The parameters for the calculation, the results of which are presented in Fig. 3 are similar to those for calculating the graphics in FIG. 2, with the difference that six curves are presented describing the dependence of the output power on the displacement, for variants of the device configured to provide rated output power at axial displacements of 10 (+), 11 (×), 12 (

) 13(

) fourteen (

) 15 (•) mm. Each option differs from the other in the value of the capacitance of the series and shunt capacitors as part of the AC generation circuit based on the design of a class E power amplifier. It can be seen that changing the capacitance of the series and shunt capacitors with a change in the axial distance allows keeping the output power close to the nominal value of 1 W. The magnitude of the difference is determined by the accuracy of the change in the value of the capacitance of the series and shunt capacitors. Thus, with an axial displacement of 12 mm, the output power is 1.02 W, provided that the capacitances of the series and shunt capacitors change in such a way that corresponds to the setting for an axial displacement of 12 mm. In theory, changing the capacitance values allows for a continuous transition from a curve corresponding to an axial displacement of 10 mm to a curve corresponding to an axial displacement of 15 mm, thereby reducing the deviations from the nominal power to negligible.

Also, FIG. 3 illustrates the process of determining the required value of the capacitance of the series and bypass capacitors in the computing unit of the tuned module. According to the measured value of the axial displacement, the corresponding pair is selected from the data array of the form "axial displacement - the capacitance of the series capacitor - the capacitance of the shunt capacitor" previously recorded in the microcontroller's memory. In this case, the array itself is formed on the basis of calculations corresponding to the graphs shown in Fig. 3: for each value of the axial distance, the capacitance values of the series and shunt capacitors are selected, corresponding to the curve having the minimum deviation from the given nominal power for a given value of axial displacement.

The calculated data show that the proposed device provides a solution to the technical problem posed - namely, it provides a significant decrease in the output power drop when the relative position of the receiving and transmitting modules changes relative to each other. In this case, the possibility of compensating for the influence of axial displacements is shown, the compensation of which is, in principle, impossible in the prototype. The calculated values of the required capacitance values of the series and shunt capacitors are within the limits of the ratings of commercially available capacitors, and thus, it can be argued that the proposed device can be implemented at the existing level of technology.

Sources of information

1. Zeng F.G. et al. Cochlear implants: system design, integration, and evaluation // IEEE reviews in biomedical engineering. - 2008. - Vol. 1. - P. 115-142.

2. Sarpeshkar R., Salthouse C., Sit J-J. An ultra-low-power programmable analog bionic ear processor // IEEE Trans. Biomed. Eng. - 2005. - Vol. 52. - No. 4. - P. 711-727.

3. Sit J.J., Sarpeshkar R. A cochlear-implant processor for encoding music and lowering stimulation power / IEEE Pervasive Computing. - 2008. - Vol. 7. - No. l. - P. 40-48.

4. Niparko, J. K., & Wilson, B. S. History of cochlear implants. Cochlear implants: Principles & practices // PA: Lippincott Williams & Wilkins. - 2000. - P. 103-107.

5. Lee H. M., Park H., Ghovanloo M. A power-efficient wireless system with adaptive supply control for deep brain stimulation // IEEE Journal of Solid-State Circuits. - 2013. - Vol. 48 (9). - P. 2203-2216.

6. Argus II Retinal Prosthesis System // Manual. - Second Sight Medical Products. - 2013. - P. 1-380.

7. da Cruz L. et al. Five-year safety and performance results from the Argus II Retinal Prosthesis System Clinical Trial // Ophthalmology. - 2016. - Vol. 123. - No. 10. - P. 2248-2254.

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20. R., N .; A., V.J .; Chokkalingam, B .; Padmanaban, S .; Leonowicz, Z.M. Class E Power Amplifier Design and Optimization for the Capacitive Coupled Wireless Power Transfer System in Biomedical Implants // Energies. - 2017. - Vol. 10. - P. 1409.

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Claims (3)

A device for wireless transcutaneous power supply of implantable medical devices, including a transmitting module with a transmitting inductance coil generating an alternating magnetic field; receiving module with receiving inductance coil; a module for determining the relative position of the receiving and transmitting modules, equipped with means of sound and / or visual signaling and / or means of data exchange with external devices for displaying information; characterized in that the device additionally includes a trimmer module connected to the power module, containing a computing unit with a microcontroller and an executive unit with an alternating current generation circuit based on the design of a class E power amplifier, and the alternating current generation circuit contains two voltage-controlled variable capacitors connected in series and parallel to the transmitting inductor, or two arrays of series-connected switched capacitors connected in series and in parallel to the transmitting inductor, or two arrays of switched capacitors in parallel connected in series and in parallel to the transmitting inductor.

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