Takahiko Yamamoto

Improvement in magnetic field immunity of externally-coupled transcutaneous energy transmission system for a totally implantable artificial heart

Transcutaneous energy transmission (TET) that uses electromagnetic induction between the external and internal coils of a transformer is the most promising method to supply driving energy to a totally implantable artificial heart without invasion. Induction-heating (IH) cookers generate magnetic flux, and if a cooker is operated near a transcutaneous transformer, the magnetic flux generated will link with the external and internal coils of the transcutaneous transformer. This will affect the performance of the TET and the artificial heart system. Hence, it is necessary to improve the magnetic field immunity of the TET system. During operation of the system, if the transcutaneous transformer is in close proximity to an IH cooker, the electric power generated by the cooker and coupled to the transformer can drive the artificial heart system. To prevent this coupling, the external coil was shielded with a conductive shield that had a slit in it. This reduces the coupling between the transformer and the magnetic field generated by the induction cooker. However, the temperature of the shield increased due to heating by eddy currents. The temperature of the shield can be reduced by separating the IH cooker and the shield.

Transcutaneous Energy Transmission System for a Totally-Implantable Artificial Heart in case Using External Battery

We have been developing the externally-coupled transcutaneous energy transmission system (ECTETS) for a totally-implantable artificial heart (TIAH). The transcutaneous energy transmission (TET) system enables the TIAH to supply the driving energy without infectious disease and reduction of patient’s QOL (quality of life). Since the TET system uses the electromagnetic induction between the external (primary) and the internal (secondary) coils, it is necessary for the TET system to be compatible electromagnetically. In the practical use of artificial heart, such as a patient going out, the artificial heart is driven by the energy from the portable rechargeable battery outside of the body. In this paper, the drive performance and the electromagnetic compatibility of the TET system were investigated in case of using the external rechargeable battery. As a result, the ECTETS, driven by the external rechargeable battery consisting of the Lithium ion battery pack with a weight of 430 g, was able to drive the TIAH actuator for 4 hours and 9 minutes. The radiated emission from the ECTETS was suppressed within the regulation of class-B and group-1 in CISPR (international special committee on radio interference) Pub.11, and the ECTETS satisfied the electrostatic discharge immunity test based on IEC61000-4-2 (International Electrotechnical Commission), the radiation immunity test based on IEC61000-4-3, and the power supply frequency magnetic field immunity test based on IEC61000-4-8. Therefore, it was concluded that the ECTETS investigated had satisfactory characteristics in the drive performance and the electromagnetic compatibility.

Development of test fixture for measurement of dielectric properties and its verification using animal tissues

The electromagnetic compatibility of implantable or wearable medical devices has often been evaluated using human phantoms to electrically mimic biological tissues. However, no currently existing test fixture can measure the electrical characteristics of gel-like materials. In this paper, we report the development of a new test fixture that consists of a coaxial tube whose outer conductor is divided along the axial direction into two sections, which facilitates filling and removal of gel-like materials in order to measure their electrical characteristics. Using this test fixture, we measured the electrical characteristics of a cows muscular tissues up to 1 h post-mortem; these measurements allowed us to obtain the relative permittivity and conductivity of the biological tissue, which should help to enable the design of new human phantoms.

Improvement of coupling coefficient by designing a spiral pattern formed on a printed circuit board

In recent times, the wireless power transfer (WPT) technology is attracting attention because of the expanding use of portable devices. In particular, extensive studies on the WPT technology using magnetic resonance are being conducted because this technology offers various advantages such as the achievement of a transmission efficiency of 90% or more from a distance of 1 m, as compared with traditional electromagnetic induction systems. However, studies on thin coils, as well as those on the improvement of the coupling coefficient, have hitherto been inadequate. Consequently, we have formed a spiral pattern on a printed circuit board and devised spiral patterns to improve the coupling coefficient, which was calculated by carrying out an electromagnetic field analysis. As a result, we found that the coupling coefficient improved by adjusting the inner radius and pitch of the spiral coil and by designing the geometry of the spiral coil.

Magnetic-Field Immunity Examination and Evaluation of Transcutaneous Energy-Transmission System for a Totally Implantable Artificial Heart

Transcutaneous energy transmission (TET) is the most promising noninvasive method for supplying driving energy to a totally implantable artificial heart. Induction-heating (IH) cookers generate a magnetic flux, and if a cooker is operated near a transcutaneous transformer, the magnetic flux generated will link with its external and internal coils. This will affect the performance of the TET and the artificial heart system. In this paper, we present the design and development of a coil to be used for a magnetic immunity test, and we detail the investigation of the magnetic immunity of a transcutaneous transformer. The experimental coil, with five turns like a solenoid, was able to generate a uniform magnetic field in the necessary bandwidth. A magnetic-field immunity examination of the TET system was performed using this coil, and the system was confirmed to have sufficient immunity to the magnetic field generated as a result of the conventional operation of induction-heating cooker.

Investigation of unifying transcutaneous transformer for transmission of energy and information

When patients are fitted with a totally implantable artificial heart (TAH), they need to be implanted with two additional devices: one for the transmission of energy and one for information. However, this is a cumbersome process that affects the quality of life of the recipient. Therefore, we investigated the use of electromagnetic coupling for the transmission of energy and information and the possibility of unifying two transcutaneous transformers for the simultaneous transmission of energy and information. While unifying the transformers, it is important to suppress the electromagnetic coupling between energy and information transmission. Therefore, we ensured that the electromagnetic fields generated from the transformer windings for the transmissions of information and energy intersected perpendicularly. If the fields are perpendicular, the electromagnetic coupling between the energy and information transmissions will be suppressed significantly. The characteristics of the simultaneous transmission of information and energy using the unified transcutaneous transformer, developed experimentally, were evaluated by changing the number of windings used for the transmission of information. The electromagnetic coupling between the energy and information transmissions was suppressed by determining the direction of the magnetic field. Moreover, the optimum number of transformer windings required for the simultaneous transmission of energy and information was determined. We concluded that the externally coupled transcutaneous transformer unified for the simultaneous transmission of energy and information performed with good transmission characteristics.

Downsizing of coreless coils for transcutaneous energy transmission in implantable devices - Improvement of coupling factor and efficiency between coils

Transcutaneous energy transmission is useful for improving patient quality of life and for supplying energy to implantable devices noninvasively. To supply highly efficient energy transmission through the skin, it is necessary to increase the coupling factor between the coils and increase the inductance of each coil. In this study, the optimal shape required for the coils to increase the coupling factor was investigated.

A study on transmission characteristics and specific absorption rate using impedance-matched electrodes for various human body communication

Human body communication (HBC) is a new communication technology that has presented potential applications in health care and elderly support systems in recent years. In this study, which is focused on a wearable transmitter and receiver for HBC in a body area network (BAN), we performed electromagnetic field analysis and simulation using the finite difference time domain (FDTD) method with various models of the human body. Further we redesigned a number of impedance-matched electrodes to allow transmission without stubs or transformers. The specific absorption rate (SAR) and transmission characteristics S21 of these electrode structures were compared for several models.

Position detection for transcutaneous energy transmission system for capsule endoscope

This paper describes a method for detecting the position of a capsule endoscope by using small, flat arrayed coils and discusses the improvement of this position detection and the energy transmission efficiency. The position of the capsule endoscope was detectable by measuring the terminal voltage variation in each small, flat coil connected in parallel. The coil that is utilized as an arrayed connection should have no crevice. Such coils can broaden the domain of high energy transmission efficiency.

Consideration of Measurement of Electrical Characteristics for Sacrificed Cow Muscles

EMC (Electro-magnetic Compatibility) of medical devices is often evaluated using human phantoms whose electrical characteristics are simulated. In order to improve the reliability of EMC evaluations, it is important to measure the electrical characteristics of human phantoms and animals. However, because cellular tissues affect their electrical characteristics in the part of frequency band, had been dead for some hours change their electrical characteristics. Therefore, it is important to measure these characteristics as soon as possible.