Kenji Shiba

Development and performance analysis of an intra-body communication device

Personal area networks would benefit from a wireless communication system in which a variety of information could be exchanged through wearable electronic devices and sensors. Intra-body communication using the human body as the transmission medium enables wireless communication without transmitting radio waves through the air. A human arm phantom is designed and used to reduce uncertainty in experiments with the human body. The phantom exhibits transmission characteristics similar to those of the human body at frequencies between 1 MHz and 10 MHz. A 10.7 MHz frequency modulation (FM) intra-body transmitter and receiver are developed which allow transmission of analog sine waves even in the presence of external noise. Digital data transmission at 9600 bps was also achieved using newly fabricated 10.7 MHz frequency shift keying (FSK) transmitter and receiver devices. The carrier frequency of 10.7 MHz, which is the intermediate frequency in FM radio receivers, means that a wide selection of commercial radio frequency (RF) devices is available.

Analysis of Current Density and Specific Absorption Rate in Biological Tissue Surrounding Transcutaneous Transformer for an Artificial Heart

This paper reports on the current density and specific absorption rate (SAR) analysis of biological tissue surrounding an air-core transcutaneous transformer for an artificial heart. The electromagnetic field in the biological tissue is analyzed by the transmission line modeling method, and the current density and SAR as a function of frequency, output voltage, output power, and coil dimension are calculated. The biological tissue of the model has three layers including the skin, fat, and muscle. The results of simulation analysis show SARs to be very small at any given transmission conditions, about 2-14 mW/kg, compared to the basic restrictions of the International Commission on nonionizing radiation protection (ICNIRP; 2 W/kg), while the current density divided by the ICNIRPs basic restrictions gets smaller as the frequency rises and the output voltage falls. It is possible to transfer energy below the ICNIRPs basic restrictions when the frequency is over 250 kHz and the output voltage is under 24 V. Also, the parts of the biological tissue that maximized the current density differ by frequencies; in the low frequency is muscle and in the high frequency is skin. The boundary is in the vicinity of the frequency 600-1000 kHz.

Design and Development of Low-Loss Transformer for Powering Small Implantable Medical Devices

Small implantable medical devices, such as wireless capsule endoscopes, that can be swallowed have previously been developed. However, these devices cannot continuously operate for more than 8 h because of battery limitations; moreover, additional functionalities cannot be introduced. This paper proposes a design method for a high-efficiency energy transmission transformer (ETT) that can transmit energy transcutaneously to small implantable medical devices using electromagnetic induction. First, the authors propose an unconventional design method to develop such a high-efficiency ETT. This method can be readily used to calculate the exact transmission efficiency for changes in the material and design parameters (i.e., the magnetic material, transmission frequency, load resistance, etc.). Next, the ac-to-ac energy transmission efficiency is calculated and compared with experimental measurements. Then, suitable conditions for practical transmission are identified. A maximum efficiency of 33.1% can be obtained at a transmission frequency of 500 kHz and a receiving power of 100 mW for a receiving coil size of ¿5 mm × 20 mm. Future design optimization is possible by using this method.

Energy Transmission Transformer for a Wireless Capsule Endoscope: Analysis of Specific Absorption Rate and Current Density in Biological Tissue

This paper reports on the electromagnetic influences on the analysis of biological tissue surrounding a prototype energy transmission system for a wireless capsule endoscope. Specific absorption rate (SAR) and current density were analyzed by electromagnetic simulator in a model consisting of primary coil and a human trunk including the skin, fat, muscle, small intestine, backbone, and blood. First, electric and magnetic strength in the same conditions as the analytical model were measured and compared to the analytical values to confirm the validity of the analysis. Then, SAR and current density as a function of frequency and output power were analyzed. The validity of the analysis was confirmed by comparing the analytical values with the measured ones. The SAR was below the basic restrictions of the International Commission on Nonionizing Radiation Protection (ICNIRP). At the same time, the results for current density show that the influence on biological tissue was lowest in the 300-400 kHz range, indicating that it was possible to transmit energy safely up to 160 mW. In addition, we confirmed that the current density has decreased by reducing the primary coils current.

A transcutaneous energy transmission system with rechargeable internal back-up battery for a totally implantable total artificial heart

We have been developing an externally coupled transcutaneous energy transmission system (ECTETS) for a totally implantable total artificial heart (TITAH). When the ECTETS is unable to supply the energy to drive the TITAH from outside the body, a rechargeable internal back-up battery (RIBB) implanted inside the body is used as a back-up to supply the required energy. This paper reports on the performance characteristics of our ECTETS with an RIBB. In this study, a lithium-ion (Li+) secondary battery was used as the RIBB. The transcutaneous energy transmission and the charging control characteristics of the ECTETS, while simultaneously supplying energy to the TITAH and the RIBB, were evaluated in an in vitro experiment. The output power and transmission efficiency of the ECTETS operating in this mode were found to vary from 20 W to 34 W and from 84% to 71%, respectively. It was also found that a sufficient power of more than 20 W could be supplied to the TITAH. The time needed to fully charge the RIBB was 117 minutes, and a fully charged RIBB could drive the TITAH, consuming 20 W for 62 minutes. It may, therefore, reasonably be concluded that the ECTETS with the RIBB is sufficient to drive the TITAH.

Transcutaneous optical telemetry system with infrared laser diode

A transcutaneous telemetry system is indispensable when monitoring and controlling the operation of an artificial heart totally implanted inside the body. A telemetry system using light is more useful than radio waves from the viewpoint of electromagnetic interference and power consumption. In this report, a transcutaneous optical coupler consisting of an infrared laser diode (LD) and a PIN photodiode (PINPD) was evaluated, and the transcutaneous optical coupling and information transmission characteristics were evaluated in in vitro experiments. The wavelength and directional angle of the LD used were 830 nm and 9.5 degrees, respectively. With regard to the directional angle of PINPD, the authors found that a PINPD with a larger directional angle allowed for more deviation between the axes optical axes of the LD and the PINPD. It was also found that the transcutaneous coupler had an optimum distance for the permissible deviation to be maximized. The information signals modulated by the phase shift keying (PSK) were transmitted at a rate of 9,600 bps through goat skin 4 mm thick, and demodulated by the phase locked loop (PLL) on the receiving side. As a result, the information signals were demodulated without any errors in deviation within 10.5 mm at a distance of 11 mm. In conclusion, the transcutaneous optical telemetry system using an infrared LD has sufficient characteristics to monitor and control the operation of an artificial heart totally implanted inside the body.

Analysis of SAR and Current Density in Human Tissue Surrounding an Energy Transmitting Coil for a Wireless Capsule Endoscope

This paper reports on a prototype energy transmission system for a wireless capsule endoscope and the electromagnetic effects that influence its use in biological tissues. Specific absorption rate (SAR) and current density were analyzed by an electromagnetic simulator in a model consisting of a primary coil and a human trunk that included eighteen different organs. SAR and current density as a function of frequency were analyzed. The SAR was maximized at muscle and fat, and was below the basic restrictions of the International Commission on Non Ionizing Radiation Protection (ICNIRP). At the same time, the results for current density were maximized at muscle and intestine, and were below the ICNIRP basic restrictions, indicating that it was possible to safely transmit energy up to 30 mW at the frequency of 300-600 kHz.

Analysis of specific absorption rate in biological tissue surrounding transcutaneous transformer for an artificial heart

Abstract This paper reports on specific absorption rate (SAR) analysis of biological tissue surrounding a transcutaneous transformer for an artificial heart. An externally coupled type of transformer was used for transcutaneous energy transmission. The secondary (internal) coil of the transformer, which is covered with skin, protrudes from the body surface, forming a skin tunnel. A primary (external) coil closely wound around a toroidal ferrite core is inserted into the skin tunnel. In this transformer, most of the magnetic flux induced by the current of the primary coil is linked with the secondary coil, and the coupling factor between the primary and secondary coils is greater than 0.98, regardless of the skin thickness. The electromagnetic field in the biological tissue surrounding the transformer was analyzed by the transmission line modeling method, and the distributions of the electric field strength and the SAR as a function of output power, the number of coil loops, and the dimensions and output voltage of the transcutaneous transformer were estimated. We found that SARs near the transcutaneous transformer were larger than at other points, that is, the SARs far from the transformer were relatively small. It was also clear that by increasing the dimensions and number of coil loops, and reducing the output voltage, we could reduce the SAR in biological tissue surrounding the transcutaneous transformer. The SAR in the present study was within the limits recommended by the Ministry of Posts and Telecommunications of Japan.

Efficiency improvement and in vivo estimation of externally-coupled transcutaneous energy transmission system for a totally implantable artificial heart

In order to enhance the implantability of the externally-coupled transcutaneous energy transmission system (ECTETS), efficiencies in various parts of the circuit system were improved to reduce heat dissipation. As a result, a DC-to-DC energy transmission efficiency of 85% or more was obtained in an in vitro experiment conducted at a power output of 19 W. In the in vivo measurement of this improved ECTETS with the internal coil and the rectifier circuit implanted under the skin of a living goad, a DC-to-DC energy transmission efficiency of 82% or more was obtained. Fluctuation of efficiency due to movement of the body was found to be less than 0.5%. When this improved ECTETS is used with the totally implantable electrohydraulic artificial heart with an overflow mock circulatory system connected as a load, the pump output flow at a changing heart rate was found to be 4.4-7.0 L/min (50-110 bpm). For continuous operation at 70 bpm, the DC-to-DC energy transmission efficiency was 81% or more, the pump output flow was 6.2 L/min, and the temperature in the part of implantation was lower than 41/spl deg/C, a temperature that can hardly affect a living body.

Analysis of Specific Absorption Rate and Current Density in an Energy Transmission System for a Wireless Capsule Endoscope

This paper reports on the electromagnetic influences on the analysis of biological tissue surrounding a prototype energy transmission system for a wireless capsule endoscope. Specific absorption rate (SAR) and current density were analyzed by electromagnetic simulator in a model consisting of primary coil and a human trunk including the skin, fat, muscle, small intestine, blood and backbone. SAR and current density as a function of frequency and output power were analyzed. The SAR was below the basic restrictions of the International Commission on Non-Ionizing Radiation Protection (ICNIRP). At the same time, the results for current density show that the influence on biological tissue was lowest in the 300-400 kHz range, indicating that it was possible to transmit energy safely up to 100 mW.