Kohji Koshiji

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.

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.

Study on respiration monitoring method using near-infrared multiple slit-lights projection

We describe the principle of the respiration monitoring by the multiple slit light irradiation and the configuration of the respiration monitoring system. In the developed system, the fiber grating vision sensor known as an active type high-speed three-dimensional sensor was applied to satisfy the non-contact and non-restraint respiration monitoring. The fiber grating vision sensor is composed of a multiple slit light projector and a CCD camera, and these are placed above the sleeping person oriented in a lengthwise direction of the bed. And the multiple slit light projector projects the slit light array on the body surface of sleeping person. In this paper, the algorithm for monitoring and analyzing of the respiration status of the sleeping person is proposed. And, the result of the preliminary experiment performed to verify the effectiveness of developed system is described. As results of preliminary experiment through the simultaneous measurements with the developed system and a spirometer, it is confirmed that respiratory waveforms obtained by this system reflect the changes of volume occurring with respiratory movement of the examinee.

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.

Non-contact Respiration Monitoring Method for Screening Sleep Respiratory Disturbance Using Slit Light Pattern Projection

We proposed the respiration monitoring method with non-contact and unrestraint, applied the projection of the near-infrared multiple slit-light pattern. In the respiration monitoring method, the shift length of multiple-slit pattern light, projected on the thoracicoabdominal part of sleeping person, is calculated by motion-image analysis. By the simultaneous meas-urement with the spirometer, the validity of the non-contact respiration monitoring by our method was indicated. As a result of all night measurement, we found that our proposed method enable the disease presentation, which was typical of obstructive sleep apnea, to be detected.

Current status of development and in vivo evaluation of the National Cardiovascular Center electrohydraulic total artificial heart system

We have been developing an electrohydraulic total artificial heart system. The system has a pumping unit, consisting of diaphragm-type blood pumps and an energy converter, and an electronics unit, consisting of an internal controller, an internal battery, and transcutaneous energy transfer and optical telemetry subunits. The energy converter, designed to be placed outside the pericardial space, reciprocates and delivers hydraulic silicone oil to the alternate blood pumps through a pair of flexible oil conduits. The left-right output balance is achieved with an interatrial shunt made in the composite atrial cuff. In vivo performance of the pumping unit has been evaluated by chronic implantation of 16 calves weighing 54–88 kg. Five calves survived for more than a week, and the longest-surviving animal lived for over 12 weeks until its accidental death. In this animal, a cardiac output of 6–81/min was maintained by the device with power consumption of 13.5±0.9W and 9%–11% efficiency. The left and right atrial pressures were 16±4 and 14±4 mm Hg, respectively, and the left-right output difference was adequately balanced with the interatrial shunt. The mixed venous oxygen saturation was 65±6% and the serum lactate level was 5±1 mg/dl, representing favorable oxygen metabolic conditions. The temperatures of the energy converter and the blood pump surfaces were 39.4±0.7° and 38.8±1.5°C, respectively, indicating that heat generation and dissipation were acceptable. The serum and tissue silicon levels were within normal (<1 μg/ml or <1 μg/g), indicating that permeation of silicone oil through the blood pump diaphragm was inconsequential and unlikely to be detrimental. We conclude that the system has the potential to be a totally implantable cardiac replacement.

A wideband antenna with fan-shaped and trapezoidal elements on printed circuit board for ultra wideband radio

In this paper, a half-sized unbalanced dipole antenna with fan-shaped and trapezoidal radiators on a printed circuit board was proposed. The VSWR and radiation patterns of the proposed antenna were investigated. As a result, the VSWR characteristics less than 2.0 and relative bandwidth of 110% over the frequency band of 3.1 GHz to 10.8 GHz from the experiments were obtained from a measurement. As the radiation patterns, the similar radiation patterns with an usual dipole antenna such as eight-shape and omni-directional radiation patterns were obtained at 3.1 GHz. Although the radiation patterns at 6.8 GHz and 10.6 GHz were slightly distorted compared with those of the usual dipole antennas, it is acceptable in practical use because the orientation of mobile devices in which the antenna could be built may change frequently, depending on how a user uses the devices.

Wireless body area communication using electromagnetic resonance coupling

In this paper, a new highly efficient wireless communication link around human body using electromagnetic resonance coupling was proposed and investigated. The communication between wearable devices located on forearm and upper arm, like a wristwatch or armband, is assumed as a model for body area communication. The transmission characteristics S21, between transmitting and receiving antenna which is put on forearm and upper arm, respectively, like a wristwatch or armband, were analyzed and measured. As a result, the transmission characteristics S21 showed the maximum value of -12 dB, and was excellent compared with that of conventional body area communication using the electrodes in contact with the body. Moreover, the SAR of the body was less than a three-hundredth compared with the safety limit of 2 W/kg. Therefore, we confirmed that the wireless communication link using magnetic resonance coupling is useful for body area communication.

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.