This study aims how to contain the environment reflection in a dynamic on-body ultra wideband (UWB) channel model. Based on a measurement approach, it is demonstrated that a complete body area channel model can be regarded as a combination of the on-body propagation characteristic and additional components from the environment. Based on such a channel model, the effect of environment reflection on the average bit error rate performance was investigated for a typical impulse radio UWB system.

This paper reviews our developed wide band human body communication technology for wearable and implantable robot control. The wearable and implantable robots are assumed to be controlled by myoelectric signals and operate according to the operator's will. The signal transmission for wearable robot control was shown to be mainly realized by electrostatic coupling, and the signal transmission for implantable robot control was shown to be mainly determined by the lossy frequency-dependent dielectric properties of human body. Based on these basic observations on signal transmission mechanisms, we developed a 10-50MHz band impulse radio transceiver based on human body communication technology, and applied it for wireless control of a robotic hand using myoelectric signals in the first time. In addition, we also examined its applicability to implantable robot control, and evaluated the communication performance of implant signal transmission using a living swine. These experimental results showed that the proposed technology is well suited for detection and transmission of biological signals for wearable and implantable robot control.

We conduct, in accordance with IEC 61000-4-2, an electrostatic discharge (ESD) test for a small size battery-operated control circuit board in a myoelectric artificial hand system to investigate the influence of the induced noises by indirect ESDs from an ESD generator to a horizontal coupling plane (HCP) and a vertical coupling plane (VCP). A photo-coupler is set between the small size control board and a motor control circuit to suppress noise in the pulse width modulation (PWM) signals. Two types of ESD noise are observed at the output pins of PWM signals. One type is the ESD noise itself (called Type A) and the other one is the ESD noise superimposed over the PWM pulses (Type B). No matter which polarity the charge voltages of the ESD generator have, both types can be observed and the Type A is dominant in the output pulses. Moreover, the ESD interference in the HCP case is found to be stronger than that in the VCP case usually. In the PWM signals observed at the photo-coupler output, on the other hand, Type A noises tend to increase for positive polarity and decrease for negative polarity, while Type B noises tend to increase at -8kV test level in the HCP case. These results suggest that the photo-coupler does not work well for ESD noise suppression. One of the reasons has been demonstrated to be due to the driving capability of the photo-coupler, and other one is due to the presence of a parasitic capacitance between the input and output of the photo-coupler. The parasitic capacitance can yield a capacitive coupling so that high-frequency ESD noises pass through the photo-coupler.

The objective of this study is to investigate the feasibility of an ultra wideband (UWB) impulse radio system for in-body to off-body wireless communication for biomedical applications. At first, a UWB antenna is designed in the UWB low band for implant use in the chest. Then the channel model is extracted and established based on the finite difference time domain (FDTD) simulation with an anatomical human body model. The established channel model consists of a small set of parameters for generating discrete time impulse responses. The generated model shows good agreement with the FDTD-calculated result in terms of key communication metrics. For effective communication over the multipath-affected channel, the pulse position modulation is employed and a 2-finger RAKE structure with a constant temporal delay is proposed in the receiver. The bit error rate performance has shown the validity of the system in the in-body to off-body chest channel.

Wireless capsule endoscopy (WCE) is now one of most important applications in implant body area networks (BANs). WCE requires high throughput performance due to its real-time data transmission, whereas the communication performance depends much on the transmit power, which is strictly regulated in order to satisfy a safety guideline in terms of specific absorption rate (SAR). Spatial diversity reception is well known to improve the wireless performance without any temporal and spectral resource expansion. Additionally, applying spatial diversity reception to WCE systems can be expected to not only improve the wireless communication performance but also to reduce SAR. Therefore, this paper investigates the impact of spatial diversity reception on SAR levels for the 400 MHz medical implant communication service (MICS) band. To begin with, based on finite-difference time-domain (FDTD) simulations for implant BAN propagation with a numerical human body model, we first calculate the BER performance and derive the required transmit power to secure a permissible BER. Then, this paper calculates the local peak SAR under the required transmit power when the implant transmitter moves through the digestive organs. Finally, our simulation results demonstrate that applying spatial diversity reception can significantly reduce SAR in implant BANs.

When using a wireless capsule endoscope (WCE), it is important to know WCE location. In this paper, we focus on a time of arrival (TOA)-based localization technique, as it has better location estimation performance than other radio frequency-based techniques. However, the propagation speed of signals transmitted from inside of a human body varies depending on which biological tissues they pass through. For this reason, almost all of conventional TOA-based methods have to obtain the relative permittivity of the passed biological tissues or the propagation speed beforehand through another measurement system, i.e., magnetic resonance imaging (MRI) or computational tomography (CT). To avoid such troublesome pre-measurement, we propose a hybrid TOA/received signal strength indicator (RSSI)-based method, which can simultaneously estimate the WCE location and the averaged relative permittivity of the human body. First, we derive the principle of RSSI-based relative permittivity estimation from an finite difference time domain (FDTD) simulation. Second, we combine the TOA-based localization and the proposed RSSI-based relative permittivity estimation, and add them to the particle filter tracking technique. Finally, we perform computer simulations to evaluate the estimation accuracy of the proposed method. The simulation results show that the proposed method can accomplish good localization performance, 1.3mm, without pre-measurement of the human body structure information.

Ultra wideband (UWB) on-body communication is attracting much attention in biomedical applications. In this paper, the performance of UWB on-body communication is investigated based on a statistically extracted on-body channel model, which provides detailed characteristics of the multi-path-affected channel with an emphasis on various body postures or body movement. The possible data rate, the possible communication distance, as well as the bit error rate (BER) performance are clarified via computer simulation. It is found that the conventional correlation receiver is incompetent in the multi-path-affected on-body channel, while the RAKE receiver outperforms the conventional correlation receiver at a cost of structure complexity. Different RAKE receiver structures are compared to show the improvement of the BER performance.

One of promising application offered by implant body area networks (BANs) is a capsule endoscope localization system. To begin with, this paper performs finite-difference time-domain (FDTD) simulations on implant BAN propagation with a numerical human model, and investigates the propagation characteristics of implant BAN signals at 400 MHz medical implant communication service (MICS) band. Then, the paper presents a capsule endoscope localization system which utilizes only received signal strength indicator (RSSI) and two estimation methods, such as a maximum likelihood (ML) estimation method and a least squares (LS) method. Furthermore, we evaluate the two localization methods by two computer simulation scenarios. Our computer simulation results demonstrate that the ML localization can improve the location estimation accuracy as compared with the LS localization, that is, our performance comparison reveals that a careful consideration the propagation characteristics of implant BANs signals is efficient in terms of estimation performance improvement in capsule endoscope localization.

The head tissue heterogeneity required in the spatial peak specific absorption rate (SAR) assessment for portable telephones was investigated by using the FDTD method in conjunction with an MRI-based human head model. The tissue heterogeneity of the head model was changed from one type of tissue to 17 types of tissue. The results showed that, at 900 MHz and 2 GHz, the homogeneous modeling results in an underestimate about 20% for the λ/2 monopole antenna portable telephones and an overestimate to the same extent for the λ/4 monopole or helical antenna portable telephones. A head model with a simple skin-fat-muscle-bone-brain structure seems to be sufficient to obtain a fairly accurate one-gram or ten-gram averaged spatial peak SAR value in computational dosimetry for portable telephone compliance.

An attempt to derive the lethal dose for mice was made at 2.45 GHz for whole body exposure. Based on a numerical dosimetry result and an experimental death rate investigation, the lethal dose was estimated to be a whole body averaged specific absorption rate (SAR) with a level at double the mouse's basal metabolic rate.

Vibrating intrinsic reverberation chamber is being used as an in-situ EMC test equipment for large and complex systems such as automobiles and aircrafts. In this paper, the stirring conditions, such as tightness and shaking amplitude of the walls, of a vibrating intrinsic reverberation chamber have been analyzed using the method of moments. From the viewpoint of quantitative evaluation of the flexible moving walls configuration, it was found that the random electromagnetic environment can be generated under the stirring conditions of loose configuration and a shaking amplitude more than one eighth of the wavelength at the test frequency above the lowest usable frequency.

A noninvasive method for measuring complex permittivity of biological tissues is proposed. The noninvasive method is based on an inverse scattering technique which employs an iterative procedure. The iterative procedure consists of solving an electric field integral equation using the method of moments and minimizing the square difference between calculated and measured scattered fields. Implementation of the noninvasive method requires the knowledge of the target shape, the incident and measured scattered fields. Based on the noninvasive method, a measuring system of complex permittivity is developed and its reliability is verified.

Tracking capsule endoscope location is one of the promising applications offered by implant body area networks (BANs). When tracking the capsule endoscope location, i.e., continuously localize it, it is effective to take the weighted sum of its past locations to its present location, in other words, to low-pass filter its past locations. Furthermore, creating an exact mathematical model of location transition will improve tracking performance. Therefore, in this paper, we investigate two tracking methods with received signal strength indicator (RSSI)-based localization in order to solve the capsule endoscope location tracking problem. One of the two tracking methods is finite impulse response (FIR) filter-based tracking, which tracks the capsule endoscope location by averaging its past locations. The other one is particle filter-based tracking in order to deal with a nonlinear transition model on the capsule endoscope. However, the particle filter requires that the particle weight is calculated according to its condition (namely, its likelihood value), while the transition model on capsule endoscope location has some model parameters which cannot be estimated from the received wireless signal. Therefore, for the purpose of applying the particle filter to capsule endoscope tracking, this paper makes some modifications in the resampling step of the particle filter algorithm. Our computer simulation results demonstrate that the two tracking methods can improve the performance as compared with the conventional maximum likelihood (ML) localization. Furthermore, we confirm that the particle filter-based tracking outperforms the conventional FIR filter-based tracking by taking the realistic capsule endoscope transition model into consideration.

In testing the possible biological effects of electromagnetic exposure from cellular telephones in small animals such as mice, it is essential to realize a highly localized head exposure as close as possible to that due to cellular telephones in humans. In this study, a 1.5GHz exposure setup was developed which has a highly localized specific absorption rate (SAR) of 2W/kg in the mouse brain and a low whole-body averaged SAR of 0.27W/kg. The low whole-body averaged SAR was realized by using a flexible magnetic sheet attachment on the mouse holder. Its validity has been carefully examined by both numerical simulation with an anatomically based mouse model and experimental simulation with a solid mouse phantom. Good agreement was obtained between the numerical and experimental results, which confirmed the effectiveness of the magnetic sheet attachment to the mouse holder.

A novel in vivo exposure setup has been developed for testing the possible promoting effects of 1.5 GHz digital cellular phones on mouse skin carcinogenesis. The exposure setup has two main features: one is the employment of an electrically short monopole antenna with capacitive-loading, which supplies the ability to realize a highly localized peak SAR above 2 W/kg without any thermal stress for a mouse; the other is the use of a transparent absorber to allow real-time observation of both the exposure process as well as mouse activities during the exposure. Dosimetric analyses for the exposure setup have been carried out both numerically and experimentally. Good agreement was confirmed between the numerical and experimental results, thereby demonstrating the validity of the novel exposure setup.

To improve the performance of capsule endoscope, it is important to add location information to the image data obtained by the capsule endoscope. There is a disadvantage that a lot of existing localization techniques require to measure channel model parameters in advance. To avoid such a troublesome pre-measurement, this paper pays attention to capsule endoscope localization based on an electromagnetic imaging technology which can estimate not only the location but also the internal structure of a human body. However, the electromagnetic imaging with high resolution has huge computational complexity, which should prevent us from carrying out real-time localization. To ensure the accurate real-time localization system without pre-measured model parameters, we apply genetic algorithm (GA) into the electromagnetic imaging-based localization method. Furthermore, we evaluate the proposed GA-based method in terms of the simulation time and the location estimation accuracy compared to the conventional methods. In addition, we show that the proposed GA-based method can perform more accurately than the other conventional methods, and also, much less computational complexity of the proposed method can be accomplished than a greedy algorithm-based method.

Discontinuity such as a bend in a micro-strip line is known as one of major radiation sources. The total radiation from the micro-strip line is, however, being generally investigated because of the difficulties in identifying the radiation from some specific location. In this paper, paying attention to the feature of TDR (Time-Domain Reflectometry) measurement, we made an attempt to extract the radiation only from the bend in a micro-strip line. Such an approach is useful in understanding its radiation mechanism. As a result, we found that the larger the bend angle is, the larger the radiation power becomes. The radiation power achieved 3.5% at maximum when the bending angle was 90at the frequencies below 1 GHz. We also examined the validity of the TDR analysis in comparison with network analyzer measurement. We obtained the radiation power versus frequency from the measured scattering parameters, which exhibited a fair agreement with the TDR result.

With the rapid increase of various uses of wireless communications in modern life, the high microwave and millimeter wave frequency bands are attracting much attention. However, the existing databases on above 6GHz radio-frequency (RF) electromagnetic (EM) field exposure of biological bodies are obviously insufficient. An in-vivo research project on local and whole-body exposure of rats to RF-EM fields above 6GHz was started in Japan in 2013. This study aims to perform a dosimetric design for the whole-body-average specific absorption rates (WBA-SARs) of unconstrained rats exposed to 6GHz RF-EM fields in a reverberation chamber (RC). The required input power into the RC is clarified using a two-step evaluation method in order to achieve a target exposure level in rats. The two-step method, which incorporates the finite-difference time-domain (FDTD) numerical solutions with electric field measurements in an RC exposure system, is used as an evaluation method to determine the whole-body exposure level in the rats. In order to verify the validity of the two-step method, we use S-parameter measurements inside the RC to experimentally derive the WBA-SARs with rat-equivalent phantoms and then compare those with the FDTD-calculated ones. It was shown that the difference between the two-step method and the S-parameter measurements is within 1.63dB, which reveals the validity and usefulness of the two-step technique.

In this study, we propose a two-step approach to evaluate electromagnetic interference (EMI) with a wearable vital signal sensor. The two-step approach combines a quasi-static electromagnetic (EM) field analysis and an electric circuit analysis, and is applied to the EMI evaluation at frequencies below 1 MHz for our developed wearable electrocardiogram (ECG) to demonstrate its usefulness. The quasi-static EM field analysis gives the common mode voltage coupled from the incident EM field at the ECG sensing electrodes, and the electric circuit analysis quantifies a differential mode voltage at the differential amplifier output of the ECG detection circuit. The differential mode voltage has been shown to come from a conversion from the common mode voltage due to an imbalance between the contact impedances of the two sensing electrodes. When the contact impedance is resistive, the induced differential mode voltage increases with frequency up to 100kHz, and keeps constant after 100kHz, i.e., exhibits a high pass filter characteristic. While when the contact impedance is capacitive, the differential mode voltage exhibits a band pass filter characteristic with the maximum at frequency of around 150kHz. The differential voltage may achieve nearly 1V at the differential amplifier output for an imbalance of 30% under 10V/m plane-wave incident electric field, and completely mask the ECG signal. It is essential to reduce the imbalance as much as possible so as to prevent a significant interference voltage in the amplified ECG signal.

Common-mode (CM) radiation from a cable attached to a conducting enclosure has a typical dipole-type antenna structure, in which an equivalent noise voltage source located at the connector excites the attached cable against the enclosure to produce radiated emissions. Based on this mechanism, a simple method for predicting the CM radiation from the cable/enclosure structure was proposed. The method combines an equivalent dipole approximation with sinusoidal current distribution and CM current measurement at a specified location on the cable. Its validity was examined in comparison with the far-field measurement and finite-difference time-domain (FDTD) modeling. The predicted resonance frequencies and CM radiation levels were validated with engineering accuracy, i.e., within 30 MHz and 6 dB, respectively, from the measured and FDTD-modeled results in the frequencies above 150 MHz.