Nozomi Haga

Characteristics of Cavity Slot Antenna for Body-Area Networks

Antennas and the propagation characteristics for body-area networks have become an active area of research. In this paper, a cavity slot antenna is proposed for onbody communications at 2.45 GHz. First, the antenna characteristics (input impedance, radiation pattern, and efficiency) are calculated by the finite-difference time-domain method. The results show that the proposed antenna has a relatively high efficiency of more than 50% even in the vicinity of the human body. Next, the onbody radio wave-propagation characteristics are investigated through numerical simulation and experimental measurements of the electric-field distributions around a phantom with a simplified shape of a human arm. Both sets of results are then compared and discussed. Finally, good agreement between the measured and the calculated results is confirmed.

Equivalent Circuit of Intrabody Communication Channels Inducing Conduction Currents Inside the Human Body

The physical channels establishing intrabody communications were first treated as capacitive circuits by Zimmerman. In Zimmermans model, the human body is approximated as a perfect conductor. The equivalent-circuit parameters of the perfect conductor models can be strictly obtained based on electrostatic analyses; however, the perfect conductor models cannot be applied if conduction currents inside the human body are not negligible. In the present paper, a theory of the equivalent circuit for lossy conductors is described, and the physical mechanism of the communication channels inducing conduction currents inside the human body is addressed.

Wearable antennas for body-centric wireless communications

In recent years, a study on body-centric wireless communications has become an active and attractive area of research because of their various applications such as e-healthcare, support systems for specialized occupations, personal communications, and so on. Whereas UHF bands are subjects of interest especially in Europe and USA, relatively low frequency bands below several megahertz are of great interest especially in Japan. Hence, all of the prospective frequencies are in an extremely wide range, and an objective idea on how to select a right frequency band for individual applications is required. Currently in our laboratory, we have been studying on frequency dependence of basic characteristics of wearable antennas as well as body-centric wireless communication channels in the range of HF to UHF (3 MHz–3 GHz). There are experimental, analytical, and numerical ways to clarify the basic characteristics of the antennas and communication channels. In experiments, we have to ensure impedance matching at certain frequency points because of sensitivity limitations; therefore, it is hard to obtain such broadband characteristics. Theoretical analysis is useful to understand physical mechanism; however, complex geometry and motion of the human body cannot be modeled. By contrast to them, numerical simulation can solve complex problems with relative ease. For example, Hall et al. have shown that the dynamics of the human body can be modeled by dividing the motion into several frames, and the simulated results agree with the measured results. Also in our study, observations of channel characteristics are conducted by employing numerical simulations. In this paper, firstly, electric field distributions around the human body wearing a small top-loaded monopole antenna are numerically calculated and compared in a wide range of HF to UHF bands. Then, received open voltages at receiving antennas which are equipped at several different points on the human body are numerically investigated. The received open voltages are also numerically calculated and compared with several different postures of the human body. Statistic characterization and experimental validation will be necessary in further studies.

Evaluations of Body-Centric Wireless Communication Channels in a Range From 3 MHz to 3 GHz

In recent years, body-centric wireless communications have been studied because they have potential to improve the qualities of various kinds of applications. Since the prospective frequencies for the body-centric wireless communications are in an extremely wide range from megahertz to gigahertz, an objective idea on how to select a right frequency band for individual applications is required. However, few publications have tackled this need. In this paper, the frequency dependence of the communication channels in the range of 3 MHz to 3 GHz is assessed based on numerical analyses.

A Cavity-Backed Slot Antenna for On-Body BAN Devices

In this paper, a cavity-backed slot antenna for on-body BAN devices has been investigated. The electric field distributions inside and around the human body are numerically analyzed by the use of the FDTD method. According to the results, in the region on and near the human body, the dominant component of electric field is vertical to the body surface, and the propagation mode is assumed to be creeping wave. On the other hand, in the region inside the human body, dominant component of electric field is horizontal to the body surface, and the propagating direction is almost vertical to the body surface. Furthermore, in order to confirm the validity of the simulated results, measurement of the electric fields around the biological-tissue equivalent phantom was performed. The results showed that the measured and simulated electric fields are agreed well, and indicated validity of the simulation. As a farther study, antenna design will be investigated in view of properties of the BAN system.

Electric field distributions around the human body with a small antenna in the frequency range of 2.5 MHz to 2.5 GHz

In recent years, body-centric wireless communications become an active area of research due to their various applications such as e-healthcare, support systems for specialized occupations, and personal communications. Since the candidate frequencies for body-centric wireless communications widely range from MHz to GHz, dielectric properties of the human body tissues, relative dimensions of the human body to wavelength, and the propagation channels around the body extremely vary with frequencies. In this paper, to bring objective and unified idea on the frequency characteristics of body-centric wireless communication channels, electric field distributions around the human body wearing a small antenna in a wide frequency range of 2.5 MHz to 2.5 GHz are numerically calculated. The results show that behavior of the electric field distributions around the human body could be broadly divided into two ranges; below 100 MHz and above 250 MHz.

System of equations describing charges of multiple conductors immersed in electrostatic fields

Problems of electrostatic fields involving multiple conductors arise in various scientific fields. It is known that the relation between the electric potentials and the charges of multiple conductors can be expressed by a system of linear equations. However, the well-known system of equations holds true only when no other charge exists external to the conductors. In this paper, we derive an extended system of equations that is valid even if the conductors are immersed in electrostatic fields due to external charges.

Basic characteristics of wearable antennas for body-centric wireless communications

In recent years, body-centric wireless communications have become an active area of research because of their various applications. Whereas UHF bands are subjects of great interest especially in Europe, relatively low frequency bands like HF bands have been used especially in Japan and Korea. Thus, all of the prospective frequencies are in an extremely wide range. Our target is to bring objective and unified idea on the frequency characteristics of body-centric wireless communication channels. In this paper, we have numerically observed the open voltage at several receiving antennas. Furthermore, we have examined several body postures and surrounding environments.

Equivalent-Circuit Expression of Environmental Noise Electric Fields in Intrabody Communication Channels

In the development of intrabody communication systems, the most challenging goal is to protect against noise due to other electronic devices. In this paper, the equivalent-circuit expression of environmental noise electric fields (the so-called radiated noise) in intrabody communication channels are derived based on the theory of electrostatic fields. In addition, numerical examples are shown by means of electrostatic analysis based on the method of moments, and the results agree with those by full-wave analysis based on the finite-difference time-domain method and those by measurements. Therefore, it is concluded that the proposed circuit model can properly express the contribution of environmental noise electric fields.

A note on signal paths in intrabody communication channels

In this study, the signal paths in intrabody communication channels are discussed by evaluating the electric fluxes between conductors and the earth ground. This study is based on the equivalent circuit model of which parameters are obtained via an electrostatic analysis. The obtained results clarified the electric flux flows in the communication channels, and they quantitatively support the previous study reported by one of the authors.