Dairoku Muramatsu

Maximization of received signal power by impedance matching in human body communication receiver

Human body communication (HBC) utilizes human body as part of the transmission channel. The present paper deals with HBC between a transmitter worn on the users wrist and an off-body stationary receiver touched by the users finger. In this configuration, transmitter-human-body system can be regarded as a signal source as viewed from the receiver. The equivalent output impedance of this signal source mainly consists of resistance of human body and capacitive reactance among the receiver, human body, and the surrounding environment. Impedance matching was achieved by inserting an inductor to cancel the capacitive reactance and adjusting the input resistor to match the resistance of the equivalent output impedance. At frequency of 10 MHz, maximum received power was obtained with 40 μH inductor and 1.5 kΩ input resistance. This suggests that the output impedance of the transmitter-human-body system is 1500-j2500 Ω.

Human body communication between fingertip and wrist using stationary and wearable devices

Human body communication (HBC) is expected to become a unique man-machine interface because the transmission path is established only when the user touches the target device. In this study, HBC between a stationary device and a wearable device worn on the wrist was investigated. Transmission characteristics between the devices and electric field around the human body model were calculated by electromagnetic field analysis. The transmission characteristics from the stationary device to the wearable device were about -56 dB, which suggests a stable bidirectional transmission. The S21 decreased more than 30 dB when stationary signal electrode and fingertip were 5 cm apart, indicating that contact is necessary for transmission.

Multilayered cylindrical human arm model for impedance analysis in human body communication

In human body communication system, it is important to investigate the input impedance characteristics of the electrodes for improving the qualities of communication. For rapid and freedom analysis, an approximation model is needed. In this paper, we compared input impedance characteristics of detailed model with that of approximation model which has a multilayered cylindrical structure. As a result, it was found that the input impedance characteristics of two models were well consistent in the frequency range of 1 MHz to 1 GHz. Moreover, it was found that electric fields around the arm were almost the same in each model. These analysis results show that the multilayered cylindrical model is useful for calculating input impedance and electric field distributions around the arm model.

Clarification of transmission mechanism in Human body communication between head-mounted wearable devices with detailed model

Facing an aging society, body area network (BAN) is expected to play a greater role in improving a quality of life of the elderly and people with disabilities Human body communication (HBC) which utilizes a part of human body as a transmission medium has been drawn much attention as a promising wireless technology for BAN. Communication between head mounted wearable devices such as hearing aids is one of the prospective applications of HBC. In this study, for clarify a transmission mechanism of HBC between head-mounted wearable devices, input impedance characteristics of transceiver antennas (electrodes), transmission characteristics and electric field distributions around the detailed head model were investigated through an electromagnetic field analysis. The analysis results showed that the signal frequency had little effect on the transmission characteristics and electric field distributions in the frequency of 10, 20, 30 MHz. However, it was found that the transmission mechanism between head-mounted wearable devices is influenced by the number of electrode of transceiver.

Input impedance analysis of wearable antenna and its experimental study with real human body

Human body communication has received a lot of attention as a promising wireless technology for Body area network. In Human body communication system, High frequency signal is excited in human body through a wearable antenna. Therefore, it is important to investigate the input impedance characteristics of the antennas considering an effect of human body. In this paper, we studied the input impedance characteristics of antenna worn on the wrist under the dry/wet skin conditions. Moreover, experiment with a prototype wearable antenna and real human body was performed in the frequency range of 1 to 100 MHz. The results showed that moisture condition of the skin and differences among individuals had great effect on the input impedance in the low frequency range. However, analytical and experimental results showed the same tendency in whole frequency range. This means a validity of the FDTD simulation using detailed human arm model.

Input impedance characteristics of wearable transmitter electrodes for intra-body communication

Intra-body communication draws attention as a promising wireless technology in order to materialize wireless body-centric networks. An electrode in intra-body communication system is a key device since the electrodes are analogous to antennas in airborne wireless communication system. However, nobody has addressed the broadband input impedance characteristics of the electrodes although there are a few study reports discussing them at one single frequency. In this paper, the input impedance characteristics of the wearable transmitter electrodes in the frequency range of 500 kHz to 1 GHz, and the electromagnetic field distributions around and inside the human arm at the frequency of 10 MHz were investigated. As a result, both magnitudes of the resistive and reactive components of the input impedance increased as frequency increased below 200 MHz. Further, it was also found that the electric field was strongly distributed only the vicinity of the human arm with a transmitter. It could be advantageous in the view points of the high-secured communication and the electromagnetic compatibility (EMC).

Transmission characteristics of wearable devices between two human bodies

Human body communication is expected as a new human interface for communications among several persons. Thus, it is necessary to analyze the transmission characteristics between human bodies. In this paper, we compared the transmission characteristics between transmitter and receiver in the viewpoint of contact situation between two bodies. Moreover, the effect of receiver position on transmission characteristics was analyzed. From the analysis, it was found that the transmission characteristics were affected by the position of the receiver. On the other hand, contact situation between two bodies has little influence on the transmission characteristics.

Measurement of human body communication transmission characteristics at 20 MHz

Transmission characteristics of human body communication at 20 MHz were measured by using a battery operated transmitter and a receiver to eliminate undesirable coupling between cables for measurement or power supply. Received signal strength indication (RSSI) was recorded on the memory of the receiver and retrieved afterward. Transmission from chest to wrist was measured, assuming a transmission of ECG signal from chest to a wearable device worn on the wrist. RSSI values were compared for different contact conditions. The largest signal was obtained when the signal electrode of the receiver was in contact with the human body and the ground electrode was floating.

Multilayered phantom for input impedance evaluation of human body communication electrodes

This paper presents the input impedance measurement of a human body communication electrode by using newly developed multilayered phantom. Based on the comparison between analysis and measurement values, it was found that the multilayered phantom can be used for accurate evaluation.

Equivalent output impedance of a transmitter-human body system as viewed from a receiver for human body communication

When a transmitter for human body communication is worn by a human user, this transmitter-human body system can be regarded as a signal source as viewed from a receiver that is in contact with the human body. We evaluated the equivalent output impedance of this signal source, which is an important parameter for front end design of a receiver. The impedance was capacitive and the value was in the order of several kΩ at 10 MHz. The impedance was smaller when the capacitive coupling between the human body and the environment was larger.