Design of a floating-ground-electrode circuit for measuring attenuation of the human body channel.

BACKGROUND: Recently, health care and disease prevention are more and more important in people's daily life. Human body communication (HBC) is an emerging short distance wireless communication mode, which is quite suitable for the communication between the wearable human health care equipment. However, most research on HBC mainly focuses on the electromagnetic model and the circuit model of equivalent human and the in vivo experiment is based on the commercial equipment. OBJECTIVE: The aim of this paper is to design a circuit device for measuring the attenuation of the human body channel based on a floating-ground-electrode method. METHODS: This paper proposed a new floating-ground-electrode method so as to solve problems of power and high frequencies interference and impedance matching. A circuit module, including signal generator, analog frontend circuit and MCU, was designed to initially replace the spectrum analyzer to measure the attenuation of the human body channel. The floating-ground-electrode added to the receiving end of the human body channel was connected to the ground of the analog frontend circuit, forming an equal potential circuit. The three-electrodes of the receiving terminal can act as a differential probe, since one electrode is connected to the ground and the other two electrodes achieved signal input and output respectively. RESULTS: The results showed that the experimental data of channel attenuation were similar to the measured value of the spectrum analyzer. The maximum absolute error was 1.148 dB and the relative error was 3.55%. In addition, different sizes of the floating-ground-electrode cannot affect the attenuation path of human body channels. Moreover, the common mode rejection ratio (CMRR) was approximated to the value of the commercial differential probe. CONCLUSION: This paper proposed a new floating-ground-electrode method for measuring the attenuation of the human body channel. It could provide the possibility for the dynamic measurement of attenuation and take the place of the spectrum analyzer and make the process of experiments simple and efficient.

Design and feasibility study of human body communication transceiver based on FDM.

BACKGROUND: The body area networks (BAN) are built by many wearable sensors to record, monitor or control the vital signals within the human body continuously. Human body communication (HBC) is a novel physical layer method to implement the BAN with low power consumption, low radiation, and strong anti-interference. However, the most existing HBC rarely consider the situation in which multiple sensors transmit data at the same time. OBJECTIVE: The aim of this paper is to investigate the feasibility of frequency division multiplexing for human body communication multiplex data transmission. METHODS: The signal was injected into the human body, and the human channel gain was measured by the spectrum analyzer. Two frequency signals were selected with smaller gain to design the transceiver. The transmitter used OOK modulation technology to design each functional unit, and the receiver recovered the original signal with a non-coherent demodulation method. RESULTS: The experimental results show that after the dual signals were transmitted through the human body, the receiver could recover the original signal correctly. In both static and dynamic situations, even if the transmission rate was as high as 115.2 kb/s, the bit error rate was only 10-4. CONCLUSIONS: The frequency division multiplexing scheme can be selected for multi-channel data transmission in human body communication.