Human body can be considered as a communication channel in which the electric field propagates around the body as an approximated surface wave, which is known as human body communication (HBC). HBC is superior to other wireless communications from the point of view of electromagnetic compatibility. Since the human body acts as a conductor below a few tens of MHz, one can detect the existence of human body by measuring the corresponding electric filed variation in close proximity of the human body. In this study, we made an effort to detect the approaching direction of human arm based on the HBC principle under the assumption of application to a user-machine interface. We also conducted an experimental validation for our simulation result, and attempted to provide an appropriate explanation of this detection system with an equivalent circuit model.
Differences in contact impedance of the ECG measurement electrodes lead to asymmetries of the signal paths and thus result in reduced common-mode rejection and artifacts. Here, the imbalance of contact impedance is investigated for different types of electrodes with capacitive coupling in terms of static imbalance as well as dynamic variation during body movement. Flexible and incompressible materials like conductive foam and fabric showed the best overall performance. The negative effect of rigidity can partly be compensated by adding conducting foam, while soft materials can profit from an increase of electrode area.
This paper proposes a received signal strength indicator (RSSI)-based maximum a posteriori (MAP) localization method with channel parameters estimation in wireless sensor networks. The proposed method makes use of not only likelihood value of the location of a target but also a priori knowledge of the target location. Furthermore, the proposed method also estimates channel model parameters with an maximum likelihood (ML) estimation technique, therefore, it can be realized with no troublesome pre-measurement on the channel parameters. Our theoretical analyses and experimental results demonstrate that the proposed MAP location estimation method is superior to a conventional ML location estimation method in term of location estimation accuracy.
Abstract Electromagnetic properties depend on the composition of materials, i.e. either angstrom scales of molecules or, for metamaterials, subwavelength periodic structures. Each material behaves differently in accordance with the frequency of an incoming electromagnetic wave due to the frequency dispersion or the resonance of the periodic structures. This indicates that if the frequency is fixed, the material always responds in the same manner unless it has nonlinearity. However, such nonlinearity is controlled by the magnitude of the incoming wave or other bias. Therefore, it is difficult to distinguish different incoming waves at the same frequency. Here we present a new concept of circuit-based metasurfaces to selectively absorb or transmit specific types of waveforms even at the same frequency. The metasurfaces, integrated with schottky diodes as well as either capacitors or inductors, selectively absorb short or long pulses, respectively. The two types of circuit elements are then combined to absorb or transmit specific waveforms in between. This waveform selectivity gives us another degree of freedom to control electromagnetic waves in various fields including wireless communications, as our simulation reveals that the metasurfaces are capable of varying bit error rates in response to different waveforms.
Ultra wideband (UWB) technology in low band is promising for implant body area network. In this paper, the performance improvement of an in-body to on-body UWB communication, which corresponds to a capsule endoscope application, is investigated. We firstly analyzed the in-body to on-body propagation characteristics and proposed a two-path impulse response channel model based on finite difference time domain numerical method (FDTD) incorporated with an anatomical human model. In view of the extracted statistical characteristics of the proposed two-path model, we then employed a spatial diversity reception technique to improve the communication performance effectively. The average bit error performance was finally investigated to clarify the diversity effect with theoretical analysis and computer simulation.
