Galvanic Coupling Intra-body Communication Research Articles

Channel Characteristics Analysis of Galvanic Coupling Intra-Body Communication

Intra-Body Communication (IBC), which employs the human body as the channel to transmit health informatics, is a potential approach for connecting wearable and implantable devices. Undoubtedly, its channel characteristics provide deep insights to select parameters that are beneficial for the physical layer design of the Body Area Network (BAN). Nevertheless, such analysis has not been systematically addressed. To this end, the transfer function from the quasi-static model in the electromagnetic field is considered at first. Then, the linearity of the galvanic coupling IBC channel is verified. Besides, the proper frequency band for data transmission is investigated using the water-filling algorithm. Moreover, the theoretical Bit Error Rate (BER) performances of different modulations are studied. Results revealed that the galvanic coupling IBC channel can be modeled as a linear band-limited Additive White Gaussian Noise (AWGN) channel. Finally, suitable modulations for various scenarios are discussed based on the channel characteristics found. Consequently, this work can further enrich the design of the IBC for medical applications.

Analysis and Fitting of a Thorax Path Loss Based on Implantable Galvanic Coupling Intra-Body Communication

Objective: The aim of this research was to study the channel transmission characteristics of living and dead animal bodies and signal path loss characteristics of implantable communication in the axial direction. Methods: By injecting fentanyl citrate injection solution, we kept the research object (a piglet) in a comatose state and then a death state, so as to analyze the channel characteristics in each state. To analyze channel gain when using an implantable device with a fixed implantation depth and varying the axial distance, we proposed an implantable two-way communication path loss model. Results: Comparing the living-body and dead-body results showed that the channel gain difference was approximately 10dB for the same position and distance; heartbeat, pulse and breathing of the living animal contributed approximately 1dB of noise. Analyzing the calculated and experimental results of the path loss model showed that the determination correlation coefficients of the model were 0.999 and 0.998, respectively. The model prediction result and the experimental verification result also agreed closely. Conclusion: The path loss model not only fits the experimental results, but also has better predictability for those positions not measured.

Design of Galvanic Coupling Intra-Body Communication Transceiver Using Direct Sequence Spread Spectrum Technology

Intra-body communication (IBC) uses the human body as the transmission medium for electrical signals, and it features the following advantages: low power consumption, strong anti-interference ability, high data security, and broad application scenarios. However, some technical issues still need to be addresses, such as the choice of the best modulation and demodulation scheme in different application scenarios, influence of human activity on IBC performance, variable signal-to-noise ratio (SNR), and influence of transmission distance change on different modulation and demodulation methods. This paper adopts direct sequence spread spectrum (DSSS) communication and phase modulation to realize DSSS-differential phase shift keying (DPSK) and DPSK modulation transmission of baseband data. Moreover, the Costas loop method is employed to achieve reliable symbol recovery. Under the same conditions, in vivo experiments were conducted to compare the performance of DSSS-DPSK and DPSK galvanic coupling IBC transceivers. Notably, these transceivers are affected by the changes in SNR, transmission distance, and human activities. Results show that the bit error rate (BER) of the DPSK scheme is 40 times larger than the DSSS-DPSK scheme in a 30 cm channel length and different SNR experiments. When the BER performance changes from extremely poor (1.40 ×10 -1 ) to excellent (1.51×10 -6 ), the SNR of DSSS-DPSK scheme only needs to be improved by 16 dB. In contrast, when the BER performance changes from extremely poor (1.54 ×10 -1 ) to good (1.65 ×10 -5 ), the SNR of DPSK scheme needs to be improved by 25 dB. With a SNR of -5 dB, the BER ratios of the DPSK scheme is 7 times larger than the DSSS-DPSK scheme. Also, DSSS-DPSK scheme is more sensitive to changes in motion status than DPSK.

Experimental Verifications of Low Frequency Path Gain ($PG$ ) Channel Modeling for Implantable Medical Device (IMD)

With the development of microelectronics and sensor technologies, implantable electronic devices are employed in many applications. These devices are distributed on or in the human bodies and are used to transmit signals wirelessly to external equipment. In conventional wireless communications, the antennas need a lot of space and power, and their strong electromagnetic interference limits the available locations for implantable devices. In the more recently developed galvanic coupling intra-body communication technology, human tissues are used as the media of signal transmission, and this method has therefore been applied to resolve the spatial limitations of conventional wireless communications methods. This paper presents a mathematical model of multi-layer galvanic coupling based on the volume conductor theory to analyze the transmission mechanism of these implantable intra-body communication devices. The proposed model is based on the quasi-static approximation conditions of Maxwell's equations, the field and potential are solved from Poisson's equation, and an equation was obtained to model the channel attenuation. The channel gain in a model of human limbs can be used to calculate within the frequency range of lesser than 1 MHz. To verify the accuracy and applicability of the model, the computed results were compared with the physiological saline and porcine tissue experimental results in the 100-kHz frequency.

Experimental Verification of Human Body Communication Path Gain Channel Modeling for Muscular-Tissue Characteristics

To study the signal transmission mechanism in the human body, the channel characteristics are generally analyzed by modeling. In current modeling methods, the human body is considered quasi-static and the human tissues isotropic, for simplifying the model and its calculation; however, this does not consider the effect of the human tissues on electric signal transmission, resulting in considerable deviations between the calculated results and the measured values. To reduce model errors and improve precision, a channel modeling method with human muscular-tissue characteristics is proposed in this study. In this method, Maxwell’s equations is used as the governing equation and a galvanic-coupling intra-body communication channel model with human-tissue characteristics is built in the cylindrical coordinate system. By building a numerical model with the same parameters as in the analytical model, the analytical solution is proved to be correct. By comparing the different-sample anisotropic models and the isotropic models with the experimental results, it is concluded that the anisotropic model with muscular-tissue characteristics is superior to the isotropic model without muscular-tissue characteristics, with respect to the curve variation tendency and error between the model calculations and the experimental results. The precision of this anisotropic model is enhanced by 200%; hence, it is more accurate. At last, in order to study the optimal communication frequency of the channel, we select 50 healthy persons as the subjects of this experiment, we find that the optimal communication frequency band of the human arm is 10 kHz to 50 kHz. Within this frequency band, the channel gain is the largest, and the mean deviation of samples is less than 2dB, which is very beneficial to signal transmission in human body

Performance Evaluation and Improvement of PER and Throughput in Galvanic-Coupling Intra-Body Communication Systems.

This study examined the following communication characteristics of contact and partially non-contact galvanic intra-body communication (IBC) systems using a human-body path loss model developed previously: 1) packet error rate (PER) calculation for the contact and partially non-contact IBC path, and PER improvement by the low-density parity check (LDPC) error correction code; and 2) signal-to-noise ratio (SNR) estimation using the blind SNR prediction method and throughput optimization using adaptive coding. The following results were obtained for these characteristics: 1) Applying the LDPC coding rate 3/4 through 1/4 can improve the required SNR by approximately 8~20 dB when PER = 10-2; and 2) the blind SNR prediction method can estimate SNR precisely, thus realizing appropriate throughput communication.

Electrical exposure analysis of galvanic-coupled intra-body communication based on the empirical arm models

BackgroundIntra-body communication (IBC) is one of the highlights in studies of body area networks. The existing IBC studies mainly focus on human channel characteristics of the physical layer, transceiver design for the application, and the protocol design for the networks. However, there are few safety analysis studies of the IBC electrical signals, especially for the galvanic-coupled type. Besides, the human channel model used in most of the studies is just a multi-layer homocentric cylinder model, which cannot accurately approximate the real human tissue layer.MethodsIn this paper, the empirical arm models were established based on the geometrical information of six subjects. The thickness of each tissue layer and the anisotropy of muscle were also taken into account. Considering the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines, the restrictions taken as the evaluation criteria were the electric field intensity lower than 1.35 × 104f V/m and the specific absorption rate (SAR) lower than 4 W/kg. The physiological electrode LT-1 was adopted in experiments whose size was 4 × 4 cm and the distance between each center of adjoining electrodes was 6 cm. The electric field intensity and localized SAR were all computed by the finite element method (FEM). The electric field intensity was set as average value of all tissues, while SAR was averaged over 10 g contiguous tissue. The computed data were compared with the 2010 ICNIRP guidelines restrictions in order to address the exposure restrictions of galvanic-coupled IBC electrical signals injected into the body with different amplitudes and frequencies.ResultsThe input alternating signal was 1 mA current or 1 V voltage with the frequency range from 10 kHz to 1 MHz. When the subject was stimulated by a 1 mA alternating current, the average electric field intensity of all subjects exceeded restrictions when the frequency was lower than 20 kHz. The maximum difference among six subjects was 1.06 V/m at 10 kHz, and the minimum difference was 0.025 V/m at 400 kHz. While the excitation signal was a 1 V alternating voltage, the electric field intensity fell within the exposure restrictions gradually as the frequency increased beyond 50 kHz. The maximum difference among the six subjects was 2.55 V/m at 20 kHz, and the minimum difference was 0.54 V/m at 1 MHz. In addition, differences between the maximum and the minimum values at each frequency also decreased gradually with the frequency increased in both situations of alternating current and voltage. When SAR was introduced as the criteria, none of the subjects exceeded the restrictions with current injected. However, subjects 2, 4, and 6 did not satisfy the restrictions with voltage applied when the signal amplitude was ≥ 3, 6, and 10 V, respectively. The SAR differences for subjects with different frequencies were 0.062–1.3 W/kg of current input, and 0.648–6.096 W/kg of voltage input.ConclusionBased on the empirical arm models established in this paper, we came to conclusion that the frequency of 100–300 kHz which belong to LF (30–300 kHz) according to the ICNIRP guidelines can be considered as the frequency restrictions of the galvanic-coupled IBC signal. This provided more choices for both intensities of current and voltage signals as well. On the other hand, it also makes great convenience for the design of transceiver hardware and artificial intelligence application. With the frequency restrictions settled, the intensity restrictions that the current signal of 1–10 mA and the voltage signal of 1–2 V were accessible. Particularly, in practical application we recommended the use of the current signals for its broad application and lower impact on the human tissue. In addition, it is noteworthy that the coupling structure design of the electrode interface should attract attention.

Multilayer Distributed Circuit Modeling for Galvanic Coupling Intrabody Communication

Characterization of the human body as a transmission medium for electrical signals is a necessity for using intrabody communication (IBC) technique into connecting wearable electronic sensors and devices. In this paper, we propose a novel multilayer distributed circuit model for galvanic-coupling type IBC, which is emphasized on the propagation characteristics in contrast with other IBC models. Based on the model, a program is written in MATLAB to investigate the propagation characteristics of a human body channel with the frequency of 10 MHz to 20 MHz and the distance of 5 cm to 10 cm. Finally, a galvanic coupling IBC measurement is implemented to verify the proposed model. The outcome proves that the model is valid and correct.

Corrigendum to “Biological Evaluation of the Effect of Galvanic Coupling Intrabody Communication on Human Skin Fibroblast Cells”

Corrigendum to “Biological Evaluation of the Effect of Galvanic Coupling Intrabody Communication on Human Skin Fibroblast Cells”

Biological Evaluation of the Effect of Galvanic Coupling Intrabody Communication on Human Skin Fibroblast Cells

Intrabody communication (IBC) is an effective way to connect various kinds of wearable devices attached on or under the surface of the body, but it is important to quantitatively evaluate the biological effects of the IBC signal on the human body before its further application. The research described in this paper analyzed the responses of HSF (human skin fibroblast) cells exposed to IBC electrical signals. A galvanic coupling IBC signal transmitting system was designed to expose the experimental samples with different amplitudes (from 0 V to 6 V or 0 mA to 4 mA), different frequencies (from 10 kHz to 1 MHz), and different duration times (12 h and 24 h). The control groups were unexcited. Cell morphology and activity were evaluated with inverted microscope and MTT assays. The cell survival rates of all the experiment groups were in the range of 90% to 110%. Then, the data was analyzed by t-tests to assess whether there were statistically significant differences. The results showed that p values were greater than 0.05, so there were no significant differences between the experimental and control groups. Therefore, it can be concluded that the IBC signals do not have a significant effect on HSF cells.

The Modeling and Simulation of the Galvanic Coupling Intra-Body Communication via Handshake Channel.

Intra-body communication (IBC) is a technology using the conductive properties of the body to transmit signal, and information interaction by handshake is regarded as one of the important applications of IBC. In this paper, a method for modeling the galvanic coupling intra-body communication via handshake channel is proposed, while the corresponding parameters are discussed. Meanwhile, the mathematical model of this kind of IBC is developed. Finally, the validity of the developed model has been verified by measurements. Moreover, its characteristics are discussed and compared with that of the IBC via single body channel. Our results indicate that the proposed method will lay a foundation for the theoretical analysis and application of the IBC via handshake channel.

Tissue Safety Analysis and Duty Cycle Planning for Galvanic Coupled Intra-Body Communication

Galvanic coupling is the enabler of closed-loop communication between implanted sensors and embedded actuating devices (such as drug injectors) by providing energy-efficient and reliable non-RF transmission through links formed within tissue. For safe deployment, it is critical to verify that the amount of heat generated within tissues during signal propagation stays within permissible bound. In this paper, we analyze the thermal distribution within tissues, for galvanic coupling-based communication for varying transmission power levels, number of collocated transmitters, and blood perfusion conditions using finite element based numerical simulation and skin-phantom based experiments. Our results confirm that tissue heating remains well below safe limit of 1 °C. Using the temperature dissipation profile, we derive the suitable transmission duty cycles, separation distances and number of concurrent sources that may co-exist without raising the tissue temperature. The proposed strategies provide up to four fold increase in bandwidth efficiency through concurrent transmissions, ensuring sufficient bandwidth for implant communications.

Path Loss Measurement and Channel Modeling with Muscular Tissue Characteristics.

Background:The galvanic coupling intra-body communication has low radiation and strong anti-interference ability, so it has many advantages in the wireless communication.Method:In order to analyze the effect of muscle tissue’s characteristics upon the communication channel, we selected the muscle of pig buttock as the experimental sample, and used it to study the attenuation property with the galvanic coupling intra-body communication channel along the parallel direction and the transverse direction relative to the muscular fibre line as well as on the surface of destroyed muscular fibre; the study frequency ranges from 1kHz to 10MHz.In the isotropic experiment, in order to destroy muscle’s fibre characteristics, we grinded the muscle four times, at least five minutes for each time. 0dbm sine-wave signal was input to measure the channel attenuation parameter S21 when the transmitter and the receiver were placed at different positions and different distances d1 and d2 (20mm, 40mm, 60mm), so as to analyze channel loss.Conclusion:Within the same frequency range and at the same communication distance, the maximum error of channel attenuation was 10dB; within the same frequency, as the communication distance was increased, the channel attenuation rose gradually, with 4dB increased every 20mm. The conclusion provides the basis for building the theoretical model in the future.

A Galvanic Coupling Method for Assessing Hydration Rates

Recent advances in biomedical sensors, data acquisition techniques, microelectronics and wireless communication systems opened up the use of wearable technology for ehealth monitoring. We introduce a galvanic coupled intrabody communication for monitoring human body hydration. Studies in hydration provide the information necessary for understanding the desired fluid levels for optimal performance of the body’s physiological and metabolic processes during exercise and activities of daily living. Current measurement techniques are mostly suitable for laboratory purposes due to their complexity and technical requirements. Less technical methods such as urine color observation and skin turgor testing are subjective and cannot be integrated into a wearable device. Bioelectrical impedance methods are popular but mostly used for estimating total body water with limited accuracy and sensitive to 800 mL–1000 mL change in body fluid levels. We introduce a non-intrusive and simple method of tracking hydration rates that can detect up to 1.30 dB reduction in attenuation when as little as 100 mL of water is consumed. Our results show that galvanic coupled intrabody signal propagation can provide qualitative hydration and dehydration rates in line with changes in an individual’s urine specific gravity and body mass. The real-time changes in galvanic coupled intrabody signal attenuation can be integrated into wearable electronic devices to evaluate body fluid levels on a particular area of interest and can aid diagnosis and treatment of fluid disorders such as lymphoedema.

Effects of human limb gestures on galvanic coupling intra-body communication for advanced healthcare system.

BackgroundIntra-Body Communication (IBC), which utilizes the human body as the transmission medium to transmit signal, is a potential communication technique for the physiological data transfer among the sensors of remote healthcare monitoring system, in which the doctors are permitted to remotely access the healthcare data without interrupt to the patients’ daily activities.MethodsThis work investigates the effects of human limb gestures including various joint angles, hand gripping force and loading on galvanic coupling IBC channel. The experiment results show that channel gain is significantly influenced by the joint angle (i.e. gain variation 1.09–11.70 dB, p < 0.014). The extension, as well as the appearance of joint in IBC channel increases the channel attenuation. While the other gestures and muscle fatigue have negligible effect (gain variation <0.77 dB, p > 0.793) on IBC channel. Moreover, the change of joint angle on human limb IBC channel causes significant variation in bit error rate (BER) performance.ConclusionsThe results reveal the dynamic behavior of galvanic coupling IBC channel, and provide suggestions for practical IBC system design.

Mathematical Model of Human Forearm Based Muscle Fiber Tissues’ Anisotropic Characteristics

On the basis of human muscle fiber tissues' characteristics, it is first proposed to establish the analytical model of galvanic coupling intra-body communication channel. In this model, the parallel and the transverse electrical characteristics of muscular tissue are fully considered, and the model accurately presents the transmission mechanism of galvanic coupling intra-body communication signals in the channel.

Channel modeling and power consumption analysis for galvanic coupling intra-body communication

Intra-body communication (IBC), using the human body as the channel to transmit data, has lower power consumption, less radiation, and easier linking than common wireless communication technologies such as Bluetooth, ZigBee, and ANT+. As a result, IBC is greatly suitable for body area network (BAN) applications, such as the medical and health care field. Furthermore, IBC can be implemented in wearable devices, including smart watches, sports bracelets, somatic game devices, and multimedia devices. However, due to the limited battery capacity of sensor nodes in a BAN, especially implanted sensor nodes, it is not convenient to charge or change the batteries. Thus, the energy effectiveness of the media access control (MAC) layer strongly affects the life span of the nodes and of the entire system. Certainly, analyzing MAC layer performance in a galvanic coupling IBC is of great importance for the overall system. To obtain the attenuation properties of IBC, in vivo experiments with seven volunteers were performed. Meanwhile, an equalizer was used to compensate the frequency distortion in consideration of frequency-selective fading characteristics of intra-body channels. In addition, a comparison of the bit error rates (BER) of different modulation methods was carried out to obtain the best modulation method. Then, the attenuation characteristics of intra-body channels were applied in a multi-node physiological signal monitor and transmission system. Finally, TDMA and CSMA/CA protocols were introduced to calculate the bit energy consumption of IBC in the practical scenario. With stable characteristics of the intra-body channels, QPSK with an equalizer had a better performance than the tests without an equalizer. As a result, the modulation method of FSK could achieve a lower BER in lower signal-to-noise ratio situations and an FSK method with TDMA for the IBC had the lowest energy consumption under different practical scenarios.

A Novel Field-Circuit FEM Modeling and Channel Gain Estimation for Galvanic Coupling Real IBC Measurements.

Existing research on human channel modeling of galvanic coupling intra-body communication (IBC) is primarily focused on the human body itself. Although galvanic coupling IBC is less disturbed by external influences during signal transmission, there are inevitable factors in real measurement scenarios such as the parasitic impedance of electrodes, impedance matching of the transceiver, etc. which might lead to deviations between the human model and the in vivo measurements. This paper proposes a field-circuit finite element method (FEM) model of galvanic coupling IBC in a real measurement environment to estimate the human channel gain. First an anisotropic concentric cylinder model of the electric field intra-body communication for human limbs was developed based on the galvanic method. Then the electric field model was combined with several impedance elements, which were equivalent in terms of parasitic impedance of the electrodes, input and output impedance of the transceiver, establishing a field-circuit FEM model. The results indicated that a circuit module equivalent to external factors can be added to the field-circuit model, which makes this model more complete, and the estimations based on the proposed field-circuit are in better agreement with the corresponding measurement results.

Signal Path Loss through the Human Arm by Galvanic Coupling Intrabody Communication Using Noncontact Electrodes on the Transmission Side

Signal Path Loss through the Human Arm by Galvanic Coupling Intrabody Communication Using Noncontact Electrodes on the Transmission Side

Signal Path Loss Simulation of Human Arm for Galvanic Coupling Intra-body Communication

Galvanic coupling intra-body communication involves the formation of a network between small terminals applied to the surface of the human body and bio-signal sensors embedded within the body. To enable the design of a communication device, it is important to fully understand the signal transmission loss characteristics of the human body, while developing a method that optimizes the transmission efficiency. This study analyzed the signal path loss during galvanic-coupling intra-body communication of a human arm through the application of a four-terminal circuit and a finite-element method (FEM) model, with special attention given to the return path. The effect of the interface circuit of an LC series–parallel circuit that injected the signal into the human body was also examined. Without the LC series–parallel circuit, the attenuation of the transmitted signal was minimized within a range of 2–5 MHz in the circuit model and 3–7 MHz in the FEM model. The addition of the LC series–parallel circuit improved the attenuation by 1.9–5.8 dB at the resonant frequency (2 MHz).