Bio-Physical Modeling, Characterization, and Optimization of Electro-Quasistatic Human Body Communication

Touchscreen communication (ToSCom): Electro-Quasistatic body communication during touch sensing

Touchscreens are a fundamental technology for human society providing the primary gateway for human-machine interaction. Today's touchscreens can only be used to detect touch and provide the location of the user's touch input but not to simultaneously communicate digital data during a touch event through the touchscreen. If communication through a touchscreen can be enabled, it promises deep societal impact by augmenting the most popular Human-Computer-Interaction interface with new possibilities such as a single application on the same device opening up personalized user-specific account data depending on the person interacting with the application. Leveraging advances in Electro-Quasistatic field based communication in the past decade, we propose and demonstrate Touchscreen Communication (ToSCom), a high-speed (>Mbps) simultaneous communication and touch sensing interface. We develop a low path loss channel across the entire touchscreen surface enabling 3 Mbps data rate communication with an average bit-error-rate of less than 5 × 10-7 through the touchscreen surface simultaneously during touch sensing. ToSCom enables a wide range of possibilities in day-to-day life like in wearable devices like transactions in a Point-of-Sale system, audio/image file transfer, and viewing personalized data in touchscreen kiosks.

Human-structure and human-structure-human interaction in electro-quasistatic regime

Augmented living equipped with electronic devices requires widespread connectivity and a low-loss communication medium for humans to interact with ambient technologies. However, traditional radiative radio frequency-based communications require wireless pairing to ensure specificity during information exchange, and with their broadcasting nature, these incur energy absorption from the surroundings. Recent advancements in electroquasistatic body-coupled communication have shown great promise by utilizing conductive objects like the human body as a communication medium. Here we propose a fundamental set of modalities of non-radiative interaction by guiding electroquasistatic signals through conductive structures between humans and surrounding electronic devices. Our approach offers pairing-free communication specificity and lower path loss during touch. Here, we propose two modalities: Human-Structure Interaction and Human-Structure Human Interaction with wearable devices. We validate our theoretical understanding with numerical electromagnetic simulations and experiments to show the feasibility of the proposed approach. A demonstration of the real-time transfer of an audio signal employing an human body communications-based Human-Structure Interaction link is presented to highlight the practical impact of this work. The proposed techniques can potentially influence Human-Machine Interaction research, including the development of assistive technology for augmented living and personalized healthcare.

Channel Variability in Human Body Communication with External Objects in Body Resonance Region

The channel variability of human body communication (HBC) in Electro-Quasistatic (EQS) region and the influence of the parasitic paths by external objects and inter-body coupling have been widely explored. However, channel variability of HBC in the body resonance (BR) region is hardly studied. In the BR region, the wavelength is comparable to the dimension of the human body which starts to resonate and act as an antenna. Electromagnetic (EM) wave patterns are generated from the transmitter dipole and formed on the human body. The external objects causing some parasitic paths influence the patterns and the channel gain. This paper explores the influence of external objects on the HBC channel gain in the BR region for the first time. Firstly, the relevant EM theories and corresponding simulation setup and results are introduced. Following that, the experiment setup and results are described and analyzed. The results show that putting the arms on the table can lead to a notch frequency shift by 77∼100 MHz and channel gain change by -17∼20 dB depending on different angles and frequencies. The channel gain variation before the notch is small, enabling stable high-speed communication.

Exploring the Effects of Encapsulated Capacitive and Galvanic Transmitters for Implant-to-Wearable Scenarios in Human Body Communication

Data transfer using human-body communication (HBC) represents an actively explored alternative solution to address the challenges related to energy-efficiency, tissue absorption, and security of conventional wireless. Although the use of HBC for wearable-to-wearable communication has been well-explored, different configurations for the transmitter (Tx) and receiver (Rx) for implant-to-wearable HBC needs further studies. This paper substantiates the hypothesis that a fully implanted galvanic Tx is more efficient than a capacitive Tx for interaction with a wearable Rx. Given the practical limitations of implanting an ideal capacitive device, we choose a galvanic device with one electrode encapsulated to model the capacitive scenario. We analyze the lumped circuit model for in-body to out-of-body communication, and perform Circuit-based as well as Finite Element Method (FEM) simulations to explore how the encapsulation thickness affects the received signal levels. We demonstrate in-vivo experimental results on live Sprague Dawley rats to validate the hypothesis, and show that compared to the galvanic Tx, the channel loss will be ≈ 20 dB higher with each additional mm thickness of capacitive encapsulation, eventually going below the noise floor for ideal capacitive Tx.

Energy-Efficient Synchronous CDMA for Multiple Channel Access in Internet of Bodies

This paper introduces an energy-efficient code-division multiple access (CDMA) architecture for wearable devices for the Internet of Bodies (IoB), which is an emerging data communication framework for connected sensor nodes around the human body. To address the challenge of simultaneous data transmission from multiple transmitters, which often leads to interference, we propose the adoption of standard-basis based CDMA encoding and decoding, which has higher energy efficiencies than the traditional Walsh code-based implementation. We also present a novel architecture for body-worn sensor nodes and data aggregators, where both the sensor nodes and the aggregator possess transceiver functionalities for (1) transmitting data from the sensors to the aggregator, and (2) sending clock synchronization information from the aggregator to the nodes. Acknowledging the synchronization requirements of CDMA, a Clock Data Recovery Circuit (CDR) module is integrated within the body-worn nodes. Experimental results with iCE40 wearable FPGAs, under the assumption of synchronized clocks, validate the effectiveness of CDMA encoding and decoding with 4 sensor nodes. The overall energy efficiency for the sensor node with circuit-level simulations using a standard 65nm process is found to be only 62 pJ/bit (> 3× better than literature) at 1 Mbps.

Dataset on the human body as a signal propagation medium for body coupled communication

Signal loss models are frequently utilized by wireless communication researchers and engineers to predict received signal strength, optimize system parameters, and conduct feasibility studies. However, novel communication methods such as Body-Coupled Communication (BCC) that are suitable for Body Area Networks formed by wearable devices currently lack readily available signal propagation models. In this data article, we present a galvanic-coupled BCC signal loss and bioimpedance dataset, which serves as a foundation for building such models. This extensive dataset consists of experimental data recorded from 30 volunteer test subjects. The experimental setup involves a tunable signal generator transmitting continuous wave signals, along with two oscilloscopes recording the transmitter-side and receiver-side voltages. From these measurements, we compute the signal loss over the body, and the transmitter-side impedance. The transmitted signal frequencies range from 50 kHz to 20 MHz, with discrete steps. The primary application of this dataset is to enable empirical-data-supported modeling in the human body as a BCC signal propagation medium, which will help to explore how the properties of the human body, the measurement locations, and the signal frequency impact the signal loss.

Non-Directional Property of Human-Body Communication Channel for Implantable Device Application

In this paper, we present the properties of a communication channel used for implantable devices. The human-body communication (HBC) channel was proposed for data communication in implantable devices. The impulse response was measured using a channel-mimicking model, which mimics electrical losses caused by human body tissues. Furthermore, we compared two types of channel-mimicking models to evaluate their applicability depending on the measurement environment. The resultant impulse responses of the HBC channel showed that HBC does not cause severe changes in the channel properties even when the implantable device is rotated.

Electro-Quasistatic Human-Structure Coupling for Human Presence Detection and Secure Data Offloading

The emergence of Human Body Communication (HBC), as an energy-efficient and physically secure mode of information exchange, has escalated the exploration of communication modalities between the human body and surrounding conducting objects. In this paper, we propose an Inter-Structure communication guided by Human Body while envisioning the need for non-contact sensing of biological objects such as humans with secure data offloading by analyzing the Structure-Human-Structure Interaction (SHSI) in Electro-Quasistatic (EQS) regime. Results show that the presence of a human between conducting structures (with Tx & Rx) can boost the received voltage by ~8 dB or more. Received signal level can be increased further by ~18 dB or more with a grounded receiver. Finite Element Method (FEM) based simulations are executed to study the positional variation of structure (with Rx) relative to body and earth's ground. Trends in simulation results are validated through experiments to develop an in-depth understanding of SHSI for EQS signals with low loss and enhanced physical security.

The Retrieval and Effect of Core Parameters for Near-Field Inter-Body Coupling Communication

The potential of the Internet of Body (IoB) to support healthcare systems in the future lies in its ability to enable proactive wellness screening through the early detection and prevention of diseases. One promising technology for facilitating IoB applications is near-field inter-body coupling communication (NF-IBCC), which features lower power consumption and higher data security when compared to conventional radio frequency (RF) communication. However, designing efficient transceivers requires a profound understanding of the channel characteristics of NF-IBCC, which remain unclear due to significant differences in the magnitude and passband characteristics of existing research. In response to this problem, this paper clarifies the physical mechanisms of the differences in the magnitude and passband characteristics of NF-IBCC channel characteristics in existing research work through the core parameters that determine the gain of the NF-IBCC system. The core parameters of NF-IBCC are extracted through the combination of transfer functions, finite element simulations, and physical experiments. The core parameters include the inter-body coupling capacitance (CH), the load impedance (ZL), and the capacitance (Cair), coupled by two floating transceiver grounds. The results illustrate that CH, and particularly Cair, primarily determine the gain magnitude. Moreover, ZL mainly determines the passband characteristics of the NF-IBCC system gain. Based on these findings, we propose a simplified equivalent circuit model containing only core parameters, which can accurately capture the gain characteristics of the NF-IBCC system and help to concisely describe the channel characteristics of the system. This work lays a theoretical foundation for developing efficient and reliable NF-IBCC systems that can support IoB for early disease detection and prevention in healthcare applications. The potential benefits of IoB and NF-IBCC technology can, thus, be fully realized by developing optimized transceiver designs based on a comprehensive understanding of the channel characteristics.

Bioelectronic Sensor Nodes for the Internet of Bodies

Energy-efficient sensing with physically secure communication for biosensors on, around, and within the human body is a major area of research for the development of low-cost health care devices, enabling continuous monitoring and/or secure perpetual operation. When used as a network of nodes, these devices form the Internet of Bodies, which poses challenges including stringent resource constraints, simultaneous sensing and communication, and security vulnerabilities. Another major challenge is to find an efficient on-body energy-harvesting method to support the sensing, communication, and security submodules. Due to limitations in the amount of energy harvested, we require a reduction in energy consumed per unit information, making the use of in-sensor analytics and processing imperative. In this article, we review the challenges and opportunities of low-power sensing, processing, and communication with possible powering modalities for future biosensor nodes. Specifically, we analyze, compare, and contrast (a) different sensing mechanisms such as voltage/current domain versus time domain, (b) low-power, secure communication modalities including wireless techniques and human body communication, and (c) different powering techniques for wearable devices and implants.

Physically Secure Wearable–Wearable Through-Body Interhuman Body Communication

Human body communication (HBC) has recently emerged as an alternative method to connect devices on and around the human body utilizing the electrical conductivity properties of the human body. HBC can be utilized to enable new interaction modalities between computing devices by enhancing the natural interaction of touch. It also provides the inherent benefit of security and energy-efficiency compared to a traditional wireless communication, such as Bluetooth, making it an attractive alternative. However, most state-of-the-art HBC demonstrations show communication between a wearable and an Earth ground–connected device, and there have been very few implementations of HBC systems demonstrating communication between two wearable devices. Also, most of the HBC implementations suffer from the problem of signal leakage out of the body which enables communication even without direct contact with the body. In this article, we present BodyWire which uses an electro-quasistatic HBC (EQS-HBC) technique to enable communication between two wearable devices and also confine the signal to a very close proximity to the body. We characterize the human body channel loss under different environment (office desk, laboratory, and outdoors), posture, and body location conditions to ascertain the effect of each of these on the overall channel loss. The measurement results show that the channel loss varies within a range of 15dB across all different posture, environmental conditions, and body location variation, illustrating the dynamic range of the signal available at the input of any receiver. Leakage measurements are also carried out from the devices to show the distance over which the signal is available away from the body to illustrate the security aspect of HBC and show its effect on the channel loss measurements. For the first time, a through-body interhuman channel loss characterization is presented. Finally, a demonstration of secure interhuman information exchange between two battery-operated wearable devices is shown through the BodyWire prototype, which shows the smallest form factor HBC demonstration according to the authors’ best knowledge.

Performance Evaluation of Magnetic Resonance Coupling Method for Intra-Body Network (IBNet)

Effective management of emerging medical devices can lead to new insights in healthcare. Thus, a human body communication (HBC) is becoming increasingly important. In this paper, we present magnetic resonance (MR) coupling as a promising method for intra-body network (IBNet). The study reveals that MR coupling can effectively send or receive signals in biological tissue, with a maximum path loss of PL 33 dB (i.e. at 13.56 MHz), which is lower than other methods (e.g., galvanic, capacitive, or RF) for the same distance. The angular orientation of the transmitter and receiver coils at short and long distances also show a minor variation of the path loss (0.19 PL 0.62 dB), but more dependency on the distance (0.0547 dB/cm). Additionally, different postures during the MR coupling essentially do not affect path loss (PL 0.21 dB). In the multi-nodal transmission scenario, the MR coupling demonstrates that two nodes can simultaneously receive signals with -16.77 dBm loss at 60 cm and 100 cm distances, respectively. Such multi-node MR transmission can be utilized for communication, sensing, and powering wearable and implantable devices.

Human Body-Electrode Interfaces for Wide-Frequency Sensing and Communication: A Review

Several on-body sensing and communication applications use electrodes in contact with the human body. Body-electrode interfaces in these cases act as a transducer, converting ionic current in the body to electronic current in the sensing and communication circuits and vice versa. An ideal body-electrode interface should have the characteristics of an electrical short, i.e., the transfer of ionic currents and electronic currents across the interface should happen without any hindrance. However, practical body-electrode interfaces often have definite impedances and potentials that hinder the free flow of currents, affecting the application's performance. Minimizing the impact of body-electrode interfaces on the application's performance requires one to understand the physics of such interfaces, how it distorts the signals passing through it, and how the interface-induced signal degradations affect the applications. Our work deals with reviewing these elements in the context of biopotential sensing and human body communication.

Channel Characterization of Magnetic Human Body Communication

OBJECTIVE

The objective of this paper is to model and experimentally validate the path loss benefits of magnetic human body communication (mHBC) using small form-factor-accurate coils operating under realistic conditions.

METHODS

A radiating near-field coupling model and numerical simulations are presented to show that the magnetic-dominant near-field coupling between resonant coils offers low path loss across the body and exhibits extra robustness to antenna misalignment compared to far-field RF schemes. To overcome the pitfalls in conventional vector-network-analyzer-based measurement configurations, we propose a standardized setup applied to broadband channel loss measurement with portable instruments. Two types of PCB coils for mHBC communication, designed for large devices such as smartphones and small devices such as earbuds, respectively, are built and measured.

RESULTS

The mHBC link for the ear-to-ear non-line-of-sight (NLOS) path measures up to -23.1 dB and -31.2dB with large and small coils, respectively, which is 50 dB more efficient than the conventional Bluetooth channels utilizing antennas of similar sizes. Ear-to-pocket and pocket-to-pocket channels also show at least 16 dB higher transmission than the Bluetooth channel.

CONCLUSION

In terms of path loss, the mHBC approach offers compelling performance for short-range applications over the body region. For coils with dimensions of several centimeters, working between 100 MHz and 200 MHz minimizes the channel loss while keeping the bandwidth above 1 MHz.

SIGNIFICANCE

The extremely high efficiency of the proposed mHBC channel provides a solution to the energy problem for miniaturized wearables, potentially leading to new wearable device designs.

In-the-Wild Interference Characterization and Modelling for Electro-Quasistatic-HBC With Miniaturized Wearables

The emergence of Human Body Communication (HBC) as an alternative to wireless body area networks (WBAN) has led to the development of small sized, energy efficient and more secure wearable and implantable devices forming a network in and around the body. Previous studies claim that though HBC is comparatively more secure than WBAN, nevertheless, the electromagnetic (EM) radiative nature of HBC in >10 MHz region makes the information susceptible to eavesdropping. Furthermore, interferences may be picked up by the body due to the human body antenna effect in the 40-400 MHz range. Alternatively, electro-quasistatic (EQS) mode of HBC forms an attractive way for covert data transmission in the sub 10 MHz region by allowing the signal to be contained within the body. However, there is a gap in the knowledge about the mechanism and sources of interference in this region (crucial in allowing for proper choice of data transmission band). In this paper, the interference coupling modality in the EQS region is explained along with its possible sources. Interferences seen by the wearable in the actual scenario is a non-trivial problem and a suitable measurement EQS HBC setup is designed to recreate it by employing a wearable sized measurement setup having a small ground plane. For the first time, a human biophysical interference pickup model is proposed and interference measurement results using a wearable device are presented up to 250 kHz in different environmental settings.

Advanced Biophysical Model to Capture Channel Variability for EQS Capacitive HBC

Human Body Communication (HBC) has come up as a promising alternative to traditional radio frequency (RF) Wireless Body Area Network (WBAN) technologies. This is essentially due to HBC providing a broadband communication channel with enhanced signal security in the physical layer due to lower radiation from the human body as compared to its RF counterparts. An in-depth understanding of the mechanism for the channel loss variability and associated biophysical model needs to be developed before electro-quasistatic (EQS) HBC can be used more frequently in WBAN consumer and medical applications. Recent developments have shown biophysical models that capture the channel response for fixed transmitter and receiver positions on the human body which do not capture the variability in the HBC channel for varying positions of the devices with respect to the body. In this study, we provide a detailed analysis of the change in path loss in a capacitive-HBC channel in the EQS domain. Causes of channel loss variability namely: inter-device coupling and effects of fringe fields due to body's shadowing effects are investigated. FEM based simulation results are used to analyze the channel response of human body for different positions and sizes of the device which are further verified using measurement results to validate the developed biophysical model. Using the biophysical model, we develop a closed form equation for the path loss in a capacitive HBC channel which is then analyzed as a function of the geometric properties of the device and the position with respect to the human body which will help pave the path towards future EQS-HBC WBAN design.

Inter-body coupling in electro-quasistatic human body communication: theory and analysis of security and interference properties

Radiative communication using electromagnetic fields is the backbone of today’s wirelessly connected world, which implies that the physical signals are available for malicious interceptors to snoop within a 5–10 m distance, also increasing interference and reducing channel capacity. Recently, Electro-quasistatic Human Body Communication (EQS-HBC) was demonstrated which utilizes the human body’s conductive properties to communicate without radiating the signals outside the body. Previous experiments showed that an attack with an antenna was unsuccessful at a distance more than 1 cm from the body surface and 15 cm from an EQS-HBC device. However, since this is a new communication modality, it calls for an investigation of new attack modalities—that can potentially exploit the physics utilized in EQS-HBC to break the system. In this study, we present a novel attack method for EQS-HBC devices, using the body of the attacker itself as a coupling surface and capacitive inter-body coupling between the user and the attacker. We develop theoretical understanding backed by experimental results for inter-body coupling, as a function of distance between the subjects. We utilize this newly developed understanding to design EQS-HBC transmitters that minimizes the attack distance through inter-body coupling, as well as the interference among multiple EQS-HBC users due to inter-body coupling. This understanding will allow us to develop more secure and robust EQS-HBC based body area networks in the future.

Electro-Quasistatic Animal Body Communication for Untethered Rodent Biopotential Recording

Continuous multi-channel monitoring of biopotential signals is vital in understanding the body as a whole, facilitating accurate models and predictions in neural research. The current state of the art in wireless technologies for untethered biopotential recordings rely on radiative electromagnetic (EM) fields. In such transmissions, only a small fraction of this energy is received since the EM fields are widely radiated resulting in lossy inefficient systems. Using the body as a communication medium (similar to a 'wire') allows for the containment of the energy within the body, yielding order(s) of magnitude lower energy than radiative EM communication. In this work, we introduce Animal Body Communication (ABC), which utilizes the concept of using the body as a medium into the domain of untethered animal biopotential recording. This work, for the first time, develops the theory and models for animal body communication circuitry and channel loss. Using this theoretical model, a sub-inch[Formula: see text] [1″ × 1″ × 0.4″], custom-designed sensor node is built using off the shelf components which is capable of sensing and transmitting biopotential signals, through the body of the rat at significantly lower powers compared to traditional wireless transmissions. In-vivo experimental analysis proves that ABC successfully transmits acquired electrocardiogram (EKG) signals through the body with correlation [Formula: see text] when compared to traditional wireless communication modalities, with a 50[Formula: see text] reduction in power consumption.

An Active Concentric Electrode for Concurrent EEG Recording and Body-Coupled Communication (BCC) Data Transmission

This paper presents a wearable active concentric electrode for concurrent EEG monitoring and Body-Coupled Communication (BCC) data transmission. A three-layer concentric electrode eliminates the usage of wires. A common mode averaging unit (CMAU) is proposed to cancel not only the continuous common-mode interference (CMI) but also the instantaneous CMI of up to 51V_pp. The localized potential matching technique removes the ground electrode. An open-loop programmable gain amplifier (OPPGA) with the pseudo-resistor-based RC-divider block is presented to save the silicon area. The presented work is the first reported so far to achieve the concurrent EEG signal recording and BCC-based data transmission. The proposed chip achieves 100 dB CMRR and 110 dB PSRR, occupies 0.044 mm², and consumes 7.4 μW with an input-referred noise density of 26 nV/√Hz.

On the Safety of Human Body Communication

Human Body Communication (HBC) utilizes the electrical conductivity properties of the human body to communicate between devices in and around the body. The increased energy-efficiency and security provided by HBC compared to traditional radio wave based communication makes it a promising alternative to communicate between energy constrained wearable and implantable devices around the body.However, HBC requires electrical signals to be transmitted through the body, which makes it essential to have a thorough analysis of the safety aspects of such transmission. This paper looks into the compliance of the current density and electric/magnetic fields generated in different modalities of HBC with the established safety standards. Circuit and Finite Element Method (FEM) based simulations are carried out to quantitatively find the compliance of current density and fields with the established safety limits. The results show the currents and fields in capacitive HBC are orders of magnitude smaller than the specified limits. However, certain excitation modalties in galvanic HBC can result in current densities and fields exceeding the safety limits around the excitation point on the body near the electrode. A study with 7 human subjects (4 male, 3 female) is carried out over a month, using capacitive HBC.The study monitors the change in 5 vital parameters (Heart Rate, Mean Arterial Pressure, Respiration Rate, Peripheral Capillary Oxygen Saturation, Temperature), while wearing a HBC enabled device. Analysis of the acquired data statistically shows no significant change in any of the vital parameters of the subjects, confirming the results of the simulation study.

Robust Intra-Body Communication Using SHA1-CRC Inversion-Based Protection and Error Correction for Securing Electronic Authentication

The explosive increase in the number of IoT devices requires various types of communication methods. This paper presents secure personal authentication using electrostatic coupling Intra-body communication (IBC) based on frequency shift keying (FSK) and error correction. The proposed architecture uses GPIO for a transmitter and analog-to-digital conversion (ADC) for a receiver. We mplemented FSK modulation, demodulation, data protection, and error correction techniques in the MCU software without applying hardware devices. We used the characteristic that the carrier signal is 50% duty square wave for 1-bit error correction and applied a method of randomly inverting SHA1 hash data to protect user authentication data during transmission. The transmitter modulates binary data using a square wave as a carrier signal and transmits data through the human body. The receiver demodulates the signal using ADC and decrypts the demodulated binary data. To determine the carrier frequency from ADC results, we applied a zero-crossing algorithm which is used to detect edge characteristics in image processing. When calculating the threshold value within the zero-crossing algorithm, we implemented an adaptive threshold setting technique utilizing Otsu’s binarization technique. We found that the size of the electrode pad does not affect the signal strength, but the distance between the electrode pad and the skin has a significant effect on the signal strength. Our results show that binary data modulated with a square wave can be successfully transmitted through the human body, and, when 1-bit error correction is applied, the byte error rate on the receiver side is improved around 3.5% compared to not applying it.

Wireless Body Sensor Communication Systems Based on UWB and IBC Technologies: State-of-the-Art and Open Challenges

In recent years there has been an increasing need for miniature, low-cost, commercially accessible, and user-friendly sensor solutions for wireless body area networks (WBAN), which has led to the adoption of new physical communication interfaces providing distinctive advantages over traditional wireless technologies. Ultra-wideband (UWB) and intrabody communication (IBC) have been the subject of intensive research in recent years due to their promising characteristics as means for short-range, low-power, and low-data-rate wireless interfaces for interconnection of various sensors and devices placed on, inside, or in the close vicinity of the human body. The need for safe and standardized solutions has resulted in the development of two relevant standards, IEEE 802.15.4 (for UWB) and IEEE 802.15.6 (for UWB and IBC), respectively. This paper presents an in-depth overview of recent studies and advances in the field of application of UWB and IBC technologies for wireless body sensor communication systems.

The Role and Challenges of Body Channel Communication in Wearable Flexible Electronics

Flexible electronics are compatible with film substrates that are soft and stretchable, resulting in conformal integration with human body. Integrated with various sensors and communication ICs, wearable flexible electronics are able to effectively track human vital signs without affecting the body activities. Such a wearable flexible system contains a sensor, a front-end amplifier (FEA), an analog-to-digital converter (ADC), a micro-controller unit (MCU), a radio, a power management unit (PMU), where the radio is the design bottleneck due to its high power consumption. Different from conventional wireless communications, body channel communication (BCC) uses the human body surface as the signal transmission medium resulting in less signal loss and low power consumption. However, there are some design challenges in BCC, including body channel model, backward loss, variable contact impedance, stringent spectral mask, crystalless design, body antenna effect, etc. In this paper, we conduct a survey on BCC transceiver, and analyze its potential role and challenges in wearable flexible electronics.

Wide Frequency Characterization of Intra-Body Communication for Leadless Pacemakers

Leadless Cardiac Pacemakers (LCP) have the potential to revolutionize Cardiac Rhythm Management (CRM). Current LCPs can only pace a single location of the heart limiting their use to patients requiring single-chamber stimulation. A Multi-node system of synchronized LCPs could be used in a significantly larger patient population. Synchronization using standard communication techniques involves high power consumption decreasing the longevity of the device. In this work, we investigate Galvanic Intra Body Communication (IBC) as a method to synchronize multi-node LCP systems. First, an accurate computational torso model was used for quasi-static simulations to estimate channel pathloss in the frequency range [40 kHz-20 MHz]. The model was then verified with in-vivo measurements using a novel experimental setup, where two LCP devices were placed in the right atrium, right ventricle and left ventricle. All channels involved in a potential multi-node LCP system were characterized. The orientation of the transducers relative to each other had a great impact on the results, with the attenuation level ranging between 55 dB and 70 dB between the best and worst orientations. The best results were achieved in the MHz range. Coupled with the fact that it does not require additional electrodes, this study suggests Galvanic IBC be superior to conventional communication methods for LCP devices. This analysis defines a methodology for galvanic IBC channel characterization for LCP systems, which is an important step for the design of efficient transceivers for IBC applications. More experiments with larger datasets are needed to bring this method to practice.

An Improved Update Rate CDR for Interference Robust Broadband Human Body Communication Receiver

Broadband Human Body Communication (HBC) enables energy efficient communication between body area network devices by utilizing the electrical conductivity property of the human body. However, environmental interference remains a primary bottleneck in its implementation. An integrating front-end receiver with resettable integration followed by periodic sampling can be utilized to enable interference robust broadband HBC. However, as required in all broadband communication systems, a Clock Data Recovery (CDR) loop is necessary to correctly sample the received data at the appropriate instant. The CDR is required to be sensitive to the clock-data phase mismatch at the receiver end and take corrective action for reducing it, similar to the CDR of a traditional receiver. In addition to that, the CDR for a broadband HBC receiver also requires to be tolerant to environmental interference. This paper analyzes the traditional Baud Rate CDR for an integrating front-end receiver and proposes a modified integrating CDR architecture with a higher update rate. Simulation results show 2.5X higher clock data frequency offset tolerance of the proposed CDR compared to the traditional Baud Rate CDR, >1.25X higher clock data frequency offset tolerance in presence of interference and >10% interference frequency offset tolerance with respect to the integration clock. The proposed CDR is also implemented in a Xilinx Spartan-3E FPGA board to validate its closed loop functionality in real time.

Enabling Covert Body Area Network using Electro-Quasistatic Human Body Communication

Radiative communication using electro-magnetic (EM) fields amongst the wearable and implantable devices act as the backbone for information exchange around a human body, thereby enabling prime applications in the fields of connected healthcare, electroceuticals, neuroscience, augmented and virtual reality. However, owing to such radiative nature of the traditional wireless communication, EM signals propagate in all directions, inadvertently allowing an eavesdropper to intercept the information. In this context, the human body, primarily due to its high water content, has emerged as a medium for low-loss transmission, termed human body communication (HBC), enabling energy-efficient means for wearable communication. However, conventional HBC implementations suffer from significant radiation which also compromises security. In this article, we present Electro-Quasistatic Human Body Communication (EQS-HBC), a method for localizing signals within the body using low-frequency carrier-less (broadband) transmission, thereby making it extremely difficult for a nearby eavesdropper to intercept critical private data, thus producing a covert communication channel, i.e. the human body. This work, for the first time, demonstrates and analyzes the improvement in private space enabled by EQS-HBC. Detailed experiments, supported by theoretical modeling and analysis, reveal that the quasi-static (QS) leakage due to the on-body EQS-HBC transmitter-human body interface is detectable up to <0.15 m, whereas the human body alone leaks only up to ~0.01 m, compared to >5 m detection range for on-body EM wireless communication, highlighting the underlying advantage of EQS-HBC to enable covert communication.