Skin-Deep Communication: Using the Human Body to Transmit Biodata amongst Wearable Medical Devices
Dr. Ibrahim Elfadel showcases the first ever successful body-coupled communication transmission at the 41st Engineering in Medicine and Biology Conference in Berlin, Germany
It’s been ten years since FitBit released its first health wearable, and now, roughly one in four adults uses some kind of fitness tracking device. While most people use them to gain some insight to their sleeping patterns and daily exercise, for some, wearable data-collection tools are medically necessary. In the world of healthcare, there is huge demand for remote and continuous patient monitoring.
A research project led by Dr. Ibrahim Elfadel, Professor of Electrical Engineering and Computer Science at Khalifa University, with Dr. Shahzad Muzaffar, Postdoctoral Researcher, Dr. Jerald Yoo, former KU Associate Professor of Electrical and Computer Engineering, now with the National University of Singapore, Dr. Ayman Shabra, former KU Assistant Professor of Electrical and Computer Engineering, now with MediaTek, MA, USA, and Dr. Mihai Sanduleanu, Associate Professor of Electrical Engineering and Computer Science, has resulted in the development of a working prototype of a body-coupled communication transceiver that transmits and receives information using human skin as a communication medium. The project began in 2014, and since then, a full hardware platform showcasing the body-coupled communication link has been demonstrated. Funded in part by a grant from Al Jalila Foundation, a UAE medical foundation supporting biomedical research, the signal encoding part of the research has been published in journal articles, conference papers and book chapters. Additionally, several US patents have been filed for the technology.
“Our research aims to provide secure, ultra-low-power communication between wearable medical devices such as hearing aids, vital sign monitors, and personal safety trackers,” said Dr. Elfadel. “This research also has relevance to the healthcare component of the UAE Innovation Strategy and its 2030 vision. In particular, this research enables the development of novel secure, reliable, predictive health monitoring platforms that may be used to diagnose, monitor, and treat diseases with high UAE incidence, such as obesity and diabetes.”
Individuals with high blood pressure, for example, have always been tasked with taking at-home readings to discuss with their healthcare providers. Replacing the standard blood pressure measuring device with a simple wearable tracker makes things easier.
“Wearable devices have always been the focus of active research, and technology advances have made it possible to develop sophisticated wearable electronic devices such as smart watches, smart eyeglasses, and fitness and lifestyle monitors,” explained Dr. Elfadel. “Reliable real-time communication amongst these body-worn devices plays a key role in the synchronous collection of information about the human body and its environmental conditions, and therefore, in the enablement of a new era of portable diagnosis and personalized care.”
Beyond medical necessity, there’s commercial opportunity here too: people worldwide are used to measuring their health using tools like body mass index (BMI) and resting heart rate. Advances in wearable technology have made trackers more accessible and appealing to consumers interested in measuring more variables. Industry analyst CCS Insight says worldwide wearables sales will grow by an average of 20 percent each year over the next four years, becoming a US$29 billion market by 2022.
However, these devices are limited by their power-hungry nature. To enrich data collection, wearables—particularly fitness trackers worn on the wrist—contain multiple sensors to supply large volumes of data about location, motion, physiological condition and other metrics useful to the person wearing the device. The more sensors, the greater the power consumption.
“Existing wireless standards are power-hungry and are known to drain the batteries quickly while wired communication is in conflict with the stringent wearablility requirement,” said Dr. Elfadel. “The ability to transmit and receive data at a very low energy-per-bit is an essential characteristic of wearable devices as they need to remain operational during days, and even weeks, of continuous usage. An alternative to wired or wireless communication is body-coupled communication (BCC) which uses the human skin as a communication medium.”
Human body communication involves the body acting as the communication channel for an electrical signal, with the signal transmitted primarily through the skin. Normally, devices on the body communicate wirelessly through radio frequency technology, but BCC provides a more power efficient and secure means of communication. A transmitter injects an alternating current into the skin, which acts like a wire to carry the signal throughout the body. This signal causes a voltage to appear across two receiving electrodes elsewhere on the body.
“Using human skin as a communication medium has been attempted before but prior work has used traditional signal encoding, leading to the design of complex communication circuits. So while the medium is totally secure, such complex circuits have a high power consumption and their testing has been restricted to predictable, well-controlled signals, such as clock signals,” added Dr. Elfadel. “What makes this project unique is the use of a new signal encoding technique that facilitates the design of simple communication circuits with minimal power requirements. The medium also lends itself to tight integration with electrode-based medical monitoring devices for the brain and heart and also smart band aids.”
Because the signal is completely contained within the human body, the performance is not affected by the surrounding environment. However, the body is not a perfect wire and affects the signal in non-ideal ways, one of which is adding a delay and necessitating a transmission power limit. The injected current must be low enough as to not damage any nerves or tissue, especially when applied over a long time. Concurrently, the current also needs to be strong enough to withstand the effects of the electrical properties of the human body. The relative permittivity (how well an electromagnetic wave can pass through a material) of skin, fat, muscle, and bone affects the signal. Signal attenuation, where the signal strength weakens, increases exponentially with distance when transmitting over the arms and legs, with joints also increasing the attenuation.
Dr. Elfadel and his team used Pulse-Index Communication (PIC)-based BCC transceivers to facilitate successful bi-directional communication through the body by transmitting arbitrary 16-bit data words over a distance of 150cm and receiving them flawlessly in a round-trip configuration.
“To the best of our knowledge, this is the very first time such BCC transmission has been achieved,” said Dr. Elfadel. “Future work will tackle an integrated very-large-scale integration (VLSI) implementation of the PIC-based BCC transceiver along with the validation of such transceiver in the presence of link non-idealities such as multipath fading, variable-ground effect, and variable skin-electrode impedance.
“Our next step is the miniaturization of the BCC circuits to reduce their form factors and improve their flexibility for seamless integration with wearable medical devices. The main challenge we are currently facing in this research is the development of reliable and flexible electrodes that can be comfortably integrated with wearable healthcare monitors so that a robust body-area network can be established among them.
“We hope to demonstrate to the UAE medical and healthcare professionals the significant potential of home-grown biomedical engineering research at Khalifa University. Our research may trigger further fundamental research into the electrophysiological properties of human skin on which physiologists, dermatologists, and biomedical engineers may be able to collaborate across the boundaries of their disciplines.”
News and Features Writer
14 August 2019