Ultra low-power wireless communication through the human body using magnetic fields
Be it on the inside or the outside, the human body is becoming host to an ever-increasing array of electronic devices that need to wirelessly communicate with each other. Now engineers working at the Universityof California, San Diego (UCSD) have come up with a different type of wireless communication that sends ultra low-power magnetic fields through the human body. This makes it extraordinarily more energy efficient and secure from prying eyes than comparable wireless communication technologies.
Connecting and communicating with devices in and around the human body, such as smartwatches, implanted smart monitors, or even ingestible wireless sensors, generally requires that each of these transmit to a receiver using Bluetooth. Since the electromagnetic radiation used by Bluetooth to transmit data does not easily pass through the human body, these devices must use a lot of power and therefore also carry relatively bulky batteries to power their transmitters.
Thoughstill in development, the engineers say their new system is superiorto existing radio communications technologies in this field, claiming path losses an incredible 10 million times lower than those associated with comparable Bluetooth device communication.
"Inthe future, people are going to be wearing more electronics, such as smartwatches, fitness trackers and health monitors," says Patrick Mercier, a professor in the Department of Electrical and Computer Engineering at UCSD and lead author of the study. "All of these devices will needto communicate information with each other. Currently, these devicestransmit information using Bluetooth radios, which use a lot of power tocommunicate. We're trying to find new ways to communicate information aroundthe human body that use much less power."
Toconstruct their prototype, the engineers used coils of copper wires insulatedwith PVC tubing. At one end of this arrangement, the wires terminate at areceiver and analyzer, while at the other end the wires are formed into coils thatwind around three parts of the body: the head, the arms, and the legs. In this way, the coils act as inductors forthe application of energy and the production of magnetic fields and allowthe body itself to act as a sort of waveguide for those fields. Using this system, the researcherswere able to transmit and measure ultra-low path loss signals from from arm to arm, from arm to head, and from arm to leg.
"Thistechnique, to our knowledge, achieves the lowest path losses out of anywireless human body communication system that's been demonstrated so far," said professor Mercier. "Thistechnique will allow us to build much lower power wearable devices."
Creatingdevices with lower power requirements will, in turn, reduce batteryrequirements, leading to smaller and more efficient devices. In this way, not onlycould wearables and monitors be made smaller with longer battery life, but itwould also reduce the size of ingestible transmitters to something much easier to swallow.
"Aproblem with wearable devices like smart watches is that they have shortoperating times because they are limited to using small batteries,” saidJiwoong Park, a Ph.D student in Mercier's lab. “With this magnetic field humanbody communication system, we hope to significantly reduce power consumption aswell as how frequently users need to recharge their devices."
Accordingto the researchers, beyond the benefits of ultra-low-power energy consumption, magneticfield human body communication may offer greater security than current wireless communication technologies. This is because Bluetooth radio communication links take placethrough open air and, potentially, someone could possibly intercept these signals and compromise a person's privacy.
With magneticfield human body communication, however, the communication is contained withinthe body itself and does not need to link to separate wireless devices. When monitoring the system, the researchers measured a dramatic decrease in signals radiated from the body and almost no possibility of transmitting information from one person’s magnetic communication system to another, even in close proximity.
"Increased privacy is desirable when you're using your wearable devices to transmit information about your health," said Jiwoong Park, a Ph.D student in Mercier’s Energy-Efficient Microsystems Lab.
The major downside of the technology is, although it is suitable for devices that wrap around a part of the body, such a smart watches, headbands and belts, it won't work with things like small patches stuck on the skin. This is because the magnetic fields need circular geometries to propagate through the human body.
The results of this research were recently presented at the 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society in Milan, Italy.
Source: UC San Diego