Scientists from the Tokyo University of Science have demonstrated the potential of human body communications by designing binaural hearing aids that safely use head tissue as the transmission medium for electromagnetic signals. Progress in miniaturization and wireless communications has given rise to wearable devices for medical monitors to AR/VR headwear. While the traditional method of transmitting signals relies on wireless technology, for wearables to truly transcend, they will require a more efficient form of communication, such as wireless body area networks (WBAN). Those networks have their drawbacks, including being unsafe from a cybersecurity standpoint, absorbing electromagnetic radiation, and having a tendency to block signals.
Another solution would be to take advantage of human body communications (HBCs), which use the human body to transmit signals. HBCs work by tapping into the electric fields that propagate inside the human body, which can then be used with skin-worn devices outfitted with electrodes to communicate with other devices using low frequencies. Although the technology is over two decades old, little has been done to put it to use on a large scale.
To demonstrate its potential, the scientists designed their binaural hearing aids, which improve intelligibility and sound localization for the wearer by communicating with each other to adapt to the sound field. In a recent study, the scientists, led by Dairoku Muramatsu, investigated — via detailed numerical simulations — how electric fields emitted from an electrode in one ear are distributed in the human head and reach a receiving electrode on the opposite ear, and whether it could be leveraged in a digital communication system.
Not only did they find they could do it, but they could also do it safely. They also explored the effects of various system parameters and characteristics, leading them to determine the best electrode structure for use in HBCs.
The study shows the potential of HBCs through the use of binaural hearing aids, but that’s only the beginning of their potential use. Muramatsu answered our questions about the technology — its advantages, potential applications, and drawbacks.
1: Does skin composition make a difference with HBC? For instance, some have more layers, while others tend to sweat more.
Yes, skin composition and sweat affect the characteristics of the antenna (electrodes) and the communication quality of HBC. As an approach to this problem, we have investigated the important characteristics of HBC against individual differences by the experiment with real human subjects. The results show that individual differences can be suppressed by selecting appropriate design parameters such as carrier frequency. These results were also published in the journal Electronics.
2: While HBC devices can be used by the individual, would it be possible to communicate with others using the same technology? Is distance a factor?
Yes, HBC can be used for multi-user communication as well as for single-user communication. Communication requires physical contact between users, such as a handshake, and will not work if there is a distance between them. Read more via the Association for Computing Machinery.
3: Does the environment play a role? Would it be possible to use HBC devices underwater or in areas with extreme heat or cold?
In the example of underwater communication, general radio communication is unavailable because electromagnetic waves are absorbed by seawater, which contains a large amount of salt. Therefore, ultrasonic waves and light are usually used for wireless communication underwater. Since HBC uses the human body as a transmission channel instead of seawater, there is a possibility that HBC realizes low-loss wireless communication even underwater. Temperature does not affect the mechanism of HBC. However, since HBC devices are composed of general electronic circuits, the needs of the environment in which such circuits can operate are considered.
The researchers reported that measurements using a prototype wearable antenna and 22 human subjects revealed that HBC is “robust against the variations of individual users from the viewpoint of the voltage standing wave ratio.”