In-body communication is a key enabler for next-generation healthcare applications, allowing seamless networking of implants. Fat tissue, with its lower water content and reduced signal attenuation compared to other body tissues at microwave frequencies, has emerged as a promising medium for radio-based in-body networks. Despite this advantage, signal leakage through the body can compromise privacy, exposing sensitive data and the mere presence of implants to external adversaries. This paper investigates the feasibility of covert communication in fat tissue-based in-body networks by leveraging the previously unexplored signal attenuation properties of human tissue to transmit data undetectable to adversaries, ensuring privacy beyond encryption. We develop a system in which an implanted transmitter communicates discreetly with an implanted receiver, shielded from external passive eavesdroppers. Our theoretical analysis and experimental results demonstrate that the attenuation properties of human tissues enable covert communication at reduced transmit power levels without requiring friendly jamming, unlike over-the-air systems. To further enhance covertness, we explore the use of an external friendly jammer and show its significant benefits. Experimental results show a 500% increase in the maximum channel capacity of covert communication, from 2.86 bps/Hz at -56 dBm transmit power without jamming, to 17 bps/Hz with no bit errors at 0 dBm transmit power with a friendly jammer, using the IEEE 802.15.4 standard for communication in the 2.45 GHz frequency band. These findings highlight that covert communication is achievable in fat tissue-based in-body networks at low data rates without additional infrastructure such as an external jammer. For applications requiring higher data rates, a friendly jammer offers a scalable solution, making this approach practical for a wide range of implant communication scenarios.

Innovative medical applications based on networked implants foster the development of in-body communication technologies. Among the in-body communication technologies that are being considered, fat intra-body communication (Fat-IBC) is a very recent approach. Its main advantage lies in its higher data rate compared to earlier approaches based on capacitive and galvanic coupling. However, Fat-IBC faces privacy-, security-, as well as safety-related attacks. In this paper, we discuss security and privacy concerns about Fat-IBC, as well as corresponding countermeasures. Furthermore, we present our secure protocol stack for Fat-IBC and suggest directions for future research.

Medical implants are becoming increasingly widespread, and with that comes a need for networking multiple implants in the human body. This puts new demands on in-body communication, where conventional techniques (such as galvanic coupling) suffer from low bandwidth and data rates that can be insufficient for a network with several medical implants. Radio-based techniques at microwave frequencies can, on the other hand, provide a high-capacity communication channel, with the caveat that wave propagation through bodily materials at such frequencies is associated with significant signal loss, which limits the range. Fat tissue has been shown to have low loss compared to other tissues at frequencies such as 2.45 GHz and 5.8 GHz and could be a good choice of medium for a high-capacity channel. However, a drawback of radio-based in-body communication remains: signals may "leak'' out of the channel to the outside environment. This work investigates the leakage aspects of fat tissue-based in-body communication and explores methods for preserving the privacy of data from implants communicating through fat tissue. Through both simulations and practical experiments, we show that signals are heavily attenuated (on average by about 27 dB) when leaving the fat channel through the skin. Signal attenuation through the skin layer is similar even when the channel is not straight. Additionally, we demonstrate that reducing the transmit power as well as using an external, friendly "jamming'' signal can prevent that an external eavesdropper receives the data packets. In summary, we show that there is indeed RF leakage from in-body communication through fat tissue. However, the skin layer attenuates the signal quite heavily so that reducing the transmit power in combination with external jamming may prevent eavesdroppers outside the body from receiving sensitive in-body data.

Though fat channel communication has advantages over earlier intra-body communication (IBC) technologies based on galvanic or capacitive coupling, the development of a protocol stack on top of fat channel communication is still at its infancy. In this paper, we consider Krentz's denial-of-sleep-resilient multi-channel medium access control (MAC) layer for IEEE 802.15.4 networks as a starting point for such a protocol stack. In brief, we conducted the following experiment with a phantom that mimics human tissues. Two devices exchanged IEEE 802.15.4 radio frames in a ping-pong manner on the phantom's fat tissue using Krentz's MAC layer. The data collected from this experiment lends itself to two purposes. First, it can serve to benchmark and tune algorithms for selecting radio channels. Second, it can also serve to benchmark and tune schemes for deriving cryptographic keys from received signal strength indicator (RSSI) readings. We made the data available at https://uppsala.box.com/s/z2a6jpigswpoifd5l73yophokcfwd88b.

In the near future more and more people will have multiple implants to handle their diseases. The implants benefit from being connected using in-body sensor networks. We have previously shown that RF communication through human adipose (fat) tissue is feasible. In this poster, we argue why we believe that backscatter communication within this fat channel is possible. As security is of utmost importance for in-body communication, we also discuss how backscatter-based in-body networks can be secured.

The paper presents a novel non-invasive microwave technique for monitoring salt concentration in pure water. The technique is based on near field analysis of open ended coaxial probe (OECP) sensor with material under test (MUT) using plane wave spectrum theory. The proposed technique is compared with experimental results for various concentration of salt solution between 1GHz to 10GHz range. The computed result shows good agreement with experiment. The microwave technique shows better result at lower microwave frequency as compared to higher frequency. At 2GHz range the response of the technique and measurement shows a linear relationship with the salt concentration. The technique shows the potential of extracting the physical parameter, like permittivity, of the salty water.