# A Low-Cost Electronic System for Human-Body Communication
## 2 Related Work  
This section presents an overview of the state-of-the-art works related to human-body communication, which is a promising communication tool for body area networks. Traditional BANs commonly use air as the medium for data transmissions, which makes the system inherently insecure [3]. Data security and privacy are the critical aspects of most human-centered applications, including devices for healthcare. Hence, we advocate restricting the transmission of signals entirely within the body to prevent improper access to sensitive data. Thus, we focus on galvanic coupling communication, which is out of scope using technologies that propagate signals to the environment around the body, such as traditional radiofrequency, acoustic waves, and electromagnetic fields. Most current works focus on the design of wireless body area networks (WBANs) human-body communication architecture. In most cases, these works rely on radio frequency or electromagnetic-based communication. For example, [PERSON] et al. [6] analyze the signal transmission paths of one and two electrodes by a numerical electromagnetic field analysis based on capacitive coupling. This work analyzes the signal transmission paths by comparing the electric field vector distributions and the electric currents in the human arm. The results support using a two-electrode transmitter because of better signal quality reception. [PERSON] et al. [16] design a new class of wideband active wearable antennas for medical applications. The amplifiers may be connected to the wearable antenna feed line to increase the dynamic system range. The active slot antenna gain is 13 \(\pm\) 2 dB for frequencies from 800 MHz to 3 GHz. Finally, we can also show specific applications of HBC. For example, [PERSON] et al. [17] developed an HBC endoscopy capsule. The system is composed of one transmitter and one receiver with multiple receiving electrodes. Moreover, the authors present a selection algorithm to find the electrode pairs that result in the best receiving channel. As we previously stated, in this work we focus on galvanic coupling communication. From the literature, one can observe different studies related to galvanic communication [9; 10; 11; 12; 13; 14; 15]. The prominent and important problem addressed by the majority of these studies lies in modeling the body as a physical environment for the propagation of signals over short distances (up to 20 cm), performing an empirical analysis of the human tissue properties. Therefore, these systems do not present a commitment to hardware miniaturization, as they use transformers and even signal generators. In [10], the authors explore the development of complete and miniaturized hardware for differential signal coupling, supported by emerging HBC communication technology. The presented device allows achieving a bandwidth of 4.8 kbps through demodulation performed by a field-programmable gate array (FPGA). These values, measured in the aqueous ionic environment, simulate human electrical properties. Our work follows the same principles. However, we have unlinked the responsibility for online data decoding by a sensing amplifier. This action has added flexibility for modulation alternatives and lower project development costs. Furthermore, we reduced interference in the common mode by using the third electrode. As a result, we obtained an approximately 2.3-fold increase in flow rate, considering experiments with human tissues at a distance of 12 cm between the transmitter and receiver device electrodes. [PERSON] et al. [15] developed an equivalent electrical circuit model of the human arm-wrist-palm tissue channel to perform the pure transmission of ECG signals. The purpose of this system is to perform unilateral user authentication. The authors carry out the validation by implementing a simplified embedded system and a synthetic ghost fabric. They claim that the system works reliably, transmitting data at a distance of 10 cm while maintaining a \(10^{-6}\) bit error rate.