## 4 Biosensors in the Field of Healthcare
### Wireless Communication and Data Transfer  
Wireless technology is useful for delivering power to implantable devices but must adhere to regulated Specific Absorption Rates (SARs). That is, the power absorbed per mass of tissue in Watts/kg such as for use of implants during MRI scanning is covered under ISO/TS 10974:2018 (see [[https://www.fda.gov/](https://www.fda.gov/)]([https://www.fda.gov/](https://www.fda.gov/))). With transmitting recorded biological data to external units, WPT holds the potential to enable miniaturised and longer-lasting bio-systems compared to battery-powered alternatives. The previously mentioned WPT methods for transmitting power to biomedical implants can also be employed for data transmission, using so-called dual function antennas (DFAs). Near-field communication (NFC), a type of radiofrequency identification (RFID), is dominantly used for wireless data transfer within short distances. NFC offers secure wireless data transfer, with lower power loss and higher safety with human tissues. Thus, it is employed in many sectors, including medicine and businesses [143; 154]. The communication between an implanted device and an external system can be divided into two sections based on the signal direction. Uplink refers to data that are sent from the implant to the external system, whereas downlink is used for signals sent from the external unit to the implanted device [155]. In general, two independent wireless links are thus far mandatory: one for power transfer and another for data transmission. Power transfer is more effective with narrowband links at low frequencies, as they show high power transfer efficiency and are less susceptible to noise and dissipation in the body tissue. In contrast, data transmission demands wider bandwidth links that operate at higher frequencies to leverage high-rate data transfer [156]. Having two separate links introduce multiple coils is known as a major drawback. This is because it increases the complexity and bulkiness of the biomedical device in addition to introducing unwanted signal interference. Conversely, a single pair of coils has been proposed to carry power and data simultaneously over a single frequency. The single  
Figure 8: Schematic illustration of different methods of WPT. (**A**) IC between two short-distanced coils. The concept of IC was primarily invented by [PERSON] in the 19 th century. (**B**) Capacitive coupling demonstrated by two plates acting as transmitter and receiver coils. (**C**) MRC contains four coils. (**D**) The innovative MF benefited from a patterned metal plate with four ports that focus energy on the targeted surface, enabling efficient power penetration through the tissue. (**E**) Theoretical illustration of MD energy propagation through the body tissue, reaching the biomedical implant (red dot) at a depth of \(>\)5 cm. (**F**) FF scheme showing radiation of RF in many lobes, but predominantly towards the receiving coil. Source: [143; 149]. frequency principle has fundamental benefits that help reduce device complexity, size, and cost. However, the use of a single wireless inductive link to achieve simultaneous high power efficiency and high data rates is the desired goal but remains challenging. However, it is expected to overcome this challenge by using appropriate modulation techniques for power and data transmission over a single link [157]. Modulation techniques are defined as a conversion of signal waves into carrier waves to transmit data. This occurs by applying changes to the signal wave parameters such as amplitude, phase, and frequency. Using modulation techniques introduces numerous advantages, including low power consumption, less sensitivity to noise, and high-rate data transmission [158]. Currently, several modulations have been used to wirelessly transfer data from external units into implants (downlink). These modulations are amplitude-shift keying (ASK), phase-shift keying (PSK), and frequency-shift keying (FSK).