## 3 Wireless Communication and Power Transmission
### Wireless Information Transmission
The measurement data is transmitted to the patient monitor via RFID technology [93]. Medtronic's Chronicle, an implantable hemodynamic monitor, integrates cardiac electrophysiological monitoring with a right ventricular pressure sensor. This device aids doctors in managing heart failure patients by closely monitoring heart function and pressure variations [94]. VeriChip Corporation has developed an implantable RFID tag that can be implanted in the upper arm. By transmitting a unique serial number, it facilitates medical professionals in swiftly retrieving the patient's medical information. Even when the patient is unconscious or unresponsive during surgery, doctors can precisely obtain the necessary information. Near Field Communication: NFC provides high-speed data transmission over short distances. This transmission method has high security and can protect user privacy well. However, its effective distance is short, and it is only suitable for body surface sensors [95]. Simultaneously, when dealing with scenarios that demand high-capacity data transmission, the transmission rate of NFC often falls short of meeting the requirements. Implantable sensors leveraging near-field communication have been successfully developed [96]. These sensors can effectively address the issue of implantable sensors relying on battery power. Moreover, several commercial sensors operating on this principle have already found practical applications. For instance, the flexible NFC skin tags developed by Gentag are capable of monitoring patients' activities and vital signs. They can transmit the collected data to external devices via NFC technology. These tags utilize a flexible polymer substrate and are attached to the skin for non-invasive biophysical measurements. The data is then collected using smartphones [97]. Magnetic Induction Coupling: This transmission method is grounded in the principle of electromagnetic field resonance. The implanted component therein is, in fact, a resonator. The characteristics of the implanted resonator undergo changes in accordance with the variation in the target signal, thereby generating a signal that can be remotely measured. The parameter to be measured is traced by gauging the alteration in the resonance frequency [98]. Typically, passive transmission sensors can be classified into LC resonators, radiofrequency cavity types, patch antenna types, surface acoustic wave (SAW) types, etc. [99; 100; 101]. The merits of this wireless communication mode include the absence of a re quirement for an implanted battery, a simple structure, a compact volume, and convenience for mass production. Nevertheless, a drawback is that the reading accuracy is significantly influenced by environmental factors (such as motion interference and electromagnetic interference). Also, during the reading process, the sensor and the reader must maintain a fixed distance and a specific alignment method; otherwise, the detection results will be compromised [102]. Furthermore, the effective transmission distance of electromagnetic coupling is restricted, and a small distance needs to be maintained between the reading device and the sensor [56]. Furthermore, when multiple sensors communicate concurrently, electromagnetic field interference will arise, leading to the inability of reading the data of a single tag. Special coding or modulation techniques are thus necessary to address this issue [103]. In the commercial domain, passive transmission sensors are also extensively employed in disease monitoring and prevention. The first human implantable inferior vena cava (IVC) sensor, FUTURE-HF, can be utilized for the surveillance of cardiovascular diseases like heart failure. Its volume measurement exhibits a high degree of consistency with the CT results (R2 = 0.98). A 6-month follow-up reveals that NT-proBNP has significantly decreased (\(p\) = 0.026) and heart failure events are reduced by 80.3%, offering precise technical support for remote congestion management [104].