## 2 Sensing Method
### Capacitive Sensing and Inductive Sensing
#### 2.3.1 Applied Technologies  
Owing to the uncomplicated structure of the LC resonant circuit, researchers have conducted diverse optimizations on it. [PERSON] developed an inductor-capacitor passive wireless sensor featuring a nonlinear parity-time symmetric structure [59]. The quality factor of the LC passive wireless sensor with a PT symmetric structure, based on linear loss and saturated gain, was theoretically put forward and experimentally validatedto be improved. Under the small perturbation limit, the response singularity in this approach implies the enhancement of sensing performance (Figure 2a). Furthermore, [PERSON] conducted a structural design of the inductor within the resonant system [60]. A serpentine spiral structure inductor was employed. In contrast to the traditional spiral coil, the serpentine spiral coil offers lower radial stiffness. When the inductor is subjected to axial pressure, the spiral inductor undergoes axial compression. When the serpentine angle is zero, the inductor reverts to a traditional spiral inductor. Either increasing the distributed length or decreasing the cross-sectional area can reduce the inductance, thereby increasing the resonant frequency. Under the same axial load, the  
Figure 2: (**a**) Under different perturbations of nonlinear and linear systems, the functional relationships between the real and imaginary parts of the characteristic frequency and the coupling strength relative to the loss, as well as the wearable wireless LC sensor fabricated based on this principle. (**b**) In the design of the inductive bracket, a conductive Au ring and a non-conductive polyimide (PI) connector are used to achieve a solenoid-like current path and bracket structure. At the same time, a soft pressure sensor layer is constructed on its surface by means of a printed dielectric layer. In the third-level images, the inductive bracket design employs conductive Au rings and non-conductive polyimide connectors to realize a solenoid-like current path. Simultaneously, a printed dielectric layer is utilized to fabricate the soft pressure sensor layer. (**c**) The basic structure of PSIFS (**d**) The EndoSure sensor. (**e**) a deconstruction schematic diagram of the main components of the mode, which includes a CMOS temperature sensor chip with two exposed aluminum (Al) pads, a micro lead zirconate titanate (PZT) sensor coated with gold on both sides, an anisotropic conductive film (ACF), and a copper layer. This device can be implanted in the body with the help of a syringe. The presented content encompasses scanning electron microscope images of the microspheres. These microspheres exhibit a diameter of 300 \(\upmu\)m, a length of 380 \(\upmu\)m, a thickness of 570 \(\upmu\)m (equivalent to a volume of 0.065 mm\({}^{3}\)), and a weight of 0.3 mg. They are positioned at the tip of an 18 g needle, with an inner diameter of 0.84 mm and an outer diameter of 1.28 mm. (**f**) Design of the hydrogel-based structures used for implantation. more pronounced the change in the resonant frequency of the LC resonant sensor, the higher the sensitivity that the LC sensor can achieve. The dimensions of implantable sensors and their compatibility with vascular surgical procedures have long imposed limitations on the morphological design of implantable devices. [PERSON] developed a three-dimensional sensor that circumferentially enwraps the exterior of arterial blood vessels [61]. A conductive loop, in conjunction with non-conductive connectors, forms a conductive pathway resembling a solenoid, which serves as an inductive antenna (Figure 2b). Simultaneously, multiple soft capacitive sensors are integrated onto the inner surface of the stent. This system facilitates the concurrent monitoring of pressure, pulse rate, and flow rate. Given that the stent is fabricated using femtosecond laser technology, it can undergo stretching and contraction to accommodate arterial blood vessels of diverse shapes, thereby demonstrating excellent versatility.