# Helmholtz Coils Based WPT Coupling Analysis of Temporal Interference Electrical Stimulation System
## 4 Discussion  
This paper proposes a novel temporally interfering WPT electrical stimulation system based on Helmholtz coils. After the proposed system's theoretical derivation and model construction, the magnetic field distribution of the system after interference was obtained by numerical calculation. The results of the calculations proved the uniformity and stability of the magnetic field of the proposed system. The analysis shows that a non-physical dynamic adjustment of the stimulation location can be achieved by varying the magnitude of the emitter current. The current waveform of the receiving coil in the experimental results also verifies the feasibility of the proposed system to achieve effective stimulation of the sciatic nerve.  
This system has two main advantages compared to conventional MCR-WPT units [12; 13]. One uses the magnetic field superposition principle of temporal interference, which eliminates the need for a signal conversion device in the conventional MCR-WPT. Removing the battery-related components not only reduces the size of the implanted part but also eliminates concerns about the healthy life of the battery [7]. There is also no need to face the secondary trauma and financial burden of battery replacement [9]. The other one uses Helmholtz coils as the system's transmitting coils. In contrast to the frequency tracking method and the optimal load tracking method [34; 35], which are matched by real-time communication, this system can achieve a stable energy transmission without relying on communication between the transmitting and receiving coils by improving the coil structure. This ensures a maximum magnetic field uniformity so that the receiving coil receives a stable and continuous electrical stimulation. In contrast to SCS [4; 47], this system concentrates the area of stimulation and has no additional effect on the non-target areas, making it possible to provide an efficient and focused treatment of the lesion. In addition,  
Figure 11: Current waveform at the receiving coil.  
as this system does not involve the puncture of the spinal canal, it does not lead to several complications, such as cerebrospinal fluid leakage caused by SCS [48].  
Calculating the stimulation location of a temporally interfering magnetic field in the human body needs to consider the actual electromagnetic characteristics of the human tissue parameters. However, due to the complexity of the actual human body model, the numerical calculation is computationally intensive. In order to facilitate the calculations, this paper assumes that the conductivity of the various tissues is uniform. This means that the difference between the lateral and longitudinal conductivity of the tissue is ignored, and the calculation is only performed in a cylindrical layered human model. The effectiveness of the electrical stimulation of the sciatic nerve in the treatment of CRPS-I has been clinically validated [4]. Given the devices' variability, this stimulation method's applicability in the clinical setting and its ability to achieve similar theoretical results needs to be further validated and explored in electrophysiological and animal experiments. The main idea of this paper is to treat CRPS-I using the electrical stimulation of the sciatic nerve. In fact, due to the similarity of treatment ideas, this system can also be applied to treating other types of neurological disorders. Varying the intensity and type of stimulus to produce the desired response from the target nerve enables the treatment of the disease at its source [49]. This makes it suitable for a wide range of applications.