Electromagnetic Safety Analysis of Wireless Sensor Network Power Transfer System

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Currently, the most mature power supply method for wireless sensor networks is battery power. However, this method requires frequent battery replacements, which leads to reduced power supply reliability. Single-wire power transfer can balance transmission distance and efficiency, while also being flexible and omnidirectional, thus addressing the battery power issue in wireless sensor networks. Researchers Li Yang, Li Yao, Wang Rui, Zhai Yujie, Shi Shaobo, and Hu Taocheng from Tianjin University of Technology’s Key Laboratory of New Electrical Power Technology published related research results in the 4th issue of the Journal of Electrical Engineering in 2022. The research shows that compared to systems with capacitive spheres, the physical quantities of systems without capacitive spheres are all lower, which better complies with safety standards limiting time-varying electric and magnetic fields.

Wireless sensor networks are special networks composed of numerous micro-nodes deployed in monitoring areas, which have sensing, computing, storage, and wireless communication capabilities for comprehensive perception and precise control of the monitoring area over a large scale and long term. Due to their characteristics of low power consumption, low cost, distributed nature, and self-organization, wireless sensor networks have broad application prospects in national security, environmental monitoring, and industrial production.

Currently, the most mature power supply method for wireless sensor networks is battery power, but this method requires frequent battery replacements. Delayed battery replacements can lead to insufficient power supply, resulting in node failures or even network interruptions. To address the reliability issues of battery power in wireless sensor networks, researchers have proposed various solutions, one of which is using single-wire power transfer methods to supply power to wireless sensor networks.

Single-wire power transfer is a new type of power transmission method that only uses a single wire to connect the power source and the electrical device. Single-wire power transfer systems can be categorized into two types based on their structure: systems with capacitive spheres and systems without capacitive spheres. The coil structure can be divided into helical barrel coils and planar spiral coils. Due to the large volume of helical barrel coils, they are not suitable for power supply scenarios in wireless sensor networks, hence the planar spiral coil structure is adopted. Regardless of the structure, single-wire power transfer systems generate high-frequency time-varying electromagnetic fields during operation. Therefore, it is necessary to conduct in-depth studies on the distribution characteristics of these high-frequency time-varying electromagnetic fields and their effects on the human body.

Electromagnetic Safety Analysis of Wireless Sensor Network Power Transfer System

Figure 1 Two Types of Single-Wire Power Transfer System Structures

The research on the electromagnetic safety of single-wire power transfer systems can help understand the working process and transmission mechanism of the single-wire power transfer system; on the other hand, it provides a basis for reducing the electromagnetic radiation produced by the single-wire power transfer system. Studying the electromagnetic safety of single-wire power transfer systems requires considering the biological effects in the electromagnetic environment. A small amount of electromagnetic radiation can cause skin heating and nerve pain, while a large amount can lead to nerve disorders, heart failure, burns, or even death. Currently, the electromagnetic radiation standards adopted in China are GB 8702 2014 “Limits for Electromagnetic Environment Control,” while representative international electromagnetic field radiation standards include IEEE C95.1 and ICNIRP guidelines.

Researchers from Tianjin University of Technology’s Key Laboratory of New Electrical Power Technology first established models of single-wire power transfer systems with and without capacitive spheres, as well as human body models. They then performed simulation analysis of the electromagnetic safety of both system models, primarily comparing the spatial electromagnetic field distribution, spatial electromagnetic field intensity, internal electric field intensity, and internal current density of both systems. Finally, experimental methods were used to validate the simulation results.

Figure 2 Experimental System

After comparative analysis, the researchers pointed out:

1) From the perspective of the spatial electric field, the electric field limit distance at the emission and receiving ends of the system with spheres is higher than that of the system without spheres. Although the electric field limit distance in the middle part of the single wire system without spheres is slightly higher than that of the system with spheres, the overall coverage of the electric field limit of the system without spheres is smaller than that of the system with spheres, indicating that the system without spheres is safer.

2) From the perspective of the spatial magnetic field, the magnetic field limit coverage of the system with spheres is greater than that of the system without spheres, indicating that the system without spheres is safer.

3) From the perspective of organ electric field intensity, the maximum electric field intensity of organs in the system with spheres is approximately 1.7 to 2.3 times that of the maximum electric field intensity in the system without spheres, indicating that the system without spheres is safer.

4) From the perspective of organ current density, the maximum current density of organs in the system with spheres is approximately 1.7 to 2.3 times that of the maximum current density in the system without spheres, indicating that the system without spheres is safer.

Finally, the researchers concluded that compared to the single-wire power transfer system with spheres, the single-wire power transfer system without spheres is safer and more suitable for wireless sensor networks.

This article is adapted from the 4th issue of the Journal of Electrical Engineering in 2022, titled “Electromagnetic Safety Analysis of Wireless Sensor Network Power Transfer System,” authored by Li Yang, Li Yao, et al.

Download the PDF version of the paper, please click the lower left corner “Read the original text” to visit the journal’s website.

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This article is adapted from the 4th issue of the Journal of Electrical Engineering in 2022, titled “Electromagnetic Safety Analysis of Wireless Sensor Network Power Transfer System,” authored by Li Yang, Li Yao, et al.

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