# Wireless Power Transfer System Based on Strapping Resonators
## 1 Introduction  
Wireless power transfer (WPT) was first proposed by [PERSON] in the 19 th century [1]. However, this idea did not draw the attention of researchers for nearly a century. Since the end of the 20 th century, with the rapid development of electronic technology, a variety of consumer electronic products and medical electronic equipment has appeared in people's daily lives. These electronic devices are usually highly dependent on their power supplies. In many cases, wired charging is limited in convenience. Thus, in recent years, the concept of WPT has been revisited by researchers, and several WPT systems have been reported [2]. According to the transmission mechanism, there are three options for the wireless power transfer system [3; 4; 5; 6]. The first mechanism uses antenna or array to radiate electromagnetic waves with high power to the far field [4]. This method is suitable for long-distance WPT. The second way is based on the law of electromagnetic induction, which uses the electromagnetic induction between the metal coils to achieve wireless power transfer [5]. The third way is to use the coupling between the resonators [6; 7]. Generally, electromagnetic resonance coupling is suitable for high-frequency near-field WPT. It depends on the magnetic-electric coupling between two high-\(Q\) resonators. For example, a group from Massachusetts Institute of Technology(MIT) demonstrated that WPT efficiency can be enhanced via resonant coupling [3]. Since then, after years of development, many scientific researchers have been attracted to this concept [8; 9; 10; 11; 12; 13]. Several solutions based on various types of resonators have been proposed to deal with the most pressing problems of improving efficiency and transmission distance, and meaningful results were obtained. However, in many specific applications, such as high power WPT in microwave regime, coil resonators cannot meet the requirements [13]. In addition, the dielectric resonator (DR) is also limited in high power WPT, due to its large temperature drift [2; 14]. Therefore, resonators with higher power capacity and low temperature drift are the key to solving the above problems. In this paper, we explore a structuralmodel based on non-dielectric resonance for WPT in order to overcome the limitations mentioned above. In the new method, a strapped resonator (SR) with four vanes is designed and fabricated. The SR is often used as the anode of high power electric vacuum devices. It has the advantages of high quality factor, low temperature drift and high power capacity [15]. Usually, the internal space of the SR is divided into several sub-cavities by the vanes. When the SR resonates at the fundamental mode, the phase difference of the electric field between adjacent sub-cavities is \(\pi\). Therefore, the fundamental mode is also called \(\pi\) mode. The first high-order mode is called \(\pi+1\) mode [15]. Compared to the DR, the SR has higher mode separation [16]. The unique resonant characteristics of the strapped resonator ensure the wireless power transfer system operates in multiple modes [15]. The field distribution of the two resonant modes (\(\pi\) mode and \(\pi+1\) mode) facilitates the coupling between the resonators to achieve efficient WPT. Therefore, the strapped resonator provides a new option for high power near-field WPT systems.