## 1 Introduction  
With the demand of transferring power without physical contact, wireless power transfer (WPT) technology is gaining global popularity [1; 2; 3; 4; 5] especially for applications in harsh environments [1; 2; 6; 7; 8]. In most cases, a WPT system is designed to provide a load with constant voltage. This can be realized by an open loop design to make the output voltage insensitive to load and coupling coefficient [9] or by a closed loop method to regulate the output voltage [10; 11; 12]. The closed loop regulation can be implemented at the primary or secondary side, and the primary side regulation is implemented by changing the input power while the secondary side regulation is implemented by varying the equivalent impedance. Due to the time-varying load characteristics of a practical WPT system, closed loop regulation is more suitable since it can maintain an accurate constant output voltage for variable load resistances. In WPT applications such as electrical vehicles (EVs) and implant device charging, load status monitoring (e.g., battery status, load voltage, load current, etc.) on the primary side is usually required [13]. Thus data transmission from the secondary side to the primary side is needed. Although there exist some wireless data transmission technologies such as WiFi, Bluetooth and ZigBee, the shortcomings such as complicated paring [13; 14] between the transmitter and receiver sides push people keep trying to realize the data transmission by utilizing the inherent wireless power transfer circuit [15; 16]. Generally, the major requirement for such a WPT system with data transmission and output voltage controllability is the decoupling so the transmission of power and data are not affected by each other. As for wireless transmission of power and data in WPT systems, references [13; 15; 16] describe data transmission through the existing power coils, while [17] proposes data transmission by the use of extra data transfer coils. In references [13; 15; 16], the volume of the coupling structure (coils) is relatively small, since power and data are transferred through the same coupling coils. Nevertheless, its data processing circuit is difficult to design to increase the signal to noise ratio (SNR). In reference [17], the data processing circuit is relatively easy to design to increase SNR since the data transfer channel is separated from the power transfer channel, however, the added data inductive channel makes the volume of the coupling structure large. Reference [18] shows an alternative method for parallel transmission of power and data, whereby power is transferred through the fundamental component while data is transferred through the third-order harmonic component. Power and data are transferred through the same coupling structure, but the frequency modulation (FM) would affect the resonance of the power transfer resonant circuits. Reference [14] studied an inductive and capacitive combined parallel transmission of power and data, where data is transferred via the parasitic capacitances, but not all the applications have the required aluminum plates. Reference [13] shows that transferring information of load voltage and current only needs a slow data transfer rate. References [19; 20] illustrated that power and data can be transferred through a time division multiplexing (TDM) method, and the transmission of power and data would not be affected by each other. In this paper, an alternative wireless power and data decoupled transmission method is proposed. Compared with traditional power and data parallel transfer methods, the proposed method can utilize a short power blocking interval to transfer data and keep the power output continuous and stable at the same time. This method is beneficial for SNR improvement and high speed transmission rates. To implement this method, an AC bi-directional switch is added to control the data transmission flow and a hysteresis controller is utilized to realize the output voltage control.