Wireless Power Transmission Through Radio Frequencies: Basic Design

Introduction The radio frequency (RF) for wireless power transmission (WPT) has been enabled for a long time, but the recent development of low-power electronics and advanced waveform optimization technologies [1, 2] It has introduced a wide range of new applications where WPT can be useful. There are certain situations that make WPT more attractive than cables and batteries. First, items that are attached to moving objects, such as sensors mounted on motor shafts, which can benefit from WPT technology as cables become problematic with continuous movement over time. Second, items that are difficult to access or difficult to maintain with cables such as remote sensors in harsh environments. In addition, the items used indoors and away from direct sunlight can benefit from WPT instead of sufficient solar energy. Energy consumption, maintenance and usage cycles must be taken into consideration when assessing whether WPT is a viable option. System Overview The design of a wireless power delivery system at the transmit side (TX) and receiver end (RX) can be simplified. The system can be either an “active” closed-loop system with real-time monitoring of power delivery to the RXs to ensure optimal performance and uptime, or a “passive” system without real-time feedback and usually less efficient. Whether the solution requires an active or passive system is driven by a variety of factors such as range, number of supported receivers per transmitter, deployment scenario, and reliability requirements. Figure 1: Overview of a TFi Power Network (WPT) System Within the major component blocks there are several subsystems that need to be designed and refined in order to work efficiently with one another. The main subsystems in TX are as follows: (1) Signal generation: Using digital modulation technology such as a phase shift switch (PSK), a random message is modulated across the carrier wave with a predefined reference frequency. Then, the generated RF signal is amplified to the specified power level. (2) Beamforming: The generated and amplified RF signal should be divided into several independently controlled low power RF pathways called channels. The radio frequency (RF) signal for each channel passes through the phase conversion unit to obtain the relative phase shift compared to the other channels. The on-board MCU determines the setpoint for each phase transmission based on the feedback received from the receivers so that the throughput of the WPT is maximized, i.e. the weighted sum of the power delivered to the receivers is maximized. TransferFi is a Singapore-based startup that pioneered WPT’s packet shaping technologies using hardware (shown in Figure 2.) and internally developed software platforms. Figure 2: Built-in 8-channel TFi device Turin-1 WPT Beamformer (3) Amplification: Depending on the operating range, the RF power of each channel should be amplified after applying phase conversion before being pushed into the antenna. There are RF power amplifiers with numerical or analog control mechanisms, but it is recommended to use amplifiers with minimal phase distortion to enhance the accuracy of beamforming. (4) Antennas: A variety of antennas can be used to transmit wireless power with their advantages and disadvantages. For example, omnidirectional antennas transmit power evenly in all directions albeit with a lower energy density. Directional antennas have a much narrower field of view but with a higher energy density. I also concluded that the selection and arrangement of the antennas is a function of the deployment scenario. For example, directional antennas can be very effective with a one-to-one setting as there is no need to move the beam and focus it to other receivers. However, a multi-reception scenario can take advantage of a multi-channel multi-directional array with a wider field of view to focus energy directly on specific receivers. On the receiver side, the main subsystems are (1) the receiver antennas: Similar to the transmitter side, the receiver antennas are selected based on the desired gain and the direction of the installation. Directional antennas must be oriented towards the transmitter to achieve best results, but omnidirectional antennas do not need to be pointed in any specific direction. The multi-channel receiver antenna arrays can also be used to combine RF energy to drive higher loads. (2) Converting and storing radio frequency into DC: The RF signal must be rectified to DC voltage / current first (please refer to [3] For mathematical modeling of a general power harvesting system with an RF-to-DC rectifier). Since the transformed DC voltage is very low, it must be stepped up and regulated before being stored in an energy storage unit. This can be accomplished by using off-the-shelf power management integrated circuits such as the BQ25570 from Texas Instruments, or it can be implemented with a discrete circuit such as TransferFi’s Torino 1 rectifier shown in Figure 3. After sufficient charge has accumulated, it is released in an orderly manner at the voltage required to power the SoC and / or Other connected devices. Figure 3: Integrated TFi rectifier 4-channel TURIN-1 (3) Wireless Feedback Connections: In order to create a highly efficient, adaptive real-time WPT system, one can use a real-time feedback loop that continuously monitors the power being delivered to each device Recepion. Low power SoC like NRF52 series can be used to actively measure readings like receiver RF power level, power storage unit charge status and connected sensor readings if any. TransferFi’s OneClick platform uses the feedback data to learn the channel and calibrate the packet, and it prioritizes power sharing in a multi-receiver system. Reference
[1]. MRV Presenter, Y. Zeng and R. Zhang, “Waveform optimization for RF wireless power transmission: (invited paper),” 2017 IEEE 18 International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Sapporo, Japan, 2017 , Pages 1-6, doi: 10.1109 / SPAWC.2017.8227719.
[2]. B. Clerckx, “Wireless Information and Power Transfer: Nonlinearity, Waveform Design, and Energy Rate Swaps,” in IEEE Transactions on Signal Processing, vol. 66, no. 4, pp. 847-862, February 15 15, 2018, doi: 10.1109 / TSP.2017.2775593.
[3]. G. Ma, J. Xu, Y. Zeng and MRV Moghadam, “A Generic Receiver Architecture for MIMO Wireless Power Transfer with Nonlinear Energy Harvesting,” in IEEE Signal Processing Letters, vol. 26, no. 2, pp. 312-316, February 2019, doi: 10.1109 / LSP.2018.2890164. By TransferFi.