Microwave power transfer (MPT) is attracting increasing interest as a promising solution for supplying power to wireless devices. This study aims to achieve the non-cooperative coexistence of co-located independent MPT systems in the same frequency channel with an eye to ward widespread deployment. The achievement of effective non-cooperative coexistence can provide flexibility when deploying MPT systems in environments where multiple independent MPT systems are operational, such as factories and apartment complexes. However, when energy transmitters and receivers from independent MPT systems are in close proximity, co-channel interference (CCI) occurs either between a pilot signal for channel estimation and power transmission signal, or between pilot signals, which in turn reduces the power transmission efficiency. This study investigates the application of the spread spectrum technique to pilot signals to suppress CCI. We characterize three spreading techniques: direct sequence, frequency hopping, and chirp spread spectrum schemes. Simulations and experiments show that the frequency hopping scheme achieves superior performance compared with other methods, particularly in terms of interference from power transmission. Measurements of the beamforming gain under the power transmission interference with a signal-to-interference ratio of -20 dB demonstrate that the frequency hopping method achieves a gain that is only 0.2 dB less than the theoretical value with a pilot signal length of 0.14 ms. In the presence of a carrier frequency offset of 1 ppm, the effect of the offset can be suppressed by increasing the signal length to 0.3 ms.

This paper evaluates a computationally efficient beamforming method that employs broad nulls to enhance electromagnetic field (EMF) safety in microwave power transfer (MPT). Simulation and experimental results in an actual factory environment demonstrate that the method effectively suppresses EMF exposure in null regions while preserving high mainlobe directivity and maintaining low computational cost, validating the method’s suitability for practical real-time MPT.

This paper demonstrates that UHF RFID tags can be read without a carrier. More specifically, using an alternative reader design that does not emit a carrier, we show that it is possible to read an RFID tag that was designed to be read by a conventional RFID reader that does emit a carrier. Typical RFID tags are designed to modulate a carrier; it turns out that, in addition to modulating a carrier, a backscatter modulator circuit also modulates tag circuit noise, including Johnson noise; Johnson and other noise is present in a tag even if a carrier is not. Modulated Noise Communication (MNC) can be read by an alternative reader design. The reader for modulated noise communication is simpler than a conventional backscatter reader because it does not have to contend with the problem of selfjamming. The absence of a carrier means that the tag needs an alternative power source; this could be an energy harvester such as a photovoltaic cell, or could be a time-multiplexed continuous wave signal from the reader. The use of time multiplexing means that the reader would still inherit the benefits of not needing to counteract self jamming.

Conventional wireless power transfer technologies primarily focus on wireless charging devices, overlooking the impact of mechanical connections, such as cable tension on user interfaces. In contrast, we are exploring a wireless power transfer system with force-display functions to enable users to intuitively perceive the power supply status of electronic devices. The system used a permanent magnet on the receiver side and an electromagnet on the transmitter side. The charging status of the electronic device can be intuitively displayed to the user by adjusting the electromagnet based on the circumstances. In this paper, we present the design and implementation of single-core dual coils that realize both electromagnetic and wireless power transfer coils in a single core. Through experimental evaluations, the generation of attractive and repulsive forces up to approximately 2 N was confirmed in terms of the electromagnetic force. In addition, the maximum power transfer efficiency reached 87%.

We aim for the non-cooperative coexistence of colocated independent microwave power transfer (MPT) systems in the same frequency channel. When energy transmitters and receivers from independent MPT systems are in close proximity, co-channel interference occurs between a pilot signal for channel estimation and a power transmission signal or between pilot signals, which in turn reduces the power transmission efficiency. This study investigates spread spectrum pilot signals to suppress the co-channel interference between MPT systems. The simulation and experimental results demonstrate the effectiveness of the spread spectrum pilot signals and confirm the superiority of the frequency hopping spread spectrum technique.

Inductive power transfer (IPT) systems transmit power via magnetic field, therefore electromagnetic compatibility (EMC) and electromagnetic interference (EMI) issues are caused by the magnetic field leakage from the IPT systems. In this study, we propose a method to cancel both the fundamental and harmonic components of the magnetic field leakage in a multiple-input single-output (MISO) system by only controlling the transmitters and the receiver. The fundamental component of the input voltage and the optimum load impedance are derived to maximize power transmission efficiency (PTE) under the cancellation condition of the magnetic field leakage at the fundamental frequency. The harmonic components of the input voltage that can cancel the harmonics of the magnetic field leakage is calculated by estimating the harmonic components generated by the full-bridge rectifier on the receiver side. Circuit simulations were performed to evaluate the proposed method. As a result of the simulations, it was confirmed that the fundamental and harmonic components of the magnetic field leakage can be suppressed by more than 34 dB compared to the PTE maximization method, and that the reduction in PTE was about 1.7 %.

In wireless power transfer systems, geometries of a transmitter coil and a receiver coil considerably influence power transmission efficiency (PTE) and the magnetic field leakage. However, a method to simultaneously optimize the geometries of both the transmitter and receiver coils is yet to be devised, and custom design for each electronic device remains unfeasible. In this study, using mesh current distribution analysis, we optimized the current distribution in the design area of the transmitter and receiver coils to simultaneously optimize the geometries of the transmitter coil and the receiver coil. Two types of design methods were devised by using two types of optimization: one to maximize PTE and the other to maximize PTE under cancellation conditions of the magnetic field leakage. The first method designs the coil geometries for maximizing PTE and the second method designs for canceling the magnetic field leakage. Electromagnetic simulations and experimental analysis using a metal three-dimensional printer revealed that the design objectives were accomplished because it was confirmed that the coils designed to maximize PTE achieved higher PTE and the coils designed to cancel the magnetic field leakage achieved lower magnetic field leakage intensity. The results of this study proved that the automatic coil design can become a feasible method in various applications.

The performance of wireless power transfer (WPT) systems using magnetic resonant coupling is drastically degraded by the resonant frequency shift. In this paper, we propose a communication-less receiver-side resonant frequency tuning method using a variable reactor based on a Class-D power inverter. The proposed method can compensate for the residual reactance in the receiver without any communication being required between the transmitter and receiver. Further, the effectiveness of the proposed method is evaluated through circuit simulations assuming a 1 kW-class 85-kHz WPT system for electric vehicle charging. It is observed that resonant frequency tuning can be achieved by maximizing the power received at the load.

Multiple-input multiple-output (MIMO) wireless power transfer (WPT) systems present various advantages to users, including improved power transfer efficiency, adjustable transmission power, and reduced magnetic field leakage. An essential aspect of controlling MIMO WPT systems is the estimation of $Z$ parameters, which characterize the behavior of the linear electrical network in these systems. In this study, we propose a method to estimate all elements of the $Z$ parameters without requiring synchronization between the transmitters and receivers. Instead, the elements are estimated based on the measured complex amplitudes of voltage and current at the transmitters, as well as the direct current (DC) at the output of the full-bridge rectifiers on the receivers. Importantly, all these measurements can be obtained at a minimal cost. Further, circuit simulations and experiments are also conducted to evaluate the performance of the proposed method. Specifically, a $2 \times 2$ MIMO WPT system is employed for the circuit simulations and experiments, and the $Z$ parameters are estimated under various receiver position conditions. The evaluation of the simulation and experimental results is based on the power transmission efficiency of the system, considering the estimated $Z$ parameters. The simulation and experimental results demonstrate that the difference between the power transfer efficiency based on the estimated $Z$ parameters and the theoretical maximum efficiency based on the true $Z$ parameters is found to fall within the range of 0.06 % and 0.4 %, respectively.

Harmonics in the magnetic field leakage from inductive power transfer systems can influence existing wireless communications and nearby electronic devices. To overcome this problem, we designed an input voltage waveform at the transmitter to cancel the harmonics in the field leakage from both the transmitter and receiver. This design was achieved by analyzing the harmonics in the circuit based on the formulations of the voltage at the input of the full-bridge rectifier and the harmonics in the magnetic field leakage. To validate the effect of the proposed method, we conducted circuit simulations and experiments that confirmed that the proposed method reduces the harmonics in the magnetic field leakage by up to 14.4 dB.

The reduction of coil design cost is essential to integrating wireless power transfer (WPT) systems in electronic devices. However, the power transfer efficiency of WPT systems is influenced by operating conditions, such as the surrounding material and compatibility between transmitter and receiver coils. Further, experienced engineers are faced with the task of adjusting coil parameters using trial and error methods, which is time-consuming. To overcome this problem, we propose a general coil design method based on a current distribution analysis. This design method comprises a two-dimensional current distribution calculation method for the design of a highly efficient coil and coil layout determination method based on the current distribution. We design a coil attached to a metal plate and validate through simulations and experiments that the proposed design achieves the highest power transfer efficiency at 6.78 MHz among multiple coils designed by sweeping design parameters.

This paper proposes a method to wirelessly rewrite the CBRAM switches for chipless RFID tag IDs. The contactless driving of the CBRAM switch is achieved by inductive coupling between a writer coil and a tag coil. On the writer side, a voltage pulse is generated on a coil which induces a varying electromotive force across another coil which is connected to the CBRAM (device part). Numerical analysis and circuit simulations were performed to confirm that pulse waves are thus induced in the device coil and it allows to switch the CBRAM. In addition, experimental results showed that the CBRAM was successfully switched from the On state to the Off state by applying multiple pulses to the writer coil.

This letter analyzes the optimal transmission period to maximize the time-averaged received power using a distributed microwave power transfer (DMPT) system. DMPT requires periodic phase and frequency synchronization. The received power is maximized immediately after synchronization because the received signals from the transmitters are coherent. However, the received power gradually degrades owing to the phase drift caused by the frequency offset of the phase-locked loop (PLL) on the transmitters. Therefore, if the power transmission period is considerably long, the time-averaged received power decreases. To design the synchronization interval, we formulated the expected value of the time-averaged received power. The expected value assists in selecting PLL elements and estimating the received power before hardware implementation of the transmitters, thus enabling the rapid design of DMPT systems.

Harmonic currents in a receiver in wireless power transfer (WPT) systems can degrade performance of the receiver device by corrupting the DC power plane. The DC plane at the receiver serves as a constant reference that allows for dependent, sensitive electronics to operate with acceptable precision. However, if that reference is corrupted by noise, then the functions of the system, such as sensing and wireless communication, can degrade significantly. To reduce the harmonic current content in the receiver, and thereby improve the DC supply constancy, the optimal arbitrary voltage transmitter excitation is derived. To physically generate the derived arbitrary voltage, the signal is converted to a multilevel voltage using a phase-shifted carrier modulation. This multilevel voltage is then realized via the design of a full-bridge flying capacitor multilevel inverter and circuit simulations demonstrated the reduction of the harmonic currents in the receiver. By comparison to using a square-wave input voltage, circuit simulations demonstrate that a 5-level multilevel inverter reduces the total harmonic distortion (THD) of the received current from 6.79 % to 0.69 %, effectively reducing the harmonic currents in the receiver by 90 %.

In the automotive and robotics industries, there is an increasing demand for sensing conditions inside metal housings such as engines and motors. The inside of metal housings is narrow and complex, and wiring from the outside of the metal housing to the sensor is difficult due to safety considerations and limitations on the range of movement. To overcome these limitations, wireless communication to transmit sensor data outside of a metal enclosure is a possible solution. However, this solution suffers from reflection and multipath inside the metal enclosure, resulting in a large propagation loss of radio waves. In this study, we reduced the propagation loss by developing a direction changer that combines a small spiral antenna and a small directional antenna made of a printed circuit board to limit the direction and radiation angle of radio waves, thereby suppressing the reflection and scattering of radio waves. Experiments using a test device imitating a motor confirmed that the proposed method improved the received signal strength indicator by approximately 30 dB compared to that obtained without the direction converter.

This paper presents the fabrication of an Active Integrated Phased Array Antennas (AIPAA) sensor system prototype utilizing Information, Communication & Energy transfer (ICEt) technology. Through the high-density integration of hardware components and software algorithms, this system enables adaptive adjustments in diverse scenarios, leading to optimal system performance. The proposed prototype demonstrates the capability to fulfill sensing, communication, and energy transfer tasks in various environments, including spacecraft exploration and river disaster warning systems. This research represents a significant step towards the development of advanced wireless sensor networks with ICEt technology for multifunctional applications.

This letter presents a method to cancel magnetic field leakage while maintaining high power transfer efficiency (PTE) in multiple-input multiple-output wireless power transfer systems. To achieve low leakage and high PTE, the problem of PTE maximization under the cancellation condition of the magnetic field leakage is solved, which is a maximization problem of affinely constrained Rayleigh quotients. Subsequently, the optimal amplitudes and phases of the input voltages at the transmitter array and the optimal load impedances at the receivers are shown. This method can further reduce the magnetic field leakage by up to 31 dB compared with the PTE maximization method, while having a PTE drop within 5.5%.

The fifth generation of mobile networks evolved to serve applications with distinct requirements, which results in a high management complexity due to simultaneous real-time tasks. In the physical layer, code words that allow proper data exchange between the Base Station (BS) and the served users must be chosen. While, in higher layers, the BS must choose users to be served in a given transmission opportunity. There are approaches based on Machine Learning (ML) to solve these combined tasks. However, due to the high amount of possible inputs, a challenge is the availability of data to train the models. In some cases, there may not even exist a predefined optimal answer to use as a "label" for supervised approaches. In this paper, we evaluate solutions for the combined problems of beam selection and user scheduling with Reinforcement Learning (RL), which does not need labels, as a solution for problems without a predefined answer. The algorithms were proposed for Problem Statement 6 of the challenge organized by the International Telecommunication Union (ITU) in 2021, which ranked as the finalists. We compare the approaches in relation to the cumulative reward received by the agents and show a performance comparison of different RL approaches by comparing them with baselines developed for the challenge. The paper also shows how the action taken by the trained agents affect network operation by comparing the number of packets transmitted, which is highly related to the proper selection of users and code words.

Multiple-input multiple-output (MIMO) wireless power transfer (WPT) systems offer multiple benefits to users, such as improved power transfer efficiency, adjustable transmission power, and reduced magnetic field leakage. The estimation of the Z-parameters, which describe the behavior of the linear electrical network in the systems, is essential for the control of MIMO WPT systems. In this study, we propose a method that can estimate all the elements of the Z-parameters without requiring synchronization between the transmitters and receivers. The elements are estimated using the measured complex amplitudes of the voltage and current at the transmitters as well as the direct current (DC) at the output of the full-bridge rectifiers on the receivers, all of which can be measured at a low cost. Numerical simulations of the proposed method for MIMO WPT systems were performed for three configurations: two transmitters and two receivers $(2 \times 2)$, three transmitters and two receivers $(3 \times 2)$, and three transmitters and three receivers $(3 \times 3)$. The simulation results show that each element of the Z-parameters could be estimated within 1% of the true value after four measurements for the $2\times 2$ system, four measurements for the $3 \times 2$ system, and eight measurements for the $3 \times 3$ system.

In inductive power transfer systems, a transmitter array can maintain high power transfer efficiency (PTE), despite lateral misalignment between the transmitter and receiver. However, a control method for reducing magnetic field leakage in this situation has not been found. Therefore, a novel theory of controlling the transmitter array is necessary for electromagnetic compatibility and user safety. In this study, we optimize the input currents at the transmitter array and the load impedance at the receiver to maximize PTE under the cancellation condition of the magnetic field leakage. Simulations show that the proposed method reduces magnetic field leakage by more than 10 and 38 dB, with and without ferrite plates, respectively, compared with existing PTE maximization methods, even when there is a lateral misalignment between the transmitter and receiver. Additionally, experiments using coils having ferrite plates show that the proposed method reduces magnetic field leakage by more than 6.75 dB. The decrease in PTE is within 4.17 %, which compares favorably with existing methods.