Yoshiaki Narusue

Impedance matching method for any-hop straight wireless power transmission using magnetic resonance

Wireless power transmission using magnetic resonance is considered a key technique for cutting the last wire to electrical devices in indoor environments. We realize this concept by using multi-hop displacement of a magnetic resonator array. However, multi-hop displacement has been impractical because of the complexity of the impedance matching procedure. In this study, we have derived a simple but practical impedance matching method for multi-hop straight wireless power transmission. Our method maximizes the transmission efficiency, regardless of the number of hops in the topology. The performance of our method was evaluated by both simulations and implementation.

Passive and contactless epidermal pressure sensor printed with silver nano-particle ink

In this paper, we propose a passive and contactless epidermal pressure sensor patch printed on a paper substrate with silver nano-particle ink. This disposable patch can be used to measure the pressure between the clothes and the human body. Different from the conventional pressure sensors, the pressure can be measured wirelessly without disturbing the motion of the users. The sensor circuit pattern is printed by a conductive inkjet printer and the sensors pressure value is detected by a reader coil through the change of the capacitance of an LC resonant circuit. We propose a sensor design method that minimizes the effect of the human body. We demonstrate our sensor patch by measuring the pressure exerted by compression garments whose pressure distribution is important for the wearers health.

Virtualizing power cords by wireless power transmission and energy harvesting

In this paper, we introduce two different approaches for the virtualization of power cords for electrical devices. The first approach is a new concept for routing electric power by wireless transfer on two-dimensional surfaces, such as floors and walls. Unlike any other existing wireless power transfer scheme, this method can deliver electric power over a wide range with minimal loss. We realize this method using multi-hop displacement of a magnetic antenna array. Each array element can be selectively resonated with adjacent elements to deliver power without physical contact. The second approach utilizes far-field RF energy harvesting. Using an efficient voltage multiplier and adaptive software-based control, it is possible to operate low-power wireless sensors continuously.

Maximum efficiency point tracking by input control for a wireless power transfer system with a switching voltage regulator

In wireless power transfer (WPT) systems, changes in the receiver position and load resistance affect the output voltage and power efficiency. A receiver-side switching voltage regulator is useful for output voltage regulation, but it cannot be utilized with a DC-DC converter dedicated to conventional maximum efficiency point tracking (MEPT). As an MEPT method compatible with a switching voltage regulator and basically without feedback information, we propose MEPT by input control to make the switching voltage regulator undertake the role of the DC-DC converter of a conventional MEPT. To enable the proposed MEPT, we propose two additional essential technologies. One is a system design to remove the instability caused by a switching voltage regulator at the maximum efficiency point. The other is the activation timing of a switching voltage regulator to reach a stable point. Measurements using a 0-Ω power source and a K-inverter validate the proposed methods.

Performance evaluation of multilevel ASK communication for a multi-hop wireless resonance system

Wireless power transmission (WPT) via electromagnetic resonance has been focused on by researchers in related fields. Also, a multi-hop wireless power transmission system successfully extends power transmission distance by using multiple resonators. Sending data along with electrical power is one of the most important but missing pieces for the realization of the multi-hop WPT system. Different from radiative approach based on antennas, switching speed of waveform on the resonators is significantly slower because of resonance. Therefore it is very difficult to increase symbol rate of communication. To overcome this problem, we exploit the fact that signal-to-noise ratio (SNR) is higher in WPT because input power level is typically high. In this paper we adopt Multilevel Amplitude-Shift Keying (Mary ASK) to increase bit per symbol rather than symbol rate, aiming to improve the bit rate. We evaluate the communication performance of a multi-hop WPT system and focus on M-ary ASK for high communication speed. We conduct the experiment using M-ary ASK modulation and show the system throughput via the symbol rate and optimized bit per symbol (Log2M) for M-ary ASK.

Distributed reactance compensation for printed spiral coils in wireless power transfer

This paper proposes a distributed reactance compensation technique, which is a useful approach for reduction of dielectric loss in a substrate of printed spiral coils. Distribution of lumped capacitors between coil windings reduces voltage fluctuations, and thus the strength of electric field, finally yielding lower dielectric loss. The usefulness of the proposed technique was verified by both simulation and experimental measurements.

DC-based impedance tuning method using magnetic saturation for wireless power transfer

The transfer efficiency of a resonant wireless power transfer system highly depends on the load impedance and the reactance of the resonators. In many practical applications, these parameters fluctuate by the variation of operating conditions. Therefore, adaptive impedance tuning methods are necessary in order to continuously achieve high-efficiency power transfer. To provide a countermeasure to this problem, this paper proposes a DC-based resonator reactance tuning method which assembles a variable inductor. Based on this reactance tuning method, a DC-based load impedance tuning method which assembles a variable K-inverter is also proposed. This reactance tuning method and load impedance tuning method both utilize the non-linearity of ferrite cores. Through measurements at 6.78 MHz, it is shown that the reactance of the high-Q coil can be tuned from 80 Ω to 113 Ω and the characteristic impedance component of the K-inverter can be tuned from 39 Ω to 72 Ω using non-optimized, basic configurations of the proposed methods.

Multiple-half-wave resonator for wireless power transfer using magnetic resonant coupling

In order to extend the transfer distance in wireless power transfers using magnetic resonant coupling, it is necessary to increase the quality factor of resonators. In general, resonators with a larger number of turns may have a higher quality factor; however, the number of turns is limited by the half wavelength. To overcome this frequency limitation, we propose a multiple-half-wave resonator that consists of several half-wave resonators in order to provide an overall larger number of turns. An electromagnetic simulation shows that the proposed structure improves the transfer efficiency by 14%, 30%, and 40% over transfer distances of 50 cm, 75 cm, and 100 cm, respectively, when compared to a conventional helical resonator at 13.56 MHz.

Receiver localization for a wireless power transfer system with a 2D relay resonator array

A magnetic resonance wireless power transfer (WPT) system using a 2D relay resonator array has been proposed. To make practical use of this system, the powering paths to the receiver devices need to be created automatically. This paper presents a receiver localization method suitable for the 2D WPT system. The feasibility of this method is evaluated by both simulation and experimentation. Moreover, we have implemented a demonstration system that automatically localizes the receiver, establishes the route, and transmits the power.

Planning simulation tool for designing energy harvesting applications

Energy harvesting (EH) is a key technology for the autonomous operation of smart devices. However, designing a system based on energy harvesting is much more difficult than designing battery-powered systems. The system has to weigh the balance between harvested energy and consumed energy, while taking into account various uncertainties in the actual environment. In order to achieve this requirement, it is necessary to precisely refine and integrate hardware modules and software structures; however, it is still difficult for non-experts to design such a system from scratch. In this paper, we propose PLEH, a PLanning simulation tool for Energy Harvesting applications, which will facilitate in determining the most relevant hardware modules and the software structure. PLEH estimates energy consumption varying over time based on our abstract EH application model. We show three usage scenarios that are common to novice developers of EH applications.