The Internet of Things (IoT) is a constantly-evolving area of research and touches almost every aspect of life in the modern world. As technology moves forward, it is becoming increasingly important for these IoT devices for environmental sensing to become self-powered to enable long-term operation. This paper provides an outlook on the current state-of-the-art in terms of energy harvesting for these low-power devices. An analytical approach is taken, first defining types of environments in which energy-harvesters operate, before exploring both well-known and novel energy harvesting techniques and their uses in modern-day sensing.

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Powering the Environmental Internet of Things.

A series–series compensated capacitors topology of the wireless power transmission (WPT) system has a characteristic of increasing active power at coil misalignment when controlled using the conventional secondary dc-link voltage control. This results in a larger total capacity of the primary and secondary sides’ converters. To cope with these problems, this paper proposes a simple constant secondary active power control method, where the secondary dc-link voltage is regulated according to the onboard active power rating and secondary current. The effectiveness of the control method is verified by 100 W experimental systems. The numerical simulation that considers the harmonic components is established to be compared and justified by the experimental results, which is then used to design the capacity of a 300 kW WPT system assuming actual railway vehicle application. By the proposed method, the design criteria of the rating voltage and current of the primary and secondary sides’ components can be determined.

A Simple Active Power Control for a High-Power Wireless Power Transmission System Considering Coil Misalignment and Its Design Method

In this paper, a novel velocimeter based on laser self-mixing Doppler technology has been developed for speed measurement. The laser employed in our experiment is a distributed feedback (DFB) fiber laser, which is an all-fiber structure using only one Fiber Bragg Grating to realize optical feedback and wavelength selection. Self-mixing interference for optical velocity sensing is experimentally investigated in this novel system, and the experimental results show that the Doppler frequency is linearly proportional to the velocity of a moving target, which agrees with the theoretical analysis commendably. In our experimental system, the velocity measurement can be achieved in the range of 3.58 mm/s–2216 mm/s with a relative error under one percent, demonstrating that our novel all-fiber configuration velocimeter can implement wide-range velocity measurements with high accuracy.

https://www.mdpi.com/1424-8220/16/8/1179/pdf

All-Fiber Configuration Laser Self-Mixing Doppler Velocimeter Based on Distributed Feedback Fiber Laser.

/pdf/effectiveness-of-convolutional-perfectly-matched-layer-in-2ekif6en5f.pdf

Effectiveness of Convolutional Perfectly Matched Layer in Time-domain Numerical Analysis of Low-frequency Wireless Power Transfer

Fluid flow characterisation in randomly packed microscale porous beds with different sphere sizes using micro-particle image velocimetry

We previously reported a 60 Hz wireless power transmission (WPT) system, which is a system that uses the common utility frequency. In the study reported in paper, we solved several issues in order to install this system in a small electric vehicle. First, an accelerated finite difference time domain (FDTD) method using a graphics processing unit was developed to solve the issue of computation time. Next, theoretical equations for the transmission efficiency (η) and power (Pout) that include the stray load loss were derived from an equivalent circuit analysis. A new device was designed based on these theoretical equations, where by η = 70% and Pout = 451 W were achieved for a transmission distance of 150 mm. Finally, we attempted to wirelessly charge of a lead storage battery. The overall efficiency of the wireless charging system was maintained at 60% during battery charging.

https://www.jstage.jst.go.jp/article/ieejjia/5/6/5_429/_pdf

Development of Design Methodology for 60Hz Wireless Power Transmission System

To achieve wireless power transfer (WPT) through a stainless-steel plate, a super-low frequency (SLF) was used as a resonance frequency. In our previous study of SLF-WPT, heavy coils were prepared. In this study, we designed lightweight coils using a WPT simulator that we developed previously. As a result, the weight was reduced to 1.69 kg from 11.9 kg, the previous coil weight. At a resonance frequency of 400 Hz, the transmission efficiency and output power of advanced SLF-WPT reached 91% and 426 W, respectively, over a transmission distance of 30 mm. Furthermore, 80% efficiency and 317 W output were achieved when transmitting power through a 1 mm-thick stainless-steel plate. This performance is much better than that in previous reports. We show using both calculations and experimental results that a power-to-weight ratio of 252 W/kg is possible even when using a 400 Hz power supply frequency.

Super-low-frequency wireless power transfer with lightweight coils for passing through a stainless steel plate.

We describe a method for simulating an electromagnetic induction type wireless power transmission (WPT) device. This simulator was based on the finite-difference, time-domain method. To reduce computation time, two graphics processing units (GPUs) were used as accelerators for the electromagnetic field computation. The first GPU calculated the electromagnetic field for the non-resonance state, and the second GPU calculated the field for the resonance state. Only two physical quantities needed to be exchanged between the two GPUs: self-inductance and the magnetic coupling coefficient. Capacitors and a load resistance were virtually connected to the coils as lumped elements. The experimental and simulation results were in good agreement. It is expected that a transient response analysis of WPT devices will become possible in the future using this simulation architecture.

Development of a wireless power transmission simulator based on finite-difference time-domain using graphics accelerators

A laser Doppler velocimeter (LDV) has been developed that is capable of performing two-dimensional (2D) cross-sectional measurements. It employs two horizontal laser light sheets that intersect at an angle of 13.3°. Since the intersection region is thin, it can be used to approximately determine the 2D flow field. An 8 × 8 array of optical fibers is used to simultaneously measure Doppler frequencies at 64 points. Experiments were conducted to assess the performance of the LDV, and it was found to be capable of obtaining spatial and temporal velocity information at multiple points in a flow field. The technique is fast, noninvasive, and accurate over long sampling periods. Furthermore, its applicability to an actual flow field was confirmed by measuring the temporal velocity distribution of a pulsatile flow in a rectangular flow channel with an obstruction. The proposed device is thus a useful, compact optical instrument for conducting simultaneous 2D cross-sectional multipoint measurements.

https://iopscience.iop.org/article/10.7567/JJAP.54.012501/pdf

Tomoaki Kyoden

Papers

Development of Design Methodology for 60Hz Wireless Power Transmission System

Effectiveness of Convolutional Perfectly Matched Layer in Time-domain Numerical Analysis of Low-frequency Wireless Power Transfer

Super-low-frequency wireless power transfer with lightweight coils for passing through a stainless steel plate.

Development of a wireless power transmission simulator based on finite-difference time-domain using graphics accelerators

Multi-channel laser Doppler velocimetry using a two-dimensional optical fiber array for obtaining instantaneous velocity distribution characteristics