A Modularized IPT With Magnetic Shielding for a Wide-Range Ubiquitous Wi-Power Zone

A wide-range ubiquitous wireless power environment, called a ubiquitous Wi-power zone, where any electric devices can be charged by three-dimensional (3-D)-omnidirectional wireless charging, is newly proposed in this paper. By virtue of the proposed direct-quadrature (DQ) transmitting (Tx) coils composed of multiple Tx modules with same size, a ubiquitous Wi-power zone having the transmitting (Tx) coils can be provided over wide-range 3-D space. In this area, a number of electric devices can be simultaneously charged during operation. Therefore, the proposed IPT is expected to be the next generation of wireless power transfer (WPT), as the internet of things (IoT), mobile devices, and sensor technologies evolve. For magnetic shielding behind the Tx coils and high power efficient operation of the proposed DQ Tx coils, providing an evenly distributed magnetic field, a conductive plate is adopted, and the effects of the conductive plate for the dipole coil structure were thoroughly evaluated by a 3-D FEM simulation. To create the proposed ubiquitous Wi-power zone, simulation-based optimum design procedures are established based on four design considerations and the optimized number of modularizations for the DQ Tx coils can be found by an optimum point of figure of merit (FoM). The DQ Tx module composed of the DQ Tx coils and series resonant capacitors was adopted as a standard unit of the proposed IPTso that different sizes and shapes of 3-D space can be utilized for universal use of the proposed ubiquitous IPT; hence, a general solution to create the proposed ubiquitous IPT is provided in this paper. A prototype 5 × 5 modularized IPT composed of 25 DQ Tx modules having the same size of 10 × 10 cm × 2 cm was fabricated and experimentally verified for a 1 m × 1 m × 0.7 m ubiquitous Wipower zone. Experimental results showed that 95.5%, 92.1%, and 98.8% of high magnetic field uniformity for z₁ = 25 cm, 50 cm, and 75 cm, respectively, and 3-D omnidirectional wireless power delivery have been achieved; thus, meeting essential requirements for the proposed ubiquitous Wi-power zone. Nine Rx coils can be simultaneously charged with 14.2 W of total received load power and 8.2% power efficiency at z₁ = 70 cm.

I. Introduction

Intelligent devices such as the Internet of Things (IoT), mobile devices, wearable devices, and smart sensors are rapidly evolving with the advent of the upcoming fourth industrial revolution. Such devices tend to have relatively large batteries and efforts are being made to reduce the device size [1] –[4]. Because multiple devices might be arbitrarily positioned in a confined three-dimensional (3-D) space and small-sized batteries should be used in the devices, the battery in each device should be frequently replaced, which wastes time and energy and induces high labor costs. Accordingly, an inherent solution involving compact battery size or a batteryless approach with continuous power delivery is required to solve these issues. Wireless power transfer (WPT) is a promising solution to deliver power to multiple devices [5]–[26]. As examples, radio frequency (RF) and infrared (IR) types of WPT systems may be used for long-distance wireless power delivery characteristics [5]–[8] . However, they have a limitation to simultaneously charge multiple devices due to a one-to-one wireless charging characteristic and cannot penetrate obstacles between transmitter (Tx) and receiver (Rx). In addition, precise control methods to align the Tx and Rx are required; hence, such RF and IR types of WPT have inherent limitations for these applications. On the other hand, inductive power transfer (IPT) may be a viable solution to simultaneously charge multiple electric devices [9]–[28]. The major applications for commercially available IPT products are currently limited to contact-type cases and less than 20 cm-off distance cases between Tx and Rx coils for mobile devices, drones, sensors, and electric vehicles [9]– [17]. Furthermore, existing WPT technologies are usually available with low degrees of freedom for wireless charging, and it is difficult to provide simultaneous wireless charging service for multiple Rx coils. This may impede application in the era of ubiquitous WPT such as the Wi-power zone described in this paper, where any small electric devices can be simultaneously charged with highest wireless charging freedoms during operation anytime and anywhere, as shown in Fig. 1. Therefore, the following prerequisite conditions for the proposed ubiquitous Wi-power zone should be satisfied.