Array Designs for Long-Distance Wireless Power Transmission: State-of-the-Art and Innovative Solutions

The concept of long-range wireless power transmission (WPT) has been formulated shortly after the invention of high power microwave amplifiers. The promise of WPT, energy transfer over large distances without the need to deploy a wired electrical network, led to the development of landmark successful experiments, and provided the incentive for further research to increase the performances, efficiency, and robustness of these technological solutions. In this framework, the key-role and challenges in designing transmitting and receiving antenna arrays able to guarantee high-efficiency power transfer and cost-effective deployment for the WPT system has been soon acknowledged. Nevertheless, owing to its intrinsic complexity, the design of WPT arrays is still an open research field whose importance is growing as the possibility to transfer energy by means of electromagnetic waves gathers more and more interest from the applicative viewpoint. This paper is aimed at reviewing the array design approaches proposed in the state of the art for long-range wireless power transmission, highlighting the latest advances and innovative solutions as well as envisaging possible future trends of the research in this area.

I. Introduction

Long-range wireless power transmission (WPT) systems working in the radio-frequency (RF) range [1]–[5] are currently gathering a considerable interest (Fig. 1) for their envisaged applications in those scenarios where the deployment of electrical wired networks is unfeasible or cost ineffective [6]–[13]. Indeed, RF-based WPT is a promising technique for supplying not-accessible fixed and mobile systems and, unlike other wireless power transfer technologies exploiting near-field coupling (which guarantee efficiency up to 70% but operate over distances of the order of the wavelength [14]), or laser beaming (which still present several technological challenges [15]), to transfer power over large distances by exploiting well-assessed technologies [4]–[6], [8], [9]. Enabled applications include powering distributed electronic devices such as mobile phones and laptops [16], [17], feeding pervasive sensors and actuators (e.g., wireless sensor nodes and robots) [18], transmitting energy in inaccessible or hazardous regions to enable sustainable existence, and “fueling” electrical vehicles [19], [20], unmanned aerial vehicles (UAVs), and high altitude platforms (HAPs) [9], [21]. Moreover, WPT is one of the proposed technologies for the space-to-earth transfer of electrical energy gathered by “solar power satellites” (SPSs) [1], [3], [5], [6], [8], [22]–[25]. Fig. 1.

The number of WPT-related papers published each year (based on IEEE Xplore databases).