Spherical Helices for Resonant Wireless Power Transfer

Abstract

The capabilities of electrically small spherical helical antennas for wireless power transmission at small and moderate distances are analyzed. Influence of design on antenna radiation resistance, efficiency, and mode ratio is examined. These are the factors that, according to the theoretical considerations depicted herein, govern the maximum transfer performances. Various designs and configurations are considered for the purpose, with accent on small-size receivers suitable for implementation in powering common-sized gadgets. It is shown that spherical helix design is easily manipulated to achieve a reduced antenna size. Good radiation characteristics and impedance match are maintained by multiple-arm folded antenna design and by adjusting the separation between the arms.

Interaction Between Human and Near-Field of Wireless Power Transfer System

“…The maximum power transfer efficiency PTE max is obtained when the receiver is matched, i.e., terminated by the optimum load [6,9]:…”

“…For a given distance and frequency specified by the application, in order to achieve maximum WPT performance, it is necessary to boost the antenna radiation efficiency as much as possible [6,7,9] and to match their mode ratios if different antennas are used [9]. The problem is that, generally, ESAs exhibit low radiation efficiency because radiation resistance drops rapidly with reducing the antenna size or frequency.…”

“…The spherical helical geometry is known to be the best in utilizing the given volume and achieving great radiation properties [11,19]. So, multiple-folded spherical antennas can be used for achieving high performance of WPT systems [9].…”

“…Spirals and various other helical geometries used in WPT systems [3][4][5][6][7][8][9] are classified as electrically small antennas (ESAs), which generate only the lowest order transversally magnetic (TM) and transversally electric (TE) modes [10][11][12]. Straightforward recommendations and fundamental limitations of ESA design are given for WPT between identical antennas [6] and different antennas [9] whereas the WPT system model is based on SMT-AM.…”

“…Straightforward recommendations and fundamental limitations of ESA design are given for WPT between identical antennas [6] and different antennas [9] whereas the WPT system model is based on SMT-AM. As WPT systems operate in antennas' near field at low radio frequencies, various objects and people nearby influence their characteristics and mutual coupling.…”