KIEEME 2020, Pyeongchang, Korea
July 8 - 10, 2020 (Wed. - Fri.), Phoenix Park
Metamaterial based Wireless Power Transfer System for Neuro Stimulator
Semin Jo, Wonwoo Lee, and Hojin Lee
Abstract
Bioelectronic
devices require miniaturization, stability, and long-term operation
characteristics for sustainable monitoring and stimulation within human body. In
this regard, batteries have been widely used for the implantable device due to
the long-term operation ability, but the battery working based implantable
devices have some challenges in bulky size, limited lifetime, and need for
replacement that essentially requires surgical method. Therefore, wireless
power transfer (WPT) have been attracted significant attention as the
alternative approach to enable the long-term operation of bioelectronic devices,
and WPT based charging system for the implantable bioelectronic devices have
been reported using near-field coil-pair coupling methods. Despite the
satisfied charging capacity, however, the miniaturization of the WPT system is
remained as a critical problem since the efficiency and power transfer depth strongly
depends on the dimensions of coils. Recently, metasurface, that exhibit exotic
electromagnetic (EM) characteristics with sub-wavelength thickness, based WPT
system was introduced in Bioelectronics to enhance the efficiency and to reduce
the geometrical dimension of WPT system. In this work, we propose a novel WPT
method for biomedical implantable device using EM focusing metasurface at 5.8
GHz. The proposed metasurface has dimensions of length (l) = 49 mm, width (w) = 49
mm size, and thickness (t) = 4.69 mm which is much smaller than the operating
wavelength (<l/10). The proposed metasurface
consists of the 7 x 7 array unit cells with various shapes and sizes that shows
gradient phase distribution to control the phase front of the transmit EM wave.
Also, the proposed metasurface is designed to have 4 different layers to
realize full 2p phase coverage for
focusing the EM wave at specific depth in biological tissue. To confirm the EM wave focusing characteristics, the
electric and magnetic field distribution of transmit field at the focal point
was analyzed, and the proposed metasurface could successfully form a focal
point at 4 mm depth of the biological tissue as desired. Furthermore, the
proposed WPT enhanced the EM waves propagation efficiency from 16 % to 23 %
into biological tissue by reducing the reflection loss at the air-tissue
interface.
