Feasibility Study on Active Back Telemetry and Power Transmission Through an Inductive Link for Millimeter-Sized Biomedical Implants

Abstract

This paper presents a feasibility study of wireless power and data transmission through an inductive link to a 1-mm implant, to be used as a free-floating neural probe, distributed across a brain area of interest. The proposed structure utilizes a four-coil inductive link for back telemetry, shared with a three-coil link for wireless power transmission. We propose a design procedure for geometrical optimization of the inductive link in terms of power transmission efficiency (PTE) considering specific absorption rate and data rate. We have designed a low-power pulse-based active data transmission circuit and characterized performance of the proposed inductive link in terms of its data rate and bit error rate (BER). The 1-mm data-Tx/power-Rx coil is implemented using insulated bonding wire with diameter, resulting in measured PTE in tissue media of 2.01% at 131 MHz and 1.8-cm coil separation distance when the resonator coil inner radius is 1 cm. The measured BER at 1-Mbps data rate was and in the air and tissue environments, respectively.

Chip-Scale Coils for Millimeter-Sized Bio-Implants

“…η Rx is the ratio of the power delivered to R L to the power dissipated in the secondary coil due to its parasitic resistance, R s2 . 1) Optimizing Rx: After applying the common design constraints such as D o2 = 4 mm, each coil was designed by following the coil optimization procedure in [13], [15], [40] in a way to maximize Rx P RS , which is a multiplication between the loaded Q factor, Q 2L = wL s2 /(R s2 + R L ), and the Rx internal efficiency, η RX = R L /(R 2 + R L )). For the around-CMOS design, p 2 is fixed because this design parameter is not controllable during the semi-manual coil fabrication.…”

“…The geometrical and electrical parameters of the 2-coil inductive link for three different Rx coils are summarized in Table I. The operating frequency of each inductive link is individually optimized by adopting the methodology in [13], [15], [40]. According to optimized simulation results in Table I, around-CMOS, above-CMOS and in-CMOS coils in biological tissue environments operate at 300 MHz, 330 MH and 60 MHz, respectively.…”

Ultra-compact dual-band smart NEMS magnetoelectric antennas for simultaneous wireless energy harvesting and magnetic field sensing

“…Regardless of the powering method used, as the receiver shrinks, it becomes increasingly difficult to deliver sufficient power to operate the IMD, which can range from a few to several hundred microwatts depending on the application. This puts a heavy burden on the miniaturization of coils and piezo devices, which explains why many state-of-the-art single channel devices remain bulky [5][6][7][8][9] . Ultimately, these devices will need to be surgically implanted into the brain but the technology remains too large for human applications.…”

Robust Wireless Power Transfer to Multiple mm-Scale Freely-Positioned Neural Implants

“…This assumes parasitics due to the transcranial interconnects are negligible. The PTE can therefore be written as η = η 1,eq • η eq,4 , where η 1,eq and η eq,4 can be found from [14]. Thus, for the proposed WPT system, the PTE can be expressed as…”