title: A Figure-of-Merit for Design and Optimization of Inductive Power Transmission Links for Millimeter-Sized Biomedical Implants.
abstract: Power transmission efficiency (PTE) has been the key parameter for wireless power transmission (WPT) to biomedical implants with millimeter (mm) dimensions. It has been suggested that for mm-sized implants increasing the power carrier frequency (fp) of the WPT link to hundreds of MHz improves PTE. However, increasing fpsignificantly reduces the maximum allowable power that can be transmitted under the specific absorption rate (SAR) constraints. This paper presents a new figure-of-merit (FoM) and a design methodology for optimal WPT to mm-sized implants via inductive coupling by striking a balance between PTE and maximum delivered power under SAR constraints (PL,SAR). First, the optimal mm-sized receiver (Rx) coil geometry is identified for a wide range of fpto maximize the Rx coil quality factor (Q). Secondly, the optimal transmitter (Tx) coil geometry and fpare found to maximize the proposed FoM under a low-loss Rx matched-load condition. Finally, proper Tx coil and tissue spacing is identified based on FoM at the optimal fp. We demonstrate that fpin order of tens of MHz still offer higher PL,SARand FoM, which is key in applications that demand high power such as optogenetics. An inductive link to power a 1 mm3implant was designed based on our FoM and verified through full-wave electromagnetic field simulations and measurements using de-embedding method. In our measurements, an Rx coil with 1 mm diameter, located 10 mm inside the tissue, achieved PTE and PL,SARof 1.4% and 2.2 mW at fpof 20 MHz, respectively.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Ibrahim
authors.forename: Mehdi
authors.initials: M
authors.lastname: Kiani
mesh_terms: D000465:Algorithms; D011211:Electric Power Supplies; D004867:Equipment Design; D006801:Humans; D019736:Prostheses and Implants; D059015:Wireless Technology