A Resonant Coupler for Subcutaneous Implant

Abstract

A resonator coupler for subcutaneous implants has been developed with a new impedance matching pattern added to the conventional loop antenna. The tuning element of a concentric metal pad contributes distributed capacitance and inductance to the planar inductive loop and improves resonance significantly. It provides a better qualify factor for resonant coupling and a much lower reflection coefficient for the implant electronics. Practical constraints are taken into account for designs including the requirement of operation within a regulated frequency band and the limited thickness for a monolithic implant. In this work, two designs targeting to operate in the two industrial, scientific, and medical (ISM) bands at 903 MHz and 2.45 GHz are considered. The tuning metal pad improves their resonances significantly, compared to the conventional loop designs. Since it is difficult to tune the implant antenna after implantation, the effects of tissue depth variations due to the individual’s surgery and the appropriate implant depths are investigated. Simulations conducted with the dielectric properties of human skin documented in the literature are compared to measurements done with hydrated ground pork as phantoms. Experiments and simulations are conducted to explain the discrepancies in frequency shifts due to the uses of pork phantoms. The design method is thus validated for uses on human skin. A noninvasive localization method to identify the implant under the skin has been examined and demonstrated by both simulations and measurements. It can efficiently locate the subcutaneous implant based on the high quality-factor resonance owing to the tuning elements in both implant and transmitter couplers. The planar resonant coupler for wireless power transfer shows good performance and promise in subcutaneous applications for implants.

A Flexible Tuned Radio-Frequency Planar Resonant Loop for Noninvasive Hydration Sensing

“…However, the principle can be applied for any frequency band. Similar designs with the same impedance matching concept have been investigated in our previous work to improve the power-transfer performance in subcutaneous implants [61], [62]. The results showed that the planar tuned loop can be designed to a compact size with excellent performance in resonance.…”

“…The copper pattern was etched after photolithography was applied with a photomask on the photoresist-covered film. A previous demonstration of the tuned loop for a wirelessly-powered implant application was conducted on rigid substrates [61]. The thickness of the film is 76 µm with a dielectric constant of 3.2.…”

Approach-Based Analysis on Wireless Power Transmission for Bio-Implantable Devices

“…A resonator for implants (subcutaneous) was developed, which provides a new pattern for impedance matching to the existing loop antenna [47]. The metal pad, which is made of concentric model-tuning components, was put up and distributed inductance and capacitance to inductive loop (planar model), which improved the resonance highly.…”

A Tuned Microwave Resonant System for Subcutaneous Imaging

“…With the proposed tuning principle, loop resonators can be made into compact forms with high resonance performance, and they provide great advantages for sensing or near-field signal/power coupling. Applications have been investigated for human hydration monitoring [ 37 , 38 ], subcutaneous implant localization, and wireless power transfer [ 39 , 40 ]. This work aimed to develop a subcutaneous tumor screening system based on our tuned loop resonator.…”

“…When abnormal tissue is underneath the loop, the resonant frequency or reflection coefficient s 11 will have a noticeable shift or change. Our previous work [ 39 ] developed an implant-locating mechanism based on this principle. However, the implant has a corresponding metal loop, which creates a new resonance with the external sensing resonator to emphasize the contrast for its location.…”