Implanted medical devices may no longer need batteries, says Ajay Tikka from Victoria University in Melbourne. Instead, he and his colleagues have developed technology that can wirelessly beam power to a device implanted under the skin.
Using that power to open tiny valves remotely in implanted drug delivery technology is one potential application, according to the team from Victoria University and the University of Adelaide. Another possibility is to use such power to download data from an implanted diagnostic device, they say.
Wireless Implant Communication using Inductive Coupling
Ajay Tikka 1 , Michael Faulkner1, and Said Al-Sarawi2
1Centre for Telecommunications and Microelectronics (CTME), Victoria University, VIC 8001, Australia
2Centre for Biomedical Engineering, the University of Adelaide, South Australia 5005, Australia
The use of inductive coupling for remote interrogation and powering of a human implantable microvalve is presented. The modelling, characterisation and development of a reliable communication link is outlined by analyzing the electromagnetic field interactions with the human body.
The capability to wirelessly control fluid flow through a microvalve can emerge as an attractive technology enabling various biomedical applications such as remote drug delivery and in vitro diagnostics. Contactless powering of such a microvalve is best addressed by near field inductive coupling due to its close proximity to the external interrogator. A numerical and experimental analysis of the biotelemetry link for the microvalve was undertaken in the vicinity of numerical and physical human body phantoms, respectively. To accurately account for the path losses and to address the design optimisation, the receiver coil/antenna was solved simultaneously with the transmitter coil/antenna in the presence of a human body simulant using 3-dimensional, high frequency electromagnetic, finite element method (FEM) modelling. The received relative signal strength was numerically and experimentally derived for a miniature (6×6×0.5 mm), square spiral antenna/coil when interrogated by a hand-held 8×5×0.2 cm square spiral antenna/coil in the near field, as shown in Fig.1. Fig 1. Equivalent circuit of the inductive link with spirals for both handheld and implant coils.
II. INDUCTIVE LINK DESIGN
Fig 2. Equivalent circuit of the inductive link with spirals for both handheld and implant coils. A complete equivalent circuit of the inductive link coupling the handheld and implant coils for spiral geometries is depicted in Fig 2. Here, Rh and Lh are the ohmic resistance and inductance of the primary/handheld coil, respectively, and Ri and Li are the ohmic resistance and inductance of the secondary/implanted coil, respectively. The capacitors C1 and C2 are the tuning capacitors employed to maximise the power transfer by matching the impedances of both the coils. Fig 3. Snapshot of a 12-turn square spiral coil/antenna on a 128ο YX LiNbO3 wafer.
Fig 4. Simulated and measured coupling (S12) between the implanted and transmitter coil separated by a distance of 5 cm by human body phantom.
Ajay Tikka, firstname.lastname@example.org