Design and Optimization of Planar Spiral Coils for Powering Implantable Neural Recording Microsystem

Area of Science:

• Biomedical Engineering
• Electrical Engineering
• Materials Science

Background:

• Wireless power transfer (WPT) is crucial for implantable microsystems, but efficiency and safety are key challenges.
• Existing methods often struggle with limited space, low profiles, and high power demands for neural recording implants.
• Optimizing WPT systems requires balancing coil design, load impedance, and biological safety.

Purpose of the Study:

• To present a design and optimization method for inductive coupling coils for WPT in neural recording implants.
• To maximize power transfer efficiency while ensuring biological tissue safety.
• To decouple coil optimization from actual load impedance for design flexibility.

Main Methods:

• Combined semi-empirical and theoretical models for inductive coupling.
• Introduced optimal resonant load transformation for decoupled coil optimization.
• Defined a complete coil parameter optimization process with maximum theoretical power transfer efficiency as the objective.
• Designed planar spiral coils considering space, profile, power, and biocompatibility constraints.

Main Results:

• Achieved a measured power transfer efficiency of 70% at 13.56 MHz.
• The designed implanted coil had a 10 mm outer diameter with a 10 mm working distance.
• The measured efficiency closely matched the maximum theoretical efficiency of 71.9%.
• The load transformation network allows updates without rerunning the entire optimization process.

Conclusions:

• The proposed design and optimization method effectively maximizes power transfer efficiency for WPT in neural recording implants.
• The decoupled optimization approach offers flexibility and robustness against changing load conditions.
• The achieved efficiency validates the method's effectiveness for practical biomedical applications.