Wireless Power Transfer for Telemetric Devices With Variable Orientation, for Small Rodent Behavior Monitoring

Gathering behavioral and biological data from small rodents is important for the study of various disease models in biomedical research. Such data acquisition requires a long-term powering method for telemetry electronics and radios, for which a wireless power transfer (WPT) scheme is desirable. This paper investigates a novel WPT system to deliver power from a stationary source (primary coil) to a moving telemetric device (secondary coil) via magnetic resonance coupling. To conduct research with rodents effectively, they must be able to move freely inside their cage. However, the continuously changing orientation of the rodent leads to coupling loss/problems between the primary and secondary coils, presenting a major challenge. We propose novel configurations of the secondary employing ferrite rods placed at specific locations and orientations within the coil. Three-dimensional finite-element analysis using COMSOL software is used to find the magnetic flux density distribution surrounding these secondary configurations. The simulation results show a significant increase of flux through the coil using our ferrite arrangement, with improved coupling at most orientations. Physical prototypes of these secondary coil configurations were constructed and experiments were conducted to test their performance. Measurements show that ferrite rods improved power transfer at most orientations, beyond that of the nominal ferrite-less configuration. The use of angled ferrite rods further improved power transfer, where the medium-ferrite-angled (4MFA) configuration is best. Experiments show the maximum power collected by 4MFA was 113 mW, when parallel to the primary coil, and 28 mW when 60° to the primary coil.