Implantable neural recording and stimulation devices hold great promise in monitoring and treatment of neurological disorders, limb reanimation and, development of brain-computer interfaces among other applications. However, transcutaneous wires limit the lifetime of such devices and there is a need for self-contained fully implantable solutions. In this work, we propose a novel dual-frequency approach for simultaneous wireless power transfer and low-power communication for small form factor fully implantable neural devices. We deliver wireless power using efficient magnetically coupled resonators operating at 13.56MHz and communicate using ultra-low power backscatter communication at 915 MHz. We leverage the frequency separation to combine wireless power and communication resonators with minimal interference using a novel concentric design, which meets the stringent size restrictions. We implement the wireless power receiver and communication front end of the implanted device in 65 nm CMOS and demonstrate 25 mW power delivery and 6 Mbps communication link.

Onboard power remains a major challenge for miniature robotic platforms. Locomotion at small scales demands high power densities from all system components, while limited payload capacities place severe restrictions on the size of the energy source, resulting in integration challenges and short operating times when using conventional batteries. Wireless power delivery has the potential to allow microrobotic platforms to operate autonomously for extended periods when near a transmitter. This paper describes the first demonstration of RF wireless power transfer in an insect-scale ambulatory robot. A wireless power transmission system based on magnetically coupled resonance is designed for the latest iteration of the Harvard Ambulatory MicroRobot (HAMR), a piezoelectrically driven quadruped that had previously received power through a tether. Custom power and control electronics are designed and implemented on lightweight printed circuit boards that form a part of the mechanical structure of the robot. The integration of the onboard receiver, power and control electronics, and mechanical structure yields a 4cm, 2.1g robot that can operate autonomously in two wireless power transmission scenarios.

Optimization of coil sizes for wireless power transfer applications has a significant impact on the range and efficiency of the wireless power system. Often it is difficult to accurately analyze how a set of coils will perform before they are constructed due to the complexity of approximating the parasitic components and coupling coefficients associated with the coils. Also, for certain wireless power applications such as consumer electronic devices, implanted medical devices and industrial equipment that have physical constraints on the size and shape of the coils, it can be a difficult and time-consuming process to design and evaluate several different coil configurations for optimal range and efficiency. This paper provides simplified design equations to accurately calculate the self inductance, capacitance, resistance, quality factor and coupling coefficient in terms of coil geometries for flat, spiral coils. Experimental results validate the analysis and a design example is provided to optimize the size of a transmit coil for maximum range and wireless power efficiency to a 5.8cm receive coil used in a four-element wireless power transfer system.