In-band load modulation as a means of transferring information from a wirelessly-powered client device to a power provider in a wireless power transfer (WPT) system has long been considered to have an unacceptable impact on the efficiency of power transfer. Conventional load modulation involves either completely or severely detuning the receive coil in order to produce a detectable amplitude shift at the power provider side and thereby transfer information. In this work, we analyze the impact of load modulation on system efficiency by considering the power consumption of the transmit power amplifier (PA) and identify a tradeoff between communication capability and end-to-end wireless power transfer efficiency. We also determine how to select a load modulation strategy which reduces the degradation in power transfer efficiency while maintaining high-contrast uplink signaling. Finally, we explore the use of coherent demodulation (IQ demodulation) to reduce the mismatch requirement on a load modulation system by improving the power provider's sensitivity to load modulated signaling.

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.

Effective means of delivering wireless power to volumes of spaces will enable users the freedom and mobility to seamlessly power and recharge their devices in an unencumbered fashion. This has particular importance for consumer electronic, medical, and industrial applications, where usage models focus on unstructured and dynamic environments. However, existing wireless power technology falls short of this vision. Inductive charging solutions are limited to near-contact distances and require a docking station or precise placement for effective operation. Far-field wireless power techniques allow much greater range, but require complicated tracking systems to maintain a line-of-sight connection for high-efficiency power delivery to mobile applications. Recent work using magnetically coupled resonators (MCRs) for wireless power delivery has shown a promising intersection between range (on the order of a meter), efficiency (over 80%), and delivered power (up to tens of watts). However, unpredictable loads rapidly change system operating points, and changes in position disrupt system efficiency, which affects the ultimate usability of these systems. Dynamic adaptation to these changes in operating conditions and power transfer range is a critical capability in developing a fully functional and versatile wireless power solution. This paper provides an overview of methods used to adapt to variations in range, orientation, and load using both wideband and fixed-frequency techniques.

Wireless data communication technology has eliminated wired connections for data transfer to portable devices. Wireless power technology offers the possibility of eliminating the remaining wired connection: the power cord. For ventricular assist devices (VADs), wireless power technology will eliminate the complications and infections caused by the percutaneous wired power connection. Integrating wireless power technology into VADs will enable VAD implants to become a more viable option for heart failure patients (of which there are 80 000 in the United States each year) than heart transplants. Previous transcutaneous energy transfer systems (TETS) have attempted to wirelessly power VADs ; however, TETS-based technologies are limited in range to a few millimeters, do not tolerate angular misalignment, and suffer from poor efficiency. The free-range resonant electrical delivery (FREE-D) wireless power system aims to use magnetically coupled resonators to efficiently transfer power across a distance to a VAD implanted in the human body, and to provide robustness to geometric changes. Multiple resonator configurations are implemented to improve the range and efficiency of wireless power transmission to both a commercially available axial pump and a VentrAssist centrifugal pump [3]. An adaptive frequency tuning method allows for maximum power transfer efficiency for nearly any angular orientation over a range of separation distances. Additionally, laboratory results show the continuous operation of both pumps using the FREE-D system with a wireless power transfer efficiency upwards of 90%.