Search

Wireless power transfer (WPT) has gained renewed interest due to emerging low-power applications and high efficiency. Coupled with power in many applications is the need for communication, whether for regulation of power transfer or for transfer of information between the source and the load. Several communication methods have been proposed for use with WPT, including adjacent channel communication (non-WPT), as well as WPT-based methods, such as load modulation and passive backscattering. However, approaches using the WPT link have historically been low-speed (

Resonantly coupled wireless power transfer (RWPT) has become a popular means to deliver energy without direct contact between the source and load. One challenging application is nonstationary loads; those that move spatially in time. Such loads change the coupling between the source and load and with it the efficiency and maximum power transfer possible. One emerging application is in the automotive environment, where nonstationary loads such as powered seats and doors exist. Moreover, the automotive environment is particularly challenging due to the presence of metallic objects and the safety requirements of the passengers. In this work, we examine RWPT for nonstationary loads and present a design methodology for optimal efficiency and power transfer and show an RWPT of 70 W across a 24 cm distance in an automotive environment. We also examine the impact of the metallic environment and show how its effects can be mitigated. Finally, we examine the field intensity during RWPT and examine the safety of the passengers. We show that 70 W can be transmitted within 10 cm of a passenger while operating below safety limits.

Wireless-power transfer (WPT) has emerged as an important power delivery solution for many systems. In many of these systems, communication is equally important, but has typically been achieved through a non-WPT channel due to the historically low data rates of WPT channels. In this work, we demonstrate that WPT channels can support very high data rates through an experimental prototype that achieves an effective 50% fractional bandwidth of 6.78 Mbps on a 13.56 MHz carrier. This data rate is sufficient to stream high-definition (HD) video across a WPT link.

Adaptive tuning in wireless power transfer (WPT) systems is an important method to increase efficiency and to adapt to changes in system parameters, such as when loads are physically moved. Previous works have introduced solutions for a single load, where network methods or analytical techniques could find an optimal solution. The introduction of multiple loads in a WPT system, however, changes the system to a $N\geq 3$ port system and increases measurement and calculation complexity. We introduce a genetic algorithm approach that removes the necessity for expensive network measurements or complex calculations. We demonstrate our approach in a two-load WPT system that is able to increase relative efficiency by 23% and 800% to two loads through tuning and does so with a 96.8% reduction in tuning time compared to a brute-force approach.

We present the theory of high-order modulation for near-field RF identification (RFID) and wireless power transfer (WPT) systems. We show that while related, the design of RFID and WPT systems differ. The theory and calculation of load modulated quadrature amplitude modulation (QAM) and phase shift keying (PSK) is presented. We then present two experimental prototypes. The first demonstrates a 16-QAM RFID link achieving $>\!\! {\hbox{480 kb/s}}$ at a 2.38-MHz carrier ( $>\!\!{\hbox{19.8}}\%$ fractional bandwidth), significantly higher than the $ fractional bandwidth of traditional RFID systems. The second experimental prototype demonstrates 4-PSK for WPT applications achieving a data rate $> {\hbox{256 kb/s}}$ at a 2.38-MHz carrier (a 10.7% fractional bandwidth) with an average efficiency reduction of only 4%.

Wireless power transfer and other near-field applications can generate large magnetoquasistatic fields that can potentially be harmful to humans or interact negatively with the environment. Several shields have been proposed for the magnetic near field, such as ferrite sheets or metallic shields. While each can be effective, there are tradeoffs to each, namely loss, weight, and cost. In addition, metallic and ferrite shields are broadband and block large portions of the electromagnetic spectrum. In this letter, we introduce a new type of magnetic near-field shield, a zero-permeability near-field metamaterial (NF-MM) shield. This shield operates by canceling the incident magnetic flux without significant additional loss to the system. Moreover, the zero-permeability shield is frequency-selective, blocking only a single or small bandwidth of frequencies, enabling shielding only at the desired frequency while allowing the remainder of the electromagnetic spectrum through. We show that a zero-permeability NF-MM shield can reduce magnetic field strength by 22.84 dB in simulation and demonstrate 77% reduction in an experimental prototype.

We report on the magnetic field and coupling enhancement for increased wireless power transfer (WPT) efficiency using intermediate materials. We examine the physical mechanisms for enhancement using a metamaterial (MM) and magnetic resonant field enhancement (MR-FE) and present an analytical and simulation analysis as well as an experimental study of these enhancement mechanisms. While both increase the mutual coupling, the loss of the contrasting enhancement mechanisms significantly impacts WPT efficiency enhancement. Our analysis shows that the MR-FE approach can have up to a 4-times-higher efficiency over the MM approach due to the lower loss of its field enhancement mechanism.

Wireless Power Transfer (WPT) enables a new platform for electronic integration and system partitioning. In industrial and commercial applications, the ability to remove wired interconnect not only frees the power device from a physical connection, it can also enable improved performance. Key to supporting today's smart systems, is the need for communication and control in addition to power. In this work we present a WPT powered tail light that is able to be fully sealed to prevent any moisture or debris intrusion, while receiving full power for lighting. Communication is provided using LIN protocol through a Binary-Phase-Shift-Key (BPSK) Master and a load-modulated Slave.

In this paper we present an experimental wireless power transfer (WPT) prototype that has achieved a 118 kHz power transfer bandwidth operating at the maximum achievable efficiency. Using a simulation and analytical model we show that the power transfer bandwidth of an optimally tuned WPT system is determined by the loaded Q of the system and not by the Q of the resonant tanks. This observation lead to the realization of a WPT communication system that can transmit data at high data rates greater than 8% of the carrier frequency, a data rate significantly greater than has previously been proposed for resonant WPT and RFID systems.

We present a near field wireless power transfer (NF-WPT) link which is also capable of data communication through complex, quadrature amplitude (QAM) load modulation. We present a method for designing a 4QAM constellation that allows for minimal degradation of the NF-WPT link efficiency by minimizing the complex reflection coefficient. Using a modulation board and a resonant 4-coil NF-WPT system we demonstrate 307.2kbps data transmission, representing a 12.7% fractional bandwidth, over a distance of 1-coil diameter (29cm) at a carrier frequency of 2.428MHz. Efficiency of the NF-WPT is only reduced from 68% to approximately 63.1% when used for data communication as well as power transfer.

We present the theory and design equations for leveraging vector modulation in the form of M-ary quadrature amplitude modulation (QAM) for LF near and mid-range RFID systems, which can allow for the design of high bandwidth passive near and mid-range devices. The theory is developed through the impedance transformations that occur in coupled coil antennas. Using the developed theory along with system simulations, we determine the necessary load impedances for 4-QAM constellations at various distances for a carrier frequency of approximately 2.4 MHz and present 3 prototype boards that yield the desired reflections. The achievable data rates are investigated through a custom IQ demodulator, and we show that for communication distances of 17 cm, 29 cm, and 45 cm, which represent scaled coil diameter distances, data rates of 409.6 kbps, 307.2 kbps, and 153.6 kbps can be achieved. This corresponds to bandwidth percentages of 17%, 12%, and 6.5%, which surpasses the bandwidth percentage of typical NFC communication systems of about 3% for a carrier of 13.56 MHz (424 kbps).

We consider the use of insulated single wires as transmission lines to carry 100 MHz - 3 GHz radio frequency (RF) signals among devices implanted in biological tissue. In contrast to near-field magnetically coupled links, the use of transmission lines to carry RF signals results in higher efficiency for a given implant package size once the antenna is included, albeit with the disadvantage of tissue displacement along the path of the wire. We present a theory based on the work of Goubau and Rao that describes the transmission line loss of a single insulated wire in a lossy dielectric medium. We experimentally verify the characteristic impedance and insertion loss of transmission lines formed by thin wires insulated with Teflon fluorinated ethylene propylene (FEP). We consider media including 0.91% saline (a homogeneous tissue proxy), muscle tissue, and brain tissue, and present a launcher design based on a dielectric loaded coaxial sleeve. For example, in the saline proxy, a single FEP-insulated conductor of only 0.127 mm diameter presents a measured return loss of 10 dB in a 50Ω system, with a measured insertion loss of only 1 dB/cm at 1 GHz.

We propose to leverage UHF RFID techniques to yield a continuously wearable, battery-free wireless multichannel ECG telemetry device that is potentially disposable, low-cost and suitable for integration with multiple electrodes in a flexible circuit assembly. Such a device could have broad applicability, ranging from initial patient assessment by first responders, to continuous monitoring in various clinical settings. We employ a recently described single-chip data acquisition system including RF power harvesting to eliminate the need for a battery. The single-chip system includes 14 channels of integrated biopotential amplification, an 11-bit ADC, and a 5 Mbps digital backscatter telemetry link. We present an initial characterization of the telemetry chip in this application including battery-free, wireless 3 and 5 channel ECG recordings made from an ambulatory human subject at a range of ≈ 1 meter.

Wearable and implantable wireless biomedical devices are often constrained by the limited bandwidth and high power consumption of their communication links. The VHF or UHF transceivers (e.g. MICS radios) traditionally used for this communication function have relatively high power consumption, on the order of mW, due to the high bias currents required for the analog sections of the radio. To reduce overall power consumption, both the data rate and the duty cycle of the radio are usually minimized, because the lifetime of the device is limited by the energy density of available battery technologies.Recent innovations in modulated backscatter techniques offer the possibility of a radical reduction in the power cost and complexity of the data uplink, while significantly improving data rate. This is achieved by a re-partitioning of the communication link. Backscatter techniques shift the burden of power cost and complexity from the remote device to a base station. Instead of actively transmitting an RF signal, the remote device uplinks data to the base station by modulating its reflected field.We present two ultra-low power biotelemetry systems that leverage modulated backscatter in both the near-field and far-field propagation regimes. The first example operates in the far field and is designed to telemeter multiple channels of neural/EMG signals from dragonflies in flight. This device has a mass of 38 mg, a data rate of 5 Mbit/s, and a range of approximately 5 m. The second example operates in the near field and is designed to be implanted in mice. The sensor has a maximum implant depth of 6cm and can transmit at data rates of up to 30 Mbit/s. The power cost of the animal side of both data links is 4.9 pJ/bit and 16.4 pJ/bit respectively.

Fully implantable wireless biotelemetry devices have traditionally used active VHF/UHF transmitters or load modulation at HF frequencies. HF systems tend to be bandwidth-limited due to low frequency magnetic induction, while active VHF/UHF transmitters generally consume a significant amount of power in DC bias current. We show in this paper that UHF near-field backscatter can be used to achieve higher data rates at lower implant power budgets. We present experimental path loss measurements in a saline proxy system using a segmented loop antenna designed for UHF near-field operation. We present experimental results from a modulated backscatter test circuit at bit rates of up to 30 Mbps and penetration depths of up to 6 cm. The main communication element, an RF switch, consumes about 164 μA at 3 V while operating at a data rate of 30 Mbps, which is equivalent to approximately 16.4 pJ/bit.

We present an approach for implanting radio frequency transmission lines in biological tissue, using a single insulated wire surrounded by tissue as a variant of the Goubau single-wire transmission line (SWTL) in air. We extend the Goubau SWTL model to include SWTLs surrounded by lossy dielectrics such as tissue by assuming a propagating mode component in the tissue. We show that a thin wire of radius 63.5 μm, coated with biocompatible fluorinated ethylene propylene dielectric, exhibits a measured loss of only 1 dB/cm at a frequency of 915 MHz. The model fit to the measured insertion loss is within ±0.3 dB/cm across the 100 MHz to 3 GHz band. This SWTL presents excellent impedance matching to 50 Ω as evidenced by a measured median return loss better than 10 dB across the 100 MHz to 3 GHz range. This approach represents an alternative to near-field magnetic coupling for implanted systems where tissue displacement by a single, thin wire can be tolerated.