Joaquin J. Casanova

A Loosely Coupled Planar Wireless Power System for Multiple Receivers

Wireless power transfer is demonstrated mathematically and experimentally for M primary coils coupled to N secondary coils. Using multiple primary coils in parallel has advantages over a single primary coil. First, the reduced inductance of the transmitting coils makes the amplifier less sensitive to component variations. Second, with multiple receiving coils, the power delivery to an individual receiver is less sensitive to changes in the loads attached to other coils. By using a 16 cm by 18 cm primary and a 6 cm by 8 cm secondary coil, going from a 1:2 coupling to a 2:2 coupling, we show an increase in received power from 1.8 to 9.5 W, with only a small change in coupling efficiency. The advantages of the multiple primary coil topology increase the feasibility of charging multiple wireless portable devices simultaneously.

Design and Optimization of a Class-E Amplifier for a Loosely Coupled Planar Wireless Power System

In wireless power systems for charging battery-operated devices, the selection of component values guaranteeing certain desired performance characteristics can be a tedious trial-and-error process, either sweeping component values in circuit simulations or changing components by hand. This difficulty is compounded by the variable nature of the load resistance presented by a device under charge. This brief considers component selection for a specific wireless power system architecture, which is an open-loop class-e inverter using a series-parallel arrangement for load impedance transformation. Formulas for the optimal receiver, transmitter, and class-e components are derived given a set of constraints on the resistance, phase, quality factor, and drain voltage waveform. Using a 16 cm times 18 cm primary and a 4 cm times 5 cm secondary coil, the derived formulas are used to build a wireless power system. We show that the system has desirable performance characteristics, including a power delivery of over 3.7 W, peak efficiency of over 66%, and decreasing power delivery with increasing load resistance.

Transmitting coil achieving uniform magnetic field distribution for planar wireless power transfer system

A 20 cm by 20 cm transmitting coil is designed for an inductively-coupled power transfer system. The coil design is a spiral, whose geometry is optimized to ensure an even magnetic field distribution. This guarantees uniform power delivery regardless of recieving coil position. The transmitting coil is tested using Litz wire, a switchmode power amplifier, and a 6 cm by 8 cm recieving coil connected to a rectifier and a variable load. The system achieves a maximum efficiency of 80.9% and a maximum power delivery of 11.8 W. At a fixed load, the power delivery has a coefficient of variation of 2.2% as the recieving coils position is varied on the transmitter. In general, the system efficiency is high and insensitive to receiver placement as well as loading conditions.

Method of Load/Fault Detection for Loosely Coupled Planar Wireless Power Transfer System With Power Delivery Tracking

A method to determine various operating modes of a high-efficiency inductive wireless power transfer system which is capable of supporting more than one receiver is proposed. The three operating modes are no-load, safe, and fault modes. The detection scheme probes the transmitter circuitry periodically to determine the operating mode. For power saving, the transmitter is powered down when there is no valid receiver placed on the transmitting coil. If any conductive or magnetic object that can affect the total effective inductance of the transmitting coil is located nearby, the system will enter the fault mode and shut down the transmitter so that it will not be damaged. The safe mode is the nominal operation mode when the power transmission efficiency is high with minimum power loss and zero-voltage switching operation of the class-E transmitter is achieved. The determination of the operating mode is achieved by analyzing the transmitting coil voltage and supply current space, requiring no communication link between the transmitter and receiver. The linear relationship between the power delivery and the supply current can be used to calculate the power delivered to the load(s).

A wireless power station for laptop computers

A wireless power system via magnetic induction that can deliver 32 W to a laptop is designed and fabricated. A 60% peak end-to-end regulated efficiency is achieved. A load detection scheme is also implemented, which detects when a device is placed on the transmitter and can shut down the system if faults are detected. The system eliminates the need to plug the laptop into AC power when running or charging.

High efficiency midrange wireless power transfer system

Wireless power transfer systems using near-field magnetic coupling are attractive as they allow power transfer with high efficiency and do not require an unobstructed path between transmitter and receiver. In this work a two coil wireless power transmission system is analyzed, including the driving amplifier, and a demonstration system is built and characterized. The system achieves 76% efficiency for a distance of 1 meter for 40W transferred power. The effects of changes to the geometry of the system (pitch angle of coils, separation distance) are also examined, and the effect on amplifier topologies analyzed.

CALIBRATION OF THE CERES-MAIZE MODEL FOR LINKAGE WITH A MICROWAVE REMOTE SENSING MODEL

Stored water, i.e., soil moisture in the root zone, is the most important factor governing energy and moisture fluxes at the land surface. Crop models are typically used to estimate these fluxes and simulate crop growth and development. Remotely sensed microwave observations can be used to improve estimates of these fluxes, biomass, and yield. This research aims to calibrate a crop growth model, CERES-Maize, for a growing season of corn in north-central Florida. The CERES-Maize model was extended to weather and soil conditions of the region and calibrated using data from our second Microwave Water and Energy Balance Experiment (MicroWEX-2). The calibrated model was linked to a microwave brightness (MB) model to estimate brightness signatures of the growing corn canopy. Overall, the CERES-Maize model estimated realistic total biomass with a root mean square error (RMSE) of 1.1 Mg/ha and a Willmott d-index of 0.98. However, the partitioning of total biomass into stem and leaf biomasses were under- and overestimated, respectively. LAI matched well with the MicroWEX-2 observations with an RMSE of 0.10 and a Willmott d-index of 0.99. The model estimated realistic daily latent heat flux with an RMSE of 42 W/m2. The soil moisture and temperature profiles of deeper soil layers matched reasonably well with observations, with RMSE of 1% to 3.5% and 1.4 to 3.7 K, respectively. Near-surface (0-5 cm) soil moisture and temperatures were less realistic because the hydrological processes near the surface need to be modeled on a much shorter timestep than is allowed by the crop model. The microwave emission model was run using observed canopy and soil inputs, as well as with the modeled canopy and soil inputs (linked crop-MB). The two methods produced similar seasonal trends in brightness temperatures with an RMS difference of 18.50 K. However, the linked model could not capture diurnal variations in brightness temperatures due to its daily timestep. Such integrated crop-MB models can be used for assimilation of remotely sensed microwave brightness in future studies to improve estimates of land surface fluxes and crop growth and development.

Design of a 3-D Fractal Heatsink Antenna

A new type of dual-function structure is presented, a 3-D fractal heatsink antenna. This design is simulated at different fractal iterations in Ansoft HFSS and ePhysics to assess its electromagnetic and thermal performance, relative to a patch antenna and a finned heatsink antenna. It compares favorably to a patch antenna, improving radiation efficiency (up to 0.98) and directivity (up to 8.21 dB). As a heatsink, it decreases thermal resistance in comparison to a typical finned heatsink by an order of magnitude.

A Loosely Coupled Planar Wireless Power Transfer System Supporting Multiple Receivers

A high-efficiency wireless power transfer system which is capable of supporting more than one receiver using class E operation for transmitter via inductive coupling has been designed and fabricated. The design approach of the system is also presented in this paper. The system requires no complex external control system but relies on its natural impedance response to achieve the desired power delivery profile across a wide range of load resistances while maintaining high efficiency to prevent any heating issues. A switch circuit is used to decouple the fully charged receiver from the system so that power delivery to the other receiver can be improved. The fabricated system at 12 V supply voltage is compact and capable of approximately 2.5 W of power delivery to each of the two receivers in a dual receiver setup and 5 W to a single receiver alone or when the other receiver is decoupled by the receiver switch. During high-power delivery state, the system efficiency is between 67.5% and 77.5%.

Development of a Wireless Computer Vision Instrument to Detect Biotic Stress in Wheat

Knowledge of crop abiotic and biotic stress is important for optimal irrigation management. While spectral reflectance and infrared thermometry provide a means to quantify crop stress remotely, these measurements can be cumbersome. Computer vision offers an inexpensive way to remotely detect crop stress independent of vegetation cover. This paper presents a technique using computer vision to detect disease stress in wheat. Digital images of differentially stressed wheat were segmented into soil and vegetation pixels using expectation maximization (EM). In the first season, the algorithm to segment vegetation from soil and distinguish between healthy and stressed wheat was developed and tested using digital images taken in the field and later processed on a desktop computer. In the second season, a wireless camera with near real-time computer vision capabilities was tested in conjunction with the conventional camera and desktop computer. For wheat irrigated at different levels and inoculated with wheat streak mosaic virus (WSMV), vegetation hue determined by the EM algorithm showed significant effects from irrigation level and infection. Unstressed wheat had a higher hue (118.32) than stressed wheat (111.34). In the second season, the hue and cover measured by the wireless computer vision sensor showed significant effects from infection (p = 0.0014), as did the conventional camera (p < 0.0001). Vegetation hue obtained through a wireless computer vision system in this study is a viable option for determining biotic crop stress in irrigation scheduling. Such a low-cost system could be suitable for use in the field in automated irrigation scheduling applications.