High Intensity Laser Power Beaming for Wireless Power Transmission

This paper describes work supporting the development of a high intensity laser power beaming (HILPB) system for the purpose of wireless power transmission. The main contribution of this research is utilizing high intensity lasers to illuminate vertical multi-junction (VMJ) solar cells developed by NASA-GRC. Several HILPB receivers are designed, constructed and evaluated with various lasers to assess the performance of the VMJ cells and the receiver under a variety of conditions. Several matters such as parallel cell back-feeding, optimal receiver geometry, laser wavelength, non-uniform illumination and thermal effects at high intensities are investigated. Substantial power densities are achieved, and suggestions are made to improve the performance of the system in future iterations. Thus far, the highest amount of energy obtained from a receiver during these tests was 23.7778 watts. In addition, one VMJ cell was able to achieve a power density of 13.6 watts per cm2, at a conversion efficiency of 24 . These experiments confirm that the VMJ technology can withstand and utilize the high intensity laser energy without damage and/or significant reduction in the conversion efficienc

High Intensity Laser Power Beaming for Wireless Power Transmission

This paper describes work supporting the development of a high intensity laser power beaming (HILPB) system for the purpose of wireless power transmission. The main contribution of this research is utilizing high intensity lasers to illuminate vertical multi-junction (VMJ) solar cells developed by NASA-GRC. Several HILPB receivers are designed, constructed and evaluated with various lasers to assess the performance of the VMJ cells and the receiver under a variety of conditions. Several matters such as parallel cell back-feeding, optimal receiver geometry, laser wavelength, non-uniform illumination and thermal effects at high intensities are investigated. Substantial power densities are achieved, and suggestions are made to improve the performance of the system in future iterations. Thus far, the highest amount of energy obtained from a receiver during these tests was 23.7778 watts. In addition, one VMJ cell was able to achieve a power density of 13.6 watts per cm2, at a conversion efficiency of 24 . These experiments confirm that the VMJ technology can withstand and utilize the high intensity laser energy without damage and/or significant reduction in the conversion efficienc

Minimizing Losses in a Space Laser Power Beaming System

A mathematical model is developed to track the amount of power delivered in a wireless laser power beaming system. In a wireless system the power proceeds through several different stages before being delivered to a payload for use. Each of these stages results in power losses that are thoroughly examined and modeled, allowing for the calculation of the likely amount of power delivered. Adjusting variable factors within the model allows for the optimization of the system for a specific task. The model shows that an optimized wireless power transfer system can deliver enough power to meet the space experiment objectives. For example, to power a Hall-Effect Thruster, a laser, photovoltaic cells, satellite power distribution method, and batteries all impact the amount of power delivered. Careful selection of these components will allow the laser to power the thruster and the model provides how much power is transferred. Knowledge of the power requirements for the payload allows the model to determine how long it will be able to operate the payload with the power provided. This model will allow system engineers to answer important design questions about the selection of components to ensure that the end product delivers maximum power

Free Space Optical Communications with High Intensity Laser Power Beaming

This research demonstrates the feasibility of utilizing high intensity laser power beaming (HILPB) systems as a conduit for robust free-space optical communications over large distances and in challenging atmospheric conditions. The uniqueness of vertical multi-junction (VMJ) photovoltaic cells used in HILPB systems in their ability to receive and to convert at high efficiency, very high intensity laser light of over 200 W/cm2, presents a unique opportunity for the development of the robust free space optical communication system by modulating information signals onto the transmitted high intensity photonic energy. Experiments were conducted to investigate and validate several optical communications concepts. A laser modulator was implemented to exhibit the excellent transient response of the VMJ technology at very high illumination intensities, and thus show its applicability to optical communications. In addition, beam polarization optic stages were employed to demonstrate a secure multi-channel communications scheme. The off-axis response of the receiver and the beam profile were characterized in order to evaluate the feasibility of developing acceptable pointing and tracking geometries. Finally, the impact of signal modulation on the total converted energy was evaluated and shown to have minimal effect on the overall power transmission efficiency. Other aspects of the proposed communication system are studied including: quantifying beamwidth and directivity, signal-to-noise-ratio, information bandwidth, privacy, modulation and detection schemes, transmission channel attenuation and disturbances (atmospheric turbulence, scintillation from index of refraction fluctuations, absorption and scattering from thermal and moisture variation) and beam acquisition tracking and pointing influence on the performance metrics of optical transmission technologies. The result of this research demonstrates the feasibility of, and serves as a comprehensive design guide for the implementation of a HILPB communication system. S

Free Space Optical Communications with High Intensity Laser Power Beaming

This research demonstrates the feasibility of utilizing high intensity laser power beaming (HILPB) systems as a conduit for robust free-space optical communications over large distances and in challenging atmospheric conditions. The uniqueness of vertical multi-junction (VMJ) photovoltaic cells used in HILPB systems in their ability to receive and to convert at high efficiency, very high intensity laser light of over 200 W/cm2, presents a unique opportunity for the development of the robust free space optical communication system by modulating information signals onto the transmitted high intensity photonic energy. Experiments were conducted to investigate and validate several optical communications concepts. A laser modulator was implemented to exhibit the excellent transient response of the VMJ technology at very high illumination intensities, and thus show its applicability to optical communications. In addition, beam polarization optic stages were employed to demonstrate a secure multi-channel communications scheme. The off-axis response of the receiver and the beam profile were characterized in order to evaluate the feasibility of developing acceptable pointing and tracking geometries. Finally, the impact of signal modulation on the total converted energy was evaluated and shown to have minimal effect on the overall power transmission efficiency. Other aspects of the proposed communication system are studied including: quantifying beamwidth and directivity, signal-to-noise-ratio, information bandwidth, privacy, modulation and detection schemes, transmission channel attenuation and disturbances (atmospheric turbulence, scintillation from index of refraction fluctuations, absorption and scattering from thermal and moisture variation) and beam acquisition tracking and pointing influence on the performance metrics of optical transmission technologies. The result of this research demonstrates the feasibility of, and serves as a comprehensive design guide for the implementation of a HILPB communication system. S

Free Space Optical Communications with High Intensity Laser Power Beaming

This research demonstrates the feasibility of utilizing high intensity laser power beaming (HILPB) systems as a conduit for robust free-space optical communications over large distances and in challenging atmospheric conditions. The uniqueness of vertical multi-junction (VMJ) photovoltaic cells used in HILPB systems in their ability to receive and to convert at high efficiency, very high intensity laser light of over 200 W/cm2, presents a unique opportunity for the development of the robust free space optical communication system by modulating information signals onto the transmitted high intensity photonic energy. Experiments were conducted to investigate and validate several optical communications concepts. A laser modulator was implemented to exhibit the excellent transient response of the VMJ technology at very high illumination intensities, and thus show its applicability to optical communications. In addition, beam polarization optic stages were employed to demonstrate a secure multi-channel communications scheme. The off-axis response of the receiver and the beam profile were characterized in order to evaluate the feasibility of developing acceptable pointing and tracking geometries. Finally, the impact of signal modulation on the total converted energy was evaluated and shown to have minimal effect on the overall power transmission efficiency. Other aspects of the proposed communication system are studied including: quantifying beamwidth and directivity, signal-to-noise-ratio, information bandwidth, privacy, modulation and detection schemes, transmission channel attenuation and disturbances (atmospheric turbulence, scintillation from index of refraction fluctuations, absorption and scattering from thermal and moisture variation) and beam acquisition tracking and pointing influence on the performance metrics of optical transmission technologies. The result of this research demonstrates the feasibility of, and serves as a comprehensive design guide for the implementation of a HILPB communication system. S

High Intensity Laser Power Beaming Architecture for Space and Terrestrial Missions

High Intensity Laser Power Beaming (HILPB) has been developed as a technique to achieve Wireless Power Transmission (WPT) for both space and terrestrial applications. In this paper, the system architecture and hardware results for a terrestrial application of HILPB are presented. These results demonstrate continuous conversion of high intensity optical energy at near-IR wavelengths directly to electrical energy at output power levels as high as 6.24 W from the single cell 0.8 cm2 aperture receiver. These results are scalable, and may be realized by implementing receiver arraying and utilizing higher power source lasers. This type of system would enable long range optical refueling of electric platforms, such as MUAV s, airships, robotic exploration missions and provide power to spacecraft platforms which may utilize it to drive electric means of propulsion

Optical wireless energy transfer for self-sufficient small cells

Wireless backhaul communication and power transfer can make the deployment of outdoor small cells (SCs) more cost effective; thus, their rapid densification can be enabled. For the first time, solar cells can be leveraged for the two-fold function of energy harvesting (EH) and high speed optical wireless communication. In this thesis, two complementary concepts for power provision to SCs are researched using solar cells – the optical wireless power transfer (OWPT) in the nighttime and solar EH during daytime. A harvested power of 1W is considered to be required for an autonomous SC operation. The conditions of darkness – worst case scenario – are initially selected, because the SC needs to harvest power in the absence of ambient light. The best case scenario of daytime SC EH from sunlight is then explored to determine the required battery size and the additional power from optical sources. As a first approach, an indoor 5m experimental link is created using a white light-emitting diode for OWPT to an amorphous silicon (Si) solar panel. Despite the use of a large mirror for collimation, the harvested power and energy efficiency of the link are measured to be only 18:3mW and 0:1%, respectively. Up to five red laser diodes (LDs) with lenses and crystalline Si (c-Si) cells are used in a follow-up study to increase the link efficiency. A maximum power efficiency of 3:2% is measured for a link comprising two LDs and a mono-c-Si cell, and the efficiency of all of its components is determined. Also, the laser system is shown to achieve an improvement of the energy efficiency by 2:7 times compared with a state-of-the-art inductive power transfer system with dipole coils. Since the harvested power is only 25:7mW, an analytical model for an elliptical Gaussian beam is developed to determine the required number of LDs for harvesting 1W; this shows an estimated number of 61 red LDs with 50mW of output optical power per device. However, a beam enclosure of the developed Class 3B laser system of up to a 3:6m distance is required for eye safety. A simulation study is conducted in Zemax for the design of an outdoor 100m infrared wireless link able to harvest 1W under clear weather conditions. Harvesting 1:2W and meeting eye safety regulations for Class 1 are shown to be feasible by a 1550 nm laser link. The required number of laser power converters is estimated to be 47 with an area of 5 5mm2 per device. Also, the dimensions of the transmitter and receiver are considered to be acceptable for the practical application of SC EH. In the last part of this thesis, two multi-c-Si solar panels are initially used for EH in an outdoor environment during daytime. The power supply of at least 1W is shown to be achievable during hour periods under sunny and cloudy conditions. A maximum average power of 4:1W is measured in the partial presence of clouds using a 10W solar panel. Since the variability of weather conditions induces the harvested power to fluctuate with values of mW, the use of optical sources is required in periods of insufficient solar EH for SCs. Therefore, a hybrid solar/laser based EH design is proposed for a continuous annual SC provision of 1Win ‘darker’ places on earth such as Edinburgh, UK. The 10W multi-c-Si solar panel and the 1550 nm laser link are considered; thus, the feasibility of supplying the SC with at least 1Wper hour monthly using a battery with energy content of only 60Wh is shown through simulations. A maximum monthly average harvested power of 824mW is shown to be required by the 1550 nm laser system that has already been overachieved through simulations in Zemax

Photovoltaic Energy Harvesting for Millimeter-Scale Systems

The Internet of Things (IoT) based on mm-scale sensors is a transformational technology that opens up new capabilities for biomedical devices, surveillance, micro-robots and industrial monitoring. Energy harvesting approaches to power IoT have traditionally included thermal, vibration and radio frequency. However, the achievement of efficient energy scavenging for IoT at the mm-scale or sub mm-scale has been elusive. In this work, I show that photovoltaic (PV) cells at the mm-scale can be an alternative means of wireless power transfer to mm-scale sensors for IoT, utilizing ambient indoor lighting or intentional irradiation of near-infrared (NIR) LED sources through biological tissue. Single silicon and GaAs photovoltaic cells at the mm-scale can achieve a power conversion efficiency of more than 17 % for silicon and 30 % for GaAs under low-flux NIR irradiation at 850 nm through the optimized device structure and sidewall/surface passivation studies, which guarantees perpetual operation of mm-scale sensors. Furthermore, monolithic single-junction GaAs photovoltaic modules offer a means for series-interconnected cells to provide sufficient voltage (> 5 V) for direct battery charging, and bypassing needs for voltage up-conversion circuitry. However, there is a continuing challenge to miniaturize such PV systems down to the sub mm-scale with minimal optical losses from device isolation and metal interconnects and efficient voltage up-conversion. Vertically stacked dual-junction PV cells and modules are demonstrated to increase the output voltage per cell and minimize area losses for direct powering of miniature devices for IoT and bio-implantable applications with low-irradiance narrowband spectral illumination. Dual-junction PV cells at small dimensions (150 µm x 150 µm) demonstrate power conversion efficiency greater than 22 % with more than 1.2 V output voltage under low-flux 850 nm NIR LED illumination, which is sufficient for batteryless operation of miniaturized CMOS IC chips. The output voltage of dual-junction PV modules with eight series-connected single cells is greater than 10 V while maintaining an efficiency of more than 18 %. Finally, I demonstrate monolithic PV/LED modules at the µm-scale for brain-machine interfaces, enabling two-way optical power and data transfer in a through-tissue configuration. The wafer-level assembly plan for the 3D vertical integration of three different systems including GaAs LED/PV modules, CMOS silicon chips, and neural probes is proposed.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163261/1/esmoon_1.pd