Channel Simulation of Non-imaging Optical MIMO Communication

This paper reports a channel simulation of an indoor optical wireless multiple-input-multiple-output (MIMO) system with non-imaging receivers. The system consists of a 2×2 array of white light-emitting diodes (LEDs) and 2×2 array of PDs. An overview of the model specifications, channel impulse response and channel capacity are demonstrated in this paper. The distribution of the first reflection is analyzed. The effect of SNR and the location of receivers on non-imaging optical MIMO communications are investigated. In addition, by moving the receivers, the optimal location of the communication is found.

Overview of Concentrated Photovoltaic (CPV) Cells

Previous studies have shown that renewable energy is one of the effective ways to fight global climate change and emissions not to mention the increasing price of fossil fuels. Among the various renewable energy sources which include wind, solar, biofuel, geothermal and tidal waves, solar power has attracted much attention especially here in Africa because of the abundance of solar radiation. A lot of studies have been done on various photovoltaic (PV) cells ranging from silicon to thin film and most recently multi-junction solar cells. In this paper, we focused on concentrated photovoltaic cells (CPV) which are promising ways of converting solar energy to electricity. It is expected that if the most cost effective ways of converting solar energy to electricity is used, both the cost of installation and the running cost of concentrated photovoltaic cells will equate the utility grid electricity cost in a few years to come.

A Four-Wing Compound Parabolic Concentrator(CPC)Design for Heating and Sanitization of Waste Products

Harnessing the freely available source of energy from the sun offers a number of additional benefits. Not least of these benefits is the fact that solar energy is an environmentally sustainable alternative. A four-wing compound parabolic concentrator (CPC) was designed as a modification of the regular non-imaging CPC concentrator that has a widespread use as solar collector. The design is intended to increase the angle of acceptance as well as concentration of energy from the sun. The conceptual design, mathematical formulation as well as construction and initial trial results have been presented in this paper. Pilot trials of the four-wing concentrator used for sanitizing both liquid and waste products produced satisfactory results. Improvements in terms of design as well as material used for construction and better preservation of heat can be considered further in the future research.

Optimized design of LED freeform lens for uniform circular illumination

An optimization method is proposed for designing an LED freeform lens which produces a uniform circular pattern with high energy efficiency.This method is composed of three main aspects:design of the initial guess,parameterization of the freeform surface,and construction of the merit function.The initial guess is created by solving an ordinary differential equation numerically.An approach of selecting optimization points is introduced for parameterization of the freeform surface.The merit function is constructed by use of the irradiance uniformity and the efficiency of the lens.Design examples are given,and the results show that the irradiance distribution is well controlled with a maximum uniformity(the relative standard deviation of irradiance,RSD) of 0.0122 and a maximum efficiency of 93.88%.This optimization method can be generalized to design freeform lenses with different lighting patterns or without rotational symmetry.

Ray targeting for optimizing smooth freeform surfaces for LED non-rotational illumination

We propose an effective optimization method for generating smooth freeform surfaces for light-emitting diode(LED)non-rotational illumination based on ray targeting.This method begins with a starting design and goes through two optimization steps.An initial estimate is determined using a partial differential equation(PDE)method and a variable separation mapping.In the first optimization step the merit function is developed with ray targeting to ensure the shape of the illumination pattern.The purpose of the second optimization is to further improve the optical performance by constructing the merit function with uniformity and efficiency.Smooth freeform reflective and refractive surfaces,which can produce a uniform rectangular illumination without rotational symmetry,are designed using this method.The results show that uniform rectangular illumination is achieved and that smooth freeform surfaces are obtained.With ray targeting,the design efficiency can be significantly enhanced,and excellent optical performance can be achieved.

Light concentration using hetero-junctions of anisotropic low permittivity metamaterials

Focusing incident power into an area of high concentration is of significant interest for various applications.In optics,this has been traditionally achieved with lenses where a higher curvature and lens permittivity typically result in shorter focal distances(low f/D).In this work,we present designs and techniques for collecting,refracting and guiding incident light into an area of high power concentration(a hot spot)at extremely short distances.Specifically,a flat low-profile focusing mechanism is presented using a hetero-junction of anisotropic metamaterials(MTMs).The hetero-junction is formed from two cleaved finite slabs of low(near zero)permittivity anisotropic MTMs with rotated optical axes.The MTMs have near zero longitudinal permittivity while matched in the transverse direction.Such MTMs are shown to provide a unique ability to bend the transverse magnetic or p-polarized light away from the normal and along the interface,contrary to conventional dielectrics,and with minimal reflections;hence allowing for a low profile design.Realizations in the optical regime are presented using periodic bilayers of metal and dielectric.The proposed hetero-junction focusing device concentrates the normally incident plane wave and/or beam into a corresponding focal region similar to a lens via multiple refractions.The hetero-junction is capable of creating a hot spot very close to the device,much closer than dielectric lenses and it significantly outperforms the size requirements of thick high curvature lenses with low f/D ratios.The proposed designs can find applications in various scenarios including solar and thermo photovoltaics,photodetectors,concentrated photovoltaics,non-imaging optics,micro-and nano-Fresnel lenses.

A fractal concentrator of direct and indirect sunlight

A novel concept for concentrating both direct and indirect sunlight employing a combination of waveguiding and refractive optics is presented.More specifically,it is based on both the individual and the collective focusing effects of an array of refractive optical elements of specific geometry.An analytical framework and design principles regarding the geometry of the optical elements taking into account Fresnel reflection and refraction are presented.The principle of operation along with loss mechanisms and acceptance angles are discussed in detail.Ray-tracing simulations of a light concentrator designed accordingly indicate transmittance>90%with acceptance angles of≤65°at 3 suns for moderate refractive indices.It is further numerically demonstrated that the new approach allows the utilization of the dominant fraction of the solar radiation by harvesting the waste heat in addition to photovoltaic conversion with an operating energy efficiency for diffuse light>70%.