Milo W. Hyde

A geometrical optics polarimetric bidirectional reflectance distribution function for dielectric and metallic surfaces

A polarimetric bidirectional reflectance distribution function (pBRDF), based on geometrical optics, is presented. The pBRDF incorporates a visibility (shadowing/masking) function and a Lambertian (diffuse) component which distinguishes it from other geometrical optics pBRDFs in literature. It is shown that these additions keep the pBRDF bounded (and thus a more realistic physical model) as the angle of incidence or observation approaches grazing and better able to model the behavior of light scattered from rough, reflective surfaces. In this paper, the theoretical development of the pBRDF is shown and discussed. Simulation results of a rough, perfect reflecting surface obtained using an exact, electromagnetic solution and experimental Mueller matrix results of two, rough metallic samples are presented to validate the pBRDF.

Experimentally generating any desired partially coherent Schell-model source using phase-only control

A technique is presented to produce any desired partially coherent Schell-model source using a single phase-only liquid-crystal spatial light modulator (SLM). Existing methods use SLMs in combination with amplitude filters to manipulate the phase and amplitude of an initially coherent source. The technique presented here controls both the phase and amplitude using a single SLM, thereby making the amplitude filters unnecessary. This simplifies the optical setup and significantly increases the utility and flexibility of the resulting system. The analytical development of the technique is presented and discussed. To validate the proposed approach, experimental results of three partially coherent Schell-model sources are presented and analyzed. A brief discussion of possible applications is provided in closing.

A NONDESTRUCTIVE TECHNIQUE FOR DETERMINING COMPLEX PERMITTIVITY AND PERMEABILITY OF MAGNETIC SHEET MATERIALS USING TWO FLANGED RECTANGULAR WAVEGUIDES

In this paper,a nondestructive technique for determining the complex permittivity and permeability of magnetic sheet materials using two flanged rectangular waveguides is presented. The technique extends existing single probe methods by its ability to simultaneously measure reflection and transmission coefficients imperative for extracting both permittivity and permeability over all frequencies. Using Loves Equivalence Principle,a system of coupled magnetic field integral equations (MFIEs) is formed. Evaluation of one of the two resulting spectral domain integrals via complex plane integration is discussed. The system,solved via the Method of Moments (MoM),yields theoretical values for the reflection and transmission coefficients. These values are compared to measured values and the error minimized using nonlinear least squares to find the complex permittivity and permeability of a material. Measurement results for two magnetic materials are presented and compared to traditional methods for the purpose of validating the new technique. The techniques sensitivity to uncertainties in material thickness and waveguide alignment is also examined.

Error analysis of a two-layer method for the electromagnetic characterization of conductor-backed absorbing material using an open-ended waveguide probe

A two-layer nondestructive method for characterizing the electric and magnetic properties of lossy conductor-backed magnetic materials using a ∞anged rectangular-waveguide probe is examined. The two re∞ection measurements necessary to determine both permittivity and permeability are made by flrst applying the probe to the material under test and then applying the probe to a known-material layer placed on top of the material under test. The theoretical re∞ection coe-cient is obtained using a rigorous full-wave solution, and an extrapolation scheme is used to minimize the error due to truncating the modal expansion of the waveguide flelds. An error analysis is performed to compare the performance of the technique to the two-thickness method, which utilizes two difierent thicknesses of the material under test. The properties of the known material layer that result in the least error due to network analyzer uncertainty are determined. The sensitivity of the two-layer method is also explored and discussed.

Producing any desired far-field mean irradiance pattern using a partially-coherent Schell-model source

A new technique is presented to produce any desired mean far-field irradiance pattern using a partially-coherent Schell-model source. The new method differs from similar approaches in the literature by requiring only phase control. This permits the proposed approach to be easily implemented in the laboratory using a single spatial light modulator. The analytical development of the phase-only method is presented and discussed. Simulation and experimental results are presented to validate the proposed method. Applications for the new technique include free-space optical communications, material processing/manufacture, and particle trapping.

Material Classification of an Unknown Object Using Turbulence-Degraded Polarimetric Imagery

In this paper, a material-classification technique using polarimetric imagery degraded by atmospheric turbulence is presented. The classification technique described here determines whether an object is composed of dielectric or metallic materials. The technique implements a modified version of the LeMaster and Cain polarimetric maximum-likelihood blind-deconvolution algorithm in order to remove atmospheric distortion and correctly classify the unknown object. The dielectric/metal classification decision is based on degree-of-linear-polarization (DOLP) maximum-likelihood estimates provided by two novel DOLP priors (one being representative of dielectric materials and the other being representative of metallic materials) developed in this paper. The DOLP estimate, which maximizes the log-likelihood function, determines the image pixels classification. Included in this paper is the review and modification of the LeMaster and Cain deconvolution algorithm. Also provided is the development of the novel DOLP priors, including their mathematical forms and the physical insight underlying their formulation. Lastly, the experimental results of two dielectric and metallic samples are provided to validate the proposed classification technique.

Computational approaches for generating electromagnetic Gaussian Schell-model sources

Two different methodologies for generating an electromagnetic Gaussian-Schell model source are discussed. One approach uses a sequence of random phase screens at the source plane and the other uses a sequence of random complex transmittance screens. The relationships between the screen parameters and the desired electromagnetic Gaussian-Schell model source parameters are derived. The approaches are verified by comparing numerical simulation results with published theory. This work enables one to design an electromagnetic Gaussian-Schell model source with pre-defined characteristics for wave optics simulations or laboratory experiments.

A Novel Method for Determining the R-Card Sheet Impedance Using the Transmission Coefficient Measured in Free-Space or Waveguide Systems

Free-space and rectangular waveguide techniques for determining the effective complex permittivity and, ultimately, the effective sheet impedance of an R-card using the forward transmission coefficient are presented. The advantage of using a transmission coefficient method instead of a more traditional reflection-based technique is discussed. The exact transcendental expressions relating the transmission coefficient and effective complex permittivity are derived and approximated using the Maclaurin series for sine and cosine. It is shown that the Maclaurin series expansion leads to simple closed-form solutions to the effective complex permittivity and avoids the use of sensitive and often unstable root search algorithms, which are necessary to solve transcendental equations. The accuracy of the approximations is directly related to the R-cards thickness and wavenumber. Free-space (4-16 GHz) and waveguide (8.2-12.4 GHz) measurements are made using two R-cards of differing thicknesses and impedances to demonstrate the method and regimes of validity. An uncertainty analysis is also performed to demonstrate the robustness of the technique.

A novel and simple technique for measuring low-loss materials using the two flanged waveguides measurement geometry *

In this paper, a novel technique is developed to practically and accurately measure the permittivity and permeability of low-loss materials using the two flanged waveguides measurement geometry (originally designed to characterize strongly absorbing materials only). A review of the two flanged waveguides measurement technique (tFWMT) as well as the Greens function-based flange-design criterion is provided. This review is followed by the introduction of the novel method (called tFWMT time-domain gating). It is shown that tFWMT time-domain gating extends the range of applicability of the tFWMT to low-loss materials and provides a clear flange-size design requirement which, for low-loss materials, is approximately two orders of magnitude smaller than that stipulated by the existing Greens function-based criterion. Lastly, material-characterization measurement results of low-loss acrylic and ECCOSORB? FGM-125, using flanges of two different sizes, are presented to validate the new technique.

NONDESTRUCTIVE COMPLEX PERMITTIVITY AND PERMEABILITY EXTRACTION USING A TWO-LAYER DUAL-WAVEGUIDE PROBE MEASUREMENT GEOMETRY

A two-layer dual-waveguide probe measurement geometry is proposed to nondestructively measure the complex permittivity and permeability of planar materials. The new measurement structure consists of two rectangular waveguides attached to a PEC ∞ange plate that is placed against the material under test, followed by a known material layer backed by a PEC. The purpose for this new measurement geometry is to improve the permittivity results obtained using the existing dual-waveguide probe geometries, namely, the PEC-backed and free-space-backed geometries, by permitting a larger electric fleld into the material under test and increasing the fleld coupling between the two rectangular waveguide apertures. The theoretical development of the technique is presented extending the existing single-layer PEC-backed method to the proposed two-layer dual-waveguide probe method. The new measurement structure is theoretically analyzed by replacing the waveguide apertures with equivalent magnetic currents as stipulated by Loves equivalence theorem. Making use of the magnetic-current-excited two-layer parallel-plate Greens function and enforcing the continuity of the transverse magnetic flelds over the waveguide apertures results in a system of coupled magnetic fleld integral equations. These coupled magnetic fleld integral equations are then solved for the theoretical re∞ection and transmission coe-cients using the Method of Moments. The desired complex permittivity and permeability of the material under test are found by minimizing the root-mean-square difierence between the theoretical and measured re∞ection and transmission coe-cients, i.e., numerical inversion. Last, experimental results utilizing the new two-layer technique are presented for two magnetic