Recent Publications
|
Additive Manufacturing of Graded Dielectrics
D. Roper, B. Good, R. McCauley, S. Yarlagadda, J. Smith, A. Good and M.S. Mirotznik
A method for the fabrication of graded dielectrics within a structural composite is presented. This system employs an ultrasonic powder deposition head to print high dielectric powders onto a woven fabric composite ubstrate. It is shown how this system can integrate 3D variations of dielectric properties at millimeter resolution within a mechanically rugged substrate. To conclude, the system's practical application is demonstrated with experimental results from a graded index lens. |
|
Annular Slot Loaded High-Impedance Ground Plane
I. Mcmichael, A. Zaghloul,
and M. Mirotznik
High impedance surfaces like electromagnetic band gap (EBG) ground planes have been used to realize low profile antennas. In this paper, an alternative ground plane design is presented for antennas with circular current distributions, which consists of an annular slot backed by a thin grounded substrate. The slot ring generates a high impedance condition at a resonant frequency in the vicinity of the slot. This annular slot loaded ground plane results in efficient radiation of the low profile antenna in the broadside direction. Since the slot loaded ground plane consists of a single slot ring rather than periodic structures, it is much simpler to construct than the standard EBG ground plane. Numerical simulations and experimental measurements are shown to validate the design concept and are compared with a mushroom-type EBG ground plane. A parametric analysis was also conducted by varying the slot ring's dimensions and tuning varactors are shown to vary the ground plane's resonant frequency. *note: This paper has been accepted for future publication. Content may change in the final publication |
|
EBG Antenna for GPR Colocated With a Metal Detector for Landmine Detection
I.T. McMichael, E.C. Nallon,
V.P. Schnee, and W.R. Scott,
M.S. Mirotznik
Electromagnetic band-gap (EBG) antennas are ideal for handheld sensing applications, such as ground-penetrating radar (GPR) for landmine detection, because of their small size, efficiency, and directivity. Increased detection performance has been shown when a GPR is combined with a metal detector, but a typical EBG antenna would preclude the sensors from being colocated because of the large amount of metal in the EBG structure. An EBG composed of very thin metal is proposed in this letter for application as a GPR colocated with a metal detector, without causing a significant self-response in the metal detector. Manufacturing methods are discussed, and GPR measurements are shown from the thin-metal EBG antennas. The metal detector response from a thin metal sheet is discussed, and measurements of the EBG ground planes are shown using a laboratory wideband electromagnetic induction system. The response from the thin metal is shown to be as low as three orders of magnitude less than from a copper sheet at typical metal detector frequencies. |
|
Antenna Cross-Polarization Isolation and Calibration of Hybrid-Polarization Radars
T.J. Miller, O. Kilic,
and M. Mirotznik
This letter presents an experiment using a fully polarimetric hybrid-polarization (CL-pol) radar that employs separate spiral antennas for transmit of the orthogonal circular polarizations and operates from 8 to 16 GHz. We propose a model for the antenna cross-polarization isolation (XPI) and calibration of this radar. The transmit XPI is characterized by leveraging the Doppler shift caused by a continually rotating dihedral target illuminated by a circularly polarized wave. Experimental results show the validity of the radar model and antenna measurement technique. |
|
A Method for Determining Optimal EBG Reflection Phase for Low Profile Dipole Antennas
I.T. McMichael, A.I. Zaghloul,
and M.S. Mirotznik
An analytical method for determining the optimal reflection phase of an electromagnetic band gap (EBG) ground plane to match a low profile dipole antenna is introduced. Image theory is used to incorporate the near field coupling between a dipole antenna and the ground plane. The main contribution of this paper is to show that the optimal EBG reflection phase can be determined at discrete frequencies where a theoretically perfect return loss occurs. The optimal reflection phase is then obtained over a wider frequency band of interest and is related to the antenna's return loss for a given feed impedance and antenna height above the EBG. The resulting reflection phase can be used as a reference for designing an EBG ground plane that is well matched to the antenna without time consuming iterative full wave numerical simulations. Numerical modeling results are compared to the optimal return loss derived from the analytical method to validate the design process. It is also shown that, for certain antennas, vias are not always necessary in the construction of the EBG, which eases the manufacturing process. Finally, a dipole and EBG are constructed using the optimal design method and measurements are compared to the simulations. |
|
Broadband Electromagnetic Modeling of Woven Fabric Composites
M.S. Mirotznik,
S. Yarlagadda, R. McCauley, and P. Pa
We demonstrate a new method for predicting the broadband electromagnetic (EM) wave propagation characteristics of woven fabric composites. The method combines a rigorous EM model with effective media theory to predict the EM properties of structural composites from dc to 50 GHz. Experimental results are provided that demonstrate the validity of the method. We also describe the presence of large narrow band electromagnetic resonances that occur above 30 GHz. These resonances, which are shown to be guided mode resonances, can be predicted by solving a simple dispersion relation. |
|
Passive Infrared Sensing Using Plasmonic Resonant Dust Particles
M. Mirotznik, W. Beck,
K. Olver, J. Little, and P. Pa
We present computational and experimental results of dust particles that can be tuned to preferentially reflect or emit IR radiation within the 8-14 μm band. The particles consist of thin metallic subwavelength gratings patterned on the surface of a simple quarter wavelength cavity. This design creates distinct IR absorption resonances by combining the plasmonic resonance of the grating with the natural resonance of the cavity. We show that the resonance peaks are easily tuned by varying either the geometry of the grating or the thickness of the cavity. Here, we present a computational design algorithm along with experimental results that validate the design methodology. |
|
Integrating metamaterials within a structural composite using additive manufacturing methods
M.S. Mirotznik,
R. McCauley, S. Yarlagadda, and K. Duncan
An additive manufacturing process is presented that can be used to realize large volume, low cost and multifunctional metamaterials. Our approach integrates three-dimensional metamaterial geometries within a woven fabric composite by combining additive printing methods (e.g. screen printing) on large-scale structural fabric or select polymer film substrates followed by conventional composite processing. |
|
Design of Graded Index Flat Lenses with Integrated Antireflective Properties
B. Good, P. Ransom, S. Simmons,
A. Good, and M. Mirotznik
We describe a new methodology for designing graded index lenses at microwave wavelengths with integrated antireflective properties. The method leads to a flat lens with minimal reflection losses at a frequency of interest. Both numerical and experimental results for two different design goals are shown to demonstrate the capabilities of the methodology. |
|
Fiber optic micro sensor for the measurement of tendon forces
G. Behrmann, J. Hidler,
and M. Mirotznik
A fiber optic sensor developed for the measurement of tendon forces was designed, numerically modeled, fabricated, and experimentally evaluated. The sensor incorporated fiber Bragg gratings and micro-fabricated stainless steel housings. A fiber Bragg grating is an optical device that is spectrally sensitive to axial strain. Stainless steel housings were designed to convert radial forces applied to the housing into axial forces that could be sensed by the fiber Bragg grating. The metal housings were fabricated by several methods including laser micromachining, swaging, and hydroforming. Designs are presented that allow for simultaneous temperature and force measurements as well as for simultaneous resolution of multi-axis forces. The sensor was experimentally evaluated by hydrostatic loading and in vitro testing. A commercial hydraulic burst tester was used to provide uniform pressures on the sensor in order to establish the linearity, repeatability, and accuracy characteristics of the sensor. The in vitro experiments were performed in excised tendon and in a dynamic gait simulator to simulate biological conditions. In both experimental conditions, the sensor was found to be a sensitive and reliable method for acquiring minimally invasive measurements of soft tissue forces. Our results suggest that this sensor will prove useful in a variety of biomechanical measurements. |
|
Hardware Accelerated Design of Millimeter Wave Antireflective Surfaces: A Comparison of Field-Programmable Gate Array (FPGA) and Graphics Processing Unit (GPU) Implementations
O. Kilic, M. Huang, C. conner,
and M. S. Mirotznik
Engineered materials that demonstrate a specific response to electromagnetic energy incident on them in antenna and radio frequency component design applications are in high demand due to both military and commercial needs. The design of such engineered materials typically requires numerically intensive computations to simulate their behavior as they may have electrically small features on a large area or often the overall system performance is required, which means modeling the entire integrated system. Furthermore, to achieve an optimal performance these simulations need to be run many times until a desired solution is achieved, presenting a major hindrance in arriving at a feasible solution in a reasonable amount of time. One example of such applications is the design of antireflective (AR) surfaces at millimeter wave frequencies, which often involves sub-wavelength gratings in an electrically large multilayer structure. This paper investigates the use of field-programmable gate arrays (FPGAs) and graphics processing units (GPUs) as coprocessors to the CPU in order to expedite the computation time. Preliminary results show that the hardware implementation (100 MHz) on Xilinx Virtex4LX200 FPGA is able to outperform a single-thread software implementation on Intel Itanium 2 processor (1.66 GHz) by 20 folds. However, the performance of the FPGA implementation lags behind the single-thread implementation on a modern Xeon (2.26 GHz) by 3.6. On the other hand, modern GPUs demonstrate an evident advantage over both CPU and FPGA by achieving 20 speedup than the Xeon processor. |
|
Iterative Design of Moth-Eye Antireflective Surfaces at Millimeter Wave Frequencies
M. Mirotznik, B. Good,
P. Ransom,D. Wilkner, and J. Mait
A method for synthesizing broadband antireflective (AR) surfaces at millimeter wave frequencies is demonstrated. AR surfaces were formed by machining a multilayer subwavelength structures into nonabsorptive dielectrics. This created low-reflected energies (<-25 dB) over large bandwidths and incidence angles. Experimental results are provided demonstrating the validity of the method. |
|
Bio-inspired Optimization Techniques for the Design of Millimeter Wave Antireflective Surfaces
O. Kilic, M.S. Mirotznik,
and B. Good
This paper presents the successful application of bio-inspired optimization algorithms to electromagnetics problems. The problem considered is the design of antireflective surfaces using sub-wavelength gratings periodically created inside the substrate. We apply the rigorous coupled wave analysis to model the reflection and transmission properties of the material and utilize bio-inspired optimization methods such as the particle swarm optimization and ant colony optimization to determine the optimal parameters that achieve the desired performance. |
|
Broadband Antireflective Properties of Inverse Motheye Surfaces
M.S. Mirotznik,
B.L Good, P. Ransom, D. Wikner, and J.N. Mait
A new method for synthesizing broadband antireflective (AR) surfaces at microwave and millimeter wave frequencies is demonstrated. The AR surface, we call an inverse motheye, was formed by machining a multi-layer grating of subwavelength circular holes into a non-absorptive dielectric. This created low reflected energies (<- 30 dB) over reasonably large bandwidths and incidence angles. An optimization algorithm, based on a direct pattern search, integrated with a rigorous electromagnetic model was used to design the grating geometries. Experimental results are provided at Ka-band demonstrating the validity of the method. |
|
Photonic Crystal Filters for Multi-band Optical Filtering on a Monolithic Substrate
G. Shambat, M. Mirotznik,
G. Euliss, V. Smolski, R. Athale, and E. Johnson
Many applications require the ability to image a scene in several different narrow spectral bands simultaneously. Conventional multi-layer dielectric filters require control of film thickness to change the resonant wavelength. This makes it difficult to fabricate a mosaic of multiple narrow spectral band transmission filters monolithically. We adjusted the spectral transmission of a multi-layer dielectric filter by drilling a periodic array of subwavelength holes through the stack. Multi-band photonic crystal filters were modeled and optimized for a specific case of filtering six optical bands on a single substrate. Numerical simulations showed that there exists a particular air hole periodicity which maximizes the minimum hole diameter. Specifically for a stack of SiO2 and Si3N4 with the set of filtered wavelengths (nm): 560, 576, 600, 630, 650, and 660, the optimal hole periodicity was 282 nm. This resulted in a minimum hole diameter of 90 nm and a maximum diameter of 226 nm. Realistic fabrication tolerances were considered such as dielectric layer thickness and refractive index fluctuations, as well as vertical air hole taper. Our results provide a reproducible methodology for similar multi-band monolithic filters in either the optical or infrared regimes. |
|
94-GHz Imager With Extended Depth of Field
J.N. Mait, D.A. Wikner, M.S Mirotznik
J. van der Gracht, B.L. Good, and S.A Mathews
We describe a computational imaging technique to extend the depth-of-field of a 94-GHz imaging system. The technique uses a cubic phase element in the pupil plane of the system to render system operation relatively insensitive to object distance. However, the cubic phase element also introduces aberrations but, since these are fixed and known, we remove them using post-detection signal processing. We present experimental results that validate system performance and indicate a greater than four-fold increase in depth-of-field from 17rdquo to greater than 68rdquo. |
|
Development of Novel RF and Millimeter Wave Structures by Laser Direct-write
S. Mathews, M. Mirotznik, and A. Pique
In this work we describe the use of laser direct-write for the rapid prototyping of frequency selective Fresnel zone plate lenses. We describe a frequency selective surface which is patterned on two distinct length scales; a smaller scale that exhibits the patterning of a traditional frequency selective surface, and a larger scale that exhibits the structure of a Fresnel zone plate. We demonstrate that laser direct-write is an ideal tool for the rapid prototyping of such spatially varying or aperiodic electromagnetic structures. We present experimental results for the electromagnetic characterization of a prototype frequency selective lens fabricated using non-lithographic, laser processing. |
|
Design of Cubic-Phase Optical Elements Using Subwavelength Microstructures
M. Mirotznik, J. van der Gracht,
D. Pustai, and S. Mathews
We describe a design methodology for synthesizing cubic-phase optical elements using two-dimensional subwavelength microstructures. We combined a numerical and experimental approach to demonstrate that by spatially varying the geometric properties of binary subwavelength gratings it is possible to produce a diffractive element with a cubic-phase profile. A test element was designed and fabricated for operation in the LWIR, ~λ=10.6 µm. Experimental results verify the cubic-phase nature of the element. |
|
Design of Diffractive Elements at Millimeter Wavelengths Using Subwavelength Cylindrical Microstructures
M. Mirotznik,
T. Creazzo, and S. Mathews
We describe a design methodology for synthesizing diffractive elements based on two-dimensional subwavelength cylindrical microstructures. We combine a numerical and experimental approach to demonstrate that by varying the diameter, pitch, and depth of subwavelength cylindrical occlusions in a homogenous substrate it is possible to produce multiphase diffractive elements. |