Browsing by Author "Taylor, Zachary D."
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- Design and Characterization of Phase Holograms for Standoff Localization at Millimeter and Submillimeter Waves
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-01-01) Palli, Samu Ville; Tamminen, Aleksi; Ala-Laurinaho, Juha; Taylor, Zachary D.We present design, simulation, and experimental characterization of dual-band frequency-diverse holograms for distributed beamforming. The holograms operate in the 50-75 GHz (WR-15) and 220-330 GHz (WR-3.4) bands for millimeter-and submillimeter-wave imaging. The holograms are designed to create a dispersive field in the region of interest (RoI) located 600 mm from the aperture. The holograms lie in the front end of an imaging setup and modulate the phase of the incident collimated beam from a parabolic mirror. The distributed beamforming enables interrogation of the RoI so that the measured reflection through the dispersive propagation path conveys the spatial information of the target. Different phase modulation schemes are evaluated, and two prototype holograms are manufactured. The dispersive operation and efficiency of the hologram are characterized with both simulations and measurements. The frequency diversity of the holograms is quantified using singular-value decomposition and spatial-spectral correlation coefficient methods. The results identified a design frequency of 120 GHz, a phase quantization step of π/2 radians, and an added phase of 1.9π radians as a good dispersion-efficiency compromise. A fully connected neural network is trained to localize a corner-cube reflector in the RoI illuminated by the hologram. The localization accuracy follows the diffraction-limited resolution and confirms the best performance for the hologram considered optimal in the design metrics. - Millimeter- and Submillimeter-Wave Imaging Through Dispersive Hologram and Deep Neural Networks
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-06) Tamminen, Aleksi; Palli, Samu Ville; Ala-Laurinaho, Juha; Taylor, Zachary D.We present imaging results with dual-band millimeter- and submillimeter-wave hologram and deep neural networks (NNs). The imaging method uses a single transceiver, which interrogates the region of interest (RoI) through a dispersive transmission-type hologram. The hologram was designed to cover two bands 50-75 and 220-330 GHz. Two separate single-transceiver imaging experiments were carried out with two test objects translated in the RoI at 101 x 101 locations. NNs were trained to images of the test objects with wideband reflection spectra from the RoI as the input. The deep NNs were based on deconvolutional (DC) layers that mapped the latent information of the test objects in the spectra to image pixel values. The two ~10-cm test objects were imaged in 200 x 200 mm² and 300 x 300 mm² field-of-view at 600 mm from the hologram aperture (19°-28° angular field-of-view). The experimental resolution was estimated from point-spread functions extracted from the predicted images. The full width at half maximum resolution was 21 and 16.5 mm, for the 50-75 and 220-330 GHz bands, respectively. These are close to the theoretical limits of 25-19 mm, for the lower band, and 19-16 mm for the higher band as predicted with hologram aperture size and edge taper. Augmented reflections were constructed from corner-cube measurements to evaluate the ability to predict the images of vast collection of objects. The results with augmented data show performance comparable with the experimental ones with limited test object space. The latent representations for both the experimental and augmented data indicate sparsity--a demonstration of feasibility to generalize from reflection spectra to images. The performance of the developed imaging technique is in par with the current, multichannel state of art, and has the advantage of substantially reduced hardware complexity. - Submillimeter-wave cornea phantom sensing over an extended depth of field with an axicon-generated Bessel beam
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-03) Baggio, Mariangela; Tamminen, Aleksi; Lamberg, Joel; Grigorev, Roman; Palli, Samu Ville; Ala-Laurinaho, Juha; Nefedova, Irina; Bourges, Jean Louis; Deng, Sophie X.; Brown, Elliott R.; Wallace, Vincent P.; Taylor, Zachary D.The feasibility of a 220 - 330 GHz zero order axicon generated Bessel beam for corneal water content was explored. Simulation and experimental data from the 25-degree cone angle hyperbolic-axicon lens illuminating metallic spherical targets demonstrate a monotonically decreasing, band integrated, backscatter intensity for increasing radius of curvature from 7 – 11 mm, when lens reflector and optical axis are aligned. Further, for radii > = 9.5 mm, maximum signal was obtained with a 1 mm transverse displacement between lens and reflector optical axes arising from spatial correlation between main lobe and out of phase side lobes. Thickness and permittivity parameter estimation experiments were performed on an 8 mm radius of curvature, 1 mm thick fused quartz dome over a 10 mm axial span. Extracted thickness and permittivity varied by less than ∼ 25 μm and 0.2 respectively after correction for superluminal velocity. Estimated water permittivity and thickness of water backed gelatin phantoms showed significantly more variation due to a time varying radius of curvature. To the best of our knowledge, this is the first work that describes axicon generated Bessel beam measurements of layered spheres with varying radii of curvature, in the submillimeter range.