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1. Performance testing and end-to-end mapping of the fiber cable on the SALT NIR integral field spectrograph

   https://doi.org/10.1117/12.2630176  

   Oppor, Joshua E. ; Bershady, Matthew A. ; Wolf, Marsha J. ; Smith, Michael P. ; Chattopadhyay, Sabyasachi ; Jaehnig, Kurt P. ; Percival, Jeffrey W. ; Mulligan, Mark P. ; Jurgella, Kathleen M. ; Wirag, Briana ( August 2022 , Performance testing and end-to-end mapping of the fiber cable on the SALT NIR integral field spectrograph)

   Geyl, Roland ; Navarro, Ramón (Ed.)

   The optical fiber integral field unit (IFU) built to feed the near infrared (NIR) spectrograph for the 11-meter Southern African Large Telescope (SALT) has undergone prototyping and rigorous performance testing at Wash- burn Astronomical Laboratories of the University of Wisconsin-Madison Astronomy Department. The 43 m length of 256 fibers which make up the object and sky arrays and spares are routed from the SALT payload down into the spectrograph room in four separate cables. The IFU covers 344 arcsec2 on the sky, with the object array spanning a 552 arcsec2 near-rectangular area at roughly 56% fill-factor. Companion papers describe the mechanical design of the fiber cable that mitigates potential sources of mechanical strain on the optical fiber (Smith et al.) and details of the spectrograph (Wolf et al.). Here we present the results of the performance testing of various test cables as well as performance testing and end-to-end mapping of the fully-assembled science cable. The fiber optics experience an extreme temperature gradient at the ingress to the instrument enclosure held at -40 ◦C during operation. We find an increase in focal ratio degradation (FRD) when holding progressively longer lengths of test fiber at reduced temperature. However, we confirm that this temperature dependent FRD is negligible for our designed length of cold fiber. We also find negligible contributions to FRD from the rubber seal that breaches the room temperature strain relief box and the cold instrument enclosure. Our measure- ments characterize performance including the effects of internal fiber inhomogeneities, stress induced from fiber handling and termination, as well as any imperfections from end-polishing. We present the room-temperature laboratory performance measurements of the fully-assembled science cable; the effective total throughput the fiber cable delivers to the spectrograph collimator is 81±2.5% across all fibers accounting for all losses. 

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2. Coil Distance and Angle Misalignment Effects on the Mutual Inductance for 13.56 MHz WRAP Sensors

   Noroozi, Babak ; Morshed, Bashir I. ( January 2018 , National Radio Science Meeting)

   In the new era of smart and connected health, new technologies are needed for unobtrusive and seamless monitoring of physiological signals at real life settings. In this grand challenge, we are developing a novel technology called Wireless Resistive Analog Passive (WRAP) sensors. WRAP sensors utilizes printed spiral coil (PSC) inductive link whose sensitivity directly depends on the mutual inductance between primary and secondary coils and it changes due to the physical misalignment. We have previously reported COMSOL simulation results for distance and angular misalignments. In this paper we report experimental results of distance and angular misalignments and compare them to analytical and simulation results for distance. The experimental and analytical results are in good agreement while the simulation results are loosely correlated. For the angular misalignment, the experimental results follow similar trend as simulation results, however analytical results shows disagreement. This work is expected to aid in optimization of PSC for WRAP sensors. 

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3. Focal ratio degradation in optical fibres for the Hector integral field units

   https://doi.org/10.1093/mnras/stad1273  

   Wang, Adeline Haobing ; Brown, Rebecca ; Bryant, Julia J. ; Leon-Saval, Sergio ( April 2023 , Monthly Notices of the Royal Astronomical Society)

   Focal Ratio Degradation (FRD) in optical fibres can result in light loss. In astronomical instrumentation, FRD must be controlled because light levels are low. A new Integral Field Spectrograph (IFS) instrument called Hector, was recently completed and was installed on the Anglo-Australian Telescope (AAT) in Australia in 2021 December. The integral field units (IFUs) for Hector made with hexagonally packed multi-mode fibres are called hexabundles. In this paper, we introduce a cone-beam measurement method to measure FRD at optical wavelengths. We present the FRD and throughput performance of the hexabundles for Hector and show that the process for making hexabundles introduced no additional significant FRD beyond that of the bare fibre.

    

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4. Optimum telescope focal ratios for microlens-to-fiber coupled integral field spectrographs

   https://doi.org/10.1117/1.JATIS.8.2.025001  

   Chattopadhyay, Sabyasachi ; Bershady, Matthew A. ; Wolf, Marsha J. ; Smith, Michael P. ( April 2022 , Journal of Astronomical Telescopes, Instruments, and Systems)

   We describe the optimum telescope focal ratio for a two-element, three-surface, telecentric image-transfer microlens-to-fiber coupled integral field unit within the constraints imposed by microoptics fabrication and optical aberrations. We create a generalized analytical description of the microoptics optical parameters from first principles. We find that the optical performance, including all aberrations, of a design constrained by an analytic model considering only spherical aberration and diffraction matches within ± 4 % of a design optimized by ray-tracing software such as Zemax. The analytical model does not require any compromise on the available clear aperture; about 90% mechanical aperture of hexagonal microlens is available for light collection. The optimum telescope f-ratio for a 200-μm core fiber-fed at f / 3.5 is between f / 7 and f / 12. We find the optimum telescope focal ratio changes as a function of fiber core diameter and fiber input beam speed. A telescope focal ratio of f / 8 would support the largest range of fiber diameters (100 to 500 μm) and fiber injection speeds (between f / 3 and f / 5). The optimization of the telescope and lenslet-coupled fibers is relevant for the design of high-efficiency dedicated survey telescopes, and for retrofitting existing facilities via introducing focal macro-optics to match the instrument input requirements. 

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5. Position-Insensitive Wireless Power Transfer Based on Nonlinear Resonant Circuits

   O. B. Abdelatty, X. Wang ( March 2019 , IEEE transactions on microwave theory and techniques)

   Near-field resonant-based wireless power transfer (WPT) technology has a significant impact in many applications ranging from charging of biomedical implants to electric vehicles (EVs). The design of robust WPT systems is challenging due to its position-dependent power transfer efficiency (PTE). In this paper, a new approach is presented to address WPT's strong sensitivity to the coupling factor variation between the transmit and receive coils. The introduced technique relies on harnessing the unique properties of a specific class of nonlinear resonant circuits to design position-insensitive WPT systems that maintain a high PTE over large transmission distances and misalignments without tuning the source's operating frequency or employing tunable matching networks, as well as any active feedback/control circuitry. A nonlinear-resonant-based WPT circuit capable of transmitting 60 W at 2.25 MHz is designed and fabricated. The circuit maintains a high PTE of 86% over a transmission distance variation of 20 cm. Furthermore, transmit power and PTE are maintained over a large lateral misalignment up to ±50% of the coil diameter and angular misalignment up to ±75°. The new design approach enhances the performance of WPT systems by significantly extending the range of coupling factors over which both load power and high PTE are maintained. 

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