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1. The Design and SAR Analysis of a UWB Bow-tie Antenna for Wireless Wearable Sensors

   Kakaraparty, Karthik; Mahbub, Ifana (January 2022, THE USNC-URSI 2022 National Radio Science Meeting)

   Kakaraparty, Karthik; Mahbub, Ifana (Ed.)

   This paper presents design of a wearable flexible patch antenna and its corresponding SAR (specific absorption rate) analysis when placed on a human body. The substrate material used is polyimide with a thickness of 0.1 mm, and gold is used for the patch and ground material with 200 nm thickness. The di-electric constant and the tangent loss of the polyimide substrate are 3.5 and 0.0002, respectively. The dimensions of the proposed antenna are 30×30×0.1004 mm3. The designed antenna has the resonating frequency at 3.45 GHz and a bandwidth of 2.6 GHz. The far field gain of the designed antenna is 7.5 dBi. The SAR analysis generated an SAR value of 0.174 W/kg, which is within the safe limit of 2W/kg averaged over 10g of tissue as specified by the ICNIRP (International Commission of Non-Ionization Radiation Protection). This suggests that the designed antenna is safe and can be utilized for wireless wearable sensors. 

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2. Design of a Compact 24 GHz Antenna Array for Unmanned Aerial Vehicle-to-Vehicle (V2V) Communication

   https://doi.org/10.1109/AP-S/USNC-URSI47032.2022.9886200  

   Kakaraparty, Karthik; Roy, Sunanda; Mahbub, Ifana (September 2022, 2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (AP-S/URSI))

   This paper presents the design of a compact 4 × 4 antenna array suitable for unmanned aerial vehicle-to-vehicle (V2V) communication applications. The proposed antenna array can offer a narrow beamwidth, high gain, wide beam steering capability and is highly compact. The substrate material used is Rogers 5880 with a thickness of 0.2 mm, and copper is used for the patch and ground material with 0.14 mm thickness. The di-electric constant and the tangent loss of the Rogers substrate are 2.2 and 0.0004, respectively. 45° phase shifters are incorporated in the feeding paths to facilitate the beamsteering. The dimensions of the proposed antenna array are 32 × 32 × 0.48 mm 3 . The designed antenna array has the resonating frequency at 24 GHz and has a bandwidth of 0.83 GHz (3.5% fractional bandwidth). The measured far field gain of the designed antenna array is 16.7 dBi. The beamwidth derived from the array’s far-field radiation pattern is 14.6°, and the maximum beam steering range of the array is 102° along the θ axis. 

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3. In Situ Scanning Electron Microscopy Crack Characterization and Resistance Evolution in Cyclically-Strained Ag Nanoflake-Based Inks

   https://doi.org/10.1021/acsanm.4c05133  

   Li, Qiushi; Antoniou, Antonia; Pierron, Olivier N (December 2024, ACS Applied Nano Materials)

   The reliability of nanocomposite conductive inks under cyclic loading is the key to designing robust flexible electronics. Although resistance increases with cycling and models exist, the exact degradation mechanism is not well understood and is critical for developing inks. This study links cracking behavior to changes in electrical resistance by performing in situ cyclic stretch experiments in scanning electron microscopy (SEM) with synchronized resistance measurements. Two screen-printed conductive inks, PE874 and 5025, on thermoplastic polyurethane (TPU) and polyimide (PI) substrates, respectively, were tested using the in situ technique. The obtained SEM images were analyzed with digital image correlation (DIC) to map the strain across cycles. The strain maps show that fatigue damage mainly occurred within the cracks formed during the initial monotonic stretch. There was no delamination at the ink–substrate interface or crack extension along the surface with cycling. Instead, fatigue damage resulted from a combination of crack widening and local shearing within the existing cracks. Crack depth varied based on the ink and substrate properties. The cracks in the 5025 ink on the PI substrate were only partially through the ink thickness, while fully through-thickness cracks were more prevalent in the PE874 ink on the TPU substrate. The 5025 ink showed a faster resistance increase with cycling than the PE874 ink because fatigue damage affected more bridging ink material for partial through-thickness cracks. Higher strain amplitudes caused greater crack widening and shearing and therefore faster resistance increase per cycle. 

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4. Design and Performance Analysis of a 24 GHz Series-Fed $$1 \times 5$$ Antenna Array with Material Deformation for D2D Applications

   https://doi.org/10.1109/USNC-URSI52151.2023.10238054  

   Kakaraparty, Karthik; Mahbub, Ifana (July 2023, 2023 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (USNC-URSI))

   This paper presents the design and simulation of a 24 GHz 1×5 series-fed microstrip patch antenna array and its performance analysis with structural deformation. The optimized design comprises of 5 antenna elements arranged in series, where the entire design is symmetric about the center antenna element. The parameters such as S11 , gain vs. theta plots are analyzed with and without the material deformation. The shape deformation analysis is indeed needed to determine the performance efficiency of the designed antenna when deployed on drones, where the antenna needs to be flexible enough to be aligned with the curvature of drone's body. The simulation results are analyzed to see how best can the proposed antenna array can perform with the structural deformation. 

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5. On efficient asymptotic modelling of thin films on thermally conductive substrates

   https://doi.org/10.1017/jfm.2021.157  

   Allaire, Ryan H.; Cummings, Linda J.; Kondic, Lou (May 2021, Journal of Fluid Mechanics)

   We consider a free-surface thin film placed on a thermally conductive substrate and exposed to an external heat source in a set-up where the heat absorption depends on the local film thickness. Our focus is on modelling film evolution while the film is molten. The evolution of the film modifies local heat flow, which in turn may influence the film surface evolution through thermal variation of the film's material properties. Thermal conductivity of the substrate plays an important role in determining the heat flow and the temperature field in the evolving film and in the substrate itself. In order to reach a tractable formulation, we use asymptotic analysis to develop a novel thermal model that is accurate, computationally efficient, and that accounts for the heat flow in both the in-plane and out-of-plane directions. We apply this model to metal films of nanoscale thickness exposed to heating and melting by laser pulses, a set-up commonly used for self and directed assembly of various metal geometries via dewetting while the films are in the liquid phase. We find that thermal effects play an important role, and in particular that the inclusion of temperature dependence in the metal viscosity modifies the time scale of the evolution significantly. On the other hand, in the considered set-up the Marangoni (thermocapillary) effect turns out to be insignificant. 

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