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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

   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. High‐Performance Flexible Bismuth Telluride Thin Film from Solution Processed Colloidal Nanoplates

   https://doi.org/10.1002/admt.202000600  

   Hollar, Courtney ; Lin, Zhaoyang ; Kongara, Madhusudan ; Varghese, Tony ; Karthik, Chinnathambi ; Schimpf, Jesse ; Eixenberger, Josh ; Davis, Paul H. ; Wu, Yaqiao ; Duan, Xiangfeng ; et al ( October 2020 , Advanced Materials Technologies)

   Thermoelectric generators are an environmentally friendly and reliable solid‐state energy conversion technology. Flexible and low‐cost thermoelectric generators are especially suited to power flexible electronics and sensors using body heat or other ambient heat sources. Bismuth telluride (Bi₂Te₃) based thermoelectric materials exhibit their best performance near room temperature making them an ideal candidate to power wearable electronics and sensors using body heat. In this report, Bi₂Te₃thin films are deposited on a flexible polyimide substrate using low‐cost and scalable manufacturing methods. The synthesized Bi₂Te₃nanocrystals have a thickness of 35 ± 15 nm and a lateral dimension of 692 ± 186 nm. Thin films fabricated from these nanocrystals exhibit a peak power factor of 0.35 mW m⁻¹·K⁻²at 433 K, which is among the highest reported values for flexible thermoelectric films. In order to evaluate the flexibility of the thin films, static and dynamic bending tests are performed while monitoring the change in electrical resistivity. After 1000 bending cycles over a 50 mm radius of curvature, the change in electrical resistance of the film is 23%. Using Bi₂Te₃solutions, the ability to print thermoelectric thin films with an aerosol jet printer is demonstrated, highlighting the potential of additive manufacturing techniques for fabricating flexible thermoelectric generators.

    

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4. Ankle-targeted exosuit resistance increases paretic propulsion in people post-stroke

   https://doi.org/10.1186/s12984-023-01204-w  

   Swaminathan, Krithika ; Porciuncula, Franchino ; Park, Sungwoo ; Kannan, Harini ; Erard, Julien ; Wendel, Nicholas ; Baker, Teresa ; Ellis, Terry D. ; Awad, Louis N. ; Walsh, Conor J. ( June 2023 , Journal of NeuroEngineering and Rehabilitation)

   Individualized, targeted, and intense training is the hallmark of successful gait rehabilitation in people post-stroke. Specifically, increasing use of the impaired ankle to increase propulsion during the stance phase of gait has been linked to higher walking speeds and symmetry. Conventional progressive resistance training is one method used for individualized and intense rehabilitation, but often fails to target paretic ankle plantarflexion during walking. Wearable assistive robots have successfullyassistedankle-specific mechanisms to increase paretic propulsion in people post-stroke, suggesting their potential to provide targetedresistanceto increase propulsion, but this application remains underexamined in this population. This work investigates the effects of targeted stance-phase plantarflexion resistance training with a soft ankle exosuit on propulsion mechanics in people post-stroke.

   We conducted this study in nine individuals with chronic stroke and tested the effects of three resistive force magnitudes on peak paretic propulsion, ankle torque, and ankle power while participants walked on a treadmill at their comfortable walking speeds. For each force magnitude, participants walked for 1 min while the exosuit was inactive, 2 min with active resistance, and 1 min with the exosuit inactive, in sequence. We evaluated changes in gait biomechanics during the active resistance and post-resistance sections relative to the initial inactive section.

   Walking with active resistance increased paretic propulsion by more than the minimal detectable change of 0.8 %body weight at all tested force magnitudes, with an average increase of 1.29 ± 0.37 %body weight at the highest force magnitude. This improvement corresponded to changes of 0.13 ± 0.03 N m kg^− 1in peak biological ankle torque and 0.26 ± 0.04 W kg^− 1in peak biological ankle power. Upon removal of resistance, propulsion changes persisted for 30 seconds with an improvement of 1.49 ± 0.58 %body weight after the highest resistance level and without compensatory involvement of the unresisted joints or limb.

   Targeted exosuit-applied functional resistance of paretic ankle plantarflexors can elicit the latent propulsion reserve in people post-stroke. After-effects observed in propulsion highlight the potential for learning and restoration of propulsion mechanics. Thus, this exosuit-based resistive approach may offer new opportunities for individualized and progressive gait rehabilitation.

    

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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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