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1. Utilizing the Peltier effect for actuation of thermo-active soft robots

   https://doi.org/10.1088/1361-665X/ace225  

   Exley, Trevor; Johnson, Daniel; Jafari, Amir (July 2023, Smart Materials and Structures)

   Abstract The field of soft actuation methods in robotics is rapidly advancing and holds promise for physical interactions between humans and robots due to the adaptability of materials and compliant structures. Among these methods, thermally-responsive soft actuators are particularly unique, ensuring portability as they do not require stationary pumps, or high voltage sources, or remote magnetic field. However, since working principles of these actuators are based on Joule heating, the systems are inefficient and dramatically slow, especially due to their passive cooling process. This paper proposes using the Peltier effect as a reversible heating/cooling mechanism for thermo-active soft actuators to enable faster deformations, more efficient heat transfer, and active cooling. The proposed actuator is composed of a thin elastic membrane filled with phase-change fluid that can vaporize when heated to produce large deformations. This membrane is placed in a braided mesh to create a McKibben muscle that can lift 5 N after 60 s of heating, and is further formed into a gripper capable of manipulating objects within the environment. The effectiveness of the proposed actuator is demonstrated, and its potential applications in various fields are discussed. 

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2. Mid-Infrared Spectrometer Based on Tunable Photoresponses in Pdse ₂

   https://doi.org/10.1142/S0129156424400639  

   Lee, Jea Jung; Levi, Adi; Naveh, Doron; Xia, Fengnian (September 2024, International Journal of High Speed Electronics and Systems)

   Mid-infrared (mid-IR) photodetection is important for various applications, including biomedical diagnostics, security, chemical identification, and free-spacing optical communications. However, conventional “photon” mid-IR photodetectors require liquid nitrogen cooling (i.e., MCT). Furthermore, acquiring mid-IR spectra usually involves a complex and expensive Fourier Transform Infrared spectrometer, a tabletop instrument consisting of a meter-long interferometer and MCT detectors, which is not suitable for mobile and compact device applications. In this work, we present tunable photoresponsivity in the mid-IR wavelength in palladium diselenide (PdSe₂) – molybdenum disulfide (MoS₂) heterostructure field-effect transistors (FETs), operating at room temperature. Furthermore, we applied a tunable membrane cavity to modulate the Fabry–Pérot resonance to modulate the absorption spectrum of the device layer. We used a robust polyetherimide (PEI) membrane with CVD-grown graphene to electrically tune the membrane structure. For the next step, we will integrate the PdSe₂-based photodetector and tunable membrane to increase detection sensitivity and spectrum tunability to realize the ‘learning’-based spectroscopy. 

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3. A Novel Thermal Mapping Technique using Nano-confinement Assisted Quantum Dots for Transient Cooling Applications

   https://doi.org/10.1109/ITherm45881.2020.9190349  

   Rabbi, Khan Md.; Borden, Christopher; Putnam, Shawn A. (July 2020, 2020 19th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm))

   During air or liquid cooling, thermal resistance of the devices is measured precisely from the thermal information at the junction. But existing thermal measurement technologies fall short because of highly transient events such as unstable vortex formation (air cooling) and bubble growth (two-phase liquid cooling). In solving this problem, this paper reports a novel and low-cost thermal mapping technique that can capture highly spatio-temporal temperature evolution at the solid-liquid interface. Essentially, a robust interface is fabricated with CuInS 2 /ZnS Quantum dots (λ peak = 550 nm and 750 nm) trapped inside nanopores (20 nm-30 nm) of a ceramic membrane (50 μm) and/or everyday use paper. It is observed that such nanoconfinement assisted Quantum dots provided sustained thermal photoluminescence coefficient (-0.1 nm/°C) at high number of heating-cooling cycle. This unique yet low cost thermal mapping technique is applied to capture thermal evolution during micro-droplet impingement cooling and hemiwicking flows through anisotropic wicks which showcase commendable spatio-temporal benefits. 

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4. Spin detection with a micromechanical trampoline: towards magnetic resonance microscopy harnessing cavity optomechanics

   https://doi.org/10.1088/1367-2630/ab117a  

   Fischer, R.; McNally, D. P.; Reetz, C.; Assumpção, G. G. T.; Knief, T.; Lin, Y.; Regal, C. A. (April 2019, New Journal of Physics)

   Abstract We explore the prospects and benefits of combining the techniques of cavity optomechanics with efforts to image spins using magnetic resonance force microscopy (MRFM). In particular, we focus on a common mechanical resonator used in cavity optomechanics—high-stress stoichiometric silicon nitride (Si₃N₄) membranes. We present experimental work with a ‘trampoline’ membrane resonator that has a quality factor above 10⁶and an order of magnitude lower mass than a comparable standard membrane resonators. Such high-stress resonators are on a trajectory to reach 0.1 $\mathrm{aN}/\sqrt{\mathrm{Hz}}$force sensitivities at MHz frequencies by using techniques such as soft clamping and phononic-crystal control of acoustic radiation in combination with cryogenic cooling. We present a demonstration of force-detected electron spin resonance of an ensemble at room temperature using the trampoline resonators functionalized with a magnetic grain. We discuss prospects for combining such a resonator with an integrated Fabry–Perot cavity readout at cryogenic temperatures, and provide ideas for future impacts of membrane cavity optomechanical devices on MRFM of nuclear spins. 

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5. Inertio-Capillary Impacts

   Alventosa, Luke FL (May 2023, Brown Digital Repository)

   Droplet impacts are of fundamental importance to the natural water cycle as collision and coalescence of droplets are the primary mechanism by which warm rain forms. Additionally, droplet impacts are of paramount significance in a variety of industrial processes, including spray cooling, wet scrubbing, and even play a role in cooling nuclear reactors. Throughout this work, we utilize a combination of theoretical mod- eling and experiments to elucidate the dynamics of these common phenomena. The first problem we analyze is a droplet impacting a deep fluid bath. Millimetric drops are generated using a piezoelectric droplet-on-demand generator and normally impact a bath of the same fluid. The limit where capillarity and fluid inertia dominate the interfacial dynamics is investigated. This so-called inertio-capillary limit is shown to define an upper bound on the possible coefficient of restitution for droplet–bath im- pact. We then consider the scenario where the substrate is no longer deformable, and study the dynamics of non-wetting droplets impacting on stationary and vibrating substrates, with deterministic chaos emerging in the latter case. Extending beyond axisymmetric impacts, we then analyze droplet impact scenarios where there is some relative tangential velocity between the substrate and droplet. We determine the thresholds for coalescence, and our results suggest that substrate deformability plays an important role in transitions between the bouncing and merging regimes. Finally, we consider an analogous solid case to the normal droplet impact studies, where a small rigid sphere impacts and rebounds from a deformable elastic membrane. We perform experiments and identify new previously unreported behaviors in this simple system which are attributed to the non-negligible inertia of the membrane. Overall, the dynamics of these impact scenarios are extremely rich, producing physical phe- nomena that are inherently multi-scale, requiring information and knowledge from micron to centimeter scales. As showcased here, reduced-order modeling and con- trolled experiments are essential in distilling some simplicity out of the complexity. 

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