ABSTRACT
Skeletal muscle provides a compact solution for performing multiple tasks under diverse operational conditions, a capability lacking in many current engineered systems. Here, we evaluate if shape memory alloy (SMA) components can serve as artificial muscles with tunable mechanical performance. We experimentally impose cyclic stimuli, electric and mechanical, to an SMA wire and demonstrate that this material can mimic the response of the avian humerotriceps, a skeletal muscle that acts in the dynamic control of wing shapes. We next numerically evaluate the feasibility of using SMA springs as artificial leg muscles for a bipedal walking robot. Altering the phase offset between mechanical and electrical stimuli was sufficient for both synthetic and natural muscle to shift between actuation, braking and spring-like behaviour.
Subject(s)
Muscle, Skeletal , Wings, Animal , AnimalsABSTRACT
This work presents the design and fabrication of two multi-element structurally embedded vascular antennas (SEVAs). These are achieved through advances in additively manufactured sacrificial materials and demonstrate the ability to embed vascular microchannels in both planar and complex-curved epoxy-filled quartz fiber structural composite panels. Frequency-reconfigurable antennas are formed by these structures through the pressure-driven transport of liquid metal through the embedded microchannels. The planar multi-layer topology examines the ability to fabricate two co-located radiating structures separated by a single ply of quartz fabric within the composite layup. The multi-element linear array topology composed of microchannels embedded on to a single-layer are used to demonstrate the ability to conformally-integrate these channels into a complex curved surface that mimics an array of antennas on the leading edge of an Unmanned Aerial Vehicle (UAV). A parallel-strip antipodal dipole feed structure provides excitation and serves as the interface for fluid displacement within the microchannels to facilitate reconfiguration. The nominal design of the SEVAs achieve over a decade of frequency reconfiguration with respect to the fundamental dipole mode of the antenna. Experimental and predicted results demonstrate the operation for canonical states of the antennas. Additional results for the array topology demonstrate beam steering and contiguous operation of interconnected elements in the multi-element structure.
ABSTRACT
One of the most critical limitations for high-power electronics today is thermal management and routing thermal energy efficiently away from thermally sensitive components. A potential solution to this problem is the integration of cooling channels in close proximity to thermally sensitive materials for increased heat removal efficiency. These channels typically use single phase fluids (liquid), dual phase fluids (vapor-liquid), or suspended organic/polymer phase change material particles in a fluid (PCM slurry). Expanding upon the latter, this work demonstrates the use of inorganic Ga-In alloy nanoparticles (NPs) suspended in a traditional thermal transport fluid to simultaneously (1) increase the overall thermal diffusivity of the fluid and (2) serve as a cyclable solid-liquid PCM slurry which provides a thermal sink that is definable over a wide range of relevant temperatures for power electronics. Herein, the relationship between particle size, composition, and volume fraction are explored as they relate to the PCM slurry optimum working temperature, total energy absorption, and rheological properties. A mere 0.10 volume fraction of Ga-In NPs is reported to increase the overall thermal conductivity by nearly 50% and can be optimized to melt at temperatures as low as -46 °C. Based on thermal measurements, it was observed that these nanoparticle systems lack the preference to form αGa and have a large thermal hysteresis due to exhibiting extreme undercooling, with crystallization temperatures near -130 °C, enabling opportunities within extreme environments such as space applications or low temperature imaging systems.
