A. James Clark School of Engineering

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    The controlled impact of elastic plates on a quiescent water surface
    (Cambridge University Press, 2022-03-23) Wang, An; Wong, Kit Pan; Yu, Miao; Kiger, Kenneth T.; Duncan, James H.
    The impact of flexible rectangular aluminum plates on a quiescent water surface is studied experimentally. The plates are mounted via pinned supports at the leading and trailing edges to an instrument carriage that drives the plates at constant velocity and various angles relative to horizontal into the water surface. Time-resolved measurements of the hydrodynamic normal force (Fn) and transverse moment (Mto), the spray root position (ξr) and the plate deflection (δ) are collected during plate impacts at 25 experimental conditions for each plate. These conditions comprise a matrix of impact Froude numbers Fr = Vn(gL)−0.5, plate stiffness ratios RD = ρwV2 nL3D−1 and submergence time ratios RT = TsT−1 1w . It is found that RD is the primary dimensionless ratio controlling the role of flexibility during the impact. At conditions with low RD, maximum plate deflections on the order of 1 mm occur and the records of the dimensionless form of Fn, Mto, ξr and δc are nearly identical when plotted vs tT−1 s . In these cases, the impact occurs over time scales substantially greater than the plate’s natural period, and a quasi-static response ensues with the maximum deflection occurring approximately midway through the impact. For conditions with higher RD ( 1.0), the above-mentioned dimensionless quantities depend strongly on RD. These response features indicate a dynamic plate response and a two-way fluid–structure interaction in which the deformation of the plate causes significant changes in the hydrodynamic force and moment.
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    Single-digit-micrometer thickness wood speaker
    (Springer Nature, 2019-11-08) Gan, Wentao; Chen, Chaoji; Kim, Hyun-Tae; Lin, Zhiwei; Dai, Jiaqi; Dong, Zhihua; Zhou, Zhan; Ping, Weiwei; He, Shuaiming; Xiao, Shaoliang; Yu, Miao; Hu, Liangbing
    Thin films of several microns in thickness are ubiquitously used in packaging, electronics, and acoustic sensors. Here we demonstrate that natural wood can be directly converted into an ultrathin film with a record-small thickness of less than 10 μm through partial delignification followed by densification. Benefiting from this aligned and laminated structure, the ultrathin wood film exhibits excellent mechanical properties with a high tensile strength of 342 MPa and a Young’s modulus of 43.6 GPa, respectively. The material’s ultrathin thickness and exceptional mechanical strength enable excellent acoustic properties with a 1.83-times higher resonance frequency and a 1.25-times greater displacement amplitude than a commercial polypropylene diaphragm found in an audio speaker. As a proof-of-concept, we directly use the ultrathin wood film as a diaphragm in a real speaker that can output music. The ultrathin wood film with excellent mechanical property and acoustic performance is a promising candidate for next-generation acoustic speakers.
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    Targeted Feature Recognition Using Mechanical Spatial Filtering with a Low-Cost Compliant Strain Sensor
    (Nature Publishing Group, 2017-07-11) Barnett, Eli M.; Lofton, Julian J.; Yu, Miao; Bruck, Hugh A.; Smela, Elisabeth
    A tactile sensing architecture is presented for detection of surface features that have a particular target size, and the concept is demonstrated with a braille pattern. The approach is akin to an inverse of mechanical profilometry. The sensing structure is constructed by suspending a stretchable strainsensing membrane over a cavity. The structure is moved over the surface, and a signal is generated through mechanical spatial filtering if a feature is small enough to penetrate into the cavity. This simple design is tailorable and can be realized by standard machining or 3D printing. Images of target features can be produced with even a low-cost compliant sensor. In this work a disposable elastomeric piezoresistive strain sensor was used over a cylindrical “finger” part with a groove having a width corresponding to the braille dot size. A model was developed to help understand the working principle and guide finger design, revealing amplification when the cavity matches the feature size. The new sensing concept has the advantages of being easily reconfigured for a variety of sensing problems and retrofitted to a wide range of robotic hands, as well as compatibility with many compliant sensor types.