3D printed acoustic metamaterials with microscale gaps as sound-absorbing mask for the patients of Tourette syndrome

Microsystem Technologies - Tourette syndrome (TS) is an inherited neurophysiologic disorder with onset in childhood, characterized by multiple physical (motor) tics and at least one vocal (phonic)...     

Two-Stage Superplastic Forming of a V-Shaped Aluminum Sheet into a Trough with Deep and Irregular Contour

A sheet metal trough of aluminum alloy is manufactured by a two-stage gas forming process at 500 °C. The product with sloped side walls is of ~1.2 m length and ~260 mm opening width, comprising two near-conical-shaped sinks at two ends. The depth of one sink apex is ~350 mm, which results in the depth/width ratio reaching 1.4. To form such a deep and irregular trough, a superplastic aluminum alloy 5083 initially bent into a V-shaped groove was prepared prior to the gas forming work. Within a single die, gas pressure is used to form the V-shaped blank into a preform die cavity prior to the pressure being reversed to form the sheet into the final component cavity. The preforming of the V blank creates a uniform length of line in order to improve the thickness profile of the final part. In this work, a preform has been designed to improve the forming of a complex component by providing a superior thickness profile as compared to a conventional single-stage forming cycle. However, a serious wrinkling situation was encountered, the cause of which has been analyzed using basic mechanics as well as numerical simulation.     

Micro-pillars enhanced all vanadium redox flow batteries and the effect of assembly torque on the electrochemical performance

A uniformly distributed electrolyte system based on enhanced micro-pillars flow field design is proposed for a vanadium redox flow battery (VRFB). The uniformity experiments show that the flow uniformity can be effectively increased and normalized velocity variation for any channel is measured to be less than 18 %, demonstrating the effectiveness of micro-pillars for enhanced flow field. Experimental validation is carried out experimentally and the effect of different assembly torque is also investigated for VRB cell electrochemical performance via polarization and cyclic voltammograms (CV) test. The results show that an optimal assembly torque (11 N-m) can yield a significant improvement of 68.5 % current density when compared with the case of 10 N-m. Furthermore, the CV results clearly indicate that the optimal assembly torque with enhanced micro-pillars design can result in the 37.3 % improvement of electrochemical surface area. Moreover, the contact pressure contours from the pressure-sensitive films are measured to check the influence on the configuration of VRFB unit cell.

     

Micromachined plastic W-band bandpass filters

Results are presented for micromachined plastic waveguide bandpass iris filters for W-band applications using a cost-effective polymer micro hot embossing process in conjunction with metallic electroplating and sealing techniques. The prototype filter has an 8-μm thick electroplated gold layer on a polymeric WR-10 waveguide with a 5-cavity Chebyschev-type design. Measurement results show center frequency of 96.77 GHz with a bandwidth of 3.15%, a loaded quality factor 31.73 and an unloaded quality factor for a single cavity resonator is 1210.6, respectively. A minimum insertion loss of −1.22 dB and return loss of better than −9.3 dB have been measured over the entire passband.     

In-process surface roughness measurement of bulk metallic glass using an adaptive optics system for aberration correction

Bulk metallic glasses (BMGs) have received extensive attention recently due to amorphous-related extraordinary properties such as high strength, elasticity, and excellent corrosion resistance. In particular, Zr-based BMGs are recognized as a biocompatible material and surface roughness may affect many aspects of cell attachment, proliferation and differentiation. Therefore, this study presents an in-process measurement of surface roughness by combining an optical probe of laser-scattering phenomena and adaptive optics (AO) for aberration correction. Measurement results of six Zr-based BMGs samples with a roughness ranging from 0.06 to 0.98 μm demonstrate excellent correlation between the peak power and average roughness with a determination coefficient (R²) of 0.9974. The proposed adaptive-optics-assisted (AO-assisted) system is in good agreement with the stylus method, and less than 8.42% error values are obtained for average sample roughness in the range of 0.05–0.58 μm. The proposed system can be used as a rapid in-process roughness monitor/estimator to further increase the precision and stability of manufacturing processes for all classes of BMGs materials in situ.     

Mechanically tunable aspheric lenses via additive manufacture of hanging elastomeric droplets for microscopic applications

Abstract

Mechanically deformable lenses with dynamically tunable focal lengths have been developed in this work. The fabricated five types of aspheric polydimethylsiloxane (PDMS) lenses presented here have an initial focal length of 7.0, 7.8, 9.0, 10.0 and 10.2 mm. Incorporating two modes of operation in biconvex and concave–convex configurations, the focal lengths can be tuned dynamically as 5.2–10.2, 5.5–9.9, 6.6–11.9, 6.1–13.5 and 6.6–13.5 mm respectively. Additive manufacturing was utilized to fabricate these five types of aspheric lenses (APLs) via sequential layering of PDMS materials. Complex structures with three-dimensional features and shorter focal lengths can be successfully produced by repeatedly depositing, inverting and curing controlled PDMS volume onto previously cured PDMS droplets. From our experiments, we empirically found a direct dependence of the focal length of the lenses with the amount (volume) of deposited PDMS droplets. This new mouldless, low-cost, and flexible lens fabrication method is able to transform an ordinary commercial smartphone camera into a low-cost portable microscope. A few microscopic features can be readily visualized, such as wrinkles of ladybird pupa and printed circuit board. The fabrication technique by successively applying hanging droplet and facile mechanical focal-length-tuning set-up can be easily adopted in the development of high-performance optical lenses.     

Rapid replication and facile modulation of subwavelength antireflective polymer film using injection nanomolding and optical property of multilayer coatings

A rapid, cost-effective and high-throughput process for nanotexturing subwavelength structures with high uniformity using the polycarbonate (PC) is realized via injection nanomolding. The process enables the precise control of nanohole array (NHA) surface topography (nanohole depth, diameter, and periodicity) over large areas thereby presenting a highly versatile platform for fabricating substrates with user-defined, functional performance. Specifically, the optical property of the PC substrates were systematically characterized and tuned through the modulation of the depths of NHA. The aspect ratio submicron holes can be easily modulated and experimentally proven by simply adjusting the molding temperature. The nanotextured depths were reliably fabricated in the range of 200 to 400 nm with a period of approximately 700 nm. The fabricated PC films can reduce the reflectivity from an original bare film of 10.2% and 8.9% to 1.4% and 2.1% with 400-nm depth of nanoholes at the wavelength of 400 and 550 nm, respectively. Compared with conventional moth-like nanostructures with nanopillar arrays with heights adjustable only by an etching process, this paper proposes a facile route with submicron holes to achieve a similar antireflective function, with a significantly reduced time and facile height modulation capability. Furthermore, the effects of multilayer coatings of dielectric and metallic layers on the nanomolded NHA have been performed and potential sensing application is explored.