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1. Optimization of the spatial configuration of local defects in phononic crystals for high Q cavity

   https://doi.org/10.3389/fmech.2020.592787  

   Contreras, D.R.; Martínez, M.; Mayorga, M.; Heo, H.; Walker, E.; Neogi, A. (October 2020, Frontiers of Mechanical Engineering)

   null (Ed.)

   Defects can be introduced within a 2-D periodic lattice to realize phononic cavities or phononic crystal (PnC) waveguides at the ultrasonic frequency range. The arrangement of these defects within a PnC lattice results in the modification of the Q factor of the cavity or the waveguide. In this work, cavity defects within a PnC formed using cylindrical stainless steel scatterers in water have been modified to control the propagation and Q factor of acoustic waveguides realized through defect channels. The defects channel based waveguides within the PnC were configured horizontally, vertically, and diagonally along the direction of the propagation of the acoustic waves. Numerical simulations supported by experimental demonstration indicate that the defect-based waveguide's Q factor is improved by over 15 times for the diagonal configuration compared to the horizontal configuration. It also increases due to an increase in the scatterers' radius, varied from 0.7 -0.95 mm. 

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2. Underwater ultrasonic topological waveguides by metal additive manufacturing

   https://doi.org/10.1063/5.0086951  

   Wang, Michael Y.; Thevamaran, Mythili; Mattei, Michael Sabatini; Hacha, Brandon G.; Mazzei Capote, Gerardo Andres; Yu, Zongfu; Osswald, Tim; Goldsmith, Randall H.; Thoma, Dan J.; Ma, Chu (April 2022, Applied Physics Letters)

   Acoustic topological systems explore topological behaviors of phononic crystals. Currently, most of the experimentally demonstrated acoustic topological systems are for airborne acoustic waves and work at or below the kHz frequency range. Here, we report an underwater acoustic topological waveguide that works at the MHz frequency range. The 2D topological waveguide was formed at the interface of two hexagonal lattices with different pillar radii that were fabricated with metal additive manufacturing. We demonstrated the existence of edge stages both numerically and in underwater experiments. Our work has potential applications in underwater/biomedical sensing, energy transport, and acoustofluidics. 

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3. Traveling Waves As a De-Powdering Process for Additively Manufactured Parts

   https://doi.org/10.1115/SMASIS2018-8189  

   Tenney, Charles M.; Malladi, Vijaya V.; Musgrave, Patrick F.; Williams, Christopher B.; Tarazaga, Pablo A. (September 2018, Proceedings of the ASME 2018 Conference on Smart Materials, Adaptive Structures and Intelligent Systems)

   Steady-state traveling waves in structures have been previously investigated for a variety of purposes including propulsion of objects and agitation of a surrounding medium. In the field of additive manufacturing, powder bed fusion (PBF) is a commonly used process that uses heat to fuse regions of metallic or polymer powders within a loose bed. PBF processes require post-process removal of loose powder, which can be difficult when blind holes or complex internal geometry are present in the fabricated part. Here, a preliminary investigation of a simple part is conducted examining the use of traveling waves for post-process de-powdering of additively manufactured specimens. The generation of steady-state traveling waves in a structure is accomplished through excitation at a frequency between two adjacent resonant frequencies of the structure, resulting in two-mode excitation. This excitation can be generated by bonded piezoceramic elements actuated by a sinusoidal voltage signal. The response of the structure is affected by the parameters of the excitation, such as the particular frequency of the voltage signal, the placement of the piezoceramic actuators, and the phase difference in the signals applied to different actuators. Careful selection of these parameters allows adjustment of the quality, wavelength, and wave speed of the resulting traveling waves. In this work, open-top rectangular box specimens composed of sintered nylon powder and coated with fine sand are used to represent freshly fabricated parts yet-to-be cleaned of un-sintered powder. Steady-state traveling waves are excited in the specimens while variations in the frequency content and phase differences between actuation points of the excitation are used to affect the characteristics of the dynamic response. The effectiveness of several response types for the purpose of moving un-sintered nylon powder within the specimens is investigated. 

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4. Stochastic FDTD Modeling of Propagation Loss due to Random Surface Roughness in Sidewalls of Optical Interconnects

   https://doi.org/10.23919/USNC-URSINRSM51531.2021.9336433  

   Guiana, Brian; Zadehgol, Ata (February 2021, 2021 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM))

   null (Ed.)

   The dielectric waveguide (WG) is an important building block of high-speed and high-bandwidth optical and opto-electronic interconnect networks that operate in the THz frequency regime. At the interface of Si/SiO 2 dielectric waveguides with width above w = 2.5 μm and anisotropic surface roughness, transverse electric (TE) mode surface wave propagation can experience a loss of approximately a = 2 dB/cm; however, propagation losses increase rapidly to near a = 44 dB/cm as the width decreases to w = 500 nm, due to increased interaction of surface waves and sidewall surface roughness that exhibits random distribution inherent to the manufacturing process. Previous works have developed analytic expressions for computing propagation loss in a single dielectric waveguide exhibiting random roughness. More recent works report a = 0.4 dB/cm noting the non-trivial estimation errors in previous theoretical formulations which relied on planar approximations, and highlight the discrepancy in planar approximations vs. the 3-D Volume Current Method. A challenge that remains in the path of designing nanoscale optical interconnects is the dearth of efficient 3-D stochastic computational electromagnetic (CEM) models for multiple tightly coupled optical dielectric waveguides that characterize propagation loss due to random surface roughness in waveguide sidewalls. Through a series of theoretical and numerical experiments developed in the method of finite-difference time-domain (FDTD), we aim to develop stochastic CEM models to quantify propagation loss and facilitate signal & power integrity modeling & simulation of arbitrary configurations of multiple tightly-coupled waveguides, and to gain further insights into loss mechanisms due to random surface roughness in optical interconnects. 

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5. Double-Ridge Five Port Power Splitter Using Gap-Waveguide

   https://doi.org/10.1109/AP-S/INC-USNC-URSI52054.2024.10686999  

   Valentín–Hernández, Emmanuel; Rodríguez–Solís, Rafael A (July 2024, IEEE)

   In microwave engineering, waveguides are a key component when transmitting high frequency waves with low losses. However, these are inherently bulky in size and difficult to integrate with other microwave components. Gap-Waveguides are a good solution for mm-wave frequencies since they are easier to integrate with other components and easier to fabricate since there is no need for a complete physical shield. This work uses gap-waveguide technology to develop a 4:1 power splitter network that can operate from 20 GHz to 40 GHz with very low losses and less than 2:1 VSWR. 

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