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    Acoustic Michelson interferometer based on a phononic crystal
    (Aip Publishing, 2023) Durmuslar, Aysevil Salman; Kaya, Olgun Adem; Bicer, Ahmet; Cicek, Ahmet
    A practical and highly sensitive acoustic Michelson interferometer with a small form factor is introduced. It involves two different types of phononic crystals composed of steel rods in water acting as a medium for self-collimated waves and mirrors for the reference and sample beams, as well as a beam splitter formed by modified scatterers arranged diagonally. Finite-element method simulations are employed to demonstrate its operation around 200 kHz. Equifrequency contour analysis reveals self-collimation of ultrasonic waves between 190 and 210 kHz. Introduction of the beam splitter and mirror phononic crystals is not detrimental to self-collimation where outgoing waves from the two interferometer arms interfere such that the output intensity varies in a cosine squared manner. Consequently, maximum sensitivity is achieved when the movable mirror displacement is either zero or half of the interferometer phononic crystal period. On small intervals in these ranges, micrometer-scale displacement resolution is achievable, as the output intensity drops by 0.2% per micrometer. Thus, displacements smaller than a percent of the wavelength are easily resolvable. Nanoscale resolution can be obtained with a scaled down interferometer design. Moreover, application to liquid concentration sensing by considering ethanol-water binary mixture is demonstrated. A percent increase in weight fraction of ethanol up to 10% in the mixture leads to an intensity drop as high as 2%. Thus, significantly higher sensitivities compared to sensing schemes based on resonance frequency shift are attainable. The proposed approach can be adapted for surface acoustic waves in strain measurement or biosensing.
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    Acoustic sorting of airborne particles by a phononic crystal waveguide
    (Elsevier, 2022) Korozlu, Nurettin; Bicer, Ahmet; Sayarcan, Done; Kaya, Olgun Adem; Cicek, Ahmet
    A two-dimensional phononic crystal linear defect waveguide is utilized for size-based sorting of millimeter-sized solid particles in the air through acoustic radiation force. The waveguide channels ultrasonic waves at 20 kHz, as calculated through Finite-Element Method simulations. Spherical solid particles released from rest at the top of the vertically aligned waveguide experience the combined effect of the acoustic radiation, gravity, and drag forces. When the particles are released from the symmetry plane of the waveguide, they follow straight paths where the ones with radii smaller than a threshold value are trapped at the waveguide nodal planes, whereas larger particles are let pass through. This requires input sound pressure levels between 173 dB and 177 dB. Moreover, such particles can also be differentiated with respect to density. Alternatively, the release of particles with a slight offset from the symmetry center induces unbalanced acoustic radiation potential, and thus uneven radiation force, resulting in the initiation of horizontal displacement whose extent depends on particle radius. Thus, both simulation results and experimental findings suggest that this scheme can be employed in size-based particle separation. Sorting of spherical glass particles with 0.5 mm and 1.0 mm radii are experimentally demonstrated for low ultrasonic transducer acoustic power output up to 90 W. The proposed approach can be utilized in applications where contact-free separation of airborne particles is required.
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    Broad omnidirectional acoustic band gaps in a three-dimensional phononic crystal composed of face-centered cubic Helmholtz resonator network
    (Acoustical Soc Amer Amer Inst Physics, 2021) Bicer, Ahmet; Korozlu, Nurettin; Kaya, Olgun A.; Cicek, Ahmet
    Broad omnidirectional band gaps in a three-dimensional phononic crystal consisting of a face-centered cubic array of spherical air voids connected by cylindrical conduits in solid background are numerically and experimentally demonstrated. With a low material filling fraction of 37.7%, the first bandgap covers 3.1-13.6 kHz frequency range with 126.1% gap-over-midgap ratio. Finite-element method is employed in band structure and numerical transmission analyses. Omnidirectional band gaps are observed in only two-period thick slabs in the 100, 110, and 111 orientations. Experimental transmission characteristics are in good agreement with numerical data. The phononic crystal can be employed in low-frequency sound proofing.& nbsp;(C) 2021 Acoustical Society of America