2019_programme: TESTING OF UNDERWATER HELMHOLTZ RESONATORS FOR BIANISOTROPIC METAMATERIAL APPLICATIONS



  • Session: 16. Advances in acoustic measurement systems: Technologies and applications
    Organiser(s): Tesei Alessandra
  • Lecture: TESTING OF UNDERWATER HELMHOLTZ RESONATORS FOR BIANISOTROPIC METAMATERIAL APPLICATIONS
    Paper ID: 794
    Author(s): Cushing Colby W., Wilson Preston S., Haberman Michael R., Su Xiaoshi, Norris Andrew
    Presenter: Cushing Colby
    Presentation type: oral
    Abstract: Helmholtz resonators have been widely studied and documented for in-air environments since Hermann von Helmholtz recorded observations in the late 1800’s. The rigid wall assumption that is sufficient in air must be abandoned in water and the decreased acoustic contrast between the walls and the surrounding water yields elastic wall motion that results in asymmetric scattering. Previous work has shown that an array of tuned Helmholtz resonators can be used to achieve negative modulus behavior in ultrasonic frequency ranges for underwater environments. [Fang et al., Nature Materials 5, 452–6 (2006)]. In the current work, underwater Helmholtz resonators have been designed, fabricated, and tested for an 1800 Hz resonance while accounting for the compliance and mass of the cavity wall. The resonators were modeled using commercial finite element software to design for the desired resonance frequency. The Helmholtz resonator was then placed in a 114-liter tank on a piece of rubber to decouple any vibrations from the tank bottom. A piston-driver-generated 50–2500 Hz chirp excited the system for 3 cases: 1.) with the resonator present 2.) a baseline without the resonator in the tank and 3.) with the resonator in the tank, but the neck hole had been covered. A hydrophone was used to record the acoustic response and the baseline spectra was subtracted from the resonator responses to determine the acoustic response of the Helmholtz resonator. A scanning laser doppler vibrometer was used to quantify the movement of the resonator wall while it was being excited in the tank for cases 1 and 2. The impact on proximity of the driver to the resonator was also studied. Experimental data was compared to the simulation for resonance frequency and amplitude responses. Results, future work, and applications in bianisotropic materials will be discussed. [Work Supported by ONR.]
  • Corresponding author: Mr Cushing Colby W.
    Affiliation: University of Texas at Austin
    Country: United States
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