Acoustical Society of America, Washington DC Regional Chapter Mini Conference in Acoustics
- NONRECIPROCAL ACOUSTIC METAMATERIAL:Theory and Experiments. Petrover, Mechanical Engineering Department, University of Maryland, College Park
ABSTRACT: A class of passive nonreciprocal acoustic metamaterials is developed to control the flow and distribution of acoustic energy in acoustic cavities and systems. Such development departs radically from present methods that favor the transmission direction by using hardwired arrangements of the hardware and hence, cannot be reversed.
The proposed nonreciprocal acoustic metamaterial (NAMM) cell consists of only a one-dimensional acoustic cavity with piezoelectric flexible boundaries. These boundaries are connected to an array of anti-parallel diodes to introduce nonlinear damping effects that tend to break the reciprocity of energy flow through the NAMM cell.
A finite element model and a SPICE model of the NAMM cell are developed to investigate the nonreciprocal characteristics of the cell by optimizing the parameters that influence the nonlinear damping effects of the diodes. The predictions of the models are validated experimentally using a prototype of the NAMM cell which is tested inside an ACUPRO Impedance tube.
The performance characteristics of the NAMM cell are presented to demonstrate the effectiveness of the proposed NAMM in tuning the directivity, flow, and distribution of acoustic energy propagating though the metamaterial.
Keywords: Nonreciprocal acoustic metamaterial (ANAM), Nonlinear anti-parallel diodes, Nonlinear damping, Finite element modeling, SPICE Model of the electric analog of the NAMM, Experiments in the ACUPRO Impedance tube
- A NUMERICAL METHOD FOR LINEAR ELASTIC SHELLS ON OVERLAPPING GRIDS*
Daniel Serino, Ph.D., R&D Scientist, Applied Research in Acoustics LLC (ARiA)
Abstract: A numerical method for thin orthotropic shells is developed. The governing equations are formulated in terms of displacements and stresses on a locally orthogonal coordinate system on the mid-surface of the shell. The differential geometry of the surface is used to compute coordinate basis vectors and derivatives. The equations are written as a first-order system and are discretized by a second-order accurate finite volume scheme. An interpolation approach is adapted for vectors and tensors to connect the shell displacements and stresses between overlapping grids. The solver is verified using the method of manufactured solutions for plates, cylinders, and spheres. Additionally, vibrational modes are computed and compared against analytical benchmark solutions.
*This material is based upon work supported by the Office of Naval Research under Contract No. N6835-18-C-0533.
- Application of the CAF Mapping method to Acoustics
David Lechner, Ph.D., The Catholic University of America
Abstract: This presentation will explain the changes made to the CAF-Map functions in order to display acoustic energy on a geographic location grid. The CAF-Mapping algorithm was originally proposed for use in the electronic warfare domain to detect and track radio frequency signals. Modifications of the algorithm for use in acoustics are explained, including use of modeling to generate propagation times, sound velocity pro_les, and the wide-band cross ambiguity function. The CAF-Mapping algorithm provides a useful means of generating a geographic visualization of acoustic data. The algorithm is able to provide discrimination between multiple signals when they are broadcasting in a partially synchronized manner, and track acoustic energy without having to first classifying the signal type.