## 3aSPb8. Finite-element analysis of planar sonar arrays by a coupled finite-element/modal-expansion method.

### Session: Wednesday Morning, December 4

### Time: 10:00

**Author: John D'Angelo**

**Location: Skyblue Systems, 1223 Peoples Ave., Troy, NY 12180**

**Author: Richard E. Morrow**

**Location: Skyblue Systems, 1223 Peoples Ave., Troy, NY 12180**

**Abstract:**

This paper presents the analysis of infinitely periodic planar sonar arrays
by a coupled finite-element/modal-expansion method. Finite elements are used to
model the region containing the sonar transducer. Here, the finite-element
method solves the scalar Helmholtz equation for the acoustic potential. The
finite-element method is well suited to solving the field behavior in the
complex shape and heterogeneous material region of the sonar transducer. Coupled
to the finite-element region is the semi-infinite region where the acoustic
field behavior is periodic. In this region, the field behavior is defined by an
infinite series Floquet modal expansion. The number of modes used in the Floquet
expansion depends on the geometry and scan angle of the array. Typically, the
number of modes is comprised of all the propagating modes plus 10 to 20
evanescent modes. This technique allows for the solution of array field behavior
for any arbitrary scan angle. Being an infinite periodic analysis, however,
limits the accuracy of the solution to the sonar elements in the middle of the
array. This paper describes the use of this technique in two- and
three-dimensional analysis and shows results in two dimensions.

ASA 132nd meeting - Hawaii, December 1996