Acoustics Seminars

Generic Models of Spatially Distributed Transducers

date October 31, 1984
comments no comments.

Wednesday, October 31, 1984 12:00 p.m.

Ilene Busch-Vishniac
Department of Mechanical Engineering
The University of Texas at Austin

The typical means of modeling a transducer is to represent its behavior using discrete lumped elements. In such a model the transducer exists at a point in space and thus the distributed nature of the transducer is neglected. We have developed generic models for transducers with finite spatial extent. In one of these models the transducer is viewed as a continuum of locally-reacting, connected two-ports. In the other model, the transducer is represented by a transmission line which has been augmented to include energy exchange with the environment. In both models the physical properties of the transducer may vary with location. This amplitude shading may be used to produce desirable response characteristics.

Transient Response of an Electret Microphone

date October 24, 1984
comments no comments.

Wednesday, October 24, 1984 12:00 p.m.

Whang Cho
Department of Mechanical Engineering
The University of Texas at Austin

Simplified analysis shows that the decay rate of the transient response decreases as the frequency mode increases.

The Diverging Sound Field of a Spherical Piston

date October 17, 1984
comments no comments.

Wednesday, October 17, 1984 12:00 p.m.

Halvor Hobæk
Department of Physics
The University of Bergen
Bergen, Norway

Computations show that the nearfield of a spherical piston -in the sense that the directional properties are dependent on range- extends much farther out than for a plane source of similar dimensions. The reason for this can be seen by applying an approximate mapping of the spherical piston field to that of a plane piston with the same aperture. A simple method to characterize the structure of both fields is also discussed.

The Directivity of a Laser-induced Thermoacoustic Array

date September 26, 1984
comments no comments.

Wednesday, September 26, 1984 12:00 p.m.

Yves H. Berthelot
Applied Research Laboratories
The University of Texas at Austin

A thermoacoustic array can be generated by modulating the intensity of a laser beam illuminating a liquid. The nearfield directivity pattern of a thermoacoustic array is found by taking the Fourier transform of the impulse response of the optoacoustic system. A simple expression in integral form has been derived for the directivity of a thermoacoustic array on a pressure release boundary such as an air/water interface. The integral is easily evaluated numerically and it clearly shows the presence of side lobes in the nearfield directivity. In the limiting case of farfield radiation the directivity computed numerically reduces to the farfield direc­tivity derived analytically. Experimental results will also be discussed.

Nonlinear Effects in Sound Beams

date September 19, 1984
comments no comments.

Wednesday, September 19, 1984 12:00 p.m.

Professor Mark F. Hamilton
Department of Mechanical Engineering
The University of Texas at Austin

Finite amplitude propagation of directional sound beams is well modeled by Kuznetsov’s paraxial wave equation, which accounts consistently for nonlinearity, diffraction, and absorption. The solution of Kuznetsov’s equation is found in the form of a Fourier series expansion, and the resulting coupled equations in the harmonic amplitudes are integrated numerically. Excellent agreement between theory and experiment will be presented for axial propagation curves and farfield beam patterns. Nearfield effects resulting in the splitting of sidelobes (the appearance of so-called fingers) in the harmonic beam patterns will be discussed. The numerical method also lends itself nicely to describing reflection of finite amplitude beams, for example from both finite and infinite pressure release surfaces.

Stochastic Differential Equations for the Masses

date September 12, 1984
comments no comments.

Wednesday, September 12, 1984 12:00 p.m.

Alex Garcia
Applied Research Laboratories
The University of Texas at Austin

The field of ordinary Stochastic Differential Equations (SDE) has in the past 20 years progressed from the dangerous and unexplored jungles of the cutting edge of analysis to the paved and well-lit treatments in undergraduate texts. Soon most differential equation courses will cover SDE in that hectic last two weeks of the semester as a sort of icing on the cake. Don’t be let out of the coming stochastic revolution. This talk will briefly cover the following:

1). Interesting situations in which SDB arise
2). Fundamentals of the random processes
3). The 0-U and Wiener processes
4). Ito and Stratonavich calculus
5). Numerical techniques

No dealers, please. This talk is strictly for neophytes. Emphasis is on “cookbook” techniques, no proofs.