Acoustic Pulse Scattering from Impedance Covered Cylinders

• Main Author: Khavaran,Abbas
• Format: Report
• Language: English
• Subjects: Acoustic pulse scattering; Acoustic scattering; Acoustic waves; Acoustics; Creeping waves; Cylindrical bodies; Fourier transformation; Geometry; Harmonic pulse train; Impedance; Impedance covered cylinders; Incident plane pulses; Inverse fourier transforms; Pressure; Pulses; Saddle point method; Sommerfield Watson transformation; Test and evaluation; Theory; Theses

An expression for the acoustic scattered pressure from an impedance covered cylinder due to an incident plane pulse is obtained analytically. The application of Fourier transform on time and subsequent Sommerfield-Watson transformation results in separate expressions for geometrically reflected pressure and for creeping (or circumferential) waves. Using Cauchy contour integration theorem and saddle-point methods, the inverse Fourier transform is evaluated. The impulse response and convolution theorem have been utilized to obtain an expression for the scattered pressure for incident harmonic pulse train and FM pulses. The first arrival of acoustic wave at an observer point in the far field is shown to be due to the geometrically reflected pressure. After the first arrival, creeping waves are shown to circumnavigate the cylinder surface for an indefinite number of times and radiate off tangentially at any angle. These waves create the multiple echoes that return in the scattering of a single pulse. The circumferential waves are shown to decay exponentially as they encircle the cylinder surface. (Author)