Nonlinear control of boundary impedance in an acoustic waveguide

Abstract

Wavetubes are employed for measurements of acoustic properties in various fluids. The ability to manipulate and control the frequency-dependent boundary impedance of the tube improves the estimation accuracy. Passive solutions, which use composite materials to change the boundary impedance, enable one to realize a finite combination of boundary impedances. In this paper, the tube boundary impedance is tuned at will by using two loudspeakers. The suggested method operates in the presence of dispersion by estimating, in real-time, a parametric reduced-order model using a multichannel least mean square algorithm. The identified model is fed to a nonlinear, adaptive control algorithm to realize modal traveling wave ratio control. It has been noted that the traveling wave ratio is smooth and parabolic across closed regions in the parameter space, thus assuring the convergence of the nonlinear control. Several methods to estimate the traveling wave ratio gradient are considered and compared based on an analytical model of a rigid impedance tube. An experimental case study utilizing an air-filled impedance tube with two loudspeakers is presented. The results demonstrate the ability to control the dynamics of the principal acoustic mode at will. Thus, enabling one to set the desired tube's boundary impedance.

Automatic traveling wave excitation of structures with imperfect cyclic symmetry

“…Traveling wave excitation is used in various dynamical systems, such as ultrasonic motors (USMs) [1], acoustic levitational motors [2], impedance tubes [3], thermoacoustic electric generators [4] antennas [5],…”