Adaptive positive position feedback for actively absorbing energy in acoustic cavities

A method for adaptive energy absorption in acoustic cavities is presented. The method is based on an adaptive scheme consisting of a self-tuning regulator that has the ability to target multiple modes with a single actuator. The inner control loop of the self-tuning regulator uses positive position feedback in series with a high- and low-pass Butterworth filters for each controlled mode. The outer loop consists of an algorithm that locates the zero frequencies of the collocated signal and uses these values to update the resonance frequency of the positive position feedback filter and the cut-off and cut-on frequencies of the Butterworth filters. Experimental results are provided that show how less than a 10 percent change in the frequencies of the acoustic modes of the experimental setup will cause a non-adaptive controller (using positive position feedback and Butterworth filters) to go unstable, but the self-tuning regulator will maintain stability and continue absorbing energy through a 20 percent change in the frequencies of the acoustic modes.