Mechanical filter with acoustic sensing

摘要

A mechanical bandpass filter with acoustic sensing is disclosed, including a particularly advantageous implementation enabled thereby in the detection of automobile engine knock. A pair of cantilever beam resonators of different resonant frequencies are connected at their nodes to a single in-phase velocity source which is directly acoustically driven and which has an infinite stiffness relative to the flexure mode resonators. The resonators have piezoelectric transducers of opposite polarity electrically coupled in such a relation as to define upper and lower attenuation stopbands due to signal cancellation and to define a passband frequency, due to signal reinforcement. The passband corresponds to the frequency range between and around the resonant frequencies of the two resonators. The invention provides a wide bandwidth without spurious response mode effects.