PORTLAND, Ore. — Acoustic signal processing technologies examined at this week's Acoustical Society of America meeting here focused on cutting through noise to improve signal detection and localization using arrays of MEMS microphones.

Researchers from the National Cheng Kung University of Taiwan proposed using MEMS microphones with a time-reversal technique to improve voice reception for mobile speakerphones and laptop computers.

"Sometimes we have trouble sending or receiving messages clearly in a noisy environment," the researchers said. "In the present application, array microphones are used, and a time-reversal process is introduced to recover the original signal at the source location. This means a clearer signal with a higher signal-to-noise ratio."

The time-reversal method has been widely used for sound localization in ultrasound medical diagnositics as well as in underwater communications systems.

By processing the reversed signals from multiple-microphone arrays, together with their reflected signals, the researchers were able to localized the source, equalize the combined microphone's outputs and improved the voice's signal-to-noise ratio.

The researchers also claimed that its propagation method recovered the original signal at the source location, and it was able to separate signals from different speakers simultaneously. Future versions might use a "virtual" signal propagation path for quicker detection.

Using noise from inside jet engines to generate enough energy to run active noise suppressors was the subject of a paper presented by University of Florida acoustic engineers. The researchers showed a piezoelectric actuator that could convert vibrational energy inside a jet engine into the electricity that could be used to power a sophisticated active noise suppression system . The system could convert an ear-splitting 160-decibel sound waves into 30 mW of power.

A novel active acoustic muffler used in an electro-mechanical Helmholtz resonator was built on a compliant piezoelectric composite diaphragm. The device provided coupling between acoustic and electrical energy.

The piezoelectric diaphragm converted mechanical to electrical energy which was then used to suppress noise. The harvested energy powered a set of microphones and a wireless communication transceiver that switched on various shunt loads to appropriately adjust the resonant frequency of the sound mufflers.

In medical technology, sound waves methodologies were proposed to deliver chemicals, detect bacteria, pinpoint kidney stones, shrink enlarged prostates and relieve speech and hearing problems.

For instance, Lawrence Livermore National Laboratory researchers working with the University of Rochester showed that the an acoustic blast wave from a explosion could deform the skull of nearby soldiers. The wave could cause ripples that generate large enough pressure variations in the brain to cause concussions as severe as those caused by an impact.

The researchers proposed new suspension systems for soldiers' helmets that could block sound propagation between the helmet and the skull, thus preventing shock waves from reaching the skull.