News Scan Briefs; December 2008; Scientific American Magazine; by Charles Q. Choi; David Biello; Philip Yam; 2 Page(s)
Anyone kept awake by a neighbor¿s television
may be surprised to learn that a few holes drilled through a wall could lower the volume on sound. Francisco Meseguer of the Polytechnic University of Valencia in Spain and his colleagues placed a series of 20-centimeter-thick aluminum plates in a tank of water and found that perforated plates could diminish ultrasound waves passing through by up to another 10 decibels as compared with solid plates. This reduction was greatest when the spacing between the holes roughly equaled the sound¿s wavelength. Evidently, the incoming sound interacts with regularly spaced holes, generating acoustic waves on the plate¿s surface that destructively interfere with waves going through the plate. The findings, in the August 22 Physical Review Letters, could help soundproof machines while allowing cooling air through, remarks Meseguer, who says his team is now experimenting with audible sound.
Electric fields can boost a car¿s gas mileage by up to 20 percent, thanks to a well-known effect in which electric fields reduce the viscosity of a liquid [see ¿Electrorheological Fluids¿; Scientific American, October 1993]. Reduced fuel viscosity means that much smaller droplets can be injected into the engine, leading to more efficient combustion. Investigators at Temple University thinned fuel by attaching an electrically charged tube to a diesel engine¿s fuel line near the fuel injector. In road tests, the attachment, which consumed
less than 0.1 watt, increased highway fuel economy from 32 to 38 miles per gallon. The researchers, who describe the boost in the November 19 Energy & Fuels, expect the device will find use in all kinds of internal-combustion engines.