Pistachio nuts can be sorted using the difference in impact noise between a nut with an open and closed shell. It was found that upon impact with a steel plate, nuts with closed shells emit sound with higher signal magnitudes than do nuts with open shells.

The classification accuracy of this system is approximately 97%, and the cost of the system is about $7k per channel, which is less than conventional sorters that use color of the nuts. Increased sorting accuracy of the acoustic sorter, coupled with low cost, enables a payback period of less than one year.

Reference: “Detection of pistachio nuts with closed shells using impact acoustics”, Pearson, T.C., USDA ARS GMPRC, Manhattan, KS 66502, United States, Applied Engineering in Agriculture v 17 n 2 March 2001. p 249-253 , 2001.

Tires for vehicles have various tread patterns, usually to balance the amount of traction to the road surface during dry and wet weather. As most people know, a solid soft tyre has the greatest surface area in contact with the road and hence has the most amount of traction. The tread pattern allows water to escape when the tire is on wet roads.

When the tread is in contact with the road surface, volumes of air are formed between the road and the tread pattern in the tire, which is compressed as the tire rotates. The volumes of air are a network of small Helmholtz resonators that generate noise.

In addition, the interaction of the tread pattern with the road vibrates the body of the tire and causes the walls of the tire to radiate noise.

Read an article on tire noise by Stuart Bolton.

I read an interesting article on the Naval Sea Systems Command web site that shows pictures of the propulsion system used on the US mine hunter ships. The ships use a Vertical Axis Cycloidal Propeller system designed and manufactured by a German based company, Voith Schneider. The Voith Schneider Propeller (VSP) not only eliminates the need for conventional props and rudders, it also eliminates the requirement for bow thrusters. This propulsion system makes the boats quieter than conventional propellor boats.

Read the full article here.