Cloaking is a feat that has been a predominant area of research for military purposes to give our armed forces a decisive advantage over our opposition. The basic philosophy of developing cloaking technology involves figuring out how to minimize the scatter of waves be it light, sound or radio when they strike an object which creates a perceived signal. Objects that we are able to see are visible because of the light waves bouncing off them thus creating the visible world around us which holds similarly true for sound waves.
Research conducted by an electrical engineer, Jose Sanchez-Dehesa, out of the Polytechnic Institute of Valencia has led to the discovery of a new method to minimize the way sound waves scatter when they hit an object. Development of a plastic shell made up of a number of layer of rings has led to the discovery that manipulating the way sound waves scatter can cause noise cancellation similar to the technology used in noise canceling headphones which emits a sound to cancel out what is heard. The application of this development is the first successfully cloaked three dimensional object from sound waves.
The plastic shell is made up of 60 rings encases a sphere which utilizes the rings and their angles in a precise format calculated by a computer algorithm to achieve invisibility from sound waves. Although developed out of fairly primitive materials, the application of this technology has been precisely calibrated to achieve what many consider to be a masterpiece of stealth capability. Further development of the concepts outlined in this research is expected to be applied in sonar blocking technology for military ships and submarines for the Navy as well as minimizing sound pollution in metropolitan areas.
Previously research being conducted in invisible technology has used sophisticated synthetic materials to attempt to steer light and sound waves around an object, however the drawback has always been the cost and development time necessary to achieve this is largely unrealistic to mass produce. The technology developed by Sanchez-Dehesa uses a much simpler method of disguising sound using the reflection of audio waves within the rings to cancel each other out. The experiment conducted used a sphere encased in the ring device suspended from the ceiling in an echo free chamber while various levels of sound were emitted with a sensor behind the object to detect its presence. Although most sound waves projected were detectable, at 8.55 kilohertz (high pitch frequency) the sphere was undetectable by the sensors behind it.
Despite being in its early stages of development, the U.S. Office of Naval Research has already taken notice of this research being conducted out of Spain as it has provided funding for other programs to create technology to achieve sonar invisibility. The current technology was developed specifically for the sphere used in the experiment by using an algorithm to map the predicted sound trajectory before developing this device. This means that currently every object this is used on needs a custom design to achieve the same level of disguise which unfortunately does not look very promising for use in submarines in its current state. City planners on the other hand are very interested in the possible use of this research to develop better technology to block sound pollution caused by highways in residential areas.