There is more reporting of “structured” materials. The terminology employed to define “structured” overlaps with “metamaterials”. First metamaterials are typically an engineered assembly of various elements that are constructed in specific atomic structure arrangements to create non-natural occurring combinations and structures that provide unique properties. The properties of the structure are created in such a manner as to provide interaction with incoming waves, which can be acoustic or electromagnetic.
The Institute of Physics has an article on the “Harry Potter invisibility cloak.” [Ref. #1] The explanation is given of how metamaterials can bend electromagnetic radiation (in this case light) around an object. There is a video in Reference #2 that demonstrates the effect of bending light waves. This is an actual bending of the light rays via the material properties. There are other examples on the internet if you search for them. One issue is that the material employed and the structure design are limited to specific frequencies (wavelengths).
Acoustic metamaterials are materials designed to manipulate acoustic waves (sound waves are in this category). Reference #3 is from Duke University researchers and was among the first if not the first demonstration of cloaking an object from sound. The cloak and the material covered appear to not exist. The structure in this case was accomplished by employing a standard material, plastic, but developing the shape in such a way that the material structure appears to be completely flat. The compensation for the difference in distance are developed by the form of the structure.
What we are learning in that some of the anticipations about the arrangements of the materials is not something that is always expected. Reference #4 is an article about the atomic structure of an ultrasound material. Lead magnesium niobite, which is employed in ultrasound applications, was found to have the atoms shift along a gradient. (More details are available in reference #4 to explore the actual paper which is refenced.)
Structured materials previously had been considered the development of materials based on their mechanical properties and not on their electrical, acoustic, optical, or chemical properties. These materials could range from the sub-micron range to centimeters. As work in this area continues to smaller and smaller dimensions, other material properties are also changing. This is opening up a new world of applications.
There is always new information being published on the internet. A good source of metamaterial information is the Phys Org site [Ref. #5]. This field is even more surprising than the development of graphene. Looking at the results of finding new applications for materials with unanticipated properties is always thought provoking. And, if one considers that we have not even approached the application of singular isotopes of materials, it is very difficult to predict what new material properties will be found. The new tools being developed permit a greater understanding of the mechanisms behind the properties. Learning about these will permit applications undreamed of, except maybe for science fiction.
References:
- http://www.iop.org/resources/topic/archive/metamaterials/
- https://www.cnn.com/2016/07/20/health/invisibility-cloaks-research/index.html
- https://pratt.duke.edu/about/news/acoustic-cloaking-device-hides-objects-sound
- https://www.mse.ncsu.edu/news/structure-of-ultrasound-materials-unexpected
- https://phys.org/tags/metamaterials/
