Researchers at Aalto University have created a magical "one-way glass" that transmits light completely like glass on one side, but reflects light like a mirror on the other.
There is a "magic mirror" where the mirror can only be seen from one side, but from the other side it can be seen through like glass, but traditional mirrors do not allow light to pass through in one direction; In fact, it is a translucent material that allows light to pass through in both directions, which comes into play when there is a difference in brightness between the inside and outside of the glass. Therefore, the surroundings need to be prepared and the same transmittance as clear glass cannot be expected. However, with unidirectional glass based on NME (irreversible magnetoelectricity), light passes in only one direction, so there is no need for brightness differences.
When you think of one-way mirrors, you might think of them being used in police interrogation rooms, but they have many other practical uses. Many of them have to do with ensuring privacy. Imagine having glass windows in your home, office, or car. No matter how bright it is outside, people can't see what's inside.
In order to create this amazing glass, the researchers decided to abandon traditional materials and use metamaterials. The response of conventional materials to electric and magnetic fields, as well as to light, is determined by atoms. However, optical metamaterials replace atoms with metaatoms, which can be structurally engineered to have properties rarely found in nature, allowing them to be designed to produce a unique electromagnetic response, enabling the generation and precise operation of light at the nanoscale.
In its most prevalent form, the magnetoelectric (ME) effect refers to the coupling between the magnetic and electrical properties of a material. In conventional materials, the effect of optical frequency magnetization is negligible, but for metamaterials, the electrical component of light can cause magnetization, and the magnetic component can produce polarized light.
Previous studies have shown that magnetism is strong at microwave frequencies and produces significant ME effects in this spectral region. Despite two decades of theoretical research, it has so far been difficult to realize metamaterials that work outside of this range.
This new metamaterial takes advantage of the irreversible magnetoelectric (NME) effect. The NME effect refers to the coupling of the magnetization and polarization properties of a material with different components of light or other electromagnetic waves.
So far, the NME effect has not found a practical industrial application. Most of the proposed methods only work for microwaves, not visible light, and the technology cannot make it.
Researchers at Aalto University say they have successfully broken through both barriers. By leveraging existing and nanofabrication techniques to overcome these problems, we have succeeded in creating a three-dimensional optical NME metamaterial in which a single superatom made of the traditional materials cobalt and silicon is spontaneously magnetized.
The researchers say that unidirectional glass made with metamaterial designs not only helps protect privacy, but can also be installed on existing solar panels to provide reflections that are missing in current designs and are said to be able to capture large amounts of thermal energy. It can also replace safety glass, car windows, or one-way sunglasses that don't dim.