Invisibility is one of the marvels humans always wanted to achieve. It has been reflected in books, movies like The Invisible Man or Predator, but now scientists are getting closer and closer in tricking the human eye.
We see things because the light waves bounce back from these, being distorted. We only capture the so called visible light part of the electromagnetic spectrum; that’s between 400 and 700 nanometers of wavelength. Besides that the human eye can’t see anything without special devices like radars.
An invisibility cloak is designed to bend light around an object making it invisible. But until now these cloaks worked only to conceal very tiny objects and only from specific angles. A team of scientists from Lawrence Berkeley National Laboratory designed the first ultrathin invisibility cloak. It is made of a 50 nanometers layer of magnesium fluoride, coated with a pattern of 80 nanometers thick gold antennas.
The researchers wrapped the invisibility cloak around a 36 micrometer object and channeled a beam of light with a wavelength of 730 nanometers (near infrared) towards it. The light scattered bounced back, but the object remained invisible as if there was a mirror there. This happened thanks to the tiny gold antennas that controlled the scattering of the light and reflect it in such a way that it preserved the light’s phase and frequency.
Xiang Zhang, the lead researcher said that the new invisibility cloak, although scatters light at only 730 nanometers of wavelength, it can be improved to cope with the whole electromagnetic spectrum. And in the next few years it can be scaled up to rend invisible a tank, for example. And the uses range from military, to computing, bio-medicine displays and energy harvesting.
Other scientists are skeptical. Andrea Alu, associate professor of electrical engineering from the University of Texas, Austin argued that: “They had a small object, a little bump. With a larger object, I can’t take advantage of that … when I illuminate it, a portion is not illuminated; it’s in shadow. As such, the illusion of the perfect reflector would be broken.”
Zhang told that with a little work the tiny antennas can be calibrated to control the phase and frequency of various wavelengths and that it is a matter of time when we can see (or not) an invisibility cloak that can make a human sized object invisible.