That’s why the Romulans and the Klingons had cloaking devices for their ships, but the Federation didn’t (with very rare exceptions). It's one of the few toys that came from the series that wasn’t a Federation invention or used by them. But it was awfully cool.
You hit a button and your ship disappears for everyone looking at it. The idea wasn’t original to Star Trek, J.R.R. Tolkein had it in the Lord Of The Rings, and it was a part of many folktales hundreds of years before he gave it to Frodo. Harry Potter’s cloak is probably a direct result of Frodo’s, although the movie Predator gave it a more scientific, not magical, feel that is more reminiscent of Star Trek.
The cloaking devices in the early Star Trek episodes were not perfect, you couldn’t fire weapons while cloaked and some tracking sensors could still find you. These are some of the same problems we're having with cloaking devices today.
Oh yes, we have cloaking devices.
The Klingon bird-of-prey projected it’s invisibility through its deflector shields; we don’t have anything that cool yet, but we can make things disappear under the right conditions. However, making a ship disappear to all wavelengths of electromagnetic radiation using something projected from the ship itself is beyond us as of yet. Let’s see what we can do.
The electromagnetic spectrum is all around us, we
see with only a very small part of it. The longer the
wavelength, the lower the energy, so gamma rays are
very powerful, and radio waves can’t hurt you unless
we’re talking about your ears.
But there are so many more types of waves than just visible light. Infrared waves are longer and lower energy than visible light. Heat sources give off infrared waves, so this is how you can find people in the dark with night vision goggles. Radio waves are even lower energy, while microwaves for radar are in between infrared and radio.
Higher energy waves are on the other side of the visible spectrum; things like ultraviolet, X-rays, and Hulk-producing gamma rays. All the different types of waveforms can be detected by some kind of detector or another. They all give clues to the fact that something is out there. Star Trek cloaking devices masked all of them eventually, but we’ve only gotten to the point of hiding from a few wavelengths at a time.
As with most scientific or technological advances, first we have many of ways to try it, and we finally settle on what works best. Remember VHS vs. Betamax? As our knowledge increases, we will hone in on one or two ways to make these cloaks work, but for now, there’s a bunch.
This is not to say that we haven’t been hiding things in plain sight for a long time. Camouflage is an ancient practice, something we stole from nature. Active camouflage is a little more tech-y and recent. This technique allows the camouflage to change as the background changes.
The Adaptiv technology uses hexagonal panels on the
sides and turret of tanks to project an incorrect heat
signature. To an infrared scope, they can look like a
station wagon or truck. This is one type of active
However, when the object moves, there is a blur as the cameras catches up to the new background. Plus, like with your TV, it only works very well when you are directly in front of it. Nobody wants to be the guy watching the Super Bowl from the uncomfortable chair that’s at a 45˚ angle to the TV screen.
There is also holographic camouflage, so that as you move past the object, the background appears to move with you. Better, but still not great. And these examples are for just visible light; nothing about a hologram projected on a sheet is going to hide your heat signal from a guy with infrared night specs. The new Adaptiv system allows tanks to project a different heat signature than they normally would (see picture above).
Many of the newer techniques bend light around the object, sort of like a stone in a stream. The water comes back together on the other side and moves on as if the object weren’t there. Same with light rays that bounce off the background. Using proper technology, they can be made to travel around the object being cloaked and travel to your eye as if it wasn’t even there.
The mantle cloak technique uses a very thin layer of
metamaterial to bend light rays or cancel them out. Harry
Potter might have been hidden better, but I like our chances
with science better than magi
The metamaterials offer several different ways to hide something, like plasmonic cloaking, where the light scattered by an object is detected by the cloak. The clock then emits a canceling wave at precisely the same length but 180˚ out of phase. The two waves cancel each other out and it is as if no light was bounced toward your eye or your detector. Other metamaterials don’t cancel the signal, but truly bend it around the object as described above.
A mantle cloak is thinner, using a metamaterial screen just a few millimeters thick to produce the antiphase radiation that cancels out whatever strikes it. This was demonstrated in 2013 by Andrea Alu from the University of Texas, just as the plasmonic cloak was a few years previous. The advantage is that the thinner the cloak or mantle, the broader the range of wavelengths that it could cancel out.
The Rochester cloak uses the mirrors of different focus
lengths to bend visible light rays. Check out this website to
make one yourself. While cloaks in the visible range are the
biggest show, the military or security will be interested in
cloaks of broad wavelengths, not just visible light.
A big problem that we must overcome to mimic Star Trek cloaking is that fictional ships can scan and see what is out there via emission of their own probes or detectors, we can't do that yet. With current technologies, the object is covered or masked, so it can’t emit anything or see anything around it. Most current cloaks work by absorbing or channeling EM waves, so if the cloaked object emits anything, it can be detected.
As Frodo could see through the weave of his cloak, we need to be able to look out from a cloaked object and see what we want, or even send out some energy to detect things that might be out there. There is limited advantage to a cloaked ship that is ostensibly blind itself. However, 2012 experiments did develop a plasmonic cloak that detected light, so over a very narrow range it was an invisible device that could see.
Another low-tech cloak is using mirrors, but again, you
have to be positioned exactly right for them to give you
the right image. Plus, this is just for visible light, a true Star
Trek cloak would mask all wavelengths of
In addition, the cloaks themselves usually scatter light, so even though the object being cloaked is hidden, the cloak itself might be detected! The authors suggest that there could be a passive solution using superconductors, or that mixed metamaterials could scatter the waves bouncing off the object to be hidden and the cloak.
Next week, how about looking at our versions of phasers – we do have them, just not small enough to be hand held.
Contributed by Mark E. Lasbury, MS, MSEd, PhD
As Many Exceptions As Rules
Choi, J., & Howell, J. (2014). Paraxial ray optics cloaking Optics Express, 22 (24) DOI: 10.1364/OE.22.029465
Fan, P., Chettiar, U., Cao, L., Afshinmanesh, F., Engheta, N., & Brongersma, M. (2012). An invisible metal–semiconductor photodetector Nature Photonics, 6 (6), 380-385 DOI: 10.1038/nphoton.2012.108
Soric, J., Chen, P., Kerkhoff, A., Rainwater, D., Melin, K., & Alù, A. (2013). Demonstration of an ultralow profile cloak for scattering suppression of a finite-length rod in free space New Journal of Physics, 15 (3) DOI: 10.1088/1367-2630/15/3/033037