The last couple of weeks, we’ve been talking about the Electromagnetic Spectrum. Humans see in only a tiny range of the spectrum. Other parts of the spectrum, like x-rays or infrared radiation, can be used to ‘see’ in other ranges.

And, of course, there are cases in which you don’t want to be seen. Paul Schneider, a writer on the original Star Trek, was inspired by the ‘silent running’ mode of submarines and thought there should be a similar stealth mode for spaceships. D.C. Fontana coined the term ‘cloaking device’ for the 1968 episode “The Enterprise Incident”.

Silent running:submarines as cloaking:spaceship

Since then, cloaking devices have figured into all kinds of science fiction and fantasy, from Star Wars to Harry Potter.

…But They Are Reality!

To understand cloaking devices, you have to understand how we see. Because the whole point of a cloaking device isn’t to change the thing we’re trying to hide: It’s just to change what you see. Chameleons become invisible because they change to blend into their background. In a cloaking device, the object doesn’t change. The cloaking device fools your eye in a very different way.

What a Cloaking Device Does

Most of the time, we are looking at light reflected off the object we’re seeing. (Exceptions are if you’re seeing light that comes through something transparent or translucent; or if you’re looking at something that actually emits its own light, like a light bulb or the Sun.)

White light (which contains all the different colors) hits objects (in this case, a green, red and blue block).

The objects reflect back only certain colors of light. All the other colors are absorbed. Those reflected light rays travel to your eye and that’s why you see the 19 car as orange and the 48 car as cobalt blue (kobalt blue?)

Now let’s put something opaque between the objects (our background) and your eye. The object blocks the light rays from getting to your eyes. That means you don’t see the background.

A clocking device figures out where the light rays from the background were heading and makes it so that the same pattern of light rays reaches your eye as it would if the blockade wasn’t there. The clocking device fools you by showing you the background in front of the object it’s trying to hide.

Existing Cloaking Technology

The First Attempts

You could say the first cloaking technology was a form of art called Tromp l’oeil, which is French for “fool the eye”. It was style of photorealistic painting that created the optical illusion that something 2-dimensional, like a wall, was actually three-dimensional. The picture below is a 2-D picture. It’s just painted so well that it looks like a kid climbing out of a picture frame.

I like this example, too.

More Recent Technology

Not surprisingly, defense applications are one of the more important uses for this technology. Radar-absorbing paint, optical camouflauge, cooling the surface to prevent IR signals and other techniques are now used with some success in the field.

The “See-Through” Tank

Just a couple of weeks ago, the Army demonstrated technology for the tank that will replace the Abrams. A tank, in order to protect it’s occupants, must be impenetrable – which means metal, Kevlar and other non-transparent materials. So if you want to see out of a tank, you have to open the hatch. If there are bullets flying around, this is hardly a good idea.

Elbit Systems has invented a system called “IronVision”. A set of cameras (visible-light AND infra-red) is are mounted on the tank. The people inside wear helmets. The positions of the helmet wearer’s head is tracked, so that when he or she moves their head, the cameras show them what they are looking at outside the tank. They can see 360 degrees around, which increases their ability to see everything. They’ve also got an augmented reality overlay to show them where things like, say, hospitals are. The tank gun can also be indexed to the position of the wearer’s head, so that if you see something, you can fire right away. They estimate that the system can detect a person at 200 meters (which is about two football fields.)

Pretty impressive.

I know, it’s not hiding the tank, but you have to admit that it is pretty darn cool.

Metamaterials

You probably learned that water bends (refracts) light rays. Metamaterials are artificially structured materials that interact with electromagnetic radiation (visible light and EM radiation in a large range of frequencies) very differently than natural materials like water. Changing the composition of the materials changes how they react to EM radiation. A lot of this work is being done in infrared and microwave ranges. This is one of those very high tech, very expensive lines of research that is being pursued by the Department of Defense. You’re probably not going to see these materials being used in anything the average person encounters on a daily basis any time soon.

Simpler is Better

Remember that the point of cloaking is to bend light around the object you’re trying to hide. It turns out you can do a decent job with fairly simple lenses. The University of Rochester has been working in this field for some time.

This picture is from a video that shows how essentially four lenses can be used to project the background in front of the thing they’re trying to hide. Below, the scientist responsible for this shows you how you can make your own optical cloaking device.

He points out that it really only works in a long hall, but if you’re got one, hey…

If you want to build your own, here are the instructions. It costs less than $150 they say and that’s not bad to be able to tell people you’ve got a cloaking device.

What’s useful in this video is that he shows you the arrangement of mirrors he uses to get this effect. You’re going to see something very similar in a little while.

Their problem is that many of these optical techniques only work from a particular range of angles. The Rochester group has been working on some digital techniques that maintain the illusion from a broader range of angles. Basically, these use cameras and sensors with a digital display that figures out what direction the light would be going if it weren’t blocked and generates the background for you.

Toyota’s Cloaking Device

The problems is that once you start bringing in sensors and motors and cameras and displays, you’re ramping up cost and the probability of malfunctions.

The Problem Toyota Wants to Solve

The design of a car is constrained by many things, the foremost being safety. It would be great to have glass all the way around the driver’s line of sight, except that would be a disaster in the case of an accident. So we have the A-pillars (the metal pieces on either side of your windshield, the B-pillars (to the rear of the first set of side windows) and the C-pillars (at the rear windshield).

These are structural parts of the car, designed to keep the roof from crushing in on you if your car rolls over. Although they are meant to protect you in case of an accident, they sometimes cause accidents because they block the driver’s field of view especially when turning left. This is especially a problem with sporty cars, most of which have steeply raked windshields.

There have been attempts to address this problem in other ways. Some have proposed cameras, and some have tried putting windows in the pillar itself.

These are expensive solutions and, as noted, the more parts, the more likelihood of problems.

Toyota’s Plans

It’s all done with mirrors. Here’s what the device looks like:

Clear, right?

Try this:

Here’s what you need to know. This is a top view. The Object to Cloak (the A-Pillar) is in the middle. You are inside the car on the bottom of the picture and what I’ve labeled background is a person or car that you wouldn’t see because it’s hidden by the A-Pillar.

The key to this whole thing are the mirrors. There are eight of them. The red ones are mirrored on the outside (the sides facing away from the Object to Cloak) and opaque on the Inside.

The dashed blue lines are half-mirrors. Not like short mirrors, but special mirrors that pass some light and reflect other light. The genius of this design is that it takes advantage of the fact that light is polarized. The electric and magnetic fields oscillate back and forth in different directions. These half mirrors allow some polarizations of light to pass and block other polarizations.

Polarized sunglasses work similarly. When light reflects, it comes off the surface with all different polarizations. That produces glare. Polaroid sunglasses only allow one polarization to come through. That’s why they block glare. (Cheap sunglasses just have darker lenses. They cut down on how much light gets through period. True Polaroid sunglasses only block out glare.)

What all the lines on the first diagram are trying to show (in their own, patent lawyer-speak kind of way) is how the light comes in, bounces around off these eight different mirrors and eventually form the image of the background on the surface nearest the driver.

There are nineteen diagrams in the patent. Here’s the useful one, which shows how the device will work (in principle):

The A-pillar (which is essentially the “cloaking device”) creates an image of everything behind it on the inner surface of the pillar so that you, the driver, can essentially see right through the pillar. No camera. No fancy (expensive) materials. The half-mirrors I mentioned have been around forever. I think we may have a few of them in the storage room from physics demos we’ve done in the past.

The patent suggests that this could be used for the B and C-Pillars as well. The ability to design a car without having to worry that style or strength concerns introduce blindspots opens up a whole world of possibilities. Although there have been a lot of concept cars that look starkly different from existing cars, most of the technologies that would have to exist to make them reality are complex. This is a relatively simple approach.

The patent also shows possibilities for a device that would have a circular format. If you’re going to use it for an A-post, that would aesthetically be a lot nicer than the blocky box I showed you above.

How Could NASCAR Use This?

Manufacturers have pushed for some time now to incorporate more technology that’s on current street cars in the racing cars.

But let’s not forget that one very important aspect of motorsports is as a proving ground for manufacturers. This cloaking device is simple and doesn’t offer a lot of challenges in terms of policing: It’s literally a bunch of mirrors that would probably come as a sealed component you’d put on the car.

NASCAR has been talking about the Glass Cockpit for some time, where drivers might have a heads up display that projects information in their line of sight so they don’t have to look away from the track to see it. This is in the same vein, but way simpler. The advantages are overwhelming in terms of safety. We can talk all we want about cameras and head-up displays and augmented reality, but simply eliminating blindspots would be a big step forward.

The disadvantage I could see is that a driver whose cloaking device was damaged due to contact could be at a big disadvantage – or could end up being a danger on track because of his or her limited visibility.

The other disadvantage: That old excuse “Nothing intention, I just didn’t see him there.” ain’t gonna work anymore.

Please help me publish my next book!

The Physics of NASCAR is 15 years old. One component in getting a book deal is a healthy subscriber list. I promise not to send more than two emails per month and will never sell your information to anyone.

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Toyota’s New Cloaking Device

Did Toyota Really Just Patent a Cloaking Device?

Isn’t this Just the Media Hyping it Out of Proportion?

Cloaking Devices Exist?

The Origin is Fictional…

…But They Are Reality!

What a Cloaking Device Does

Existing Cloaking Technology

The First Attempts