US Patent Granted for Way to Look Out of Radar Cloaking

A US high tech company called Fractenna announced it had received a US patent for an ability to turn cloaking on and off, allowing a vessel that's in a radar cloak to see out of it.

The firm pioneered and invented invisibility cloaks and holds both the ‘source’ patent (8,253,639) and the related comprehensive IP portfolio.

Recently issued patent 10,027,033 is a continuation of that state of the art innovation. It discloses a novel means of turning invisibility cloaks on and off, by changing the characteristics of a boundary layer. Notes inventor Nathan Cohen: “The person or sensor inside the cloak is thus no longer blind.” Cohen asserts that not being able to sense the outside has previously been the number one impediment to the use of invisibility cloaks.

So Star Trek had it right - the Romulans had to drop their cloaks to see out and use sensors.  The fact that the cloaking technology has worked both ways (keeping the cloaked from looking out as well as keeping an outsider from looking into the cloak) has been an impediment to the development of cloaking technology, which has tremendous military potential, as well as civilian uses.  Unfortunately, I couldn't find a description of how the cloak is turned off.

The hams in the audience might recognize Factenna, because Nathan Cohen is better known as W1YW, and known on the bands as 'Chip'.  Chip was an early adopter of fractal antenna technology and an advocate of the technology when most other hams were dismissing them as obvious derivatives of existing antennas.  The best write up on the technology isn't on that "Business Wire" link at the top, it's on the forum section of ham radio callsign lookup site, QRZ.

The newest patent, 10,030,917, describes related technology where electromagnetic energy is absorbed by fractal-based metamaterials. Called ‘fractal absorbers’, the innovation uses evanescent waves to divert such impinging energy off to the sides, where it is absorbed in a resistive layer. Previously, absorbers relied on the thickness, not the width, of materials to accomplish this. Now these very thin fractal absorbers accomplish the same result with dramatic thickness and weight reductions.

Fractal absorbers have been known and recognized as important for many years. Explains Cohen: “It is outrageous and bizarre to see teams from PRC (China) claiming invention of fractal absorbers. They have received unusual attention for their alleged invention, under the premise of so-called ‘supermaterials’. Fractal absorbers were discovered many years ago, at this firm, and the new patent conclusively establishes fractal absorbers as an American invention that pre-dates others’ alleged invention: we didn’t give it to them. We held it under wraps, waiting for this patent issuance. The patent application was withheld from publication. Ironic for them, the Chinese have unwittingly established credibility for our invention and its American uses. And, in my opinion, they are now very far behind in the game.”

Cohen sees a variety of commercial applications for fractal absorbers, whose broad bandwidths and ultra-thinness are especially sought.

Fractal absorber with some material sanded away so that the some of the fractal pattern can be seen.  Fractenna photo.

If you really want to read a fun piece, Chip was awarded a Technical Achievement Award at the Dayton Hamvention this year, and talks a lot about his background on his callsign lookup page.   Go to https://www.qrz.com/lookup and enter W1YW in the box on the top left of the page.  For hams using RTTY (Radio TeleType) communications, there was a tradition of writing a few things about themselves to send to everyone they contacted as an introduction.  It was saved on a tape that was fed into a paper tape reader (then cassette audio reader, then a text file on the computer) that's known as a "brag tape".  This is the first few paragraphs of Chip's brag tape.

Well, I was the kid who stuck his finger in the light socket. Some of you may think that explains a lot. I made my first invention at age 6.  At 11,  I got my license. There was no holding me back, immersed in a friendly wireless world fabulously unlike my limiting hometown. 

Human nature being what it is, not everyone is friendly. Some of you are aware of the tortuous 30 year path of the innovation of fractal antennas, fractal resonators and electronics,  the invisibility cloak, and so on.  You can’t not see the very verbal resistance to that amongst some of our ranks. But this is typical territory for innovators who understand the outrageous realities of Darwinism with its die-offs and resurrection.

I was allowing none of that on fractal antennas. I became champion for the technology I created and took more than my share of arrows. I shot quite a few of them back. The pioneer didn’t die and the technology, today, is exploding on a global scale across wireless and telecom. Kids get taught it in math class.College students get graded on it at universities. DIY’ers praise me for bringing in Green Acres reruns from 150 miles away.

 Bottom line: I did it, from the beginning, with ham radio. I haunted flea markets. I had a love-hate relationship with Radio Shack and MFJ. I built my own antenna range . I  used crystal controlled 2M rigs.  I funded it from slim earnings, and unlike this first-class meal here, cornflakes and ramen noodles. I hate  ramen noodles.

Bottom line: Fractal antennas are ham-grown. I am proud to be a ham. You should be too.

So what's a fractal antenna?

Here's an example from Fractenna literature.  First off, notice that there's a large number of identical, repeating elements called tiles (one is highlighted in white).  Think of each element's largest overall length as a full-wavelength loop.  (If you're not comfortable with the idea that radio waves have physical size, I do a little explanation here).  Each of the bends turns an electrical length into smaller pieces.  Start with the smallest little square you can see near the inside center of one of those tiles.  The smallest sections resonate on frequencies where they're close to 1/4 wave long,  if we include the next short section, it gets longer, lowering the resonant frequency.  We continue to include more and more of the square squiggles, and eventually the biggest pieces resonate where all of those lines, and the interactions between them, add up to be 1/4 wave.  The combination of all those squiggles gives the pattern a wide frequency response, from the lowest frequency that fits around the entire perimeter of the tile to the highest frequencies of the smallest little lengths, and the art of the design is creating all those lengths so that wide bandwidths are covered. 

How do they cloak a device?  We've talked about it before here, in particular, we talked about the technique of evanescent surface waves, or ESW.  Chip links to a video showing their system working. 

Evanescent surface waves going around an object, so that it doesn't interrupt the signal.  Similarly, radar hitting an aircraft's body will go around the plane as an ESW and not reflecting a return signal to the ground that reveals the aircraft to a radar looking for it. 

As I've said before, optical cloaking is probably still somewhat off in the future, but I think the same idea would work.