Questions and Answers with Nathan Cohen

© 2012 pictures and text

PART 1 August 2012

Nathan Cohen with son A.J., July 2012

Q: Thanks for meeting. Just want to say I’d like to concentrate on you and the

cloak rather than business and cloak applications.

A: Sure.

Q: Tell us about the invisibility cloak.

A: Although the technology applies also to light and infrared, we developed it with

microwaves. It hides things by projecting the back view around to the front, so

the appearance mimics being invisible. It conceals the object. The microwaves

slip-stream around the hidden object so you don’t know it’s there. It’s not a lens.

Instead it uses evanescent waves and lots of itty bitty fractal patterns. It requires

fractals. It is totally passive, no power, and is made from bendable circuit boards.

No electronic parts. It is quite high fidelity and operates over a large frequency

range. It is typically shaped like a cylinder (see reference below) for simplicity of

demonstration. It can take other shapes.

Q: How did you come up with it?

A: I’d been thinking about it over 10 years or so, but didn’t understand that there

would be any big interest. There was no single ‘ahah!’ moment. I was motivated

to tell people about it after they seemed fascinated with someone solving the

problem. I do have an image in my mind from many decades ago from a 1930’s

sci-fi pulp magazine I read in 1972. I actually found it a couple of years back

(below). Notice the guy in the –cylinder! Sci-fi is always a motivator. But fiction is

not fact. Making fact is a lot of work.

1930’s scifi--now the patent office awards the cloak invention to Nathan Cohen

Q: What about Harry Potter?

A: That didn’t motivate me but I appreciate that millions of people were inspired

by this mythical cloak. Mine has no wizard embroidery and doesn’t look like a

cape.

“Fiction is not fact. Making fact is a lot of work.”

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Q: Can you make one that works at infrared? Visual light?

A: Yes. Yes. Takes some engineering effort because the fractal resonators are very

tiny. We will do it when there is a customer and a need.

Q: So who are you?

A: I am a physicist and astronomer and inventor. I am an American. I am an

entrepreneur. I am a family guy. I am a million other things that you need to

negotiate the tortuous path. I am a hiker. I am a skier. I am a writer. I am a

photographer. I am a ham. Most of all, I am a survivor.

Q: A ham?

A: Ham radio. Proud of it.

Q: I understand some call you the ‘Source’.

A: Looks like I am also a tributary of a river…

Q: What do they mean by that?

A: I started the field of practical fractal electronics and that makes me the

‘source’. I am amused when people call me that. I am OK with it.

Q: How old are you?

A: I remember the launching of Sputnik. I am told I look much younger than I am.

Q: For unknown reasons, some people don’t ‘get’ your background.

A: They probably expect a character from ‘Big Bang Theory’—and I am not like

that at all. With respect to cloaks, I started a new category of inventive enterprise.

I say that with no hubris nor boast, but as a matter of fact. The US patent office

issued the first invisibility cloaking patent-- with me as the inventor. Patent

number 8,253,639. It has turned down others, including Pendry, Smith, and

Schurig, who the popular press has portrayed incorrectly as the inventors. Here’s

one video of one of my cloaks: http://www.youtube.com/watch?v=2BrVxpPYMiA

Q: Did the patent office treat this properly?

A: I was frustrated by the delays. Apparently ALL of the cloak patent applications

were/are being heavily scrutinized. At the patent office it’s taboo to issue a

patent for any of the following ‘fiction’ inventions: perpetual motion; time

machine; anti-gravity; warp drive; invisibility cloak. In other words, the burden on

the inventor is especially severe to demonstrate ‘enablement’. Obviously I did

that. I know for a fact that my patent application was reviewed by a panel of

senior examiners, in addition to the regular examiner, who is himself extremely

skilled and senior. That’s very unusual. It took them almost 500 additional days to

go over it, beyond the normal process.

Having lifted that ‘fiction patent’ barrier—my patent and invention is legit-- I

would bet there’s more than a few people at the patent office tickled to see

fiction become fact. So I am actually very impressed with their efforts on this.

They deserve some thanks and congrats too. They have the pulse of innovation in

America. They are new-tech enthusiasts—they just aren’t allowed to let it bias

their work. They are difficult to convince but always fair.

Q: Is there another cloak patent?

A: The patent you mention is: 8,164,505. The object and the cloak are the same—

the object has holes in it which are filled with waveguides. It would be like taking

someone, and drilling holes into them to let light shine through the other side. A

cloak let’s electromagnetic radiation pass around, without disturbing the object.

It doesn’t put things that literally clunk through the object and make holes. The

inventors do not describe it as an ‘invisibility cloak’. It’s not.

Q: Are you an expert in optics?

A: Most of my work has revolved around optics, in such diverse aspects as

gravitational lenses, telescopes, dolphin sonar imaging, ultrasound devices, real-

time large scale deblurring (deconvolution),antennas, interferometry, arrays,

radar, and so on. I was an editor for the journal INTERNATIONAL JOURNAL OF

IMAGING SCIENCE AND TECHNOLOGY. I wear reading glasses.

Q: I sense a bit of humor here.

A: I’ve worked very hard at my knowledge and abilities, for many decades.

Knowledge is not an accident. It is a journey. I paid a price but see the benefits.

Cohen’s 1990 invention of real-time deblurring pioneered modern ultrasound

Q: And you use fractals?

A: Wonderful tool. Some people say I am the world’s foremost ‘fractal engineer’.

That’s amusing because I am not an engineer. I am an ‘applied scientist’.

Engineers get upset when you use the term ‘engineer ‘ loosely.

Q: I understand you work with a team of engineers.

A: Yes, they are very good. They are patent pending inventors on cloak stuff too.

Q: How many patents—U.S. and foreign-- do you have?

A: Oh, maybe 36, 40. I stopped counting a couple of years ago.

Q: How long have you been inventing?

A: Since I was six. But I didn’t have resources to apply for patents until I was 35.

Life can be a tough slog. Still is.

Q: If you had the resources, how many patents do you think you’d have now?

A: Hmmm, probably 400 . Five hundred. I still have to turn myself down for cost

reasons.

Q: Do you have any advice for young inventors?

A: Don’t define yourself by others. Understand the difference between ‘want’s

and ‘needs’. Invention is rarely accomplished by ‘teams’. As I said, ideas are not

inventions. Venture capitalists have a <5% success rate so don’t be jazzed.

Remember that the patent office always says no the first time—like dating.

“I didn’t have resources to apply for patents until I was 35. Life can be a tough slog.”

___________________________________________________________________

Q: You also have a doctorate and were an academic.

A: Yes. I have a Ph.D. in astrophysics. I started my research career at Harvard at

17. Returned there more than a decade later. I am a radio astronomer. I was a

professor for a long time, at Boston University. I was in academia for 30 years.

Cohen at his Harvard office—1980’s

Q: Why did you leave?

A: I was needed after 9/11 for enabling the protection of people and things.

Q: Would you still be at a university if 9/11 didn’t happen?

A: In part. I like teaching, students.

Q: How does a radio astronomer come to invent an invisibility cloak?

A: The first true radio astronomer was an engineer, inventor, and ham radio

operator named Grote Reber. I am in good company historically.

Q: What do you think of John Pendry?

A: He’s a classic physicist of the Martin Ryle and Fred Hoyle era. That’s a

compliment. I was taught by a British physicist so I know that style well.

Q: Do you think he understands cloaking?

A: Analytically, of course. Conformal warping is not new; he used it on Fermat’s

principle with a nice invariance result. Fred Hoyle did something similar in

cosmology 38 years ago. The problem is that the resultant math does not lend

itself to telling you how to build a cloak. Einstein showed insight into stimulated

emission but it took almost 50 years more to figure out the ruby laser.

Q: So how did they (Duke group) try to build a cloak?

A: Schurig did a gradient of split ring resonators by changing the capacitive end

loading over many layers of circuit board. It’s tough to get something useful. It

rarely happens the first pass; this was no exception. IMO this should have been

meant as an attempt at showing science principles, not an invention. Notice that

there has been no public follow-up; no ‘improved’ version by the Duke based

group.

Q: Did it work?

A: IMO, no. It was lossy, narrow band, and had shadows. We built a

Pendry/Smith/Schurig cloak here quite a while back and were surprised how

marginal &mediocre it was—if memory serves the antipodal point was 5-8 dB

down at peak. That’s approaching opaque, not transparent, and monochromatic.

Incredibly hi Q—narrow band. Less than 1% bandwidth. Amazing how people

locked into it. I guess they saw it as a first step.

Q: Can you show us their cloak attempt?

A: That’s for the Durham guys to show. But here’s a piece of their cloak

approach’s rings to corroborate their results. We built one here from their

published approach. Our own invisibility cloaks look very different from their

cloak approach. Ours do not rely on split ring resonators. Our cloak designs work.

Split rings used in a Pendry-Smith-Schurig cloak experiment

Q: You used fractals?

A: Invisibility cloaks have been enabled by fractals.

Q; Why was the Pendry et al. cloak attempt important?

A: You can’t always judge what’s important to others. It was astounding to see the

world physics community lock on like it was a Manhattan project. As if

metamaterials are now the future of physics. The Pendry cloak papers galvanized

the entire field. There is certainly irrational exuberance. I’ve seen that

overreaction by the physics community 25 years ago for hi temp superconductors

(fizzled) and then cold fusion (which ended up being bogus). Both have failed to

produce a legacy of utility. Hi temp superconductors have been ‘just around the

corner’ for 25 years. Physicists need to stop saying that stuff.

Q: Will we see the same thing here?

A: Maybe. The problem is that many metamaterial solutions may have the same

import as ‘winkies’.

Q: Winkies?

A: Those plastic rings, also called flicker rings, that change the image as you shift

them. There’s some interesting optics there. Trivialized to a cheap toy. Some

metamaterial solutions will become cheap toys. Hopefully not mine!

Q: I understand you have traced the start of metamaterials to Marconi.

A: Marconi and Franklin in 1919. Patent. Resonator antennas patterned right next

to each other. Used them to make a reflector. This exact configuration is

prominently used in many metamaterial apps. See, for example,

http://metamaterials.duke.edu/news/infrared-metamaterial-phase-holograms-

nature-materials . Not mine though.

Page from Marconi & Franklin 1919 patent w/Fig 11 blowup

________________________________________________________________

Q: Wow. What do others think of that?

A: They ignore it. IMO, makes them look like late comers: jeopardize the funding.

Q: Did it jeopardize yours?

A: No ; I just wrote the check.

Q: The U.S. government has spent hundreds of millions or more on

metamaterials and funded research far and wide, even to researchers in , of all

places, Croatia--and you spent, what, a few thousand? Why did the United

States pay Croatia to explore invisibility cloaks?

A: It looks like the Air Force wanted Croatia to come up with a simpler invisibility

cloak. Now with the new patent , the grand slam has been hit. The U.S.

government itself has deemed that the invention of the invisibility cloak has been

resolved. It wasn’t done at a ‘funk works’ or a university. Or by a Russian scientist

living in Germany, or a team of PRC Chinese researchers. It wasn’t done by a

Croatian, or a Martian, either.

Q: So you are not taking stuff from a crashed UFO and releasing it.

Invisibility cloak did not start at Roswell (cool museum though!)

A: It’s amazing how often I hear that. It’s insulting in a creepy way. Why is it that

when something new comes along it ‘must’ come from aliens? No. I used my

head. Human. I know of no aliens.

Q: And you have nothing against Croats?

A: Of course not. I have many ham radio friends in Croatia. I have contacts with

them all the time on short wave. If some Croatian researchers want to work on

invisibility cloaks, it’s fine with me. But I am of the opinion that American

taxpayers shouldn’t pay for it.

Q: Have you let the U.S. government independently verify the cloak results?

A: We’ve invited the Army to test with us. Nothing yet. Also, NIST can test with us

too. The Army, Navy, Air Force, and agencies have seen the cloak in action.

Q: Is that independent?

A: It is if I sit with my latte while others are busy bees☺ Helps to be around when

questions come up. Fun to see others discover what you’ve already seen.

Q: I am intrigued by your background in gravity lenses and wonder how it may

have inspired the invisibility cloak.

A: Gravity lenses are caused by the warping of time and space by the gravitational

field of an intervening mass, such as a galaxy or black hole. Light travels on

geodesics. The geodesics get warped and produce mirage images of background

objects, which are normally occulted by the intervening mass. The ‘lens’ would be

analogous to the ‘object’ in an invisibility cloak. But unlike an invisibility cloak, the

background is imaged into a ring or crescent. It is not diverted around. A cloak is

not a lens.

Gravity lenses didn’t directly inspire the cloak, but then again, my brain does take

a bunch of seemingly irrelevant facts and helps me assemble them into new

ideas, visualize them, and assess them. It’s ‘ideas by analogy’. It’s playtime. Most

get discarded as unrealizable, others get tested. All have to pass the muster of my

scientific skepticism and knowledge base. Also, I never viewed a cloak as a type of

lens. There is no focus, for example.

Q: Can you show your involvement with gravitational lenses?

A: Heheheh! Really?

Q: Some might find it helpful. Others claim they find it hard to believe. It’s an

unlikely coincidence.

A: Not to me. It’s all in focus with my interests. There’s my Ph.D. thesis to start:

”Milliarcsecond Morphology of the Twin Quasar: The View Through a

Gravitational Lens”. Cornell, 1985. There’s a SCIENCE paper and an

ASTROPHYSICAL JOURNAL paper, and a popular book called ‘GRAVITY’S LENS’

from J. Wiley, that sold very well. Many young scientists know me from writing

book reports from that as kids. I get emails even today saying: ‘Oooh, YOUR’E the

guy that turned me on to science!’ I love that.

Q: Who was the author?

A: I am the author.

Cohen’s 1988 best selling popular book was a spinoff of his Ph.D. thesis

Q: Thank you. You seem to have a unique set of knowledge and skills.

A: They don’t seem unique to me. It’s who I am. Sometimes I don’t understand

why more folks don’t reach for a broad set of skills. I would discuss this with

Benoit Mandelbrot. He also was perplexed by it. Look at it this way: When you

cook in the kitchen you learn all the art and collect all the tools. You don’t just

learn to burn ramen noodles.

Q: Correction applied.

A: OK, continue.

Q: Did you find the metamaterial community helpful in your efforts?

A: That’s a story for another day. It’s continuing.

Q: Science is now known to be full of examples where the pioneers have been

excluded from attribution. Their baby is taken away by others. It happens

especially in modern times. There’s even a recent book out on that called PRIZE

FIGHT. Are you being excluded?

A: I am well aware of the outrageous story of streptomycin (the grad student

discoverer was tricked into signing off his patent rights), and Ray Damadian, who

invented MRI and was not part of the Nobel Prize. There is definitely a degree of

institutional dysfunction happening in this field too. Because I am not as well

known, I am the ‘wrong person’ to do something this important. The insult is

pretty deep: I challenge the physics community to present another physicist with

the depth of experience and diverse knowledge to match mine, in what was

needed to solve this problem. I am not a reductionist. I invented the invisibility

cloak, and I go out giving public demo’s to show it working. Who else can say

that? This is what inventors do.

Q: How did you get to be so knowledgeable on these diverse technical subjects?

A: In the old days I would lock myself in the libraries, such as Brandeis, Cornell,

MIT, Harvard, BU, and the Boston Public Library (for patents). And I would

experiment. Now the internet and a credit card get you everything needed for

information. That makes this the ‘era of innovation’ for those who know how to

suck the marrow out of strife (to paraphrase Thoreau amusingly). To be direct, I

worked very hard at acquiring an encyclopedic knowledge base. There’s been a

great deal of isolation and sacrifice and time spent and pulling myself up by my

bootstraps. No one helped me. Many later took public delight in trying to see me

fail. It gets ugly sometimes. But the bottom line is if I see an interesting problem I

go after it.

Q: So is it possible today to do cutting edge research and technology without a

huge university lab and library?

Boston Public Library—a patent regional depository

A: In many cases, yes. You don’t need the libraries and oftentimes PC simulations

or simple hardware go a long way. I bought all my test equipment for fractal

antennas at the MIT Flea market when I started out. I didn’t write a grant

proposal. Universities have a mixed record and are historically poor at coming up

with and shepherding useful new technologies. Both high temperature

superconductors and cold fusion came out of universities. By the way, I do miss

libraries and they still have their worth. They were a home in uncertain times.

They are just not a necessity for an inventor.

Q: You are so technical but went to a liberal arts school (Brandeis).

A: It was perfect for me. And I was a physics major. I could solve Maxwell’s

equations while reading ARTNEWS and watching out for pretty girls in the library.

I minored in music and math. I had a great time in my French classes. I had some

balance. If I had been at MIT, for example, I would have fizzed early and boiled

away. That’s me. Sure it may be different for others.

Q: Have you been in contact with other ‘names’ in the field?

A: A vast majority. Yes.

Q: Can you give a typical response?

A: My work was/is done with offers of collegiality which are rarely met.

Q: Can you comment about the government’s interest or role in the invisibility

cloak?

A: It’s our project; beyond that I am not at liberty to discuss.

Q: But there must be defense applications.

A: One would think.

Q: Can you say anything about it?

A: Their heart is in the right place. They’re learning the ropes.

Q: Does the invisibility cloak thwart radar?

A: At some level which I will not discuss.

Q: What about PRC (Communist China)? What is their interest?

A: PRC is now the world leader in research in metamaterials, and in fractals. They

are the only place in the world now that has conferences in fractal engineering.

While everyone bitch-fights (or bastard-fights) here in the States, and argues

about ‘centers of excellence’, they forge ahead in staggering and increasing

numbers of researchers and with more than ample resources.

Q: Yet you argue that you don’t need to centralize.

A: You can’t solve all problems like they are Manhattan Projects. And you don’t

need breathtaking new buildings with custom bean bag chairs and a dozen grad

students running $100,000 copies of software and the ‘machines that go ping’.

You need young people who haven’t been jaded into believing ‘it can’t be done’.

You need knowledge, experience, and talent, and what it takes to get the job

done. No more, no less. This is a rare combination apparently.

Appl. Phys. Lett. 101, 031903 (2012); http://dx.doi.org/10.1063/1.4737411 (4 pages)

An inside-out Eaton lens made of H-fractal metamaterials

Qiannan Wu1, Xiaoyi Feng1, Ruirui Chen1, Chendong Gu1, Sucheng Li1, Hui Li1, Yadong Xu1, Yun Lai1, Bo Hou1, Huanyang Chen1, and Yunhui Li2

1School of Physical Science and Technology, Soochow University, Suzhou, Jiangsu 215006, China 2Key Laboratory of Advanced Micro-structure Materials, Ministry of Education, Tongji University, Shanghai 200092, China

(Received 4 June 2012; accepted 1 July 2012; published online 17 July 2012)

We report an experiment on an inside-out Eaton lens fabricated using H-fractal metamaterials, copper printed on printed

circuit boards in H-fractal patterns. The lens can perform good imaging functionality with both sources and images inside the

vacuum core. The H-fractal metamaterials also provide design technique to achieve refractive index ranging in [0,1] with little

loss in microwave spectrum. Excellent agreements between numerical and experimental results have been demonstrated.

Abstract of a recent 2012 PRC fractal metamaterials paper--11 authors!

______________________________________________________________

Q: How many researchers are doing fractals in electronics in PRC?

A: I would guess maybe 5000…

Q: Wow! How many in the U.S.? Other places?

A: Maybe a couple of dozen U.S. 1000 elsewhere besides PRC. Of course I

haven’t left much to be mopped up. I don’t think anyone here understood the

significance of fractals in the invisibility cloak problem. Except me.

“(Cloak) is an American invention.. from a 60’s kid

who went to the New York World’s Fair, saw

Futurama--and wanted to make that future.”

___________________________________________________________________

Q: A couple of DOZEN in the U.S.?

A: Pretty amusing. Fractals are not the ‘flavor’ of the month in ‘funding clique’

circles right now. PRC is a different story. Just one of their scholarly papers can

have that many authors on it. Of course look at the home town advantage I

garnered as a result of being the big fish in a small population...

Q: So why wasn’t the invisibility cloak invented in PRC ?

A: They are probably a year or less away (my speculation) from trying something.

They worry too much about ‘losing face’. In contrast, I wasn’t afraid to fail. I do

not live in an environment driven by fear and punishment. I eat failure for lunch.

You have to try out ideas. Not all of them are sufficiently constrained by the

analytics for practical embodiments to fall out from the math. Partial differential

equations don’t tell you how an invisibility cloak gets built. As for the U.S. : There

is an air of freedom and innovation in America that transcends limitations and

even the reductionism of academia. It’s part of my heritage and part of our

culture. I am proud of it. America ‘enables’ me. If you allow it, it ‘enables’ you.

This does not exist in Europe nor PRC. There are no suicide nets in America—a

PRC invention. We and understand the notion of invention—and reinvention.

Q: Would you support further development of the invisibility cloak in PRC?

A: This is an American invention. It was invented here and belongs here as it

develops further. Aren’t you proud of it? This comes from a 60’s kid who went to

the New York World’s Fair, saw Futurama--and wanted to make that future.

Q: I understand you knew Jerome Lemelson, the prolific inventor.

A: I was introduced to him in 1990 in Reno. He lived at Lake Tahoe. I was doing

medical ultrasound for some Reno docs. He played wise old sage. I needed that.

Scientists are serial...inventors are parallel

___________________________________________________________________

Q: What was he like?

A: Friendly. Very knowledgeable. I discovered that many of my sensibilities were

shared. It could be because we were East Coast and Jewish. I wish I had spent

more time with him. Same with Benoit Mandelbrot.

Q: I understand you had a disagreement with Lemelson.

A: No, a difference of approach. We just disagreed on what you could do with

academia. Jerry thought that you could train inventors through universities. I

knew, first hand, that was impossible. I was a professor at the time.

Q: Why?

A: Inventors are not part of the teaching system. They have scientist and

academic engineers who ‘play’ inventor; rarely does a bona fide one emerge. For

example, I was an inventor before I was a scientist. One of Jerry’s most used

inventions today is a ‘talking thermometer’. Good luck getting a professor to see

that is a path a student should take. Academics are elitists. Inventors are

pluralists.

Q: What is the difference of approach?

A: Inventors want to solve problems to the point of owning them. Academics

want to solve a piece and then solve another piece, ad nauseum. Inventors can’t

afford to be purely reductionist-- they have dozens of problems to solve to make

any invention viable. Scientists and engineers are serial. Inventors are parallel.

Also, academics look at inventors as ‘gadgeteers’.

Q: You are both serial and parallel?

A: Yes. Took decades to have both mindsets.

Q: I don’t think folks understand that you solved an invariance property of

Maxwell’s Equations

A: With a colleague. That was definitely serial.

Q: So how do inventors come out of universities?

A: They stumble into it , spin out, and then get their learning curve, usually at

small companies. Universities essentially act like ‘clubs’ for inventors, such as the

‘chess club’ or ‘physics club’. You are expected to do that outside of class. If you

are a prof, well, you better be tenured already or you will be run over.

Q: I do understand that there is a big announcement in cloaking.

A: Yes. It’s big. In the next part. Remember that guy in the cylinder…. from the

sci-fi pulp magazine? I did. Here’s reality circa 2012. Here’s a diagram of Biggie

Cloak, successfully up and running as of Aug 13,2012. More in the next interview.