Terahertz Millimeter-Wave Scanners

Interesting article on terahertz millimeter-wave scanners and their uses to detect terrorist bombers.

The heart of the device is a block of electronics about the size of a 1990s tower personal computer. It comes housed in a musician's black case, akin to the one Spinal Tap might use on tour. At the front: a large, square white plate, the terahertz camera and, just above it, an ordinary closed-circuit television (CCTV) camera. Mounted on a shelf inside the case is a laptop that displays the CCTV image and the blobby terahertz image side by side.

An operator compares the two images as people flow past, looking for unexplained dark areas that could represent firearms or suicide vests. Most images that might be mistaken for a weapon­ -- backpacks or a big patch of sweat on the back of a person's shirt­ -- are easily evaluated by observing the terahertz image alongside an unaltered video picture of the passenger.

It is up to the operator­ -- in LA's case, presumably a transport police officer­ -- to query people when dark areas on the terahertz image suggest concealed large weapons or suicide vests. The device cannot see inside bodies, backpacks or shoes. "If you look at previous incidents on public transit systems, this technology would have detected those," Sotero says, noting LA Metro worked "closely" with the TSA for over a year to test this and other technologies. "It definitely has the backing of TSA."

How the technology works in practice depends heavily on the operator's training. According to Evans, "A lot of tradecraft goes into understanding where the threat item is likely to be on the body." He sees the crucial role played by the operator as giving back control to security guards and allowing them to use their common sense.

I am quoted in the article as being skeptical of the technology, particularly how its deployed.

Posted on October 3, 2018 at 7:11 AM • 20 Comments


PhaeteOctober 3, 2018 9:22 AM

"They are called “terahertz” because instead of visible light they “see” at .25 trillion hertz."

The people in the science department call this Infrared Light

I'm off to the store, buying a new galactic strength bullshit detector, my old one broke on this one.

David RudlingOctober 3, 2018 9:22 AM

The scanner is supposedly intended to detect e.g. concealed weapons or suicide vests.
The article quotes you as saying "It makes no sense, because all it does is force an attacker to make minor changes to their plans”. If the plan was to take a concealed weapon or a suicide vest and foreknowledge of the scanner means they don't take the concealed weapon of the suicide vest that seems to involve a little more than "minor changes to their plans". I suspect the article quotes selectively. I would be very interested to see the full text of your skepticism as I suspect it makes a much stronger case in full.

solaricOctober 3, 2018 9:38 AM

@David Rudling

The general criticism for all such technologies tends to be that terrorism, by definition, isn't going after specific targets and doesn't represent any existential threat. The point is right there in the word, it's to cause terror in the general population and convince a superior stronger population to turn its own strength against itself, and thus achieve effects greater then the attackers would be able to ever accomplish by sheer force of arms.

So if you come up with some super duper perfect security technology for scanning at entry points to airports or mass transit? Just blow up the lines of people waiting right? Hence "minor change of plans", for a terrorist blowing up the plane itself isn't actually that important, it's not like a military operation where the goal is to specifically reduce the enemy's logistical capability or something, any public attack on groups of people can work. Here they set up some system to scan people coming down the escalator? Ok, set off the suicide vest on the escalator. Or at the top! Or at the cafe people are grabbing a coffee at before getting on the bus/train. Etc etc etc, there is no inherent end to it, beyond at some point people saying "ok, like natural disasters we do what we can and then focus on rebuilding and moving on afterwards" or else a descent into a panopticon, where the cure is far, far worse then the disease.

For any security measure to actually be worth it there should be some clear specific singular high value thing it's defending, and preferably the security should be near fully passive and the minimal required to accomplish that, not a general "defense against terror". So reinforced cockpit doors and appropriate security practices for entry for example (or perhaps some future aircraft design might flatout create permanent compartmentalization there). That has no effect on any public practices at all, and accomplishes the specific high energy goal of defending a high value asset and preventing a physical form of force multiplication.

But the general defense against "terror" isn't technology; it's courage. Simple as that.

Impossibly StupidOctober 3, 2018 9:42 AM

"It definitely has the backing of TSA."

That's more of an undorsement than an endorsement.

Exactly how many "concealed large weapons or suicide vests" incidents have there been in recent years that this would have been useful for? Compared to the number of false positives it's obviously going to generate? Just another case of people continuing to fight the last battle despite the fact that terrorists have moved on to different tactics.

ChelloveckOctober 3, 2018 10:00 AM

@solaric: I've been saying the same thing for 17 years now. If the Bad Guys really wanted to screw us over all they'd have to do is detonate a bomb in an airport security line. One would be bad enough, but multiple coordinated attacks around the country would paralyze air traffic for weeks. Hit a couple major commuter rail hubs while you're at it and Congress would fall all over themselves tearing up the Bill of Rights in their effort to do "something". That this hasn't happened yet suggests that maybe there isn't really a legion of Bad Guys out there actively plotting our destruction. Or if there is, they're *really* unimaginative.

TelstradiOctober 3, 2018 10:03 AM

I already refuse to fly (and have for nearly 10 years at this point) because I don't want to be subjected to TSA security theatre, particularly the body scanners. Now I'm going to have to avoid other forms of public transit as well?

At what point is it going to be impossible to avoid these things?

echoOctober 3, 2018 10:29 AM

If all this machine does is allow an operator to confirm the person passing through indeeddoes have sweaty armpits and carrying, gosh wow, a backpack and not an optical or drug induced hallucination I have to ask what use is this machine?

Is this machine a clever audit test or a riff on the ADE 651?


Blockquote>Rafid Ahmed Alwan al-Janabi (Arabic: رافد أحمد علوان الجنابي‎, Rāfid Aḥmad Alwān; born 1968), known by the Defense Intelligence Agency cryptonym "Curveball", is a German citizen who defected from Iraq in 1999, claiming that he had worked as a chemical engineer at a plant that manufactured mobile biological weapon laboratories as part of an Iraqi weapons of mass destruction program. Alwan's allegations were subsequently shown to be false by the Iraq Survey Group's final report published in 2004.


The ADE 651 is a fake bomb detector[1] that was produced by ATSC (UK), which claimed that the device could effectively and accurately, from long range, detect the presence and location of various types of explosives, drugs, ivory, and other substances. The device has been sold to 20 countries in the Middle East and Asia, including Iraq and Afghanistan, for as much as US$60,000 each. The Iraqi government is said to have spent £52 million on the devices.

Bob PaddockOctober 3, 2018 10:50 AM

From 2009:

"How Terahertz Waves Tear Apart DNA

A new model of the way the THz waves interact with DNA explains how the damage is done and why evidence has been so hard to gather" -


"DNA Breathing Dynamics in the Presence of a Terahertz Field" -


When it comes to medical imaging sadly we are still in the Stone Knives and Bearskin area of technology. :-( For example try to differentiate between Cerebral Spinal Fluid and water or body tissue, in a live person, without harm...

Security Imaging is in even a worse state.

Karl KoscherOctober 3, 2018 12:42 PM

@Bob Paddock:

This is a passive scanner than relies on blackbody radiation from the person. The heat of your body is generating the THz radiation. The article even mentions that weapons at body temperature disappear.

But it's still a dumb idea. It looks like they only look at people going down certain escalators. What about the elevator? And unless they ban all bags (which seems highly improbable), a would-be terrorist would only have to hide their weapons in a bag.

ArcherOctober 3, 2018 12:53 PM

The device cannot see inside bodies, backpacks or shoes.

Then it's useless. I could continue to conceal my (lawfully-carried) handgun by using the age-old trick any two-year-old knows: keep it on the side of my body facing away from the scanning device.

Alternatively, a person could keep someone else -- or a few someone elses -- between themselves and the scanning device.

And as stated by other commenters, if it can't see inside backpacks or shoes, then it can't see inside clothing.

Naturally, the TSA approves ... because the TSA is committed to doing the two things any bureaucracy ultimately does to keep running: justify its own existence (and therefore, its budget) and expand its domain. At the end of the day, however, the TSA is A Security Theater[TM] (as evidenced by how easily and often "penetration testing" gets weapons through the checkpoints -- read "weapons" as in "guns and knives", not "pointy toothbrushes and nail clippers"), and any alleged "improvements" (hah!) they've made to airport security have been because they individually search each and every traveler and bag.

This new scanning device does nothing like that.

Then there's this:

How the technology works in practice depends heavily on the operator's training. According to Evans, "A lot of tradecraft goes into understanding where the threat item is likely to be on the body."

So we're back to profiling and reading body language. There are a finite number of places on the body to carry a "threat", after all. Why do we need a new scanning device, then?

And this:

He sees the crucial role played by the operator as giving back control to security guards and allowing them to use their common sense.

Yep. Profiling and body language...

... and the same "common sense" that demands "enhanced screenings" on toddlers and wheelchair-bound grandmothers.

Based on the article, it's a very high-tech, very expensive "solution", that only provides a very small improvement over a naked-eye visual scan at distance.

But it's OK. Move along people. Nothing to see here.

albertOctober 3, 2018 2:13 PM

@Phaeto, etc.

"...They are called “terahertz” because instead of visible light they “see” at .25 trillion hertz...."

No, they are called that because they couldn't sell $100,000 IR cameras.

This is a terrific example of modern marketing techniques, AKA BS. What's really sad is that scientificamerican.com bought the whole story. And wasting taxpayers dollars, which no one seems to mind.

This "technology" is said to be patented. I'll bet those patents are works of art.

@Bob Paddock,
It's my understanding that these things don't transmit anything (what would be the point?)

But thanks for the DNA link.

. .. . .. --- ....

echoOctober 3, 2018 4:25 PM


It's this kind of thing which makes me shy away from buying US products. Similar might be said of US companies being tricky with data protection.

The way US companies often behave after takovers of UK companoes is disgusting not to mention the agenda they lobbied and pushed for during the now abandoned TTIP negotiations.

Clive RobinsonOctober 3, 2018 6:15 PM

@ Otter,

If it cannot see inside a backpack, it cannot see inside clothing.

It depends on what you mean by "see inside". All EM energy has a penetration depth based on a number of factors. Much like your microwave oven only heats upto around half an inch depth into wet food items like meat. "Terror Hurts" rays as someone glibly named them are several orders of magnitude greater than the ~2.45GHz of the family microwave oven therefore it's penetration depth is considerably less (which is maybe why the USM was looking at using them as "non-lethal weapons").

It does not matter how much you increase the power the depth stays more or less constant with frequeny, unless the material you are illuminating goes through some change due to sufficient temprature increase due to RF heating[1] etc that changes the property of the material (ir it cooks your goose).

Irespective of actual generated power the effective energy of EM signals increases with frequency. As you move from microwaves through terahertz into long and short Infra Red then visable light the ability to damage cell tissue remains low (and is considered in I^2R "heating" effects caused by the free standing EM fields). However above the visable spectrum EM radiation starts to cause other effects including ionisation effects which can be quite dangerous. Eventually the wavelengths involved become comparable to molecular length where IR heating is nolonger the dominant issue.

Currently the EM model prefered by the likes of the NRPB is the IR heating model. Spme people believe that terahertz radiation is more harmfull than lower frequencies. However as we have only quite recently been able to generate terahertz radiation of any power the jury is out due to lack of total test time on individual biological specimens.

[1] Believe it or not RF heating works by causing certain --usually OH-- molecular bonds to vibrate, thus in effect it's heat from friction.

JackOctober 4, 2018 12:25 AM

What, they made a blackbox to identify US-airforce Al-Qaeda suporting terrorist-bombers ?
Great idea, hook them up to the S-300 system and lets get rid of the terrorists F-35's..

albertOctober 4, 2018 1:06 PM

In fairness, the product in question is marketed to the TSA, and LE, neither of which are tech giants. As long as your sales pitch includes the words "spotting terrorists", those deep pockets are waiting to be emptied. It's all part of the Security Theater, Screen No. 1, at 9AM, 10AM, 12PM, 5PM, 6PM, 10PM. Check your newspaper for listings.

''RF heating'' has been the industrys favorite strawman argument for decades now. "If it doesn't cause heating, it's OK." Yes, these are basically marketing arguments, but science is also to blame. The Scientific Establishment has absolutely no idea of the importance of energy in the human body. As I've said before, frequencies in the GHz are dangerous to humans and animals alike. Our bodies are not designed to withstand them. We can, with simple instruments, produce frequencies in the 40 to 4000Hz range. These are safe, and can often produce interesting effects. But these are sound waves, not RF fields. RF technology is an unnatural human construct, and should be viewed with skepticism and caution.

Regarding heating. It's interesting to note that heat transfer can occur through direct contact, contact through a medium (air, water, etc.), and RF energy transfer. (Note that ultrasonic welding uses solid aluminum blocks as a transfer medium). I don't believe that scientists totally understand the process of heating, and more research is needed in this seemingly trivial area.

. .. . .. --- ....

TrullinatorOctober 4, 2018 2:57 PM

My fav airport uses to rub your hands for explosives when the metal detector beeps. Do remember never play with pyrotechnics when you intend bringing a knife a board...

Clive RobinsonOctober 4, 2018 8:16 PM

@ Bauke Jan Douma,

Terrorist bombers come in F-15's. Ask the Yemeni.

The original meaning of "Terrorism" was when a state inflicted fear in it's own or another nations citizens, who could not defend themselves against it.

It's only in more modern times that political wordsmiths have changed it to point the finger of blaim at those who would fight such tyranny in any which way they could, hence they would call themselves "freedom fighters"...

Wordsmithing has become a despicable art in the past hundred years or so. As we have seen demonstrated by amongst others the NSA and CIA, and many other nation states agencies and entities, it continues with more alacrity in this very young and tender millennium...

Mic MacOctober 5, 2018 3:18 PM

These scanners are very useful in quality control on many assembly lines. -- Alert salesmen! -- Basically the mass surveillance is very similar to assembly lines' quality control.

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