Ambient Radiation Sensors

Here's a piece of interesting research out of Ohio State: it's a passive sensor that could be cheaper, better, and less intrusive than technologies like backscatter X-rays:

"Unlike X-ray machines or radar instruments, the sensor doesn't have to generate a signal to detect objects ­ it spots them based on how brightly they reflect the natural radiation that is all around us every day."

"It's basically just a really bad tunnel diode," he explained. "I thought, heck, we can make a bad diode! We made lots of them back when we were figuring out how to make good ones."

First millimeter-wave detection systems, and now this. There's some interesting research in remote sensing going on, and there are sure to be some cool security applications.

Posted on August 24, 2005 at 8:17 AM • 12 Comments

Comments

DarkFireAugust 24, 2005 8:58 AM

Personally I'm highly sceptical about the concept of using this sort of device to scan people & luggage.

Using a hugely broad spectrum of ambient radiation has a whole hoast of technical difficulties that in my oppinion are incredibly challenging to overcome:

1) Different locations have wildly differing levels of ambient radiation of all forms.

2) Having a sensor not physically in contact with the target would mean that the signal one is looking for is submerged in the very sea of ambient radiation that is being used as an illumination source. This would present tremendous signal-to-noise ratio problems.

3) Most ambient radiation will be in RF bands. I seriously question the assertion that this is good enough to provide an imaging capability. Traditionally it has been very difficult to image anything below the wavelength of the radiation being used. Advanced signal processing might make this feasable down to maybe quarter-wavelength but this stil presents a problem.

I can see this being very useful for pilots of airliners being able to see a runway because a runway is a huge lump. A small knife in someones pocket presents a whole different problem - you need imaging capability that is 2-3 orders of magnitude more detailed.

I would imagine that signal analysis could maybe porovide a working system, but we would be talking about signal processing about a generation better than what's in a modern submarine. Expensive.

To sumn up, I can't see this being a viable technology with regards to imaging small objects without an active source of illumination.

Chung LeongAugust 24, 2005 9:32 AM

Very interesting. If it can be made to work, this could be groundbreaking technology. Without the use of a radiation source, such devices would be relatively small and inexpensive. Most importantly, people won't object to being scanned for health reason. They could be deployed in places where X-ray machines and metal detectors are impractical: schools, stadiums, clubs, metro stations, etc..

Eric K.August 24, 2005 10:02 AM

@DarkFire

1) Different locations have wildly
differing levels of ambient radiation
of all forms.

This is a given.

2) Having a sensor not physically in
contact with the target would mean
that the signal one is looking for is
submerged in the very sea of ambient
radiation that is being used as an
illumination source. This would
present tremendous signal-to-noise
ratio problems.

Cameras and eyeballs don't have a problem with sensing remotely while not physically in contact with the object they're trying to image. The photons they're trying to detect are indeed "submerged in the very sea of ambient radiation that is being used as an illumination source"

3) Most ambient radiation will be in RF
bands. I seriously question the
assertion that this is good enough to
provide an imaging capability.
Traditionally it has been very difficult
to image anything below the
wavelength of the radiation being
used. Advanced signal processing
might make this feasable down to
maybe quarter-wavelength but this
still presents a problem.

One excellent way to answer problems for which you have serious questions is *research* as opposed to armchair theorization and speculation. That's where you find out what the image quality is really like. That's where you find out what parts of the radiation spectrum are usable and which are useless. That's where you find out if it works.

Making guesses ahead of time and deciding not to do so based on those guesses isn't research.

If you want to claim it can't work, *Prove It*.

Those who want to claim it *can* are trying to do exactly that.

Glauber RibeiroAugust 24, 2005 10:24 AM

Don't worry, if they're expensive enough, we'll have some of these in American airports, eventually.

Bruce SchneierAugust 24, 2005 10:39 AM

"Don't worry, if they're expensive enough, we'll have some of these in American airports, eventually."

Sadly, I think you're correct. But wouldn't it be grand if the proper word was "effective" and not "expensive"?

Matthew SkalaAugust 24, 2005 11:10 AM

It seems to me that although DarkFire's arguments against the feasibility of this technology do make some sense, those same arguments can also be applied to human eyes - which we know work.

DarkFireAugust 24, 2005 1:04 PM

Did I say that I was opposed to research based on perceived difficulties? No. I was merely speculating, based on personal experience of electromagneit experiments that I have conducted (having a masters degree in experimental nuclear physics, I know a little bit about what the word research means), that this technology will have some serious but maybe not insurmountable obstacles to overcome before it matures to the point of being a good quality usable tool for the application described in the orriginal news item and Bruce's post.

On the subject of human eyes - this "technology" not only works solely in the visible spectrum (very short wavelengths --> good imaging ability) but has taken millions of years to develop! Granted, evolution is far slower than active research, but I maintain that this technology *for the stated application* will not be as quickly introduced and as fantastically capable as the news report states.

Obviously visible light is incapable of penetrating most solid objects such as bags and cases and therefore is of limited use for scanning such items.

Perhaps I ought to have made my initial post clearer, but I stand by my observations.

Eric K.August 24, 2005 1:40 PM

@DarkFire

So the meat of your posts boils down to "It's going to be hard and my guess is it's probably going to be fuzzy," as you haven't actually *observed* anything yet.

Sure, it'll be hard. Doesn't mean impossible and doesn't mean it's not worth trying, so we'll ignore that little 'observation' as irrelevant.

As for fuzzy, well, there are ways to deal with that. Not Hollywood-style "Image enhancement, but more practical solutions, such as combining the input from more than one such sensor.

While you can't get decent detail at resolutions under the wavelength of the radiation being used, you can use a combination of multiple wavelengths and/or you can take and combine images from multiple positions. A small array of sensors or a single sensor that moves slightly between images or captures two halves of an image through a splitter or any of a few hundred other ways to get more detail from a single image without simply relying on the shortest possible wavelengths.

There are plenty of out-of-the-box ideas that can be used to solve this little puzzle.

jammitAugust 24, 2005 2:14 PM

It sounds like it's the new pin type of diode. Pin diodes are useful in microwave applications doing things like detecting, oscillator, and switch. But a tunnel diode isn't really good for anything except an oscillator or synchronous detector. Normally other devices are used in its place. It sounds like this is basically a diode that can rectify in the IR range without super cooling.

Joseph MilnerAugust 24, 2005 3:50 PM

@DarkFire

"On the subject of human eyes - this "technology" not only works solely in the visible spectrum (very short wavelengths --> good imaging ability) but has taken millions of years to develop!"

We seem to have been able to produce CCDs quite quickly, so the "Millions of Years" for human eyes is irrelevant. Perhaps it would take millions of years for *humans* to develop this sensing ability...

Filias CupioAugust 24, 2005 4:06 PM

@Darkfire:

"...the signal one is looking for is submerged in the very sea of ambient radiation that is being used as an illumination source."

@Erik K.
"Cameras and eyeballs don't have a problem with sensing remotely ..."

Eyeballs use photons which are:
1) hugely abundant (lots of signal)
2) non-penetrating (generally only one object seen along a line of sight)
3) short wavelength (easy to focus, in combination with "non-penetrating".)

Microwaves, radio waves and X-rays don't have all of these advantages.

Party Pooper NiswOctober 5, 2005 3:48 PM

The "Science Daily" article does not even say what types/frequencies of radiation the "really bad tunnel diode" is supposed to detect. The most it says is: "There is always a certain amount of radiation – light, heat, and even microwaves – in the environment." (Sensitivity data would be nice too: levels of radiation, directionality, etc. relative to frequencies.)

One reason you people are arguing is because the article doesn't give even the basic facts. So you are reduced to speculating and trying to read between the lines of BS.

Suggested moral: This press release is not science--it's mostly blowing smoke.

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