In graduate school, I had a seminar course where one of the sections was about X-ray crystallography. I was excited, because being able to discern the three-dimensional structure of macromolecules just by shining X-rays on them seemed like magic to me. And thanks to a lackluster professor, after the section it remained just as much of a mystery.
If only I’d had [Steve Mould] as a teacher back then. His latest video does an outstanding job explaining X-ray crystallography by scaling up the problem considerably, using the longer wavelength of light and a macroscopic target. He begins with a review of diffraction patterns, those alternating light and dark bands of constructive and destructive interference that result when light shines on two closely spaced slits — the famous “Double-Slit Experiment” that showed light behaves both as a particle and as a wave and provided our first glimpse of quantum mechanics. [Steve] then doubled down on the double-slit, placing another pair of slits in the path of the first. This revealed a grid of spots rather than alternating bands, with the angle between axes dependent on the angle of the slit pairs to each other.
Photograph 51, an X-ray crystallogram of the B-form of DNA, by Gosling and Franklin, 1952. Source: Wikipedia
To complete the demonstration, [Steve] then used diffraction to image the helical tungsten filament of an incandescent light bulb. Shining a laser through the helix resulted in a pattern bearing a striking resemblance to what’s probably the most famous X-ray crystallogram ever: [Rosalind Franklin]’s portrait of DNA. It all makes perfect sense, and it’s easy to see how the process works when scaled down both in terms of the target size and the wavelength of light used to probe it.
Hats off to [Steve] for making something that’s ordinarily complex so easily understandable, and for filling in a long-standing gap in my knowledge.
At risk of getting any ASMR buffs who might be reading cranky because there’s no audio, [Chris], or [@no1089] on Twitter, has gifted us with this visually stunning scan of his Maxim MAX86160 in-ear heart monitor mounted on a rigidflex PCB. You can take a look, in the video below the break.
If you’re wondering why anyone would scan a board, other than boredom, know that it’s actually quite common. X-Ray machines are commonly used as a quick, passive way to check a board that’s fresh off the production line. These aren’t the X-Rays like those of broken bones you’re (hopefully not too) used to seeing though, they’re Computed Tomography scans (CT scans, CAT scans), in effect just 3D X-Rays.
For electronics manufacturers and assemblers, CT scans are incredibly useful because they provide a non-destructive way to check for errors. For example, how do you know if that middle BGA pin is actually soldered correctly? You could run a functional test and make sure everything is working (at least, everything you check), but that takes time. The longer it takes to validate, the higher the manufacturing cost. In manager speak: “cost bad. Fast good.”
It’s also common to use a CT scan to create a full 3D model of a board. This makes it easy to check every little detail, especially the ones that are visually obscured by surface mount devices or critical signal paths that are buried under board layers.
But we know you really want more of this video, but better. And we’ve got the goods. For the chill folk among you, here’s a 55-minute version without all the CT scan info cluttering the screen. For those of you currently blasting eDM in your headphones, here’s a 30 second clip of it looping at ~5x speed. Eat your heart out:
Given the sheer volume of science going on as the International Space Station circles above our heads every 90 minutes or so, it would be hard for any one experiment to stand out. ISS expeditions conduct experiments on everything from space medicine to astrophysics and beyond, and the instruments needed to do the science have been slowly accreting over the years. There’s so much stuff up there that almost everywhere you turn there’s a box or pallet stuck down with hook-and-loop fasteners or bolted to some bulkhead, each one of them doing something interesting.
The science on the ISS isn’t contained completely within the hull, of course. The outside of the station fairly bristles with science, with packages nestled in among the solar panels and other infrastructure needed to run the spacecraft. Peering off into space and swiveling around to track targets is an instrument with the friendly name NICER, for “Neutron Star Interior Composition Explorer.” What it does and how it does it is interesting stuff, and what it’s learning about the mysteries of neutron stars could end up having practical uses as humanity pushes out into the solar system and beyond.
If you’ve been around long enough, you’ll know there’s a long history of advances in materials science that get blown far out of proportion by both the technical and the popular media. Most of the recent ones seem to center on the chemistry of carbon, particularly graphene and nanotubes. Head back a little in time and superconductors were all the rage, and before that it was advanced ceramics, semiconductors, and synthetic diamonds. There’s always some new miracle material to be breathlessly and endlessly reported on by the media, with hopeful tales of how one or the other will be our salvation from <insert catastrophe du jour here>.
While there’s no denying that each of these materials has led to huge advancements in science, industry, and the quality of life for billions, the development cycle from lab to commercialization is generally a tad slower than the press would have one believe. And so when a new material starts to gain traction in the headlines, as perovskites have recently, we feel like it’s a good opportunity to take a close look, to try to smooth out the ups and downs of the hype curve and manage expectations.
Hundreds of years from now, the story of humanity’s inevitable spread across the solar system will be a collection of engineering problems solved, some probably in heroic fashion. We’ve already tackled a lot of these problems in our first furtive steps into the wider galaxy. Our engineering solutions have taken humans to the Moon and back, but that’s as far as we’ve been able to send our fragile and precious selves.
While we figure out how to solve the problems keeping us trapped in the Earth-Moon system, we’ve sent fleets of robotic emissaries to do our exploration by proxy, to make the observations we need to frame the next set of engineering problems to be solved. But as we reach further out into the solar system and beyond, our exploration capabilities are increasingly suffering from communications bottlenecks that restrict how much data we can ship back to Earth.
We need to find a way to send vast amounts of data back as quickly as possible using as few resources as possible on both ends of the communications link. Doing so may mean turning away from traditional radio communications and going way, way up the dial and developing practical means for communicating with X-rays.
Elliot Williams and Mike Szczys look at all that’s happening in hackerdom. This week we dive deep into super-accurate clock chips, SPI and microcontroller trickery, a new (and cheap) part on the microcontroller block, touch-sensitive cloth, and taking a home X-ray to the third dimension. We’re saying our goodbyes to the magnificent A380, looking with skepticism on the V2V tech known as DSRC, and also trying to predict weather with automotive data. And finally, what’s the deal with that growing problem of electronic waste?
Links for all discussed on the show are found below. As always, join in the comments below as we’ll be watching those as we work on next week’s episode!
We all know CERN as that cool place where physicists play with massive, superconducting rings to smash atoms and subatomic particles to uncover secrets of matter in the Universe. To achieve this aim, they need to do a ton of research in other areas, such as development of special particle detectors.
While such developments are essential to the core research needs of the Centre, they also lead to spinoff applications for the benefit of society at large. One such outcome has been the Medipix Collaborations – a family of read-out chips for particle imaging and detection that can count single photons, allowing X-rays and gamma rays to be converted to electrical signals. It may not be possible for us hackers to get our hands on these esoteric sensors, but these devices are pretty interesting and deserve a closer look. Medipix sensors work like a camera, detecting and counting each individual particle hitting the pixels when its electronic shutter is open. This enables high-resolution, high-contrast, noise hit free images – making it unique for imaging applications.
Some months back, CERN announced the first 3D color X-ray of a human made possible using the Medipix devices. The result is a high-resolution, 3D, color image of not just living structures like bones, muscular tissues and vessels, but metal objects too like the wrist watch, seen in the accompanying photograph. The Medipix sensors have been in development since the 1990’s and are presently in their 4th “generation”. Each chip consists of a top semiconducting sensor array, made from gallium arsenide or cadmium telluride. The charge collected by each pixel is transported to the CMOS ASIC electronics via “bump bonds”. The integration is vertical, with each sensing pixel connected via the bump bond to an analog section followed by a digital processing layer. Earlier versions were limited, by technology, in their tiling ability for creating larger matrices of multiple sensors. They could be abutted on three sides only, with the fourth being used for on-chip peripheral logic and wire-bond pads that permit electronic read-out. The latest Medipix4 Collaboration, still under some development, eliminates this short coming. Through-silicon-via (TSV) technology provides the possibility of reading the chips through copper-filled holes that bring the signals from the front side of the chip to its rear. All communication with the pixel matrix flows through the rear of the chip – the peripheral logic and control elements are integrated inside the pixel matrix.
The Analog front end consists of a pre-amplifier followed by a window discriminator which has upper and lower threshold levels. The discriminator has four bits for threshold adjustment as well as polarity sensing. This allows the capture window to be precisely set. The rest of the digital electronics – multiplexers, shift registers, shutter and logic control – helps extract the data.
Further development of the Medipix (Tech Brief, PDF) devices led to a separate version called Timepix (Tech Brief, PDF). These new devices, besides being able to count photons, are capable of two additional modes. The first mode records “Time-Over-Threshold”, providing rough analog information about the energy of the photon. It does this by counting clock pulses for the duration when the signal stays above the discrimination levels. The other mode, “Time of Arrival”, measures arrival time of the first particle to impinge on the pixel. The counters record time between a trigger and detection of radiation quanta with energy above the discrimination level, allowing time-of-flight applications in imaging.
Besides medical imaging, the devices have applications in space, material analysis, education and of course, high energy physics. Hopefully, in a few years, hackers will lay their hands on these interesting devices and we can get to know them better. At the moment, the Medipix website has some more details and data sheets if you would like to dig deeper. For an overview on the development of such single photon detectors, check out this presentation from CERN – “Single X-Ray Photon Counting Systems: Existing Systems, Systems Under Development And Future Trends” (PDF).