Plastics are unfortunately so cheap useful that they’ve ended up everywhere. They’re filling our landfills, polluting our rivers, and even infiltrating our food chain as microplastics. As much as we think of plastic as recyclable, too, that’s often not the case—while some plastics like PET (polyethylene terephthalate) are easily reused, others just aren’t.
Indeed, the world currently produces an immense amount of polyethylene and polypropylene waste. These materials are used for everything from plastic bags to milk jugs and for microwavable containers—and it’s all really hard to recycle. However, a team at UC Berkeley might have just figured out how to deal with this problem.
Space is a challenging environment for semiconductors, but researchers have shown that a specific type of memristor (the hafnium oxide memristor, to be exact) actually reacts quite usefully when exposed to gamma radiation. In fact, it’s even able to leverage this behavior as a way to measure radiation exposure. In essence, it’s able to act as both memory and a sensor.
Being able to resist radiation exposure is highly desirable for space applications. Efficient ways to measure radiation exposure are just as valuable. The hafnium oxide memristor looks like it might be able to do both, but before going into how that works, let’s take a moment for a memristor refresher.
A memristor is essentially two conductive plates between which bridges can be made by applying a voltage to “write” to the device, by which one sets it to a particular resistance. A positive voltage causes bridging to occur between the two ends, lowering the device’s resistance, and a negative voltage reverses the process, increasing the resistance. The exact formulation of a memristor can vary. The memristor was conceived in the 1970s by Leon Chua, and HP Labs created a working one in 2008. An (expensive) 16-pin DIP was first made available in 2015.
A hafnium oxide memristor is a bit different. Normally it would be write-once, meaning a negative voltage does not reset the device, but researchers discovered that exposing it to gamma radiation appears to weaken the bridging, allowing a negative voltage to reset the device as expected. Exposure to radiation also caused a higher voltage to be required to set the memristor; a behavior researchers were able to leverage into using the memristor to measure radiation exposure. Given time, a hafnium oxide memristor exposed to radiation, causing it to require higher-than-normal voltages to be “set”, eventually lost this attribute. After 30 days, the exposed memristors appeared to recover completely from the effects of radiation exposure and no longer required an elevated voltage for writing. This is the behavior the article refers to as “self-healing”.
The research paper has all the details, and it’s interesting to see new things relating to memristors. After all, when it comes to electronic components it’s been quite a long time since we’ve seen something genuinely new.
Whether you’re a kid or a nerdy adult, you’ll probably agree that the interactive exhibitions at the museum are the best. If you happened to get down to the Oregon Science Festival in the last couple of years, you might have enjoyed “Catch The Wave!”—a public education project to teach people about electromagnets and waves. Even better, [Justin Miller] has written up how he built this exciting project.
Catch The Wave! consists of four small tabletop cabinets. Each has physical controls and a screen, and each plays its role in teaching a lesson about electromagnets and sound waves, with a context of audio recording and playback.
The first station allows the user to power up an electromagnet and interact with it using paper clips. They can also see the effect it has on a nearby compass. The second illustrates how reversing current through an electromagnet can reverse its polarity, and demonstrates this by using it to swing a pendulum. The third station then ties this to the action of a speaker, which is effectively a fancy electromagnet—and demonstrates how it creates sound waves in this way. Finally, the fourth station demonstrates the use of a microphone to record a voice, and throws in some wacky effects for good fun.
If you’ve ever tried to explain how sound is recorded and reproduced, you’d probably have loved to had tools like these to do so. We love a good educational project around these parts, too.
Static electricity often just seems like an everyday annoyance when a wool sweater crackles as you pull it off, or when a doorknob delivers an unexpected zap. Regardless, the phenomenon is much more fascinating and complex than these simple examples suggest. In fact, static electricity is direct observable evidence of the actions of subatomic particles and the charges they carry.
While zaps from a fuzzy carpet or playground slide are funny, humanity has learned how to harness this naturally occurring force in far more deliberate and intriguing ways. In this article, we’ll dive into some of the most iconic machines that generate static electricity and explore how they work.
To anyone who has spent some time in photovoltaic (PV) power circles, the word ‘perovskite’ probably sounds familiar. Offering arguably better bandgap properties than traditional silicon cells, perovskite-based PV panels also promise to be cheaper and (literally) more flexible, but commercialization has been elusive. This is something which Oxford PV seeks to change, with the claim that they will be shipping the first hybrid perovskite-silicon panels to a US customer.
Although Oxford PV prefers to keep the details of their technology classified, there have been decades of research on pure perovskite PV cells as well as tandem perovskite-silicon versions. The reason for the tandem (i.e. stacked) construction is to use more of the solar rays’ spectrum and total energy to increase output. The obvious disadvantage of this approach is that you need to find ways to make each layer integrate in a stable fashion, with ideally the connecting electrodes being transparent. A good primer on the topic is found in this 2021 review article by [Yuanhang Cheng] and [Liming Ding].
The primary disadvantage of perovskites has always been their lack of longevity, with humidity, UV irradiation, temperature and other environmental factors conspiring against their continued existence. In a 2022 study by [Jiang Liu] et al. in Science it was reported that a perovskite-silicon tandem solar cell lost about 5% of its initial performance after 1,000 hours. A 2024 study by [Yongbin Jin] et al. in Advanced Materials measured a loss of 2% after approximately the same timespan. At a loss of 2%/1,000 hours, the perovskite layer would be at 50% of its initial output after 25,000 hours, or a hair over 2.85 years.
A quick glance through the Oxford PV website didn’t reveal any datasheets or other technical information which might elucidate the true loss rate, so it would seem that we’ll have to wait a while longer on real data to see whether this plucky little startup has truly cracked the perovskite stability issue.
Top image: Summary of tandem perovskite-silicon solar cell workings. (Credit: Yuanhang Cheng, Liming Ding, SusMat, 2021)
[Project 326] wanted to know exactly what gas was in some glass tubes. The answer, of course, is to use a spectrometer, but that’s an expensive piece of gear, right? Not really. Sure, these cheap devices aren’t perfect, but they are serviceable and, as the video below shows, there are ways to work around some of the limitations.
The two units in question are “The Little Garden” spectrometer and a TLM-2. Neither are especially sensitive, but both are well under $100, so you can’t expect much. Because the spectrometers were not very sensitive, a 3D printed jig and lens were used to collect more light and block ambient light interference. The jigs also allowed the inclusion of special filters, which enhanced performance quite a bit. The neon bulbs give off the greatest glow when exposed to high voltage. Other bulbs contain things like helium, xenon, and carbon dioxide. There were also tubes with mercury vapor and even deuterium.
We’ll admit it. Not everyone needs a spectrometer, but if you do, there’s a lot of really interesting info on how to get the most out of these cheap devices. Apparently, [Project 326] was frustrated that he couldn’t buy an X-ray spectrometer and has vowed to create one, so we’ll be interested to see how that goes.
YouTuber The Science Furry has been attempting to make a split-anode magnetron and, after earlier failures, is having another crack at it. This also failed, but they’ve learned where to focus their efforts for the future, and it sure is fun to follow along.
The magnetron theory is simple enough, and we’ve covered this many times, but the split anode arrangement differs slightly from the microwave in your kitchen. The idea is to make a heated filament the cathode, so electrons are ejected from the hot surface by thermionic emission. These are forced into a spiral path using a perpendicular magnetic field. This is a result of the Lorentz force. A simple pair of magnets external to the tube is all that is needed for that. Depending on the diameter of the cavity and the gap width, a standing wave will be emitted. The anodes must be supplied with an alternating potential for this arrangement to work. This causes the electrons to ‘bunch up’ as they cross the gaps, producing the required RF oscillation. The split electrodes also allow an inductor to be added to tune the frequency of this standing wave. That is what makes this special.
Fizz, pop, ah well.
The construction starts with pre-made end seals with the tungsten wire electrode wire passing through. In the first video, they attempted to coat the cathode with barium nitrate, but this flaked off, ruining the tube. The second attempt replaces the coiled filament with a straight wire and uses a coating paste made from Barium Carbonate mixed with nitrocellulose in a bit of acetone. When heated, the nitrocellulose and the carbonate will decompose, hopefully leaving the barium coating intact. After inserting the electrode assembly into a section of a test tube and welding on the ends, the vacuum could be pulled and sealed off. After preheating the cathode, some gasses will be emitted into the vacuum, which is then adsorbed into a nearby titanium wire getter. At least, that’s the theory.
Upon testing, this second version burned out early on for an unknown reason, so they tried again, this time with an uncoated cathode. Measuring the emission current showed only 50 uA, which is nowhere near enough, and making the filament this hot caused it to boil off and coat the tube! They decide that perhaps this is one step too many and need to experiment with the barium coating by making simpler diode tubes to get the hang of the process!
