Conservation of energy isn’t just a good idea: It is the law. In particular, it is the first law of thermodynamics. But, apparently, a lot of people don’t really get that because history is replete with inventions that purport to run forever or produce more energy than they consume. Sometimes these are hoaxes, and sometimes they are frauds. We expect sometimes they are also simple misunderstandings.

We thought about this when we ran across the viral photo of an EV with a generator connected to the back wheel. Of course, EVs and hybrids do try to reclaim power through regenerative braking, but that’s recovering a fraction of the energy already spent. You can never pull more power out than you put in, and, in fact, you’ll pull out substantially less.

Not a New Problem

If you think this is a scourge of social media and modern vehicles, you’d be wrong. Leonardo da Vinci, back in 1494, said:

Oh ye seekers after perpetual motion, how many vain chimeras have you pursued? Go and take your place with the alchemists.

There was a rumor in the 8th century that someone built a “magic wheel,” but this appears to be little more than a myth. An Indian mathematician also claimed to have a wheel that would run forever, but there’s little proof of that, either. It was probably an overbalanced wheel where the wheel spins due to weight and gravity with enough force to keep the wheel spinning.

An architect named Villard de Honnecourt drew an impractical perpetual motion machine in the 13th century that was also an overbalanced wheel. His device, and other similar ones, would require a complete lack of friction to work. Even Leonardo da Vinci, who did not think such a device was possible, did some sketches of overbalanced wheels, hoping to find a solution.

Types of Machines

There isn’t just a single kind of perpetual motion machine. A type I machine claims to produce work without any input energy. For example, a wheel that spins for no reason would be a type I machine.

Type II machines violate the second law of thermodynamics. For example, the “zeromoter” — developed in the 1800s by John Gamgee, used ammonia and a piston to move by boiling and cooling ammonia. While the machine was, of course, debunked, Gamgee has the honor of being the inventor of the world’s first mechanically frozen ice rink in 1844.

Type III machines claim to use some means to reduce friction to zero to allow a machine to work that would otherwise run down. For example, you can make a flywheel with very low friction bearings, and with no load, it may spin for years. However, it will still spin down.

Often, machines that claim to be perpetual either don’t really last forever — like the flywheel — or they actually draw power from an unintended source. For example, in 1760, James Cox and John Joseph Merlin developed Cox’s timepiece and claimed it ran perpetually. However, it actually drew power from changes in barometric pressure.

Frauds

These inventions were often mere frauds. E.P. Willis in 1870 made money from his machine but it actually had a hidden source of power. So did John Ernst Worrell Keely’s induction resonance motion motor that actually used hidden air pressure tubes to power itself. Harry Perrigo, an MIT graduate, also demonstrated a perpetual motion machine to the US Congress in 1917. That device had a secret battery.

However, some inventors probably weren’t frauds. Nikola Tesla was certainly a smart guy. He claimed to have found a principle that would allow for the construction of a Type II perpetual motion machine. However, he never built it.

There have been hosts of others, and it isn’t always clear who really thought they had a good idea and how many were just out to make a buck. But some people have created machines as a joke. Dave Jones, in 1981, created a bicycle wheel in a clear container that never stopped spinning. But he always said it was a fake and that he had built it as a joke. Adam Savage looks at that machine in the video below. He wrote his secret in a sealed envelope before he died, and supposedly, only two people know how it works.

Methods

Most perpetual machines try to use force from magnets. Gravity is also a popular agent of action. Other machines depend on buoyancy (like the one in the video below) or gas expansion and condensation.

The US Patent and Trademark Office manual of patent examining practice says:

With the exception of cases involving perpetual motion, a model is not ordinarily required by the Office to demonstrate the operability of a device. If operability of a device is questioned, the applicant must establish it to the satisfaction of the examiner, but he or she may choose his or her own way of so doing.

The UK Patent Office also forbids perpetual motion machine patents. The European Patent Classification system has classes for “alleged perpetua mobilia”

Of course, having a patent doesn’t mean something works; it just means the patent office thought it was original and can’t figure out why it wouldn’t work. Consider Tom Bearden’s motionless electromagnetic generator, which claims to generate power without any external input. Despite widespread denouncement of the supposed operating principle — Bearden claimed the device extracted vacuum energy — the patent office issued a patent in 2002.

The Most Insidious

The best machines are ones that use energy from some source that isn’t apparent. For example, a Crookes radiometer looks like a lightbulb with a little propeller inside. Light makes it move. It is also a common method to use magnetic fields to move something without obviously spinning it. For example, the egg of Columbus (see the video below) is a magnet, and a moving magnetic field makes the egg spin. This isn’t dissimilar from a sealed pump where a magnet turns on the dry side and moves the impeller, which is totally immersed in liquid.

Some low-friction systems, like the flywheel, can seem to be perpetual motion machines if you aren’t patient enough. But eventually, they all wear down.

Crazy or Conspiracy?

Venues like YouTube are full of people claiming to have free energy devices that also claim to be suppressed by “the establishment”. While we hate to be on the wrong side of history if someone does pull it off, we are going to go out on a limb and say that there can’t be a true perpetual motion machine. Unless you cheat, of course.

This is the place we usually tell you to get hacking and come up with something cool. But, sadly, for this time we’ll entreat you to spend your time on something more productive, like a useless box or put Linux on your Commodore 64.

Last week, [Al Williams] wrote up a his experience with a book that provided almost too much detailed information on how to build a DIY x-ray machine for his (then) young soul to bear. He almost had to build it! Where the “almost” is probably both a bummer because he didn’t have an x-ray machine as a kid, but also a great good because it was a super dangerous build, of a typical sort for the 1950s in which it was published.

Part of me really loves the matter-of-factness with which “A Boy’s First Book of Linear Accelerators” tells you how you (yes you!) can build a 500 kV van der Graff generator. But at the same time, modern me does find the lack of safety precautions in many of these mid-century books to be a little bit spooky. Contrast this with modern books where sometimes I get the feeling that the publisher’s legal team won’t let us read about folding paper airplanes for fear of getting cut.

A number of us have built dangerous projects in our lives, and many of us have gotten away with it. Part of the reason that many of us are still here is that we understood the dangers, but I would be lying if I said that I always fully understood them. But thinking about the dangers is still our first and best line of defense. Humility about how well you understand all of the dangers of a certain project is also very healthy – if you go into it keeping an eye out for the unknown unknowns, you’re in better shape.

Safety isn’t avoiding danger, but rather minimizing it. When we publish dangerous hacks, we really try to at least highlight the most important hazards so that you know what to look out for. And over the years, I’ve learned a ton of interesting safety tricks from the comments and fellow hackers alike. My ideal, then, is the spirit of the 1950s x-ray book, which encourages you to get the hack built, but modernized so that it tells you where the dangers lie and how to handle them. If you’re shooting electrons, shouldn’t the book also tell you how to stay out of the way?

Fusion power has long held the promise of delivering near-endless energy without as many unfortunate side effects as nuclear fission. But despite huge investment and some fascinating science, the old adage about practical power generation being 20 years away seems just as true as ever. But is that really the case? [Brian Potter] has written a review article for Construction Physics, which takes us through the decades of fusion research.

For a start, it’s fascinating to learn about the many historical fusion process, the magnetic pinch, the stelarator, and finally the basis of many modern reactors, the tokamak. He demonstrates that we’ve made an impressive amount of progress, but at the same time warns against misleading comparisons. There’s a graph comparing fusion progress with Moore’s Law that he debunks, but he ends on a positive note. Who knows, we might not need a Mr. Fusion to arrive from the future after all!

Fusion reactors are surprisingly easy to make, assuming you don’t mind putting far more energy in than you’d ever receive in return. We’ve featured more than one Farnsworth fusor over the years.

Have you ever tired of playing with your latest robot invention and wished you could just eat it? Well, that’s exactly what a team of researchers is investigating. There is a fully funded research initiative (not an April Fools’ joke, as far as we know) delving into the possibilities of edible electronics and mechanical systems used in robotics. The team, led by EPFL in Switzerland, combines food process engineering, printed and molecular electronics, and soft robotics to create fully functional and practical robots that can be consumed at the end of their lifespan. While the concept of food-based robots may seem unusual, the potential applications in medicine and reducing waste during food delivery are significant driving factors behind this idea.

The Robofood project (some articles are paywalled!) has clearly made some inroads into the many components needed. Take, for example, batteries. Normally, ingesting a battery would result in a trip to the emergency room, but an edible battery can be made from an anode of riboflavin (found in almonds and egg whites) and a cathode of quercetin, as we covered a while ago. The team proposed another battery using activated charcoal (AC) electrodes on a gelatin substrate. Water is split into its constituent oxygen and hydrogen by applying a voltage to the structure. These gasses adsorb into the AC surface and later recombine back into the water, providing a usable one-volt output for ten minutes with a similar charge time. This simple structure is reusable and, once expired, dissolves harmlessly in (simulated) gastric fluid in twenty minutes. Such a device could potentially power a GI-tract exploratory robot or other sensor devices.

But what use is power without control? (as some car tyre advert once said) Microfluidic control circuits can be created using a stack of edible materials, primarily oleogels, like ethyl cellulose, mixed with an organic oil such as olive oil. A microfluidic NOT gate combines a pressure-controlled switch with a fluid resistor as the ‘pull-up’. The switch has a horizontal flow channel with a blockage that is cleared when a control pressure is applied. As every electronic engineer knows, once you have a controlled switch and a resistor, you can build NOT gates and all the other logic functions, flip-flops, and memories. Although they are very slow, the control components are importantly edible.

Edible electronics don’t feature here often, but we did dig up this simple edible chocolate bunny that screams when you bite it. Who wouldn’t want one of those?

The last time we used a scanning electron microscope (a SEM), it looked like something from a bad 1950s science fiction movie. These days SEMs, like the one at the IBM research center, look like computers with a big tank poised nearby. Interestingly, the SEM is so sensitive that it has to be in a quiet room to prevent sound from interfering with images.

As a demo of the machine’s impressive capability, [John Ott] loads two US pennies, one facing up and one face down. [John] notes that Lincoln appears on both sides of the penny and then proves the assertion correct using moderate magnification under the electron beam.

Some electron microscopes pass electrons through thin samples much as light passes through a sample on a microscope slide. However, SEMs and REMs (reflection electron microscopes) use either secondary electron emission or reflected electrons from the surface of items like the penny.

You often see SEMs also fitted with EDS — energy dispersive X-ray spectrometers, sometimes called EDX — that can reveal the composition of a sample’s surface. There are other ways to examine surfaces, like auger spectrometers (pronounced like OJ), which can isolate thin films on surfaces. There’s also SIMS (secondary ion mass spectrometry) which mills bits of material away using an ion beam. and Rutherford backscattering spectrometry, which also uses an ion beam.

We keep waiting for someone to share plans to make a cheap, repeatable SEM. There are a few attempts out there, but we don’t see many in the wild. While the device is conceptually simple, you do need precise high voltages and high vacuums,. Also, you frequently need ancillary devices to do things like sputter gold in argon gas to coat nonconductive samples, so the barrier to entry is high.

Although it’s generally accepted that synthesized voices which mimic real people’s voices (so-called ‘deepfakes’) can be pretty convincing, what does our brain really think of these mimicry attempts? To answer this question, researchers at the University of Zurich put a number of volunteers into fMRI scanners, allowing them to observe how their brains would react to real and a synthesized voices.  The perhaps somewhat surprising finding is that the human brain shows differences in two brain regions depending on whether it’s hearing a real or fake voice, meaning that on some level we are aware of the fact that we are listening to a deepfake.

The detailed findings by [Claudia Roswandowitz] and colleagues are published in Communications Biology. For the study, 25 volunteers were asked to accept or reject the voice samples they heard as being natural or synthesized, as well as perform identity matching with the supposed speaker. The natural voices came from four male (German) speakers, whose voices were also used to train the synthesis model with. Not only did identity matching performance crater with the synthesized voices, the resulting fMRI scans showed very different brain activity depending on whether it was the natural or synthesized voice.

One of these regions was the auditory cortex, which clearly indicates that there were acoustic differences between the natural and fake voice, the other was the nucleus accumbens (NAcc). This part of the basal forebrain is involved in the cognitive processing of e.g. motivation, reward and reinforcement learning, which plays a key role in social, maternal and addictive behavior. Overall, the deepfake voices are characterized by acoustic imperfections, and do not elicit the same sense of recognition (and thus reward sensation) as natural voices do.

Until deepfake voices can be made much better, it would appear that we are still safe, for now.

We take easy communications for granted these days. It’s no bother to turn on a lightbulb remotely via a radio link or sense the water level in your petunias, but how does a drilling rig sense data from the drill head whilst deep underground, below the sea bed? The answer is with mud pulse telemetry, about which a group of researchers have produced a study, specifically about modelling the signal impairments and strategies for maintaining the data rate and improving the signal quality.

If you’re still confused, mud pulse telemetry (MPT) works by sending a modulated pressure wave vertically through the column of mud inside the drilling tube. It’s essential to obtain real-time data during drilling operations on the exact angle and direction the drill bit is pointing (so it can be corrected) and details of geological formations so decisions can be made promptly. The goal is to reduce drilling time and, therefore, costs and minimize environmental impact — although some would strongly argue about that last point.

One challenge with MPT is that the transmission media can be inconsistent. It may contain rocks and gas, leading to variations in physical properties like density, compressibility, and viscosity throughout the column, which can affect signal transmissibility. The MPT system includes a pressure transducer at the drill head that encodes data about local parameters such as temperature and pressure. The paper also describes other sources of noise that can distort the signal, including vibrations from the drill head and pressure pulses from the drilling mud pumps.

From what we can gather the MPT system is bidirectional, using mechanical means via ‘poppet valves’ to create positive or negative pressure pulses and a rotating slotted disk to generate continuous waves. It’s possible to achieve a data rate of 20 bps from depths of over 6 km. The paper also discusses other data transmission methods as part of the logging-while-drilling (LWD) system, some of which are used alongside MPT in specific circumstances. All of these methods face challenges when transmitting data through this complex medium.

We couldn’t find much on Hackaday about this topic, but we did recall an interesting piece about dealing with oil spills and who could forget this one about fracking?

Thanks to [Derek] for the tip!

The featured image is courtesy of Dynamic Graphics, Inc.

Electrohydrodynamics (EHD) involves the dynamics of electrically charged fluids, which effectively means making fluids move using nothing but electric fields, making it an attractive idea for creating a pump out of. This is the topic of a 2023 paper by [Michael Smith] and colleagues in Science, titled “Fiber pumps for wearable fluidic systems”. The ‘fiber pumps’ as they call the EHD pumps in this study are manufactured by twisting two helical, 80 µm thick copper electrodes around a central mandrel, along with TPU (thermoplastic polyurethane) before applying heat. This creates a tube where the two continuous electrodes are in contact with any fluids inside the tube.

For the fluid a dielectric fluid is required to create the ions, which was 3M Novec 7100, a methoxy-fluorocarbon. Because of the used voltage of 8 kV, a high electrical breakdown of the fluid is required. After ionization the required current is relatively low, reported as 0.9 W/m, with one meter of this pump generating a pressure of up to 100 kilopascals and a flowrate of 55 mL/minute. One major limitation is still that after 6 days of continuous pumping, the copper electrodes are rendered inert due to deposits, requiring the entire system to be rinsed. Among the applications the researchers see artificial muscles and flexible tubing in clothing to cool, heat and provide sensory feedback in VR applications.

While the lack of moving parts as with traditional pumps is nice, the limitations are still pretty severe. What is however interesting about this manufacturing method is that it is available to just about any hobbyist who happens to have some copper wiring, TPU filament and something that could serve as a mandrel lying around.

Thanks to [Aaron Eiche] for the tip.

Lord Kelvin’s name comes up anytime you start looking at the history of science and technology. In addition to working on transatlantic cables and thermodynamics, he also built an early computing device to predict tides. Kelvin, whose real name was William Thomson, became interested in tides in a roundabout way, as explained in a recent IEEE Spectrum article.

He’d made plenty of money on his patents related to the telegraph cable, but his wife died, so he decided to buy a yacht, the Lalla Rookh. He used it as a summer home. If you live on a boat, the tides are an important part of your day.

Today, you could just ask your favorite search engine or AI about the tides, but in 1870, that wasn’t possible. Also, in a day when sea power made or broke empires, tide charts were often top secret. Not that the tides were a total mystery. Newton explained what was happening back in 1687. Laplace realized they were tied to oscillations almost a century later. Thomson made a machine that could do the math Laplace envisioned.

We know today that the tides depend on hundreds of different motions, but many of them have relatively insignificant contributions, and we only track 37 of them, according to the post. Kelvin’s machine — an intricate mesh of gears and cranks — tracked only 10 components.

In operation, the user turned a crank, and a pen traced a curve on a roll of paper. A small mark showed the hour with a special mark for noon. You could process a year’s worth of tides in about 4 hours. While Kelvin received credit for the machine’s creation, he acknowledged the help of many others in his paper, from craftsmen to his brother.

We actually did a deep dive into tides, including Kelvin’s machine, a few years ago. He shows up a number of times in our posts.

When you are young, you take it for granted that you can pick out a voice in a crowded room or a factory floor. But as you get older, your hearing often gets to the point where a noisy room merges into a mishmash of sounds. University of Washington researchers have developed what they call Target Speech Hearing. In plain English, it is an AI-powered headphone that lets you look at someone and pull their voice out of the chatter. For best results, however, have to enroll their voice first, so it wouldn’t make a great eavesdropping device.

If you want to dive into the technical details, their paper goes into how it works. The prototype uses a Sony noise-cancelling headset. However, the system requires binaural microphones so additional microphones attach to the outside of the headphones.

Given training data, we wonder if traditional correlation methods would be just as effective. In other words, you could use facial recognition to figure out who’s talking and pull their voice out using more traditional signal processing techniques. However, this system can potentially pick up sound from unknown speakers, figuring direction from the binaural microphones, so even if the correlation method worked well on known speakers, the new system is likely superior in new situations.

There’s more to noise-cancelling headgear than you might think. Or you can just go low-tech.

Most people have heard of or seen slide rules, with older generations likely having used these devices in school and at their jobs. As purely analog computers these ingenious devices use precomputed scales on slides, which when positioned to a specific input can give the output to a wide range of calculations, ranging from simple divisions and multiplications to operations that we generally use a scientific calculator for these days. Even so, these simple devices are both very versatile and can be extremely precise, as [Bob, the Science Guy] demonstrates in a recent video.

Slide rules at their core are very simple: you got different scales (marked by a label) which can slide relative to each other. Simple slide rules will only have the A through D scales, with an input provided by moving one scale relative to the relevant other scale (e.g. C and D for multiplication/division) after which the result can be read out. Of course, it seems reasonable that the larger your slide rule is, the more precision you can get out of it. Except that if you have e.g. the W1 and W2 scales on a shorter (e.g. 10″) slide rule, you can use those to get the precision of a much larger (20″) slide rule, as [Bob] demonstrates.

Even though slide rules have a steeper learning curve than punching numbers into a scientific calculator, it is hard to argue the benefits of understanding such relationships between the different scales, and why they exist in the first place.

It’s hard to imagine a world without chocolate, and yet it is undeniable that there are problems associated both with its manufacturing and its consumption. Much of this is due to the addition of sugar, as well as the discarding of a significant part of the cacao pod, which harbors the pulp and seeds. According to a study by [Kim Mishra] and colleagues in Nature Food, it might be possible to ditch the sugar and instead use a mixture of cacao pulp juice (CPJC) and endocarp powder (ECP), which are turned into a sweetening gel.

This gel replaces the combination of sugar with an emulsifier (lecithin or something similar) in current chocolate while effectively using all of the cacao pod except for the husk. A lab ran a small-scale production, with two different types of whole-fruit chocolate produced, each with a different level of sweetness, and given to volunteers for sampling. Samples had various ECP ratios in the gel and gel ratios in the chocolate mixture with the cacao mass (CM).

With too much of either, the chocolate becomes crumbly, while with too little, no solid chocolate forms. Eventually, they identified a happy set of ratios, leading to the taste test, which got an overall good score in terms of chocolate taste and sweetness. In addition to being able to skip the refined sugar addition, this manufacturing method also cuts out a whole supply chain while adding significantly more fiber to chocolate. One gotcha here is that this study focused on dark chocolate, but then some chocolate fans would argue vehemently that anything below 50% cacao doesn’t qualify as chocolate anymore, while others scoff at anything below 75%.

Matters of taste aside, this study shows a promising way to make our regular chocolate treat that much healthier and potentially greener. Of course, we want to know how it will print. Barring that, maybe how it engraves.

The use of concrete and steel have both become the bedrock of modern-day construction, which of course also means that there is a lot of both which ends up as waste once said construction gets demolished again. While steel is readily recyclable, the Portland cement that forms the basis of concrete so far is not. Although the aggregate from crushed concrete can be reclaimed, the remainder tends to end up in a landfill, requiring fresh input of limestone to create more cement. Now a team of researchers from the University of Cambridge claim to have found a way to recycle hydrated Portland cement by using it as flux during steel production in electric arc furnaces (EAFs).

Not only does this save a lot of space in landfills, it also stands to reduce a lot of the carbon dioxide produced during cement and steel production, which is primarily from the use of limestone for cement and lime-dolomite for steel. The details can be found in the open access paper in Nature by [Cyrille F. Dunant] and colleagues. Essentially reclaimed cement paste is mixed with some fresh material to form the flux that shields the molten steel in an EAF from the atmosphere. The flux creates the slag layer that floats on top of the molten steel, with this slag after cooling down being ground up and turned into cement clinker, which is then mixed to create fresh cement.

The process has been patented by Cambridge, who call the product ‘Cambridge Electric Cement‘, with the claim that if using low-carbon power sources for the EAF like hydro and nuclear, it would constitute ‘no emissions’ and ‘no landfill’ cement. We have to see how this works out on an industrial scale, of course, but it would definitely be nice to keep concrete and cement in general out of landfills, while cutting back on limestone mining, as well as questionable practices like adding heavy metal-laden fly ash as filler to concrete.

Thanks to [cscott] for the tip.

Watching an eclipse from the ground is pretty fun. Depending on where you live, you might even get a decent view. But what if you wanted a truly unique vantage point? You could replicate the work of [Tarik Agcayazi] and [kemfic], who set about filming the recent eclipse from an altitude of 80,000 feet.

The duo didn’t rent a high-performance aircraft from the US military. Instead, they relied on a high-altitude balloon carrying a glider with a camera payload. The idea was for the balloon to go up, and have the camera capture the eclipse. Then, it would be released so that it could glide back home in controlled flight. However, time constraints made that too hard. Instead, they simplified to a parachute recovery method.

The project video covers the development process, the balloon launch itself, and of course, the filming of the eclipse. High altitude balloon launches are stressful enough, but having a short eclipse as a target made everything even more difficult. But that just makes things more exciting!

The project builds on earlier work from the duo that we discussed back in 2017.

Helicopters are perhaps at their coolest when they’re being used as flying cranes — from a long dangling cable, they can carry everything from cars, to crates, to giant hanging saws.

What you might find altogether more curious are the helicopters that fly around carrying gigantic flat antenna arrays. When you spot one in the field, it’s not exactly intuitive to figure out what they’re doing, but these helicopters are tasked with important geological work!

Looking Down From Above

In the popular imagination, the Earth’s magnetic field is useful for finding north with a compass. In day to day life, that barely comes up, and we don’t give the magnetic field much thought beyond that. However, the reality of Earth’s magnetic field is that it is variable all over the surface of our planet. By measuring it, we can gain great insight into what lies beneath our feet.

Magnetic surveys are an important tool in geology and archaeology. In the latter regard, they were perhaps best popularized by the TV show Time Team. The series would often employ geomagnetic surveys to discover artifacts or structures beneath the ground. The typical technique used on the show involved someone walking around a site with a magnetometer while logging the magnetic field strength as they went. By running the magnetometer in a grid pattern across a site, it was possible to build up a local map of the magnetic field, which could reveal anomalies lurking underground.

That’s all well and good if you wish to survey a small garden or perhaps a single field. If you want to survey a larger area, though, doing a survey on foot isn’t really practical. But you can apply the same techniques in the air at speed, and you can even extend them further, too!

You can do magnetic surveys much faster using a helicopter instead. The basic theory is the same, carrying a magnetic sensor over terrain allows the measurement of the local magnetic field. The difference is that a helicopter can move much faster and thus cover a greater area more quickly, albeit at somewhat reduced resolution. Magnetic field data is great, but there’s so much more that can be gained by exploring the electromagnetic spectrum, too.

By transmitting radio waves from a giant antenna, it’s possible to excite eddy currents in the ground itself which can then be picked up by a sensitive receiver similarly dangling from the aircraft. A single aerial survey aircraft can carry both magnetic sensors and EM equipment on the same mission to gather both kinds of data at once.

Aerial electromagnetic surveys (AEM), as they are known, aren’t so much used for finding Roman coins or small structures under the ground. Instead, they’re used to better understand the makeup of the ground itself. An aerial survey can reveal electrically conductive materials in the ground, of which there are many.

Graphite, clays, sulfides, or salty groundwater all show up differently on an electromagnetic survey compared to non-conductive minerals or fresh water. These elements can be revealed by an antenna dangling from a helicopter, in combination with other geological data and careful analysis.

Typical AEM missions involve flying at moderate speeds of 70 to 120 km/h along the ground, generally on a path of parallel lines to cover a given area. Altitudes are low, on the order of 100 meters or even less, to keep the antennas close to the ground. Excitation and receiver antennas usually measure tens of meters in diameter. AEM surveys can be remarkably sensitive. It’s possible to pick up variations in the conductivity of the soil up to several hundred meters deep with the right equipment. As you might expect, the local ground composition plays a role in what’s possible, too.

Often, an aerial study is designed to zero in on a particular geological feature or material of interest. Then, the survey area and equipment can be tuned to ideally reveal the expected contrast in conductivity or magnetic field.

Governments and private enterprises using the technique more commonly than you might think. For example, the California Department of Water Resources uses AEM surveys to hunt for underground aquifers. might be using an AEM survey to find an underground aquifer, or a conductive graphite seam deep in the ground.  The US Geological Survey uses the technique for all kinds of purposes, and has been doing so since the 1970s. It has looked for subsurface water and underground minerals, amongst other things. There’s an interactive tool for finding survey data, much of which is available to the public.

There is a great deal of mistrust in the wider public these days, with conspiracies around chemtrails, 5G cellular networks, and so many other similar topics. It won’t shock you to know that there are people that freak out when they see a helicopter hauling a gigantic antenna array at low altitude.

For this reason, many government agencies specifically release documents to explain the purpose of AEM surveys, and to highlight that they pose no risk to the public, wildlife, or the natural environment itself. It may seem silly, but AEM survey craft do look a fair bit more sci-fi than most other flying vehicles, so the cautious approach is understandable.

You probably won’t spot an AEM survey craft in the suburbs, but if you’re out in some wide open natural area, you just might. If you’re really keen on seeing one in the flesh, though, you’re best advised to get yourself a geology degree and a job in the field. Then, you might even pick up the skills necessary to specify, execute, and interpret the results of an electromagnetic aerial survey. When you do, be sure to let the world know what you found out!

While it doesn’t look like a traditional robot, the hydrogel robot from [Zi Liang Wu] forms a möbius strip and can be activated by light. They also experimented with shaping the hydrogels as a Seifert ribbon.

The key is that the hydrogels contain gold nanoparticles. Light heats the gold particles and this causes the hydrogels to move. The connections between the strips of hydrogels causes them to move in predictable ways. You can see a video about the experiments below.

These robots aren’t going to be for warehouse or factory work. But they can do tasks like collecting plastic beads, something difficult for conventional robots to do. They also hope to demonstrate that these soft robots could work in the body for taking samples or delivering a drug, although it isn’t apparent how light would get to them inside your body.

The dark side of the material tends to turn towards the light. The continuous loop structure means it never runs to the end of its travel. Watching it move on a string is pretty impressive.

Crawling and slithering robots may be the answer for certain specialized applications. After all, it works well in nature.

When analyzing data, one can use a variety of transformations on the data to massage it into a form that works better to tease out the information one is interested in. One such example is the application of the Fourier transform, which transforms a data set from the time domain into the frequency domain. Yet what is this frequency domain really? After enticing us to follow the white rabbit down a sudden plummet into the intangible question of what is and what is not, [lcamtuf] shows us around aspects of the frequency domain and kin.

One thing about the (discrete) Fourier transform is that it is excellent at analyzing data that consists out of sinewaves, such as audio signals. Yet when using the Fourier transform for square waves, the resulting output is less than useful, almost as if square waves are not real. Similarly, other transforms exist which work great for square waves, but turn everything else into meaningless harmonics. Starting with the discrete cosine transform (DCT), this gets us into Walsh and Hadamard matrices and the Walsh-Hadamard Transform (WHT), and their usage with transforming data from the time into the frequency domain.

Ultimately it would seem that the frequency domain is as real as it needs to be, albeit that its appearance is wholly dependent on the algorithm used to create it, whether this the DFT, DCT, WHT or something else entirely.

Metal-oxide semiconductor field-effect transistors (MOSFETs) see common use in applications ranging from the very small (like CPU transistors) to very large (power) switching applications. Although its main advantage is its high power efficiency, MOSFETs are not ideal switches with a perfect on or off state. Understanding the three main sources of switching losses is crucial when designing with MOSFETs, with a recent All About Circuits article by [Robert Keim] providing a primer on the subject.

As it’s a primer, the subthreshold mode of MOSFET modes of operation is omitted, leaving the focus on the linear (ohmic) mode where the MOSFET’s drain-source is conducting, but with a resistance that’s determined by the gate voltage. In the saturated mode the drain-source resistance is relatively minor (though still relevant), but the turn-on time (R_DS(on)) before this mode is reached is where major switching losses occur. Simply switching faster is not a solution, as driving the gate incurs its own losses, leaving the circuit designer to carefully balance the properties of the MOSFET.

For those interested in a more in-depth study of MOSFETs in e.g. power supplies, there are many articles on the subject, such as this article (PDF) from Texas Instruments.

As our climate changes, we fear that warmer temperatures and drier conditions could make life hard for us. In most locations, it’s a future concern that feels uncomfortably near, but for some locations, it’s already very real. Take the Sahara desert, for example, and the degraded landscapes to the south in the Sahel. These arid regions are so dry that they struggle to support life at all, and temperatures there are rising faster than almost anywhere else on the planet.

In the face of this escalating threat, one of the most visionary initiatives underway is the Great Green Wall of Africa. It’s a mega-sized project that aims to restore life to barren terrain.

A Living Wall

Launched in 2007 by the African Union, the Great Green Wall was originally an attempt to halt the desert in its tracks. The Sahara Desert has long been expanding, and the Sahel region has been losing the battle against desertification. The Green Wall hopes to put a stop to this, while also improving food security in the area.

The concept of the wall is simple. The idea is to take degraded land and restore it to life, creating a green band across the breadth of Africa which would resist the spread of desertification to the south. Intended to span the continent from Senegal in the west to Djibouti in the east, it was originally intended to be 15 kilometers wide and a full 7,775 kilometers long. The hope was to complete the wall by 2030.

The Great Green Wall concept moved past initial ideas around simply planting a literal wall of trees. It eventually morphed into a broader project to create a “mosaic” of green and productive landscapes that can support local communities in the region.

Reforestation is at the heart of the Great Green Wall. Millions of trees have been planted, with species chosen carefully to maximise success. Trees like Acacia, Baobab, and Moringa are commonly planted not only for their resilience in arid environments but also for their economic benefits. Acacia trees, for instance, produce gum arabic—a valuable ingredient in the food and pharmaceutical industries—while Moringa trees are celebrated for their nutritious leaves.

Choosing plants with economic value has a very important side effect that sustains the project. If random trees of little value were planted solely as an environmental measure, they probably wouldn’t last long. They could be harvested by the local community for firewood in short order, completely negating all the hard work done to plant them. Instead, by choosing species that have ongoing productive value, it gives the local community a reason to maintain and support the plants.

Special earthworks are also aiding in the fight to repair barren lands. In places like Mauritania, communities have been digging  half-moon divots into the ground. Water can easily run off or flow away on hard, compacted dirt. However, the half-moon structures trap water in the divots, and the raised border forms a protective barrier. These divots can then be used to plant various species where they will be sustained by the captured water. Do this enough times over a barren landscape, and with a little rain, formerly dead land can be brought back to life. It’s a traditional technique that is both cheap and effective at turning brown lands green again.

Progress

The initiative plans to restore 100 million hectares of currently degraded land, while also sequestering 250 million tons of carbon to help fight against climate change. Progress has been sizable, but at the same time, limited. As of mid-2023, the project had restored approximately 18 million hectares of formerly degraded land. That’s a lot of land by any measure. And yet, it’s less than a fifth of the total that the project hoped to achieve. The project has been frustrated by funding issues, delays, and the degraded security situation in some of the areas involved. Put together, this all bodes poorly for the project’s chances of reaching its goal by 2030, given 17 years have passed and we draw ever closer to 2030.

While the project may not have met its loftiest goals, that’s not to say it has all been in vain. The Great Green Wall need not be seen as an all or nothing proposition. Those 18 million hectares that have been reclaimed are not nothing, and one imagines the communities in these areas are enjoying the boons of their newly improved land.

In the driest parts of the world, good land can be hard to come by. While the Great Green Wall may not span the African continent yet, it’s still having an effect. It’s showing communities that with the right techniques, it’s possible to bring some barren zones from the brink, turning hem back into useful productive land. That, at least, is a good legacy, and if the projects full goals can be realized? All the better.