Electrostatic motors are now common in MEMS applications, but researchers at the University of Wisconsin and spinoff C-Motive Technologies have brought macroscale electrostatic motors back. [via MSN/WSJ]

While the first real application of an electric motor was Ben Franklin’s electrostatically-driven turkey rotisserie, electromagnetic type motors largely supplanted the technology due to the types of materials available to engineers of the time. Newer dielectric fluids and power electronics now allow electrostatic motors to be better at some applications than their electromagnetic peers.

The main advantage of electrostatic motors is their reduced critical materials use. In particular, electrostatic motors don’t require copper windings or any rare earth magnets which are getting more expensive as demand grows for electrically-powered machines. C-Motive is initially targeting direct drive industrial applications, and the “voltage driven nature of an electrostatic machine” means they require less cooling than an electromagnetic motor. They also don’t use much if any power when stalled.

Would you like a refresher on how to make static electricity or a deeper dive on how these motors work?

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.

What Is It?

Before we look at the fancy science gear, we should actually define what we’re talking about here. In simple terms, static electricity is the result of an imbalance of electric charges within or on the surface of a material. While positively-charged protons tend to stay put, electrons, with their negative charges, can move between materials when they come into contact or rub against one another. When one material gains electrons and becomes negatively charged, and another loses electrons and becomes positively charged, a static electric field is created. The most visible result of this is when those charges are released—often in the form of a sudden spark.

Since it forms so easily on common materials, humans have been aware of static electricity for quite some time. One of the earliest recorded studies of the phenomenon came from the ancient Greeks. Around 1000 BC, they noticed that rubbing amber with fur would then allow it to attract small objects like feathers. Little came of this discovery, which was ascribed as a curious property of amber itself. Fast forward to the 17th century, though, and scientists were creating the first machines designed to intentionally store or generate static electricity. These devices helped shape our understanding of electricity and paved the way for the advanced electrical technologies we use today. Let’s explore a few key examples of these machines, each of which demonstrates a different approach to building and manipulating static charge.

The Leyden Jar

Though not exactly a machine for generating static electricity, the Leyden jar is a critical part of early electrostatic experiments. Effectively a static electricity storage device, it was independently discovered twice, first by a German named Ewald Georg von Kleist in 1745. However, it gained its common name when it was discovered by Pieter van Musschenbroek, a Dutch physicist, sometime between 1745 and 1746. The earliest versions were very simple, consisting of water in a glass jar that was charged with static electricity conducted to it via a metal rod. The experimenter’s hand holding the jar served as one plate of what was a rudimentary capacitor, the water being the other. The Leyden jar thus stored static electricity in the water and the experimenter’s hand.

Eventually the common design became a glass jar with layers of metal foil both inside and outside, separated by the glass. Early experimenters would charge the jar using electrostatic generators, and then discharge it with a dramatic spark.

The Leyden jar is one of the first devices that allowed humans to store and release static electricity on command. It demonstrated that static charge could be accumulated and held for later use, which was a critical step in understanding the principles that would lead to modern capacitors. The Leyden jar can still be used in demonstrations of electrostatic phenomena and continues to serve as a fascinating link to the history of electrical science.

The Van de Graaff Generator

Perhaps the most iconic machine associated with generating static electricity is the Van de Graaff generator. Developed in the 1920s by American physicist Robert J. Van de Graaff, this machine became a staple of science classrooms and physics demonstrations worldwide. The device is instantly recognizable thanks to its large, polished metal sphere that often causes hair to stand on end when a person touches it.

The Van de Graaff generator works by transferring electrons through mechanical movement. It uses a motor-driven belt made of insulating material, like rubber or nylon, which runs between two rollers. At the bottom roller, plastic in this example, a comb or brush (called the lower electrode) is placed very close to the belt. As the belt moves, electrons are transferred from the lower roller onto the belt due to friction in what is known as the triboelectric effect. This leaves the lower roller positively charged and the belt carrying excess electrons, giving it a negative charge. The electric field surrounding the positively charged roller tends to ionize the surrounding air and attracts more negative charges from the lower electrode.

As the belt moves upward, it carries these electrons to the top of the generator, where another comb or brush (the upper electrode) is positioned near the large metal sphere. The upper roller is usually metal in these cases, which stays neutral rather than becoming intensely charged like the bottom roller. The upper electrode pulls the electrons off the belt, and they are transferred to the surface of the metal sphere. Because the metal sphere is insulated and not connected to anything that can allow the electrons to escape, the negative charge on the sphere keeps building up to very high voltages, often in the range of hundreds of thousands of volts. Alternatively, the whole thing can be reversed in polarity by changing the belt or roller materials, or by using a high voltage power supply to charge the belt instead of the triboelectric effect.

The result is a machine capable of producing massive static charges and dramatic sparks. In addition to its use as a demonstration tool, Van de Graaff generators have applications in particle physics. Since they can generate incredibly high voltages, they were once used to accelerate particles to high speeds for physics experiments. These days, though, our particle accelerators are altogether more complex. 

The Whimsical Wimshurst Machine

Another fascinating machine for generating static electricity is the Wimshurst machine, invented in the late 19th century by British engineer James Wimshurst. While less famous than the Van de Graaff generator, the Wimshurst machine is equally impressive in its operation and design.

The key functional parts of the machine are the two large, circular disks made of insulating material—originally glass, but plastic works too. These disks are mounted on a shared axle, but they rotate in opposite directions when the hand crank is turned. The surfaces of the disks have small metal sectors—typically aluminum or brass—which play a key role in generating static charge. As the disks rotate, brushes made of fine metal wire or other conductive material lightly touch their surfaces near the outer edges. These brushes don’t generate the initial charge but help to collect and amplify it once it is present.

The key to the Wimshurst machine’s operation lies in a process called electrostatic induction, which is essentially the influence that a charged object can exert on nearby objects, even without touching them. At any given moment, one small area of the rotating disk may randomly pick up a small amount of charge from the surrounding air or by friction. This tiny initial charge is enough to start the process. As this charged area on the disk moves past the metal brushes, it induces an opposite charge in the metal sectors on the other disk, which is rotating in the opposite direction.

For example, if a positively charged area on one disk passes by a brush, it will induce a negative charge on the metal sectors of the opposite disk at the same position. These newly induced charges are then collected by a pair of metal combs located above and below the disks. The combs are typically connected to Leyden jars to store the charge, until the voltage builds up high enough to jump a spark over a gap between two terminals.

The Wimshurst machine doesn’t create static electricity out of nothing; rather, it amplifies small random charges through the process of electrostatic induction as the disks rotate. As the charge is collected by brushes and combs, it builds up on the machine’s terminals, resulting in a high-voltage output that can produce dramatic sparks. This self-amplifying loop is what makes the Wimshurst machine so effective at generating static electricity.

The Wimshurst machine is seen largely as a curio today, but it did have genuine scientific applications back in the day. Beyond simply using it to investigate static electricity, its output could be discharged into Crookes tubes to create X-rays in a very rudimentary way.

The Electrophorus: Simple Yet Ingenious

One of the simplest machines for working with static electricity is the electrophorus, a device that dates back to 1762. Invented by Swedish scientist Johan Carl Wilcke, the electrophorus consists of two key parts: a flat dielectric plate and a metal disk with an insulating handle. The dielectric plate was originally made of resinous material, but plastic works too. Meanwhile, the metal disk is naturally conductive.

To generate static electricity with the electrophorus, the dielectric plate is first rubbed with a cloth to create a static charge through friction. This is another example of the triboelectric effect, as also used in the Van de Graaff generator. Once the plate is charged, the metal disk is placed on top of it. The disc then becomes charged by induction. It’s much the same principle as the Wimshurst machine, with the electrostatic field of the dielectric plate pushing around the charges in the metal plate until it too has a distinct charge.

For example, if the dielectric plate has been given a negative charge by rubbing, it will repel negative charges in the metal plate to the opposite side, giving the near surface a positive charge, and the opposite surface a negative charge. The net charge, though, remains neutral. But, if the metal disk is then grounded—for example, by briefly touching it with a finger—the negative charge on the disk can drained away, leaving it positively charged as a whole. This process does not deplete the charge on the dielectric, so it can be used to charge the metal disk multiple times, though the dielectric’s charge will slowly leak away in time.

Though it’s simple in design, the electrophorus remains a remarkable demonstration of static electricity generation and was widely used in early electrostatic experiments. A particularly well-known example is that of Georg Lichtenberg. He used a version a full two meters in diameter to create large discharges for his famous Lichtenberg figures. Overall, it’s an excellent tool for teaching the basic principles of electrostatics and charge separation—particularly given how simple it is in construction compared to some of the above machines.

Zap

Static electricity, once a mysterious and elusive force, has long since been tamed and turned into a valuable tool for scientific inquiry and education. Humans have developed numerous machines to generate, manipulate, and study static electricity—these are just some of the stars of the field. Each of these devices played an important role in furthering humanity’s understanding of electrostatics, and to a degree, physics in general.

Today, these machines continue to serve as educational tools and historical curiosities, offering a glimpse into the early days of electrical science—and they still spark fascination on the regular, quite literally. Static electricity may be an everyday phenomenon, but the machines that harness its power are still captivating today. Just go to any local science museum for the proof!

Not every computer can make use of a disk drive when it needs to store persistent data. Embedded systems especially have pushed the development of a series of erasable programmable read-only memories (EPROMs) because of their need for speed and reliability. But erasing memory and writing it over again, whether it’s an EPROM, an EEPROM, an FPGA, or some other type of configurable solid-state memory is just scratching the surface of what it might be possible to get integrated circuits and their transistors to do. This team has created a transistor that itself is programmable.

Rather than doping the semiconductor material with impurities to create the electrical characteristics needed for the transistor, the team from TU Wien in Vienna has developed a way to “electrostatically dope” the semiconductor, using electric fields instead of physical impurities to achieve the performance needed in the material. A second gate, called the program gate, can be used to reconfigure the electric fields within the transistor, changing its properties on the fly. This still requires some electrical control, though, so the team doesn’t expect their new invention to outright replace all transistors in the future, and they also note that it’s unlikely that these could be made as small as existing transistors due to the extra complexity.

While the article from IEEE lists some potential applications for this technology in the broad sense, we’d like to see what these transistors are actually capable of doing on a more specific level. It seems like these types of circuits could improve efficiency, as fewer transistors might be needed for a wider variety of tasks, and that there are certainly some enhanced security features these could provide as well. For a refresher on the operation of an everyday transistor, though, take a look at this guide to the field-effect transistor.

A prerequisite for photovoltaic (PV) and concentrated solar power (CSP) technologies to work efficiently is as direct an exposure to the electromagnetic radiation from the sun as possible. Since dust and similar particulates are excellent at blocking the parts of the EM spectrum that determine their efficiency, keeping the panels and mirrors free from the build-up of dust, lichen, bird droppings and other perks of planetary life is a daily task for solar farm operators. Generally cleaning the panels and mirrors involves having trucks drive around with a large water tank to pressure wash the dirt off, but the use of so much water is problematic in many regions.

Keeping PV panels clean is also a consideration on other planets than Earth. So far multiple Mars rovers and landers have found their demise at the hands of Martian dust after a layer covered their PV panels, and Moon dust (lunar regolith) is little better. Despite repeated suggestions by the peanut gallery to install wipers, blowers or similar dust removal techniques, keeping particulates from sticking to a surface is not as easy an engineering challenge as it may seem, even before considering details such as the scaling issues between a singular robot on Mars versus millions of panels and mirrors on Earth.

There has been research into the use of the electrostatic effect to repel dust, but is there a method that can keep both solar-powered robots on Mars and solar farms on Earth clean and sparkling, rather than soiled and dark?

Defining The Problem

Surfaces on Earth as well as on other planetary bodies, including Earth’s Moon tend to get covered with particulate matter through a variety of mechanisms, resulting in a phenomenon referred to as ‘soiling‘. While on the Moon there aren’t many mechanisms for this – in the absence of a significant atmosphere and birds – beyond mechanical disturbances, on Mars and Earth particulate matter is constantly transported by the atmosphere and deposited through phenomena such as wind and dust devils.

Although the same atmospheric motion can also remove part of the thus deposited material – as has happened repeatedly to solar-powered Mars rovers from passing dust devils – much of the material is retained on the surface, through static charges, absorption of moisture and other mechanisms that are strong enough to prevent gravity and a gentle breeze from removing it. On Earth there’s the added challenge of so-called pioneer species, which mostly include lichen.

Wherever there’s sufficient moisture, lichen are likely to be found on any available surface that’s not already populated by other species. They can find purchase on surfaces ranging from soil, to bark and rock, as well as the glass covering PV solar panels, making lichen growth on these panels especially a problem in (semi-)tropical and moderate climates. Meanwhile in desert regions mineral dust is the most prominent soiling issue, which happen to be also the regions where solar farms are the most efficient and thus making electrostatic and similar self-cleaning panel technologies the most effective.

As for lichen, algae and similar, here the solution seems to be either elbow grease and good scrubbing of affected panels before the glass surface is too far damaged, or experimental coatings that are supposed to inhibit the growth of these pioneer species. As someone famous once said, life finds a way. Beyond biocides and similar antifouling mechanisms, there does not seem to be a lot that can be done against the growth of these biofilms, but fortunately they develop much slower than a solid coating of dust.

The loss of power output from PV solar panels due to soiling with mineral dust is quite dramatic. For example, a 2018 paper by Cordero and colleagues in Scientific Reports which studied the impact of dust on PV panels in the Atacama Desert noted that with no cleaning the panels lost up to 39% of the output after a year, which improved with panels located closer to regions where it rained more frequently.

In desert regions with more severe mineral dust storms, dust accumulation on PV panels is a very rapid process, as noted by Sreedath Panat and colleague in a 2022 paper in Science Advances (MIT press release) in which they demonstrate an electrostatic repelling method for PV panels. In some regions (with dust accumulation rates close to 1 g/m² per day) panel output can be reduced by as much as 50% after a month, making regular cleaning (multiple times a month) with pressurized water jets essential. Although mechanical cleaning means are also possible, these risk scratching and otherwise damaging the panel’s glass, which would negatively affect performance in a more permanent manner than dust would.

Wiping Away Problems

The proposed solution by Sreedath Panan et al. involves a contraption that moves perpendicular over the surface to be cleaned of mineral dust, not unlike picking up bits of paper with a statically charged balloon. An important detail noted in the paper is that the mineral dust (30 – 75% consisting out of silica) is electrically insulating by itself, but becomes conductive when it adsorbs moisture, which allows it to be charged when is exposed to an electrode.

In the experimental setup using a desert dust analog (Arizona Test Dust, from Powder Technology Inc.) the two important factors were the moisture content of the dust and the size of the particles, with around 30% relative humidity required. Depending on the size of the particles, PV panel output was recovered from around 20% (dust-covered) to 80 – 95% (cleaned). Here the 30 μm sized particles were the hardest to remove, leading to the lowest recovery of lost output power.

Using this method, cleaning using water jets would not be rendered unnecessary, but it’s conceivable that the number of cleanings could be reduced, assuming this small-scale prototype can be adapted to a version that’d work with large-scale farms. Each panel would likely need to have its own plate like this, as well as an equivalent to the aluminium-doped zinc oxide (AZO) coating used as the electrode on the panel’s glass. Here the extra cost of a mechanical system and custom panel coating would need to compete economically with a water truck and a handful of blokes to handle the pressure washer.

Out Of This World

Attentive readers may have noticed a slight issue with the electrostatic method proposed by Sreedath Panan et al., in that it requires the presence of moisture to work. This is a property that would make both lunar and Mars researchers overjoyed if true, but in the absence of moisture a different mechanism is possible in the form of both electrostatic and dieelectrophoretic forces as researched by C.I. Calle et al. (2011, PDF) at NASA with a focus on lunar and Martian expeditions.

Rather than Arizona’s finest, these experiments were run with a Martian (JSC Mars-1) and lunar (JSC-1A & JSC-1AF) dust analogs in a high vacuum, showing the experimental PV panels to be able to shed most of the dust after a few minutes, recovering about 90% of the output. After this continued application of power to the system the output power continued to gradually improve.

As noted by Calle et al., this electrodynamic dust removal technique is not new, but was first developed as an ‘electric curtain’ concept by F.B. Tatom et al. at NASA, with additional research performed at the University of Tokyo in the 1970s. So far this technology has not been applied to PV panels or other surfaces (e.g. optical lenses) on operational missions such as the Mars rovers. At its core it’s a fairly simple system that creates a traveling wave by having a series of parallel electrodes connected to a three-phase alternating current source.

Because here the (transparent) electrodes are placed on top of the PV panel or fabric (see 2008 paper for additional details), there is no mechanical system requirement and little additional space is required. This makes it highly suitable for space missions where weight and space are at a premium and mechanical elements are problematic at best. Whether such a system could also be adapted for use on PV solar panels and solar mirrors on Earth is still an open question, but with some luck future solar-powered rovers on Mars will be able to shake off the dust on their PV panels if this technology gets approved on future missions.

Mylar has a lot of useful properties, and as such as see it pop up pretty often, not just in DIY projects but in our day-to-day lives. But until today, we’ve never seen a piece of Mylar jump up and try to get our attention. But that’s precisely the promise offered by ElectriPop, a fascinating project from Carnegie Mellon University’s Future Interfaces Group.

The core principle at work here is fairly simple. When electrostatically charged, a strip of Mylar can be made to lift up vertically into the air. Cut that strip down the center, and the two sides will repel each other and produce a “Y” shape. By expanding on that concept with enough carefully placed cuts, it’s possible to create surprisingly complex three dimensional shapes that pop up once a charge is applied. A certain degree of motion can even be introduced by adjusting the input power. The video after the break offers several examples of this principle in action: such as a 3D flower that either stands up tall or wilts in relation to an external source of data, or an avatar that flails its arms wildly to get the user’s attention.

As the relationship between the nested cuts, slits, and holes placed in the Mylar sheet and the final 3D shape isn’t particularly intuitive, the team has developed a visualization tool that can be used in conjunction with existing vector art programs to create a 2D cut file. Once you’re satisfied the design will inflate to the intended shape, it can quickly be implemented with a vinyl cutter or laser. The low barrier to entry makes this project particularly well suited for DIY replication, and we’re eager to see how the maker community could put this concept to work.

There are plenty of ways that you can charge up your new shape-changing Mylar display, but we particularly liked the team’s miniature Arduino-controlled Van de Graaff generator. It may represent the smallest and most simplistic implementation of this classic high-voltage generator that we’ve ever seen, and looks like a fun little project in itself.

ElectriPop was developed by [Cathy Mengying Fang], [Jianzhe Gu], and [Lining Yao] in collaboration with the director of the Future Interfaces Group, [Chris Harrison]. Readers may recall that in 2018 we covered VibroSight, another project from [Chris] and his students, which ultimately was scaled up to demonstrate laser non-contact sensing on city-scale just last year. Stay tuned for more from this innovative lab in the near future.

To say that that the commercially available garden path lights commonly available at dollar stores are cheap is a vast overstatement of their true worthlessness. These solar-powered lights are so cheaply built that there’s almost no point in buying them, a fact that led [Mark Presling] down a fabrication rabbit hole that ends with some great tips on powder coating parts with difficult geometries.

Powder coating might seem a bit overkill for something as mundane as garden lights, but [Mark] has a point — if you buy something and it fails after a few weeks in the sun, you might as well build it right yourself. And a proper finish is a big part of not only getting the right look, but to making these totally un-Tardis-like light fixtures last in the weather. The video series below covers the entire design and build process, which ended up having an aluminum grille with some deep grooves. Such features prove hard to reach with powder coating, where the tiny particles of the coating are attracted to the workpiece thanks to a high potential difference between them. After coating, the part is heated to melt the particles and form a tough, beautiful finish.

But for grooves and other high-aspect-ratio features, the particles tend to avoid collecting in the nooks and crannies, leading to an uneven finish. [Mark]’s solution was to turn to “hot flocking”, where the part is heated before applying uncharged coating to the deep features. This gets the corners and grooves well coated before the rest of the coating is applied in the standard way, leading to a much better finish.

We love [Presser]’s attention to detail on this build, as well as the excellent fabrication tips and tricks sprinkled throughout the series. You might want to check out some of his other builds, like this professional-looking spot welder.

Remember DSRC? If the initialism doesn’t ring a bell, don’t worry — Dedicated Short-Range Communications, a radio service intended to let cars in traffic talk to each other, never really caught on. Back in 1999, when the Federal Communications Commission set aside 75 MHz of spectrum in the 5.9-GHz band, it probably seemed like a good idea — after all, the flying cars of the future would surely need a way to communicate with each other. Only about 15,000 vehicles in the US have DSRC, and so the FCC decided to snatch back the whole 75-MHz slice and reallocate it. The lower 45 MHz will be tacked onto the existing unlicensed 5.8-GHz band where WiFi now lives, providing interesting opportunities in wireless networking. Fans of chatty cars need not fret, though — the upper 30 MHz block is being reallocated to a different Intelligent Transportation System Service called C-V2X, for Cellular Vehicle to Everything, which by its name alone is far cooler and therefore more likely to succeed.

NASA keeps dropping cool teasers of the Mars 2020 mission as the package containing the Perseverance rover hurtles across space on its way to a February rendezvous with the Red Planet. The latest: you can listen to the faint sounds the rover is making as it gets ready for its date with destiny. While we’ve heard sounds from Mars before — the InSight lander used its seismometer to record the Martian wind — Perseverance is the first Mars rover equipped with actual microphones. It’s pretty neat to hear the faint whirring of the rover’s thermal management system pump doing its thing in interplanetary space, and even cooler to think that we’ll soon hear what it sounds like to land on Mars.

Speaking of space, back at the beginning of 2020 — you know, a couple of million years ago — we kicked off the Hack Chat series by talking with Alberto Caballero about his “Habitable Exoplanets” project, a crowd-sourced search for “Earth 2.0”. We found it fascinating that amateur astronomers using off-the-shelf gear could detect the subtle signs of planets orbiting stars half a galaxy away. We’ve kept in touch with Alberto since then, and he recently tipped us off to his new SETI Project. Following the citizen-science model of the Habitable Exoplanets project, Alberto is looking to recruit amateur radio astronomers willing to turn their antennas in the direction of stars similar to the Sun, where it just might be possible for intelligent life to have formed. Check out the PDF summary of the project which includes the modest technical requirements for getting in on the SETI action.

A few months ago we reported that Boston Dynamics was finally finding customers with use cases that fit their flagship product, the “Big Dog” robot nicknamed Spot. The customer was Ford and the application involved periodic surveys of their enormous transmission plant, normally performed by engineers. At the same time, BP was training Spot for a far more dangerous job: oil rig inspections. Normally, operators on offshore oil platforms make the rounds several times a day to spot anything out of the ordinary: leaks, corrosion, or other situations that can pose a hazard to the platform and the people on it. After oil rig simulator training, Spot moved on to BP’s “Mad Dog” rig in the Gulf of Mexico, where it wanders about making sure everything’s copacetic. They’ve even trained Spot to read gauges and discern valve handle positions, and they’ve equipped the robot with sensors for methane to detect leaks.

And finally, how about a little high-voltage fun? Jay Bowles over at Plasma Channel just released a new video where he explores electrostatic levitation. We had Jay on for a Hack Chat not too long ago where we discussed his passion for plasma. The new video doesn’t have much plasma, but it does focus on how to use a 70-kV voltage multiplier to float scraps of tinfoil in the air. Jay even throws himself into the circuit at one point, levitating things with his bare hands. It seems like good fun, even if we wouldn’t recommend it as particularly safe.