Powering Airplanes With Microwaves: An Aviation Physics Challenge Amidst Many

June 27, 2024 by Maya Posch 19 Comments

Falling firmly under the fascinating science category of ‘What if…?’ comes the idea of powering airplanes with beamed microwaves. Although the idea isn’t crazy by itself, since we can even keep airplanes flying using just solar power (though with no real useful payload), running through the numbers as [Ian McKay] does in a recent article in IEEE Spectrum makes it clear that there are still some major hurdles if we want to make such a technology reality. Yet is beamed microwave power that much more far out than other alternative ways to power aviation?

Most of the issues are rather hard limits with the assumed technology (phased microwave arrays), with the need for 170 meter diameter ground transmitters every 100 km along the route (including floating transmitters on the oceans with massive power cables, apparently). Due to the limited surface area on something like a Boeing 737-800 you’d need to cram the full take-off power needs (~30 MW) on its ~1,000 m² surface area available for receiver elements, or 150 Watt per rectifying antenna (rectenna) element assuming a wavelength of 5 cm.

The good news is that the passengers inside would probably survive if the microwave-like shielding keeps up, and birds passing through the beams are likely to survive if they’re fast enough. It’d ruin a whole part of the local radio spectrum from leaked microwaves, of course. Unfortunately beaming MW levels of microwaves across 100 km is still beyond our capabilities.

After this fun science session, [Ian] then looks at alternatives like batteries and hydrogen, neither of which come even close to the energy density (or relative safety) of commercial aviation fuels. Perhaps synthetic aviation fuel might be the ticket, but at this point beamed microwave power is as likely to replace aviation fuel as batteries or hydrogen, though more likely than countries like the United States building out a fast & cheap high-speed rail network.

pulse oximeter as a small sticker that sticks on your fingernail and measures heart rate, motion, and blood oxygen

This Fingernail Sticker Can Detect When You Stop Breathing

January 1, 2023 by Orlando Hoilett 8 Comments

Sometimes we dig through the archives to see what kind of crazy hacks we can pull out of the depths of the world wide web and this one was worth sharing. Researchers at Northwestern University developed a sticker that’s applied to the fingernail and measures heart rate, motion, and blood oxygen, all without a battery.

The photoplethysmograph (PPG) system is similar to what we’ve covered before and the motion sensor is simply an accelerometer, so we won’t go over those aspects of the device. The parts of the device that did catch our attention were the battery-less operation as well as its size. It’s just so dang small! And fits snuggly on a fingernail or on even on your earlobe. The size here is actually a very interesting feature and not just a marketing plug. Because the device is so small and lightweight, it is very easy to adhere to the fingernail or skin with very little sensory perception. Basically, the person wearing the device won’t even notice it’s there. That’s definitely an advantage over the traditional, bulky, hospital-grade instruments we’ve grown accustomed to.

The device adheres really well given its small and lightweight design, so motion artifacts are significantly reduced. Motion artifacts in PPG-based devices are due to the relative motion between the optode (LED and photodiode) and the skin. The traditional approaches of ensuring the device don’t move are for the patient to keep very still during a recording, to wear the device tightly against the skin (think of how tightly you need to wear your smartwatch to get consistent readings), or use some seriously tough and uncomfortable adhesive as you may have done if you’ve ever gotten an electrocardiogram reading before. This device eliminates those three problems.

The other aspect of the device that caught our attention is its use of wireless power instead of a battery. In some senses, this could be seen as an advantage or as a disadvantage. The device relies on NFC for power and data transmission, a pretty common approach for devices that only need to be used intermittently. Wireless power could be a bit problematic for continuous monitoring devices which provide readings every second or several times a second. But who knows, wireless power seems to be everywhere these days.

Digging into the details a bit, the double-layer antenna is designed around the circumference of the device using wet etching to create traces on a copper polyimide foil. The team electroplated holes through the different layers of the device (optode layer, first antenna layer, polyimide, second antenna layer, component layer, protective top coat) connecting the antenna to the die pad NFC chip (SL13A, AMS AG). Connecting the chip requires some pretty fine-pitch soldering techniques, but nothing we’re not accustomed to here at Hackaday. Overall, they seemed pretty successful, obtaining a Q factor of 16 and a transmission distance of 30 mm using a smartphone and not some giant reader antenna.

Definitely, a really cool project that we recommend checking out.

High Voltage Experiment Pipes Power With Water

May 15, 2020 by Tom Nardi 27 Comments

The idea of transferring energy with water isn’t exactly new. In fact, it’s downright ancient. Running water has been tapped to power our contrivances since folks were getting excited about that new library they were opening up over in Alexandria. But what if there was a way to deliver power with water that wasn’t kinetic, and instead relied on the electrical properties of the planet’s favorite libation?

That’s exactly what [Jay Bowles] set out to explore with his latest experiment. Since water (we know, not pure water) conducts electricity, it stands to reason that it could be used as a stand-in for traditional copper wiring. Why would you want to do such a thing? Because unlike wires, water can easily morph into whatever shape may be required, and can be moved around and controlled with nothing more complex than ball valves.

To test this concept, [Jay] put together a water distribution system out of simple acrylic tubing. A reservoir was attached to one of his high voltage generators, and copper caps were placed at the end of the tubes to serve as direct attachment points for devices.

But thanks to capacitive coupling, the fluorescent lights he uses don’t actually need to be physically connected to light up. As demonstrated in the video after the break, the lights surrounding the system can be independently controlled just by turning their respective valves on and off; all without any physical contact being made.

Of course, compared to traditional wiring there are plenty of downsides to this idea. Copper wires don’t tend to freeze in the winter and spring a leak, nor do they build up bubbles of explosive hydrogen gas. So it’s safe to say the wiring in your house probably won’t ever be replaced with a tube of charged water. But [Jay] does have some interesting ideas of how this technique could be used in non-traditional ways. For example, he describes how outdoor lighting could be powered by the energy radiating from a small stream.

Even if the practical applications of this technique are somewhat limited, there’s no question that it’s a fascinating idea. Believing that he’s the first person to ever demonstrate power transmission under these specific circumstances, he’s decided to call the concept “Bowles Transmission”. We’d love to see somebody use this principle in one of their projects, and we’re willing to bet so would [Jay].

As with his recent ozone sterilization experiments, we imagine this idea is going to be met with some debate. But that’s sort of the point. [Jay] doesn’t claim to have all the answers, and hopes these videos get people thinking and talking. As they say, nothing great was ever achieved without enthusiasm.

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Wireless Charging Without So Many Chargers

January 15, 2019 by Brian McEvoy 11 Comments

[Nikola Tesla] believed he could wirelessly supply power to the world, but his calculations were off. We can, in fact, supply power wirelessly and we are getting better but far from the dreams of the historical inventor. The mainstream version is the Qi chargers which are what phones use to charge when you lay them on a base. Magnetic coupling is what allows the power to move through the air. The transmitter and receiver are two halves of an air-core transformer, so the distance between the coils exponentially reduces efficiency and don’t even think of putting two phones on a single base. Well, you could but it would not do any good. [Chris Mi] at San Diego State University is working with colleagues to introduce receivers which feature a pass-through architecture so a whole stack of devices can be powered from a single base.

Efficiency across ten loads is recorded at 83.9% which is phenomenal considering the distance between each load is 6 cm. Traditional air-gap transformers are not designed for 6 cm, much less 60 cm. The trick is to include another transmitter coil alongside the receiving coil. By doing this, the coils are never more than 6 cm apart, even when the farthest unit is a long ways from the first supply. Another advantage to this configuration is that tuned groups continue to work even when a load changes in the system. For this reason, putting ten chargeables on a single system is a big deal because they don’t need to be retuned when one finishes charging.

We would love to see more of this convenient charging and hope that it catches on.

Via IEEE Spectrum.

Epoxy Embedded Electronic Art Running On Pyramid Power

September 2, 2018 by Steven Dufresne 25 Comments

We sometimes get our inspirations from art. When [kodera2t] saw some Japanese art of fish drawings embedded in clear epoxy he just had to make his own. But while skilled in electronics, he wasn’t skilled at drawing. We’d still call him an artist, though, after seeing what he came up with in his electronics embedded in crystal clear epoxy.

His first works of electronic art were a couple of transistors and some ICs, including an 80386, encased in epoxy. But then he realized that he wanted the electronics to do something interesting. However, once encased in epoxy, how do you keep the electronics powered forever?

He tried a solar cell charging a battery which then powered an LED but he didn’t like the idea of chemical batteries encased in epoxy for a long time.

He then switched to wireless power transmission with a receiving coil in the base of epoxy pyramids. For one of them, the coil powers a BLE board with an attached LED which he can control from his phone. And his latest contains an ESP32-PICO with an OLED display. The code allows him to upload new firmware over the air but on his Hackaday.io page, he shows the difference between code which can brick the ESP32 versus code which won’t. But don’t take our word for it. Check out the video below to see his artistry for yourself.

While embedding electronics in epoxy is new to [kodera2t], we’ve seen it a few times before. once in the form of an amplifier circuit done beautifully, dead bug style, and a more experimental attempt with a solar lantern.

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Suddenly, Wireless Power Transmission Is Everywhere

February 23, 2017 by Brian Benchoff 91 Comments

Wireless power transfer exists right now, but it’s not as cool as Tesla’s Wardenclyffe tower and it’s not as stupid as an OSHA-unapproved ultrasonic power transfer system. Wireless power transfer today is a Qi charger for your phone. It’s low power – just a few amps — and very short range. This makes sense; after all, we’re dealing with the inverse square law here, and wireless power transfer isn’t very efficient.

Now, suddenly, we can transfer nearly two kilowatts wirelessly to electronic baubles scattered all over a room. It’s a project from Disney Research, it’s coming out of Columbia University, it’s just been published in PLOS one, and inexplicably it’s also an Indiegogo campaign. Somehow or another, the stars have aligned and 2017 is the year of wirelessly powering your laptop.

The first instance of wireless power transfer that’s more than just charging a phone comes from Disney Research. This paper describes quasistatic cavity resonance (QSCR) to transfer up to 1900 Watts to a coil across a room. In an experimental demonstration, this QSCR can power small receivers scattered around a 50 square meter room with efficiencies ranging from 40% to 95%. In short, the abstract for this paper promises a safe, efficient wireless power transfer that completely removes the need for wall outlets.

In practice, the QSCR from Disney Research takes the form of a copper pole situated in the center of a room with the walls, ceiling, and floor clad in aluminum. This copper pole isn’t continuous from floor to ceiling – it’s made of two segments, connected by capacitors. When enough RF energy is dumped into this pole, power can be extracted from a coil of wire. The video below does a good job of walking you through the setup.

As with all wireless power transmission schemes, there is the question of safety. Using finite element analysis, the Disney team found this room was safe, even for people with pacemakers and other implanted electronics. The team successfully installed lamps, fans, and a remote-controlled car in this room, all powered wirelessly with three coils oriented orthogonally to each other. The discussion goes on to mention this setup can be used to charge mobile phones, although we’re not sure if charging a phone in a Faraday cage makes sense.

If the project from Disney research isn’t enough, here’s the MotherBox, a completely unrelated Indiegogo campaign that was launched this week. This isn’t just any crowdfunding campaign; this work comes straight out of Columbia University and has been certified by Arrow Electronics. This is, by all accounts, a legitimate thing.

The MotherBox crowdfunding campaign promises true wireless charging. They’re not going for a lot of power here – the campaign only promises enough to charge your phone – but it does it at a distance of up to twenty inches.

At the heart of the MotherBox is a set of three coils oriented perpendicular to each other. The argument, or sales pitch, says current wireless chargers only work because the magnetic fields are oriented to each other. The coil in the phone case is parallel to the coil in the charging mat, for instance. With three coils arranged perpendicular to each other, the MotherBox allows for ‘three-dimensional charging’.

Does the MotherBox work? Well, if you dump enough energy into a coil, something is going to happen. The data for the expected charging ranges versus power delivered is reasonably linear, although that doesn’t quite make sense in a three-dimensional universe.

Is it finally time to get rid of all those clumsy wall outlets? No, not quite yet. The system from Disney Research works, but you have to charge your phone in a Faraday cage. It would be a great environment to test autonomous quadcopters, though. For MotherBox, Ivy League engineers started a crowdfunding campaign instead of writing a paper or selling the idea to an established company. It may not be time to buy a phone case so you can charge your phone wirelessly at Starbucks, but at least people are working on the problem. This time around, some of the tech actually works.

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Power Over WiFi Might Not Be A Unicorn After All

November 27, 2015 by Brandon Dunson 54 Comments

There have been a few reports of power over WiFi (PoWiFi) on the intertubes lately. If this is a real thing it’s definitely going to blow all of the IoT fanboys skirts up (sorry to the rest of you *buzzword* fanboys, the IoT kids flash-mobbed the scene and they mean business).

All of the recent information we found points to an article by [Popular Science] titled “Best of What’s New 2015”. The brief write up includes a short summary lacking technical info, and fair play to [PopSci] as it’s a “Best Of” list for which they hadn’t advertised as an in-depth investigation.

However, we tend to live by the “If you’re gonna get wet, you might as well swim.” mentality, so we decided to get a little more information on the subject. After a bit of digging around we came across the actual article on [Cornell University]’s e-print archive where you can download the PDF that was published.

The paper goes into detailed explanation of the power harvesting theory including a schematic of the receiving end hardware. They had to create a constant transmission for the harvester to get over its minimum required voltage of operation. This was done with one of the wireless router’s unused channels to fill the voids of packet-less silence between normal WiFi communication.

As you can imagine PoWiFi is currently limited to powering/charging very low power devices that are used intermittently. The research team was able to charge a Jawbone headset at a rate of 2.3mA for 2.5 hours which resulted in the battery going from 0-41%. The punchline here is the distance, the device being charged was only 5-7cm from the PoWiFi router which is getting close to inductive charging range. The researchers stated in the paper that they were looking into integrating the harvesting circuitry and antenna into the headset while working towards a larger charging distance.

Rate of update vs time.

WiFi packets and silence.

Power harvesting schematic.

At the time of writing this article it seems that PoWiFi is best suited for devices such as: low powered sensors and motion activated cameras that have increased energy storage capacity, which the team mentioned as one of the continued research possibilities.

We’ve covered numerous wireless power projects before, some legit and some we still get a kick out of. Where do you think this one falls on that spectrum? Let us know in the comments below.

Thanks to [ScottVR] for the tip.