Holograms: The Art Of Recording Wavefronts

December 3, 2024 by Maya Posch 22 Comments

The difference between holography and photography can be summarized perhaps most succinctly as the difference between recording the effect photons have on a surface, versus recording the wavefront which is responsible for allowing photographs to be created in the first place. Since the whole idea of ‘visible light’ pertains to a small fragment of the electromagnetic (EM) spectrum, and thus what we are perceiving with our eyes is simply the result of this EM radiation interacting with objects in the scene and interfering with each other, it logically follows that if we can freeze this EM pattern (i.e. the wavefront) in time, we can then repeat this particular pattern ad infinitum.

Close-up of the wavefront pattern recorded on the holographic film (Credit: 3Blue1Brown, YouTube)

In a recent video by [3Blue1Brown], this process of recording the wavefront with holography is examined in detail, accompanied by the usual delightful visualizations that accompany the videos on [3Blue1Brown]’s channel. The type of hologram that is created in the video is the simplest type, called a transmission hologram, as it requires a laser light to illuminate the holographic film from behind to recreate the scene. This contrasts with a white light reflection hologram, which can be observed with regular daylight illumination from the front, and which is the type that people are probably most familiar with.

The main challenge is, perhaps unsurprisingly, how to record the wavefront. This is where the laser used with recording comes into play, as it forms the reference wave with which the waves originating from the scene interact, which allows for the holographic film to record the latter. The full recording setup also has to compensate for polarization issues, and the exposure time is measured in minutes, so it is very sensitive to any changes. This is very much like early photography, where monochromatic film took minutes to expose. The physics here are significant more complex, of course, which the video tries to gently guide the viewer through.

Also demonstrated in the video is how each part of the exposed holographic film contains enough of the wavefront that cutting out a section of it still shows the entire scene, which when you think of how wavefronts work is quite intuitive. Although we’re still not quite in the ‘portable color holocamera’ phase of holography today, it’s quite possible that holography and hologram-based displays will become the standard in the future.

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Exploring The Sounds And Sights Of Alien Worlds

December 2, 2024 by Maya Posch 14 Comments

The 20th century saw humankind’s first careful steps outside of the biosphere in which our species has evolved. Whereas before humans had experienced the bitter cold of high altitudes, the crushing pressures in Earth’s oceans, as well as the various soundscapes and vistas offered in Earth’s biosphere, beyond Earth’s atmosphere we encountered something completely new. Departing Earth’s gravitational embrace, the first humans who ventured into space could see the glowing biosphere superimposed against the seemingly black void of space, in which stars, planets and more would only appear when blending out the intense light from the Earth and its life-giving Sun.

Years later, the first humans to set foot on the Moon experienced again something unlike anything anyone has experienced since. Walking around on the lunar regolith in almost complete vacuum and with very low gravity compared to Earth, it was both strangely familiar and hauntingly alien. Although humans haven’t set foot on Mars yet, we have done the next best thing, with a range of robotic explorers with cameras and microphones to record the experience for us here back on Earth.

Unlike the Moon, Mars has a thin but very real atmosphere which permits the travel of soundwaves, so what does the planet sound like? Despite what fictional stories like Weir’s The Martian like to claim, reality is in fact stranger than fiction, with for example a 2024 research article by Martin Gillier et al. as published in JGR Planets finding highly variable acoustics during Mars’ seasons. How much of what we consider to be ‘normal’ is just Earth’s normal?

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The Many Reasons For Putting Microphones In Rainforests

November 30, 2024 by Maya Posch 8 Comments

If a tree falls in a forest with nobody around, does it make a noise? In the case of the rainforests equipped with the Rainforest Connection’s Guardian system someone most assuredly will.

Rainforest Connection’s Guardian system up close, with microphone visible. (Credit: RFCx)

Originally created by the people behind the US nonprofit Rainforest Connection (RFCx) using upcycled smartphones to detect the sounds of illegal logging, their project now has grown into something much larger, keeping not only tabs on sounds of illegal activity, but also performing bioacoustic monitoring for scientific purposes.

Currently active in ten countries, the so-called Guardian Platform no longer features smartphones, but custom hardware inside an IP66 weatherproof enclosure and a whole range of communication options, ranging from cellular bands to satellite communications. The petal-shaped solar panels provide the module with up to 30 watts of power, and double as a shield to help protect it from the elements.

Not only is the real-time microphone data incredibly useful for rangers trying to stop illegal logging, it also provides researchers access to countless hours of audio data, which will require detailed, automated analysis. Even better is that if the audio data is available to the general public as well, via their Android & iOS apps (bottom of page), just in case you wanted to hear what that sneaky wildlife in the jungle of Peru is up to right now.

Modernizing An Apple IPod, Or: A Modern-Day Ship Of Theseus

November 29, 2024 by Maya Posch 24 Comments

Back in the day the Apple iPod was the personal music player (PMP) to get even if mostly because everyone and their dogs had one. These days most people just use their smartphone as a PMP, but what if you were to take, say, a 5th generation iPod and modernized it? That was the basic idea that [Zac Builds] picked up and ran with, with the results as shown in the video he made about it.

The 5th gen iPod was the first one capable of playing video, and was released in October of 2005. Powering it is a Broadcom BCM2722 for video playback, and came with a 30 or 60 GB HDD. First thing that [Zac] tosses is the old (3.7V, 650 mAh) battery, which appears to be already a replacement for the original, followed by the 60 GB 1.8″ HDD. Next tossed is the 2.5″ 320×240 QVGA screen, which gets replaced by a compatible modern LCD. The case is replaced with a transparent case, along with a transparent touch wheel, and the HDD is replaced with a 256 GB SD card in an iFlash Solo SD card adapter for iPods.

Next up was the installation of more off-the-shelf mods, such as a ‘taptic mod’ – which adds a rumble motor – and replacing the iPod’s 30-pin connector with a USB-C connector, requiring some fiddly soldering and desoldering. Following this a Bluetooth audio transmitter was added, extreme PCB mods performed with a cut-off wheel to make everything fit with a custom midframe and rear case.

Ultimately, the parts left of the original iPod were most of the mainboard and some flex cable, which raises the question of whether it might not have been faster and easier to start off with designing a custom PCB. Perhaps the true value is in the modding journey and not the destination?

Thanks to [Keith Olson] for the tip.

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A Laser With Mirrors Makes A CRT-like Display

November 26, 2024 by Maya Posch 22 Comments

[bitluni]’s laser-based display pretending to be a an old-school vector CRT.

Phosphor-based displays like CRTs rely on the phosphor to emit light for a set amount of time after being activated, allowing them to display a seemingly persistent image with one drawing beam per color. Translated to UV-sensitive PLA filament, this means that you can totally use a printed sheet of this material in combination with a 405 nm laser diode to create a display that doesn’t look dissimilar to an early CRT. This is exactly what [bitluni] did in a recent video, meshing together said laser diode, UV-sensitive PLA, stepper motors and two mirrors with an Arduino-based controller to create a rather interesting vector display.

In the video, [bitluni] goes over the development steps, including a range of improvements like being able to turn off the laser when moving between the end of a line and the beginning of a new one. While the Arduino Nano board does the driving of the stepper motor controllers, an ESP32 provides the drawing instructions. The STL and other project files including Nano & ESP32 firmware can be found on the GitHub project page.

While far from being a practical display with a single-digit Hz refresh rate, it does provide an interesting demonstration of these types of persistence of vision based displays, and without the use of exotic MEMS mirror modules or the like.

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Creating And Control Of Magnetic Skyrmions In Ferromagnetic Film Demonstrated

November 21, 2024 by Maya Posch 23 Comments

Visualization of magnetic skyrmions. (Credit: KRISS)

Magnetic skyrmions are stable quasi-particles that can be generated in (some) ferromagnetic materials with conceivable solutions in electronics, assuming they can be created and moved at will. The creation and moving of such skyrmions has now been demonstrated by [Yubin Ji] et al. with a research article in Advanced Materials. This first ever achievement by these researchers of the Korea Research Institute of Standards and Science (KRISS) was more power efficient than previously demonstrated manipulation of magnetic skyrmions in thicker (3D) materials.

Magnetic skyrmions are sometimes described as ‘magnetic vortices’, forming statically stable solitons. For magnetic skyrmions their stability comes from the topological stability, as changing the atomic spin of the atoms inside the skyrmion would require overcoming a significant energy barrier.

In the case of the KRISS researchers, electrical pulses together with a magnetic field were used to create magnetic skyrmions in the ferromagnetic (Fe₃GaTe₂, or FGaT) film, after which a brief (50 µs) electric current pulse was applied. This demonstrated that the magnetic skyrmions can be moved this way, with the solitons moving parallel to the electron flow injection, making them quite steerable.

While practical applications of magnetic skyrmions are likely to be many years off, it is this kind of fundamental research that will enable future magnetic storage and spintronics-related devices.

Featured image: Direct imaging of the magnetic skyrmions. The scale bars represent 300 nm. (Credit:Yubin Ji et al., Adv. Mat. 2024)

Rendering of a JetZero blended wing body aircraft with US Air Force markings. (Credit: US Air Force)

Blended Wing Body Passenger Airplanes And The End Of Winged Tubes

November 21, 2024 by Maya Posch 69 Comments

The SR-71 with its blended wing body design. (Photo by Tech. Sgt. Michael Haggerty, US Air Force, 1988)

Ask someone to picture an airplane and they’re likely to think of what is essentially a tube with wings and a stabilizing tail tacked onto one end of said tube. Yet it is also no secret that the lift produced by such a tube is rather poor, even if they’re straightforward for loading cargo (static and self-loading) into them and for deciding where to put in windows. Over the decades a number of alternative airplane designs have been developed, with some of them also ending up being produced. Here most people are probably quite familiar with the US Air Force’s B-2 Spirit bomber and its characteristic flying wing design, while blended wing body (BWB) maintains a somewhat distinctive fuselage, as with for example the B-1 Lancer.

Outside of military airplanes BWBs are a pretty rare sight. Within the world of passenger airplanes the tube-with-wings pattern that the first ever passenger airplanes adopted has persisted with the newest designs, making it often tricky to distinguish one airplane from another. This could soon change, however, with a strong interest within the industry for passenger-oriented BWBs. The reason for this are the significant boosts in efficiency, quieter performance and more internal (useful) volume, which makes airline operators very happy, but which may also benefit passengers.

With that said, how close are we truly to the first BWB passenger airplane delivery to an airline?

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