Enlarge / A new lens-free and compact system for facial recognition scans a bust of Michelangelo’s David and reconstructs the image using less power than existing 3D-surface imaging systems. (credit: W-C Hsu et al., Nano Letters, 2024)

Facial recognition is a common feature for unlocking smartphones and gaming systems , among other uses. But the technology currently relies upon bulky projectors and lenses, hindering its broader application. Scientists have now developed a new facial recognition system that employs flatter, simpler optics that also requires less energy, according to a recent paper published in the journal Nano Letters. The team tested their prototype system with a 3D replica of Michelangelo's famous David sculpture, and found it recognized the face as well as existing smartphone facial recognition.

The current commercial 3D imaging systems in smartphones (like Apple's iPhone) extract depth information via structured light. A dot projector uses a laser to project a pseudorandom beam pattern onto the face of the person looking at a locked screen. It does so thanks to several other built-in components: a collimator, light guide, and special lenses (known as diffractive optical elements, or DOEs) that break the laser beam apart into an array of some 32,000 infrared dots. The camera can then interpret that projected beam pattern to confirm the person's identity.

Packing in all those optical components like lasers makes commercial dot projectors rather bulky, so it can be harder to integrate for some applications such as robotics and augmented reality, as well as the next generation of facial recognition technology. They also consume significant power. So Wen-Chen Hsu, of National Yang Ming Chiao Tung University and the Hon Hai Research Institute in Taiwan, and colleagues turned to ultrathin optical components known as metasurfaces for a potential solution. These metasurfaces can replace bulkier components for modulating light and have proven popular for depth sensors, endoscopes, tomography. and augmented reality systems, among other emerging applications.

Who among us hasn't wondered about how animals perceive the world, which is often different from how humans do so? There are various methods by which scientists, photographers, filmmakers, and others attempt to reconstruct, say, the colors that a bee sees as it hunts for a flower ripe for pollinating. Now an interdisciplinary team has developed an innovative camera system that is faster and more flexible in terms of lighting conditions than existing systems, allowing it to capture moving images of animals in their natural setting, according to a new paper published in the journal PLoS Biology.

“We’ve long been fascinated by how animals see the world. Modern techniques in sensory ecology allow us to infer how static scenes might appear to an animal," said co-author Daniel Hanley , a biologist at George Mason University in Fairfax, Virginia. "However, animals often make crucial decisions on moving targets (e.g., detecting food items, evaluating a potential mate’s display, etc.). Here, we introduce hardware and software tools for ecologists and filmmakers that can capture and display animal-perceived colors in motion.”

Per Hanley and his co-authors, different animal species possess unique sets of photoreceptors that are sensitive to a wide range of wavelengths, from ultraviolet to the infrared, dependent on each animal's specific ecological needs. Some animals can even detect polarized light. So every species will perceive color a bit differently. Honeybees and birds, for instance, are sensitive to UV light, which isn't visible to human eyes. "As neither our eyes nor commercial cameras capture such variations in light, wide swaths of visual domains remain unexplored," the authors wrote. "This makes false color imagery of animal vision powerful and compelling."

Enlarge / Microscopic view of photonic crystals on the surface of ancient Roman glass. (credit: Giulia Guidetti)

Nature is the ultimate nanofabricator. The latest evidence of that is an unusual shard of ancient Roman glass (dubbed the "wow glass") that boasts a thin, golden-hued patina. Roman glass shards are noteworthy for their iridescent hues of blue, green, and orange—the result of the corrosion process slowly restructuring the glass to form photonic crystals —and this particular shard's shimmering mirror-like gold sheen is a rare example with unusual optical properties, according to a new paper published in the Proceedings of the National Academy of Sciences.

It's yet another example of naturally occurring structural coloration. As previously reported , the bright iridescent colors in butterfly wings , soap bubbles , opals, or beetle shells don't come from any pigment molecules but from how they are structured—naturally occurring photonic crystals . In nature, scales of chitin (a polysaccharide common to insects), for example, are arranged like roof tiles. Essentially, they form a diffraction grating , except photonic crystals only produce specific colors, or wavelengths, of light, while a diffraction grating will produce the entire spectrum, much like a prism.

Also known as photonic band-gap materials, photonic crystals are "tunable," which means they are precisely ordered to block certain wavelengths of light while letting others through. Alter the structure by changing the size of the tiles, and the crystals become sensitive to a different wavelength. They are used in optical communications as waveguides and switches, as well as in filters, lasers, mirrors, and various anti-reflection stealth devices.

Enlarge / H.G. Wells' The Invisible Man inspired a 1933 film. It's just one cultural example of the human fascination with invisibility. (credit: Universal Pictures)

There's a well-known story in Plato's Republic in which a humble shepherd named Gyges finds a magical gold ring that renders whoever wears it invisible. Gyges proceeds to use his newfound power to murder a king and take over the throne. Plato intended it as a cautionary tale about whether a man could act justly even if the fear of consequence was removed. (The fictional Gyges clearly failed that moral test.) The parable famously inspired J.R.R. Tolkien's Lord of the Rings trilogy, among other works. And it's one of the earliest examples of the longstanding human fascination with invisibility in both fiction and scientific pursuits.

"Invisibility represents the perfect merger of not being seen while being able to see others, which would be great if you were a primitive hunter-gatherer," Greg Gbur, a physicist at the University of North Carolina, Chapel Hill, told Ars. "But more purely, it represents power. You see that in the story of the Ring of Gyges, where the ability to make yourself unseen gives you a tremendous advantage over others. So it's fascinating as a symbol of pure power and how people might use and abuse it."

Gbur is the author of a new book from Yale University Press, Invisibility: The History and Science of How Not to Be Seen , covering the earliest discoveries in optical physics through to the present, along with how invisibility has been portrayed in science fiction (a longstanding passion for Gbur). He's also the author of 2019's fascinating Falling Felines and Fundamental Physics , which explored the surprisingly complicated physics of why cats always seem to land on their feet, ferreting out several obscure scientific papers spanning decades of research in the process. His interest in invisibility science dates back to his graduate school days when his advisor assigned him a project on the topic.

Enlarge / The BPClip in action. (credit: Yinan Xuan et al.)

Given that 47 percent of adults in the US alone have hypertension, keeping on top of your blood pressure readings is a smart thing to do. And doing so could become much more convenient, requiring nothing more than your phone and an $0.80 piece of plastic, thanks to new research from the University of California, San Diego.

The school's device, called BPClip, gives broadly comparable readings to those taken with a traditional cuff but functions as a simple cell phone attachment. It relies on the flashlight and the smartphone’s camera—along with some simple physics.

BPClip consists of a plastic clip with a spring mechanism that lets the user squeeze the device and two light channels: one to direct a flashlight to your finger and the other to direct the reflected light to the camera for image processing. A custom-made Android app handles the data processing and guides users through the measurement.

Enlarge / Certain squid have the ability to camouflage themselves by making themselves transparent and/or changing their coloration. (credit: YouTube/KQED Deep Look )

Certain cephalopods like cuttlefish, octopuses, and squid have the ability to camouflage themselves by making themselves transparent and/or changing their coloration. Scientists would like to learn more about the precise mechanisms underlying this unique ability, but it's not possible to culture squid skin cells in the lab. Researchers at the University of California, Irvine, have discovered a viable solution: replicating the properties of squid skin cells in mammalian (human) cells in the lab. They presented their research at a meeting of the American Chemical Society being held this week in Indianapolis.

"In general, there's two ways you can achieve transparency," UC Irvine's Alon Gorodetsky, who has been fascinated by squid camouflage for the last decade or so, said during a media briefing at the ACS meeting. "One way is by reducing how much light is absorbed—pigment-based coloration, typically. Another way is by changing how light is scattered, typically by modifying differences in the refractive index." The latter is the focus of his lab's research.

Squid skin is translucent and features an outer layer of pigment cells called chromatophores that control light absorption. Each chromatophore is attached to muscle fibers that line the skin's surface, and those fibers, in turn, are connected to a nerve fiber. It's a simple matter to stimulate those nerves with electrical pulses, causing the muscles to contract. And because the muscles pull in different directions, the cell expands, along with the pigmented areas, which changes the color. When the cell shrinks, so do the pigmented areas.

Enlarge / Bodleian MS. Selden Supra 30 open at pp. 18-19. (credit: John Barrett)

Jessica Hodgson, a graduate student at the University of Leicester, was poring over a medieval manuscript in the Bodleian Libraries ' collection at the University of Oxford when she spotted a faint etched inscription on one of the pages. It seemed to spell out the name "Eadburg," but the etching was too faint for full confirmation. So Hodgson turned to John Barrett, technical leader for a recent project at the Bodleian called ARCHiOx (Analyzing and Recording Cultural Heritage in Oxford), for help.

Thanks to the project's prototype photometric stereo recording and 3D scanning systems, Barrett confirmed Hodgson's discovery. The analysis also revealed multiple other etchings of the name "Eadburg" (in both full and abbreviated forms), along with several etched doodles in the margins. Who was Eadburg? Hodgson believes she was a highly educated woman of high status—possibly a female scribe or an abbess —who lived sometime in the early medieval period (between 700 and 750 CE). This latest discovery bolsters a 1935 discovery of the letters "EADB" and "+E+" in the lower margin of another page in the same manuscript, both believed to be abbreviated forms of "Eadburh/Eadburg."

The ARCHiOx Project

The ARCHiOx Project is a partnership between the Bodleian Libraries and the Factum Foundation, set up by Adam Lowe, an artist who trained at Oxford in the 1990s. In 2001, Lowe moved to Madrid to set up what he described to Ars as "a multidisciplinary workshop that's really a playground for artists, where we build bridges between new technologies and traditional skills." By 2009, there was so much interest from various historical projects regarding the group's technologies that Lowe established the Factum Foundation for digital technology and preservation. Today it serves as a research hub for high-resolution, three-dimensional recording of the surfaces of objects housed in museums and institutions around the world—including tombs, paintings, and books and manuscripts like those housed at the Bodleian.

Enlarge / The laser beam passes near the lightning rod on the Säntis Tower. (credit: TRUMPF/Martin Stollberg )

Lightning rods protect buildings by providing a low-resistance path for charges to flow between the clouds and the ground. But they only work if lightning finds that path first. The actual strike is chaotic, and there's never a guarantee that the processes that initiate it will happen close enough to the lightning rod to ensure that things will work as intended.

A team of European researchers decided they didn't like that randomness and managed to direct a few lightning strikes safely into a telecom tower located on top of a Swiss mountain. Their secret? Lasers, which were used to create a path of charged ions to smooth the path to the lightning rod.

Everything’s better with lasers

The basic challenge with directing lightning bolts is that the atmospheric events that create charged particles occur at significant altitudes relative to lightning rods. This allows lightning to find paths to the ground that don't involve the lightning rod. People have successfully created a connection between the two by using small rockets to shoot conductive cables to the heights where the charges were. But using this regularly would eventually require a lot of rockets and leave the surroundings draped in cables.

Enlarge / Researchers manipulated light with liquid crystals to create a sculpted laser beam capable of producing this photorealistic image of a cat. (credit: P.F. Silva & S.R. Muniz, 2022)

Every cat owner knows how their feline companions delight in chasing a tiny pinpoint of light from a simple laser pointer. Now, Brazilian physicists have figured out how to trap and bend laser light into intricate shapes, producing the impressive photorealistic image of a cat pictured above. Among other potential applications, their method—described in a recent paper posted to the physics arXiv—could prove useful for building better optical traps to create clouds of ultra-cold atoms for a variety of quantum experiments.

The ability to produce and precisely control the shape of laser beams with high fidelity is vital for many segments of research and industry, according to co-authors Pedro Silva and Sergio Muniz of the University of Sao Paolo. They group most wavefront engineering approaches into two basic categories.

The first includes such approaches as digital micro mirrors (DMDs) and acoustic optical modulators (AOMs), which are easy to implement and boast a fast response for near real-time feedback control. But they have a limited ability to control the phase of the light field and can't create certain kinds of structured light. They are also prone to speckle, diffraction, or other distortions.