Thermal cloak passively keeps electric vehicles cool in the summer and warm in the winter

Science Daily  July 11, 2023 Despite intensive efforts invested, high-efficacy, all-season temperature regulation on real-world objects has not yet been achieved through truly passive, reliable structures. Researchers in China proposed and experimentally realized a Janus thermal cloak (JTC) composed of an all-ceramic, radiative-cooling phononic metafabric facing the sky and a photon-recycling foil facing indoor space. The phononic metafabric, which supports broadband hyperbolic phonon polaritons (HPhPs) and strong scattering of phonon transport, showed resilience under harsh thermal, mechanical, and corrosive environments. Field tests on electric vehicles showed that the JTC realized daytime sub-ambient cooling by 8.0°C in summer and nighttime supra-ambient […]

A new technique to detect invisibility cloaks

Phys.org  June 13, 1023 So far, most efforts in invisibility science have been devoted to achieving practically realizable cloak designs and to improving the effectiveness of these devices in reducing their scattering cross-section. Little attention has been paid to the opposite side of the technology – the development of more efficient techniques for the detection of invisibility devices. Researchers in Spain proposed a path taking advantage of the smarter way in which diffraction tomography processes all overlooked information to improve the efficiency in unveiling the presence of invisibility devices. This approach not only resulted in a considerable sensitivity enhancement in […]

Making an object invisible under fluid flow

Phys.org  January 7, 2022 Without any obstacle, the fluid flows along a straight line. If an obstacle is present, the straight streamline will be defected, and an observer can sense the size, shape, and position of the obstacle. Guiding the fluid to flow faster closer to the obstacle and slower farther from it conceals the distortions and restore original straight streamlines. Instead of engineering the mass density of the fluid to control the speed of the fluid flow, researchers in Singapore simply engineered the thickness of the fluid channel. They showed that thicker fluid channel gives rise to smaller mass […]

Scientists Built a New Kind of Invisibility Cloak, But It’s Not For Your Eyes

Science Alert  September 4, 2021 An international team of researchers (Switzerland, UK) has achieved active acoustic cloaking and holography without prior knowledge of the wavefield so that objects remain invisible and illusions remain intact even for broadband moving sources. In the new approach, there’s a lot more versatility in making objects disappear – and it can even work the other way around to make it sound as if a non-existent object is taking up space in the room. FPGAs can respond to the audio speaker outputs with virtually no delay at all. So far, the researchers have managed to get […]

Bending light for safer driving; invisibility cloaks to come?

Nanowerk June 15, 2021 Perfect optical cloaking requires the total scattering of electromagnetic waves around an object at all angles, all polarizations, over a wide frequency range, irrespective of the medium. By simplifying the invisibility requirements, pioneering work on spherical transformation cloaks, carpet cloaks, plasmonic cloaks, and mantle cloaks has been realized in narrowband microwave, infrared, and even optical wavelengths. In a tutorial a team of researchers in the US (University of Michigan, industry) review the theoretical basis for invisibility cloaking, from spherical transformational optics to non-Euclidian cases, and discuss their limitations. Because the human eye is insensitive to the […]

Single-Molecule Cloak

American Physical Society  September 3, 2020 Ordinarily the transmission of light from a laser can be cut in half when obscured by such a nanoparticle, but the molecule’s presence causes 10% more light to be transmitted. With better control of the system, the molecule-nanoparticle combination could potentially become transparent to the laser. The effect could lead to optical switches in which light transmission would be controlled by single molecules. Researchers in Germany have demonstrated that the extinction cross section of a large gold nanoparticle can be substantially reduced—i.e., the particle becomes more transparent—if a single molecule is placed in its […]

Designing a flexible material to protect buildings, military personnel

Phys.org  May 27, 2020 Cloaking materials are mature because the properties of acoustic (radar, sonar) and optical waves (infrared) are well-understood. However, cloaking for elastic waves in solid media is lagging. A team of researchers in the US (University of Missouri, MIT) has designed and fabricated a new class of cloaking materials which is composed of a functionally graded lattice embedded in an isotropic continuum background. The layers were 3-D printed and manually assembled. They experimentally and numerically investigated the characteristics of the proposed cloak and found very good cloaking performance under both tension and shear loadings. Potential applications for […]

Camouflage made of quantum material could hide you from infrared cameras

Phys.org  December 17, 2019 For most solids, the thermally emitted power increases monotonically with temperature in a one-to-one relationship that enables applications such as infrared imaging and noncontact thermometry. A team of researchers in the US (University of Wisconsin, Harvard University, Purdue University, MIT, Brookhaven National Laboratory) has shown that ultrathin samarium nickel oxide undergoes a fully reversible, temperature-driven solid-state phase transition. Its smooth transition enabled them to engineer the temperature dependence of emissivity to precisely cancel out the intrinsic blackbody profile for both heating and cooling. The design results in temperature-independent thermally emitted power within the long-wave atmospheric transparency […]

Sound-redirecting prototype could fool eavesdroppers

Phys.org  November 12, 2019 Though the idea of engineering materials or surfaces to strategically refract sound waves is well-established, most existing designs are static. An international team of researchers (China, University of Nebraska) has designed a tunable metasurface with Helmholtz resonance. Moving sliders in the design allow full phase shift with a high transmission ratio in a broad frequency bandwidth. The design can be used for tunable wave front redirection, focusing with varying wavelengths and sound source illusion, as shown in numerical and experimental examples. The technique may be used in applications that range from magnifying signals to disorienting adversaries…read […]

Study opens a new route to achieving invisibility without using metamaterials

Phys.org  April 23, 2019 Researchers in Japan report a way of making a cylinder invisible without a cloak for monochromatic illumination at optical frequency including those visible to the human eye. Based on Mie scattering they looked for a region indicating very low scattering efficiency, which they knew would correspond to the cylinder’s invisibility and determined that in this region invisibility would occur when the refractive index of the cylinder ranges from 2.7 to 3.8. Natural materials such as silicon, aluminum arsenide and germanium arsenide, which are commonly used in semiconductor technology fall in this category. They found that the […]