3D printed metamaterial can cause energy gain

Hao Xin, a professor of electrical and computer engineering, has discovered synthetic materials which might one day be used to build microscopes with superlenses and even ‘shields’ which could render military equipment and people invisible to the naked eye.

Xin uses metamaterial building blocks and 3D printing to create startling results.

These metamaterials, which can be made via 3D printing from plastics, metals, and a variety of other substances, look a bit like porous plastic balls, tubes, and tiny copper wire circuit boards, but it’s their specialized geometrical patterns which give them their amazing properties. The metamaterial structures can bend waves of energy in unheard of ways so that they exhibit a property called ‘negative refraction.’

One of the biggest problems with metamaterials is that they produce energy loss. The waves decay as they pass through the artificial material,” Xin says. “We have designed a metamaterial that retains negative refraction but does not diminish energy.”

The synthetic material constructs do more than prevent energy loss. Xin says they actually cause energy gain, and at least in the case of microwaves, intensify the strength of waves as they passed through this novel material via embedded, battery-powered tunnel diodes and the advantages of micro-nanofabrication techniques.

Nature Communications – Microwave gain medium with negative refractive index

Abstract – Microwave gain medium with negative refractive index

Artificial effective media are attractive because of the fantastic applications they may enable, such as super lensing and electromagnetic invisibility. However, the inevitable loss due to their strongly dispersive nature is one of the fundamental challenges preventing such applications from becoming a reality. In this study, we demonstrate an effective gain medium based on negative resistance, to overcompensate the loss of a conventional passive metamaterial, meanwhile keeping its original negative-index property. Energy conservation-based theory, full-wave simulation and experimental measurement show that a fabricated sample consisting of conventional sub-wavelength building blocks with embedded microwave tunnel diodes exhibits a band-limited Lorentzian dispersion simultaneously with a negative refractive index and a net gain. Our work provides experimental evidence to the assertion that a stable net gain in negative-index gain medium is achievable, proposing a potential solution for the critical challenge current metamaterial technology faces in practical applications.

Other research – Rochester Cloak for invisibility in the visible spectrum

Arxiv – Paraxial ray optics cloaking

Abstract: Despite much interest and progress in optical spatial cloaking, a three-dimensional (3D), transmitting, continuously multidirectional cloak in the visible regime has not yet been demonstrated. Here we experimentally demonstrate such a cloak using ray optics, albeit with some edge effects. Our device requires no new materials, uses isotropic off-the-shelf optics, scales easily to cloak arbitrarily large objects, and is as broadband as the choice of optical material, all of which have been challenges for current cloaking schemes. In addition, we provide a concise formalism that quantifies and produces perfect optical cloaks in the small-angle (‘paraxial’) limit.

Rochester researchers have defined what a perfect cloak should do in ray optics. They then provided a sufficient and necessary algebraic condition for a perfect cloak in the first-order, or paraxial, approximation. They finally derived a device that fits this definition, and experimentally demonstrated two cloaks for continuous ranges of directions. In addition to hiding an object, these cloaking devices can also make an object behind a barrier visible, or deflect light rays. Transformation optics and quasiconformal mapping are general formalisms used for cloaking fields. Here we provided another formalism that can effectively describe ray optics invisibility.

SOURCES – Youtube, Arxiv, Nature Communication, 3DPrint