Acoustic holographic metamaterials present a powerful new platform for manipulating acoustic wave fields in fluids and solids. Furthering their development, we introduce a new concept of multi-holographic metamaterials (MHM)—complex media storing multiple volumetric holograms. Such media lack any distributed electromechanical components, yet offer dynamic functionality using only a few electronic components. This novel engineering paradigm shifts device fabrication cost from hardware to computation, presenting the designer with an NP-hard problem of resolving the complex relationship between structure and physical properties. Focused on airborne ultrasonic metamaterials, we treat them as a free-form composite of a fluid and solid(s). This unlocks a huge number of structural degrees of freedom, compared to the standard treatment of metamaterials as periodic arrays of geometrically similar unit cells. While analytical methods for finding all optima of an analytical function are scarce and largely impractical (Groebner basis computation being a notable example), we turn to machine learning methodologies to design MHMs efficiently. We show that unsupervised machine learning, a basic form of Artificial Intelligence, can completely replace human input into the design of MHMs. Experimental demonstrations include airborne ultrasonic metamaterials for coherent beamforming, with applications ranging from directive speakers to contactless manipulation of objects.

We present a 5.8 GHz Fresnel-zone microwave wireless power transfer experiment leveraging a large planar holographic metasurface reflectarray to form a focused spot at a distance of 6.5 m. The 1.5 m 2 holographic metasurface is fabricated from 15 panels having total dimensions of 122×127 cm, and is comprised of over 4,000 reflective patch resonators on the top surface of a 3.0 mm thick FR-4 substrate. A constrained hologram approach is used to discretize the desired hologram and approximate the desired focal spot given the Lorentzian coupled amplitude-phase response of the patch resonators. When the metasurface is illuminated by a 20 dB standard-gain horn 1.8 m away, it produces a spot with a 3 dB beam waist (FWHM) of approximately 50 cm. The experimentally measured beam profile matches the simulated beam profile to ± 1 dB within the beam, and we estimate almost 40% of the transmitted power was incident onto the receiver at the focus point.

Theory and practical implementations for wake-free propulsion systems are proposed and proven with computational fluid dynamic modeling. Introduced earlier, the concept of active hydrodynamic metamaterials is advanced by introducing magnetohydrodynamic metamaterials, structures with custom-designed volumetric distribution of Lorentz forces acting on a conducting fluid. Distributions of volume forces leading to wake-free, laminar flows are designed using multivariate optimization. Theoretical indications are presented that such flows can be sustained at arbitrarily high Reynolds numbers. Moreover, it is shown that in the limit Re≫10^{2}, a fixed volume force distribution may lead to a forced laminar flow across a wide range of Re numbers, without the need to reconfigure the force-generating metamaterial. Power requirements for such a device are studied as a function of the fluid conductivity. Implications to the design of distributed propulsion systems underwater and in space are discussed.

Wireless power transfer (WPT) has been an active topic of research, with a number of WPT schemes implemented in the near-field (coupling) and far-field (radiation) regimes. Here, we consider a beamed WPT scheme based on a dynamically reconfigurable source aperture transferring power to receiving devices within the Fresnel region. In this context, the dynamic aperture resembles a reconfigurable lens capable of focusing power to a well-defined spot, whose dimension can be related to a point spread function. The necessary amplitude and phase distribution of the field imposed over the aperture can be determined in a holographic sense, by interfering a hypothetical point source located at the receiver location with a plane wave at the aperture location. While conventional technologies, such as phased arrays, can achieve the required control over phase and amplitude, they typically do so at a high cost; alternatively, metasurface apertures can achieve dynamic focusing with potentially lower cost. We present an initial tradeoff analysis of the Fresnel region WPT concept assuming a metasurface aperture, relating the key parameters such as spot size, aperture size, wavelength, and focal distance, as well as reviewing system considerations such as the availability of sources and power transfer efficiency. We find that approximate design formulas derived from the Gaussian optics approximation provide useful estimates of system performance, including transfer efficiency and coverage volume. The accuracy of these formulas is confirmed through numerical studies.

Optical metamaterials with an artificial subwavelength structure offer new approaches to implement advanced optical devices. However, some of the biggest challenges associated with the development of metamaterials in the visible spectrum are the high costs and slow production speeds of the nanofabrication processes. Here, we demonstrate a macroscale (>35 mm) transformation-optics wave bender (293 mm 2 ) and Luneburg lens (855 mm 2 ) in the broadband white-light visible wavelength range using the concept of elasto-optic metamaterials that combines optics and solid mechanics. Our metamaterials consist of mesoscopically homogeneous chunks of bulk aerogels with superior, broadband optical transparency across the visible spectrum and an adjustable, stress-tuneable refractive index ranging from 1.43 down to nearly the free space index (∼1.074). The experimental results show that broadband light can be controlled and redirected in a volume of >10 5 λ × 10 5 λ × 10 3 λ , which enables natural light to be processed directly by metamaterial-based optical devices without any additional coupling components.

Acoustic metamaterial structures with discrete and continuous rotational symmetries attract interest of theorists and engineers due to the relative simplicity of their design and fabrication. They are also likely candidates for omnidirectional acoustic cloaking and other transformation-acoustical novelties. In this paper, we employ a stratified description of such structures, and develop the theory and an efficient symbolic/numerical algorithm for analyzing the scattering properties of such structures immersed in homogeneous fluid environments. The algorithm calculates the partial scattering amplitudes and the related scattering phases for an arbitrary layered distribution of acoustic material properties. The efficiency of the algorithm enables us to find approximate solutions to certain inverse scattering problems through quasi-global optimization. The scattering problems addressed here are the three forms of cloaking: (1) extinction cross-section suppression, the canonical form of cloaking, (2) monostatic sonar invisibility (backscattering suppression), and (3) acoustic force cloaking (transport cross-section suppression). We also address the efficiency-bandwidth tradeoff and design approximate cloaks with wider bandwidth using a new optimization formulation.

Wake reduction is a crucial link in the chain leading to undetectable watercraft. Here, we explore a volumetric approach to controlling the wake in a stationary flow past cylindrical and spherical objects. In this approach, these objects are coupled with rigid, fluid-permeable structures prescribed by a macroscopic design approach where all solid boundaries are parameterized and modeled explicitly. Local, gradient-based optimization is employed which permits topological changes in the manifold describing the composite solid component(s) while still allowing the use of adjoint optimization methods. This formalism works below small Reynolds number (Re) turbulent flow (Re≈100–10,000) when simulated using small Reynolds-averaged Navier-Stokes (RANS) models. The output of this topology optimization yields geometries that can be fabricated immediately using fused deposition modeling (FDM). Our prototypes have been verified in an experimental water tunnel facility, where the use of Particle Image Velocimetry (PIV) described the velocity profile. Comparisons with our computational models show excellent agreement for the spherical shapes and reasonable match for cylindrical shapes, with well-understood sources of error. Two important figures of merit are considered: domain-wide wake (DWW) and maximum local wake (MLW), metrics of the flow field disturbance whose definitions are described.

The control of quasi-static magnetic fields is of considerable interest in applications including the reduction of electromagnetic interference (EMI), wireless power transfer (WPT) and magnetic resonance imaging (MRI). The shielding of static or quasi-static magnetic fields is typically accomplished through the use of inherently magnetic materials with large magnetic permeability, such as ferrites, used sometimes in combination with metallic sheets and/or active field cancellation. Ferrite materials, however, can be expensive, heavy and brittle. Inspired by recent demonstrations of epsilon-, mu- and index-near-zero metamaterials, here we show how a longitudinal mu-near-zero (LMNZ) layer can serve as a strong frequency-selective reflector of magnetic fields when operating in the near-field region of dipole-like sources. Experimental measurements with a fabricated LMNZ sheet constructed from an artificial magnetic conductor – formed from non-magnetic, conducting, metamaterial elements – confirm that the artificial structure provides significantly improved shielding as compared with a commercially available ferrite of the same size. Furthermore, we design a structure to shield simultaneously at the fundamental and first harmonic frequencies. Such frequency-selective behavior can be potentially useful for shielding electromagnetic sources that may also generate higher order harmonics, while leaving the transmission of other frequencies unaffected.

We explore the possibility of controlling the wake and drag of a spherical object independently of each other, using radial distributions of permeability in the Brinkman-Stokes formalism. By discretizing a graded-permeability shell into discrete, macroscopically homogeneous layers, we are able to sample the entire functional space of spherically-symmetric permeabilities and observe quick convergence to a certain manifold in the wake-drag coordinates. Monte Carlo samplings with 10^{4}-10^{5} points have become possible thanks to our new algorithm, which is based on exact analytical solutions for the Stokes flow through an arbitrary multilayer porous sphere. The algorithm is not restricted to the Brinkman-Stokes equation and can be modified to account for other types of scattering problems for spherically-symmetric systems with arbitrary radial complexity. Our main practical finding for Stokes flow is that it is possible to reduce a certain measure of wake of a spherical object without any energy penalty and without active (power-consuming) force generation.

Embodiments disclosed herein relate to an interactive surgical drape and system including at least one sensor and at least one controller that operates indicating sensing feedback from the at least one sensor to cause display of information on a dynamic display integrated with the interactive surgical drape. The dynamic display assists the surgical team while performing surgery and can operate to improve the efficiency and/or effectiveness of the surgical team.

The ability to wirelessly power electrical devices is becoming of greater urgency as a component of energy conservation and sustainability efforts. Due to health and safety concerns, most wireless power transfer (WPT) schemes utilize very low frequency, quasi-static, magnetic fields; power transfer occurs via magneto-inductive (MI) coupling between conducting loops serving as transmitter and receiver. At the "long range" regime - referring to distances larger than the diameter of the largest loop - WPT efficiency in free space falls off as (1/d)(6); power loss quickly approaches 100% and limits practical implementations of WPT to relatively tight distances between power source and device. A "superlens", however, can concentrate the magnetic near fields of a source. Here, we demonstrate the impact of a magnetic metamaterial (MM) superlens on long-range near-field WPT, quantitatively confirming in simulation and measurement at 13-16 MHz the conditions under which the superlens can enhance power transfer efficiency compared to the lens-less free-space system.

Synergistic integration of electromagnetic (EM) and mechanical properties of metamaterials, a concept known as smart metamaterials, promises new applications across the spectrum, from flexible waveguides to shape-conforming cloaks. These applications became possible thanks to smart transformation optics (STO), a design methodology that utilizes coordinate transformations to control both EM wave propagation and mechanical deformation of the device. Here, we demonstrate several STO devices based on extremely auxetic (Poisson ratio −1) elasto-electromagnetic metamaterials, both of which exhibit enormous flexibility and sustain efficient operation upon a wide range of deformations. Spatial maps of microwave electric fields across these devices confirm our ability to deform carpet cloaks, bent waveguides and potentially other quasi-conformal TO-based devices operating at 7 ~ 8 GHz. These devices are each fabricated from a single sheet of initially uniform (double-periodic) square-lattice metamaterial, which acquires the necessary distribution of effective permittivity entirely from the mechanical deformation of its boundary. By integrating transformation optics and continuum mechanics theory, we provide analytical derivations for the design of STO devices. Additionally, we clarify an important point relating to two-dimensional STO devices: the difference between plane stress and plane strain assumptions, which lead to elastic metamaterials with Poisson ratio −1 and −∞, respectively.

Axisymmetric radiating and scattering structures whose rotational invariance is broken by non-axisymmetric excitations present an important class of problems in electromagnetics. For such problems, a cylindrical wave decomposition formalism can be used to efficiently obtain numerical solutions to the full-wave frequency-domain problem. Often, the far-field, or Fraunhofer region is of particular interest in scattering cross-section and radiation pattern calculations; yet, it is usually impractical to compute full-wave solutions for this region. Here, we propose a generalization of the Stratton-Chu far-field integral adapted for 2.5D formalism. The integration over a closed, axially symmetric surface is analytically reduced to a line integral on a meridional plane. We benchmark this computational technique by comparing it with analytical Mie solutions for a plasmonic nanoparticle, and apply it to the design of a three-dimensional polarization-insensitive cloak.

We report stereolithographic polymer-based fabrication and experimental operation of a microwave X-band cloaking device. The device is a relatively thin (about one wavelength thick) shell of an air-dielectric composite, in which the dielectric component has negligible loss and dispersion. In a finite band (9.7-10.1 GHz), the shell eliminates the shadow and strongly suppresses scattering from a conducting cylinder of six-wavelength diameter for TE-polarized free-space plane waves. The device does not require an immersion liquid or conducting ground planes for its operation. The dielectric constant of the polymer is low enough (ε=2.45) to suggest that this cloaking technique would be suitable for higher frequency radiation, including visible light.

We introduce a microwave cloak composed of smart metamaterials whose electromagnetic properties can be effectively changed by mechanical deformation. Against mechanical deformations, our smart metamaterials self-adjust own flexible elasto-electromagnetic crystal structure for obeying transformation optics rules. With this idea, we built microwave cloak made of flexible silicone rubber tube array and experimentally demonstrated self-adjustable carpet cloak in broadband ranges (8-12GHz) with variable deformations.