Showing papers on "Reflection (physics) published in 2014"

Ultrasonic Guided Waves in Solid Media

Abstract: Preface Acknowledgments 1. Introduction 2. Dispersion principles 3. Unbounded isotropic and anisotropic media 4. Reflection and refraction 5. Oblique incidence 6. Waves in plates 7. Surface and subsurface waves 8. Finite element method for guided wave mechanics 9. The semi-analytical finite element method (SAFE) 10. Guided waves in hollow cylinders 11. Circumferential guided waves 12. Guided waves in layered structures 13. Source influence on guided wave excitation 14. Horizontal shear 15. Guided waves in anisotropic media 16. Guided wave phased arrays in piping 17. Guided waves in viscoelastic media 18. Ultrasonic vibrations 19. Guided wave array transducers 20. Introduction to guided wave nonlinear methods 21. Guided wave imaging methods Appendix A: ultrasonic nondestructive testing principles, analysis and display technology Appendix B: basic formulas and concepts in the theory of elasticity Appendix C: physically based signal processing concepts for guided waves Appendix D: guided wave mode and frequency selection tips.

Controllable transmission and total reflection through an impedance-matched acoustic metasurface

Abstract: A general design paradigm for a novel type of acoustic metasurface is proposed by introducing periodically repeated supercells on a rigid thin plate, where each supercell contains multiple cut-through slits that are filled with materials possessing different refractive indices but the same impedance as that of the host medium. When the wavelength of the incident wave is smaller than the periodicity, the direction of the transmitted wave with nearly unity transmittance can be chosen by engineering the phase discontinuities along the transverse direction. When the wavelength is larger than the periodicity, even though the metasurface is impedance matched to the host medium, most of the incident energy is reflected back and the remaining portion is converted into a surface-bound mode. We show that both the transmitted wave control and the high reflection with the surface mode excitation can be interpreted by a unified analytic model based on mode-coupling theory. Our general design principle not only supplies the functionalities of reflection-type acoustic metasurfaces, but also exhibits unprecedented flexibility and efficiency in various domains of wave manipulation for possible applications in fields like refracting, collimating, focusing or absorbing wave energy.

Optical magnetic mirrors without metals

Abstract: The reflection of an optical wave from metal, arising from strong interactions between the optical electric field and the free carriers of the metal, is accompanied by a phase reversal of the reflected electric field. A far less common route to achieving high reflectivity exploits strong interactions between the material and the optical magnetic field to produce a “magnetic mirror” that does not reverse the phase of the reflected electric field. At optical frequencies, the magnetic properties required for strong interaction can be achieved only by using artificially tailored materials. Here, we experimentally demonstrate, for the first time to the best of our knowledge, the magnetic mirror behavior of a low-loss all-dielectric metasurface at infrared optical frequencies through direct measurements of the phase and amplitude of the reflected optical wave. The enhanced absorption and emission of transverse-electric dipoles placed close to magnetic mirrors can lead to exciting new advances in sensors, photodetectors, and light sources.

Seismic reflector imaging using internal multiples with Marchenko-type equations

Abstract: We present an imaging method that creates a map of reflection coefficients in correct one-way time with no contamination from internal multiples using purely a filtering approach. The filter is computed from the measured reflection response and does not require a background model. We demonstrate that the filter is a focusing wavefield that focuses inside a layered medium and removes all internal multiples between the surface and the focus depth. The reflection response and the focusing wavefield can then be used for retrieving virtual vertical seismic profile data, thereby redatuming the source to the focus depth. Deconvolving the upgoing by the downgoing vertical seismic profile data redatums the receiver to the focus depth and gives the desired image. We then show that, for oblique angles of incidence in horizontally layered media, the image of the same quality as for 1D waves can be constructed. This step can be followed by a linear operation to determine velocity and density as a function of depth. Numerical simulations show the method can handle finite frequency bandwidth data and the effect of tunneling through thin layers.

Diffuse Mirrors: 3D Reconstruction from Diffuse Indirect Illumination Using Inexpensive Time-of-Flight Sensors

Abstract: The functional difference between a diffuse wall and a mirror is well understood: one scatters back into all directions, and the other one preserves the directionality of reflected light. The temporal structure of the light, however, is left intact by both: assuming simple surface reflection, photons that arrive first are reflected first. In this paper, we exploit this insight to recover objects outside the line of sight from second-order diffuse reflections, effectively turning walls into mirrors. We formulate the reconstruction task as a linear inverse problem on the transient response of a scene, which we acquire using an affordable setup consisting of a modulated light source and a time-of-flight image sensor. By exploiting sparsity in the reconstruction domain, we achieve resolutions in the order of a few centimeters for object shape (depth and laterally) and albedo. Our method is robust to ambient light and works for large room-sized scenes. It is drastically faster and less expensive than previous approaches using femtosecond lasers and streak cameras, and does not require any moving parts.

Optical broadband angular selectivity.

Abstract: Light selection based purely on the angle of propagation is a long-standing scientific challenge. In angularly selective systems, however, the transmission of light usually also depends on the light frequency. We tailored the overlap of the band gaps of multiple one-dimensional photonic crystals, each with a different periodicity, in such a way as to preserve the characteristic Brewster modes across a broadband spectrum. We provide theory as well as an experimental realization with an all-visible spectrum, p-polarized angularly selective material system. Our method enables transparency throughout the visible spectrum at one angle--the generalized Brewster angle--and reflection at every other viewing angle.

Optical Magnetic Mirrors without Metals

Abstract: The reflection of an optical wave from a metal, arising from strong interactions between the optical electric field and the free carriers of the metal, is accompanied by a phase reversal of the reflected electric field. A far less common route to achieve high reflectivity exploits strong interactions between the material and the optical magnetic field to produce a magnetic mirror which does not reverse the phase of the reflected electric field. At optical frequencies, the magnetic properties required for strong interaction can only be achieved through the use of artificially tailored materials. Here we experimentally demonstrate, for the first time, the magnetic mirror behavior of a low-loss, all-dielectric metasurface at infrared optical frequencies through direct measurements of the phase and amplitude of the reflected optical wave. The enhanced absorption and emission of transverse electric dipoles placed very close to magnetic mirrors can lead to exciting new advances in sensors, photodetectors, and light sources.

Optical Huygens' Metasurfaces with Independent Control of the Magnitude and Phase of the Local Reflection Coefficients

Abstract: Implementation of abrupt phase discontinuities along a surface has been the theme of recent research on electromagnetic metasurfaces. Simple functionalities such as reflecting, refracting, or focusing plane waves have been demonstrated with devices featuring phase discontinuities, but optical surfaces allowing independent magnitude and phase control on the scattered waves have yet to emerge. In this paper, we propose the first true optical Huygens’ surface, which explicitly utilizes orthogonal electric and magnetic responses to realize total control on an optical surface’s local reflection coefficients. This extends the functionality of metasurfaces to an unprecedented level. We first demonstrate that a nanorod gap-surface plasmon resonator can act as a Huygens’ source. Thereafter, by properly tuning and rotating these resonators, we realize arbitrary reflection optical metasurfaces—surfaces for which the local reflection coefficients can be independently tailored in both magnitude and phase. We demonstrate the versatility of this approach through designs of a metasurface that asymmetrically reflects two copolarized beams and a Dolph-Tschebyscheff optical reflectarray.

Material erosion monitoring system and method

Abstract: Disclosed is an improved system and method to evaluate the status of a material The system and method are operative to identify flaws and measure the erosion profile and thickness of different materials, including refractory materials, using electromagnetic waves The system is designed to reduce a plurality of reflections, associated with the propagation of electromagnetic waves launched into the material under evaluation, by a sufficient extent so as to enable detection of electromagnetic waves of interest reflected from remote discontinuities of the material Furthermore, the system and method utilize a configuration and signal processing techniques that reduce clutter and enable the isolation of electromagnetic waves of interest Moreover, the launcher is impedance matched to the material under evaluation, and the feeding mechanism is designed to mitigate multiple reflection effects to further suppress clutter

Reflection and transmission of plane waves at surfaces carrying material properties and embedded in second-gradient materials

Abstract: In this paper reflection and transmission of compression and shear waves at structured interfaces between second-gradient continua is investigated. Two semi-infinite spaces filled with the same sec...

The NuSTAR spectrum of Mrk 335: extreme relativistic effects within two gravitational radii of the event horizon?

Abstract: We present 3–50keV NuSTAR observations of the active galactic nuclei Mrk 335 in a very low flux state. The spectrum is dominated by very strong features at the energies of the iron line at 5–7keV and Compton hump from 10–30keV. The source is variable during the observation, withthevariabilityconcentratedatlowenergies,whichsuggestingeitherarelativisticreflection oravariableabsorptionscenario.Inthiswork,wefocusonthereflectioninterpretation,making use of new relativistic reflection models that self consistently calculate the reflection fraction, relativistic blurring and angle-dependent reflection spectrum for different coronal heights to model the spectra. We find that the spectra can be well fitted with relativistic reflection, and that the lowest flux state spectrum is described by reflection alone, suggesting the effects of extreme light-bending occurring within ∼2 gravitational radii (RG) of the event horizon. The reflection fraction decreases sharply with increasing flux, consistent with a point source moving up to above 10 RG as the source brightens. We constrain the spin parameter to greater than 0.9 at the 3σ confidence level. By adding a spin-dependent upper limit on the reflection fraction to our models, we demonstrate that this can be a powerful way of constraining the spin parameter, particularly in reflection dominated states. We also calculate a detailed emissivity profile for the iron line, and find that it closely matches theoretical predictions for a compact source within a few RG of the black hole.

On-board radar apparatus

Abstract: An on-board radar apparatus includes an antenna unit configured by combining one of a lens and a reflector, and a plurality of antenna elements, a transmission and reception unit configured to emit a radio wave using, for at least one of transmission or reception, a partial antenna of a plurality of patterns configured by the antenna elements that are part of the plurality of antenna elements, and to receive a reflection wave obtained by reflection of the radio wave from an object, and a detection unit configured to detect the object based on the reflection wave received by the transmission and reception unit.

Reflection and transmission of electromagnetic waves at a temporal boundary.

Abstract: We consider propagation of an electromagnetic (EM) wave through a dynamic optical medium whose refractive index varies with time. Specifically, we focus on the reflection and transmission of EM waves from a temporal boundary and clarify the two different physical processes that contribute to them. One process is related to impedance mismatch, while the other results from temporal scaling related to a sudden change in the speed of light at the temporal boundary. Our results show that temporal scaling of the electric field must be considered for light propagation in dynamic media. Numerical solutions of Maxwell’s equations are in full agreement with our theory.

Characterizing damage in CFRP structures using flash thermography in reflection and transmission configurations

Abstract: Carbon fiber reinforced polymer (CFRP) specimens with artificial delaminations and with impact damage have been characterized using active thermography with flash excitation. Systematic investigations have been performed in four different experimental configurations of flash lamps and infrared (IR) camera in transmission as well as in reflection alignment. It is shown here that the diffusivities determined for the sound and for the damaged areas give a good measure for damage characterization. Although reflection measurements also give information about defect depth, reflection measurements from only one side are not sufficient for assessing the whole cross section of the specimens. Thus, depending on sample thickness the lateral size of damage could only be determined from reflections measurements from both sides or from transmission measurements. In this paper, measurement accuracy and limits of flash thermography for the investigation of CFRP specimens are presented in detail together with quantitative data concerning the defects.

Green's function retrieval from reflection data, in absence of a receiver at the virtual source position

Abstract: The methodology of Green’s function retrieval by cross-correlation has led to many interesting applications for passive and controlled-source acoustic measurements. In all applications, a virtual source is created at the position of a receiver. Here a method is discussed for Green’s function retrieval from controlled-source reflection data, which circumvents the requirement of having an actual receiver at the position of the virtual source. The method requires, apart from the reflection data, an estimate of the direct arrival of the Green’s function. A single-sided three-dimensional (3D) Marchenko equation underlies the method. This equation relates the reflection response, measured at one side of the medium, to the scattering coda of a so-called focusing function. By iteratively solving the 3D Marchenko equation, this scattering coda is retrieved from the reflection response. Once the scattering coda has been resolved, the Green’s function (including all multiple scattering) can be constructed from the reflection response and the focusing function. The proposed methodology has interesting applications in acoustic imaging, properly accounting for internal multiple scattering.

Coherent control of Snell's law at metasurfaces

Abstract: It was recently demonstrated that the well-known Snell’s law must be corrected for phase gradient metasurfaces to account for their spatially varying phase, leading to normal and anomalous transmission and reflection of light on such metasurfaces. Here we show that the efficiency of normal and anomalous transmission and reflection of light can be controlled by the intensity or phase of a second coherent wave. The phenomenon is illustrated using gradient metasurfaces based on V-shaped and rectangular apertures in a metal film. This coherent control effect can be exploited for wave front shaping and signal routing.

Seismic isolation of two dimensional periodic foundations

Abstract: Phononic crystal is now used to control acoustic waves. When the crystal goes to a larger scale, it is called periodic structure. The band gaps of the periodic structure can be reduced to range from 0.5 Hz to 50 Hz. Therefore, the periodic structure has potential applications in seismic wave reflection. In civil engineering, the periodic structure can be served as the foundation of upper structure. This type of foundation consisting of periodic structure is called periodic foundation. When the frequency of seismic waves falls into the band gaps of the periodic foundation, the seismic wave can be blocked. Field experiments of a scaled two dimensional (2D) periodic foundation with an upper structure were conducted to verify the band gap effects. Test results showed the 2D periodic foundation can effectively reduce the response of the upper structure for excitations with frequencies within the frequency band gaps. When the experimental and the finite element analysis results are compared, they agree well with each other, indicating that 2D periodic foundation is a feasible way of reducing seismic vibrations.

Reflectivity Spectra for Commonly Used Reflectors

Abstract: Reflectivity Spectra for Commonly Used Reflectors Martin Janecek Abstract—Monte Carlo simulations play an important role in developing and evaluating the performance of radiation detection systems. To accurately model a reflector in an optical Monte Carlo simulation, the reflector’s spectral response has to be known. We have measured the reflection coefficient for many commonly used reflectors for wavelengths from 250 nm to 800 nm. The reflectors were also screened for fluorescence and angular distribution changes with wavelength. The reflectors examined in this work include several polytetrafluoroethylene (PTFE) reflectors, Spectralon, GORE diffuse reflector, titanium dioxide paint, magnesium oxide, nitrocellulose filter paper, Tyvek paper, Lumirror, Melinex, ESR films, and aluminum foil. All PTFE films exhibited decreasing reflectivity with longer wavelengths due to transmission. To achieve reflectivity in the 380 to 500 nm range, the PTFE films have to be at least 0.5 mm thick—nitrocellulose is a good alternative if a thin diffuse reflector is needed. Several of the reflectors have sharp declines in reflectivity below a cut-off wavelength, including (420 nm), ESR film (395 nm), nitrocellulose (330 nm), Lumirror (325 nm), and Melinex (325 nm). PTFE-like reflectors were the only examined reflectors that had reflectivity above 0.90 for wavelengths below 300 nm. Lumirror, Melinex, and ESR film exhibited fluorescence. Lumirror and Melinex are excited by wavelengths between 320 and 420 nm and have their emission peaks located at 440 nm, while ESR film is excited by wavelengths below 400 nm and the emission peak is located at 430 nm. Lumirror and Melinex also exhibited changing angular distributions with wavelength. Index Terms—Fluorescence, Lambertian reflection, reflection coefficient, specular reflection. I. I NTRODUCTION S cintillating crystals emit light in a broad range of wavelengths, with many of them having their peak emissions located between 375 and 480 nm [1-6]. In order to convert this optical signal into a sizable electrical signal, the light has to be directed into a photodetector by the means of surrounding the scintillating crystal with a reflective material. This reflector should maximize the light collection and the reflector has to be chosen to provide high reflection coefficients at the scintillator’s emission wavelengths. Monte Carlo simulations play an important role in developing and evaluating the performance of radiation detection systems. The simulations offer a way of evaluating the system as a whole by exploring system parameters without the added cost of constructing the system or any of its Manuscript received September 23, 2011; revised December 14, 2011; accepted January 04, 2012. This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The author is with the Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA (phone: 510-486-5579; fax: 510-486-4768; e-mail: mjanecek@lbl.gov). Fig. 1. Schematic of an integrating sphere. Note that the light enters at a slight angle in relation to the examined sample (~8o) in order to be able to detect the specular reflection from the sample. The inside surface of the integrating sphere is coated with a diffuse reflector creating a uniform angular distribution at the photodetector. To force the light to reflect multiple times within the integrated sphere, baffles (i.e., light barriers) are located between the illuminated sample and the photodetector as well between the in-port and the photodetector, eliminating any direct optical paths. components. For these simulations, the reflection’s angular distribution [7] and the reflection coefficient (as a function of wavelength) has to be known for the results to be accurate. Reflectivity measurements are generally performed with an integrating sphere, where the entire angular distribution of the reflected light is collected and thus contributes to the photodetector response. As the light is reflected many times within the integrating sphere before detection, it is important to coat the inside of the sphere with a highly reflective “white” material. The reflection data acquired using this technique do not always provide sufficient information to perform an accurate Monte Carlo simulation — some reflectors are fluorescent or change their angular reflectance distributions with incidence angle. Integrating sphere materials include barium sulfate (BaSO 4 ) [8-14], magnesium oxide (MgO) [8, 11-17], and polytetrafluorethylene (PTFE) based reflectors [18-20], and these reflector materials have been extensively studied. Other reflectors that are frequently used in optical systems include titanium dioxide (TiO 2 ) paint [11, 16, 21], Tyvek ® paper [22, 23], ESR (Enhanced Specular Reflector) film [24, 25], and Spectralon [19, 26]. In addition, some commonly used reflectors have not been reported on in the literature, including nitrocellulose, GORE ® , Lumirror ® , and Melinex ® . The aim of this work is to measure the reflection coefficients as a function of wavelength for the most common reflectors used in the radiation detection field, and to screen them for fluorescence and angular distribution changes with wavelength.

Full Transmission and Reflection of Waves Propagating through a Maze of Disorder

Abstract: Thirty years ago, theorists showed that a properly designed combination of incident waves could be fully transmitted through (or reflected by) a disordered medium, based on the existence of propagation channels which are essentially either closed or open (bimodal law). In this Letter, we study elastic waves in a disordered waveguide and present direct experimental evidence of the bimodal law. Full transmission and reflection are achieved. The wave field is monitored by laser interferometry and highlights the interference effects that take place within the scattering medium.

Tailoring Reflections From Thin Composite Metamirrors

Abstract: We propose an effective route to fully control the phase of plane waves reflected from electrically (optically) thin composite sheets. This becomes possible using engineered artificial full-reflection layers (metamirrors) formed by arrays of electrically small resonant bi-anisotropic particles. In this scenario, fully reflecting mirrors do not contain any continuous ground plane, but only arrays of small particles. Bi-anisotropic omega coupling is required to get asymmetric response in reflection phase for plane waves incident from the opposite sides of the composite mirror. It is shown that with this concept one can independently tailor the phase of electromagnetic waves reflected from both sides of the mirror array.

An x-ray spectral model for clumpy tori in active galactic nuclei

Abstract: We construct an X-ray spectral model for the clumpy torus in an active galactic nucleus (AGN) using Geant4, which includes the physical processes of the photoelectric effect, Compton scattering, Rayleigh scattering, gamma conversion, fluorescence line, and Auger process. Since the electrons in the torus are expected to be bounded instead of free, the deviation of the scattering cross section from the Klein-Nishina cross section has also been included, which changes the X-ray spectra by up to 25% below 10 keV. We have investigated the effect of the clumpiness parameters on the reflection spectra and the strength of the fluorescent line Fe K alpha. The volume filling factor of the clouds in the clumpy torus only slightly influences the reflection spectra, however, the total column density and the number of clouds along the line of sight significantly change the shapes and amplitudes of the reflection spectra. The effect of column density is similar to the case of a smooth torus, while a small number of clouds along the line of sight will smooth out the anisotropy of the reflection spectra and the fluorescent line Fe K alpha. The smoothing effect is mild in the low column density case (N-H = 10(23) cm(-2)), whereas it is much more evident in the high column density case (N-H = 10(25) cm(-2)). Our model provides a quantitative tool for the spectral analysis of the clumpy torus. We suggest that the joint fits of the broad band spectral energy distributions of AGNs (from X-ray to infrared) should better constrain the structure of the torus.

Paper‐Based Anti‐Reflection Coatings for Photovoltaics

Abstract: DOI: 10.1002/aenm.201301804 coatings are manufactured by fi lm deposition techniques such as chemical vapor deposition (CVD), sputtering, or evaporation, which have many disadvantages in terms of cost and the possibility of high temperature environments that are unsuitable for certain solar cell architectures. Thus, how cheaply and easily these layers can be made and how effective they are is of signifi cant importance to future PV technologies. One alternative to thin-fi lm anti-refl ection coatings is the use of metal or dielectric nanostructures. [ 3–22 ] The scattering properties of metal nanoparticles can be tuned by modifying their size, shape, or the surrounding environment and can lead to preferential forward scattering when placed on top of a high index substrate, such as a solar cell. [ 23 ] High index dielectric or semiconductor scattering objects can also yield improved forward scattering via coupling to Mie resonances. [ 4,24 ] These structures have shown improved anti-refl ection characteristics; however, they are generally more complicated to fabricate, as they rely on subwavelength structures that require microand nano-scale lithography. To circumvent the aforementioned diffi culties, we present the use of an inexpensive and easy to process transparent paper for anti-refl ection coatings. The transparent paper, consisting of cellulose fi bers, is used to reduce the index contrast between air and the semiconducting absorber layer, which ultimately increases light absorption within the solar cell. Furthermore, surface texturing of the cellulose leads to angle insensitive behavior over all wavelengths under consideration. Because of the ease of this process, the approach described here is a potential candidate for next generation ARCs that replace the conventional coatings, which rely on high-cost, vacuum deposition methods. Additionally, these cellulose materials are lightweight, fl exible, and recyclable. These properties have allowed for the recent use of cellulose papers as substrates for polymer solar cells and batteries. [ 25–30 ] These renewable and sustainable materials have good mechanical properties, low densities, low thermal expansion, tunable optical properties, and low toxicity. [ 25,31–39 ]

Transmission channels for light in absorbing random media: from diffusive to ballistic-like transport

Abstract: While the absorption of light is ubiquitous in nature and in applications, the question remains how absorption modifies the transmission channels in random media. We present a numerical study on the effects of optical absorption on the maximal transmission and minimal reflection channels in a two-dimensional disordered waveguide. In the weak absorption regime, where the system length is less than the diffusive absorption length, the maximal transmission channel is dominated by diffusive transport and it is equivalent to the minimal reflection channel. Its frequency bandwidth is determined by the underlying quasimode width. However, when the absorption is strong, light transport in the maximal transmission channel undergoes a sharp transition and exhibits ballistic-like transport. Its frequency bandwidth increases with absorption, and the exact scaling varies with the sample's realization. The minimal reflection channel becomes different from the maximal transmission channel and becomes dominated by absorption. Counterintuitively, we observe in some samples that the minimum reflection eigenvalue increases with absorption. Our results show that strong absorption turns open channels in random media from diffusive to ballistic-like transport.

Understanding Midlatitude Jet Variability and Change Using Rossby Wave Chromatography: Poleward-Shifted Jets in Response to External Forcing

Abstract: Rossby wave chromatography (RWC) is implemented in a linearized barotropic model as a tool to understand the response of the midlatitude jet to external forcing. Given the background zonal-mean flow and the space‐time structure of the baroclinic wave activity source, RWC calculates the space‐time structure of the upper-tropospheric eddy momentum fluxes. RWC is used to diagnose and understand the poleward shift of the jet in an idealized GCM using the convergence of the vertical EP flux in the upper troposphere as the wave activity source. The poleward-shifted jet is maintained via a selective ‘‘reflecting level’’ on the poleward flank of jet: for a given wavenumber, low phase speed waves are reflected but high phase speed waves are absorbed at the critical level on the polewardflank of jet. When the zonal-mean zonal wind increases on the polewardflank of the jet, a wider range of poleward-propagating waves encounter a reflecting level instead of a critical level on the poleward flank. The increased wave reflection leads to increased equatorward-propagating waves (and, therefore, poleward momentum flux) across the jet. Increases in wave phase speeds directly oppose the poleward shift because, in addition to the well-recognized effect of phase speed on wave dissipation in the subtropics, increased phase speeds imply more wave dissipation rather than reflection on the poleward flank via the selective reflecting level.

Tailoring reflections from thin composite metamirrors

Abstract: We propose an effective route to fully control the phase of plane waves reflected from electrically (optically) thin sheets. This becomes possible using engineered artificial full-reflection layers (metamirrors) as arrays of electrically small resonant bi-anisotropic particles. In this scenario, fully reflecting mirrors do not contain any continuous ground plane, but only arrays of small particles. Bi-anisotropic omega coupling is required to get asymmetric response in reflection phase for plane waves incident from the opposite sides of the composite mirror. It is shown that with this concept one can independently tailor the phase of electromagnetic waves reflected from both sides of the mirror array.