Cylindrical Concave Research Articles

Reflective photonic nanojets generated from cylindrical concave micro-mirrors

Reflective photonic nanojets (r-PNJs) produced by cylindrical concave micro-mirrors are numerically investigated. Simulation shows that the full-width at half-maximum (FWHM) of the r-PNJ is associated with the angle of the cylindrical concave mirror. It is found that the FWHM of the r-PNJ can achieve 0.37 of the wavelength, when the mirror with the angle θ = 130° is put in air. For the concave mirror immersed in water with θ = 100°, the FWHM of the r-PNJ can reach about 0.3λ. Two symmetric vortexes of Poynting vectors are close to the r-PNJ, which leads to the narrowed r-PNJ. Through combining a dielectric micro-cylinder with the concave mirror immersed in water, the waist of the r-PNJ can achieve 0.27 of the incident wavelength.

Miniaturized multi-pass cell based photoacoustic gas sensor for parts-per-billion level acetylene detection

A highly sensitive photoacoustic (PA) gas sensor using a miniaturized Herriott-type multi-pass cell is reported. A cylindrical concave mirror and a cylindrical planar mirror are utilized as the two reflectors of the Herriott cell. The total length of optical path is optimized to be 0.609 m with 29 reflections. To eliminate the effect of the cell wall absorption, we employ the second-harmonic (2f) wavelength modulation spectroscopy (2f-WMS) method. Trace acetylene (C2H2) was introduced into the PA cell to investigate the performance of the sensor. Experimental results show that this gas sensor has an excellent linear characteristic and a long-term stability. Allan-Werle deviation analysis results show that the minimum detection concentration (MDC) is calculated as 12.2 ppb with a 400-s average time. Moreover, a normalized noise-equivalent absorption (NNEA) coefficient was achieved to be 3.3 × 10−9 Wcm-1 Hz-1/2.

Effect of bending and padding on the electromagnetic performance of a laser-cut fabric patch antenna

A fabrication and characterization procedure is detailed for a flexible planar antenna integrated into textiles by interfacing thin metal-coated fabric sheets on a polyester fabric substrate. From the full-wave electromagnetic simulations and measurements, it is observed that the low dielectric dissipation in the porous woven polyester enables the fabric antenna to achieve a high gain of 8.4 dBi. It is comparable to other antennas fabricated with engineered substrates of low-loss polymer composites. Using this antenna, the impact of cylindrical concave bending deformation is observed in terms of the impedance matching and radiation performance. The simulated and measured results agree reasonably well. A 1.2% frequency shift is observed when the antenna is bent concavely along its length, while bending along its width showed only a marginal impact. On the other hand, the gain is reduced by as much as 1.0 and 0.5 dB when the antenna is bent along its length and width, respectively. The impact of padding layers was also investigated when placed above the radiating patch and below the ground plane. Because the textile padding layers have complex permittivity closer to air due to their highly porous structure, it is expected to observe only small influence on the radiation performance. However, the simulations and measurements show that padding the radiating patch lowers both the operating frequency and the realized gain by up to 1.6% and by up to 0.9 dB, respectively, due to dielectric loading and dissipation.

Acoustic Power Measurement for a Cylindrical Concave Transducer by using the Self-Reciprocity Method

A novel solution of measuring the acoustic power for a convergent cylindrical wave is proposed based on the self-reciprocity method, which turns the acoustic-power measurement to an electrical-parameters measurement. The formula for estimating the acoustic power was derived for a cylindrical concave transducer. The diffraction and the reflection corrections were also investigated for the precise measurement of the acoustic power. The performance of this method was compared with that of the radiation force balance (RFB) method. The experimental results showed good agreement. Moreover, the self-reciprocity method is more robust to the environment than the traditional RFB method and in practice can be extended to low-level acoustic power measurements.

Existence and Nonexistence for Elliptic Equation with Cylindrical Potentials, Subcritical Exponent and Concave Term

In this paper, we consider the existence and nonexistence of non-trivial solutions to elliptic equations with cylindrical potentials, concave term and subcritical exponent. First, we shall obtain a local minimizer by using the Ekeland’s variational principle. Secondly, we deduce a Pohozaev-type identity and obtain a nonexistence result.

Analysis of the reflected image by the cylindrical concave surface of the mobile display

AbstractReflection from the display surface affects the user's viewing experience. Cylindrical concave displays had been reported to be used for TV and mobile smart phone. The position and magnification of reflection at the curved mobile display were determined by the user's position and the focal distance of the cylindrical concave surface of the curved display. If the focal position of the curved surface was smaller or nearer to the user position, the enlarged reflection of the user would block the lights from the surrounding, and the curved display would be effective to reduce the inconvenience due to reflection. As the curvature of the cylindrical surface was different for the vertical and horizontal directions, the reflected image was not located at one distance. Hence, the refractive power of the eye of the user would be difficult to adjust to the position of the reflected image, and the reflected image would look defocused or hazed even for the display surface of the specular reflection.

Numerical simulation and design of a thermomagnetic motor

The increasing demand for energy has driven society to explore different energy sources, seeking to achieve sustainability. In this sense, we have focused to design a rotary motor using solar power with similar working principle as a Curie wheel. This paper describes the modeling, simulation and design of a Curie thermomagnetic motor. Three materials were analyzed for the rotor, out of which two of them present a second order phase transition a 30% FeNi alloy and Gd, and the MnAs that presents a first order transition. In addition, the heat transfer inherent to the conversion process of solar energy and natural convection were studied utilizing a one-dimensional finite difference model, and the best performance for the assumed initial conditions for the motor for all materials was with a convention coefficient of 10 W/(m2 K). A model for the magnetic circuit was also developed. It could be verified that Gd and MnAs offers about one order of magnitude more power when compared to 30% NiFe alloy. An experimental bench engine prototype was also designed, but not built, utilizing the same parameter values and considerations applied to the simulation, in order to fit it with the mathematical model. Moreover, a cylindrical concave mirror and mechanism was designed to harness the needed solar energy, which can be adjusted to keep incident solar rays always perpendicular to the mirror.

Radiation force calculation and acoustic power measurement for a cylindrical concave transducer based on the ray acoustic model

New relationships between the radiation force and the acoustic power for a cylindrical concave transducer were derived based on the ray acoustic model. The performance of this model is compared with that of the far-field integration model. The numerical results showed excellent agreement. Thus, these two models can be applied in the correction of measured results. Moreover, the formula based on the ray acoustic model can be applied more widely in practice because of its simplicity. The experimental results demonstrated further the reliability of the relationships between the radiation force and the acoustic power in theory, and the feasibility of using cylindrical concave transducers based on the ray acoustic model in practice.

Superscatterer: Enhancement of scattering with complementary media

Based on the concept of complementary media, we propose a novel design which can enhance the electromagnetic wave scattering cross section of an object so that it looks like a scatterer bigger than the scale of the device. Such a "superscatterer" is realized by coating a negative refractive material shell on a perfect electrical conductor cylinder. The scattering field is analytically obtained by Mie scattering theory, and confirmed by full-wave simulations numerically. Such a device can be regarded as a cylindrical concave mirror for all angles.

Novel time-domain asymptotic solution for transient whispering-gallery mode radiation from a cylindrical concave conducting boundary

We derive a novel time-domain asymptotic solution for a transient whispering-gallery (WG) mode radiation from the aperture plane of a cylindrical concave conducting boundary. The WG mode is excited by a Gaussian-type modulated pulse source. We show that the WG mode radiation field propagates with the phase velocity coincident with the speed of light and the newly derived group velocity. The validity of the time-domain asymptotic solution is confirmed by comparing with the reference solution calculated numerically. We show that the asymptotic solution proposed here is easy to understand the physical phenomena of the transient WG mode radiation field.

Nonstationary shock reflection over nonstraight surfaces: an approach with a method of multiple steps

Shock reflection phenomena over nonstraight surfaces have been investigated. The models used in this experiment are ordinary circular cylindrical concave and convex wedges and step-like wedges which simulate the former. The step-like wedges were used to investigate the process of reflected-wave formation over circular cylindrical wedges (method of multiple steps). The reflected-wave structure has been photographed with a schlieren apparatus. The formation of the reflected wave over circular cylindrical wedges is physically well understood by comparing it with shock reflection over step-like wedges. In particular, the reason why the reflected wave over a concave circular cylindrical wedge is very weak away from the reflection point is elucidated. Moreover, the structure and the formation mechanism of the so-called transitioned regular reflection (TRR) are illustrated in detail. As a by-product, based on acoustic theory, analytical formulae for the transition wedge angle are found. They are in good agreement with experiments.

Asymptotic analysis of whispering‐gallery mode radiation from the aperture of cylindrical concave conducting boundary

AbstractAn asymptotic analysis is discussed for the radiating field when a whispering gallery (WG) mode is radiated from the edge aperture plane of a cylindrical concave conducting boundary and is propagated as a beam. the integral representing the radiation field derived by the method similar to the one used in the problem of diffraction of a plane wave from a semiinfinite conducting plane is evaluated by means of the saddle point method taking into account the existence of the poles and the residue theorem.An asymptotic representation for the beam wave is a combination of the geometric optical ray and the edge diffracted ray. the phenomenon of the radiation of a geometric optical ray from the edge aperture and the phenomenon of diffraction of the modal ray at the terminating edge are clarified. the asymptotic solutions applicable in the shadow boundary, reflection boundary, and the nearby transition region caused by the incidence of the modal ray onto the edge are compared with those obtained by the Fresnel‐Kirchhoff formula so that the effectiveness of the asymptotic expression is determined. Also, it is demonstrated numerically that the radiation field expression based on the diffraction coefficients by the GTD cannot provide good results in the transition region. Further, propagation phenomena of beam fields are clarified from numerical results and the geometrical picture obtained from the ray tracing technique.

Investigations of Mach Reflection of a Shock Wave : 4th Report, The Transition between Regular and Mach Reflections

The transition between regular and Mach reflections of an oblique shock wave has been investigated by many researchers for steady, pseudo-steady and unsteady flows. However the problem for unsteady flows such as the reflection of a shock wave at cylindrical concave or convex walls has not been fully understood. The problem, considered in this report, is that of transition from Mach to regular reflection of a shock wave over a concave wall. Experimental investigations have been performed using a model of concave wall. The wall is composed of two straight sections, and the downstream second section is more inclined than the upstream first one. The process of shock reflection over this wall has been observed in detail, and the transition criterion from Mach to regular reflection in this case has been presented experimentally.

Investigations of Mach reflection of a shock wave (Part 4, The transition between regular and Mach reflections)

The transition between regular and Mach reflection of an oblique shock wave has been investigated by many researchers for steady, pseudo-steady and unsteady Flows, However the problem for unsteady Flows such as the reflection of a shock wave at cylindrical concave or convex walls has not been fully understood. The problem considered in this report is that of transition from Mach to regular reflection of a shock wave at a concave wall. Experimental investigations have been performed using a model concave wall. The wall is composed of two straight walls, and the second wall in more inclined than the first one. The process of shock reflection at this wall has been observed in detail, and the transition criterion from Mach to regular reflection in this case has been presented experimentally.

Cylindrical concave diffraction grating utilising thin silicon chip

A unique manufacturing method for concave diffraction gratings is proposed. Also, a cylindrical concave diffraction grating was manufactured with a multimode slab waveguide. A silicon plane diffraction grating was bent cylindrically in this method. The efficiency of the concave diffraction grating was 82% at a 1.3 μm wavelength. The efficiency was about the same as that of the plane diffraction grating.