Quarter-wavelength

PVDF film is readily commercially available in thicknesses up to 110 pm. If film of this thickness is bonded to a rigid substrate, the peak response is at a frequency of about 3.7 MHz which corresponds to the thickness of the layer being a quarter wavelength. This frequency is rather high for most Lamb wave testing since Fig 1 shows that even on a I mm thick... 

Viertel-kreis, m. quarter circle, quadrant, -stunde,/. quarter of an hour, -wellenlknge, /. quarter wavelength, viertens, adt. fourthly, in the fourth place. Vierundzwanzigflachner, m. icositetrahedron. vierwandig, a. four-walled. 

The two limitations of optical interferometry, the one-quarter wavelength of light limit and the low resolution, have been addressed by using a combination of a fixedthickness spacer layer and spectral analysis of the reflected beam. The first of these overcomes the minimum film thickness that can normally be measured and the second addresses the limited resolution of conventional chromatic interferometry. 

At large radii the widths of the Bragg layers converges asymptotically to the conventional (Cartesian) quarter-wavelength condition. Mathematically, this can be explained by noting that for large radii the Bessel function can be approximated by a sinusoidal function divided by square root of the radius. From the physical... 

A larger frequency shift is possible if the laser is placed in longitudinal or transverse magnetic fields which cause a Zeeman splitting of the upper and lower laser level. With polarizers and quarter wavelength plates one can select the shifted a+ or a- component... 

Chalcogenide-glass-film quarter-wavelength matching layer... 

Some attention has to be given to the degree of circular polarization y and thus to the creation of cpl. Two experimental principles are common the use of a quarter wavelength plate and the use of a Fresnel rhomb or a Solcil-Babinet compensator in a few experiments, radiation from a cyclotron after passage through a polarizing undulator was used. The degree of circular polarization is easily jeopardized when a X/4 plate is employed, as this is an interference device... 

The condition for reinforcement used in Sec. 3-2 is that the waves involved must differ in path length, that is, in phase, by exactly an integral number of wavelengths. But suppose that the angle Q in Fig. 3-2 is such that the path difference for rays scattered by the first and second planes is only a quarter wavelength. These rays do not annul one another but, as we saw in Fig. 3-1, simply unite to form a beam of smaller amplitude than that formed by two rays which are completely in phase. How then does destructive interference take place The answer lies in the contributions from planes deeper in the crystal. Under the assumed... 

Figure 13. Producing circularly polarized light by means of a quarter wavelength retarder. A, Two beams, plane polarized at right angles, traverse a birefringent plate. B, On emerging the two beams are 90° (one quarter of a wavelength) out of phase. C, Shows the two beams recombined. The result is perfectly circularly polarized light. See text for discussion. Reproduced, with permission, from [4].

Stability plots for two methane-air flames using the analytical solution of Bychkov [17] with parameters for equivalence ratios of 0.8 and 1.3 are shown in Fig. 7.4. The y-axis corresponds to the acoustic velocity normalized by the laminar-flame speed, and the x-axis is the wave number scaled by the flame thickness. However, within this model the Markstein parameter (Eq. (8) in [17]) was modified to incorporate an effective Lewis number to allow use of the model for mixtures at and near stoichiometric composition [11]. A frequency of 920 radians per second is selected, which corresponds to the quarter-wavelength frequency of the TC burner during the parametric instability, and the activation... 

Acharya Yes, we see a quarter-wavelength mode and the Helmholtz mode. Of course, the dynamics will depend on the facility resonance. 

Part of the incident light will be reflected at the top and bottom surfaces of the antireflection film, and in both cases the reflection will take place in a medium of lower refractive index than the adjoining medium. Thus, to ensure that the relative phase shift is 180°, the optical thickness of the film should be made one quarter wavelength so that the total difference in phase between the two beams will correspond to twice one quarter wavelength, that is 180°. This is the phase condition ... 

Figure 14.20 The reflectivity of a thin film varies sinusoidally with the film thickness, being zero when the optical thickness is a multiple of a half wavelength, and maximum when the thickness is an odd multiple of a quarter wavelength...

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