Radial Mode Coupling Research Articles

Radial breathing modes coupling in plasmonic molecules.

Metallic hexamer, very much the plasmonic analog of benzene molecule, provides an ideal platform to mimic modes coupling and hybridization in molecular systems. To demonstrate this, we present a detailed study on radial breathing mode (RBM) coupling in a plasmonic dual-hexamers. We excite RBMs of hexamers by symmetrically matching the polarization state of the illumination with the distribution of electric dipole moments of the dual-hexamer. It is found that the RBM coupling exhibits a nonexponential decay when the inter-hexamer separation is increased, owing to the dark mode nature of RBM. When the outer hexamer is subjected to the in-plane twisting, resonant wavelengths of two coupled RBMs as well as the coupling constant show cosine variations with the twist angle, indicating the symmetry of hexamer structure plays a critical role in the coupling of RBMs. Moreover, it is demonstrated that the coupling of RBMs is dominated by the in-plane interaction as the outer hexamer is under an out-of-plane tilting, causing convergence of resonant wavelengths of the two coupled RBMs with increasing tilt angle. Our results not only provide an insight into the plasmonic RBM coupling mechanism, but also pave the way to systematically control the spectral response of plasmonic molecules.

Role of secondary long wavelength structures in the saturation of electron temperature gradient driven turbulence

The dynamics of secondary long wavelength structures (LWSs) in electron temperature gradient (ETG) driven turbulence are investigated by performing gyrofluid simulations and modeling analyses in a slab geometry with an emphasis of the underlying nonlinear interaction processes. It is shown that the back-reaction of the secondary LWS on the ambient fluctuations essentially contributes to saturating ETG instability and limiting the electron transport. The LWS is nonlinearly generated mainly through the beating of the most unstable ETG modes, even a weak modulation instability. The back-reaction is identified as the enhanced stabilization of the ETG modes due to the streamer-type feature of the LWS, which dominantly produces a local poloidal mode coupling among unstable and highly damped spectral components to form a global mode, besides the suppression effect of the LWS due to the radial shearing decorrelation and/or the radial mode coupling. Finally, the correspondence between the LWS in the slab model and the quasimode observed in toroidal ETG simulation [Z. Lin et al., Phys. Plasmas 12, 056125 (2005)] and the importance of the nonlinear mode coupling in the multiscale turbulence interaction are discussed.

Radial Mode Piezoelectric Response of La Modified Lead Zirconate Titanate in Morphotropic Phase Boundary Region

Room temperature radial mode piezoelectric response of Lanthanum modified Lead Zirconate Titanate (Pb(Zr0.57Ti0.43)O3+X at%La) (PLZT) is characterized by Vector Impedance Spectroscopy. Piezoelectric parameters (electromechanical constants KP, K31, elastic compliance sE11, strain constants d31, dh, voltage constant g31and planar piezoelectric constants radial mode coupling constant kp, piezoelectric constant ep31and mechanical constant cp11) have been determined for La doping ranging from 3 to 12 at%. Piezoelectric parameters KP, kp, d33and d31peak at 5–6 at%of La while dielectric constants˜T33,˜P33and piezoelectric constant ep31peak at 8 at%. An average value of Poisson's ratioσEis found to be 0.34±0.01. The conductivity of PLZTs follows the universal behavior.

Induction of combinatory characteristics by relaxor modification of Pb(Zr0.5Ti0.5)O3

This letter reports a Pb(Zr0.5Ti0.5)O3 (PZT) based composition, which provides high piezoelectric and electromechanical properties. The general form of the composition is Pb(Zn1/3Nb2/3)x(B1/3I′B2/3II′)y(Zr0.5Ti0.5)1−x−yO3+0.5 wt % MnO2 (x+y=0.2). Four compositions corresponding to the earlier formulation were studied. For the composition corresponding to y=0, the radial mode coupling factor (kp) of 0.58, longitudinal mode piezoelectric constant (d33) of 277 pC/N, dielectric constant (ε33/ε0) of 946, and mechanical quality factor (Qm) of 1402 are obtained. X-ray diffraction, dielectric, and polarization-electric field measurements were done to investigate the origin for this high performance. It was found that high soft properties are obtained due to the shifting of PZT composition towards morphotropic phase boundary and high hard properties are obtained due to the generation of dipolar defects which pin the polarization.

Novel High Power Piezoelectrics for Transformers and Actuators

ABSTRACTThis letter reports a Pb(Zr0.5Ti0.5)O3 (PZT) based composition, which provides high dielectric, piezoelectric and electromechanical properties. The composition corresponding to 0.2 PZN – 0.8 PZT + 0.5 wt% MnO2 provides the radial mode coupling factor (kp) of 0.58, longitudinal mode piezoelectric constant (d33) of 277 pC/N, dielectric constant (ε33/εo) of 946 and mechanical quality factor (Qm) of 1402. X-ray diffraction, dielectric and polarization-electric field measurements were done to investigate the origin for this high performance. It was found that high soft properties are obtained due to the shifting of PZT composition towards morphotropic phase boundary (MPB) and high hard properties are obtained due to the generation of dipolar defects which pin the polarization. The properties of the composition corresponding to 0.9 PZT – 0.1PMnN (Zr/Ti = 0.51/0.49) modified with 6 mol% Sr were found to be: kp = 0.53, Qm = 800, d33 = 274, ε33/εo = 1290 and tanδ = 1.1 %, with a TCF of -8 ppm/oC (-20 to 80°C). High piezoelectric properties with low TCF shows the suitability of this composition for ultrasonic devices used under fluctuating thermal environment.

Microwave instability in electron storage rings

Tracking simulations, with the aim of studying the microwave regime with short and intense bunches, suggest different instability mechanisms, according to the impedance model. In order to get a better insight of the source of the instability, i.e. azimuthal or radial mode coupling, we choose to follow the Sacherer (IEEE Trans. Nucl. Sci. NS-24, 1977 1393) approach to investigate the stability of the stationnary solution. The generalized Sacherer's integral, including mode coupling and potential well distortion, is then solved by using the “step function technique” for the expansion of the radial function, as proposed by Oide and Yokoya (KEK Preprint-90-10, April, 1990). For illustration, the effect of the resonant frequency of a broadband resonator in the SOLEIL storage ring is studied. When the resonator frequency is much higher than the bunch spectrum width, azimuthal mode coupling can occur before radial mode coupling. When the resonator frequency is lower, radial mode coupling comes usually first, but two or more bunchlets are produced at relatively low current. The diffusion process between the bunchlets, which leads to the well-known “saw-tooth” behavior, originates actually from a fast-growing microwave instability. Lastly, the beneficial effect of an harmonic cavity on the microwave instability is estimated and discussed.

Radial mode coupling saturation of a flute mode

The structure and properties of a centrifugal flute mode driven by E × B rotation of a plasma column have been studied experimentally and theoretically. This mode appears as a single mode (m = 1, k = 0). The bispectral analysis of the mode clearly indicates strong three-wave coupling in the narrow spectral width of the mode. The amplitudes of the individual frequencies across the plasma cross section are also tracked, giving the radial structure of different frequency amplitudes. Frequencies with self-similar radial structures are grouped together to belong to the same radial harmonic. Clearly, these radial harmonics contribute to the spectral width. These observations suggest that the nonlinear mode coupling between these radial harmonics is the saturation mechanism, as well as the underlying cause of anomalous transport. Prompted by the above observations a three-wave nonlinear coupling model using radial harmonics has been formulated. A proper treatment of two-dimensional (azimuthal and radial) nature of the polarization drift nonlinearity and the inclusion of damped radial harmonics to insure a steady-state have been done. The analysis reveals the generation of damped higher-order radial harmonics by the unstable fundamental radial harmonic, which is the saturation mechanism. The resulting root mean square fluctuation and levels of higher harmonic generation are in fair agreement with the experimental observations.

A thin film technique for spatial apodization of disc-shaped piezoceramic transducers

Conventional piezoelectric disc transducers suffer from some inherent disadvantages as a result of diffraction and multimode wave interaction within the radiated sound field. It is shown that significant improvements may be achieved by employing a continually varying resistive taper as a front or rear face electrode, thereby minimizing the influence of aperture diffraction, radial mode coupling, and electric field variations on the spatial response. The theoretical operation of such devices is discussed and good agreement is obtained from a selection of experimental observations on different transducer materials.

Definition and measurement of radial mode coupling factors in piezoelectric ceramic materials with large variations in Poisson's ratio : Meitzler, A.H., O'Bryan Jr, H.M., Tiersten, H.F., SU-20 (July 1973) 233–239

Definition and measurement of radial mode coupling factors in piezoelectric ceramic materials with large variations in Poisson's ratio : Meitzler, A.H., O'Bryan Jr, H.M., Tiersten, H.F., SU-20 (July 1973) 233–239

Definition and Measurement of Radial Mode Coupling Factors in Piezoelectric Ceramic Materials with Large Variations in Poisson's Ratio

Abstracr-The standard procedure (IEEE Standard 179) of determining radial mode coupling factor k, in piezoelectric ceramic disks assumes that the variations in Poisson’s ratio # with material composition may be neglected. Furthermore, the analysis from which the equations defining k, were derived was originally formulated for an elastically isotropic, electrically biased, electrostrictive medium. This paper 1 j reports on analysis using the linear piezoelectric constitutive equations including the full elastic anisotropy of a poled ceramic; 2) defines a new radial mode coupling factor kP , 3) relates kP to the standard k, ; 4) describes a measuring procedure that determines # and kP; and 5) applies these techniques to measurements of PLZT ceramics.