Propagation and control of shear waves in piezoelectric composite waveguides with metallized interfaces

This paper investigates coupled electro-elastic shear waves propagating along a piezoelectric finite width waveguide consisting of layers separated by metallized interfaces and arranged in a periodic way along the guide. The modified matrix method is applied to obtain the dispersion equation for a waveguide with straight walls. Bragg resonances and the presence of trapped modes and slow waves are revealed and analyzed for a periodic structure consisting of unit cells made up firstly from two different piezoelectric materials, and secondly from two identical piezoelectric materials. An analytical expression for the transmission coefficient for the waveguide with a defect layer is found that can be used to accurately detect and control the position of the passband within a stopband. This can be instrumental for constructing a tuneable waveguide made of layers of identical piezoelectric crystals separated by metallized interfaces

Internal resonances in a periodic magneto-electro-elastic structure

Propagation of electro-magneto-acoustic waves in a three phase magneto-electro-elastic periodic structure has been investigated with full coupling between mechanical, electric, and magnetic fields. Due to simultaneous piezoelectric and piezomagnetic effects, an orthogonally polarised electromagnetic wave couples with the similarly polarised lattice vibration, resulting in a both dielectric and magnetic phonon-polaritons. The closed form of dispersion relation has been used to demonstrate the phonon-polariton coupling not only in the long wave region at high acoustic microwave frequencies but also for shorter waves at optical infrared frequencies. The results also show that neither at acoustic nor at optical frequencies the magneto-electro-elastic effect affects the band structure due to the Bragg scattering

Atmospheric residence time of 210Pb determined from the activity ratios with its daughter radionuclides 210Bi and 210Po

The residence time of 210Pb created in the atmosphere by the decay of gaseous 222Rn is a key parameter controlling its distribution and fallout onto the landscape. These in turn are key parameters governing the use of this natural radionuclide for dating and interpreting environmental records stored in natural archives such as lake sediments. One of the principal methods for estimating the atmospheric residence time is through measurements of the activities of the daughter radionuclides 210Bi and 210Po, and in particular the 210Bi/210Pb and 210Po/210Pb activity ratios. Calculations used in early empirical studies assumed that these were governed by a simple series of equilibrium equations. This approach does however have two failings; it takes no account of the effect of global circulation on spatial variations in the activity ratios, and no allowance is made for the impact of transport processes across the tropopause. This paper presents a simple model for calculating the distributions of 210Pb, 210Bi and 210Po at northern mid-latitudes (30°-65°N), a region containing almost all the available empirical data. By comparing modelled 210Bi/210Pb activity ratios with empirical data a best estimate for the tropospheric residence time of around 10 days is obtained. This is significantly longer than earlier estimates of between 4 and 7 days. The process whereby 210Pb is transported into the stratosphere when tropospheric concentrations are high and returned from it when they are low, significantly increases the effective residence time in the atmosphere as a whole. The effect of this is to significantly enhance the long range transport of 210Pb from its source locations. The impact is illustrated by calculations showing the distribution of 210Pb fallout versus longitude at northern mid-latitudes

Magneto-electro-elastic polariton coupling in a periodic structure

Propagation of electro-magneto-acoustic waves in a magneto-electro-elastic (MEE) periodic structure has been investigated with a three phase coupling between mechanical, electric and magnetic fields in each constituent layer. Due to this coupling electromagnetic waves couple with lattice vibrations resulting in both dielectric and magnetic phonon–polaritons which couple via the magneto-electric effect. Propagation properties of acoustic longitudinal and transverse vibrations in this superlattice have been investigated. For longitudinal acoustic vibrations perpendicular to the poling direction, the coupling of piezoelectric and piezomagnetic polaritons results in a propagating mode. For transverse lattice vibrations with the coupled MEE wave propagating parallel to the poling direction, there is a coupled piezoelectric–piezomagnetic phonon polariton gap. The MEE superlattice produces either negative permittivity or negative permeability functions but not double negativity to result in negative refraction crystal