The versatility of surface acoustic wave (SAW) devices stems from the accessibility of the propagation path to modification and detection. This has led to the integration of SAWs in a variety of novel fields, including quantum information processing. The development of technologically competitive devices requires the use of gigahertz frequency SAWs. This thesis develops fabrication processes for high frequency interdigital transducers on gallium arsenide. Optically lithography was used to create linear and stepped transducers, with a minimum feature size of 2 um, that were driven at their fifth harmonic. The highest frequency achieved was 1435 MHz, but the power absorbed was less than 3% and insertion losses were greater than -80 dB. Further improvements in the design and fabrication are required if optically fabricated transducers are to be an alternative to transducers with narrower finger widths. Electron-beam lithography techniques were developed and used to create transducers with finger widths of 500 and 400 nm, with fundamental resonance frequencies of 1387 and 1744 MHz, respectively. The power absorbed was 3 to 6% with insertion losses greater than -45 dB. The performance characteristics can be improved by the removal of residual resist on the surface of the transducer. An indispensable tool for the characterization of one-port transducers is an all optical probe to measure the displacement field of a SAW. This work details the design and construction of a scanning Sagnac interferometer, that is capable of measuring the outward displacement of a surface. The spatial resolution of the interferometer was 2.4 +/- 0.2 um and the displacement sensitivity was determined to be 4 +/- 1 pm. The instrument was used to map the SAW displacement field from a 358 MHz transducer, with results showing the resonant cavity behaviour of the fingers due to Bragg reflections. It also allowed for the direct detection of the SAW amplitude as a function of the driving frequency of the transducer. The results showed good agreement with the related S21 scattering parameter. Lastly, the interferometer was used to image the attenuated propagation of SAWs through a phononic crystal. Results showed good agreement with theoretical simulations. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-12-08 12:28:35.962

Micropulsation data recorded at Palo Alto, California during 1963-4 and Ralston, Alberta during 1967 have been used to study "Intervals of pulsations of diminishing period" (IPDP). IPDP's are found to be generated in the dusk-midnight quadrant of the magnetosphere at an equatorial distance of about 6 earth radii. An intensive study of the Ralston data reveals that IPDP's occur during the expansive phase of magnetospheric substorms. It is proposed that IPDP's are generated by a cyclotron instability between energetic protons and left-hand ion cyclotron waves. Their main characteristics are determined by the perturbations of the dusk-midnight sector of the magnetosphere by magnetospheric substorms. One of the main disturbances in that region is a slow decrease and then sudden increase in the magnetic field corresponding to the buildup and decay of a partial ring current. IPDP's show an increase in midfrequency due to the change in the cyclotron instability frequency produced by the increasing magnetic field. This theory is tested by a comparison of frequency increase of IPDP's observed at Ralston and magnetic field increase in the magnetosphere observed by the ATS-1 satellite. Other conditions necessary for IPDP generation are then discussed. It is shown that different combinations of these conditions result in the generation of hm emissions and band type micropulsations. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

This thesis contains an experimental and theoretical study of the response of a plasma to the motion of the positive space-charge sheath which bounds it. It is known theoretically that, if a sheath edge is moved at a speed less than the speed of ion acoustic waves, a region of ion rarefaction propagates into the plasma at the ion acoustic speed. In the past, difficulty has been encountered with the theory of ion acoustic wave generation from moving sheath edges, where compressions are necessary in addition to rarefactions. The initial conditions of many previous calculations omit the formation of a steady-state presheath where ions are accelerated to form the sheath. Some calculations are described which include the effects of an initial presheath by constructing a one-dimensional plasma solution where a production term balances the losses of ions to the walls. The plasma response to the motion of one boundary is found using the method of characteristics with appropriate boundary conditions. Ion rarefaction waves are associated with expanding sheaths while ion 'enhancement' waves (compressive features) are formed on sheath collapse. In each case the wave front moves at the local ion acoustic speed which includes the effects of ion drift. The presence of the presheath is essential to the generation of enhancements. The constructional details of a multidipole device are discussed, and the results of Langmuir probe and ion acoustic wave experiments are used to determine the parameters of a quiescent argon plasma. Some experiments on moving sheaths in such a plasma are then considered. Negative voltage ramps are applied to a plate and the plasma response is measured using sampled probe techniques. As the plate-plasma voltage increases, the ion-rich sheath expands at a speed which depends on the applied voltage waveform. For sheath edge speeds less than the ion acoustic speed, an ion rarefaction wave is formed. As the voltage decreases, the sheath collapses and an ion enhancement wave propagates into the plasma. Both wavefronts are observed to move at the local ion acoustic speed which increases with distance from the plate in agreement with theory.

by Lo Veng-cheong. / Bibliography : leaves 95-96 / Thesis (M.Phil.)--Chinese University of Hong Kong, 1982

The control of surface acoustic waves (SAWs) using arrays of annular holes was investigated both experimentally and through numerical modelling. Periodic elastic composites, phononic crystals (PnCs), were designed using these annular holes as constituent elements. Local resonances associated with the annular hole structure were found to induce phonon bandgaps of a highly frequency tailorable nature, at frequencies where radiation of acoustic energy into the bulk of the substrate medium is avoided. These bandgaps are numerically demonstrated to exhibit order-of-magnitude improved extinction ratios for finite numbers of PnC elements, relative to the commonly used cylindrical pillar architecture. Devices fabricated on commercially available lithium niobate SAW delay lines verify the predicted behaviour. Through laser knife-edge detector vibrometry, a bandgap attenuation of 24.5 dB at 97 MHz was measured, in excellent agreement with finite element method (FEM) simulations. The first reported experimental evidence of subwavelength confinement of propagating SAWs was realised using the same annular hole PnC concept. Defect holes of perturbed resonant frequencies are included within the PnC to define waveguides and cavities. Confinement within these defects was demonstrated to occur at subwavelength frequencies which was experimentally observed in fabricated cavities using standard SAW transducers, as measured by laser Doppler vibrometry. The success of this result was attributed to the impedance matching of hybridised modes to Rayleigh SAWs in un-patterned substrates at the defect resonance. The work here has the potential to transform the field by providing a method to enhance SAW interactions, which is a route towards the realisation of many lab-on-chip applications. Finally, the use of annular hole arrays as negative refraction metamaterials was investigated. The symmetry was broken of the unit cells by alternating either the locally resonant frequencies or the distance separating the constituent elements. Both methods, called the bi-dispersive and bi-periodic methods, were numerically demonstrated to exhibit negative group velocity bands within the first Brillouin zone. Preliminary experimental results show that the design has the potential to be used in superlensing, where a SAW spot was imaged over a subwavelength flat lens. Future research looks to demonstrate that this result can be attributed to negative refraction.

This thesis deals with the dependence of the linear spatial growth rate of the cross-field ion acoustic instability on various plasma parameters. A kinetic theory model, with elastic and inelastic ion-neutral collisions included, is presented and used to conduct a numerical survey of the instability. The growth rate is computed as a function of distance into the plasma, taking into account the attenuation of the ion beam by charge exchange collisions. Further calculations show the variation in growth rate as a function of the following quantities: electron and ion beam temperature, electron density, beam velocity, background ion temperature, magnetic field, the angle between magnetic field direction and wave vector and the finite width of the plasma. The instability was observed in a double plasma device where an ion beam was passed through a background of stationary magnetized electrons. The magnetic field was sufficiently weak to allow approximately rectilinear ion motion. The growth rate of the wave was studied using interferometer techniques. It was identified by the dispersion relation as the cross-field ion acoustic wave propagating as the slow mode of the beam. It was found that the background ions play an important role in determining the phase velocity. Experimental data of the growth rate dependence on wave number, beam velocity and magnetic field strength were found to be well described by the theoretical model. The growth rate dependence of magnetic field direction on plasma width was furthermore found to be in qualitative agreement with the model. / Thesis (M.Sc.)-University of Natal, Durban, 1990.

The unique frequency range and robustness of surface acoustic wave (SAW) devices has been a catalyst for their adoption as integral components in a range of consumer and military electronics. Furthermore, the strain and piezoelectric fields associated with SAWs are finding novel applications in nanostructured devices. In this thesis, the interaction of SAWs with periodic elastic structures, such as photonic or phononic crystals (PnCs), is studied both computationally and experimentally. To predict the behaviour of elastic waves in PnCs, a finite-difference time-domain simulator (PnCSim) was developed using C++. PnCSim was designed to calculate band structures and transmission spectra of elastic waves through two-dimensional PnCs. By developing appropriate boundary conditions, bulk waves, surface acoustic waves, and plate waves can be simulated. Results obtained using PnCSim demonstrate good agreement with theoretical data reported in the literature. To experimentally investigate the behaviour of SAWs in PnCs, fabrication procedures were developed to create interdigitated transducers (IDTs) and PnCs. Using lift-off photolithography, IDTs with finger widths as low as 1.8 um were fabricated on gallium arsenide (GaAs), corresponding to a SAW frequency of 397 MHz. A citric acid and hydrogen peroxide wet-etching solution was used to create shallow air hole PnCs in square and triangular lattice configurations, with lattice constants of 8 um and 12 um, respectively. The relative transmission of SAWs through these PnCs as a function of frequency was determined by comparing the insertion losses before and after etching the PnCs. In addition, using a scanning Sagnac interferometer, displacement maps were measured for SAWs incident on square lattice PnCs by Mathew (Creating and Imaging Surface Acoustic Waves on GaAs, Master’s Thesis). Reasonable agreement was found between simulations and measurements. Additional simulations indicate that SAW waveguiding should be possible with a PnC consiting of air holes in GaAs. The phononic properties of a commonly used photonic plate were also determined. Band structure simulations of the plate displayed no complete elastic band gaps. However, transmission simulations indicated that a pseudo-gap may form for elastic waves polarized in the sagittal plane. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-12-23 16:24:33.164

Measurements of broadband electrostatic wave emIssons in conjunction with particle distributions in the earth's magnetosphere, have provided motivation for a number of studies of waves in plasmas with two electron components. One such wave-the electron-acoustic wave-arises when the two electron components have widely disparate temperatures (Watanabe & Taniuti 1977), and has a characteristic frequency that lies between the ion and electron plasma frequencies. Because of this broadband nature and because it is predominantly electrostatic, it provides a likely candidate for the explanation of the electrostatic component of "cusp auroral hiss" observed in the dayside polar cusp at between 2 and 4 earth radii as well as the broadband electrostatic noise (BEN) observed in the dayside polar regions and in the geomagnetic tail. The electron-acoustic wave and its properties provide the subjects for much of the investigation undertaken in this thesis. The thesis is divided into two parts. Part I is concerned with certain aspects of the linear theory of the electron-acoustic wave and is based on a kinetic description of the plasma. The dispersion relation for plane electrostatic waves obtained via linearisation of the Vlasov-Poisson system is studied in detail using analytical and numerical/geometrical techniques, and conditions under which the electron-acoustic wave arises are expounded. This work represents an extension of earlier works on Langmuir waves (Dell, Gledhill & Hellberg 1987) and the electron-acoustic wave (Gary & Tokar 1985). The effects of electron drifts and magnetization are investigated. These result, respectively, in a destabilization of the electron-acoustic wave and a modification of the dispersive properties. In this plasma configuration the model more closely replicates the conditions to be found in the terrestrial polar regions. We extend the parameter regimes considered in earlier works (Tokar &Gary 1984) and in addition, identify another electron sound branch related to the electron-cyclotron wave/instability. Effects of ion-beam destabilization of the electron-acoustic wave are also investigated briefly with a view to explaining BEN in the geomagnetic tail and also to provide a comparison with the electron-driven instability. In part II the nonlinear electron-acoustic wave is studied by employing a warm hydrodynamic model of the plasma components. We first consider weak nonlinearity and employ the asymptotic reductive perturbation technique of Washimi &Taniuti (1966) to render the hydrodynamical equations in the form of simpler evolutionary equations describing weakly-nonlinear electron-acoustic waves. These equations admit solitary-wave or soliton solutions which are studied in detail. Wherever possible we have justified our small amplitude results with full numerical integration of the original hydrodynamical equations. In so doing we extended the range of validity of our results to arbitrary wave amplitudes and also find some interesting features not directly predicted by the small amplitude wave equations. In this respect we were able to determine the important role played by the cool- to-hot electron temperature ratio for soliton existence. This important effect is in accordance with linear theory where the electron temperature ratio is found to be critical for electron-acoustic wave existence. The effects of magnetization on electron-acoustic soliton propagation is examined. We found that the magnetized electron-acoustic solitons are governed by a Korteweg-de Vries-Zakharov-Kusnetsov equation. In addition, it is shown that in very strong magnetic fields ion magnetization can become important yielding significant changes in the soliton characteristics. Multi-dimensional electron-acoustic solitons, which have greater stability than their plane counterparts, are also briefly discussed. Employing a weakly-relativistic hydrodynamic model of the plasma, the effect of a cool, relativistic electron beam on such soliton parameters as width, amplitude and speed is studied in detail. Both small- and large amplitude solitons are considered. The arbitrary-amplitude theory of Baboolal et al. (1988) is generalised to include relativistic streaming as well as relativistic thermal effects. The importance of the cool electron (beam)to- hot electron temperature in conjunction with the beam speed is pointed out. Finally, we derive a modified Korteweg-de Vries (mKdV) equation in an attempt to establish whether electron-acoustic double layers are admitted by our fluid model. Although double layers formally appear as stationary solutions to the mKdV equation, the parameter values required are prohibitive. This is borne out by the full fluid theory where no double layer solutions are found. / Thesis (Ph.D.)-University of Natal, Durban, 1991.

Abstract available in PDF file. / Thesis (Ph.D.)-University of Natal, 1979.

Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains v, 127 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 94-98).