No description available.

No description available.

Among communication filters, SAW Filters have been largely used in RF and IF filters of mobile phone because of their small size, high reliability, and the capability to be mass produced. But with increasing of working frequency and miniaturization of SAW package, SAW filters are more sensitive to interference introduced by the package and SAW Pattern. Discrepancy in performance between design and measurement can be large if the packaging effects are not considered. In this thesis, we use the full wave analysis approach that combining full wave simulator HFSS (High Frequency Structure Simulator) with circuit software to simulate the package effects and the electromagnetic effects of SAW pattern. Our approach has been applied to several cases and measurements are also carried out to verify our results. Good agreements are obtained. We also use this method to discuss the electromagnetic effects inside package, such as the change of the bond wire length. With an accurate prediction, we can save factory design time and production cost.

In this thesis we investigate various aspects of SAW devices and strain sensitive spin species in ZnO and LiNbO₃ for coupling surface acoustic waves to spin ensembles. Firstly, we performed a series of ESR experiments exploring the potential of Fe³⁺ impurities in ZnO for spin-lattice coupling. This spin system has already been identified as a high potential quantum technology component due to its long coherence time. We show that the system also has good properties for spin-lattice coupling experiments, with a strain-coupling parameter G₃₃ = 280 ± 5GHz/strain, which is about 16 times larger than the largest reported for NV centres in diamond. We found that the LEFE effect as well as the spin Hamiltonian parameter D have a linear temperature dependence. As the relative change in each coincide, this strongly supports the notion that the modification of D by an electric field is a multiplicative effect rather than an additive one, D = D₀(1 + κΕ). The LEFE coefficient we measured is several times larger for Fe³⁺:ZnO than for Mn²⁺:ZnO. Secondly, we have fabricated and characterised SAW devices on bulk ZnO crystals and Fe doped lithium niobate. We found that the nominally pure ZnO was conductive at room temperature due to n-type intrinsic doping, and electrical losses inhibited any transmission through a SAW delay line above T = 200K. The one-port resonator measured down to milli-Kelvin temperatures showed excellent quality factors of up to Q ≃ 1.5 x 10⁵ in its superconducting state. Finally, we performed a surface acoustic wave spin resonance (SAWSR) experiment using a one-port SAW resonator fabricated on Fe²⁺:LN. We observed a clear signal at T ≃ 25 K, at a field near the expected one for a Δm_s = 2 transition between the |−1⟩ and |+1⟩ states. We concluded it to be a transition induced by acoustic coupling since the signal intensity did not tend to zero when the magnetic field was parallel to the crystal anisotropy axis. Furthermore, this tells us that the coupling is due to a modulation of the E zero-field splitting parameter rather than D. We investigated the dependence on microwave power and found the saturation limit. We performed a measurement of Fe³⁺:LN as well to reassure ourselves that the resonance is not magnetically excited by the field around the IDT.

No / A numerical method for sound propagation of higher-order cross-sectional modes in a duct of arbitrary cross-section and boundary conditions with nonzero, complex acoustic admittance has been considered. This method assumes that the cross-section of the duct is uniform and that the duct is of a considerable length so that the longitudinal modes can be neglected. The problem is reduced to a two-dimensional (2D) finite element (FE) solution, from which a set of cross-sectional eigen-values and eigen-functions are determined. This result is used to obtain the modal frequencies, velocities and the attenuation coefficients. The 2D FE solution is then extended to three-dimensional via the normal mode decomposition technique. The numerical solution is validated against experimental data for sound propagation in a pipe with inner walls partially covered by coarse sand or granulated rubber. The values of the eigen-frequencies calculated from the proposed numerical model are validated against those predicted by the standard analytical solution for both a circular and rectangular pipe with rigid walls. It is shown that the considered numerical method is useful for predicting the sound pressure distribution, attenuation, and eigen-frequencies in a duct with acoustically nonrigid boundary conditions. The purpose of this work is to pave the way for the development of an efficient inverse problem solution for the remote characterization of the acoustic boundary conditions in natural and artificial waveguides.

No description available.

A surface acoustic wave (SAW) is a combination of a mechanical wave and a potential wave propagating on the surface of a piezoelectric substrate at the speed of sound. Such waves are widely applied in not only the communication industry, but also in quantum physics research, such as nanoelectronics, spintronics, quantum optics, and even quantum information processing. Here, I focus on low-dimensional electron transport and SAWs in GaAs and ZnO semiconductor heterostructures. The ability to pattern quantum nanostructures using gates has stimulated intense interest in research into mesoscopic physics. We have performed a series of simulations of gate structures, and having with the optimised boundary conditions and we find them to match experimental results, such as the pinch-off voltage of one-dimensional channels and SAW charge transport in induced n-i-n and n-i-p junctions. Using the improved boundary conditions, it is straightforward to model quantum devices quite accurately using standard software. With the calculated potential, we have modelled the process how a dynamic quantum dot is driven by a SAW and have analysed error mechanisms in SAW-driven quantisation (I=Nef, where N is the number of electrons in each SAW minimum, and f is the SAW resonant frequency). From energy spectroscopy measurements, we probe the electron energy inside a SAW-driven dynamic quantum dot and find that the small addition energy, which is around 3meV, is the main limitation for the SAW quantisation. To increase the confinement of SAW-driven quantum dots, we deposit a thin ZnO film, with a better piezoelectric coupling than GaAs, on a GaAs/AlGaAs heterostructure using high-target-utilisation sputtering (an Al2O3 buffer layer is deposited to protect the 2DEG during sputtering). With the ZnO, the SAW amplitude is greatly improved to 100 meV and the RF power required for pumping electrons using a SAW is greatly reduced. Finally, we have studied low-dimensional electron transport in a MgZnO/ZnO heterostructure. We have developed a technique for patterning gates using a parylene insulator, and used these to create one-dimensional quantum wires and observe electron ballistic transport with conductance quantised in units of 2e2/h The increasing electron effective mass as the 1D electron density decreases indicate that the electron-electron interaction in this MgZnO/ZnO heterostructure is strong. Because of these strong interactions, the 0.7 anomaly is observed just below each quantised plateau, and are much stronger than in GaAs quantum wires. Furthermore, we have also calculated the SAW-modulated spontaneous and piezoelectric polarisation in the ZnO heterostructure, and have observed a sign of this SAW-modulation in 2DEG density, which is different from the classical SAW-pumping mechanism. Our results show that a ZnO heterostructure should provide a good alternative to conventional III-V semiconductors for spintronics and quantum computing as they have less nuclear spins. This paves the way for the development of qubits benefiting from the low scattering of an undoped heterostructure together with potentially long spin lifetimes.

Mercury (Hg) has always been a serious risk to the environment and human health. It is a very common contamination in petroleum industry, which may lower product quality, threaten operation safety and worker’s health even at a very low concentration. Consequently the detection of mercury is very necessary. Gold is widely used as sensing material of mercury because it has a specific affinity with mercury and the adsorption of mercury changes characteristics of gold such as resistivity and effective mass density. In this thesis, common methods for sensing mercury vapor concentration were summarized and a surface acoustic wave (SAW) sensor utilizing the adsorption of mercury on gold electrodes was proposed for 1 μg/m3 level low concentration mercury vapor detection. The working principle of SAW sensor was studied and finite element method models were built to optimize the sensor design. The influence of several physical structure parameters such as electrode width and pitch on the sensor sensitivity and response time were studied using the simulation model. According to the simulation results a prototype of SAW sensor was designed and fabricated. The sensor was then analyzed with network analyzer and tested with mercury vapor. Preliminary results were presented and analyzed in this work. Finally potential future work was proposed and discussed.

In this thesis, the author proposes and develops novel multilayered Surface Acoustic Wave (SAW) devices with unique attributes for gas sensing applications. The design, simulation, fabrication and gas sensing performance of three multilayered SAW structures has been undertaken. The investigated structures are based on two substrates having high electromechanical coupling coefficient: lithium niobate (LiNbO3) and lithium tantalate (LiTaO3), with a piezoelectric zinc oxide (ZnO) intermediate layer. Sensitivity towards target gas analytes is provided by thin film indium oxide (InOx) or tungsten trioxide (WO3). The high performance of the gas sensors is achieved by adjusting the intermediate ZnO layer thickness. Sensitivity calculations, undertaken with perturbation theory illustrate how the intermediate ZnO layer can be employed to modify the velocity-permittivity product of the supported SAW modes, resulting in highly sensitive conductometric SAW gas sensors. The work contained within this thesis addresses a broad spectrum of issues relating to multilayered SAW gas sensors. Topics include finite-element modelling, perturbation theory, micro-fabrication, metal oxide deposition, material characterisation and experiential evaluation of the layered SAW sensors towards nitrogen dioxide (NO2), hydrogen (H2) and ethanol gas phase analytes. The development of two-dimensional (2D) and three dimensional (3D) finite-element models provides a deep insight and understanding of acoustic wave propagation in layered anisotropic media, whilst also illustrating that the entire surface of the device can and should be used as the active sensing area. Additionally, the unique and distinctive surface morphology of the layered structures are examined by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The crystalline structure and orientation of the ZnO and WO3 layers are also examined by X-ray Diffraction Spectroscopy (XRD). The novel multilayered SAW structures a re shown to be highly sensitive, capable of sensing NO2 and ethanol concentration levels in the parts-per-billion and parts-per-million range, respectively, and H2 concentrations below 1.00% in air. The addition of platinum or gold catalyst activator layers on the WO3 sensitive layer is shown to improve sensitivity and dynamic performance, with response magnitudes up to 50 times larger than bare WO3. The gas sensing performance of the investigated structures provide strong evidence that high sensitivity can be achieved utilising multilayered SAW structures for conductometric gas sensing applications.

For centuries scientific ingenuity and innovation have been influenced by Mother Natures perfect design. One of her more elusive designs is that of the sensory olfactory system, an array of highly sensitive receptors responsible for chemical vapor recognition. In the animal kingdom this ability is magnified among canines where ppt (parts per trillion) sensitivity values have been reported. Today, detection dogs are considered an essential part of the US drug and explosives detection schemes. However, growing concerns about their susceptibility to extraneous odors have inspired the development of highly sensitive analytical detection tools or biosensors known as electronic noses. In general, biosensors are distinguished from chemical sensors in that they use an entity of biological origin (e.g. antibody, cell, enzyme) immobilized onto a surface as the chemically-sensitive film on the device. The colloquial view is that the term biosensors refers to devices which detect the presence of entities of biological origin, such as proteins or single-stranded DNA and that this detection must take place in a liquid. Our biosensor utilizes biomolecules, specifically IgG monoclonal antibodies, to achieve molecular recognition of relatively small molecules in the vapor phase.