Optimum sensitive area of surface acoustic wave resonator chemical and bio-sensors

A model is developed to map the variation of sensitivity of a surface acoustic wave (SAW) resonator sensor over its surface, in order to find the region with maximum sensitivity. The model is based on a combined coupling of modes (COM) and periodic Green's function analysis. In order to extend the analysis to layered media, a new efficient technique is introduced to account for the mechanical interactions with buried electrodes. Using this technique the sensitivity calculations are found to be in good agreement with measurements. It is also shown that whilst changes in other parameters influence the sensitivity, it is the velocity change which most strongly determines the overall frequency change

Spatial sensitivity distribution of surface acoustic wave resonator sensors

The sensitivity distribution of surface acoustic wave (SAW) resonator sensors is investigated by theoretical and experimental means. It is shown that the sensitivity to mass loading varies strongly across the surface due to the confinement of acoustic energy toward the center of the device. A model is developed for this phenomenon based on the extraction of coupling of modes parameters from a rigorous boundary element method analysis based on a periodic Green's function. As SAW sensors for many applications include a layer covering the electrodes, a new technique is introduced to account for the mechanical interactions with buried electrodes. Using this technique, the sensitivity calculations are found to be in good agreement with measurements. It is also shown that while changes in other parameters influence sensitivity, it is velocity change that most strongly determines overall frequency change

Development of nano-structured titanium oxide thin films using a gas carving technique

A method is developed for producing nano-structured titanium oxide thin films using H2 gas interaction with titanium thin film at a high temperature. These nano-structured thin films have been formed on a quartz crystal substrate. Titanium (Ti) thin films were deposited on the quartz crystal using a RF magnetron sputterer. The samples were placed in the oven at 500-800°C for 5 hours. The gas mixture of 1% H2 in N2 was introduced in the oven. The process of Ti annealing in the presence of H2 carves Ti films into nano-structure shapes. The process is a gas-solid interaction. Thin films were characterised using Scanning Electron Microscopes (SEM) and X-Ray Diffraction (XRD) technique. The nano structures formed have dimensions in a range of 25nm - 150nm obtained after gas carving

Risks of chronic metabolic acidosis in patients with chronic kidney disease

Risks of chronic metabolic acidosis in patients with chronic kidney disease Metabolic acidosis is associated with chronic renal failure (CRF). Often, maintenance dialysis therapies are not able to reverse this condition. The major systemic consequences of chronic metabolic acidosis are increased protein catabolism, decreased protein synthesis, and a negative protein balance that improves after bicarbonate supplementation. Metabolic acidosis also induces insulin resistance and a decrease in the elevated serum leptin levels associated with CRF. These three factors may promote protein catabolism in maintenance dialysis patients. Available data suggest that metabolic acidosis is both catabolic and anti-anabolic. Several clinical studies have shown that correction of metabolic acidosis in maintenance dialysis patients is associated with modest improvements in nutritional status. Preliminary evidence indicates that metabolic acidosis may play a role in β2-microglobulin accumulation, as well as the hypertriglyceridemia seen in renal failure. Interventional studies for metabolic acidosis have yielded inconsistent results in CRF and maintenance hemodialysis patients. In chronic peritoneal dialysis patients, the mitigation of acidemia appears more consistently to improve nutritional status and reduce hospitalizations. Large-scale, prospective, randomized interventional studies are needed to ascertain the potential benefits of correcting acidemia in maintenance hemodialysis patients. To avoid adverse events, an aggressive management approach is necessary to correct metabolic acidosis. Clinicians should attempt to adhere to the National Kidney Foundation Kidney Disease Outcome Quality Initiative (K/DOQI) guidelines for maintenance dialysis patients. The guidelines recommend maintenance of serum bicarbonate levels at 22 mEq/L or greater

A layered SAW device based on ZnO/LiTaO3 for liquid media sensing applications

Surface Acoustic Wave (SAW) sensors comprising a zinc oxide guiding layer deposited on a 36°-YX lithium tantalate substrate were developed. They were found to have greater mass sensitivity than other LiTaO3 based SAW sensors, such as the -SiO2/LiTaO3 configuration. In this paper, the fabrication of the ZnO/LiTaO3 sensor is described and micro-characterisation of the deposited films is presented. Sensitivity of these devices to surface mass and dielectric perturbations is then presented, followed by an analysis of temperature stability

Polyaniline nanofiber based surface acoustic wave gas sensors - effect of nanofiber diameter on H2 response

A template-free rapidly mixed reaction was employed to synthesize polyaniline nanofibers using chemical oxidative polymerization of aniline. Hydrochloric acid (HCl) and camphor sulfonic acid (CSA) were used in the synthesis to obtain 30- and 50-nm average diameter polyaniline nanofibers. The nanofibers were deposited onto layered ZnO/64 degrees YX LiNbO3 surface-acoustic-wave transducers. The sensors were tested toward hydrogen (H-2) gas while operating at room temperature. The dopant for the polyaniline nanofiber synthesis was found to have a significant effect on the device sensitivity. The sensor response was found to be larger for the 50-nmdiameter CSA-doped nanofiber based sensors, while the response and recovery times were faster for the 30-nm diameter HCl-doped nanofibers

Plastic Deformation in Laser-Induced Shock Compression of Monocrystalline Copper

Copper monocrystals were subjected to shock compression at pressures of 10–60 GPa by a short (3 ns initial) duration laser pulse. Transmission electron microscopy revealed features consistent with previous observations of shock-compressed copper, albeit at pulse durations in the µs regime. The results suggest that the defect structure is generated at the shock front. A mechanism for dislocation generation is presented, providing a realistic prediction of dislocation density as a function of pressure. The threshold stress for deformation twinning in shock compression is calculated from the constitutive equations for slip, twinning, and the Swegle-Grady relationship

Production of e+e- pairs in proton-deuteron capture to 3He

The process p+d \leftrightarrow 3He + \gamma* at intermediate energies is described using a covariant and gauge-invariant model, and a realistic pd3He vertex. Both photodisintegration of 3He and proton-deuteron capture with production of e+e- pairs are studied, and results for cross sections and response functions are presented. The effect of time-like formfactors on the dilepton cross sections is investigated as well.Comment: 10 pages, 4 figures, Revtex, to be published in Physics Letters

H2 and NO2 gas sensors with ZnO nanobelt layer on 36° LiTaO3 and 64° LiNbO3 SAW transducers

Single crystal nanobelts of ZnO were synthesized and deposited onto 36° YX LiTaO<sub>3</sub> and 64° YX LiNbO<sub>3</sub> surface acoustic wave (SAW) devices for gas sensing applications. Sensor response, defined as the change in resonant frequency, was measured for H<sub>2</sub> and NO<sub>2</sub> between 20 and 200°C. Measured sensor responses were 3.5 kHz towards 10 ppm NO<sub>2</sub> for a 64° LiNbO<sub>3</sub> SAW transducer operating at 160°C and 3 kHz towards 1% H<sub>2</sub> for a 36° LiTaO<sub>3</sub> SAW transducer operating at 185°C temperature