Pump Requirements for Parametric Amplification and Generation of Surface Waves on YZ LiNbO3
Absfract-Expressions are developed for estimating the threshold electric fields required for parametric amplification or generation of surface waves in piezoelectric materials utilizing the nonlinear characteristics of the material. When applied to Y Z LiNbOa, they yield values in excess of 20 kV/cm under the most optimistic, yet still realistic, conditions. These values are too Iarge for amplification or generation to be considered for practical applications. Several pump electrode geometries and circuit matching techniques were investigated to determine the best obtainable pump circuit performance. An interdigital electrode separated from the crystal by a small gap was found to be the most efficient pump electrode geometry and was capable of producing approximately ZkV/cm of field per watt’‘2 of input pump power.
Frequency conversion through nonlinear mixing in acoustic waves
Frequency conversion is an essential tool in modern communication devices. Traditionally, frequency conversion is achieved through parametric coupling via nonlinear inductors or capacitors whose reactance is modulated by a carrier wave. In this study, nonlinear acoustic Lamb wave devices are explored for simultaneous signal filtering and frequency conversion. Three sets of interdigitated transducers are fabricated on a piezoelectric aluminum nitride (AlN) thin film to provide a carrier wave, a low-power signal wave, and to receive a frequency converted mixed wave. Two devices are fabricated and tested to demonstrate frequency upconversion and downconversion by utilizing mechanical nonlinearity of AlN, and the results are compared to a nonlinear circuit model. The nonlinear circuit model is used to link experimentally observed phenomenon to the acoustic material's intrinsic nonlinearity. The nonlinearity of AlN reaches a maximum of 2.8% with a carrier wave power at 28 dBm. An analytical model is used to predict device performance along with physical dimensions. These analytical results show that nonlinear acoustic mixers and filters can approach sub-millimeter sizes, which is orders-of-magnitude smaller than conventional structures using nonlinear inductors and capacitors.
Gill diseases of cultured salmonids in Ontario.
Between 1977 and 1981, the Fish Pathology Laboratory of the Ontario Veterinary College received 239 cases from trout farms of southern Ontario, 51 (21.3%) of which had diseased gills. Branchial lesions in 86.3% of these 51 cases were characterized by marked lamellar epithelial hyperplasia with epithelial hypertrophy and lamellar fusion. Filamentous bacteria were seen on the surface of the branchial filaments and lamellae in 68.6% of the cases. Our observations highlight the importance of gill diseases as a production problem of farmed salmonids in southern Ontario.