Sound propagation in inhomogeneous waveguides with sound-speed profiles using the multimodal admittance method

The multimodal admittance method and its improvement are presented to deal with various aspects in underwater acoustics,mostly for the sound propagation in inhomogeneous waveguides with sound-speed profiles,arbitrary-shaped liquid-like scatterers,and range-dependent environments.In all cases,the propagation problem governed by the Helmholtz equation is transformed into initial value problems of two coupled first-order evolution equations with respect to the modal components of field quantities(sound pressure and its derivative),by projecting the Helmholtz equation on a constructed orthogonal and complete local basis.The admittance matrix,which is the modal representation of Direchlet-to-Neumann operator,is introduced to compute the first-order evolution equations with no numerical instability caused by evanescent modes.The fourth-order Magnus scheme is used for the numerical integration of differential equations in the numerical implementation.The numerical experiments of sound field in underwater inhomogeneous waveguides generated by point sources are performed.Besides,the numerical results computed by simulation software COMSOL Multiphysics are given to validate the correction of the multimodal admittance method.It is shown that the multimodal admittance method is an efficient and stable numerical method to solve the wave propagation problem in inhomogeneous underwater waveguides with sound-speed profiles,liquid-like scatterers,and range-dependent environments.The extension of the method to more complicated waveguides such as horizontally stratified waveguides is available.

Nullors, and Nullor Circuits;There Applications in Symbolic Circuit Analysis and Design

The objective in this presentation is to introduce some of the unique properties and applications of nullors in active circuit analysis and designs. The emphasis is to discuss the role nullors can play in symbolic representation of transfer functions. To show this we adopt the topological platform for the circuit analysis and use a recently developed Admittance Method (AM) to achieve the Sum of Tree Products (STP), replacing the determinant and cofactors of the Nodal Admittance Matrix (NAM) of the circuit. To construct a transfer function, we start with a given active circuit and convert all its controlled sources and I/O-ports to nullors. Now, with a solid nullor circuit (passive elements and nullors) we first eliminate the passive elements through AM operations. This produces the STPs. Second, the all-nullor circuit is then used to find the signs or the STPs. Finally, the transfer function (in symbolic, if chosen) is obtained from the ratio between the STPs.

Effect of prism material on design of surface plasmon resonance sensor by admittance loci method

A theoretical study on the design of surface plasmon resonance （SPR） based sensor by admittance loci method has been reported in this paper with the main emphasis being given to the effect of the prism material in a conventional Kretschmann structure in attenuated total internal reflection （ATIR） mode. Several sensing media such as water, acetone, methanol etc have been investi- gated using different types of prism materials to study their effect on SPR sensing and validated by corresponding admittance loci plots as well as respective SPR curves. The performance of the sensor based on choice of the prism material has been discussed with the help of sensitivity plots giving due to the importance of dynamic range of the designed sensor. Simulations have been carried out in MATLAB 7.1 environment.

Systematic Synthesis of Compressive VDTA-Based T-T Filter with Orthogonal Control of f_o and Q

Based on sixteen nullor-mirror models of the voltage differencing transconductance amplifier (VDTA) and port admittance matrices of the tow-Thomas (T-T) filter with orthogonal control between the characteristic frequency(f_0) and figure of merit (Q),two different categories of the voltage-mode and transconductance-mode T-T filters are synthesized by the means of the nodal admittance matrix (NAM) expansion method.The category A filter that employs two compressive VDTAs and two grounded capacitors includes four structures,and the category B filter that uses two compressive VDTAs,two grounded capacitors,and one grounded resistor,also includes four structures.These circuits are suitable for integrated circuit manufacture,and their parameters f_0 and Q can be orthogonally adjusted with varying the bias currents of VDTAs.After the paper and pencil test is completed,the computer analyses,including alternating current (AC),parameter sweep,Monte Carlo (MC),and noise analyses,are performed to support the synthesis approach.