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.

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.

Transformation of Voltage Mode Filter Circuit Based on Op-Amp to Circuit Based on CCII

In this paper, firstly we demonstrate the use of nodal admittance matrix to convert a low-pass band-pass filter based on operational amplifier（op-amp） to a circuit based on a second-generation current conveyor（CCII）. This technique allows us to get eight presumptions of filter circuits. Secondly, we present a novel architecture circuit of CCII, which can operate at low supply voltage of ±0.75 V. All simulations are performed by TSPICE models. The simulation results show that this circuit has a low impedance at terminal X（R X=1.01 Ω）, a very high input impedance at terminal Y, and wide bandwidth current and voltage. The center frequency of the proposed filter is variable on the interval [157 k Hz, 196 MHz].

Stability Monitoring and Control of Generation Based on the Synchronized Measurements in Nodes of Its Connection

Synchronized distributed measurements of mode parameters create a technical feasibility for development and implementing new technologies of control the mode stability and the admissibility of EPS （electric power system） mode. Discussion will focus on different models obtained from data synchronized measurements for operational and automatic emergency control without EPS being totally controlled. According to the proposed technology, the generator＇s output power restrictions are determined in real-time by the terms a static stability using the generators＇ mode model as a multipole with connection nodes of generators＇ electromotive forces （the matrix of SMA （self and mutual admittances） of electromotive forces of generators）. Potential applications of the technology are distribution network with the main substation and generators of commensurable capacity, and transmission network with large power plants （generators） distributed into the network. The one-level control system for all of generators with defining the generator＇s power limits relative to the main substation is implemented in the first case. In the second case, the two-level control system is brought in, based on the separation of large and small generation motion. The results of the method and technology efficiency verification are shown in the paper, by both computer simulations of the power system modes and its physical model.

Synthesis for Current-Mode Sallen-Key Filter Using VDTAs

In this work, an original Sallen-Key second-order low-pass filter is first turned into a current-mode one by means of the adjoint network theorem. Two nodal admittance matrices(NAM) of the filter are then educed. Furthermore, these two matrices are expanded through NAM expansion approach, generating one current-mode Sallen-Key filter, which uses two compact voltage differential trans-conductance amplifiers(VDTAs) and two grounded capacitors, implements not only one low-pass transfer function but two band-pass transfer functions, and provides the non-interrelated control between the natural frequency and quality factor. As an example of the synthesized filter, a second-order VDTA filter with fo=1 MHz, Q=1, HLP=-HBP1=HBP2=1 is designed. The used synthesis approach has been confirmed with the help of circuit and computer analysis.

Pathological Models of EXCCCII and Its Applications in Oscillator Synthesis

After giving six different forms of the extra X second-generation current-controlled conveyor(EXCCCII),pathological models of six EXCCCIIs are found by the nodal admittance matrix(NAM)expansion approach.Furthermore,these ideal pathological circuit models are employed and 36 Wien oscillators and 8 third-order quadrature oscillators are synthesized by the NAM expansion.The hand analysis and computer analysis are introduced to prove the synthesized circuits are correct and effective.