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Pnramerer trade-off for mrnimizing high-speed pulse disrortion on a microstrip line is in wsrigared. The sensiriviry nf physical parameters to conducror loss. dielecrric loss. and inpectiorl frequency is first or high resistivity, the dc attenuation could also be significant. Many researchers have derived empirical formulas for the effective relative permittivity [l-31, conductor loss [4-61, and dielectric loss [5, 71 for microstrip lines. However. it is not KEY TERMSTrade-off design. arreriuatiori. disper.tion. inflectton frequent?.. 5 13-522. ABSTRACTA fabrication method of strip-loaded waveguide on litliiiirn outdif fused lithium niobate substrate is presented. The fabricated waveguide provides good characteristics. such us single trunsverse niagnetic ( T M ) or electric (TE) polarization and without having a thick surface guide on the srrbsiraie. Also i r takes less rime io fubricaie the waveguide, and hence, less damage on the substraie is expected. A nunierical simulation shows ihat the normalized amplitude coriiours of the fundamental waveguide mode can be crpanded for eficien t fiber coupling or condensed for enhancing the electro-optic effect depending on ihe refraciive index of the loaded strip. The ouiput power profile of the waveguide, detected by a linear array of charge coupled devices. is in good agreement with that calciiluted nurneritally. 0 1992 John Wiles & Sons. lnc.

A review and critique of different laminate theories used for the modeling and analysis of laminated composite beams or plate structures is presented. Many finite-element models use classical laminate theory (CLT), also known as first-order shear deformation theory (FSDT), for the numerical simulation of active structures. The basic assumptions of this model have evolved from those proposed for composite laminate models and are based on thin-plate theory with resulting approximations for the elastic displacement, stress and strain components. In the case of piezoelectric laminates, the approximations spill over into the electric potential and electric field components. No studies and simulations have been documented for the dynamical electromechanical field variations through the thickness of the laminate structure at the resonant frequencies of the structure. This is essential to the understanding of the validity and range of applicability of thin-plate assumptions for active vibration control of structures. On the one hand, thin-plate models result in a computationally tractable model for smart structures, but they should not compromise on the electromechanical coupling effect, which is at the basis of active control. This paper first presents a three-dimensional (3D) complete field solution for active laminates based on a modal, Fourier series solution approach that is used to compute all the through-thickness electromechanical fields near the dominant resonance frequency of a beam plate with two piezoelectric (sensor and actuator) and one structural layers. Then a detailed review of the extant laminate models used for piezoelectric laminates, emphasizing the underlying assumptions in each case, is presented. The non-zero, through-thickness field components are computed under these assumptions. The results of the 3D model and FSDT model are compared for two aspect ratios ((ARs)-thickness-to-width of the layers). An AR of 20 is at the limit of the FSDT and an AR of 50 well within the assumptions of the FSDT. It is concluded that for moderate ARs, several of the approximations of the FSDT are questionable at resonance frequencies. A detailed set of pertinent and general references to papers dealing with piezoelectric laminates is also included. It is hoped that this study will be a reference source for those who want to use FSDT and for those want to understand the dynamical behavior of the internal fields in a smart laminate.

Finite element modelling is used to study the response of plate structures on which piezoelectric active devices are mounted. Such devices are typically small in relation to the size of the structure which can be modelled as a plate or shell structure. In modelling the response of such devices, it is necessary to use a detailed model of the device but to do the same for the whole structure is computationally expensive and unnecessary. Full three‐dimensional elements are used to model the piezoelectric devices because such devices are anisotropic, couple electric and elastic fields and satisfy boundary conditions independently on the two fields. Shell elements, approximated by many flat‐shell elements are used in modelling the structure. Transition elements have been derived to connect the three‐dimensional solid elements in the piezoelectric region to the flat‐shell elements used for the plate. This approach has merits in terms of accuracy in modelling the piezoelectric device and computational economy for the plate structure. The use of shell elements is preferred for the structure since brick elements lead to unnatural stiffening of the plate and artificially high natural frequencies. The aspect ratio of the transition elements are first optimized through a numerical study and the sensor and actuator performance of the devices is then verified. © 1997 by John Wiley & Sons, Ltd.

The technology referred to by the terms 'microelectromechanical systems' (MEMS), 'interdigital transducers' (IDTs), and 'smart systems' is a multidisciplinary one which has generated a great deal of interest in the chemical, mechanical, electrical engineering, medical, materials science, and food science communities in recent years. The term 'smart system' refers to a device or an array of devices that can sense changes in its environment and makes a useful or optimal response by changing its material properties, geometry, or mechanical or electromagnetic response. Both the sensor and actuator functions with the appropriate feedback must be integrated, and comprise the 'brain' of the material. The materials belonging to this category include a range of artificial materials, from optically active or chiral polymers to multifunctional polymers, carbon nanotubes, piezoelectrics, ferroelectrics, and other active ceramics. The miniaturization of sensors and subsequently that of the MEMS incorporating the sensors, actuators, and electronic circuitry for signal processing and control feedback have been made possible by advances in technologies originating in the semiconductor industry, and the emerging field has grown rapidly during the past ten years. Recently, microstereolithography has revolutionized the MEMS industry through multifunctional polymeric materials incorporating organic thin-film transistors with three-dimensional MEMS which is not possible with silicon processing.The integration of MEMS, IDTs, and the required microelectronics and conformal antenna in the multifunctional smart materials and composites results in a smart wireless system suitable for sensing and control of a variety of functions in automobile, aerospace, marine, and civil structures, and the food and medical industries. This unique combination of technologies also results in novel conformal sensors that can be remotely accessed by an antenna system with the advantage of no power requirements at the sensor site.After giving a brief overview of microsensors and MEMS, the paper focuses on the design and fabrication of MEMS devices and their use in engineering and medical applications. Examples include: (1) accelerometers and gyroscopes for automobiles, inertial navigation, etc; (2) drag sensing and reduction for aircraft; (3) sensing and control of ice formation and de-icing for aircraft; (4) remote measurement of tip deflection for helicopters;(5) health monitoring of structures; and (6) a 'smart tongue and electronic nose'.

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A scattering matrix approach, that involves only the transition matrix of a single obstacle, is proposed for studying the multiple scattering of elastic waves in a medium (matrix) containing identical, long, parallel, randomly distributed cylinders of arbitrary cross section. The elastic properties of the cylinders are assumed to be different from those of the matrix. A statistical approach in conjunction with Lax’s ’’quasicrystalline’’ approximation is employed to obtain equations for the average amplitudes of the scattered and exciting fields which may then be solved to yield the dispersion relations of the composite medium. Dynamic elastic properties of the composite medium containing circular and elliptical cylinders are found in the Rayleigh or low-frequency limit. Numerical results displaying phase velocity and damping effect of the composite medium are presented for a wide range of frequencies.