Frequencies Of Lateral Modes Research Articles

Design, preparation and electromechanical characteristics analysis of piezoelectric 1-3-type composites with sandwich polymer structures

Aiming at the shortcomings of the traditional 200 kHz 1–3 piezoelectric composites with a thickness of 7.5 mm, which have a lower electromechanical coupling coefficient, lower resolution and larger acoustic impedance, a piezoelectric 1–3-type composites with sandwich polymer structures with higher electromechanical coupling coefficient and lower acoustic impedance was designed in this paper. First, the piezoelectric composites with different volume fractions of piezoelectric ceramics and silicone rubber were simulated by COMSOL software, and the optimal volume fractions of piezoelectric ceramics and silicone rubber were obtained. Second, the first and second lateral mode frequencies of the piezoelectric 1–3-type composites with sandwich polymer structures with different kerf widths were calculated. Then, based on the electromechanical equivalent circuit, the electromechanical characteristics of the piezoelectric 1–3-type composites with sandwich polymer structures were analyzed, and the equivalent performance parameters of the piezoelectric composite were obtained. Compared with other 7.5 mm thickness 1–3 piezoelectric composites, it was found that the electromechanical coupling coefficient of the piezoelectric 1–3-type composites with sandwich polymer structures is significantly increased, and the acoustic impedance is significantly decreased. Therefore, the piezoelectric 1–3-type composites with sandwich polymer structures has great potential advantages in the preparation of high-performance piezoelectric ultrasonic transducers.

Influence of Slip Table of the Shaker System on the Experimentally Obtained Fundamental Lateral Mode Frequency of a Spacecraft

Influence of Slip Table of the Shaker System on the Experimentally Obtained Fundamental Lateral Mode Frequency of a Spacecraft

Determination of the Fundamental Lateral Bending Mode Frequency of a Spacecraft from its Static Deflection

The primary structure of a spacecraft that involves the central cylinder is designed to meet a specific value of fundamental lateral mode frequency. Though this frequency can be theoretically estimated by using a finite element model, its experimental verification is only possible when the entire spacecraft is made ready. However, static load tests are done on the primary structure of the spacecraft as soon as the structure is realized. In this work, a methodology to determine the fundamental bending mode frequency of a spacecraft from the deflections measured when the structure alone is subjected to static load tests is developed. An expression relating the fundamental lateral bending mode frequency of a spacecraft, having several masses attached at different locations, and the deflection at its tip is derived. Two spacecraft, one of 3000kg class and the other of 6000kg class are taken as examples. The fundamental lateral frequencies are determined using this methodology. These frequencies are also obtained through resonance search tests. It is shown that the derived expression will be very useful in estimating the fundamental lateral mode frequency of a spacecraft with the help of the measured deflection.

Design and fabrication of non-periodic 1–3 composite structure for ultrasonic transducer application

Piezoelectric composite materials (PCMs), combing the advantages of both piezoelectric materials and polymers, have been extensively used in piezoelectric material ultrasonic transducers (PCUTs). However, PCMs induce lateral modes in PCUTs, which can degrade their performance. In this study, a mathematical model for the lateral mode frequency was deduced. A novel 1–3 composite structure with non-periodicity in one dimension was designed based on the proposed model to eliminate the effect of the lateral mode. In addition, the PZFlex software was used to simulate and verify the performance of the PCUT. The non-periodic 1–3 PCM was fabricated and used to package 4 MHz PCUT. A PCUT with a normal 1–3 PCM was fabricated for comparison. Then, the electrical and acoustic properties of the PCUTs were then systematically characterized. The PCUT with the non-periodic 1–3 PCM had a broader −6 dB bandwidth (38.9 %), larger electromechanical coupling coefficient (0.68), higher peak-to-peak voltage (2.44 V) and smaller insertion loss (-17.40 dB) than those of the PCUT with normal 1–3 PCM (28.4 %, 0.55, 1.19 V and –22.86 dB). The results show that non-periodic 1–3 composite structure can break the limits of the lateral mode and has great potential for the development of high-performance PCUTs.

System identification of the suspension tower of Runyang Bridge based on ambient vibration tests

A series of field vibration tests are conducted on the Runyang Suspension Bridge during both the construction and operational stages. The purpose of this study is devoted to the analysis of the dynamic characteristics of the suspension tower. After the tower was erected, an array of accelerometers was deployed to study the evolution of its modal parameters during the construction process. Dynamic tests were first performed under the freestanding tower condition and then under the tower-cable condition after the superstructure was installed. Based on the identified modal parameters, the effect of the pile-soil-structure interaction on dynamic characteristics of the suspension tower is investigated. Moreover, the stiffness of the pile foundation is successfully identified using a probabilistic finite model updating method. Furthermore, challenges of identifying the dynamic properties of the tower from the coupled responses of the tower-cable system are discussed in detail. It\'s found that compared with the identified results from the freestanding tower, the longitudinal and torsional natural frequencies of the tower in the tower-cable system have changed significantly, while the lateral mode frequencies change slightly. The identified modal results from measurements by the structural health monitoring system further confirmed that the vibrations of the bridge subsystems (i.e., the tower, the suspended deck and the main cable) are strongly coupled with one another.

Effect of Initial Stress on the Lateral Modes in 1-3 Piezocomposites

An investigation of the effect of initial stress on the lateral modes in 1-3 piezocomposites is conducted. The Governing equations, taking into account the piezoelectricity, initial stress, and initial strain, are developed for the piezocomposites. Analytical solutions of the mechanical displacement and electric potential function are obtained based on the Bloch waves theory. Influence of the initial stress on the lateral modes frequencies and the stop band are discussed in detail, respectively. The conclusion reached indicates that the lateral mode frequencies increase with the piezoelectricity of the piezocomposites, but decrease with the poling initial stress in piezocomposites.

Lateral resonances in initial stressed 1–3 piezocomposites

A theoretical analysis of the lateral resonances in 1–3 piezocomposites with poling initial stress is conducted using the Bloch wave theory. Based on the linear piezoelectricity theory, theoretical formulations that include initial stress for the propagation of acoustic plane waves are made. Numerical calculations are performed to study the effects of the initial stress on the lateral mode frequencies and the stop band. It is found that lateral mode frequencies increase with the piezoelectricity of the piezocomposites, but decrease with the poling initial stress. The influence of the initial shear stress on the lateral mode frequencies is minimal, and can thus be neglected.

Enhanced mass sensing using torsional and lateral resonances in microcantilevers

We present a method to detect, with enhanced sensitivity, a target mass particle attached eccentrically to a microcantilever by measuring multiple three-dimensional modes in the microcantilever vibration spectrum. Peaks in the spectrum reveal a complex coupling between the bending, torsional, and lateral motions and detailed finite element models assist in their interpretation. The mass sensitivities of the torsional and lateral mode frequencies are an order of magnitude greater, and their Q factors significantly higher, than that of the conventionally used fundamental bending mode. These modes offer significantly enhanced mass sensing capabilities within the realm of existing microcantilever technology.

Direct Method for Determining Natural Frequencies of Marine Risers in Deep Water

This paper presents a direct method for determining natural frequencies of lateral modes of vibration for marine risers in deep water. This method applies to marine risers that are vertical, relatively straight, and attached at both ends. The method is particularly useful for determining natural frequencies of higher modes that are sometimes difficult to obtain analytically or numerically. Comparisons of numerical results with published data show that even though the method of solution is approximate, the calculation procedure gives useful engineering results. The algorithm is based on classical vibration theory and can easily be programmed on portable computers for direct use on offshore oil rigs.

Third-order nonlinearity induced lateral-mode frequency locking and beam instability in the high-power operation of narrow-ridge semiconductor lasers

Lateral-mode frequency locking in the high-power operation of narrow-ridge semiconductor lasers is shown to be attributable to carrier-induced third-order nonlinearities. Not only are known experimental characteristics of beam steering explained with this theory, but new insights into the nature of beam steering, such as its inherent bistable behavior, are obtained.

Evaluation of piezocomposites for ultrasonic transducer applications influence of the unit cell dimensions and the properties of constituents on the performance of 2-2 piezocomposites

A theoretical model on piezoceramic polymer composites with laminar periodic structure is presented. A salient feature of this model is that it can treat explicitly how the unit cell dimensions and other material properties influence the performance of an ultrasonic transducer made of 2-2 piezocomposites. The model predicts that there exist a series of modes associated with the periodic structure of a composite, which is beyond the stop-band edge resonance prediction. One of the main concerns in designing a composite transducer is how the surface vibration profile changes with frequency and how this is influenced by the aspect ratio of the ceramic plate. It was predicted that as long as the thickness resonance is below the first lateral mode frequency, there is always a frequency f/sub 1/ which is near the thickness resonance and at which the polymer and ceramic vibrate in unison. The effect of aspect ratio is to change the position of f/sub 1/ with respect to the thickness resonance frequency and the bandwidth in which polymer and ceramic have nearly the same vibration amplitude and phase. It is also predicted that, when operated in a fluid medium such as water, there will be a resonance mode which has a frequency determined by the velocity of the fluid medium and the unit cell length d and is associated with the oscillation of the fluid. The behavior of a composite plate as an acoustic transmitter and receiver and the influence of the aspect ratio of the ceramic plate on them are also investigated.

Theoretical and experimental investigations of lateral modes in 1-3 piezocomposites

Materials with a periodic microstructure show resonances caused by the elastic wave Bragg diffraction. This paper presents a simple approach to describe these resonances (called lateral resonances) in 1-3 piezoelectric composite materials which have a 2-D periodicity. Our model is based on the analysis of the propagation of transverse waves in a 2-D periodic medium of infinite thickness and takes into account the periodic and interfacial boundary conditions. This model predicts the displacement field vectors and frequencies of lateral resonances from which the phase velocity of lateral waves is determined. The theoretical and experimental variations of this velocity versus the ceramic rod width to pitch ratio are compared. It is shown that the first lateral mode frequency is maximum when the ceramic volume fraction is around 0.65. Theoretical predictions of the mechanical displacement at the composite surface are compared with measurements obtained by an interferometric laser technique. A good agreement is observed, showing that lateral waves are mainly vertically polarized.

Lateral resonances in 1–3 piezoelectric periodic composite: Modeling and experimental results

The objective of this work is to provide an accurate model of the lateral resonance modes in 1–3 piezoelectric composite materials. These materials are widely used in ultrasonic transducers and the lowest lateral mode frequency gives the upper limit for the usable transducer bandwidth. Considering the propagation of purely transverse waves in a 2-D periodic medium of infinite thickness, two different approaches for obtaining the solutions are presented and compared. The first approach is based on the use of the Bloch waves theory. The second is a straightforward method (a so-called membrane method) which consists in numerically solving the propagation equation in the two-phase medium while taking into account the periodic boundary conditions. Methods based on both models are described that allow the calculation of the dispersion curves and the stop band limits, as well as the frequencies and the displacement fields of the lateral modes. A test case is used to compare and discuss the theoretical predictions provided by each model. The calculations of the first lateral mode frequency are compared with experimental values obtained for samples with different ceramic volume fractions. The conclusion reached indicates that the infinite thickness assumption is valid for plates of practical interest and that the membrane model enables the prediction of lateral mode frequency with low computation effort and an accuracy better than 5%.