A theoretical investigation of 2-2 composite transducers with high shear attenuation in the passive phase

This paper is about a theoretical investigation of 2-2 composite transducers with high shear attenuation in the passive phase. It was presented at the Étude de la propagation ultrasonore en milieux non homogènes en vue du contrôle non-destructif in 2007

Incorporation of viscoelastic loss into the plane wave expansion approach to modelling composite transducers

The plane wave expansion (PWE) method has been proposed as a theoretical model for periodic composite ultrasonic transducers. This paper extends previous work by importantly including viscoelastic loss in the material parameters. Some of the issues with model formulation, such as ill-conditioning in the large matrices, have been addressed through parameter scaling and Tikhonov regularisation. Identification of each mode of vibration has been carried out by visualising the spatial and temporal profiles of the displacement, electrical potential and Poynting vector. A comparison between the theoretical predictions and experimental data from a piezoelectric composite device is presented. The effect that the elastic properties of the passive phase have on device performance is also investigated. It is found that high shear attenuation in the passive phase gives rise to a large frequency stop band gap around the fundamental thickness mode

Analysis of ultrasonic transducers with fractal architecture

Ultrasonic transducers composed of a periodic piezoelectric composite are generally accepted as the design of choice in many applications. Their architecture is normally very regular and this is due to manufacturing constraints rather than performance optimisation. Many of these manufacturing restrictions no longer hold due to new production methods such as computer controlled, laser cutting, and so there is now freedom to investigate new types of geometry. In this paper, the plane wave expansion model is utilised to investigate the behaviour of a transducer with a self-similar architecture. The Cantor set is utilised to design a 2-2 conguration, and a 1-3 conguration is investigated with a Sierpinski Carpet geometry

Gas coupled polymeric capacitive transducers via pad printing

Micropatterning of polymer substrates has been shown to be effective methodology for the manufacture of capacitive transducers. The method involves creating a positive mask of sessile liquid droplets on a polymer substrate. The droplets define the cavity dimensions and spatial distribution, a subsequent processing stage independently defines the cavity depth. Droplets can be defined in a variety of ways – this paper explores the patterning the droplets, and hence cavities, on the polymer substrate via a pad-printing technique. The printing pad is manufactured using 3D printing technique, an example pad is illustrated in Figure 1 – essentially the pad comprises an array of styli. The lateral dimensions and spatial distribution of the styli are replicated via the pattern of deposited droplets on the polymer substrate. The morphology of the styli tips has been explored - planar tips were found to droplet patterns with the highest fidelity. Single element air coupled devices operating with a nominal centre frequency of 500kHz have been constructed and evaluated experimentally. Transducer bandwidths in excess of 100% were observed with two-way insertion loss of 60dB being typical

Harmonic analysis of lossy piezoelectric composite transducers using the plane wave expansion method

Periodic composite ultrasonic transducers oer many advantages but the periodic pillar architecture can give rise to unwanted modes of vibration which interfere with the piston like motion of the fundamental thickness mode. In this paper, viscoelastic loss is incorporated into a three dimensional plane wave expansion model (PWE) of these transducers. A comparison with experimental and nite element data is conducted and a design to damp out these lateral modes is investigated. Scaling and regularisation techniques are introduced to the PWE method to reduceill-conditioning in the large matrices which can arise. The identication of the modes of vibration is aided by examining proles of the displacements, electrical potentialand Poynting vector. The dispersive behaviour of a 2-2 composite transducer with high shear attenuation in the passive phase is examined. The model shows thatthe use of a high shear attenuation ller material improves the frequency band gap surrounding the fundamental thickness mode

Leadership and succession in Trinidadian family businesses

This research examines the qualities required for establishing effective leadership succession in private Family Businesses (pFB) in Trinidad, private meaning those still wholly-owned by family members. Trinidad’s pFB are major employers and contributors to economies globally and, yet, prior research shows that only around a quarter to a third survive to a second generation and only one-in-ten to a third. Therefore, identifying and developing the factors that support pFB continuity and transition are important both locally and internationally. This study identifies the key leadership and related elements for successful pFB continuity and succession in the Caribbean nation of Trinidad. The research is based on a qualitative approach, using in-depth, semi-structured, and open-ended interviews with eleven purposively-selected local pFB leaders. Interviewees comprised first- and second-generation leaders with ten existing pFB’s and one now-dormant pFB. The results show that none had established formal succession plans, but achieved success principally through effective face-to-face conversations between the leader, typically the parent, and the successor, typically one of the parents’ children. The research provides a valuable insight into the critical qualities deemed necessary for leaders to achieve continuity in their family business. The eight qualities identified for pFB success emanated from the data gathered (capability; honesty; and integrity), from the conceptual framework developed based on prior literature (vision; and effective communication), and from the discussions held (industry knowledge; a sound knowledge of the pFB organisational structures; and the support of the incumbent leader). These, alongside some measures of financial performance, lead to long-term success, and therefore generational continuity. This research extends current knowledge on how pFB continuity in Trinidad may be achieved, based on identifying the leadership qualities required. Further research is recommended on refining such knowledge across the Caribbean and into different territories, sectors, markets and industries

Theoretical modelling of frequency dependent elastic loss in composite piezoelectric transducers

The large number of degrees of freedom in the design of piezoelectric transducers requires a theoretical model that is computationally efficient so that a large number of iterations can be performed in the design optimisation. The materials used are often lossy, and indeed loss can be used to enhance the operational characteristics of these designs. Motivated by these needs, this paper extends the one-dimensional linear systems model to incorporate frequency dependent elastic loss. The reception sensitivity, electrical impedance and electromechanical coupling coefficient of a 1-3 composite transducer, with frequency dependent loss in the polymer filler, are investigated. By plotting these operating characteristics as a function of the volume fraction of piezoelectric ceramic an optimum design is obtained. A device with a non-standard, high shear attenuation polymer is also simulated and this leads to an increase in the electromechanical coupling coefficient. A comparison with finite element simulations is then performed. This shows that the two methods are in reasonable agreement in their electrical impedance profiles in all the cases considered. The plots are almost identical away from the main resonant peak where the frequency location of the peaks are comparable but there is in some cases a 20% discrepancy in the magnitude of the peak value and in its bandwidth. The finite element model also shows that the use of a high shear attenuation polymer filler damps out the unwanted, low frequency modes whilst maintaining a reasonable impedance magnitude