G. Harvey

Review of high-power ultrasound-industrial applications and measurement methods

Applications involving high-power ultrasound are expanding rapidly as ultrasonic intensification opportunities are identified in new fields. This is facilitated through new technological developments and an evolution of current systems to tackle challenging problems. It is therefore important to continually update both the scientific and commercial communities on current system performance and limitations. To achieve this objective, this paper addresses two key aspects of high-power ultrasonic systems. In the first part, the review of high-power applications focuses on industrial applications and documents the developing technology from its early cleaning applications through to the advanced sonochemistry, cutting, and water treatment applications used today. The second part provides a comprehensive overview of measurement techniques used in conjunction with high-power ultrasonic systems. This is an important and evolving field which enables design and process engineers to optimize the behavior and/or operation of key metrics of system performance, such as field distribution or cavitation intensity.

Flexible ultrasonic transducers incorporating piezoelectric fibres

It is possible to produce a high-performance, flexible 1-3 connectivity piezoelectric ceramic composite with conventional methods but the process is difficult and time-consuming. Extensive finite element modeling was used to design a piezocomposite structure which incorporated randomly positioned piezoceramic fibers in a polymer matrix. Simple manufacturing techniques were developed which resulted in the production of large numbers of fully populated fiber composites that offered performance comparable with a conventional 1-3 piezocomposite. A modified process facilitated the production of efficient fiber piezocomposite elements separated by polymer channels which conformed to a highly flexible (13 mm radius of curvature), 2-D matrix array configuration. This arrangement has been termed a Composite Element Composite Array Transducer, or CECAT. These devices were evaluated in terms of their impedance spectra, pulse-echo response, and surface displacement characteristics. The random piezoceramic fiber arrangements showed comparable sensitivity and bandwidth to periodic devices while minimizing the parasitic interpillar modes associated with periodic structures. Investigations have indicated that CECAT arrays constructed with 250 mum diameter fibers can be operated at frequencies of up to 3 MHz and transducers incorporating 10 mum diameter fibers can extend the frequency range above 6 MHz. Conversely, improved low-frequency devices can be produced with taller pillars than possible with conventional manufacturing techniques.

Noninvasive field measurement of low-frequency ultrasonic transducers operating in sealed vessels

This paper describes a noninvasive technique utilizing the acousto-optic effect, laser interferometry, and tomographic principles that have been implemented to measure the acoustic fields generated by low-frequency ultrasonic transducers operating into sealed, water-loaded vessels commonly used in industrial processing applications. A customized scanning frame, incorporating both linear and rotational stages, has been developed to facilitate manipulation of the laser head and vessel under evaluation. First, transmitted pressure profiles in air are predicted from surface displacement data acquired directly by laser measurement of the vibrating aperture. These profiles were then used to verify the measured fields obtained via conventional tomographic scanning procedures, coupled with laser interferometry, applied within a draft-proof scanning facility under free-field conditions. Next, the finite element code PZFlex was employed for the prediction of pressure fields within cylindrical cell configurations. Finally, precise manipulation of the laser firing angle and position was implemented in order to compensate for the effects of refraction at the cell wall boundaries, and to re-establish the projections required for the reconstruction algorithm. The experimental results demonstrate good corroboration with the PZFlex predictions, validating its application of ultrasound as a virtual prototyping tool for the design of high power ultrasonic test vessels

Ultrasonic field measurement in test cells combining the acousto-optic effect, laser interferometry and tomography

This paper describes a non-invasive measurement technique for the characterisation of acoustic fields generated by a commercially available 33 kHz Tonpilz transducer in fluid loaded cylindrical test cells. Firstly, a harmonic field prediction model was used to verify the experimentally measured pressure fields at various distances from the device front face under free field conditions. Next, the finite element code PZFlex was employed for the prediction of pressure field within cylindrical cell configurations. Finally, precise manipulation of the laser firing angle and position was implemented in order to compensate for the breakdown of the reconstruction procedure due to refraction at the cell walls. Results demonstrate reasonable correlation with the PZFlex predictions.

Simulation and measurement of nonlinear behavior in a high-power test cell

High-power ultrasound has many diverse uses in process applications in industries ranging from food to pharmaceutical. Because cavitation is frequently a desirable effect within many high-power, low-frequency systems, these systems are commonly expected to feature highly nonlinear acoustic propagation because of the high input levels employed. This generation of harmonics significantly alters the field profile compared with that of a linear system, making accurate field modeling difficult. However, when the short propagation distances involved are considered, it is not unreasonable to assume that these systems may remain largely linear until the onset of cavitation, in terms of classical acoustic propagation. The purpose of this paper is to investigate the possible nonlinear effects within such systems before the onset of cavitation. A theoretical description of nonlinear propagation will be presented and the merits of common analytical models will be discussed. Following this, a numerical model of nonlinearity will be outlined and the advantages it presents for representing nonlinear effects in bounded fields will be discussed. Next, the driving equipment and transducers will be evaluated for linearity to disengage any effects from those formed in the transmission load. Finally, the linearity of the system will be measured using an acoustic hydrophone and compared with finite element analysis to confirm that nonlinear effects are not prevalent in such systems at the onset of cavitation.

RELIABLE CRACK DETECTION IN TURBINE BLADES USING THERMOSONICS: AN EMPIRICAL STUDY

Excitation generated by ultrasonic horns typically used in thermosonics (or Sonic IR) is non‐reproducible, raising concerns that cracks in some locations can be missed. This paper presents an empirical study on the thermosonic inspection of turbine blades. The objective is to assess the reliability of thermosonics as an NDT screening method for findings crack in turbine blades. First, a study was carried out to establish the operating parameters that generated the highest possible temperature rise from a crack. Next, a repeatability study was conducted to measure consistency of results in 300 tests, which showed 100% repeatability. Finally, 60 cracked blades were inspected, with the known cracks in 57 blades detected. These results show the potential of thermosonics as a reliable NDT screening method for finding cracks in turbine blades.

P2O-2 Exploring the Advantages of a Random 1-3 Connectivity Piezocomposite Structure Incorporating Piezoelectric Fibres as the Active Element

This paper describes the use of piezoelectric ceramic fibres (PZT5A) for the fabrication of 1-3 composite transducers. Importantly, extensive FE analysis, using the PZFlex code, of these devices has been undertaken with complete 3D models utilised to reflect the random nature of the device structure. The manufacturing process is based on the place-and-fill method. A fibre composite block is produced, from which it is then possible to slice a number of layers of piezoelectric material with a thickness corresponding to the desired frequency of operation. These layers have electrodes applied and are then poled. Electrical impedance profiles of each device demonstrate excellent unimodal behaviour at the thickness resonance frequency, and show excellent correspondence with the FE models. Moreover, these devices possess high electromechanical coupling coefficients (kt > 0.65) for a ceramic volume fraction of 50% and a medium-set polymer (CIBA GEIGY CY221-HY956). Laser vibrometry scans of transducer surface motion corroborate the FE predictions of average uniform surface displacement notwithstanding local variations due to the random nature of the microstructure. Experimental pulse-echo assessments, when operating into a water load, demonstrate comparable sensitivity and bandwidth characteristics between a random fibre and conventional 1-3 composite, with similar specification

A model based bayesian solution for characterization of complex damage scenarios in aerospace composite structures

HIGHLIGHTSA composite laminate ultrasonic inspection finite element model is implemented.Waveform analysis is used to compare experimental and simulated inspection data.Composite material properties are characterized to validate the model.A composite delamination site is enveloped through a Bayesian inverse solution.Damage characterization uncertainties are quantified. ABSTRACT Ultrasonic damage detection and characterization is commonly used in nondestructive evaluation (NDE) of aerospace composite components. In recent years there has been an increased development of guided wave based methods. In real materials and structures, these dispersive waves result in complicated behavior in the presence of complex damage scenarios. Model‐based characterization methods utilize accurate three dimensional finite element models (FEMs) of guided wave interaction with realistic damage scenarios to aid in defect identification and classification. This work describes an inverse solution for realistic composite damage characterization by comparing the wavenumber‐frequency spectra of experimental and simulated ultrasonic inspections. The composite laminate material properties are first verified through a Bayesian solution (Markov chain Monte Carlo), enabling uncertainty quantification surrounding the characterization. A study is undertaken to assess the efficacy of the proposed damage model and comparative metrics between the experimental and simulated output. The FEM is then parameterized with a damage model capable of describing the typical complex damage created by impact events in composites. The damage is characterized through a transdimensional Markov chain Monte Carlo solution, enabling a flexible damage model capable of adapting to the complex damage geometry investigated here. The posterior probability distributions of the individual delamination petals as well as the overall envelope of the damage site are determined.

An investigation of acoustic beam patterns for the sonar localization problem using a beam based method.

Target localization can be accomplished through an ultrasonic sonar system equipped with an emitter and two receivers. Time of flight of the sonar echoes allows the calculation of the distance of the target. The orientation can be estimated from knowledge of the beam pattern of the receivers and the ratio, in the frequency domain, between the emitted and the received signals after compensation for distance effects and air absorption. The localization method is described and, as its performance strongly depends on the beam pattern, the search of the most appropriate sonar receiver in order to ensure the highest accuracy of target orientation estimations is developed in this paper. The structure designs considered are inspired by the ear shapes of some bat species. Parameters like flare rate, truncation angle, and tragus are considered in the design of the receiver structures. Simulations of the localization method allow us to state which combination of those parameters could provide the best real world implementation. Simulation results show the estimates of target orientations are, in the worst case, 2° with SNR = 50 dB using the receiver structure chosen for a potential practical implementation of a sonar system.

DEVELOPMENT OF AN EFFICIENT CONFORMABLE ARRAY STRUCTURE

The inspection of non-planar surfaces encountered in NDT poses difficulties that can only be satisfactorily addressed by a transducer whose active surface is comprised of an efficient conformable piezoelectric material. This paper describes a novel composite 2D array structure in which each element is a fine-scale array of piezoceramic fibres in a random arrangement. Device flexibility is imparted by the relatively soft flexible polymer phase which separates the elements. A comprehensive modelling programme, using the finite element package PZFlex, has produced the resulting structure which is termed a Composite Element Composite Array Transducer or CECAT. To facilitate the initial characterisation of the devices, the primary investigations have implemented the transducers as 1D arrays by the application of appropriate electrode patterns. However, the 2D physical arrangement gives the material excellent conformability over surfaces with two axes of curvature, e.g. an elbow or the root of a welded nozzle. Experimental measurements of electrical impedance and surface displacement are presented which demonstrate the high sensitivity of the devices. In addition, pulse-echo tests show comparable performance to a commercial rigid, 2MHz transducer when operated into a steel test sample.