Ana Lopez‐Sanchez

Simplified Method for Complete Characterization of an Ultrasonic NDE Measurement System

The electroacoustic measurement model (EAM model) is a model that combines models and measurements for all the electrical and electromechanical components and the acoustic/elastic wave propagation and scattering processes present in an ultrasonic measurement system to predict the measured output voltage. A new approach for implementing the EAM model is described. This approach uses a recently developed model-based pulse–echo method for determining the transducer electrical impedance and sensitivity. This method greatly simplifies the determination of the transducer sensitivity and as a consequence makes the entire EAM model more practical to implement. The experimental protocols needed to implement this simplified EAM model are described, and examples of experimentally determined characteristics of all the different system components are presented. These measured/modeled parameters of the system components are combined to predict the output signal in an ultrasonic immersion measurement system. It is shown that output signals obtained in this fashion agree well with the directly measured signals.

Modeling the Response of Ultrasonic Reference Reflectors

Reference reflectors characterized as flat-bottom hole (FBH), side-drilled hole (SDH), and spherical void (SPH) are commonly used in ultrasonic nondestructive evaluation (NDE) for calibration purposes. Here the measurement models currently available to simulate the A-scan response from those types of reference reflectors are examined. Measurement models suitable for both large and small reflectors are described and used to study the effect of beam variations over the surface of the reflector. The adequacy of the Kirchhoff approximation for predicting the waves scattered by these reference reflectors is also studied by comparing the results of that approximation to those obtained from more exact scattering solutions. The waveforms predicted by these various models are compared with experimentally determined responses in a pulse-echo immersion setup, and the accuracy of the models is discussed.

Ultrasonic Nondestructive Measurement Systems – Models and Measurements

The electroacoustic measurement model is an explicit model of an entire ultrasonic measurement system, including the pulser/receiver, cabling, and transducers. A summary is given of the measurement procedures needed for characterizing all the system elements contained in this measurement model, including a description of a new pulse-echo method for obtaining the sensitivity and impedance of an ultrasonic transducer. It is demonstrated that these models and measurement procedures can be combined to accurately simulate the measured voltage of a pulseecho immersion system.

K-space Prony's method for generating the basis functions of multi-Gaussian beam models.

The expansion coefficients of a multi-Gaussian ultrasonic beam model are obtained by a new approach that applies Prony s method in a K-space domain. This method allows the fitting of the Gaussian beam directly at the face of the transducer with very high computational efficiency. It is demonstrated that the K-space Pronys method can be used to accurately model the transducer field of planar and focused piston transducers, as well as probes that do not act as pistons. The choice of parameters appearing in the method and their influence on performance are discussed.

Characterization of an Ultrasonic Transducer in a Pulse‐Echo Setup

The effect that a transducer has on an ultrasonic measurement system can be completely characterized in terms of its input electrical impedance and sensitivity. Here, a simple model‐based approach is described to determine both of these transducer parameters in a pulse‐echo setup. It is demonstrated that it is important to compensate for cabling effects in the determination of these transducer parameters. The transducer sensitivity obtained using this new approach is compared to the sensitivity found using a more complex three‐transducer method originally developed for lower‐frequency acoustic transducers.. Also, the influence of the pulser/receiver settings on the measurements of the transducer impedance and sensitivity is discussed.

Models of Standard Ultrasonic Reference Reflectors and Their Experimental Validation

In this paper, models of the pulse‐echo ultrasonic immersion responses of three types of reference reflectors are given. The reference reflectors considered are a flat‐bottom hole (FBH), a side‐drilled hole (SDH) and a spherical void (SPH). Reciprocity‐based measurement models suitable for large and small size reflectors are given, where the variations of the incident fields over the surface of the reflector are either considered or neglected, respectively. The scattering responses of these reflectors are modeled with the Kirchhoff approximation and more exact solutions. The received waveforms predicted by these models are compared with experimentally determined responses and the accuracy of the models is discussed.

Generating the Gaussian Basis Functions for Multi‐Gaussian Beam Models

A new K‐space Prony’s method is developed to determine the amplitude and phase terms of the Gaussians used in a multi‐Gaussian beam model. Unlike the previous uses of Prony’s method this new K‐space approach allows the fitting of the Gaussian beams directly at the face of the transducer. The ability of the K‐space Prony’s method to model the transducer wave field of planar and focused piston transducers is demonstrated. It is shown that while this method is very fast there are also some stability and sensitivity issues associated with this approach.

Recent Advances in Modeling All the Components of an Ultrasonic Measurement System

Models and measurements are described that allow one to characterize all the elements of an ultrasonic measurement system, including the pulser/receiver, cabling, transducers, and the acoustic and elastic wave propagation and scattering processes present. By incorporating a newly developed pulse‐echo method for easily determining a transducer’s sensitivity and impedance, it is shown that it is now possible to completely characterize the entire measurement system with mostly simple electrical measurements and accurately simulate the output voltage of the system.

Measurement Models for Predicting the Ultrasonic Response from Side‐Drilled Holes

We develop measurement models and scattering models that allow us to predict the ultrasonic response from a side‐drilled hole (SDH). The scattering models considered include an explicit model based on the Kirchhoff approximation, as well as an “exact” separation of variables solution. Two measurement models are also derived. One allows for the variation of the incident fields over the cross‐section of the SDH while a simpler model neglects those variations. The predicted responses are compared with experimental signals.