Directivity Pattern Of Transducer Research Articles

Development of a 2D analytical model for the prediction of directivity pattern of transducers in the generation of guided wave modes

The guided waves (GW) are extensively used in the nondestructive testing (NDT) and structure health monitoring (SHM) of the large and complex structures. It enables to detect the defects up to few meters away from the transducers. However, the defects could occur at longer distances. In order to cover the test area of interest for the estimation of defects and to find the exact position of the transducers to be glued/ embedded, the directivity pattern of the transducers must be known. The aim of the presented work is to develop the 2D analytical model for the estimation of directivity patterns of the transducers at various frequencies and distances. The model was developed using the Huygens's principle of wave propagation distances with considering the known phase dispersive characteristics of the guided wave modes in the medium. The principle of modelling will work to plot the directivity pattern at any distance, at any excitation frequency and with any configuration and shape of the transducers. In order to demonstrate the model, the directivity patterns of P1-type macro-fiber composite (MFC) transducer in the generation of fundamental Lamb modes and shear horizontal mode at 300 mm from the center of MFC were obtained. The input signal used was 80 kHz, 3 period signal and propagation medium was Al plate of 2 mm thickness. The prediction about the position of where MFC transducer should be placed or glued on the object and selection of proper wave modes in order to estimate the defects in various materials is also discussed. The results were validated using finite element analysis (FEA) performed in ANSYS and further verified by the experimental analysis using low-frequency (LF) ultrasonic measurement system ULTRALAB, developed by Ultrasound Research Institute, Kaunas University of Technology. The proposed analytical model will not only facilitate to decide the position and number of transducers but also leads to choosing the configuration of transducer and wave modes suitable to be used for the inspection of defects.

The design and realization of projecting transducer directivity pattern field-testing instrument

The design and realization of projecting transducer directivity pattern field-testing instrument

Frequency dependence of backscatter from thin, oblique, finite-length cylinders measured with a focused transducer-with applications in cancellous bone

A model is presented for the echo from a thin, oblique, finite-length cylinder. The echo is calculated from the line integral of the transducer directivity pattern along the cylinder axis. The model was validated with broadband pulse-echo measurements from (1) a perpendicular (to the ultrasound beam) nylon wire as a function of lateral displacement from the beam center, (2) a tilted nylon wire as a function of the angle of inclination relative to the ultrasound beam, and (3) a quasi-parallel-nylon-wire phantom, which mimicked the scattering properties of cancellous bone. The transducer directivity pattern (as a function of position and frequency) was measured with a membrane hydrophone. The model predicts an approximately cubic frequency dependence of backscatter coefficient from the phantom, as has been observed experimentally in cancellous bone. The model also predicts the relationship between the cylinder length and the exponent of a power law fit to backscatter coefficient versus frequency, which is 4 for very short (compared to a wavelength) cylinders and asymptotically approaches 3 for very long cylinders.

Application of echo-trace analysis to estimation of behaviour and target strength of fish.

The echo trace of a single fish is theoretically analyzed. The shape and echo level at each point on the trace are expressed as functions of the target strength, orientation, velocity of the fish, the directivity pattern of transducer, etc. From the theoretical results, we derive estimation methods of the fish target strength, swimming velocity and orientation. These methods are applicable not only to a single-beam echo sounder but also to a dual-beam and a split-beam echo sounders. When the swimming speed of a fish is faster enough than a ship speed or when the split-beam sounder is used, even the tilt angle dependence of the target strength can be observed. We developed a quantitative echo-sounder suitable for the echo-trace analysis. These make it possible to read echo levels and ranges at each point on echo traces. The accuracy and effectiveness of the methods were confirmed by analyzing the echoes of calibrated steel spheres. Field observations on fish were performed and the results were examined.

Ultrasonic imaging system incorporating computer-aided coherent processing

An ultrasonic imaging system incorporating two-dimensional coherent data processing and computer image processing has been built and tested. The system consists of two parts: data acquisition, and computer processing and display. The data acquisition portion coherently detects both the amplitude and phase of an ultrasonic diffraction pattern emitted by or reflected from an object. This diffraction pattern is then quantized and entered into the computer memory. The computer portion of the system processes the data and displays the resulting image on a high-resolution computer-controlled graphics terminal. The presence of both amplitude and phase information as the input to the processing portion of the system offers advantages in that coherent processing techniques can be used to process the data as well as incoherent techniques. This processing capability allows one to perform such operations as matched filtering, removal of the receiving transducer directivity pattern, edge enhancement, etc. Application of the system to ultrasonic imaging, acoustic transducer calibration, and studies of scalar wave propagation and phenomena will be given.