Mitsuhiro Koike

An Ultrasonic Pulse Compression System for Nondestructive Testing Using Complementary Series Phase Modulation

An ultrasonic pulse compression system is presented, which employs complementary series phase modulated signals as transmit signals to obtain theoretically zero range sidelobes and high efficiency. In correlation based signal processing, echoes are correlated with reference signals that have the same wave forms as the echoes. The effectiveness of this signal processing over the conventional one using transmit signals as reference signals is verified by experiments.

A New Hybrid Model to Calculate Echoes and Ultrasonic Fields Scattered by Flaws Combining FDTD Method with Rayleigh Integral

A new hybrid model to calculate echoes and ultrasonic fields scattered by flaws is presented. In this model, transmitted fields by a transducer and fields scattered by flaws are calculated using the Rayleigh integral and the FDTD method, respectively. Received echo signals by the transducer are obtained by the inner product of the transmitted fields and the scattered ones at each grid for the FDTD method, and integrating those in a calculation area. Since the calculation area for the FDTD method can be limited around flaws, the calculation time is short and computer memory usage can be reduced. Experiments are done for two types of test object to confirm the validity of the hybrid model. As a result, experimental results are in good agreement with calculated ones.

Discussion on Transmission and Reception of Shear Vertical Wave Propagating along Surface of Test Object

It is shown that a shear vertical (SV) wave propagating along a surface of a test object can be transmitted and received by angle probes whose angle of refraction is close to a critical angle. In order to investigate this phenomenon, simulation is carried out using the finite difference time domain method. According to the acoustic fields obtained by the simulation, the beam width of a SV wave increases with propagation, and energy associated with the SV wave exists at the surface. Therefore, the transmitted pulse can be received. The phenomenon of SV wave propagation is referred to as SVC (SV wave for a critical angle). This simulation result is verified by an experiment, which showed that the transmitted pulse is applicable to the measurement of SV wave velocity.

Residual thickness measurement method of corroded steel plate using ultrasonic SH array transducer

Recently, the maintenance of aging structures such as steel bridge has become an important subject. For example, it is reported that corrosion occurred in a steel plate have broken the steel plate. So, development of the measurement method for residual thickness is desired.

Approximate Expression of Far Field Generated by Ultrasonic Angle Probe and its Application to Synthetic Aperture Focusing Technique

Geometrical optics approximation [1,2] provides good prediction of the field generated by an ultrasonic angle probe. However, it requires integration over the aperture of an ultrasonic transducer constituting the ultrasonic angle probe to calculate the field, and so it can not be applied directly to image reconstruction using synthetic aperture focusing technique [3,4].

A Pulse Compression Ultrasonic Test Instrument and Its Applications

In recent years, so called “digital ultrasonic test instruments” have been commercially available. These conventional instruments employ electrical impulse excitation of ultrasonic probes. In this configuration, waveforms of ultrasonic pulses into a test object are determined only by the characteristics of probes. This means that variation of probe characteristics causes variation of evaluated results and reproducibility of evaluation is poor. Furthermore, some of the conventional instruments do not provide enough information required for quantitative nondestructive evaluation (QNDE) about a test object, since ultrasonic echo signals are A/D converted after an envelope detector in a receiver and only information of echo height and position is obtained.

NEW SETS OF TESTING CODES PROVIDING ZERO RANGE SIDELOBES FOR ULTRASONIC PULSE COMPRESSION STRUCTIVE TESTING SYSTEMS

Abstract In conventional ultrasonic pulse compression nondestructive testing systems, complementary codes have been used for modulation of transmit signals in order to obtain zero range sidelobes. In this paper,new sets of testing codes for modulation of transmit signals are shown. The sets are composed of four or more codes and provide zero range sidelobes. In the code lengths less than fifty, the new sets exist at least in twelve different kinds of lengths, for which the conventional complementary codes do not exist. The new sets of testing codes expand the selection range of code lengths providing zero range sidelobes, and thus. arc useful for reduction of dead time in a system using a transducer for both transmission and reception. Sidelobe cancellation using the new sets is demonstrated by experiments.