Kazuhiko Imano

Real Time Extraction System Using Double-Layered Piezoelectric Transducer for Second-Harmonic Ultrasonic Pulse Waves

A novel detection system for second harmonic ultrasonic pulse waves is constructed by modifying an existing system using a double-layered piezoelectric transducer (DLPT). Two unique methods are introduced into the system, namely, the switching of the electrical connection of the DLPT and the pulse inversion excitation method, in which the DLPT is excited by both in-phase and out-of-phase pulses alternatively and averaged to cancel the fundamental and odd harmonic components. As a result of using these two methods, enhanced second harmonic waves are displayed on an oscilloscope in real time, and an improved sensitivity of 80 dB is obtained. Finally, drilled holes are imaged as an application of the new system and to demonstrate its usefulness.

Real time detection of second-harmonic components generated from plastic-deformed metal rod using double-layered piezoelectric transducer

Second-harmonic components generated from plastic-deformed metal rods are detected in real time using a double-layered piezoelectric transducer (DLPT). The DLPT is composed of two transducers with the resonance frequency f0; its resonance frequencies are f0/2 when the transducers are connected in parallel and f0 when the transducers are connected in series. The performance of the DLPT used in this ultrasonic system is evaluated. Samples of plastic-deformed metal rods are prepared using tensile test equipment. The relative amplitude of the second-harmonic component of the metal rod increased by approximately 25 dB after the tensile tests compared with that before the tensile tests. The variation in tensile load of the second-harmonic components generated by plastic-deformed metal rods is accurately measured by our system.

Detection of defects on reverse side of metal plate using MHz-range air-coupled lamb wave

A novel noncontact air-coupled ultrasonic system using MHz-range Lamb waves was constructed. In both the S0- and A0-modes, dispersion curves agreed well with the k– f image, which was obtained by applying a two-dimensional Fourier transform of the received waveforms using our system. The detection of square, flat-bottomed defects on the reverse side of a metal plate was demonstrated using two types of experimental arrangement. The position and width of the defects were estimated using the arrival time of the Lamb wave reflected from the defects. The profiling of the defect using the change in the amplitude of the Lamb wave confirms the usefulness of this system in the field of noncontact nondestructive evaluation.

Novel Detection System Using Double-Layered Piezoelectric Transducer in Same Polarization Direction for Sub-Harmonic Components Generated from Plastic-Deformed Metal Rod

A novel detection system for sub-harmonic components of ultrasonic pulse waves is constructed. A new double-layered piezoelectric transducer (DLPT), having the same polarization direction for each layer, is introduced to enhance the sensitivity for sub-harmonic components. In the case of DLPT stacked and bonded to one another in the same polarization direction, the resonance frequencies of the DLPT, fr, are f0 in a parallel connection and f0/2 in a series connection. As a result, the receiving sensitivity of the sub-harmonic components is increased by approximately 30 dB and the receiving sensitivity of fundamental components is decreased by approximately 20 dB, compared with those in the parallel connection. As an application of this system, the detection of sub-harmonic components generated from plastic-deformed metal rods is demonstrated. The DLPT system can be used to detect some deformed samples, while sub-harmonic components cannot be detected using a single transducer system.

Application of a Double-Layered Piezoelectric Transducer in the Generation of Short Ultrasonic Pulses

A double-layered piezoelectric disk-type transducer (DLPT) without a backing and/or an intermediate layer is newly constructed and analyzed to generate short ultrasonic pulses. One of the disks is excited for the purpose of transmission and the other is used for canceling the ringing of the pulse. The driving conditions of the system, including the DLPT and the peripheral electronic component for generating the short ultrasonic pulse, are optimized by analysis using the cascade connection of a transmission line model. Experiments using the active ringing cancellation method with DLPT in water are also demonstrated. The analysis and experimental results were mostly in agreement with each other. A short ultrasonic pulse having a pulse width of 1.5 wavelengths is achieved.

Experimental Study of Acoustic Properties of (0-3) Composite Materials for Intermediate Layer or Backing of Ultrasonic Transducers

The acoustic properties of composite materials used for an intermediate layer or backing of an ultrasonic transducer are studied experimentally. (0-3) composite materials are formed from a mixture of epoxy resin and tungsten powder for various weight ratios and their acoustic properties are measured. The experimental results are compared with the results predicted by different models, which are based on the elastic-wave scattering theory, to verify if the measured acoustic properties agree with theoretical estimations. For the ultrasonic velocities, the estimations of the Devaney model were closest to the experimental results. The weight fractions of tungsten powder for the composite materials, which have objective acoustic properties, can easily be estimated by theoretical calculations using the Devaney model.

Low-Frequency Air-Coupled Ultrasonic System beyond Diffraction Limit Using Pinhole

A novel noncontact air-coupled ultrasonic system introducing a conical acoustic probe (CAP) with a pinhole is constructed at low frequency. A 40 kHz ultrasonic wave in air goes through the pinhole, which has a diameter much smaller than the ultrasonic wavelength λ (9 mm), and forms a unique sound field. The lateral -3 dB widths of both theoretical and experimental sound fields approximately coincide with the pinhole diameter. A lateral resolution of λ/30 (0.3 mm) beyond the diffraction limit has been achieved using this system. As an application of the system, the surface profile for a 0.5 mm (λ/18) drilled hole in an aluminum plate was successfully imaged. The surface topographical profile of a step difference of 1 µm (λ/9000) was also measured.

Nanometer-Order Resolution Displacement Measurement System by Air-Coupled Ultrasonic Wave Introducing Maximum Phase-Sensitivity Tuning

An improved system introducing an automatic tuning of the maximum phase sensitivity of ultrasonic signals is constructed for detecting displacements with a nanometer-order resolution. The phases of multiple-reference waves introduced in our previous system are controlled and appropriately set to tune the phase sensitivity. To evaluate our system, the displacement of a high-precision mechanical stage was measured using 40 kHz air-coupled ultrasonic waves. The resolution of the phase detection for our system is improved more than ten times our previous system. A resolution of 40 nm (λ/200,000) displacement has been achieved with a measurable displacement range of 8 mm (λ).

Precise Displacement Measurements Using Phase Information of 40 kHz Ultrasonic Waves in Pinhole-Based Air-Coupled Ultrasonic System

Noncontact precise displacement measurements, including surface profiling, were demonstrated using the phase information of narrow-band 40 kHz continuous waves (wavelength λ=9 mm) in a pinhole-based air-coupled ultrasonic system beyond the diffraction limit. Real-time displacement measurements with a distance resolution of λ/900,000 (10 nm) were accomplished using a highly sensitive phase variation when the distance between the pinhole and the surface of an object was in the range from approximately 5 to 10 µm. To extend the working distance of our system while maintaining a high resolution, an automatic distance control system was constructed and introduced in our system. Using this advanced system, a surface topographical profile of 16 µm height was successfully measured, while maintaining maximum phase sensitivity. These results demonstrate the usefulness of our system when applied to noncontact precise displacement measurements.

Possibilities of nondestructive evaluation of a pipe using air-coupled ultrasonic wave in the MHz range

A trial for the excitation of a guided wave using a MHz range air-coupled ultrasonic wave in a hollow pipe is attempted. A guided wave is propagated in a 1mm thick aluminum pipe at a critical angle and transmission and reception via air are successfully accomplished. The flexural mode guided wave is detected using wavelet transformation.