Our research aims to develop an ultrahigh frequency resonator with high Q value to realize high sensitivity mass detective sensor for an application as a biosensor. A nano thin film deposited on a substrate is used as an oscillator, and we add a fullerene layer between a film and a substrate to prevent that vibrational energy leaks to a substrate. Ultrahigh frequency oscillation was generated in a Pt film deposited on a Si substrate using Picosecond laser ultrasound method, and resonance frequency and Q value were measured. As the results, we confirmed that adding a fullerene layers can increase Q value, and it has potential to improve the sensitivity of the mass detective sensor.

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In this study, we developed elastic-constant measurement in thin films at low temperatures using picosecond laser ultrasound spectroscopy. Specimens are cooled with liquid He through a heat exchanger in a cryostat, and an ultrahigh-frequency acoustic pulse is generated using a femtosecond light pulse, which propagates in the film-thickness directioa Acoustic-phonon resonances are observed by the changes in reflectivity of the time-delayed probe light and give the longitudinal-wave out-of-plane elastic constant We observed the temperature dependence of elastic constant C^<111> of a Pd thin film. This method is useful for studying the elastic properties of metallic thin films at cryogenic temperatures.

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Thin-film mechanical resonators are promising for high frequency bandpass filters. Amorphous oxide thin films are expected to be important candidates because they are free from grain scattering loss. However, it has been difficult to characterize their acoustic properties, especially attenuation, which is a key parameter for designing a high-Q resonator. Here, we present a novel methodology for evaluating ultrasonic attenuation of amorphous oxide thin films deposited on silicon substrate at very high frequencies between 200 and 300 GHz. This method uses the high sensitivity of the refractive index of light in silicon near to the wavelength near 400 nm. Detecting Brillouin oscillations from silicon substrate, which is caused by the transmitted acoustic wave, we can evaluate the frequency dependence of the attenuation coefficient in the thin film through an inverse calculation.

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Integrated piezoelectric ultrasonic transducer (IUT) has been developed as an ultrasonic sensor for high temperature measurement in recent years. It is expected that the application range extends further if the drive and detection method can be done by noncontact method for the practical use. Therefore, the power supply to IUT and the detection of an ultrasonic wave in IUT by the induction coil were tried. In this report, lift-off characteristic results by using various specifications of coils are reported.

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Generation laser scanning (GLS) method is one of the methods that achieve visualizing ultrasonic wave in a real material. In this paper, a novel method of a simultaneous measurement of both the phase and group velocities was proposed using the unique features of the GLS method. First, we introduced the GLS method briefly, and showed some images of the Lamb and Rayleigh wave propagations. The principle and verification of the simultaneous measurement was described in the later part of the paper.

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The application of an air-coupled ultrasound to noncontact evaluations of a spot welding is presented. A new type of air-coupled ultrasonic sensor with a focused lens is designed and fabricated. The acoustic lens is designed to generate not only a longitudinal wave but also a shear wave and/or a plate wave in the specimen which is a steel plate of 2.8 mm. C-scan measurements of spot weld model specimens are carried out in a transmission mode, to verify the performance of the developed sensor. It has been demonstrated that the intensity and signal-to-noise ratio of the transmitted signals through the specimen are higher (almost double) than those obtained using a conventional focused air-coupled ultrasonic sensor. Thus, it is expected that the developed sensor could be a useful tool for making quantitative evaluation of a nugget of spot weld.

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A simple ultrasound method for measuring a surface temperature distribution of a material being heated is presented. The principle of the method is based on the temperature dependence of a surface acoustic wave (SAW). SAWs are generated at different positions on a material surface consecutively by pulsed laser irradiation scanning (Nd:YAG, wavelength=1064 nm, energy 200 mJ/pulse, pulse width 3 ns) using a one-dimensional galvanometer scanner, and each SAW is detected at position using a laser interferometer based on photorefractive two-wave mixing (Nd:YAG, wavelength=532 nm, energy 200 mW). The ultrasonic method has been applied to the surface temperature measurement of an aluminum plate whose single side is being heated. The surface temperature distributions determined by the ultrasonic method almost aeree with those measured using an infrared camera.

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A novel method for noncontact measurement of wall thinning of a hollow cylinder using circumferential Lamb waves generated and detected by a pair of air-coupled ultrasonic transducers was proposed. In the method, wave-packets of multiple-turnaround C-Lamb wave are superposed and interfere themselves when the number of tone-burst cycle takes large enough. An amplitude of the superposed signal is determined by the angular wave number due to both the wall thickness and frequency. In the verifications, the wall thinnings were determined within the maximum error of 6 μm in comparison to the theoretical estimations.

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A lot of FRP storage tanks are used in chemical plants due to its superior anti-corrosion performance. However, it is difficult to estimate degree of degradation of FRP by an eye inspection. This study aims to evaluate the degree of degradation of an unsaturated polyester resin plate which is used as a matrix of FRP by zero-group-velocity (ZGV) lamb waves. The samples were degraded by immersing the resin into hot water of 90 ℃. ZGV Lamb wave was generated and detected by a Q-switched YAG laser with diameter of 4 mm and a heterodyne type laser interferometer with probe diameter of 0.1 mm. Measured Frequency of ZGV lamb wave for degraded samples decreased with immersion period. This Drop of the measured frequency means that elastic properties of the degraded samples reduced. Depth of discolored area of cross-section of the samples observed by optical micro-scope increased with immersion period and corresponded with gradated depth of the sample. However, no cracks were not observed in the discolored area. It is found that ZGV lamb wave can detect early stage of degradation of the resin.

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The authors have constructed a broadband ultrasonic propagation system using MFC actuators and FBG sensors. These components can be integrated into composite laminates. In this research, we used this system to detect delamination damage in a CFRP quasi-isotropic laminate. First, we identified the multiple modes of Lamb waves in the laminate by transmitting and receiving the symmetric and antisymmetric modes separately. Then the mode conversions at both tips of a delamination were investigated. After that, we proposed a new delamination detection method based on mode conversions and carried out experiments on laminates with an artificial delamination. The frequency dispersions of the received modes changed depending on the delamination length owing to the mode conversions. Since these phenomena were also confirmed by FEA, our new method is effective in detecting a delamination in CFRP laminates.

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Higher modes of SH (shear horizontal) guided wave cannot propagate in a plate which is thinner than the cut-off thickness because of the dispersive character. When a plate contains such a thinning region, a higher mode is converted to a lower one, causing discontinuous velocity change. For the purpose of developing a novel nondestructive evaluation method based on the velocity change, the mode conversion in aluminum plates with thinning region is experimentally explored. Fundamental symmetric SH_0 and the first asymmetric SH_1 modes were generated by an EMAT (electromagnetic acoustic transducer) and propagated in the plates containing artificial thinning regions. The propagated SH waves were picked up at various locations with a piezoelectric pinducer, which is capable of broad range acoustic detection. This experiment observes directly that the generated SH, mode converts to SH0 mode when it enters the defected area, and it converts back to the SH_1 mode after passing through the defect.

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Experimental investigation of mode conversions of a guided wave through a pipe tee has been carried out. Based on the particle displacement of the guided wave modes, the mode conversions from the T(0,1) mode to circumferentially higher order modes, the T(1,1) and T(2,1) modes, were confirmed. The experiments were carried out with 8 sensor elements located circumferential positions to detect the modes. A simple signal processing method for preferential detection for each mode was shown.

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Sensitivity of defect detections using T(0,1) mode guided waves of welded elbow pipes has been experimentally evaluated. The artificial defects were introduced at the outer side of the elbow and the place near the weld-lines. To evaluate the sensitivity, the artificial defects were gradually increased up to 2 mm by 0.05 mm increment. It was confirmed that the sensitivities of the outer side defects at the elbow part was larger than those obtained at the straight part. The experimental results and related discussion were described.

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From the appearance of HVOF thermal spray system on 1980s, WC cermet coatings have been used as an antiwear coating in many industrial manufacturing. Recently, WC cermet spray materials were applied to new thermal spray method such as Warm Spray and Cold Spray under research phase. The research target of spray materials were standard contents such as WC-Co or WC-Ni used by HVOF. However, there is a potential that any other WC cermet materials are better for Warm Spray and Cold Spray because the characteristics of metal binder is conclusive factor. In this study, WC-Fe alloy cermet spray material was sprayed by cold spray to investigate the influence of Fe alloy binder. The results indicate that the WC-Fe alloy cermet material is better than standard WC-Co in spray efficiently and coating properties.

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Cold spraying has been developed as a high-quality coating process. However, the bonding mechanisms of cold sprayed solid particles have not been clarified yet. In this study, copper particles were deposited on an aluminum nitride substrate coated by the sputtering of copper and titanium at a low pressure of less than 1.0 MPa, making this approach suitable for a wide range of engineering applications. The interfacial boundaries were carefully observed in thin foils from the cross sections of the specimen with a high-resolution transmission electron microscope (TEM). The cold-sprayed copper particles are connected directly without any oxidation film due to the appearance of new metallic surfaces. A wavy boundary was observed between cold-sprayed copper and the substrate, as seen in the joint boundary by explosive welding, which is caused by shear instability. TEM data clearly revealed some phenomena related to the impact of spraying powder toward the substrate.

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Cold spraying has been developed as a high-quality metallic coating process. However, the deposition mechanism and optimum spray conditions have not been well understood. This study investigates the effects of powder morphology on deposition behavior and adhesion strength of cold-sprayed coatings. It was observed that irregular shaped powders were deposited easier than spherical shaped powders. It was also easier to fabricate thick coating using the irregular shaped powders. However, the adhesion strength of the coating fabricated using the spherical shaped powder was higher than that of the irregular shaped powders. Higher adhesion strength was caused by larger adherence contact area of deposited particle-to-substrate and particle-to-particle. It is concluded that although the irregular shaped powders can be deposited easier, but its adhesion strength is lower than that of the spherical shaped powder.

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The adhesion mechanism of deposits-substrate interface prepared by cold spray method has still been obscure up to now. It seems that the adhesion strength is mainly determined by the mechanical (including the plastic deformation of particle and substrate) and thermal interaction between the particle and substrate when the particles impact onto the substrate with high velocity. In order to understand the adhesion mechanism, the influences of particle impact velocity on the adhesion strength were investigated in this study. The particle velocity was obtained with DPV-2000 measurement and CFD simulatioa The relationships between the adhesion strength of deposits-substrate interface and particle velocity were discussed

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Tribological properties of WC cermet coating layers which are thermal sprayed are researched. On the assumption of the severe sliding condition in which large compress and tensile stress are applied to a surface layer simultaneously, relatively hard material is chosen as counter parts and additional tensile stress is applied. WC/12%Co is employed as coating material by High Velocity Oxy-Fuel (HVOF) spray and Warm Spray processes. From the experimental results, it is found that the WC cermet sprayed coatings are inferior to sintered WC/Co with regard to fracture toughness near the surface and pseudo-plastic deformation which are main wear behavior in severe sliding condition.

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In the case of cold spraying, small particles are accelerated to subsonic or supersonic velocity by high temperature and supersonic gas flow, and then impact onto a substrate. When particles impact onto a substrate, kinetic energy of the particles is converted to plastic deformation energy, namely plastic deformation is required for deposition. Because of requirement of plastic deformation, hard materials, such as high carbon steels, can be difficult to deposit on the substrate. And also, due to large plastic deformation, work hardening can be occurred. In this study, in order to develop an innovative repairing technique for high carbon steel by cold spraying, microstructures and hardness property of cold sprayed high carbon steel coatings using high carbon steel powders were evaluated. In order to improve and control the hardness of the coating, spray conditions were optimized and mixed powders of high carbon and mild steels were used. By applying mixed powders, a dense and thick coating with appropriate hardness was obtained.

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Cold spraying is an attractive process upon fabrication of a high-quality metallic coating. However, the adhesion strength of cold-sprayed coatings often presents an issue. In this paper, the adhesion strength of cold-sprayed individual copper particles on a stainless steel substrate is evaluated by nano-scratch test. Though there are not any tendencies between the adhesion strength and process gas conditions, it was possible to measure by nano-scratch test. The adhesion strength of the particles was much higher than that of the coatings fabricated with same spray conditions. A residual stress decreased the adhesion strength according to form a thick coating. The substrate surface after removing the particle by nano-scratch test exhibited the interfacial morphology. The substrate surface morphology was observed by atomic force microscope (AFM). The surface deformation according to the particle collision was very small. These results show that the cold sprayed particles deposit with high adhesion strength and small deformation of the interface. The main bonding mechanism of cold-sprayed copper particle on stainless steel substrate is considered to be a metallic bond.

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As a novel deposit process, many researchers have focused on Cold Spray. Up to now, few studies about mechanical properties of Cold Spray deposits have been reported and it has still not been well understood how they are determined in cold spray process. In the case of industrial applications for Cold Spray technology, since lack of data on deposit properties such as physical, mechanical and electrical properties, the prevalence of the technology has been obstructed. In this study, we investigated mechanical properties of Cold Spray deposits both as sprayed and heat-treated such as Cu, Al, Stainless Steel 316L and Ti. It was found that the higher operating gas temperature leads to the stronger rupture strength for each deposit. All the deposits as sprayed had no elongation. But after heat treatment of the deposits, some showed elongation and the others showed no elongation.

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Cold spray (CS) is a new coating technology for the production of high quality metallic based coatings. This process involves the deposition of metallic layers and structures from propelled fine powders using a high-speed gas jet flow without melting. Low-pressure type CS process, which consists of small and compact equipment, is expected to be used for on-site repairing application. In this work, the possibility of the repair for zinc plating by low-pressure type CS technique was discussed. We have successfully obtained thick (mm order) Zn deposition by low-pressure type CS technique. Moreover, from the investigation results of environmental resistant properties, it may be considered that CS technique have high possibility to apply the repairing application for the Zn plating.

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