Makiko Kobayashi | Kumamoto University (original) (raw)

Papers by Makiko Kobayashi

Diagnostics, 2019

We have newly developed coaxial and confocal optical-resolution photoacoustic microscopy based on... more We have newly developed coaxial and confocal optical-resolution photoacoustic microscopy based on sol-gel composite materials. This transducer contains a concave-shaped piezoelectric layer with a focus depth of 5 mm and a hole with a diameter of 3 mm at the center to pass a laser beam into a phantom. Therefore, this system can directly detect an excited photoacoustic signal without prisms or acoustic lenses. We demonstrate the capability of the system through pulse-echo and photoacoustic imaging experiments. The center frequency of the fabricated transducer is approximately 7 MHz, and its relative bandwidth is 86%. An ex-vivo experiment is conducted, and photoacoustic signals are clearly obtained. As a result, 2- and 3-dimensional maximum amplitude projection images are reconstructed.

Advancements in Civil Engineering & Technology, 2019

Non-destructive testing (NDT) of infrastructure such as bridges and tunnels has become more impor... more Non-destructive testing (NDT) of infrastructure such as bridges and tunnels has become more important since it has aging problem and traffic was heavier than expected. Thin film ultrasonic sensors would be attractive because it is easy to integrate on huge structure. However, NDT of huge structure is still challenging because of sensor accessibility. Semi-noncontact ultrasonic sensors were proposed in this manuscript. 20cm diameter copper coil transmit/receive electrical signal from a pulser/receiver instrument and a thin film ultrasonic sensor and reflected echo from 12.7mm thick steel plate successfully. By this method, measurement using drone could be possible and it increases application possibility for huge infrastructure monitoring.

Ultrasonic non-destructive testing (NDT) is used in various industries for cost effectiveness and... more Ultrasonic non-destructive testing (NDT) is used in various industries for cost effectiveness and sub-surface defect/flaw detection capability. Ultrasonic transducers made by sol-gel composite could be good candidates for industrial applications because of high temperature durability, high-signal-to-noise ratio (SNR), and physical flexibility when sol-gel composite films are fabricated onto flexible substrate, such as metal foil. Since industrial structures have many curved surfaces and the surface temperature could be high during operation so flexible high temperature ultrasonic transducers have been desired. Fabrication cost of stencil printing method could be lower than spray method due to short fabrication time. However, fabrication of flexible ultrasonic transducer made by stencil printing method is difficult and low film adhesion strength was an issue. In this study, PZT/PZT films were fabricated by stencil printing method on metal foil substrates. In order to improve adhesion...

Ultrasonic transducer using a sol-gel composite method has been investigated in the field of non-... more Ultrasonic transducer using a sol-gel composite method has been investigated in the field of non-destructive testing. Sol-gel composite material is made by mixture of piezoelectric powder and sol-gel solution1), and the combination of piezoelectric powder and sol-gel solution in the sol-gel composite method has been studied for the development of new composite materials with desirable characteristics. It is known that the dielectric constants of the sol-gel phase and the piezoelectric powder phase influence the sol-gel composite performance. Pb(Zr,Ti)O3 (PZT)/Al2O3, which is composite of PZT piezoelectric powder and aluminum oxide sol-gel solution, showed about 80pC/N lower piezoelectric constant d33 than that of PZT/PZT.2) From this result, it seems that the high dielectric constant of the sol-gel phase is preferable. In addition, it was suspected that the composite consisting of sol-gel solution with high dielectric constant and piezoelectric powder with low dielectric constant co...

Piezoelectric film has been widely used for ultrasonic non-destructive testing due to the simmpli... more Piezoelectric film has been widely used for ultrasonic non-destructive testing due to the simmplicity and cost effectiveness. Sol-gel techiqnue is one of the major thin film fabrication methods because of low instalation cost and mass production possibility. However, it is reralatively difficult to fabricate 1 m by one coating due to high internal stress during thermal process, and this thickness is too low for many industrial non-destructive applications. Sol-gel composite materials have been developed to overcome thickness limitation. Spray technique could be attrative because of curved surface suitablity, though spray coating process and thermal process must be still repeated in order to achieve desired thickness. Electrospray deposition (ESD) could realise desired thickness by one coating process. ESD was developed to fabricate uniform radioactive thin film in 1950s, then this technique was used to fabricate metal oxide thin film in 1990s. In this method, a polymer solution is s...

Proceedings of Meetings on Acoustics, 2017

We have developed a kerfless phased array transducer using sol-gel composite spraying technique. ... more We have developed a kerfless phased array transducer using sol-gel composite spraying technique. This technique is a method for developing piezoelectric transducer by spraying composite material of piezoelectric sol-gel solution and powder, and it has attracted great attention especially in non-destructive testing over the years because of its features such as curved surface suitability, flexibility, and high-temperature durability. The porosity can contribute to a decrease in crosstalk among elements. As a preliminary experiment, a kerfless linear array transducer with a center frequency of 5 MHz and pitch of 500e-6 m using the sol-gel composite spraying technique was fabricated and fundamental performance was evaluated. As a result, approximately-130 dB of crosstalk was obtained.

Japanese Journal of Applied Physics, 2018

CaBi 4 Ti 4 O 15 (CBiT)-based lead-free sol-gel composites were developed for high-temperature ul... more CaBi 4 Ti 4 O 15 (CBiT)-based lead-free sol-gel composites were developed for high-temperature ultrasonic transducer application. In this study, two types of lead-free sol-gel solution, Ba 0.7 Sr 0.3 TiO 3 (BST) and Bi 4 Ti 3 O 12 (BiT), were used for consistency to fabricate >50-µm-thick CBiT/BST and CBiT/BiT films on 3-mm-thick titanium substrates by a sol-gel spray technique. BST and BiT were chosen because of their high dielectric constant and high Curie temperature, respectively, in addition to their being lead-free materials. A thermal cycle test was carried out between RT and 600°C, and clear multiple echoes were confirmed during three thermal cycles for both materials. In addition, the sensitivity of CBiT/BiT was higher than that of CBiT/BST although a higher poling temperature is required for CBiT/BiT. Therefore, an ultrasonic transducer potential for high-temperature application was successfully demonstrated.

Journal of Sensor Technology, 2014

The nondestructive inspection of a high temperature structure is required in order to guarantee i... more The nondestructive inspection of a high temperature structure is required in order to guarantee its safety. However, there are no useful sensors for high temperature structures. Some of them cannot work at temperatures over 50˚C. Another concern is that they are too expensive to use. A sensing system, which can transmit and receive an ultrasonic wave that travels a long distance using a long waveguide, has been studied. We confirmed that the optimal guided ultrasonic wave could travel more than 10 m using an electromagnetic transducer (EMAT) with a thin Ni-sheet surrounded on the surface of the bar and a 2-mm diameter bar as the waveguide. However, we had the difficult problem of receiving the reflected ultrasonic wave from the inside of a test specimen. We tried to improve the trial inspection system using an acoustic horn. An experiment in which the temperature of the test block was heated to about 500˚C has now been completed. Finally, the condition of the bend in the waveguide to pass without reflection was confirmed.

2007 IEEE Ultrasonics Symposium Proceedings, 2007

The nondestructive inspection of a high temperature structure is required to guarantee its safety... more The nondestructive inspection of a high temperature structure is required to guarantee its safety. However, there are not any useful sensors for high temperature structures. Some of them cannot work at temperatures over 50°C. Another concern is that they are too expensive to use. The sensing system, which can transmit and receive an ultrasonic wave that travels a long distance using a long waveguide, has been studied. We could confirm that an optimal guided ultrasonic wave can travel more than 50cm using a thin 2mm diameter bar as the waveguide. However, we had a difficult problem of receiving a reflected ultrasonic wave from the bottom surface of a test specimen. We tried to improve the trial inspection system using an ultrasonic horn. Finally, an experiment in which the temperature of a test block was heated to about 270°C has been done and the reflected ultrasonic wave from the bottom surface was successfully detected.

Transmitting a longitudinal wave and a traverse wave into a composite material in a molten state ... more Transmitting a longitudinal wave and a traverse wave into a composite material in a molten state has been studied in the online control of the composite material which cannot be evaluated by a conventional ultrasonic sensor as a final analysis, using the difference in the propagation characteristics of both modes. It is especially expected that measurement of the physical quantity which was not able to be conventionally measured can be performed by carrying out coincidence measurement of the ultrasonic wave in both modes. Therefore, in this research study, an ultrasonic probe, which can simultaneously transmit and receive a longitudinal wave and a traverse wave has been developed using an electromagnetic acoustic transducer (EMAT) because it has the advantage of measuring high temperature samples. In this study, two methods have been compared. The 1st method uses a traverse wave EMAT that travels in a vertical direction and a bar wave by which the low order mode is equivalent to longitudinal wave vibration. The other method is to carry out the mode conversion of the traverse wave by a traverse wave-EMAT. The longitudinal converted from the transverse wave are spread in the axis direction. As the experimental results of both optimizations of the drive conditions, it has been confirmed that the 2nd mode conversion method was promising. This paper reports about the trial process and the experimental results.

2008 IEEE Ultrasonics Symposium, 2008

Polymer Engineering & Science, 2005

Real-time process monitoring of the fabrication process of microfluidic devices using a polymer i... more Real-time process monitoring of the fabrication process of microfluidic devices using a polymer injection molding machine was carried out using miniature ultrasonic probes. A thick piezoelectric lead-zirconate-titanate film as an ultrasonic transducer (UT) was fabricated onto one end of a 4-mm diameter and 12-mm long steel buffer rods using a sol gel spray technique. The center frequency and 6 dB bandwidth of this UT were 17 MHz and 14 MHz, respectively. A signal-to-noise ratio of more than 30 dB for ultrasonic signals reflected at the probing end was achieved. The probe can operate continuously at 200°C without ultrasonic couplant and cooling. Clear ultrasonic signals were obtained during injection molding of a 1-mm-thick part having test patterns on its surface. Shrinkage of the molded part and part detachment from the mold were successfully monitored. Surface imperfections of the molded parts due to a lack of the sufficient holding pressure is discussed with regard to the ultrasonic velocity obtained. The presented ultrasonic probes and technique enable on-line quality control of the molded part by optimizing the holding pressure and improvement of process efficiency by reducing the cycle time.

Journal of Intelligent Material Systems and Structures, 2009

Two types of ultrasonic sensors are presented for structural health monitoring (SHM) and non-dest... more Two types of ultrasonic sensors are presented for structural health monitoring (SHM) and non-destructive testing (NDT) of graphite/epoxy (Gr/Ep) composites of thickness ranging from 1 mm to 12.7 mm. These piezoelectric film-based sensors are fabricated using a sol-gel spray technique. The center operation frequency of these sensors ranges from 1.3 MHz to 14.5 MHz. For the first sensor type, piezoelectric films of thickness ≥30 μm were deposited directly onto planar and curved Gr/Ep composites surfaces as integrated sensors. Ultrasonic signals propagating in a distance of more than 300 mm have been obtained. Anisotropy of 08 and 908 cross ply Gr/Ep composite is measured and delamination detected. For the second sensor type, piezoelectric films are coated onto a 50 μm thick polyimide membrane as flexible sensors that may be attached to a host composite structure with planar or curved surfaces. An induction type non-contact method for the interrogation of the Gr/Ep composites using int...

Japanese Journal of Applied Physics, 2007

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2006

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