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(K0.88Na0.12)NbO3 (KNN) thick films with various thicknesses were prepared on Ni-based metal substrates by hydrothermal method. Although the deposition of KNN films was hardly observed directly on metal substrates until 12 h, the amount of KNN films deposited on both SrRuO3/LaNiO3- and SrRuO3-covered Ni based metal substrates increased to about 5 µm with increasing deposition time above 3 h. X-ray diffraction studies confirmed the formation of {100}c- and randomly-oriented KNN films on SrRuO3/LaNiO3- and SrRuO3-covered metal substrates, respectively. Ferroelecctric property studies revealed an improved remanent polarization and an improved piezoelectric response of {100}c-oriented KNN films over the randomly-oriented KNN films. In addition, the values for {100}c-oriented KNN films were similar to those of {100}c-oriented epitaxial KNN films prepared on (100)cSrRuO3//SrTiO3 substrates.

KNbO3 thick films were deposited on (100)c SrRuO3//(100)SrTiO3 substrates at 240 °C for 3 h by hydrothermal method. Film thickness increased linearly with increasing the deposition number of times and 130 μm thickness was achieved by the 6 time deposition. XRD analysis showed the growth of epitaxial orthorhombic films with the mixture orientation of (100), (010) and (001). Cross-sectional SEM observation showed that the 130 μm-thick film was dense and no obvious voids inside the film. In addition, the crystal structure change along film thickness direction was not detected from the cross-sectional Raman spectral observation.

Two types of transducers for small ultrasound probes were fabricated. Titanium or epoxy resin was used for the backing material of the transducers. The piezoelectric material was lead zirconate titanate (PZT) that was deposited by the hydrothermal method. These transducers were built into a small ultrasound probe and the characteristics were evaluated. As a result, we succeeded in the fabrication of a wideband ultrasound probe with a distance resolution of 16 μm, a frequency bandwidth of 69 MHz in the range of 39 to 98 MHz, and a fractional bandwidth of 86% at the epoxy resin backing probe. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(3): 1–8, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10419

Miniature ultrasonic probes were developed by hydrothermally depositing lead zirconate titanate (PZT) polycrystalline films on a titanium (Ti) wire. The small ultrasound probes were fabricated using hydrothermally deposited PZT polycrystalline film on the end of a titanium wire with a diameter of 0.6 mm and a length of 50 mm. The performances of the prototype small ultrasound probes were measured. As a result, it was confirmed that the probe has a center frequency of 16 MHz, a fractional bandwidth of 70%, and a distance resolution of better than about 130 µm without using an acoustic matching layer. It was also found that the beam width was 0.55 mm for a distance of 4 mm between the string target and the miniature ultrasound probe.

We have studied transmission methods of high-frequency ultrasonic waves through a thin fiber for direct observation of the microscopic image of the tissue. We reported previously that C-mode images of an artificial bone and an animal bone placed in water were obtained by reflection method using a fused quartz fiber as the probe. In this paper, we describe that the C-mode images of the tissue on the glass in water were obtained by penetration method.

We have studied transmission methods of high-frequency ultrasonic waves through a thin fiber for direct observation of the microscopic image of the tissue. We reported that high frequency ultrasonic waves (70 - 175MHz) transmitted approximately 1.6mm in the acoustic coupling medium, and a C-mode image of a coin placed in water was obtained using a tapered fused quartz fiber as the probe. In this paper, we describe that the lateral resolution was improved by focusing ultrasonic-beams radiated from a fused quartz fiber, and the improved C-mode image of an animal bone was obtained.

Recently, our laboratory has explored the possibility of using lead zirconate titanate [PZT] polycrystalline film deposited hydrothermally on titanium substrate to fabricate a small actuator and ultrasound sensor. Hydrothermally deposited PZT polycrystalline films have piezoelectricity without a poling process, and it is easy to deposit PZT polycrystalline films on substrates that are tiny or complexly shaped. We confirmed that hydrothermally synthesized PZT polycrystalline films have wideband frequency characteristics with sensitivities in the megahertz band. It is thought that miniature ultrasound probes with wide- frequency band characteristics can be fabricated using hydrothermally synthesized PZT polycrystalline films. In our last report we assessed methods to produce a miniature ultrasound probe and transceiver characteristics. Here, the reception and transmission directivities of such a probe were measured at 5, 10, 15, and 20 MHz. The results showed that, except at 5 MHz, the theoretical and experimental values agreed. The difference at 5 MHz is attributed to the effect of the resonance frequency of the diameter direction.

High frequency, wide band characteristic and high intensity ultrasonic transducer was fabricated by hydrothermal deposition technique of lead zirconate titanate (PZT) polycrystalline thick film. The transducer had a 20-µm-thick PZT layer on a 40-µm-thick titanium substrate in an active area of 1.5 mm × 8 mm. The mechanical resonance frequency was approximated by the phase velocity of the dilatational wave of Ti substrate and the hydrothermal PZT thick film. The half wavelength resonance frequency of the vibration plate of the Ti substrate and the hydrothermal PZT thick film was about 40 MHz. This ultrasonic transducer radiated ultrasounds in the frequency range from 2 to 40 MHz within a 6 dB deviation using thickness vibration mode. This is first report of the ultrasonic transducer using the hydrothermal PZT thick film at over 20 MHz operation characteristics.

A PZT piezoelectric film synthesized hydrothermally was studied actively in our laboratory. However, since PZT is a chemical compound including lead, we are anxious about malign influence of PZT on health and environment recently. Therefore, we tried to synthesize a BNT lead free piezoelectric film hydrothermally on the titanium substrate. BNT lead free piezoelectric poly-crystalline films synthesized on the titanium substrates were estimated with. SEM images, XRD pattern, and EDS data. We fabricated the bimorph vibrator which has the synthesized BNT lead free piezoelectric film, and evaluated their material characteristics.

Recently, the PZT poly-crystalline film deposited on titanium substrate by hydrothermal method has been studied actively for development of a small actuator and ultrasonic sensor in our laboratory. The PZT poly-crystalline films were deposited on a titanium substrate in KOH solution used as mineralizer which included Pb ion, Ti ion, and Zr ion under high temperature (about 150degC) and high pressure (about 4 kPa). We reported on the needle type miniature hydrophone and the ultrasonic transducer with hydrothermally synthesized PZT poly-crystalline films in 2005 IEEE International Ultrasonics Symposium in Rotterdam. It has confirmed that the hydrothermally synthesized PZT poly-crystalline films showed wide band frequency characteristics in MHz band of the sensitivities. It is thought that miniature ultrasonic probe with wide frequency band characteristics of sensitivities can be fabricated by using the hydrothermally synthesized PZT poly-crystalline films. The miniature ultrasonic probes were fabricated by hydrothermally deposited PZT poly-crystalline film on an end of the titanium wire with diameter of 0.6 mm and length of 50mm. The performances of trially fabricated ultrasound probes were measured. Ultrasonic imaging experiments using a target in water were performed with the trially fabricated ultrasonic probe with hydrothermally synthesized PZT films. As a result, it was confirmed that this probe has a center frequency of 16 MHz, a bandwidth of 80%, and distance resolution more than 80 micrometers. We will report about the structure and performance of the fabricated ultrasound probe with hydrothermally synthesized PZT poly-crystalline film and the results of imaging experiments under water

Films of solid solution in KNbO3–NaNbO3 (KNN) were deposited at 240 °C on (100)cSrRuO3∥(100)SrTiO3 substrates by the hydrothermal method. (K x Na1-x )NbO3 films with x = 0–1.0 were synthesized by changing the fraction of KOH in a solution of KOH and NaOH. The x in (K x Na1-x )NbO3 continuously changed with the volume fraction of KOH, while the deposition amount strongly depended on x. Epitaxial films with 100 orientation were obtained in the entire composition range and their out-of-plane lattice spacing changed with x. All the films showed ferroelectricity and their remanent polarization became larger than what above x = 0.58.

Deposition behavior and the crystal structure of the epitaxial KNbO3 films, grown at 240 °C on (100)cSrRrO3∥(100)SrTiO3 substrates using hydrothermal method, as well as their ferroelectric and piezoelectric properties were systematically investigated. Film deposition was detected to have begun after 2 h from the start, and the thickness increased with increasing the deposition time up to 4 h, but contrary decreased after 9 h due to the etching by KOH. X-ray diffraction (XRD) patterns of the films were basically the same regardless of the deposition time. However, the films deposited for 15 h introduces large amount of voids than those for 2 h. Ferroelectric and piezoelectric response of the films deposited for 2 and 15 h were measured to have similar film thickness, but the maximum applied electric field for the 2-h films was twice as that for the 15-h ones. The prototype ultrasonic transducer was fabricated using the KNbO3 films, which were deposited by hydrothermal method at 240 °C for 3 h, and proved to be able to transmit and receive ultrasonic signals above 90 MHz in degassed water.

KNbO3 films were grown at 240 °C by the hydrothermal method using KOH and Nb2O5 as source materials. Film thickness increased with reaction time up to 3 h, however decreased for longer reaction times. A 16-µm-thick epitaxially grown KNbO3 film with {100}pc orientation were successfully grown on (100)cSrRuO3∥SrTiO3 substrate for 3 h. The relative dielectric constant and dielectric loss at 100 kHz were 415 and 8%, respectively. Clear hysteresis loops originating from ferroelectricity were observed and the remanent polarization was 20 µC/cm2 at the maximum applied electric field of 220 kV/cm. The effective longitudinal piezoelectric constant, d33eff, obtained using a laser Doppler velocimeter, was 86 pm/V.

Recently, a PZT poly‐crystalline film deposited on titanium substrate using the hydrothermal method was studied actively in our laboratory for development of an ultrasonic sensor. These PZT poly‐crystalline films can form PZT poly‐crystalline films easily on substrates of complex shape using hydrothermal method. We reported a needle‐type miniature hydrophone and the ultrasonic transducer with hydrothermally synthesized PZT poly‐crystalline films. Results confirmed that the hydrothermally synthesized PZT poly‐crystalline films showed wideband frequency characteristics in the megahertz band of sensitivities. A miniature ultrasonic probe with wide frequency band characteristics of sensitivities is thought to be producible using hydrothermally synthesized PZT poly‐crystalline films. Miniature ultrasonic probes were fabricated using hydrothermally deposited PZT poly‐crystalline film on the end of 0.6‐mm‐diam titanium wires. Ultrasonic imaging experiments of a target in water were performed using a fabricated u...

Recently, high‐frequency miniature medical ultrasound probes with high resolution were actively developed. However, it is difficult to fabricate such tiny ultrasound probes using piezoelectric ceramic vibrator with thickness less than 100 μm. We deposited a PZT poly‐crystalline film on a titanium substrate using the hydrothermal method and developed transducers using the PZT poly‐crystalline film for ultrasound probes. In this study, we applied it to a miniature medical one‐dimensional (1‐D)‐array‐type ultrasound probe with resonance frequency of 10 MHz. After sputtering of pure titanium on the surface of a hydroxyapatite substrate, the titanium film was etched using the photolithography method to form a 1‐D titanium film electrode array with 75 μm element pitch, 40 μm element width, and 4 mm element length to scan an ultrasound beam electronically by sector scan mode using phased‐array technique. Thereby we fabricated a miniature 1‐D‐array‐type ultrasound probe. A transmitted ultrasound pulse from 10 MHz commercial ultrasound probe was received by this fabricated 1‐D‐array type ultrasound probe with hydrothermally synthesized PZT poly‐crystalline film vibrators.

This prototype ultrasonic transducer had about a 30‐μm thick hydrothermal PZT layer on a 50‐μm thick titanium substrate. An active area of this transducer was 3.5 mm in diameter. Material constants of this hydrothermal PZT thick film were measured. Electromechanical coupling coefficient kt was over 0.25 and acoustic impedance was 6 Mrayl. A mechanical resonance frequency in the thickness mode of the prototype ultrasonic transducer was approximated by a mason’s equivalent circuit using the thickness and the material constants of the hydrothermal PZT film and the Ti substrate. The prototype ultrasonic transducer had a double broad peak spectrum of about 15 and 30 MHz in simulation. Also, these broad peaks were a half wavelength and a quarter wavelength resonance frequency in a combined structure of the hydrothermal PZT thick film and the Ti substrate. The prototype ultrasonic transducer transmitted ultrasound in water. Experimental results were the prototype ultrasonic transducer radiated ultrasound at the frequency range from 1 to 50 MHz as wideband using respective resonance frequency. A reason for the wideband characteristics radiation of ultrasound was the prototype ultrasonic transducer has low acoustic impedance and double broad peak.

An audio signal coding apparatus includes a first-stage encoder for quantizing the time-to-frequency transformed audio signal and second-and-subsequent-stages of encoders each for quantizing a quantization error output from the previous-stage encoder A characteristic decision unit is provided which decides the frequency band of an audio signal to be quantized by each encoder of multiple-stage encoders, and a coding band control unit receives the frequency band decided by the characteristic decision unit and the time-to-frequency transformed audio signal, decides the order of connecting the respective encoders, and transforms the quantization bands of the encoders and the connecting order to code sequences. Therefore, it is possible to provide an audio signal coding apparatus performing adaptive scalable coding, which exhibits sufficient performance when coding various audio signals.