Chitose Nakaya

Piezoelectric loudspeaker and a method for manufacturing the same

Disclosed is a piezoelectric loudspeaker. According to the present invention, a piezoelectric loudspeaker comprises: a flat compound piezoelectric sheet in which multiple piezoelectric devices are arranged in an organic material; electrodes which are provided on respective surfaces of the compound piezoelectric sheet; an acoustic impedance matching support layer for maintaining the flat compound piezoelectric sheet in a curved shape and for matching an acoustic impedance; and a support frame for supporting the compound piezoelectric sheet at its circumference. Thus, sound reproduction with a desirable frequency properties that have little distortion can be performed.

PZT/Polymer composites for medical ultrasonic probes

Abstract PZT/polymer composite sheets (PZT pillars embedded in polymer matrix) for high frequency use are fabricated using a dicing and filling technique. These piezo-composite sheets are intended for use as medical ultrasonic probes. It is found that dielectric and electromechanical properties depend not only on the PZT volume fraction v PZT but also on the PZT pillar shape w/t (width-to-thickness ratio). Thickness dilatational electromechanical coupling factor k t is as high as 0.75 when v PZT = 0.25 and w/t = 0.5 ∼ 0.6. The period of the embedded PZT pillar lattice, d, is also important in determining the electromechanical properties. When d is close to the wavelength of laterally propagating transverse waves, lateral mode resonances are observed.

Relaxor ferroelectric transducers

Novel ultrasonic transducers whose sensitivity can be controlled with a DC bias field have been developed by utilizing relaxor ferroelectrics as a transducer material in place of conventional piezoelectrics. Relaxor ferroelectrics have a large bias-field-induced piezoelectricity as well as a giant electrostrictive effect due to their extremely large dielectric constant ( approximately 10/sup 4/). Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/ (PMN) is a typical relaxor ferroelectric having a diffuse phase transition at around 0 degrees C. The addition of 9 mol.% of PbTiO/sub 3/ to the PMN is found to produce a transducer material whose electromechanical coupling factor for the thickness mode is comparable to that of PZT ceramics for a practical DC bias field. It is suggested that the application of recent piezoceramic/polymer composite technology to this relaxor ferroelectric transducer can play an important role in developing two-dimensional arrays.<<ETX>>

Highly Anisotropic Piezoelectric Ceramics and Their Application in Ultrasonic Probes

New piezoelectric ceramics with extremely large electromechanical anisotropies are reviewed. They are modified lead titanate ceramics (Pb.Sm) (Ti,Mn)Oj and (Pb,Ca)(Ti,(Col/ 2W1/2)03 +MnO.NiO and lead zirconate ceramics modified by adding small amounts of Pb(CERAmnl/3 Nb2/3 )O3 and PbTiOj. In these ceramics, the planar electromechanical coupling factor kp is much less than the thickness dilatational electromechanical coupling factor kt (kt/kp >lo). These ceramics are especially useful for use in high-frequency array transducers. In contrast to ordinary ceramics such as PZT, the width-to-thickness ratio of a transducer element (w/t) can be larger than unity. The features of a high-frequency linear array and of single element ultrasonic probes employing modified lead titanate ceramics are also described.

Acoustic Properties of Lens Materials for Ultrasonic Probes

The acoustic velocities and densities of 20 types of commercial rubber have been measured at a frequency of 2 MHz at room temperature, and they are evaluated in terms of their application to an acoustic lens or an acoustic window of probes of an ultrasonic diagnostic instrument. Fluorosilicone rubber and phoshazene rubber have lower acoustic velocities than the human body, and they have excellent impedance matching with the human body. Both the acoustic velocities and densities of butadiene rubber, polybutadiene rubber, acrylic rubber and polyurethane match those of the human body. It is also described that rubber having good impedance matching with the human body can be fabricated by adjusting the volume fraction of the added filler.

Medical ultrasonic probe using electrostrictive-ceramics/polymer composite

A medical ultrasonic probe the sensitivity of which is controlled by a DC bias field is developed using an electrostrictive-ceramics-polymer composite as a transducer material. (1-x)Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-xPbTiO/sub 3/ electrostrictive-ceramics ((1-x)PMN-xPt) are used because they have a large electromechanical coupling factor for the thickness vibrational mode, k/sub t/, under a practical bias field. 0.91PMN-0.09PT/polyurethane 1-3 composites (thickness 0.22 mm, 7.5 MHz) are fabricated using a dicing and filling technique. The 0.91PMN-0.09PT has no residual k/sub t/ after removing the DC bias field around room temperature. Pulse-echo experimentation shows that the echo amplitude increases with the bias field, as expected from the relationship between k/sub t/ and the bias field.<<ETX>>

Electrostrictive Materials for Ultrasonic Probes in the Pb(Mg1/3Nb2/3)O3–PbTiO3 System

Electrostrictive ceramics in the Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) solid solution system are investigated as the transducer material for ultrasonic probes whose electro-acoustic conversion efficiency is controlled by an applied DC bias voltage. Considering the electromechanical coupling factors induced under practical DC bias voltage and the normal using temperature, it is concluded that the most promising composition is 0.09 mole fraction of PbTiO3. A basic pulse-echo measurement confirmed that electro-acoustic conversion efficiency of an ultrasonic probe made of electrostrictive ceramics is controlled by an applied DC bias field.

Sm-Substituted Lead Titanate Ceramics for High Frequency Ultrasonic Probes

Modified lead titanate ceramics with exceptionally large electromechanical anisotropy (ratio of electromechanical coupling factor for thickness vibration to that for planar vibration is more than 15) are produced. These ceramics have a chemical formula (Pb1-(3x/2)Smx) (Ti1-yMny)O3. They are found to be very useful in ultrasonic probe applications due to their extremely small coupling factor of unwanted lateral vibration (k31, kp). High frequency (7.5~15 MHz) ultrasonic probes using these ceramics are developed for medical use.

A high-speed MRI simulator using the transition matrix method and periodicity of magnetization

An MRI simulator is a tool for understanding MR phenomena and developing new pulse sequences, which determine picture quality and information included in MR signals. Conventional simulators calculate the Bloch equations approximately to reduce the computation time. This paper presents a technique for solving the equations exactly at high speed and for creating images. The processing time is made practical by using the transition matrix method and the periodicity of the magnetization.