Shigeru Jyomura

Electromechanical properties of (Pb, Ln) (Ti, Mn) O3 ceramics (Ln = rare earths)

Electromechanical properties of PbTiO3 ceramics modified by the partial substitution of rare earths for Pb, particularly, (Pb, Ln) (Ti, Mn) O3 (Ln = La, Pr, Nd, Sm, or Gd) ceramics, are examined. It is found that the Sm substitution for Pb dramatically increases the ratio of electromechanical coupling factor of the thickness dilatational mode to that of the planar extensional mode. Extensive studies of the resonant properties of rectangular strip resonators make it clear that the Sm‐substituted PbTiO3 ceramics are very useful for high‐frequency array transducer applications. It is also shown that the pulse responses of array transducers can be improved using Sm substituted PbTiO3 ceramics instead of the other PbTiO3 ceramics studied here.

Temperature‐compensated PbTiO3 ceramics for surface acoustic wave applications

Lead titanate PbTiO3 ceramics with a zero temperature coefficient of surface wave delay time are developed by addition of Nd2O3, In2O3, and MnO2. These ceramics have very small temperature coefficients of less than 1 ppm/ °C over a wide temperature range (−10–+60 °C). They have a large electromechanical coupling factor and low dielectric constant. The propagation loss is 4 dB/cm at 57 MHz. These modified PbTiO3 ceramics have high potential for use in surface wave applications, e.g., filters.

Surface acoustic wave and piezoelectric properties of (Pb, Ln) (Ti, Mn)O3 ceramics (Ln = rare earths)

The surface acoustic wave (SAW) and piezoelectric properties of PbTi03 ceramics modified by the partial substitution of rare earths for Pb, particularly (Pb, Ln) (Ti, Mn)03 (Ln = La, Ce, Pr, Nd, Sm, or Gd) ceramics, are examined. The effects of the rare earths introduced on these properties are noted. Properties, such as velocities and electromechanical coupling factors, for bulk wave and SAW vary monotonically with the ionic sizes of the rare earths. On the other hand, the temperature coefficient of SAW delay time takes a minimum value when the Ln is Nd. It is shown that the variation of the temperature coefficient with rare earths corresponds well with those of the temperature coefficients of elastic constants CE33 and CE44.

Surface acoustic wave properties of (Pb,Ln)(Ti, Mn, In)O3 ceramics (Ln = La and Nd)

The surface acoustic wave properties of PbTiO3 ceramics are improved. The ceramic systems investigated are (Pb,Ln)(Ti,Mn,In)O3(Ln = La,Nd). The temperature coefficients of delay time are lowered to 46×10−6/ °C, when Ln is La. A zero temperature coefficient of delay can be achieved when Ln is Nd. The Nd and In substitution also cause the electromechanical coupling factor to increase and the dielectric constant to decrease.

SAW propagation loss mechanism in piezoelectric ceramics

The surface acoustic wave (SAW) propagation loss mechanism of piezoelectric ceramics is examined using lead titanate (PbTiO3) ceramics modified with additives of Nd2O3, MnO2, and In2O3, which have zero temperature coefficients of SAW delay time. The propagation loss L in the frequency range 30 to 300 MHz consists of two parts. One is the Rayleigh scattering loss LS caused by grain, and the other is the true dissipative loss LF caused by internal friction. Thus, total loss results in L(dB/cm) = LS+LF = 3.2×103D3f4+6.8×10−4f2 (where D and f denote average grain size in cm and frequency in MHz, respectively). It is also revealed experimentally that the internal friction causing the latter loss has a close correlation with the dielectric loss through piezoelectric combination. Therefore, materials with fine grain (<0.5 μm) and low dielectric loss (<10−3) must be developed to reduce SAW propagation losses which prevent the piezoelectric ceramics from being used in higher frequency (≳100 MHz) SAW applications. ...

Rare-earth substituted piezoelectric PbTiO3 ceramics for acoustic wave applications

Electromechanical and surface acoustic wave (SAW) properties of PbTiO3, ceramics modified by partial substitution of rare-earth for the Pb, specifically (Pb, Ln) (Ti, Mn)O3 (Ln=La, Ce, Pr, Nd, Sm, Eu, or Gd) ceramics, are extensively investigated. The SAW delay time temperature coefficient is found to be minimum when Ln=Nd. A zero temperature coefficient can be achieved in the (Pb, Nd) (Ti, In, Mn)O3 system with appropriate compositions. High frequency SAW filters are fabricated using these ceramics. It is also found that (Pb, Sm) (Ti, Mn)O3 ceramics have exceptionally large electromechanical anisotropy (ratio of electromechanical coupling factor for thickness vibration to that for planar vibration is above 15). A 7.5MHz linear array ultrasonic probe employing these ceramics is developed for medical use.

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.

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 7.5 MHz Linear Array Ultrasonic Probe Using Modified PbTiO 3 Ceramics

A high frequency (7.5MHz) linear array ultrasonic probe developed for medical use is presented. It employs modified PbTi03 ceramics having exceptionally large electromechanical anisotropy (ratio of electromechanical coupling factor for thickness vibration to that for planar vibration is more than 15). The advantage of employing such ceramics instead of usual PZT ceramics is that the width-to-thickness ratio of a transducer element can be chosen as w/t>l because of the very small planar or lateral electromechanical coupling factor. This advantage facilitates fabrication of high frequency linear array ultrasonic probes. These probes also employ two acoustic matching layers and a silicone compound lens with a low attenuation coefficient. The 7.5MHz linear array probe produces acoustic beams whose -6dB-width is less than 1.5mm. Some examples of 7.5MHz imaging present much better resolution than 5MHz imaging using PZT probes.