Kazuhiro Itsumi

Effects of Fine Metal Oxide Particle Dopant on the Acoustic Properties of Silicone Rubber Lens for Medical Array Probe

The effects of fine metal oxide particles, particularly those of high-density elements (7.7 to 9.7 times 10³ kg/m³), on the acoustic properties of silicone rubber have been investigated in order to develop an acoustic lens with a low acoustic attenuation. Silicone rubber doped with Yb₂O₃ powder having nanoparticle size of 16 nm showed a lower acoustic attenuation than silicone rubber doped with powders of CeO₂, Bi₂O₃, Lu₂O₃ and HfO₂. The silicone rubber doped with Yb₂O₃ powder showed a sound speed of 0.88 km/s, an acoustic impedance of 1.35 times 10⁶ kg/m²s, an acoustic attenuation of 0.93 dB/mmMHz, and a Shore A hardness of 55 at 37degC. Although typical silicone rubber doped with SiO₂ (2.6 times 10³ kg/m³) shows a sound speed of about 1.00 km/s, heavy metal oxide particles decreased the sound velocities to lower than 0.93 km/s. Therefore, an acoustic lens of silicone rubber doped with Yb₂O₃ powder provides increased sensitivity because it realizes a thinner acoustic lens than is conventionally used due to its low sound speed. Moreover, it has an advantage in that a focus point is not changed when the acoustic lens is pressed to a human body due to its reasonable hardness.

Temperature Dependence of Dielectric and Piezoelectric Properties of Pb(Zn1/3Nb2/3)O3–PbTiO3 Piezoelectric Single Crystals

Temperature dependence of the dielectric and piezoelectric properties of xPb(Zn1/3Nb2/3)O3–yPbTiO3 (PZNT 100x/100y) piezoelectric single crystals (PSC) was investigated to estimate the heat stability of their properties. The coupling factor rectangular bar mode k33′=81% of PZNT 91/9 decreased sharply at about 70°C and then decreased gradually toward the Curie temperature, Tc. On the other hand, the k33′=62% of PZNT 95.5/4.5 hardly changed up to 110°C, although it was lower than that of PZNT 91/9 at room temperature. The degradation temperatures of the k33′ value were roughly in agreement with the phase-transition temperature, Trt, from rhombohedral to tetragonal, measured using the poled PZNT PSC. A large dielectric hysteresis was observed when PZNT PSC was heated to a temperature higher than the Trt, measured using poled PZNT PSC. Although PZNT 95.5/4.5 with reduced Ti content had a higher Trt, the obtained piezoelectric properties were inferior to those of PZNT 91/9 near the morphotropic phase boundary (MPB). Therefore, it is necessary to design the PSC composition carefully, considering specific applications in order to achieve the optimum balance between piezoelectric property and its heat stability.

Effects of Sub-100 nm Platinum Metal Particle on the Acoustic Attenuation Properties of Silicone Rubber Lens for Medical Array Probe

The acoustic attenuation properties of room temperature vulcanization (RTV) silicone rubber lenses with platinum (Pt) metal particle sizes ranging from 10 to 94 nm were investigated for the acoustic lens application for a medical ultrasound array probe. Pt particle size did not change their sound velocities, 858–861 m/s, but changed their acoustic attenuation property noticeably. RTV silicone rubber doped with the largest Pt particle, 94 nm, showed the largest attenuation, 2.24 dB/mmMHz, whereas, RTV silicone rubber doped with the smallest Pt particle, 10 nm, showed the smallest attenuation, 0.84 dB/mmMHz, with an acoustic impedance of 1.31 MRayls. The fine particle size with the application of a high-density dopant to RTV silicone rubber is important for realizing a low-acoustic-attenuation silicone lens for a probe for high-frequencies of higher than 5 MHz.

Effects of Metal Particle Dopant on Acoustic Attenuation Properties of Silicone Rubber Lens for Medical Echo Array Probe

A low-acoustic-attenuation silicone rubber lens was developed by using a nanometer-size fine metal powder as a dopant for silicone rubber. Ten-nanometer-platinum (Pt)-powder-doped silicone rubber material showed not only a low sound velocity of 0.858 km/s, but also low acoustic attenuation properties, 0.84 dB/mmMHz with an acoustic impedance of 1.37 MRalys. By virtue of its low sound velocity and low attenuation, the Pt-doped silicone rubber provides a better figure of merit (attenuation x sound velocity) for the acoustic lens material of medical array probes than does silicone-rubber doped with conventional inorganic powders, namely, SiO2, TiO2, or Al2O3. The Pt-doped silicone lens material provides increased sensitivity for the high-frequency, 5 to 10-MHz-probe application because it can be used to realize a thinner lens than conventionally used.

Effects of Ceramic Nanopowder Dopants on Acoustic Attenuation Properties of Silicone Rubber Lens for Medical Echo Probe

The effects of fine ceramic powder dopants, namely, TiO2, Al2O3, BaSO4, Fe2O3, ZrO2, and Yb2O3 with primary particle sizes of 16–100 nm, on the acoustic properties of silicone rubber have been investigated, in order to develop an acoustic lens material for medical echo probes with a low acoustic attenuation (α). Silicone rubber doped with Yb2O3 powder having a high density (ρ) of 9.2×103 kg/m3 and an average particle size of 16 nm showed a lower acoustic attenuation than silicone rubber doped with other powders. The materials showed ρ=1.54×103 kg/m3, a sound velocity (c)=882 m/s, an acoustic impedance ρc (Z)=1.36×106 kg m-2 s-1, and an acoustic attenuation α=0.93 dB mm-1 MHz-1 at 37 °C. Silicone rubber doped with Fe2O3 powder having ρ=5.2×103 kg/m3 and an average particle size of 30 nm showed the highest α=2.36 dB mm-1 MHz-1 and Z=1.47×106 kg m-2 s-1. Microstructure observation of the rubber by scanning microscopy revealed that the α of the powder-doped rubber is not only determined by the primary particle size of the powders but also by the dispersion and agglomeration of the secondary particles in the rubber matrix. The discovery of the process parameter required to reduce the α of the nanopowder-doped silicone rubber has an important practical consequence.

Effects of Manganese Oxides/Gold Composite Electrode on Piezoelectric Properties of Lead Magnesium Niobate Titanate Single Crystal

We have confirmed a high dielectric constant after poling e33T/e0 of 7700 and piezoelectric constant d33 = 2250 pC/N, which are 40% larger than those of the initial sample, for a lead magnesium niobate–lead titanate 0.72 Pb(Mg1/3Nb2/3)O3–0.28 PbTiO3 single crystal plate with a manganese oxide/gold (Au) composite electrode. The increased e33T/e0 and d33 may be attributable to the smaller domains realized by fine patterning semiconductor manganese oxide and conductive Au composite electrodes on the single crystal plate. The use of a semiconductor/conductor composite electrode is an effective method of improving the properties of piezoelectric single-crystal transducers.

Low acoustic attenuation silicone rubber lens for medical ultrasonic array probe

Effects of heavy density (p = 9.2 x 103 kg/m3) Yb2O3 fine dopant (16 nm in diameter) on the acoustic properties of a high-temperature-vulcanization (HTV) silicone rubber have been investigated, to develop a new acoustic lens material with a low acoustic attenuation (alpha) for the medical array probe application. The HTV silicone rubber has advantages in that it shows a lower alpha than that of a room-temperature-vulcanization (RTV) silicone rubber and it can be mixed by applying shear stress, using roll-milling equipment. Roll-milling time dependence of the HTV silicone rubber indicates that the alpha is closely affected by the dispersion of nanopowders in the rubber matrix. The 8 vol% Yb2O3-doped HTV silicone rubber mixed for 30 min showed the lowest alpha of 0.73 dB/mmMHz with an acoustic impedance [AI = sound speed (c) times density (p)] of 1.43 times 106 kg/m2s at 37degC. Moreover, simulation results reveal that a 5 MHz linear probe using the HTV silicone rubber doped with Yb2O3 powder showed relative sensitivity around 2.6 to 3.0 dB higher than a probe using RTV silicone rubber doped with Yb2O3 powder or SiO2-doped conventional silicone rubber for the ultrasonic medical application.

Effects of Ytterbium Oxide Nanopowder Particle Size on the Acoustic Properties of Silicone Rubber Lens for Medical Echo Array Probe

The effects of Yb2O3 powder particle size, namely, 2000, 16, and 8 nm, on the physical and acoustic properties of a high-temperature-vulcanization (HTV) silicone (Q) rubber have been investigated in order to develop an acoustic lens material with a low sound velocity (c) and acoustic attenuation coefficient (α). The Yb2O3-doped HTV Q rubber with the large particle size of 2000 nm showed a density (ρ) of 1.6×103 kg/m3, with c = 828 m/s, characteristic acoustic impedance (Z) = 1.32×106 kgm-2s-1, α= 1.32 dBmm-1MHz-1, and an α-figure of merit (FOM) (α×c) of 1090 at 5 MHz at 37 °C. For the Yb2O3-doped Q rubber with the small particle size of 8 nm, ρ= 1.57×103 kg/m3, c = 864 m/s, Z = 1.36×106 kgm-2s-1, α= 0.68 dBmm-1MHz-1, and α-FOM = 590. The 16 nm Yb2O3-doped Q rubber had intermediate values of α= 0.88 dBmm-1MHz-1 and α-FOM = 760. These results show that there is a clear dopant particle size dependence on the acoustic properties of Yb2O3-doped HTV Q rubbers. The 8-nm-doped HTV Q rubber also showed an excellent mechanical properties for practical application. Microstructure observation revealed that the low-α rubber shows a uniform Yb2O3 nanopowder distribution in the HTV Q rubber matrix.

Sub-10 nm Ytterbium Oxide Nanopowder-doped Silicone Rubber Acoustic Lens Material for Medical Echo Array Probe

The effects of 8-nm-Yb2O3-nanopowders dopant, on the physical and acoustical properties of high-temperature-vulcanization (HTV) silicone (Q) rubber have been investigated, to develop a low acoustic attenuation (α) lens material for medical array probes. A 35 wt % (6 vol %) Yb2O3-doped HTV Q rubber showed a sound velocity (c) = 867 m/s, an acoustic impedance (Z) = 1.36×106 kgm-2s-1, an acoustic attenuation α= 0.66 dBmm-1MHz-1, and an α-figure of merits (FOM) (α×c) = 574 at 37 °C. The α-FOM value with Z = 1.36×106 kgm-2s-1 for a Q rubber lens material is the lowest attenuation ever reported. Microstructure observation revealed that the low-α rubber showed a uniform Yb2O3 nanopowder distribution in the rubber matrix.

Effects of Electrodes on Dielectric and Piezoelectric Properties of Lead Magnesium Niobate–Lead Titanate Single-Crystal Transducer

The effects of four types of electrodes, sputtered gold (Au), titanium/Au (Ti/Au), chromium/Au (Cr/Au), and fired silver (Ag), on the dielectric and piezoelectric properties of a lead magnesium niobate–lead titanate (PMN–PT) single-crystal transducer near the morphotropic phase boundary composition were investigated to obtain better properties of the transducer for application in medical ultrasound probes. The Au electrode sample showed the highest piezoelectric constant d33 = 1710 pC/N and the Cr/Au electrode sample showed the highest coercive field Ec = 3.1 kV/cm. Those differences were derived from several factors, namely, the dielectric constant at phase change temperature, the crystallinity on the surface caused by electrode forming treatment, adhesion strength, and the thickness of the electrodes. Changing the electrode is an easier way to realize the desired piezoelectric properties than crystal composition control. Thus, this information can prove useful for the application of the PMN–PT transducer in medical ultrasound probes.