Piezoelectric unimorph miroactuators with X-shaped structure composed of PZT thin films

In this study, we report piezoelectric microactuators composed of Pb(Zr,Ti)O₃ (PZT) films for low-voltage RF-MEMS switches. In order to realize a flat beam shape as well as a large displacement, we have adopted an X-shaped connector at the center of the beam. Finite element method (FEM) simulation indicates that the bending motion of the beam is almost same as two connected cantilevers, and the maximum displacement reaches 3.2 μm/5 V. To fabricate the microactuators, piezoelectric PZT films were deposited on Si substrates using rf-sputtering and microfabricated into the PZT/Cr unimorph actuators of 800 μm in length and 200 μm in width, respectively. Although the X-shaped connector effectively releases the stress of the multilayered beam so that the beam shape is almost flat, small residual stress caused slight concave curvature along the width. The displacement at the center of the beam was measured using a laser Doppler vibrometer. The measurement revealed that the displacement was 0.5 μm/5 V which was lower than the FEM result. The reduction of the displacement is attributed to the increase of the stiffness of the beam due to the concave curvature of the beam width.     

Fabrication of particle free epitaxal AlN thin films by reactive PLD combined with an electron beam and a rotating crucible

An AlN epitaxial film without projections or spiral growth features was successfully fabricated on a (0 0 0 1) sapphire substrate by reactive laser ablation of a liquid Al target in NH₃ using a 248 nm laser. The liquid Al target was prepared with an electron beam in a rotating crucible. The surface of the rotating liquid Al target was always smooth. Spiral growth features were greatly suppressed. AlN films have a surface roughness less than 0.3 nm. The X-ray rocking curve's narrowest FWHM was 180 arcsec, which is nearly identical to that recently reported in films grown by MOCVD or reactive MBE.     

Biomimetic coating of an apatite layer on poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid); improvement of adhesive strength of the coating

A biodegradable polymer coated with a bonelike apatite layer on its surface would be useful as a scaffold for bone tissue regeneration. In this study, poly(l-lactic acid) (PLLA) was treated with oxygen plasma to produce oxygen-containing functional groups on its surface. The plasma-treated specimen was then alternately dipped in aqueous CaCl₂ and K₂HPO₄·3H₂O solutions three times, to deposit apatite precursors onto the surface. The surface-modified specimen then successfully formed a dense and uniform bonelike surface apatite layer after immersion for 24 h in a simulated body fluid with ion concentrations approximately equal to those of human blood plasma. The adhesive strength between the apatite layer and the specimen surface increased as the power density of the oxygen plasma used increased. The maximum adhesive strength of the apatite layer to the specimen was significantly higher than that to the commercially available artificial bone, HAPEX^TM. The resultant bonelike apatite–PLLA composite would be useful as a scaffold for bone tissue regeneration.     

Synthesis of 10-μm-Thick Lead Zirconate Titanate Films on 2-in. Si Substrates for Piezoelectric Film Devices

To achieve micro-machined piezoelectric film devices, crack-free and dense 10-μm-thick lead zirconate titanate (PZT) films were successfully deposited onto 2-in. Pt/Ti/SiO₂/Si substrates using an automatic coating system, and disk-shaped structures with a diameter from 20 to 100 μm were fabricated by an RIE process. The prepared PZT thick film disks showed well-saturated P–E hysteresis curves and butterfly-shaped longitudinal displacement curves. The AFM-measured piezoelectric constant of the 30-μm-diameter PZT thick film disk after poling at 100 V for 10 min was AFM d ₃₃=290 pm/V. The resonant and anti-resonant frequencies of the thickness oscillation mode were observed at 180 MHz. The calculated thickness mode effective coupling factor was ( k _eff)²=0.1 for the poled 30-μm-diameter PZT thick film disks. These results suggest that the prepared PZT thick film disks are applicable for piezoelectric micro devices such as micro-machined ultrasonic transducers.     

Piezoresistive effect of plain-weave CFRP fabric subjected to cyclic loading

The present study deals with electrical resistance changes in woven-fabric CFRP during loading. Four kinds of plain weave woven-fabric CFRP laminated specimens are prepared and subjected to cyclic tensile loading that does not cause any damages, and the electrical resistance changes of the specimens are measured experimentally by the four-probe method. As a result, the present study shows that the electrical resistance of a specimen comprised of six ±45° plies decreases remarkably with increasing number of loading cycles. The decrease is caused by shear plastic deformation of ±45° plies. The thickness shrinkage caused by shear plastic deformation increases the number of fiber contacts, and this decreases the interlaminar contact resistance between the plies. For a single ±45° ply, the same electrical resistance decrease caused by the shear plastic deformation is observed, and the magnitude of the decrease is smaller than that of the six-ply laminate tested. This is because the effect of interlaminar contact resistance decrease does not exist for a single ±45° ply. For the six 0°/90° plies, the present study shows that electrical resistance in the through-thickness direction is decreased by out-of-plane plastic deformation of carbon fiber and misalignment of the plies.     

Flooding and flow reversal of two-phase annular flow

The flooding and flow reversal conditions of two-phase annular flow are mathematically defined in terms of a characteristic function representing a force balance. Sufficiently below the flooding point in counter-current flow, the interface is smooth and the characteristic equation reduces to the Nusselt relationship. Just below the flooding point and above the flow reversal point in cocurrent flow, the interface is “wavy”, so that the interfacial shear effect plays an important role. The theoretical analysis is compared with experimental results by others. It is suggested that the various length effects which have been experimentally observed may be accounted for by the spatial variation of the droplet entrainment.     

The Sympathetic Nervous System Contributes to the Establishment of Pre-Metastatic Pulmonary Microenvironments

Emerging evidence suggests that neural activity contributes to tumor initiation and its acquisition of metastatic properties. More specifically, it has been reported that the sympathetic nervous system regulates tumor angiogenesis, tumor growth, and metastasis. The function of the sympathetic nervous system in primary tumors has been gradually elucidated. However, its functions in pre-metastatic environments and/or the preparation of metastatic environments far from the primary sites are still unknown. To investigate the role of the sympathetic nervous system in pre-metastatic environments, we performed chemical sympathectomy using 6-OHDA in mice and observed a decrease in lung metastasis by attenuating the recruitment of myeloid-derived suppressor cells. Furthermore, we note that neuro-immune cell interactions could be observed in tumor-bearing mouse lungs in conjunction with the decreased expression of Sema3A. These data indicate that the sympathetic nervous system contributes to the preparation of pre-metastatic microenvironments in the lungs, which are mediated by neuro-immune cell interactions.     

Effect of membrane preparation conditions on solute permeability in chitosan membrane

Chitosan membrane was prepared in various conditions and diffusive permeabilities of theophylline and vitamin B₁₂ were investigated. The membrane preparation procedure consists of dissolving chitosan in acid solution, cast on the glass plate, drying the dope solution, and immersion of the plate in the gelating agent. Effects of the kinds of acids to dissolve chitosan, chitosan concentration, drying time of the dope solution, and the kinds of the gelating agent on the membrane structure and performance were studied in detail. With increasing the chitosan concentration, the solute permeability decreased, while the selectivity of theophylline to vitamin B₁₂ increased. The membrane changed from the wholly porous structure to the asymmetric structure by the increase of the chitosan concentration. Furthermore, the use of ethanol as the gelating agent brought about the wholly porous structure with the high permeability and the low selectivity. The asymmetric structure and the wholly dense structure were obtained in the cases of the gelating agents, such as aqueous NaOH solution and dimethyl sulfoxide (DMSO), respectively. Thus, the membrane structure can be controlled by the kinds of gelating agent. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2715–2725, 1999     

Solvatochromic study of water sorption in polymer films

A solvatochromic method was used to characterize the water sorption behavior of polymer films. Four different dyes were dissolved in various solid polymers and the relative water vapor pressure in the atmosphere was changed. Evaluated solvatochromic parameters depended not only on the amount of sorbed water but also on the kind of polymer. A linear correlation between the E_T(30) value and Taft's multiparameter was confirmed in both the dried and the water sorbed polymers. The correlation equation was almost identical to that obtained by other researchers in liquid solvents. These results suggest that the dissolved dyes behave as indicators of microenvironmental changes in the solid polymer film. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1681–1691, 1997