Porous PZT ceramics for receiving transducers

PZT-air (porous PZT) and PZT-polymer (polymer impregnated porous PZT) piezocomposites with varying porosity/polymer volume fractions have been manufactured. The composites were characterized in terms of hydrostatic charge (d/sub h/) and voltage (g/sub h/) coefficients, permittivity, hydrostatic figure of merit (d/sub h/.g/sub h/), and absolute sensitivity (M). With decreasing PZT ceramic volume, g/sub h/ increased, and d/sub h/.g/sub h/ had a broad maximum around 80 to 90% porosity/polymer content. The absolute sensitivity was also increased. In each case, PZT-air piezocomposites performed better than PZT-polymer piezocomposites. Hydrophones constructed from piezocomposites showed slightly lower measured receiving sensitivities than calculated values for piezocomposite materials, which was due to the loading effect of the cable and the low permittivity associated with the piezocomposites.     

Modeling plastic deformation effects in steel on hysteresis loops with the same maximum flux density

Plastic deformation affects the hysteretic magnetic properties of steels because it changes the dislocation density, which affects domain-wall movement and pinning, and also because it places the specimen under residual strain. An earlier paper proposed a model for computing hysteresis loops on the basis of the effect of grain size d and dislocation density /spl zeta//sub d/. In that paper, hysteresis loops were compared that all had the same maximum flux density B/sub max/. The result was that coercivity H/sub c/ exhibited a linear relationship with inverse grain size (1/d) and /spl zeta//sub d//sup 1/2/. The same was true of hysteresis loss W/sub H/. If one compared hysteresis loops all with the same H/sub max/, these linear dependences were only approximately found. Because the relationships are simpler for loops of constant B/sub max/, core loss experimenters compare loops that all have the same B/sub max/. In this paper, we modify the model to study the effect of plastic tensile deformation on hysteresis loops with the same B/sub max/. We found linear relationships between H/sub c/ and residual plastic strain /spl epsiv//sub r/ and between W/sub H/ and /spl epsiv//sub r/. With increasing residual tensile strain, H/sub c/ increases (whereas with increasing elastic tensile strain, H/sub c/ decreases). Also, with increasing residual tensile strain, the slope of the hysteresis loop decreases (whereas with increasing elastic tensile strain, the slope increases). We also consider the effect of compressive plastic deformation.     

A 0-phase circuit for QCM-based measurements in highly viscous liquid environments

Currently, the series resonant frequency f/sub s/ and the motional resistance Rm of liquid loaded quartz crystal microbalance (QCM) sensors are extracted either directly, through network analyzer (NWA) impedance measurements, or from QCM-stabilized oscillator circuits. Both methods have serious drawbacks that may affect measurement accuracy, especially if the sensor is operated under highly viscous load conditions and Rm exceeds 1 k/spl Omega/. This paper presents a simple passive low-loss impedance transformation LC network which greatly reduces additional electrical loading of the QCM by the measurement system or sensor electronics and maintains a symmetric resonance and a steep 0-phase crossing at f/sub s/, even if Rm increases by several orders of magnitude as a result of liquid loading. A simple S21 transmission measurement allows direct f/sub s/ reading at the 0-phase frequency, while Rm is obtained from the circuit loss at f/sub s/. Circuit operation was verified at 9 MHz by QCM measurements in a liquid with known density and viscosity. The agreement between predicted and experimental data, which was obtained by a temperature-controlled measurement, was within 1%, even in very high viscosity ranges in which Rm exceeds 10 k/spl Omega/.     

Standardized evaluation of chemical compositions of LiTaO3 single crystals for SAW devices using the LFB ultrasonic material characterization system

The line-focus-beam ultrasonic material characterization (LIFB-UMC) system is applied to compare and evaluate tolerances provided independently for the Curie temperature T/sub C/ and lattice constant /spl alpha/ to evaluate commercial LiTaO/sub 3/ single crystals by measuring the Rayleigh-type leaky surface acoustic wave (LSAW) velocities V/sub LSAW/. The relationships between VLSAW, and T/sub C/ and /spl alpha/ measured by individual manufacturers were obtained experimentally using 42/spl deg/YX-LiTaO/sub 3/ wafers as specimens from three crystal manufacturers. In addition, the relationship between VLSAW and SH-type SAW velocities V/sub SAW/ that are actually used for the SAW device wafers was obtained through calculations, using the chemical composition dependences of the acoustical physical constants for LiTaO/sub 3/ crystals reported previously. The result of a comparison between the T/sub C/ tolerance of /spl plusmn/3/spl deg/C and the /spl alpha/ tolerance of /spl plusmn/0.00002 nm through the common scale of VLSAW or VSAW demonstrated that the /spl alpha/ tolerance is 1.6 times larger than the T/sub C/ tolerance. Furthermore, we performed a standardized comparison of statistical data of T/sub C/ and /spl alpha/ for LiTaO/sub 3/ crystals grown by two manufacturers during 1999 and 2000, using VLSAW. The results clarified the differences of the average chemical compositions and of the chemical composition distributions among the crystal ingots between the two manufacturers. A guideline for the standardized evaluation procedure has been established for the SAW-device wafer specifications by the LFB-UMC system.     

High-frequency performance projections for ballistic carbon-nanotube transistors

A quasi-static approach is combined with a theory of ballistic nanotransistors to assess the high-frequency performance potential of carbon-nanotube field-effect transistors. A simple equivalent circuit, which applies in the ballistic limit of operation, is developed for the intrinsic device, and then employed to determine the behavior of the unity-current-gain frequency (f/sub T/) with gate voltage. The circuit is shown to reduce to the expected forms in the so-called "MOS" and "bipolar" limits. The f/sub T/ is shown to approach a maximum value of v/sub F//2/spl pi/L/spl ap/130 GHz/L (/spl mu/m) at high gate voltage, where v/sub F/ is the nanotube's Fermi velocity and L is the channel length, and to fall at low gate voltage due to the presence of source and drain electrostatic capacitances. The impact of the gate electrostatic capacitance on the f/sub T/ is also discussed. Numerical simulations on a "MOSFET-like" or "bulk-switched" carbon-nanotube transistor are shown to support the conclusions.     

Optimization of attenuation estimation in reflection for in vivo human dermis characterization at 20 MHz

In vivo skin attenuation estimators must be applicable to backscattered radio frequency signals obtained in a pulse-echo configuration. This work compares three such estimators: short-time Fourier multinarrowband (MNB), short-time Fourier centroid shift (FC), and autoregressive centroid shift (ARC). All provide estimations of the attenuation slope (/spl beta/, dB.cm/sup -1/.MHz/sup -1/); MNB also provides an independent estimation of the mean attenuation level (IA, dB.cm/sup -1/). Practical approaches are proposed for data windowing, spectral variance characterization, and bandwidth selection. Then, based on simulated data, FC and ARC were selected as the best (compromise between bias and variance) attenuation slope estimators. The FC, ARC, and MNB were applied to in vivo human skin data acquired at 20 MHz to estimate /spl beta//sub FC/, /spl beta//sub ARC/, and IA/sub MNB/, respectively (without diffraction correction, between 11 and 27 MHz). Lateral heterogeneity had less effect and day-today reproducibility was smaller for IA than for /spl beta/. The IA and /spl beta//sub ARC/ were dependent on pressure applied to skin during acquisition and IA on room and skin-surface temperatures. Negative values of IA imply that IA and /spl beta/ may be influenced not only by skin's attenuation but also by structural heterogeneity across dermal depth. Even so, IA was correlated to subject age and IA, /spl beta//sub FC/, and /spl beta//sub ARC/ were dependent on subject gender. Thus, in vivo attenuation measurements reveal interesting variations with subject age and gender and thus appeared promising to detect skin structure modifications.     

Structure, properties, and thermal stability of nanocrystallite Fe-Ti-N soft magnetic films

We deposited Fe-Ti-N magnetic films with a high sputtering power of 7 W/cm/sup 2/. When the composition of the films was in the range of Fe-Ti(3.9 at.%)-N(8.8 at.%) to Fe-Ti(3.3 at.%)-N(13.5 at.%), the films were composed of /spl alpha/' and Ti/sub 2/N precipitates. With the addition of nitrogen, 4/spl pi/M/sub s/ became higher than that of pure iron, reaching a maximum of 23.8 kG. At the same time, H/sub c/ was reduced to a minimum of 1.12 Oe. The best films can meet the needs of the recording head in dual-element giant magnetoresistive/inductive heads, yielding high storage density (10 Gb/in/sup 2/). The incorporation of N in /spl alpha/-Fe brought about the /spl alpha/' phase with its higher saturation magnetization. Ti additions inhibited the equilibrium decomposition /spl alpha/'/spl rarr//spl alpha/+/spl gamma/'. Because H/sub C//sup D//spl prop/D/sup 6/, where D is average grain diameter, grain size control is very important. The nitrogen induces severe distortion of the /spl alpha/' lattice, which can cause the grains to break into pieces and reduce the grain size. High sputtering power also led to the formation of fine grains, with diameter in the order of 14 nm. Probably Ti/sub 2/N is preferentially precipitated on the grain boundary, pinning the grain boundary and stabilizing the grain size during high-temperature heat treatment. The temperature limit for stability of the structure and its associated low coercivity was not less than 520/spl deg/C.     

Optical frequency standards based on the /sup 199/Hg/sup +/ ion

We report on work directed toward the systematic evaluation of an optical frequency standard based on the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition of a single, laser-cooled, trapped /sup 199/Hg/sup +/ ion, whose resonance frequency is 1.06/spl times/10/sup 15/ Hz. For the purpose of the evaluation, a second /sup 199/Hg/sup +/ standard has been constructed. In the cooling-laser system built for the second standard, an injection-locking scheme has been applied to a CW Ti-sapphire laser. We also report optical frequency measurements of the clock transition performed over the past 21 months with the first standard. During this term, the variation of the clock transition frequency is found to be less than /spl plusmn/1/spl times/10/sup -14/.     

Determination of the shear impedance of viscoelastic liquids using cylindrical piezoceramic resonators

In this paper, a new method for determining the rheological parameters of viscoelastic liquids is presented. To this end, we used the perturbation method applied to shear vibrations of cylindrical piezoceramic resonators. The resonator was viscoelastically loaded on the outer cylindrical surface. Due to this loading, the resonant frequency and quality factor of the resonator changed. According to the perturbation method, the change in the complex resonant frequency /spl Delta/~/spl omega/ = /spl Delta/w/sup re/ + j/spl Delta//spl omega//sup im/ is directly proportional to the specific acoustic impedance for cylindrical waves Zc of a viscoelastic liquid surrounding the resonator, i.e., /spl Delta/~w /spl sim/ jZ/sub c/, where j = (-1)/sup 1/2/. Hence, the measurement of the real and imaginary parts of the complex resonant frequency determines the real part, R/sub c/, and imaginary part, X/sub c/, of the complex acoustic impedance for cylindrical waves Z/sub c/ of an investigated liquid. Further-more, the specific impedance Z/sub L/ for plane waves was related to the specific impedance Z/sub c/ for cylindrical waves. Using theoretical formulas established and the results of the experiments performed, the shear storage modulus /spl mu/ and the viscosity /spl eta/ for various liquids (e.g., epoxy resins) were determined. Moreover, the authors derived for cylindrical resonators a formula that relates the shift in resonant frequency to the viscosity of the liquid. This formula is analogous to the Kanazawa-Gordon formula that was derived for planar resonators and Newtonian liquids.     

Inspection of intrinsic critical currents for spin-transfer magnetization switching

We examined the relationships between critical current, I/sub c/, and switching time, /spl tau//sub p/, for spin-transfer switching in two regions: (region I) /spl tau//sub p//spl Gt//spl tau//sub 0/, where thermal switching is accompanied and (region II) /spl tau//sub p/< several tens times /spl tau//sub 0/, where /spl tau//sub 0/ is the attempt time for thermal switching (/spl ap/1 ns). We estimated I/sub c0/, defined as the intrinsic I/sub c/ at 0 K, for both regions and confirmed experimentally that those I/sub c0/ coincided with each other at room temperature (RT). The value of I/sub c/ at /spl tau//sub p/=1 ns, measured with microwaves, was approximately 1.6 times the I/sub c0/. This suggested that we use at least two times I/sub c0/ as the writing currents of magnetic memory devices for nsec spin-transfer switching at RT. Although I/sub c0/ for both regions were defined as I/sub c/ at 0 K (I/sub c//sup 0K/) in theory, they showed temperature dependence at low temperatures; |I/sub c0/| for region I increased with decreasing temperature, and the estimated I/sub c//sup 0K/ was approximately three times I/sub c0/ for RT. This temperature dependence was quite different from that for region II.     

基于锆钛酸铅薄膜的变形镜微致动器

以锆钛酸铅（PZT）薄膜作为驱动材料,制备了变形镜的微致动器阵列．使用有限元软件对致动器进行了模拟仿真,得到了驱动器上电极尺寸、Si弹性层厚度等参数对致动器性能的影响,获得了最优化的致动器结构．以钙钛矿相的镍酸镧（LNO）作为PZT薄膜在Pt衬底上生长的缓冲层,增强了PZT薄膜的（100）取向,减小了PZT薄膜的内部应力,提高了致动器的驱动性能．最终制备出的1μm厚PZT薄膜驱动的变形镜微致动器,在10V直流电压的激励下,具有2．0μm的变形量．以PZT薄膜作为驱动材料制备的变形镜微致动器阵列,对变形镜致动器的微型化和系统集成度的提高具有重要意义．     

Design and fabrication of a novel crystal SiGeC far infrared sensor with wavelength 8-14 micrometer

In this paper, we report the design, fabrication, and performance of a novel crystal SiGeC infrared sensor with wavelength 8-14 /spl mu/m by bulk micromachining technology for portable far infrared ray (FIR) in rehabilitation system application. The working principle of the sensor is based on the change of thermistor's resistance under the irradiation FIR light. The thermistor in the IR detector is made of Si/sub 0.68/Ge/sub 0.31/C/sub 0.01/ thin films for its large activation energy of 0.21 ev and the temperature coefficient (TCR) of -2.74%, respectively. Finite element method package ANSYS has been employed for analyze of the thermal isolation and stress distribution in the IR detector. The dimension of the microbridge fabricated by anisotropic wet etching is 2000 /spl times/ 2000 /spl times/ 25 /spl mu/m/sup 3/. The developed FIR sensor exhibits the thermal conductance of 1.85 /spl times/ 10/sup -1/ WK/sup -1/ and the heat capacity as 7.4 /spl times/ 10/sup -7/ JK/sup -1/ under air ambient at room temperature. The responsivity is 523 VW/sup -1/ in the waveband 8-14 /spl mu/m with nickel absorber under a bias voltage 1.5 V.     

Multidimensional CMOS in-plane stress sensor

This paper reports a novel multidimensional complementary metal-oxide semiconductor (CMOS) based stress sensor. The device uses an octagonal n-well in a p-substrate and eight peripheral contacts enabling the current to be switched in eight directions rotated by an angle of /spl pi//4. By taking full advantage of the piezoresistive behavior of single-crystal silicon, the measurement of all in-plane stress tensor components, i.e., /spl sigma//sub xx/, /spl sigma//sub yy/, and /spl sigma//sub xy/, is demonstrated. This information is derived from the zeroth and second angular-order Fourier components of voltage signals parallel and perpendicular to the switched current. Nonlinearities of the system are reduced by proper bias conditions using a center contact. The device was calibrated by applying defined normal stresses using a bending bridge setup. The device behavior was modeled including piezoresistive effects and the junction field effect by a combination of the finite element method and a nonlinear simulation program with integrated circuits emphasis (SPICE) network simulation using junction field effect transistor (JFET) elements. Stress sensitivities of 200 /spl mu/V V/sup -1/ MPa/sup -1/ are demonstrated for the determination of the three stress components.     

Influence of AC magnetic field amplitude on the surface magnetoimpedance tensor in amorphous wire with helical magnetic anisotropy

We have performed experimental and theoretical studies on the influence of ac magnetic field amplitude on the magnetoimpedance tensor in an amorphous wire with helical magnetic anisotropy. For the experimental measurements, we used an amorphous wire of composition (Co/sub 0.94/Fe/sub 0.06/)/sub 72.5/Si/sub 12.5/B/sub 15/ with negative, nearly zero magnetostriction constant, excited either by an ac circular h/sub /spl phi// or by an axial h/sub z/ magnetic field created by an ac electric current. We changed the ac current amplitude from 7.5 to 40 mA and the current frequency f from 1.5 to 20 MHz. The values of the asymmetric giant magnetoimpedance ratio associated with the sweeping direction of the dc field H/sub ex/ and the corresponding sensitivity were 211% and 0.64 V/Oe, respectively, for an ac current of 37.5 mA at 3 MHz. For the theoretical study based on the magnetization rotation, we obtained the second-order harmonic of the ac magnetization m/spl I.oarr//sup (2)/ induced by the relatively high ac magnetic field by solving the Landau-Lifshitz-Gilbert (LLG) equation. We also considered a second-order surface impedance tensor /spl sigmav//spl circ//sup (2)/, which allowed us to analyze quantitatively the influence of the ac magnetic field amplitude on the impedance tensor of the wire. We obtained the domain model of the wire with helical magnetic anisotropy having multidomains and the magnetization vector /spl plusmn/M/sub 0/ directed in the easy direction, and the corresponding static magnetic configurations, by solving the static LLG equation. For the given magnetic configurations, we calculated the second-order impedance tensor /spl sigmav//spl circ//sup (2)/. The results can well explain the irregular field characteristics of the voltage responses at low dc field value, when the wire was excited at high frequency and at large ac magnetic field.     

Demagnetizing factors for rectangular prisms

For rectangular prisms of dimensions 2a/spl times/2b/spl times/2c with constant material susceptibility /spl chi/, we have calculated and tabulated the fluxmetric and magnetometric demagnetizing factors N/sub f/ and N/sub m/, defined along the 2c dimension as functions of c/(ab)/sup 1/2/(=1/spl sim/500), a/b(=1/spl sim/256), and /spl chi/(=0/spl sim/10/sup 9/). We introduce an interpolation technique for obtaining N/sub f,m/ with arbitrary values of c/(ab)/sup 1/2/, a/b, and /spl chi/.     

Recent developments in high curie temperature perovskite single crystals

The temperature behavior of various relaxor-PT piezoelectric single crystals was investigated. Owing to a strongly-curved morphotropic phase boundary, the usage temperature of these perovskite single crystals is limited by T/sub R-T/- the rhombohedral to tetragonal phase transformation temperature - which occurs at the significantly lower temperatures than the Curie temperature T/sub c/. Attempts to modify the temperature usage range of Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/ (PZNT) and Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/ (PMNT) rhombohedral crystals (T/sub c/ /spl sim/ 150-170/spl deg/C, T/sub R-T/ /spl sim/ 60-120/spl deg/C) using minor dopant modifications were limited, with little success. Of significant potential are crystals near the morphotropic phase boundary in the Pb(Yb/sub 1/2/Nb/sub 1/2/)O/sub 3/-PbTiO/sub 3/ (PYNT) system, with a T/sub c/ > 330/spl deg/C, even though T/sub R-T/ was found to be only half the value at /spl sim/160/spl deg/C. Single crystals in the novel BiScO/sub 3/-PbTiO/sub 3/ system offer significantly higher T/sub c/s > 400/spl deg/C, while exhibiting electromechanical coupling coefficients k/sub 33/ > 90% being nearly constant till the T/sub R-T/ temperature around 350/spl deg/C, which greatly increases the temperature range for transducer applications.     

High-potential magnetic anisotropy of CoPtCr-SiO/sub 2/ perpendicular recording media

The magnetic anisotropy of CoPtCr-SiO/sub 2/ perpendicular recording media, including higher energy terms, was studied as a function of film composition and seed layer materials. All series of CoPtCr films with various Cr content, deposited on Ru seed layers, show maximum values of total anisotropy K/sub u/ at 25-30 at%Pt. The maximum value for CoPt(Cr=0) films reaches /spl sim/15/spl times/10/sup 6/ erg/cm/sup 3/. The addition of SiO/sub 2/ to the CoPtCr films reduces the grain K/sub u/, however the grain K/sub u/ maintains a large value of 8/spl times/10/sup 6/ erg/cm/sup 3/ even when 10at%SiO/sub 2/ is added to (Co/sub 90/Cr/sub 10/)/sub 80/Pt/sub 20/, for instance, which indicates the high-potential thermal stability. Theoretical calculations for media designs of 400 Gbits/in/sup 2/ revealed that the ratio of the high-energy anisotropy term K/sub u2/ to K/sub u1/(K/sub u/=K/sub u1/+K/sub u2/) is required to be 0.2-0.35 to enhance the energy barrier for the remanent state, without a notable change in switching field. The films deposited on Ru seed layers were found to show negligibly small K/sub u2/ values, however, the values of K/sub u1/ and K/sub u2/ vary significantly with the seed layer material used. K/sub u1/ decreases almost linearly as the K/sub u2/ value increases. It is concluded that CoPtCr films have a sufficient potential in the values of K/sub u1/ and K/sub u2/ for high-density perpendicular media.     

Electric fields within cells as a function of membrane resistivity--a model study

Externally applied electric fields play an important role in many therapeutic modalities, but the fields they produce inside cells remain largely unknown. This study makes use of a three-dimensional model to determine the electric field that exists in the intracellular domain of a 10-/spl mu/m spherical cell exposed to an applied field of 100 V/cm. The transmembrane potential resulting from the applied field was also determined and its change was compared to those of the intracellular field. The intracellular field increased as the membrane resistance decreased over a wide range of values. The results showed that the intracellular electric field was about 1.1 mV/cm for R/sub m/ of 10 000 /spl Omega//spl middot/cm/sup 2/, increasing to about 111 mV/cm as R/sub m/ decreased to 100 /spl Omega//spl middot/cm/sup 2/. Over this range of R/sub m/ the transmembrane potential was nearly constant. The transmembrane potential declined only as R/sub m/ decreased below 1 /spl Omega//spl middot/cm/sup 2/. The simulation results suggest that intracellular electric field depends on R/sub m/ in its physiologic range, and may not be negligible in understanding some mechanisms of electric field-mediated therapies.     

Single-mode rib optical waveguides on SOG/SU-8 polymer and integrated Mach-Zehnder for designing thermal sensors

This paper presents a successful design, realization,and characterization of single-mode rib optical waveguides on SOG/SU-8 polymers in order to highlight a new approach to designing heat sensors. The basic principle of this new thermal-sensing method relies on the differential thermal behavior regarding both acting arms of a micro Mach-Zehnder Interferometer(MZI). First, two families of single-mode straight rib waveguides composed of SOG/SU-8 polymers are analyzed. Hence, optical losses for TE/sub 00/ and TM/sub 00/ optical modes for structures on Si/SiO/sub 2//SU-8 have been estimated respectively as 1,36 /spl plusmn/ 0,02 and 2,01/spl plusmn/0,02 dB/spl middot/cm/sup -1/, while the second one composed of Si/SiO/sub 2//SOG/SU-8 presented losses of 2,33 /spl plusmn/ 0,02 and 2,95/spl plusmn/0,02 dB/spl middot/cm/sup -1/. Then, owing to modeling results, an experimental sensor is realized as an integrated device made up of SU-8 polymer mounted on a standard silicon wafer. When subjected to a radiant source, as a laser light (980 nm) is injected across the cleaved input face of the MZI, the significant change of output signal allows us to consider a new approach to measuring radiant heat flowrate. Experimental results are given regarding the obtained phase shift against the subjected thermal power. According to the modeling results, one can expect new highly sensitive devices to be developed in the next coming years, with advantageous prospective industrial applications.