The optical viscometer based on the vibrating fiber partially submerged in fluid

The vibrating fiber partially submerged in fluid has been shown to be an effective device for the viscosity sensing. In this study, small vibrational amplitude of the fiber (<1.0 μm) is detected by the optical method utilizing a forward light scattering pattern. An analytical solution of the partially submerged fiber vibration with damping has been found and results agree well with experimental data in the wide ranges of the different liquids and depths. It has been shown that variations of the maximum vibrational amplitude (MVA) and the bandwidth depend linearly on (ρ_lμ_l)^1/2 and split over the liquid depth. Based on the results a simple way for the viscosity extraction from both the MVA and the bandwidth has been suggested and an explicit formula for the achievable accuracy of the viscosity sensing has been derived. Experiments have confirmed the method of the viscosity extraction.     

Low-cost polymer microfluidic device for on-chip extraction of bacterial DNA

A polymer microfluidic device for on-chip extraction of bacterial DNA has been developed for molecular diagnostics. In order to manufacture a low-cost, disposable microchip, micropillar arrays of high surface-to-volume ratio (0.152 μm⁻¹) were constructed on polymethyl methacrylate (PMMA) by hot embossing with an electroformed Ni mold, and their surface was modified with SiO₂ and an organosilane compound in subsequent steps. To seal open microchannels, the organosilane layer on top plane of the micropillars was selectively removed through photocatalytic oxidation via TiO₂/UV treatment at room temperature. As a result, the underlying SiO₂ surface was exposed without deteriorating the organosilane layer coated on lateral surface of the micropillars that could serve as bacterial cell adhesion moiety. Afterwards, a plasma-treated PDMS substrate was bonded to the exposed SiO₂ surface, completing the device fabrication. To optimize manufacturing throughput and process integration, the whole fabrication process was performed at 6 inch wafer-level including polymer imprinting, organosilane coating, and bonding. Preparation of bacterial DNA was carried out with the fabricated PDMS/PMMA chip according to the following procedure: bacterial cell capture, washing, in situ lysis, and DNA elution. The polymer-based microchip presented here demonstrated similar performance to Glass/Si chip in terms of bacterial cell capture efficiency and polymerase chain reaction (PCR) compatibility.     

Micromachined PZT cantilever based on SOI structure for low frequency vibration energy harvesting

A PZT piezoelectric cantilever with a micromachined Si proof mass is designed and fabricated for a low frequency vibration energy harvesting application. The SiO₂ layer in the SOI wafer promotes accurate control of the silicon thickness that is used as a supporting layer in the cantilever beam structure. The entire effective volume of the fabricated device is about 0.7690 mm³. When excited at 0.75g (g = 9.81 m/s²) acceleration amplitude at its resonant frequency of 183.8 Hz, the AC output measured across a resistive load of 16 kΩ connecting to the device in parallel has an amplitude of 101 mV. The average power and power density determined by the same measurement conditions are, respectively, 0.32 μW and 416 μW/cm³.     

Murray’s law and the bifurcation angle in the arterial micro-circulation system and their application to the design of microfluidics

Murray’s law which is related to the bifurcations of vascular blood vessels states that the cube of a parent vessel’s diameter equals the sum of the cubes of the daughter vessels’ diameters D₀³ = D₁³ + D₂³ , a = D₀³ /( D₁³ + D₂³ ) = 1, D_{0}^{3} = D_{1}^{3} + D_{2}^{3} ,\,\alpha = D_{0}^{3} /\left( {D_{1}^{3} + D_{2}^{3} } \right) = 1, where D ₀, D ₁, and D ₂ are the diameters of the parent and two daughter vessels, respectively and α is the ratio). The structural characteristics of the vessels are crucial in the development of the cardiovascular system as well as for the proper functioning of an organism. In order to understand the vascular circulation system, it is essential to understand the design rules or scaling laws of the system under a homeostatic condition. In this study, Murray’s law in the extraembryonic arterial bifurcations and its relationship with the bifurcation angle (θ) using 3-day-old chicken embryos in vivo has been investigated. Bifurcation is an important geometric factor in biological systems, having a significant influence on the circulation in the vascular system. Parameters such as diameter and bifurcation angle of all the 140 vessels tested were measured using image analysis softwares. The experimental results for α (= 1.053 ± 0.188) showed a good agreement with the ratio of 1 for Murray’s law. Furthermore, the diameter relation α approached the theoretical value of 1 as the diameter of parent vessel D ₀ decreased below 100 μm. The bifurcation angle θ decreased as D ₀ increased and vice versa. For the arterial bifurcations of chicken embryos tested in this study, the bifurcation pattern appears to be symmetric (D ₁ = D ₂). The bifurcation angle exhibited a nearly constant value of 77°, close to the theoretical value of 75° for a symmetric bifurcation.     

Neural network modeling of microwave FETs based on third‐order distortion characterization

A new method for characterization of HEMT distortion parameters, which extracts the coefficents of a Taylor series expansion of I_ds(V_gs, V_ds), including all cross‐terms, is developed from low‐frequency harmonic measurements. The extracted parameters will be used either in a Volterra series model around a fixed bias point for 3^rd‐order characterization of small‐signal I_ds nonlinearity, or in a large‐signal model of I_ds characteristic, where its partial derivatives are locally characterized up to the 3^rd order in the whole bias region, using a novel neural‐network representation. The two models are verified by one‐tone and two‐tone intermodulation distortion (IMD) tests on a PHEMT device. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

A penalty method for the approximation of projections over cones in Hilbert spaces

Given a closed convex coneK in a Hilbert spaceH and a vectoru ₀ ∈H, a penalty method is built up in order to approximate the projection ofu ₀ over the polar coneK ^* ofK, without making use of the inverse transform of the canonical mapping ofH into its dual spaceH′. Such method is outlined in n⁰ 1, 2. In n⁰3 a complete analysis of the errors of the method is explained. In n⁰4 the method is applied to find error bounds for the numerical approximation of the projection ofu ₀ onK.     

Investigation on nanocrystalline copper-doped zirconia thin films for optical sensing of carbon monoxide at high temperature

Nanocrystalline copper-doped zirconia (CDZ; Cu:Zr = 16:84) thin films have been synthesized on long-period fiber gratings (CDZ-LPFG) by a polymeric precursor method. The CDZ-LPFG device was demonstrated to have high sensitivity and good reversibility for low-concentration CO sensing at high temperatures. The CDZ-LPFG responds with red shifts of its resonant wavelength (λ_R) to CO-containing gases and the λ_R shift reverses when it is exposed to air. The optical response of the CDZ-LPFG to CO is due primarily to the CDZ refractive index variations resulted from the reversible redox reactions (i.e. Cu²⁺ ⇔ Cu⁺) in reducing and oxidizing atmospheres. The magnitude of the λ_R shift exhibited a strong dependence on CO concentration in a range from 0 to 1000 ppm that is potentially useful for quantitative measurement.     

The reduction of driving voltage in organic light-emitting devices by inserting step barrier layer

The electron injection and transport in OLEDs have been improved by using a tris-[8-hydroxyquinoline] gallium (Gaq) layer as step barrier between tris-[8-hydroxyquinoline]aluminum (Alq₃) (or 4,7-diphyenyl-1,10-phenanthroline (Bphen)) and 2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN). Since the LUMO (lowest unoccupied molecular orbital) of Gaq (2.9 eV) lies in between that of Alq₃ (3.1 eV) (or Bphen (3.0 eV)) and TBADN (2.8 eV), step barrier from Alq₃ (or BPhen) though Gaq to TBADN can be formed. The experimental results indicate that the J–V characteristics of both the electron-only and the complete devices show the increase of the current density in devices with step barrier compared with the devices without step barrier. For electron-only devices, the driving voltage at the current density of 20 mA/cm² is reduced from 7.9 V to 4.9 V for devices with Alq₃, and from 4.2 V to 3.1 V for devices with BPhen, respectively, owing to the introduction of step barrier. For the complete devices, when Gaq step barrier is introduced, at 20 mA/cm², the driving voltage is reduced from 7 V to 5.8 V for devices with Alq₃ and from 6.2 V to 5.1 V for devices with BPhen. It has also been observed that for devices with step barrier layer, the luminance at 200 mA/cm² is increased from 1992 cd/m² to 3281 cd/m² for device with Alq₃, and from 1745 cd/m² to 2876 cd/m² for devices with BPhen, respectively. The highest luminance reaches 3420 cd/m² in devices with Alq₃ as ETL and 3176 cd/m² in devices with BPhen as ETL after the introduction of step barrier. The phenomena are explained by using tunnel theory.     

Analysis of interface states of metal–insulator–semiconductor photodiode with n-type silicon by conductance technique

A metal–insulator–semiconductor photodiode (MIS-PD) as active layer with n-type silicon as interdigitated Schottky electrodes has been fabricated. The current–voltage characteristics, density of interface states and photovoltaic properties of the MIS-PD diode have been investigated. The diode has a metal–insulator–semiconductor configuration with ideality factor higher than unity. The electronic parameters (ideality factor, series resistance and barrier height) of the diode were found to be 1.94, 2.23 × 10⁴ Ω and 0.74, respectively. At voltages between 0.13 and 0.50 V, the charge transport mechanism of the diode is controlled by space charge-limited current mechanism. The interface state density of the diode was found to vary from 5.54 × 10¹² to 5.67 × 10¹² eV⁻¹ cm⁻² with bias voltage. The Au/SiO₂/n-Si/Al device shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 97.7 mV and short-circuit current I_sc of 17.4 μA under lower illumination intensities. The obtained electronic parameters confirm that the Au/SiO₂/n-Si/Al diode is a MIS type photodiode.     

Novel back-contact back-junction SiGe (BC-BJ SiGe) solar cell for improved power conversion efficiency

In this paper, a SiGe based Back-Contact Back-Junction (BC-BJ) device structure called BC-BJ SiGe solar cell has been proposed. Photo reflection is significantly reduced in UV/Visible spectrum region in case of SiC/Si₃N₄/SiO₂ passivated BC-BJ SiGe solar cell. Result, indicates that presence of SiC play an important role in photoelectric conversion. Ray tracing and finite difference time domain (FDTD) algorithms are used to simulate optoelectronics characteristics of the device. Simulation achieves the barrier height of 0.8 eV for holes at the interface which results in a higher field. The lower interface recombination rate of the order of 10¹⁷ cm^?3 s^?1 has been obtained. The device shows improved photovoltaic parameters. External quantum efficiency >84 % in the spectrum range of 450–700 nm wavelength and more than 80 % in the range of 350–700 nm wavelength is obtained. Further, we obtained the fill-factor (FF) and power conversion efficiency (PCE), 79 %, 17.8 % and 79 %, 14.8 %, using FDTD and ray tracing methods, respectively. All the simulations have been done using atlas and devedit device simulator.     

Temperature sensor based on the Er green upconverted emission in a fluorotellurite glass

The temperature dependence of the green upconverted emission from the two thermally coupled ²H_11/2 and ⁴S_3/2 levels of the Er³⁺ ion in a fluorotellurite glass has been analyzed as a function of the optically active ion concentration in order to check its availability as a temperature sensor. The infrared-to-green upconverted emission have been observed by the naked eyes after a cw laser diode excitation at 800 nm. The fluorescence intensity ratio between the thermally coupled emitting levels as well as the temperature sensitivity has been experimentally obtained up to 540 K. A better behaviour as a temperature sensor has been obtained for the less Er³⁺ concentrated glass with a maximum sensitivity of 54 × 10⁻⁴ K⁻¹ at 540 K, one of the highest found in rare-earth doped transparent materials.     

Decomposition of Polynomials with Respect to the Cyclic Group of Orderm

Given a polynomial solution of a differential equation, its m -ary decomposition, i.e. its decomposition as a sum of m polynomials P^{[ j ]}(x)  = ∑_kα_j,kx^{λ_{j, k}}containing only exponentsλ_{j, k} with λ_{j,k  + 1} − λ_j,k = m, is considered. A general algorithm is proposed in order to build holonomic equations for the m -ary parts P^{[ j ]}(x) starting from the initial one, which, in addition, provides a factorized form of them. Moreover, these differential equations are used to compute expansions of the m -ary parts of a given polynomial in terms of classical orthogonal polynomials. As illustration, binary and ternary decomposition of these classical families are worked out in detail.     

Analysis of Galerkin Methods for the Fully Nonlinear Monge-Ampère Equation

This paper develops and analyzes finite element Galerkin and spectral Galerkin methods for approximating viscosity solutions of the fully nonlinear Monge-Ampère equation det (D ² u ⁰)=f (>0) based on the vanishing moment method which was developed by the authors in Feng and Neilan (J. Sci. Comput. 38:74–98, 2009) and Feng (Convergence of the vanishing moment method for the Monge-Ampère equation, submitted). In this approach, the Monge-Ampère equation is approximated by the fourth order quasilinear equation −εΔ² u ^ε +det D ² u ^ε =f accompanied by appropriate boundary conditions. This new approach enables us to construct convergent Galerkin numerical methods for the fully nonlinear Monge-Ampère equation (and other fully nonlinear second order partial differential equations), a task which has been impracticable before. In this paper, we first develop some finite element and spectral Galerkin methods for approximating the solution u ^ε of the regularized problem. We then derive optimal order error estimates for the proposed numerical methods. In particular, we track explicitly the dependence of the error bounds on the parameter ε, for the error u^e-u^e_hu^{\varepsilon}-u^{\varepsilon}_{h}. Due to the strong nonlinearity of the underlying equation, the standard error estimate technique, which has been widely used for error analysis of finite element approximations of nonlinear problems, does not work here. To overcome the difficulty, we employ a fixed point technique which strongly makes use of the stability property of the linearized problem and its finite element approximations. Finally, using the Argyris finite element method as an example, we present a detailed numerical study of the rates of convergence in terms of powers of ε for the error u⁰-u_h^eu^{0}-u_{h}^{\varepsilon}, and numerically examine what is the “best” mesh size h in relation to ε in order to achieve these rates.     

A Posteriori Error Estimates and an Adaptive Finite Element Method for the Allen–Cahn Equation and the Mean Curvature Flow

This paper develops an a posteriori error estimate of residual type for finite element approximations of the Allen–Cahn equation u_t − Δu+ ε⁻² f(u)=0. It is shown that the error depends on ε⁻¹ only in some low polynomial order, instead of exponential order. Based on the proposed a posteriori error estimator, we construct an adaptive algorithm for computing the Allen–Cahn equation and its sharp interface limit, the mean curvature flow. Numerical experiments are also presented to show the robustness and effectiveness of the proposed error estimator and the adaptive algorithm.     

Validity and reliability of the Spineangel® lumbo-pelvic postural monitor

Objective: to determine the reliability and the concurrent validity of the Spineangel^® lumbo-pelvic postural monitoring device. Methods: the dynamic lumbo-pelvic posture of 25 participants was simultaneously monitored by the Spineangel^® and Fastrak^TM devices. Participants performed six different functional tasks in random order. Within-task, within-session and between-day intraclass correlation coefficients (ICC(3,1), ICC(3,5), ICC(2,5), respectively) reliability were calculated for Spineangel^® measurements. Concurrent validity of the Spineangel^® was assessed by means of a Bland and Altman plot and by means of Pearson's correlation coefficient and paired t-test. Results: within-task, within-session and between-day ICC for the Spineangel^® were found to be excellent (>0.93). The Spineangel^® and Fastrak^TM pelvic measurements were found to have a good correlation (R = 0.77). Conclusion: the Spineangel^® is a reliable and valid device for monitoring general lumbo-pelvic movements when clipped on the belt or waistband of workers' clothing during various occupational activities.

Practitioner summary: The Spineangel^® can be used for assessing lumbo-pelvic posture during work or daily-life activities. This device was found to provide reliable and valid measurements for lumbo-pelvic movements. Further research is required to determine whether the use of this device is clinically relevant for patients presenting with low back pain.     

Development and characterization of a microthermoelectric generator with plated copper/constantan thermocouples

This work reports the development and the characterization of a microthermoelectric generator (μTEG) based on planar technology using electrochemically deposited constantan and copper thermocouples on a micro machined silicon substrate with a SiO₂/Si₃N₄/SiO₂ thermally insulating membrane to create a thermal gradient. The μTEG has been designed and optimized by finite element simulation in order to exploit the different thermal conductivity of silicon and membrane in order to obtain the maximum temperature difference on the planar surface between the hot and cold junctions of the thermocouples. The temperature difference was dependent on the nitrogen (N₂) flow velocity applied to the upper part of the device. The fabricated thermoelectric generator presented maximum output voltage and power of 118 mV/cm² and of 1.1 μW/cm², respectively, for a device with 180 thermocouples, 3 kΩ of internal resistance, and under a N₂ flow velocity of 6 m/s. The maximum efficiency (performance) was 2 × 10^?3 μW/cm² K².     

Modeling power and intermodulation behavior of microwave transistors with unified small‐signal/large‐signal neural network models

This article presents a detailed procedure to learn a nonlinear model and its derivatives to as many orders as desired with multilayer perceptron (MLP) neural networks. A modular neural network modeling a nonlinear function and its derivatives is introduced. The method has been used for the extraction of the large‐signal model of a power MESFET device, modeling the nonlinear relationship of drain‐source current I_ds as well as gate and drain charge Q_g and Q_d with respect to intrinsic voltages V_gs and V_ds over the whole operational bias region. The neural models have been implemented into a user‐defined nonlinear model of a commercial microwave simulator to predict output power performance as well as intermodulation distortion. The accuracy of the device model is verified by harmonic load‐pull measurements. This neural network approach has demonstrated to predict nonlinear behavior with enough accuracy even if based only on first‐order derivative information. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 276–284, 2003.     

Digitally-controlled array of solid-state microcoolers for use in surgery

This paper presents an approach for generating a well-defined cooling pattern over an area of tissue. An array of solid-state microcoolers is used, which could be included in a probe that provides local cooling. This medical instrument can be used for removal of scar tissue in the eye or for the rapid stopping of bleeding due to micro-cuts, which makes it a useful tool to medical doctors and could make surgery more secure to the patient. The array of microcoolers is composed of 64 independent thermo-electric elements, each controlled using an integrated circuit designed in CMOS. The independent control allows the flexible programming of the surface temperature profile. This type of control is very suitable in case abrupt temperature steps should be avoided. Cooling by lateral heat flow was selected in order to minimize the influence of heat by dissipation from the electronic circuits. Moreover, a thermo-electric component with lateral heat allows fabrication of the cooling elements using planar thin-film technology, lithography and wet etching on top of the silicon wafer. This approach is potentially CMOS compatible, which would allow for the fabrication of the thermo-electric elements on top of a pre-fabricated CMOS wafer as a post-process step. Each pixel is composed of thin-films of n-type bismuth telluride, Bi₂Te₃ and p-type antimony telluride, Sb₂Te₃, which are electrically interconnected as thermocouple. These materials have excellent thermoelectric characteristics, such as thermoelectric figures-of-merit, ZT, at room temperatures of 0.84 and 0.5, respectively, which is equivalent to power-factors, PF, of 3.62 × 10⁻³ W K⁻¹ m⁻² and 2.81 × 10⁻³ W K⁻¹ m⁻², respectively. The theoretical study presented here demonstrates a cooling capability of 15°C at room temperature (300 K ≈ 27°C). This cooling performance is sufficient to maintain a local tissue temperature at 25°C, which makes it suitable for the intended application. A first prototype was successfully fabricated to demonstrate the concept.     

Integrated micro Pirani gauge based hermetical package monitoring for uncooled VO x bolometer FPAs

This paper presents the design and fabrication of a micro Pirani gauge using VO _x as the sensitive material for monitoring the pressure inside a hermetical package for micro bolometer focal plane arrays (FPAs). The designed Pirani gauge working in heat dissipating mode was intentionally fabricated using standard MEMS processing which is highly compatible with the FPAs fabrication. The functional layer of the micro Pirani gauge is a VO _x thin film designed as a 100 × 200 μm pixel, suspended 2 μm above the substrate. By modeling of rarefied gas heat conduction using the Extended Fourier’s law, finite element analysis is used to investigate the sensitivity of the pressure gauge. Also the thermal interactions between the micro Pirani gauge and bolometer FPAs are verified. From the fabricated prototype, the measured device TCR is about −0.8% K⁻¹ and the sensitivity about 1.84 × 10⁻³ W K⁻¹ mbar⁻¹.     

Study of enhanced DC and analog/radio frequency performance of a vertical super-thin body FET by high-k gate dielectrics

This article reports the DC and analog/radio frequency (RF) response of a newly invented device called vertical super-thin body (VSTB) FET towards high-k (Si₃N₄/HfO₂) and low-k (SiO₂) gate dielectrics in conjunction with the scaling effect through a well-calibrated Sentaurus TCAD tool. At channel length (L_G) of 20 nm, compared to SiO₂, Si₃N₄ improves various DC parameters such as off-state leakage current (I_off), on-current (I_on), on-to-off current ratio (I_on/I_off ratio), subthreshold swing (SS), and drain-induced-barrier-lowering (DIBL) by 77.15%, 26.2%, one order of magnitude, 15.78%, and 36.2%, respectively. On the other hand, a higher improvement is seen in all these DC parameters for the HfO₂ gate dielectric (I_off, I_on, I_on/I_off ratio, SS, DIBL improves respectively by 91.8%, 41.57%, two orders of magnitude, 28.28%, and 62.71%). The underlying physics behind such excellent improvement is explained by the device off-state energy band diagram, electrostatic potential, and channel electron density profile for each dielectric. Further, for all the gate dielectrics considered, the device characteristics were studied for a wide range of L_G from 10 to 50 nm to reveal the scaling impact on the device performance. Irrespective of the gate dielectric material, the device exhibits excellent performance at L_G = 10 nm, which in turn indicates to the brilliant scalability of this new device. Besides, although Si₃N₄ and HfO₂ increase gate capacitance (C_gg)/gate-drain capacitance (C_gd), due to the extremely low values of C_gg/C_gd, enhanced unit gain cut-off frequency, and gain-bandwidth-product is achieved. In addition, the increased transconductance (g_m) of the device applying Si₃N₄/HfO₂ gate dielectric leads to a higher peak value of TGF, intrinsic gain, TFP, GFP, and GTFP. This study intends to expand the fundamental knowledge about such a new device as a VSTB FET and hence, aims to be utilized in the future research of this novel device.