Millisecond Response Time Research Articles

Electro-Optical Properties of UV Stabilized Sub-Micron Dispersion with Low Liquid Crystal Content

ABSTRACT We study a nematic dispersion formed in a UV-polymerized matrix with a low content of a liquid crystal component. The dispersions contains sub-micrometer liquid crystal droplets obtained in a two-step process: (a) phase separation during a fast cooling process (b) stabilization of droplets size by photo-polymerization caused by a low power UV exposure. The dispersion is homogeneous, highly transparent and shows little light scattering at wavelength 633 nm. We demonstrate that it can be used as an electrically-controlled birefringent slab with a relatively low driving voltage and a short response time. For example, application of the electric field 6 V/µm changes phase retardation by π/4 with the characteristic response time of several milliseconds.

Focus on Analytical Instruments

Focus on Analytical Instruments

High dynamic control of a three-level voltage-source-converter drive for a main strip mill

A high dynamic control system for the Alspa VDM 7000 medium-voltage drive was implemented, which provides fast torque response times of a few milliseconds despite the typically low switching frequency of gate-turn-off thyristors which is necessary to achieve high efficiency. The drive system consists of a three-level voltage-source converter with active front end and a synchronous motor. The drive has most recently been applied to a main strip mill. It provides a maximum of 8.3-MW mechanical power with a rated motor voltage of 3 kV. Besides motor torque as the main control objective, the control system has to comply with a number of additional objectives and constraints like DC-link voltage regulation and balancing, current and torque harmonics, motor flux, and excitation.

Microwave microstrip ring resonator as a paper moisture sensor: study withdifferent grammage

This paper reports use of a nondestructive, miniaturized, microwave microstripring resonator for moisture sensing application in papers. Advantages offered bythis sensor over the prevailing sensors are room-temperature operation, responsetime in milliseconds, measurements unaffected by dusty environment and ionicconductivity of samples. Samples of eleven types were tested, with grammage (gramsper square metre) and thickness varying from 21 to 70 g m−2 and 24 to 80 µmrespectively. The wet basis moisture normalization (with respect to instantaneousmoisture content in the sample) was established to remove scatter and to bringout clearly grammage dependence, thus avoiding error in moisture prediction dueto density variations, using only scalar measurements. A single equation forfrvariations is realized in terms of grammage and normalized percentage moisture(Mww)which is valid for all types of tested paper. A model of the wet paper is suggested mainlybased on water–dry paper interaction, also considering parameters like thicknessand surface roughness, to explain trends of the sensitivity curves. The estimated%Mww shows an error of ±0.9%in the estimated value as compared to the actual value.

High-pressure bridgman grown CdZnTe for electro-optic applications

The linear electro-optic response of high pressure Bridgman growth semi-insulating Cd0.9Zn0.1Te bulk samples has been characterized. Measurements have been performed in the third optical window for telecommunications around = 1.5 m. The dependence of the Pockels figure of merit on the modulation frequency and on the intensity of the optical probe beam is presented and discussed. Despite the residual optical absorption, Cd0.9Zn0.1Te is not affected by photo-generated auto-inhibition of the Pockels effect. This can be attributed to the action of an efficient intragap recombination center. It is, therefore, a suitable basic material for electro-optic switching of near-infrared beams at low frequency and quasi-continuous wave (cw) regimes. The implementation of a Cd0.9Zn0.1Te-based cross-bar switch for optical communication applications is also presented, which reaches −30 dB of extinction ratio and sub millisecond response time.

Influence of the Charge Transport Characteristics on the Holographic Response of Organic Photorefractive Materials

Organic photorefractive materials have attracted a lot of interest recently. Their optical response times of a few milliseconds, however, are not yet adequate for the desired commercial applications. We present an investigation on the correlation between the optical response time and photoelectric quantities, such as the hole mobility and the dispersivity of charge carrier transport.

Rare earth optical temperature sensor

A new optical temperature sensor suitable for high temperatures (⩾1700 K) and harsh environments is introduced. The key component of the sensor is the rare earth material contained at the end of a sensor that is in contact with the sample being measured. The measured narrow wavelength band emission from the rare earth is used to deduce the sample temperature. A simplified relation between the temperature and measured radiation was verified experimentally. The upper temperature limit of the sensor is determined by material limits to be approximately 2000 °C. The lower limit, determined by the minimum detectable radiation, is found to be approximately 700 K. At high temperatures 1 K resolution is predicted. Also, millisecond response times are calculated.

Static Theory of a Self-Driven Photo-Thermoelectrical High-Temperature Superconductor Bolometer

At the present time, radiation detection in the far infrared with millisecond response time requires use of complicated technology to obtain mK-degree operating temperatures and very high quality, critical temperature materials (e.g., W, Al). It is also customary to use films of nanometer thickness in the manufacture of such devices. In this paper, we present theory and computations for the performance a composite high-temperature superconductor (HTSC)–thermolectric materials bolometer, operated at 77 K and with films of thickness around 1 μ. A practical device with performance comparable to available photoelectrical bolometers is investigated. The simplicity of the technology involved makes it an attractive proposition. A semimetal film leg (SML; e.g., BiSb) is connected in parallel with a HTSC leg (HTSCL; e.g., YBCO). The bolometer is operated in a photovoltaic mode with no external source of bias power. The thermoelectric voltage developed across the SML leg due to radiation absorbed on the sensitive area of the bolometer remains shorted till there is a sufficient temperature rise of the HTSCL so that its resistance becomes comparable to that of the SML. The voltage thus developed across the bolometer would drive an external electronic readout circuit.

High temperature oxygen sensors based on doped SrTiO 3

The sensor properties of semiconducting strontium titanate can be modified by dopants. On the one hand, the ambiguous dependence of the electrical conductivity on the oxygen partial pressure can be changed by a small lanthanum (donor) concentration to an unambiguous one over a wide oxygen partial pressure range. Polycrystalline Sr 0.995La 0.005TiO 3 and/or thick films have response times of few milliseconds, caused by a surface type mechanism of the conductivity. The bulk type mechanism is very slow and is responsible for the long-term behaviour. On the other hand, the temperature dependence of strontium titanate can almost be suppressed for a small oxygen partial pressure range by a high iron (acceptor) content. On the basis of SrTi 0.65Fe 0.35O 3 a fast thick film oxygen sensor is proposed, which can be applied to control of lean-burn engines.

Characterization and Electro-Optical Properties of the Homopolymer and Copolymers of Ferroelectric Side-Chain Liquid Crystalline Polysiloxanes Containing Two Chiral Center Side Groups

Aggregation and electro-optical effects in the chiral smectic C phase of the ferroelectric liquid crystalline homopolymer and two copolymers were investigated. The smectic layers of homopolymer and copolymer were constructed by overlapping about 1.2 and 1.4 times the length of the side-chain mesogenic groups, respectively. The transient scattering mode was obtained by repeated voltage polarity reversal. Ferroelectric liquid crystalline polysiloxanes (FLCPs) exhibit large spontaneous polyarization (Ps) and Ps of homopolymers are larger than those of copolymers. The response times of homopolymers are longer than that of copolymers due to high viscosity. Reversible and bistable transparent-opaque change was successfully realized for the chiral smectic C phase upon applications of dc electric fields with a response time of several milliseconds at room temperature.

Comparison of Work of Breathing between Two Neonatal Ventilators utilizing a Neonatal Pig Model † 1667

Introduction: Little is known about the amount of work of breathing (WOB) associated with infants breathing on neonatal ventilators. We proposed that differences in the response time of different trigger systems would lead to differences in resistive WOB (WOBR) in ventilated preterm neonates. Methods: Twenty five intubated, sedated, spontaneously breathing neonatal piglets weighing 1,000 grams were studied. Resistive WOB[WOBR (gm cm/kg)] was measured utilizing an esophageal balloon and a flow transducer attached to a Bicore Neonatal CP-100 monitor. Each breath was further analyzed for response time in milliseconds (ms) with a computerized data acquisition program. Each animal was studied with two neonatal ventilators on at least three separate days [Siemens SV300 and Drager Babylog(DBL) in CPAP of 0,3,5 cm H20 and with the SV300 in pressure support 5 cm H20. All data were analyzed utilizing a Wilcoxon Signed Rank Test.Results: Comparing the SV300 and DBL, WOBR for CPAP=0 was 63±27 vs. 78±32 (p=0.004), for CPAP=3 was 72±29 vs. 94±31(p=0.001), and for CPAP=5 was 76±38 vs. 105±40(p=0.001) respectively. Overall WOBR for the SV300 was 71±31and for the DBL was 92±34 at all levels of CPAP, representing a decreased WOBR of 31% with the SV300. Pressure support of +5 cm H20 with the SV300 further decreased the WOBR by 27% compared to CPAP=5(p= 0.01) on the DBL.The trigger phase with the SV300 was 351ms and 442ms with the DBL (p=0.03), this 26% difference in the ventilator response time from the first negative deflection to intiation of gas flow may explain the increased WOBR with the DBL. Another distinct difference between these two ventilators was in the beginning of the trigger phase. It was observed of the mean time span of pressure deflection of each breath was 331ms or 260% greater in the DBL vs. the SV300. Conclusion: In intubated patients, maximum energy expenditure occurs at initiation of ventilators breaths. WOBR in premature piglets was significantly increased by the slower response times of the DBL vs the SV300 ventilator. These differences have important implications for energy kinetics and weight gain in ventilated preterm neonates.

A small-area high-T c superconducting bolometer with Y-Ba-Cu-O thin film

A small-area high-Tc superconducting bolometer with a dense YBCO meander wire on a (100) Zr(Y)O2 substrate has been tested at λ=1.5 μm using a diode laser as the radiation source. The infrared power absorbed by the bolometer was calibrated using a dc infrared substitution method. Responsivities of hundreds of V/W with a millisecond response time were obtained at a temperature of 86.5 K in the modulation frequency range of 10–3000 Hz. A minimum noise equivalent power of 6×10−11 W/Hz1/2 was measured at 1000 Hz. The experimental results are compared with those obtained from a thermal analysis of the substrate-supported microbolometer. No nonbolometric effect was distinguished.

Submicrometer intracellular chemical optical fiber sensors.

A thousandfold miniaturization of immobilized optical fiber sensors, a millionfold or more sample reduction, and at least a hundredfold shorter response time, all simultaneously, were achieved by combining nanofabricated optical fiber tips with near-field photopolymerization. Specifically, pH optical fiber sensors were prepared with internal calibration, making use of the differences in both fluorescence and absorption of the acidic and basic dye species. The submicrometer sensors have excellent detection limits, as well as photostability, reversibility, and millisecond response times. Successful applications include intracellular and intraembryonic measurements. Potential applications include spatially and temporally resolved chemical analysis and kinetics inside single biological cells and their substructures.

Anomalous liquid crystal undershoot effect resulting in a nematic liquid crystal-based spatial light modulator with one millisecond response time

We report here, a single crystal silicon-based spatial light modulator demonstrating a millisecond response time using a nematic liquid crystal operated in the surface mode configuration. This unexpected fast response time can be explained by a combination of liquid crystal voltage undershoot and the transient nematic effect. The fast response time measured is concurrent with high spatial resolution and gray scale capability which make this device unique in its class.

Design considerations of metal-film bolometer with micromachined floating membrane

A metal-film microbolometer formed on a glass membrane suspended on a silicon substrate has been fabricated by the anisotropic etching technique. The rectangular glass membrane is supported by its four leads connected to the corners of an etched V-groove cavity. This structure allows flexible thermal management and sensitivity optimization of the bolometer for different kinds of application, with a trade-off between lead thermal impedance and device active area. Optimizations of the structure applied to both a focal-plane array and a single detector are interpreted. A thermal impedance as high as 4 × 10 5 °C/W with a response time of several milliseconds can be achieved. For a 320 μm x 320 μm detector, theoretical predictions give a responsivity and normalized detectivity of over 700 V/W and 10 9 cm √/Hz/W, respectively. For dimensions of 128 μm × 128 μm, suitable for a focal-plane-array detector, theory predicts a D* of 5.5 × 10 8. A discrepancy exists between the experiment and the theory, which is also discussed.

Enzyme-modified carbon-fiber microelectrodes with millisecond response times

Enzyme-modified carbon-fiber microelectrodes with millisecond response times

Output grating couplers on planar waveguides as integrated optical chemical sensors

We have demonstrated that output grating couplers on thin SiO 2-TiO 2 waveguides are sensors which respond (i) with sub-monomolecular sensitivity to the adsorption of molecules out of a gaseous or liquid sample covering the waveguide in the grating region, and (ii) to changes in the refractive index of the sample. The effects (i) and (ii) induce changes in the effective refractive indices of the guided TE 0 and TM 0 modes, to which the sensors respond with a change in direction of the outcoupled beams, which were measured with position-sensitive detectors having (sub)-milli-second response times. Waveguides coated with thin chemoresponsive adlayers are proposed as sensitive (bio)chemical sensors. Work on immunosensors or immunoassays is in progress.

Measurement and simulation of thermistor response time in the millisecond range

The Finite Element Simulation Technique (FEST) has been applied to the design of hermetically-sealed thermistors with millisecond response times. These thermistors are used in stopped-flow calorimeters developed especially for investigations of biological reactions. FEST is also used to reconstruct the reaction kinetics obtained with these thermistors by correcting for their finite sensor response times and temperature loss.

Apparatus for millinewton force measurements with millisecond response time

Apparatus is described which is capable of measuring forces in the range 10-4-10-2 N with a response time of the order of a millisecond. The use of piezoresistive strain-gauge transducers extends the response to DC. The noise level of less than 10-5 N is achieved with the aid of a simple but effective antivibration, screened enclosure. Application to dynamic meniscus rise measurements illustrates the capabilities of the system.

A Technique to Measure Submillimeter Tokamak Synchrotron Radiation Spectra

A wire-mesh Fabry-Perot interferometer with millisecond response time has been constructed. The application of this instrument to study the millimeter and submilliieter synchrotrons radiation emitted by magnetically confined Tokamak plasmas is discussed.