摘要:

A novel contactless method for conductivity sensing is introduced that utilizes a driving coil and two tunable and near resonant coils. The design uses only inexpensive electronic components and a variable frequency rf generator. An algebraic expression for the response has been derived and simulations indicate a linear response to surface conductivity changes over at least four orders of magnitude. The sensitivity is shown to depend on the conductivity of the substrate, with a limit to conductivity changes as low as 10−4&OHgr;−1for insulating substrates. An ultrahigh vacuum compatible version of this probe has been used to monitorin situaluminum thin film growth by chemical vapor deposition on a native oxide covered, highly doped, Si(111) wafer. On this semiconducting substrate (3 &OHgr;−1) a sensitivity to sheet conductivity changes as low as ∼2×10−2&OHgr;−1has been demonstrated. The Al films show a discrete jump in differential sheet conductivity associated with Al cluster coalescence during growth. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147927

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A dynamic pulsed plasma reactor (DPPR) capable of chemical vapor deposition of advanced materials on substrates located in a supersonic expansion nozzle is described. The DPPR combines plasma, shock tube, and supersonic expansion nozzle techniques in obtaining vapor phase quenching rates of 107–108K/s for nanometric particle size formation. Deposition of Ti(s) and TiN(s) from Ar–TiCl4, Ar–H2–TiCl4, and N2–H2–TiCl4reactants were experimentally investigated with deposition products characterized by scanning electron microscopy, atomic force microscopy, and energy dispersive x-ray analytical techniques. Theoretical gas dynamics describing wave motion and propagation of reactants in the DPPR are presented and resulted in identifying deposition mechanisms of homogeneous and heterogeneous nucleation for Ti(s) and TiN(s) on Pyrex substrates, respectively. This article describes reactor design, operating characteristics, and theoretical wave dynamics in the experimental system. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147928

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A phase modulation system for a waveguide Mach–Zehnder interferometer sensor system has been developed which is capable of direct detection of optical phase changes smaller than 2.2&pgr; milliradians. When implemented in a chemical sensor interferometer system this corresponds to a sensitivity for refractive index changes of the analyte of better than 10−6, provided temperature variations are kept below 0.1 °C during the measuring period. The sensitivity of the instrument is demonstrated by a stepwise addition of low concentrations of glucose in water. The possibility to reset the instrument by a whole number of fringes makes it feasible to combine the high sensitivity with a virtually unlimited range. The accuracy of the detection system is independent of interferometer visibility changes during the measurement. This makes it possible to perform accurate measurements in solutions with varying degrees of opaqueness, such as milk, blood, or wastewater. These features are demonstrated with adsorption experiments of proteins to the underlying waveguide substrate. Also, the possibility to have the visibility as an extra parameter during the measurements can be of importance for further investigation of protein adsorption processes. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147929

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fetal magnetocardigraphy (fMCG) provides a unique method for noninvasive observations of the fetal heart. Electrical currents generated by excitable tissues within the fetal heart yield measurable external magnetic fields. Measurements are performed with superconducting quantum interference devices inductively coupled to magnetometer or gradiometer coils, and the resulting signals are converted to digital form in the data acquisition system. The measured fields are usually contaminated by fetal and maternal movements (usually respiration), other physiological fields such as skeletal muscle contraction, the maternal cardiac signal, and environmental electromagnetic fields. Sensitivity to relatively distant sources, both physiological and environmental, is substantially reduced by the use of magnetic gradiometers. Other contaminants may be removed by proper signal conditioning which may be automatically applied using “black box” algorithms that are transparent to the user and highly efficient. These procedures can rapidly reduce the complex signal plus noise waveforms to the desired fMCG with minimal operator interference. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147930

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article analyzes electronic self-generated noise, signal-to-noise ratio and sensitivity for electrically compensated pyranometers. The conclusion from this study is that the source of self-generated noise in this kind of instrument depends mainly on the electrical resistance ratio on its sensors. A sensitivity analysis also demonstrated that the voltage output of these pyranometers is most sensitive to variation in resistance value of the compensation sensor. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147931

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A ±300 V dynamic range, battery-powered, and inexpensive electrometer system is described that has been used with passive horizontal wire antennas to measure the atmospheric electric potential at 1 and 2 m above the earth’s surface. Input currents drawn by the electrometer circuit are of order femtoamperes, and a guard drive output is provided to minimize leakage. The implementation of the passive wire antenna is described, using rigorous insulation and signal guarding, together with results obtained in fair weather conditions. Linearity of the portable electrometer over the input range is demonstrated to be comparable with a commercial laboratory electrometer, and the antenna potential can be determined to within a few volts in the fair weather electric field. Several such portable systems can be cheaply combined, sharing a common high tension supply, to measure the profile of the atmospheric electrical potential above the surface, at a remote site. Damage to the electrometer sustained in electrical storms can be cheaply repaired. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147932

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on our investigation into the development of electrostatic mirror based charged particle analyzers for space plasma physics experimentation. For this work, we tested an elliptical mirror analyzer which was designed to provide a wide, 2-dimensional field of view with high throughput and good angular resolution. Measurements with an ion beam demonstrated 2° full width at half-maximum angular resolution over a 16×16° field of view (FOV) and 4° resolution over a 40×40° FOV for an optical system with a linear dimension (entrance aperture to the particle detector) of 20 cm. The energy resolution is variable, similar in operation to a retarding-potential-analyzer or a modulated grid Faraday cup, with a geometric factor of 3.2×10−3cm2str&Dgr;E/Efor an energy resolution setting of 10&percent;. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147933

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A simple high current power supply is described. It can be assembled from readily available and relatively cheap components which can be itemized as follows: (1) commercial batteries; (2) fast high current switch; (3) feedback sensor; (4) PC with peripherals for controlling the switch. The apparatus was assembled for heating at very high heating rate with a low resistant load such as a graphite or vitreous carbon tube used as an atomizer in electrothermal atomization-atomic absorption spectroscopy measurements. The high heating rate must, however, be combined with a fairly good control of the temperature of the tube at various levels. This was obtained with a PC and relative peripherals which, directly or through a feedback circuit, control the switch. The system can be easily modified and adapted for other kinds of measurements as long as the high noise of the switching does not interfere with signal recovery. With the atomic spectrometer used (Perkin–Elmer Model 1100B), however, no worsening of the signal noise was observed. The level of current that can be used is mainly determined by the switch since, within a certain range, the voltage and the internal resistance of the power supply can be changed by the type of batteries and the way they are connected. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147934

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Design and operation of two simple capacitive transducer systems are described here. The first design uses a spring for the air-gap variations of a capacitor, while the second one employs a cantilever steel beam as a restoring element in a capacitive transducing arrangement. The reported setup makes it possible to detect mass changes of the order of 0.1 g in a 250 g range. A comparison has been made between the results of two sensors, and the second design shows a better performance in terms of repeatability, linearity, and sensitivity. It has a repeatability of better than 4&percent; for this range of operation. This device is suitable for mass measurements of medium resolution and dynamic range and has the advantage of simplicity in design and construction. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147935

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Cutting of irradiated zircaloy metal clad ceramic fuel pellets requires a special cutting saw that can be remotely operated. The remote operation is essential because of the pyrophoric nature of zircaloy metal and high radiation field associated with the irradiated fuel elements. Conventional saws cannot meet the operational requirements because these are not readily amenable for remote operation and maintenance. Hence we have developed a new laboratory scale cutting saw for cutting radioactive samples remotely. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147936

出版商:AIP    

年代:1997

数据来源: AIP