Electrical Filter Research Articles

Design and test of a particle mass spectrometer (PMS)

In the present paper a newly developed particle mass spectrometer (PMS) is described which allows determination of the mass of charged ultrafine particles or large molecules. It combines different physical principles: a molecular beam technique to generate a particle beam, an electrical deflection and filter system which classifies the particles due to their kinetic energy and velocity in the beam, and a detection system for the charged particles. From all three, the probability density distribution of m p z · e (i.e. the particle mass per number of charges) can directly be determined. These characteristics form the basis of a mass spectrometer suitable for particles in the mass range 10 −21 g ⩽ m p ⩽ 10 −18 g (600 amu ⩽ m p ⩽ 600,000 amu). The PMS was tested to measure the particle mass distribution in a sooting low pressure premixed flame as well as in an aerosol containing silver particles.

Explicit expressions for the receiver sensitivity and system penalties of optically preamplified direct-detection systems

Novel analytical closed-form expressions for the receiver sensitivity of an optically preamplified direct-detection transmission system and the system power penalties arising from excess electrical and optical filter bandwidths and finite extinction ratio are presented. An explicit analytical expression covering the combined effects of APD noise, receiver circuit noise, finite extinction ratio, electrical and optical filter bandwidths, amplifier noise, and input coupling loss is given. These results form a useful basis for the design of high sensitivity optically preamplified transmission systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spatial and temporal analysis of solid-state imaging systems

Temporal and spatial properties of the image that is stored in the digital memory of a frame grabber through a solid-state image sensor, which employs the X-Y addressing method for scanning the image, are analyzed in the space-time domain by using the mathematical expression that we have obtained. This expression includes not only the static effects of the finite picture-cell size of the sensor and the image sampling in both the sensor and the grabber but also the dynamic effects of the temporal response of photoelectric conversion in the sensor, a one-dimensional electrical filter of the camera controller, and the asynchronous sampling with regard to time in both the sensor and the grabber. Results of the experiment and the numerical simulations based on the mathematical expression are presented for a time-varying one-dimensional object with good agreement.

Transmission-line laser modelling of semiconductor laser amplified optical communications systems

Previously, the transmission-line laser model (TLLM) has been used to simulate the optical noise characteristics of semiconductor lasers and semiconductor laser amplifiers in the time-domain. The paper shows that, with the addition of a suitable photodiode model, the base-band electrical noise characteristics of amplified optical systems can also be simulated with the TLLM. A simple theory of the baseband noise properties of a detected optical signal is presented and photodiode model for the TLLM is developed. The baseband electrical noise spectra of travelling-wave, Fabry–Perot and DFB laser amplifiers are numerically simulated, and the travelling-wave laser amplifier spectrum is in excellent agreement with simple theory. This new approach to amplified optical communications system modelling allows the effects of different optical and electrical filters on the signal and the noise to be studied simultaneously over a wide bandwidth. As an example, a 10 Gbit/s system is simulated, and the effects of the optical filter on the signal and the noise are investigated.

Equivalence between preamplified direct detection and heterodyne receivers

The interrelationship of heterodyne receivers and preamplified direct-detection receivers is explained. The authors compare the performances of the two lightwave receiver schemes, taking into account all of the essential functional blocks needed in a real receiver. This includes analysis of the laser phase noise, the limiting noise processes, the optical and electrical carrier wave filters, the nonlinear demodulation functions, and the baseband filters. Even with these realistic effects included, the two receivers have mathematically equivalent performance under certain conditions, which are rigorously identified. It is shown that this is a general result which is independent of the modulation format used. The established equivalence suggests that the analytical and practical design criteria used for one scheme can also be used for the other.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low‐frequency cutoff in fluid‐saturated porous piezoelectric ceramics

Voided piezoelectric ceramics show interesting properties, particularly under hydrostatting solicitations. The 3.3 composite structure can be regarded as a porous solid frame with different scales of open porous cell (like an open cell foam). The high value of the dH piezoelectric coefficient is obtained by closing the surface cell openings to avoid external fluid entrances. The present work concerns the analysis of viscous fluid saturation effects on piezoelectric properties of porous LZT ceramics. Experimental results are presented that show a three‐regime behavior of the hydrostatic sensitivity: a low‐frequency regime characterized by a flat weak response that corresponds to the “local hydrostatic regime,” a high‐frequency regime characterized by voided material response, and a transition regime characterized by a first‐order cutoff response. This behavior can be explained in terms of competition between permeability and elasticity with an “RC” electrical filter analogy.

Pressure measurement artifact with analog-to-digital conversion

Pressure was transduced with the use of a fluid-filled catheter and standard medical monitoring equipment. When the signal was sampled at 200 Hz with an analog-to-digital converter, an artifact was observed. The 3.5-Hz artifact had an amplitude of 0.3 to 0.9 mm Hg and was caused by aliasing of a noise contaminant from the 2,403.5-Hz electrical excitation signal of the transducer. The artifact was completely eliminated with a 100-Hz low-pass filter. Electrical filtering is necessary for accurate acquisition of pressure measurements with analog-to-digital conversion, even when the sampling rate satisfies the Nyquist criterion for the frequency response of the mechanical system. Although the impact of the artifact is small in the clinical area, it is important under some research circumstances.

High sensitivity photoacoustic spectrometer for variable temperature solution studies

A single beam, dual cell, photoacoustic spectrometer has been developed for use with solutions from ambient temperature to the boiling point of the liquid. The optical absorbance sensitivity of the apparatus is 3×10−7 absorbance units per cm (base 10 logarithm, 1000 pulse average, 13 mJ/pulse) for solutes in aqueous solution at 90 °C, using an excimer-pumped dye laser as the light source. The cell assembly is designed to thermally isolate the acoustic detector and prevent evaporative loss of the solvent. High accuracy subtraction of solvent optical absorption is achieved using preamplifiers with continuously variable gain, matched electrical bandpass filters, and a high common mode rejection ratio differential amplifier. Design constraints resulting from factors such as the temperature dependence of solute photoacoustic signal amplitude are discussed and results of experimental tests probing some limits of the identified constraints are presented. A data analysis method is described which substantially reduces the effect of transient acoustic interference from suspended particles in sample solutions.

Comprehensive moment generating function characterisation of optically preamplified receivers

An accurate and soundly based representation of the complex stochastic processes encountered with optical preamplification in direct detection receivers is obtained. The objective of this study is the identification of a comprehensive moment generating function (MGF) characterisation for practical optically preamplified receivers. To effect this we build on a skeleton abstract formulation outlined some time ago with only limited physical and structural interpretation by Personick. Here we develop a MGF for the postdetection noise processes which takes into account a comprehensive set of key amplifier and receiver parameters, including gain and spontaneous noise characteristics of the semiconductor laser amplifier (SLA), amplifier facet reflectivity, bandwidth of the associated optical filter and postdetection electrical receiver filter characteristics. This comprehensive MGF may be used to obtain, via an independent route, the simple mean and variance characterisation of Yamamoto. We demonstrate this correspondence on a term-by-term basis and identify also minor discrepancies in two terms of the Yamamoto noise representation. The importance of the new MGF formulation is that it provides, for the first time, a sound formal basis which may be adopted for receiver design and analysis; this will enable, in any given situation, the adequacy or otherwise of a simple Gaussian approximation to be assessed.

Acoustical stethoscope with electrical filter

The stethoscope comprises a membrane (2) sensor (1) connected by a tube (3) to ear-pieces (8 & 9). The tube (3) traverses a casing (10) containing an electrical unit connected by a cable (12) to an electrical sensor (11). The electrical unit is sensitive to a given frequency range and comprises an electro-acoustic emitter (19) supplying acoustic signals into conduit (3) which are obtained in response to signals coming from the sensor (11) according to a predetermined scheme.

Envelope statistics for filtered optical signals corrupted by phase noise

Consideration is given to the case of an optical pulse containing phase noise which is passed through either an optical filter or (following heterodyne lightwave detection) an electrical filter. Because of the phase noise, the envelope of the filter output at any instant is a random variable. An analytical method is developed for estimating the probability density function (pdf) of this envelope for different kinds of filter responses and for realistic combinations of phase noise severity and filter bandwidth. Obvious applications are to detection analyses of coherent lightwave systems, wherein finite laser linewidths constitute an important source of impairment. For each of the several types of filters considered, the envelope PDF can be accurately fitted by an exponential function approximation, where the decay constant is related in a simple way to known system parameters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The development of transmission at an identified molluscan synapse. II. A quantal analysis of transmission.

1. A quantal analysis of transmission at the identified molluscan synapse, V2-RPr1, was performed during development. The study was intended to determine the pre- and postsynaptic contributions to the marked changes in transmitter release described in the previous report. 2. The success of the quantal analysis was predicated on overcoming the problems associated with extending the quantal analysis technique to central synapses. This involved adopting the following strategies: 1) using a low-noise recording system coupled with electrical filtering; 2) establishing objective criteria for failures recognition; and 3) using three methods to determine the quantal content: amplitude histograms, failures analysis, and the coefficient of variation. 3. The correlation of the results obtained from an analysis of amplitude histograms and from failures analysis were highly significant (P less than 0.01) at all times studied. A similar significant correlation was observed between the failures method and the coefficient of variation methods. 4. The amplitude of the quantal unit declined progressively during development (range: 131-25 microV), in parallel with the decrease in the postsynaptic input resistance (range: 103-5 M omega). 5. At both frequencies of stimulation (0.02 and 0.2 Hz), there is an approximately 20-fold increase in quantal content over the period of the study. Frequency facilitation at the synapse is due to an increase in quantal content. 6. Possible structural correlates for the developmental increase in quantal content were discussed.

A Novel Real-Time Chirp Measurement Method for Ultrashort Optical Pulses

Rapid measurements of ultrashort optical pulse chirping were realized with a newly developed real-time chirp monitor. The application of a moving coil translator and electrical filters enabled the rapid measurement and decoding of fringe-resolved second-harmonic-generation (FRSHG) autocorrelation. The prototype system displayed chirping characteristics at a repetition rate higher than a few hertz, which demonstrates the usefulness of this monitor for dye laser system alignment.

A New 510-Element CCD Camcorder for ENG

The new Sony BVW-105 camcorder employs three 510 horizontal by 492 vertical element charge-coupled devices (CCDs) in a 2/3-in. imaging format. The characteristics of this particular device combine to produce a camera ideal for ENG applications. This article describes the CCD device employed and its transfer mechanism. The design criteria established to optimize the imaging resolution while ensuring minimum aliasing — including details of the spatial-offset technique employed, the optical low-pass prefilter, and the electrical filtering — is outlined. A summary of the physical attributes of this new camcorder and how they relate to the needs of a modern ENG news crew is included.

The falling weight impact test applied to some glass-fibre reinforced nylons

Measurements on five glass-fibre reinforced compounds have shown that at fibre weight fractions of 0.3 and 0.5 increased mean fibre length confers greater resistance to impact as measured by a conventional flexed-plate method. The results were consistent with notional fracture surface energies that were deduced from the lengths of crack generated by various low energy blows and from the lengths recorded by flash photography at various stages of impact events. The velocity of impact was not influential over the range investigated (1 to 5 m sec−1 ). The investigation was not straightforward because when a test specimen of this class of material is impacted at room temperature the observed response is either heavily contaminated with extraneous vibrations due to the absence of an electrical filter or of questionable purity due to the presence of a filter. In that respect, and others, the paper is linked to an earlier one (J. Mater. Sci.21 (1986) 3153).

An assessment of industrial robots: Capabilities, economics, and impacts

An assessment of industrial robots: Capabilities, economics, and impacts

The practical use of thermocouples for temperature measurement in clinical hyperthermia.

The use of thermocouples as invasive thermometers in clinical hyperthermia is comprehensively and critically reviewed. The ability to construct thermocouple probes as small-bore, multiple junction assemblies is a major reason for their popularity and full constructional details are given. The potential sources of measurement error when using thermocouples both in temperature gradients and in electromagnetic or ultrasonic heating fields are discussed. Emphasis is placed upon simple practical solutions to these problems and a combination of good measurement practice and electrical filtering can reduce errors to an insignificant level. Techniques are suggested for the assessment of thermocouple performance during clinical measurement. With careful use, thermocouples can be reliable and convenient thermometers.

Photoconductive Detectors Employing An Optically Induced Nonlinear Resistance

A new mode of operation of photoconductive detectors in which a nonlinear current-voltage characteristic is induced by illumination is described. Outputs at harmonic frequencies can be obtained from devices biased with alternating current or at the modulation frequency of a modulated, alternating bias. Several different ways to achieve the nonlinearity are described, one of which uses conventional detector structures. The advantages of this mode of operation are that the large bias-voltage pedestal, normally associated with long-wavelength photoconductive detectors, can be separated from the photo-signal by simple electrical filters and that the problem of flicker noise, in both the detector and the following electronics, is considerably reduced. Photoconductive devices thus become competitive with photodiodes, which may be more difficult to produce with ideal performance and stable characteristics, in detect-ing radiation with very low modulation frequencies. Possible applications for the device may be in slow, parallel-scanned linear arrays; in staring arrays; in ultrasensitive detectors employing long integration times; and in position-sensitive, point-source detectors.

Analysis of a force balance accelerometer

Theoretical and Experimental Analyses of a commercial Force Balance Accelerometer are presented. Through detailed analysis of the feedback logic and electrical low pass filters, differential equation of the overall system has been developed. It is found that, for the accelerometer type tested, the representation of the transducer response by means of a single degree of freedom viscously damped system is not adequate.

Optical code-multiplex transmission by gold sequences

This paper describes a transmission system that uses passive optical multiplexing with gold sequences. The system is composed of an optical fiber network and electrical matched filters, and allows for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N + 2</tex> asynchronous stations each with a gold sequence address of length <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> . We analyze, theoretically, the error probability of the system and verify the results with experimental data. We further show that, in the synchronous case, the maximal error-free multiplexity is, in practice, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N + 1</tex> . The features of the System are as follows: 1) The system uses optical multiplexing instead of conventional electrical multiplexing. 2) The number of assignable addresses is large. 3) In the asynchronous case, each station can transmit a code at any time irrespective of other stations' timings.