Noise Considerations Research Articles

Resolution of sensor array: Noise considerations and design implications

A deeper insight into sensor array resolution is given. Under the hypothesis of a minimum-sized array design, relationships between resolution and sensor parameters are explained. A representation space is introduced, where resolution and parameters can be simultaneously handled. New conceptual and graphical tools for array design are derived.

Virtual Hopf precursor of period-doubling route in directly modulated semiconductor lasers

The effects of noise on the period-doubling route in deeply modulated laser diodes are investigated. The dynamics are studied by employing the single-mode rate equations with consideration of Langevin noise. It is found that the period-doubling event in laser diodes has a virtual Hopf precursor and is enhanced by the existing Langevin noise.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

UV/visible Fourier transform spectroscopy using an inductively-coupled plasma: dual-channel noise cancellation

Although technological advances have extended the range of Fourier transform spectroscopy (FTS) into the UV/visible spectral domain, its application to spectroscopic and spectrometric problems has been hampered-relative to such applications in the infrared domain-by noise considerations. Although the technique retains high resolution, accurate wavelength registration, and simultaneous broad band coverage, the multiplex advantage present in the IR is severely compromised in the UV/visible due to the relative insignificance of detector noise. In particular, signal-carried noise distributes widely through the spectrum, degrading the dynamic range needed for many spectroscopic and analytical applications. This study demonstrates the use of complementary optical output channels in a commercial FTS to achieve up to ten-fold noise reductions for spectra acquired from an analytical inductively-coupled plasma with conventional pneumatic sample aspiration. The study also demonstrates the advisability of increasing the sampling rate of future instruments to exceed the maximum noise frequency characteristic of droplet evaporation effects.

Phase noise considerations in coherent optical FMCW reflectometry

An analysis of coherent optical FMCW is presented. It shows the limitations imposed on measurements of discrete reflections and of Rayleigh backscattering due to phase noise originating in the finite coherence length of the optical source. The dependence of the range for accurate measurements on particular parameters of the optical system is discussed in the general case and for three specific laser sources. >

Cavity detection — an engineering application for gravity

Gravity surveys, as applied to geotechnical engineering problems, have been extensively used as a method for the detection of cavities. Through careful data analysis and modern presentation techniques, a much better overall geological model can be derived. A case history is presented from the Thompsons Creek Dam Site, NSW which illustrates that the gravitational method, through the careful use of standard survey procedures and equipment, has potential as a geological mapping tool in urban or industrial settings deemed inappropriate for other techniques due to environmental issues or geophysical noise considerations. Rock density determinations based on regression analysis of gravity data detected significant anomalies over the survey area. Image processing was used to enhance Bouguer gravity intensity maps, which enabled the location of additional cavities in the vicinity of the proposed dam site.

Noise considerations in the design of long haul lightwave communication systems

Magnitude of the signal relative to noise determines the ultimate quality of all information transmission. In a lightwave system, there are several fundamental and nonfundamental noise mechanisms that govern the system performance. In this paper, concepts related to these issues will be developed and a review of the current status of this rapidly evolving field will be given.

On the construction of detection coils for a vectorial vibrating sample magnetometer

The construction of a coil system for a three-dimensional detection of the magnetization in a vibrating sample magnetometer is described in detail. Calculations of the sensitivity and signal to noise considerations assuming different noise sources are performed for an eight coil arrangement (Bowden arrangement). The system is constructed with special reference to thin-film samples which require a low position dependence at a high sensitivity.

Performance implications of time delay and responsivity mismatch for balanced CPFSK lightwave receivers

The performance implications of time delay mismatch and photodiode responsivity mismatch are assessed for balanced CPFSK heterodyne receivers with differential detection. The receiver sensitivity is determined using a technique which combines computer simulation for characterizing the signal at the receiver output with a formula-based method of evaluating the bit error ratio. This approach permits consideration of laser phase noise, local oscillator intensity noise, nonlinear signal processing, and nonideal components. The numerical results quantify the penalty in receiver sensitivity due to mismatch, for different levels of local oscillator intensity noise. It is determined that time delay mismatch primarily affects the intensity noise contribution to the IF signal, while responsivity mismatch primarily affects the received signal component of the IF signal.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance evaluation of CPFSK lightwave systems

The receiver sensitivity of polarization diversity continuous-phase frequency-shift-keyed (CPFSK) lightwave systems with differential detection is determined using a technique which combines computer simulation, to determine a probabilistic characterization of the signal at the receiver output, with a formula-based method of evaluating the bit error ratio. This approach permits consideration of laser phase noise, nonlinear signal processing, and nonideal components within a general framework. In particular, the technique captures the asymmetry in the probability density function of the sampled signal at the received output. Numerical results yield a sensitivity at a bit error ratio of 10/sup -9/, which is 4 dB better than that obtained with a simpler Gaussian approximation. >

Noise, resolution, and sensitivity considerations in the design of a single‐slice emission–transmission computed tomographic system

A prototype Emission-Transmission Computed Tomography (ETCT) system is being developed that will acquire single-slice x-ray transmission CT images simultaneously with single photon emission computed tomography (SPECT) images. This system will permit the correlation of anatomical information from x-ray CT with functional information from SPECT images. The patient-specific attenuation map derived from the x-ray CT images can be used to perform attenuation correction of the SPECT images, so that accurate quantitative information can be obtained. The fan-beam scanning geometry and the use of a segmented HPGe detector array impose special constraints on the design of the collimator for the system. Based on a signal detection model, an efficiency-resolution figure of merit (ERFM) as a function of the collimator geometric efficiency, system resolution width, and object diameter is defined. The ERFM is proportional to the square of the detection signal-to-noise ratio. The collimator design parameters can then be optimized by optimizing the ERFM for an anticipated object diameter. The collimator point-spread function, geometric efficiency, and resolution are calculated. The collimator optimized for the detection of a 1-cm object will have a single-slice point source efficiency of 1.2 X 10(-4), and a FWHM of 6.5 mm at the center of the reconstruction circle, at 12 cm from the collimator face. The minimum object contrast which will give a detection SNR of 5 is 74%, for a total accumulated count per slice of 2 X 10(6).

Carrier recovery and inter-burst interference in a symbol-synchronous tdma system

ESA is studying future communications satellite systems involving switching and processing on board the satellite. One concept uses a symbol-synchronous MF-TDMA system with very short data bursts. This paper investigates QPSK carrier phase estimation for coherent demodulation in such a system. The Viterbi and Viterbi algorithm is used to produce one phase estimate separately for each data burst. The algorithm and its properties are reviewed and computer simulation results are presented to show its performance. It offers excellent performance under the conditions planned for the MF-TDMA system and is robust against distortions and interference. One potential problem in such a system, with no interburst guard-time and possible level differences between adjacent bursts, is interburst interference. It is found that clear-weather level differences of several dB can be tolerated easily. Atmospheric attenuation of the wanted burst may result in major level differences between adjacent bursts, but the interburst interference itself does not increase with respect to the thermal noise environment and so does not contribute any new problems. Any requirement for power control, for instance, will be determined by considerations of noise rather than interference. The burst timing accuracy in such a system is set by normal intersymbol interference considerations, rather than by the interburst interference or the needs of the phase estimator.

General considerations of noise in microphone preamplifiers

In this paper a study of the noise performance of electret microphone systems as a part of hearing aids is presented. The signal-to-noise ratio of the microphone-preamplifier combination, containing a field-effect transistor (FET) and a high value resistive bias element in a hybrid configuration, is mainly determined by the noise generated in the preamplifier circuit. A theoretical analysis of the noise sources in a source follower is given. The dominating noise sources are the channel noise of the FET, the thermal noise of the gate bias element, and finally the noise due to the gate leakage current of the FET and its package. It is shown that for the systems investigated, the noise performance does not depend on the choice of the amplifying device (JFET or MOSFET) itself, but only on its packages. Besides this, it is found that it is necessary to keep the parasitic capacitances as small as possible and to make the resistance of the bias element as large as possible.

The theory of bandpass sampling

The sampling of bandpass signals is discussed with respect to band position, noise considerations, and parameter sensitivity. For first-order sampling, the acceptable and unacceptable sample rates are presented, with specific discussion of the practical rates which are nonminimum. It is shown that the minimum sampling rate is pathological in that any imperfection in the implementation will cause aliasing. In applying bandpass sampling to relocate signals to a base-band position, the signal-to-noise ratio is not preserved owing to the out-of-band noise being aliased. The degradation in signal-to-noise ratio is quantified in terms of the position of the bandpass signal. For the construction of a bandpass signal from second-order samples, the cost of implementing the interpolant (dynamic range and length) depends on Kohlenberg's sampling factor (1953) k, the relative delay between the uniform sampling streams. An elaboration on the disallowed discrete values of k shows that some allowed values are better than others for implementation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Laser Induced Fluorescence for Temperature Measurement in Reacting Flows

AbstractOH vibrational Thermally Assisted Fluorescence (THAF) temperature measurements have been demonstrated in both premixed and diffusion flames. The accuracy of the measurements is generally better than 100 K over a wide range of flame conditions for which the collisional quenching rate varies considerably. Application of this technique for temperature measurement in Chemical Vapor Deposition (CVD) flows, for which the quenching rate is relatively constant, should exhibit greater accuracy. THAF measurements in these flows are limited by signal to noise considerations, and should be possible down to pressures of 103-104 Pa or less.

An optical matrix-vector multiplier project

The implementation of an optical matrix vector multiplier (OMVM) as a project to demonstrate to undergraduates the parallel capabilities of computing with light, the advantages and disadvantages of analog computers, and noise considerations for accurate results is discussed. The OMVM is designed using waveguides and is interfaced to an Apple IIGS. Software and hardware designs are explained in detail. The Hartley transform is developed as an application, with the transforming elements input on a film mask, the input represented by the intensity of LEDS, and the output detected using photodiodes. Test and measurements using the architecture are discussed. Simple methods for improving the performance of the system are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thermal noise in piezoresistive silicon microphones

Recent developments in micromachining of silicon devices and piezoresistive silicon pressure sensors have led to the consideration of the limitations of silicon pressure sensors as a microphone. Fundamental and technological limits to device scaling are presented, which provide design criteria for sensitivity and pressure accuracy, along with dynamic range and bandwidth. An analysis on the nature of noise and fundamental noise mechanisms is presented to determine the theoretically achievable input resolution. Primary noise considerations are given with regard to thermal noise and shot effects. Performance variation of the sensor in both offset voltage and sensitivity is discussed as a function of temperature and impurity density of a standard bridge configuration. Finally, models of the various noise mechanisms are proposed.

Chaos, noise, and extinction in models of population growth

A “hump-with-tail” map (i.e., with two extremum values) is derived to describe the growth of bobwhite quail populations. Although this map is shown to be capable of producing chaotic dynamics, analysis of field data suggests that the population is at a stable equilibrium. Thus the observed fluctuations in population density likely reflect random perturbations. It is shown that populations governed by hump-with-tail maps are less prone to extinction in randomly fluctuating environments than hypothetical populations whose growth is governed by “one hump” maps, i.e., maps with a maximum as their only extremal value. Our observations emphasize the importance of considerations of noise in theoretical analysis of population growth and stability.

Investigation of a capacitance-based displacement transducer

A capacitance-based displacement transducer consisting of three concentric cylinders is introduced and analyzed. The design eliminates measurable humidity effects and reduces temperature effects to below 10 p.p.m./ degrees C over the temperature range of 20 degrees C to 60 degrees C. Electric noise considerations lead to a design of a 0.5-in-span (12-mm) transducer with 0.01% accuracy. >

Noise in sensors

Significant advances in the field of sensors and the need for improving the resolution in the measurement of physical, chemical and biological quantities, are increasing the importance of the characterization of the noise sources in sensors. The noise in fact limits the ultimate performances that can be obtained from a given device in terms of signal to noise ratio. After a brief review of the fundamental noise sources, particular attention is dedicated to some examples of specific sensors for which noise aspects are presented and discussed. Noise considerations will concern temperature, gas, displacement, weak force and photon sensors.

Signal and noise considerations of non-dispersive laser-excited atomic fluorescence in a graphite tube atomiser with front-surface illumination

Download options Please wait... Article information DOI https://doi.org/10.1039/JA9900500249 Article type Paper Download Citation J. Anal. At. Spectrom., 1990,5, 249-259 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Signal and noise considerations of non-dispersive laser-excited atomic fluorescence in a graphite tube atomiser with front-surface illumination G. Wei, J. P. Dougherty, F. R. Preli and R. G. Michel, J. Anal. At. Spectrom., 1990, 5, 249 DOI: 10.1039/JA9900500249 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Guor-Tzo Wei Joseph P. Dougherty Francis R. Preli, Jr. Robert G. Michel