Double Doppler ranging system using FM ultrasound

A new system which detects change in distance between a sound source and a receiver, using FM ultrasound has been developed, the principle of which is based on the Doppler phase shift. The use of FM ultrasound allows simultaneous detection both by carrier signal and by demodulated signal, and by using these methods together, stable measurements with good resolution are possible. Experiments in air and an anechoic water tank confirmed the accuracy of plus or minus half a wavelength for change of distance.     

用于测量流量和含沙量的超声波液位测定系统

本文介绍了实验室内用于测量流量和含沙量的超声波液位测定系统，此系统采用气介式方案，选用复合材料高频换能器作为超声波发射／接收器件，结构简单，静态测量时测量误差在１５０ｍｍ范围内不超过１ｍｍ，并可与微机进行远距离通讯。     

Focusing of longitudinal ultrasonic waves in air with an aperiodic flat lens

Modeling and experimental results of an ultrasonic aperiodic flat lens for use in air are presented. Predictive modeling of the lens is performed using a hybrid genetic-greedy algorithm constrained to a linear structure. The optimized design parameters are used to fabricate a lens. A method combining a fiber-disk arrangement and scanning laser vibrometer measurements is developed to characterize the acoustic field distribution generated by the lens. The focal spot size is determined to be 0.88 of the incident wavelength of 80-90 kHz at a distance of 2.5 mm from the lens. Theoretically computed field distributions, optimized frequency of operation, and spatial resolution focal length are compared with experimental measurements. The differences between experimental measurements and the theoretical computations are analyzed. The theoretical calculation of the focal spot diameter is 1.7 mm which is 48% of the experimental measurement at a frequency of 80-90 kHz. This work illustrates the capabilities of a hybrid algorithm approach to design of flat acoustic lenses to operate in air with a resolution of greater than the incident wavelength and the challenges of characterizing acoustic field distribution in air.     

Resolution improvement in vertical-cavity-surface-emitting-laser diode interferometry based on linear least-squares estimation of phase gradients of phase-locked fringes

A frequency scanning interferometer using a vertical-cavity-surface-emitting-laser diode (VCSEL) capable of wide-frequency scanning has been constructed for precise distance measurements. The frequency scanning velocity of the VCSEL has been stabilized by the phase-locked loop technique, which enables us to precisely determine the phase gradient of the scanned interference fringe by linear least-squares fitting. In our test measurements, the absolute lengths from 8 to 14mm have been measured with a resolution of nearly sub-micrometer. Compared with a conventional frequency scanning interferometer using a Fabry-Perot laser diode, the resolution of length measurement has been improved by two orders of magnitude.     

Photoacoustic multicomponent gas analysis using a Levenberg–Marquardt fitting algorithm

2 laser photoacoustic spectrometer has been developed for the in-situ monitoring of atmospheric trace gases in different environments. Numerous air pollutants, such as ammonia, ethene, ozone and alcohols, can be monitored with a time resolution of a few minutes. A new fitting algorithm based on the numerical method of Levenberg–Marquardt is discussed and applied to the derivation of individual gas concentrations from measured photoacoustic signal amplitudes and phases at selected CO₂ laser wavelengths. The algorithm has been tested with artificially generated multicomponent gas mixtures exhibiting gas concentrations in the ppb to ppm range. Furthermore, its potential is demonstrated with the analysis of an air sample from a fruit storage chamber and with ambient air measurements during a field study in a rural environment. Received: 23 March 1998/Revised version: 18 June 1998     

多针电晕增强大气压辉光放电稳定性研究

利用多针电晕增强放电装置，在无气流和存在高速气流的情况下都得到了稳定的大气压辉光.通过纪录发光图片、电流-电压波形和伏安特性曲线的方法对影响放电稳定性的因素做了细致地研究，发现了在从电晕放电到辉光放电的过程中存在着过渡阶段，表现为出现带有直流成分的Trichel脉冲.气流速度、极板间距以及针尖锥度和凹坑曲率半径的匹配程度都对放电的稳定性和电流密度有着重要的影响. 关键词： 大气压辉光放电 多针电晕 等离子体     

Attenuation of shock parameters in air and water

This paper describes the results of shock pressure measurements in the range of 1–25 MPa in water and in the range of 60–500 kPa in air. Pressure pulses were generated by exploding wire technique and measured with a quartz piezo-electric transducer. The attenuation with distance of shock overpressure, impulse and energy in shock front has been studied. Experimental data on shock attenuation in air is scarce and the results presented here confirm the attenuation behaviour derived from theoretical considerations.     

BOXCARS测量燃烧场的温度

 介绍了用BOXCARS技术测量CH₄/air火焰的温度。给出了甲烷气体不同流量下和火焰不同高度处的温度测量结果，分析了温度随甲烷气体流量变化和火焰高度变化的变化趋势，根据实际的实验参数计算了相应的空间分辨率。实验结果表明：利用BOXCARS技术可进行高精度、高空间分辨的温度测量。     

Direct detection of acetylene in air by continuous wave cavity ring-down spectroscopy

Diode laser-based continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared region has been used to measure the mixing ratio of acetylene (C₂H₂) in ambient air. Detection limits of 120 parts per trillion by volume (pptv) for 20 min and 340 pptv for 70 s acquisition time were achieved without sample pre-concentration, measuring on a C₂H₂ absorption line at 6565.620 cm^?1 (～1523 nm). Several indoor and outdoor air samples were collected at different locations in the Helsinki metropolitan area and analyzed using static-cell measurements. In addition, flow measurements of indoor and outdoor air have been performed continuously over several days with a time resolution of down to one minute. Baseline acetylene levels in the range of 0.4 to 3 parts per billion by volume (ppbv), with a maximum around midday and a minimum during the night, were measured. Sudden high mixing ratios of up to 60 ppbv were observed in outdoor air during daytime on a minute time scale. In general, the indoor mixing ratios were found to be higher than those in outdoor air. The acetylene levels correlated with the ambient CO levels and with outdoor temperature.     

In-situ alpha spectrometry from air filters at ambient air pressure

The effect of collimation to the alpha-particle energy spectra was investigated for two different types of air filters, when the measurements were performed at ambient air pressure. Significant improvement of the energy resolution is possible if appropriate collimator is used. This is because only those alpha particles are detected entering the detector almost perpendicularly. We also show that although in-situ alpha spectrometry from air filters at ambient air pressure and with good energy resolution is possible, the accumulation of alpha-particle emitting aerosols in the surface of the collimator and the detector may deteriorate the registered spectrum. Therefore, the presence of possible spurious alpha peaks must be taken into account in continuous air monitoring.     

Non-contact sound speed measurement by optical probing of beam deflection due to sound wave

We report a non-contact and non-invasive method of sound speed measurement by optical probing of deflected laser beam due to normally incident degenerated shock wave. In this study the shock wave from an exploding wire was degenerated to an ordinary sound wave at the distance exceeding 0.23 m. Temporal resolution of the deflected beam signal was improved by passing through an adequate electronic high-pass filter, as a result we obtained a better temporal resolution than that of the acoustic pressure detection by PZT transducer in terms of rising time. The spatial resolution was improved by passing the refracted beam signal into the edge of focusing lens to make a larger deflection angle. Sound speed was calculated by monitoring the time of flight of transient deflected signal at the predetermined position. Sound speed has been measured in air, distilled water and acryl, agreed well with the published values. The sound speed measured in the solution of glycerin, magnesium sulfate (MgSO4), and dimethylformamide with various mole fractions also agrees within 3% of relative error with those measured in the present work by ultrasonic pulse echo method. The results suggest that the method proposed is to be reliable and reproducible.     

New guidelines regarding the positioning of protective air terminations on structures using e-field modelling techniques

An important consideration in the design of any air termination system is the maximum distance at which the terminations can be placed from the “vulnerable points” on structures, i.e., typically those points that create the highest degree of electric field intensification. This paper extends a previous, preliminary analysis of the problem in three significant ways. Firstly, the height range of the air terminations has been extended by a factor of 4 with a series of additional calculations. Secondly, account is taken of the material of construction of the building on which the air terminations are installed. Thirdly, and most importantly, a field study has been carried out in a high-lightning area as real check on the model results. All of the results are compared and some quantitative guidelines are provided for the maximum distance at which air terminations should be installed from the vulnerable points of structures.     

Accuracy of the random-incidence scattering coefficient measurement

The experimental results presented in this study aim at providing an useful insight into the accuracy of the measurement procedure of the random-incidence scattering coefficient as defined in ISO 17497-1:2004. A systematic experimental investigation has been conducted in a full-scale reverberation room. The tested diffusers are characterized by different geometrical distributions of hollow wooden cubes with an edge length of 20 cm, and different configurations of the measurement set-up. The accuracy of the measurement results has been evaluated considering the contribution of the different undefined aspects of the ISO method such as the microphones height, the air gap underneath the turntable, the sample shape, and the correction of the effects of the absorption and scattering coefficients of the base plate. The results showed that the accuracy of the measurement increases when a more rigid turntable and a circular sample are used, and when the air gap below the turntable is covered. Furthermore, the distance of the microphones from the sample surface was found to affect significantly the results, thus to influence the accuracy of the measurements.     

Study on the structure functions of electrons and the energy flow in the soft component of cosmic-ray extensive air showers

Summary Cosmic-ray air shower structure functions for the distance dependence of electron density in cosmic-ray air showers in the size range 10⁴⋎10⁸ have been computed for their intercomparison and comparison with Monte Carlo simulation results and measurements from recent experiments. The analysis has yielded the present status of theoretical structure functionsvis à vis experimental results and Monte Carlo simulation distributions. The effect of core location error on the lateral distribution of electrons is also discussed from the point of view of different theoretical and experimental results. The energy flow in the soft component of air showers of size ∼4·10⁵ has been evaluated within a ring of radius 10m about the axis of the showers.     

微分吸收激光雷达在遥感大气密度过程中的探测误差、最优化发射功率和测量精度等问题的探讨

详细地讨论了微分吸收激光雷达测量气体密度时中心频率的漂移所引起的测量误差。计算结果表明,中心频率的漂移是微分吸收激光雷达主要的误差来源。还探讨了微分吸收激光雷达的发射功率的优化和探测精度的优化等问题。计算结果表明,优化前的中心频率的发射功率大于优化后的发射功率,随着探测距离的增大,两者的比值越来越大。而且优化后的精度高于优化前的精度,随着距离分辨率的减小,两者的比值也越来越大。因此,在探测距离比较大和距离分辨率比较小的情况下,微分吸收激光雷达的优化显得特别重要。     

Kinetic energies of excited atoms ejected from ion-bombarded surfaces

The decay of photon yield from sputtered excited atoms as a function of the perpendicular distance from an ion-bombarded surface has been measured for four particular transitions using an intensified silicon intensifier target (ISIT) detector and an optical multichannel analyzer (OMA) with 512 channels. This experimental approach has resulted in greatly improved spatial resolution than previous attempts, making it possible to examine in detail the decay from departing atoms close to the target surface, thereby circumventing to some extent the long-lived cascade contribution. The kinetic energies derived are compared with previous measurements and their implication to the excitation process in sputtering is discussed.     

Low-energy electron current image diffraction (CID) of the basal plane of titanium

The basal plane of titanium has been studied by low-energy electron current image diffraction. Using a simple model, the average inner potential and surface interlayer distance were deduced from Bragg scattering features in the diffraction patterns which were obtained from a series of photographs of crystal surface images obtained at various primary beam energies. Computed geometric changes of Bragg scattering as a function of angle of incidence are presented for the energy range 0–200 eV. It is suggested that an energy monochromator incorporated in the electron gun would improve the pattern resolution and bring out energy sensitive lines which are not observed under the present conditions. Image enhancement methods would also increase the precision of the measurements.     

New Method for Estimating the Energy of Extensive Air Showers from Signals of Ground-Based Detectors of the Yakutsk Extensive Air Shower Array

A new method has been proposed for estimating the energy of inclined extensive air showers from signals of ground-based scintillation detectors of the Yakutsk extensive air shower array that are located at a distance of 600 m from the shower axis in the plane of the array and from the calculations of these signals within two hadron interaction models. New estimates of the energy have been obtained for 116 showers detected in different years. It has been shown that the energy spectra of particles of primary cosmic radiation measured at the Yakutsk array are in agreement with world data.     

High accuracy ranging with Yb-doped fiber-ring frequency-shifted feedback laser with phase-modulated seed

This paper demonstrates that a frequency-shifted feedback laser, when seeded by a phase-modulated narrow-band radiation field, is a powerful tool for distance measurements to accuracy better than 10 μm and resolution better than 100 μm, for distances of a few meters. In such measurements the unknown distance forms one arm of a Michelson interferometer, in which the intensity of the output signal is modulated at the phase-modulation frequency of the seed. The amplitude of the output-signal modulation exhibits a resonance for every distinct signal delay, i.e. for each distinct distance within the laser spot on the target. The use of a phase-modulated input seed allows one to use a very narrow-bandwidth filter when measuring the return signal. The results reported in this paper are in excellent agreement with previous theoretical predictions [L. Yatsenko et al., Opt. Commun. 242 (2004) 581] for the resolution limit and high signal-to-noise ratio for this new technique.     

具有位移和绝对距离测量能力的回馈干涉系统

提出一种基于半导体激光器泵浦Nd∶YAG微片激光器的回馈干涉系统，适合于非配合目标的位移和绝对距离测量。该测量系统包括移频回馈干涉光学系统，基于泵浦调制的微片激光器调频系统和相敏检波信号处理系统3部分。介绍了移频回馈干涉的原理，给出了位移测量和绝对距离测量应用的原理和测量方法，分析了测量的分辨率。实际测量了发黑工件表面的位移和绝对距离。实验结果表明，该回馈干涉系统灵敏度高，对被测表面反射率的要求很低，兼有对非配合目标的高分辨率位移测量和绝对距离测量的能力。