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.     

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.     

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。     

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.