共查询到17条相似文献,搜索用时 46 毫秒
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辐射压力法与声光法测定超声功率 总被引:2,自引:0,他引:2
本文介绍两种相互独立的超声功率绝对测量方法——辐射压力法和声光法,并对同一标准超声源进行测量,以验证声光法的可靠性。一、两种测量方法的原理及测量装置辐射压力法的测量原理是:在小振幅平面超声场中,两种媒质交界面上出现的时间平均单向压力即辐射压力,其值等于界面两边声能密度的差值。由此产生的辐射压力可用一个置于超声场中的靶来测定。超声换能器所辐射的总功率w与作用在全反射靶上的辐射力之间的关系为: W=CF/2cos~2θ (1)式中,W——总声功率,W; F——沿超声波轴线方向作用于靶上的力,N; c——超声在液体中的传播速度,m/s; θ——靶面法线与入射声束之间的夹角。瓦级超声功率所产生的辐射力约为零点几至几十毫牛顿。 相似文献
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超声多普勒胎心仪超声源检定方法探讨 总被引:1,自引:0,他引:1
超声多普勒胎心仪超声源是临床诊断的重要手段之一。本文主要介绍了超声多普勒胎心仪超声源检定项目、技术要求及检定方法并介绍了所需要的测量装置,对测量过程进行了阐述。给出了计算公式和推算过程及测量精度。 相似文献
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一、测量依据JJG639-1998《医用超声诊断仪超声源》检定规程。二、测量方法采用直接测量法,按规程要求用毫瓦级超声功率计对同一探头进行不少于3次声功率测量,取其测量结果的算术平均值作为被检仪器配用指定探头的输出声功率。 相似文献
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输出声强是医用超声诊断仪超声源的一个重要计量指标.其值大于10mW/cm^2时就禁止用于孕产妇的胎儿检查。输出声强测量值的准确与否将决定该台超声诊断仪超声源的用途.对测量值的不确定度评价在其中起到了重要作用.资料一般仅对配线阵探头的医用超声诊断仪超声源输出声强不确定度评价.但现实中一台医用超声诊断仪超声源配用的探头是多种多样的。 相似文献
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Ultrasound has wide applications in medical instruments for both diagnostic and therapeutic purposes. As medical ultrasound is being used on human bodies, it is particularly important that the output power level must be well known for safety reasons. To meet this increasing need, we have realized a medical ultrasound power measurement system based on radiation force balance method. In this paper, we will discuss the system set-up in the National Metrology Centre (NMC), Agency for Science, Technology and Research (A*STAR), Singapore and the uncertainty evaluation of this system. 相似文献
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《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2009,56(8):1642-1653
This paper presents an approach to measure human subcutaneous fat thickness automatically using ultrasound radio frequency (RF) signals. We propose using spatially compounded spectrum properties extracted from the RF signals of ultrasound for the purpose of fat boundary detection. Our fat detection framework consists of 4 main steps. The first step is to capture RF data from 11 ultrasound beam angles and at 4 different focal positions. Second, spectrum dispersion is calculated from the local spectrum of RF data using the shorttime Fourier transform and moment analysis. The values of the spectrum dispersion are encoded as gray-scale parametric images. Third, averaging is used to reduce speckle noise in the parametric image and improve the visualization of the subcutaneous fat layer. Finally, we apply Rosin?s thresholding and random sample consensus boundary detection to extract the fat boundary. Our method was applied on 36 samples obtained in vivo at the suprailiac, thigh, and triceps of 9 human participants. In our study, high correlations between the manual and automatic ultrasound measurements (r > 0.7 at all body sites), and between the skinfold caliper and automatic ultrasound measurements (r > 0.7 at all body sites) were observed. 相似文献
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本文以超声诊断的原理为出发点,分析了超声诊断过程中的生物效应对人体带来的损伤,并阐述了影响超声功率测量准确性的几个重要因素,最后提出了一个新的测量参数——热指数,并分析了其测量方法和安全指标。 相似文献
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超声骨密度仪校准结果的不确定度评定,主要内容就是评定声速测量的不确定度。本文分析了影响超声骨密度仪声速测量值的不确定度因素,主要包括:测量重复性、温度误差对测量声速的影响、模体声速引入的误差,进而引入这些因素对超声骨密度仪声速测量进行不确定度评定,为超声骨密度仪的校准提供参考依据。 相似文献
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双面光伏组件由于正反两面均能发电而受到关注,如何测试其功率是当下研究的热点。对目前行业内最新的3项标准草案和1项测试方案进行了介绍和比较,并对其测试方法提出了参考建议。通过试验发现:在不同标准的指导下,同一块组件功率的测试结果差异较大,双面光伏组件的功率测试需要统一的方案。 相似文献
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《IEEE transactions on instrumentation and measurement》1970,19(1):28-34
An accurate power measurement technique is described, which makes possible the determination of the net power delivered to a load of arbitrary impedance over a wide power range. A standard power meter is employed to fix a reference power level. Subsequent measurements consist of dimensionless ratios that can be obtained from precision attenuators. The method is applicable to a very wide range of frequencies and was demonstrated at a frequency of 30 MHz with power measurements extending from 10-2 to 10-14 watt. Maximum uncertainties ranged from ~0.5 to 1.5 percent. This technique is applicable in the measurement of the sensitivity of very-low-level detectors, receivers, radiometers, etc. 相似文献