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一、工作原理用同一个晶体管发射超声单脉冲和调制波的声速仪的工作原理如图1所示.图1中脉冲回波重合法时序逻辑电路周期性地产生发射同步信号,信号经开关K1选通后,分别被送往单脉冲形成电路或调制波形成电路,然后再经过开关K2送在发射电路.当电源切换开关K3将高压直流电压VH送入发射电路时,该超声波声速仪处于发射超声单脉冲波的工作状态,发射电路输出幅度很高、边沿很陡的电脉冲,经过输出高频插座去激励压电晶片产生单脉冲的超声波,压电晶片与电感构成一个调谐回路路.当电源切换开关K3转向另一侧,将低压直流电压VL送入发射电路,该声速… 相似文献
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在普通物理的教學中,講到力學中機械能守恆定律、動量守恆定律和角動量守恆定律的時候,我們對於這三條定律的適用範圍,往往不很强調或不很注意。我們摘引梁寶洪所譯的福里斯—季莫列娃普通物理學中的幾段有關的材料來看一下。在第一卷第66頁上有着關於動量不滅定律的敘述:“構成一封閉系統的各物體底動量底向量和,即這封閉系統底總動量向量,在整個的運動期間內保持不變”。而關於封閉系統的敘述則是“物體彼此之間相互作用,但不舆這系統外部的物體相互作用”。在93頁有着能底不滅和轉换定律的敘述:“對於一封閉的系統(外力之功等於零),當一切過程在這系統內部發生時,這系統底能量保持不變,在此情形下,能量可以從某種形式轉變為另一 相似文献
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声波从第一媒貭垂直投射于第一媒貭和第二媒质的分界面时,一部分反射,另一部分透入第二媒质中(見下图)。当波在第二媒貭中传播至无限远处而沒有反射时,根据压強連續和速度連續的边界条件,可以推得声压透射系数为 p_2+/p_1+=2γ/γ+1。 (1) 相似文献
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The pulse echo overlap method using electrostaic transducers for accurate measurement ofultrasonic velocity in solid media is discussed in this paper.Owing to the advantage of non-contactfor electrostatic transducers,the correction for coupling layer can be eliminated and the correct cyclicoverlap can be easily achieved,thus the performance of the echo measuring system is significanitlyimproved.In this paper the diffraction correction is calculated for the echo measuring system usingelectrostatic transducers,and an ultrasonic velocity measuring instrument and its transducers arealso described.The measuring results for several specimens of glass and aluminium show that themeasuring accuracy of transmission time in this system reaches 1/500 of RF period,that means themeasnring accuracy reaches 0.2 ns at 10 MHz. 相似文献
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This paper describes the design and characters of a novel coupled resonant photoacoustic cell.It is called T-type cell,because it consists of two cylinders,one is thin and long,another is wide andshort.Its resonance frequencies are calculated on the basis of pressure integral expression in a cavityand Green's function.The coupled resonance frequencies of a prototype of T-cell are numericallyand are experimentally examined.The experimental and calculated results are in good agreement.When the length of the small cylinder equals to 3λ/4,another resonance occures.At this frequencythe background signal is in opposite phase with photoacoustic signal.Therefore it becomes possibleto record in real-time the PA spectra of samples(background signal having been subtracted).Itsdetection sensitivities for vapor concentration of C_6H_6 and CH_3OH have reached 7×10~(-8)/W HZ~(1/2)and 1×l0~(-8)/W Hz~(1/2) respectively. 相似文献
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超声在固体中的散射是声学的一个基本问题,也是超声无损检测的根本问题.只有充分认识超声在固体中界面或障碍物处的散射规律,才能解决散射的逆问题,从测得的散射信息逆推缺陷的位置、形状大小和性质,从而实现既定性又定量的超声无损评价.中国科学院声学研究所的应崇福院土、早在人们尚未普遍认识超声散射重要性的50年代中期,就在国外发表了有关固体中超声散射的论文.从80年代初期开始的十年中,他又与同事们对固体中的超声散射进行了系统研究,取得了丰硕成果.本书就是他和张守玉、沈建中两位研究员把研究成果进行系统整理而写成的… 相似文献