毕业论文外文翻译-在空气中超声测距

1、附录a英文原文ultasonic ranging in airg. e. rudashevski and a. a. gorbatovudc 534,321.9:531.71.083.7one of the most important problems in instrumentation technology is the remote,contactless measurement of distances in the order of 0.2 to 10 m in air.such a problem occurs,for instance,when measuring the re

2、lativethre edimensional position of separate machine members or structural units.interesting possibilities for its solution are opened up by utilizing ultrasonic vibrations as an information carrier.the physical properties of air,in which the measurements are made,permit vibrations to be employed at

3、 frequencies up to 500 khz for distances up to 0.5 m between a member and the transducer.or up to 60 khz when ranging on obstacles located at distances up to 10 m.the problem of measuring distances in air is somewhat different from other problems in the a pplication of ultrasound. although the possi

4、bility of using acoustic ranging for this purpose has been known for a long time,and at first glance appears very simple,nevertheless at the present time there are only a small number of developments using this method that are suitable for practical purposes.the main difficulty here is in providing

5、a reliable acoustic three-dimensional contact with the test object during severe changes in the air's characteristicpractically all acoustic arrangements presently known for checking distances use a method of measuring the propagation time for certain information samples from the radiator to the

6、 reflecting member and backthe unmodulated acoustic(ultrasonic)vibrations radiated by a transducer are not in themselves a source of infonnation.in order to transmit some infonnational communication that can then be selected at the receiving end after reflection from the test member,the radiated vib

7、rations must be modulated.in this case the ultrasonic vibrations are the carrier of the information which lies in the modulationsignalj.e.they are the means for establishing the spatial contact between the measuring instrument and the object being measuredthis conclusion,however,does not mean that t

8、he analysis and selection of parameters for the carrier vibrations is of minor importance.on the contrary,the frequency of the carrier vibrations is linked in a very close manner with the coding method for the informational communication,with the passband of the receiving and radiating elements in t

9、he apparatus,with the spatial characteristics of the ultrasonic communication channel,and with the measuring accuracy.let us dwell on the questions of general importance for ultrasonic ranging in air,namely:on the choice of a carrier frequency and the amount of acoustic power received.an analysis sh

10、ows that with conical directivity diagrams for the radiator and receiver,and assuming that the distance between radiator and receiver is substantially smaller than the distance to the obstacle,the amount of acoustic power arriving at the receiving area pr for the case of reflection from an ideal pla

11、ne surface located at right angles to the acoustic axis of the transducer comes towhere prad is the amount of acoustic power radiated,b is the absorption coefficient for a plane wave in the medium,l is the distance between the electroacoustic transducer and the test me -mber.d is the diameter of the

12、 radiator(receiver),assuming they are equal,and cis the angle of the directivity diagram for the electroacoustic transducer in the radiator.d. cmfigfiff. 2both in eq.(l)and below.the absorption coefficient is dependent on the amplitude and not on the intensity as in some worksfl,and therefore we thi

13、nk it necessary to stress this difference.in the various problems of sound ranging on the test members o f machines and structures,the relationship between the signal attenuations due to the absorption of a planewave and due to the geometrical properties of the sound beam arenas a rule,quite differe

14、nt.lt must be pointed out that the choice of the geometrical parameters for the beam in specific practical cases is dictated by the shape of the reflecting surface and its spatial distortion relative to some average positionlet us consider in more detail the relationship betweenthe geometric and the

15、 power parameters of acoustic beams for the most common cases of ranging on plane and cylindrical structural members.it is well known that the directional characteristic w of a circular piston vibrating in an infinite baffle is a function of the ratio of the piston's diameter to the wavelength d

16、/x as found from the following expression:where ji is a bessel function of the first order and a is the angle between a normal to the piston and a line projected from the center of the piston to the point of observation(radiation).from eq.(2)it is readily found that a t w o-t o-o n e reduction in th

17、e sensitivity of a radiator with respect to sound pressure will occur at the angle0.762©or = arcsinfor angles a<20.eq.(3)can be simplified to(4)0.76c0() 5 =fd where c is the velocity of sound in the medimaa and f is the frequency of the radiated vibrations.it follows from eq.(4)that when rad

18、iating into air where c=330 m/s e c.the necessary diameter of the radiator for a spedfied angle of the directivity diagram at the 0.5 level of pressure taken with respect to the axis can befound to be(5)71400a «where disincmf is in khz,and a is in degrees of anglecurves are shown in fig.l plott

19、ed from eq.(5)for six angles of a radiator's directivity diagram.the directivity diagrm needed for a radiator is dictated by the maximum distance to be measured and by the spatial disposition of the test member relative to the other structural members.in order to avoid the incidence of signals r

20、eflected from adjacent members onto the acoustic receiverjt is necessary to provide a small angle of divergence for the sound beam and,as far as possibles small-diameter radiator.these two requirements are mutually inconsistent since for a given radiation frequency a reduction of the beamfs divergen

21、ce angle requires an increased radiator diameter.in fact,the diameter of thensonicatednspot is controlled by two variables,namely:the diameter of the radiator and the divergence angle of the sound beam.in the general case the minimum diameter of thensonicatednspot dmin on a plane surface normally di

22、sposed to the radiator's axis is given bywhere l is the least distance to the test surface.the specified value of dmin corresponds to a radiator with a diameterd =as seen from eqs.(,6)and(7),the1.5cl(7)innnum diameter of thehsonieatednspot at themaximum required distancecannot be less than two r

23、adiator diameters.naturally,with shorter distances to the obstacle the size of themsonicatedn surface is less.let us consider the case of sound ranging on a cylindrically shaped object of radius r.the problem is to measure the distance from the electroacoustic transducer to the side surface of the c

24、ylinder with its various possible displacements along the x and y axes.the necessary angleaof the radiator's directivity diagram is given in this case by the expression(8)wherea is the value of the angle for the directivity diagram,ymax is the maximum displacement of the cylinder's center fr

25、om the acoustic axis,and lmin is the minimum distance from the center of the electroacoustic transducer to the reflecting surface measured along the straight line connecting the center of the m e m b e r with the center of the transducer.it is clear that when measuring distance,thehrunningntime of t

26、he information signal is controlled by the length of the path in a direction nonnal to the cylinder's surface.or in other words.the measure distance is always the shortest one.this statement is correct for all cases of specular reflection of the vibrations from the test surface.the simultaneous

27、solution of eqs.(2)and(8)when w=0.5 leads to the following expression:d = 0.76亦宴匾(9)v j niaxin the particular case where the sound ranging takes place in air having c=33o m/sec,and on the asstunption that l min«r，the necessary diameter of a unidirectional piston radiator d can be found from the

28、 fomula25 rd fyj j max(10)where d is in cm and f is in khz.curves are shown in fig.2 for determining the necessary diameter of the radiator as a function of the ratio of the cylinder's radius to the maximum displacement from the axis for four radiation frequencies.also shown in this figure is th

29、e directivity diagram angle as a function of r and yrnax for four ratios of minimum distance to radius.the ultrasonic absorption in air is the second factor in determining the resolution of ultrasonic ranging devices and their range of action.the results of physical investigations concerning the mea

30、surement of ultrasonic vibrations air are given inl-3.up until now there has been no unambiguous explanation of the discrepancy between the theoretical and expe -rimental absorption results for ultrasonic vibrations in air.thusjor frequencies in the order of 50 to 60 khz at a temperature oft-25°

31、;c and a relative humidity of 37%the energy absorption coefficient for a plane wave is about 2.5db/m while the theoretical value is 0.3 d b/m.the absorption coefficient b as a function of frequency for a temperature or25°cand a humidity of 37%according to the data in2can be described by table 1

32、.the absorption coefficient depends on the relative humidity.thusjor frequencies in the order of 10 to 20khz the highest value of the absorption coefficient occurs at 20%humidity3,and at 40%humidity the absorption is reduced by about two to one.for frequencies in the order of 60 khz the maximum abso

33、rption occurs at 30.7o humidity.dropping when it is increased to 98% or lowered to 10%by a factor of approximately four to onethe air temperature also has an appreciable effect on the ultrasonic absorption 1 .when the temperature of the medium is increased from+10 to+30,the absorption for frequencie

34、s between 30 and 50 khz increases by about three to onetaking all the factors noted above into account we arrive at the following approximate values for the absorption coefficient:at a frequency of 60 khz /3min=0.15 m'1 andmax=05;at a frequency of 200 khz/min=06 m'1 and bmax=2 m'1.the re

35、lationships under consideration are shown graphically in fig.3.in the upper part of the diagram curves of g=f(l)are plotted for five values of the total angle in the radiator's directivity diagram, where (.21 (11)thevaluesfortheminimum minandrnaxil-nummax”transmittance"coefficients were obt

36、ained in the a bsence of aerosols and rain.their difference is the result of the possible variations in temperature over the range from -3 0 to+50and in relative hmnidity over the range from 10 to 98%.the overall value of themtransmittancenis obtained by multiplying the values of g and 0 for given v

37、alues of l,f；and d.literaturecited1 .l.bergman?ultrasonicsrussian translationjzd.inostr.lit.?moscow(1957).2v.akrasil'nikov,sonic and ultrasonic wavesin russian,f i z m a t g i z，moscow(1960).3.m.mokhtar and e.richardson,proceedings of the royal society, 184( 1945).附录b中文翻译在空气中超声测距g. e. rudashevsk

38、i and a. a. gorbatovudc 534,321.9:531.71.083.7在仪器技术中远程是最重要的一个问题。在空气中，从0.2米至10米非接 触式测量距离时，涉及到了这个问题，例如，在测量时个别机件或结构单位的相 对三维位置。有趣的是，是利用超声振动作为信息运输工具，开启了解决办法的 可能性在空气这个自然道具中，进行测量的是雇用成员和传感器之间距离0.5 米的时候，允许振动频率高达500千赫，或当与障碍物之间修止距离延仲达10 米时候，振动频率高达60千赫兹。应用超声波在空气中测量距离不同于其他的问题。虽然能否利用声波修止 测距的可行性已经研究了很长一段时间，乍一看似乎很简

39、单，但是目前只有为数 不多的新发明使用这种适合实际目的方法，主耍困难是在有严重特有变化的空气 中提供一个可靠试验对象去接触三维声波。几乎所有的目前已知用来校验距离使用的，都是为了某些来自用来反射成员 和后面的散热器信息样本，测量传播时间解决声音的办法。该未解调的声（超声）振动由传感器辐射的，本身并不是一个信息来源.在接收 端，来自测试会员反射后，为了传递一些情报信息，因而被选定后，辐射振动一 定会被调制。在这种情况下，超声波振动是在于调制信号的信息的承运人，即他 们就是在测量仪器和测量稳定的对象之间建立了空间三维接触的手段。这一结论，但是，并不意味着分析和选择的参数承运人振动重要性小止相 反，

40、承运人振动频率与信息沟通编码方法，与接收通频带和仪器中的辐射元素, 与超声波空间特有的沟通渠道，以及测量精度是具有非常密切的联系方式。 让我们谈具有普遍意义的空气中超声波测距问题，即：载波频率和的被普遍认为 标准的声音数额的选择。p. = p”在pad辐射声功率，b是平面波在介质中吸收系数为，l是声电传感器和 测试箱之间的距离，d是散热器（接收）的直径，c是的电声换能器的散热 器方向性图的角度。在均衡器（1 ）及以下，和作品1一样，吸收系数依赖于振幅和而不是 强度，因此，我们认为有必要强调这种差异。d. cm图1图2图3在声音的各种问题上，包括成员测试设备和结构的关系，由于信号衰减吸收 的平面

41、和适当的几何性质的声束是，作为一项规则，一定是相差甚远的需要指 岀的是，选择的实际情况中光束具休的儿何参数，是基于形状的反射面和空间的 一些失真相对平均排布。让我们考虑一下更详细的儿何关系和声束的动力参数这个最常见包括平面 和圆柱结构的成员情况。众所周知，定向特性瓦的一个圆形活塞振动无限挡板是一个活塞比例函数,d/入为下列表达式基础:2j,7td . smaa7hl sinza(2)从均衡器（2 ）中很容易发现，在减少两到一个敏感性散热器方面，声压级角度将会引起注意。0.762°05=arcsin dfokhz10203040506080100150200300500卩 odb/m0

42、.5().71.21.522.63.54691640表1对角可以简化为(x < 2o.eq.°0.50.76c(4)fd其中c是中期声速，f是辐射震动的频率它遵循均衡器（4 ）,当辐射到空中，其中c = 300米/秒，在0.5级的压力面，散热器为采取的轴的直径用于指定角度的方向性图上是必要的(5)71400a =其中d是厘米，khz是千赫，a是度角。在图1中显示的曲线图是均衡器（5 ）中6个角度散热器的方向性图。事实上，直径的“超声波降解标本”现场控制的两个变量，即：直径的散热 器和发散角的声音束一般情况下，最小直径的“超声波降解标本”在现场飞机 表面处理，通常倾向于散热器的轴

43、心。对应的散热器直径l是测试表面最小的距离。7(6)(7)（7）作为从均衡器（6 ）及（）,“声振”现场最小直径，最高要求散热器直径距离不得少丁 2.自然的,以短距离的障碍的大小，“声振“表面的更少。其中d是厘米，khz的在千赫,a是度角让我们考虑在半径为r的中声波测距的情况。问题是在x和y中坐标轴上衡量从声电传感器的到圆柱形物体侧表面的距离缸 其各种可能的位移沿x和y轴，散热器的方向性图角度a的必耍性在这种情况下被用词组的形式表示岀来。y maxa > arcsinr + 厶 nin(8)在这里是a的价值角度的方向性图，ymax是声学轴中心最大位移气瓶，lmin 是从中央电传感器的反射

44、面测量沿直线连接的中心与中心会员的传感器之间最 短距离很显然，当测量距离，在信息信号“运行”时，对于在圆柱体表面来说在一 个标准方向上，轨迹的长度是受控制的。或者换句话说，始终衡量距离是最短的一个。对于所有来自测试表面一次性 往复震动镜面反射情况这个声明都是正确的。当w = 0.5时决均衡器（2 ）及（8 ）的连立解有下面的表达式： =0.76久依+厶讪）（9）y max在特定情况下发生的各种声音在空气中传播有速度是? = 300米/秒，并假定 lmin«r,必要的单向散热器的直径d的必要性可以从公式找到心空（10）仇ax其中d的单位是厘米,f的单位是千赫。在图2中曲线图显示，以确定

45、以来自最大位移的四辐射频率轴的圆柱形直径 作为散热器比例函数的必要性.,这个数字是方向性图角的函数r与yn林四个比 率为半径最小距离也在其中显示。在空气中超声的吸收是在决心解决超声波测距装置及其一系列功能的第二 个因素.在13中给岀了空气中关于测量超声波振动物理调查结果。到目前为 止，在空气中吸收超声波振动结果实验在理论解释和实验之间己有没有明确的 的差异，因此，对于频率为50至60千赫，在温度的25°c和相对湿度37 %时， 平面波能量吸收系数为2.5db/m,与此同时理论值为0.3db/mo吸收系数b,温 度25 °c,湿度为37 %时的数据显示在2表1中吸收系数取决于

46、相对湿度因此，为了得到吸收系数最高价值为10到20khz, 发生在湿度3 时为20 %，并在吸收湿度减少约二分之一时为40 %。对于最 大吸收频率为60千赫的情况，在30°c时湿度下降，结果会提高到98 %或下降 到10 %,其系数约为四比一。空气温度超声吸收也有明显的影响1 。当温度从+10°c升至中期+30°c, 吸收的频率在30至50千赫期间增加了约三分之一。所有因素考虑进来我们获得了如下近似值：吸声系数：在频率为60khz时 pmin= 0.15 m1,pmax= 0.5 m_1 ;在频率为 200khz 时 pmin= 0.6 m",卩max

47、= 2 m1 o正在审议的关系，生动地显示在图3中。在上部曲线图的g = f (l)中将散热器的方向性总角度的价值分为五个，在那里(11)参考文献1. l.bergman?ultrasonicsrussian translationjzd.inostr.lit.?moscow(1957).2. v.akrasitnikov,sonic and ultrasonic wavesin russian,f i z m a t g iz,moscow(1960).3. m.mokhtar and e.richardson.proceedings of the royal society, 184( 1

48、945).五分钟搞定5000字毕业论文外文翻译，你想要的工具都在这里!在科研过程中阅读翻译外文文献是一个非常重要的环节，许多领 域高水平的文献都是外文文献，借鉴一些外文文献翻译的经验是非常 必要的。由于特殊原因我翻译外文文献的机会比较多，慢慢地就发现 了外文文献翻译过程中的三大利器：google“翻译,濒道、金山词霸(完 整版本)和cnki“翻译助手”。具体操作过程如下：1先打开金山词霸自动取词功能，然后阅读文献；2遇到无法理解的长句时，可以交给google处理，处理后的结 果猛一看，不堪入目，可是经过大脑的再处理后句子的意思基本就明 tt；3如果通过google仍然无法理解，感觉就是不同，那肯定是对 其中某个“常用单词"理解有误，因为某些单词看似很简单，但是在文 献中有特殊的意思，这时就可以通过cnki的“翻译助手"来查询相关 单词的意思，由