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1、附录A 英文原文ULTASONIC RANGING IN AIRG. E. Rudashevski and A. A. Gorbatov One 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 relativethre edimensional
2、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 frequencies up to 500 k
3、Hz 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 possibility of using acousti
4、c 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 a reliable acoustic thr
5、ee-dimensional contact with the test object during severe changes in the airs characteristic. Practically 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 reflecting member and bac
6、k.The unmodulated acoustic(ultrasonic)vibrations radiated by a transducer are not in themselves a source of information.In order to transmit some informational communication that can then be selected at the receiving end after reflection from the test member,the radiated vibrations must be modulated
7、.In this case the ultrasonic vibrations are the carrier of the information which lies in the modulation signal,i.e.,they are the means for establishing the spatial contact between the measuring instrument and the object being measured.This conclusion,however,does not mean that the analysis and selec
8、tion 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 the apparatus,with the
9、 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 shows that with conical
10、 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 plane surface located at
11、 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 radiator(receiver),a
12、ssuming they are equal,and cis the angle of the directivity diagram for the electroacoustic transducer in the radiator.Both in Eq.(1)and below,the absorption coefficient is dependent on the amplitude and not on the intensity as in some works1,and therefore we think it necessary to stress this differ
13、ence.In the various problems of sound ranging on the test members of 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 are,as a rule,quite different.It must be pointed out that the cho
14、ice 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 position.Let us consider in more detail the relationship betweenthe geometric and the power parameters of acoustic beams f
15、or 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 pistons diameter to the wavelength d/ as found from the following expression:
16、(2)where Jl is a Bessel function of the first order and 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 the sensitivity of a radiator with respect
17、to sound pressure will occur at the angle（3）For angles 20.Eq.(3)can be simplified to （4） 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 radiating into air where c=330 m/s e c,the necessary diameter of the radiator for
18、 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） where disincm,f is in kHz,and is in degrees of angle.Curves are shown in Fig.1 plotted from Eq.(5)for six angles of a radiators directivity diagram.The directivity diagrm ne
19、eded 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 reflected from adjacent members onto the acoustic receiver,it is necessary to provide a small a
20、ngle of divergence for the sound beam and,as far as possible,a small-diameter radiator.These two requirements are mutually inconsistent since for a given radiation frequency a reduction of the beams divergence angle requires an increased radiator diameter.In fact,the diameter of thesonicatedspot is
21、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 thesonicatedspot Dmin on a plane surface normally disposed to the radiators axis is given by （6）where L is the least distance to the test surface.The
22、 specified value of Dmin corresponds to a radiator with a diameter （7）As seen from Eqs.(,6)and(7),the minimum diameter of thesonieatedspot at the maximum required distancecannot be less than two radiator diameters.Naturally,with shorter distances to the obstacle the size of thesonicated surface is l
23、ess.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 cylinder with its various possible displacements along the X and Y axes.The necessary angleof the radiators
24、 directivity diagram is given in this case by the expression （8）where is the value of the angle for the directivity diagram,Ymax is the maximum displacement of the cylinders center from the acoustic axis,and Lmin is the minimum distance from the center of the electroacoustic transducer to the reflec
25、ting 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,therunningtime of the information signal is controlled by the length of the path in a direction normal to the cylinders surface,or in othe
26、r 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 solution of Eqs.(2)and(8)when W=0.5 leads to the following expression: (9)In the particular case where the sound ranging tak
27、es place in air having c=330 m/sec,and on the asstunption that L minR,the necessary d i a m e t e r of a unidirectional piston radiator d can be found from the fomula (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 o
28、f the ratio of the cylinders radius to the maximum displacement from the axis for four radiation frequencies.Also shown in this figure is the directivity diagram angle as a function of R and Yrnax for four ratios of m i n i m u m distance to radius.The ultrasonic absorption in air is the second fact
29、or in determining the resolution of ultrasonic ranging devices and their range of action.The results of physical investigations concerning the measurement of ultrasonic vibrations air are given in1-3.Up until now there has been no unambiguous explanation of the discrepancy between the theoretical an
30、d expe -rimental absorption results for ultrasonic vibrations in air.Thus,for frequencies in the order of 50 to 60 kHz at a temperature of+25oC 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 co
31、efficient B as a function of frequency for a temperature of+25oCand a humidity of 37%according to the data in2can be described by Table 1.The absorption coefficient depends on the relative humidity.Thus,for frequencies in the order of 10 to 20kHz the highest value of the absorption coefficient occur
32、s 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 absorption occurs at 30.7o humidity,dropping when it is increased to 98% or lowered to 10%by a factor of approximately four to one.The air temperature also has an app
33、reciable effect on the ultrasonic absorption1.When the temperature of the medium is increased from+10 to+30,the absorption for frequencies between 30 and 50 kHz increases by about three to one.Taking all the factors noted above into account we arrive at the following approximate values for the absor
34、ption coefficient:at a frequency of 60 kHz /3min=0.15 m-1 andmax=0.5-1;at a frequency of 200 kHz/min=0.6 m-1 and Bmax=2 m-1. （11）The values for the minimummin and rnaxil-nummaxtransmittancecoefficients were obtained in the a bsence of aerosols and rain.Their difference is the result of the possible
35、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 thetransmittanceis obtained by multiplying the values of g and 0 for given values of L,f,and d.L I T E R A T U R E C I T E DMoscow(1957).Moscow(1960).附录B 中文翻译在空气中超声测距G.
36、 E. Rudashevski and A. A. Gorbatov 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正距离延伸达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正测距的可行性已经研究了很长一段时间，乍一看似乎很简单，但是目前只有为数不多的新发明
37、使用这种适合实际目的方法，主要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.正相反，承运人振动频率与信息沟通编码方法，与接收
38、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。 （1）在Prad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。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和适当的几何性质的声束是，作为一项规则，一定是相差
39、甚远的.需要指出的是，选择的实际情况中光束具体的几何参数，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几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/ 为下列表达式基础： （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。 （3）表1f0kHz102030405060801001502003005000dB/m0.50.71.21.522.63.54691640对角可以简化为 20.Eq. （ 3 ） （4）其中c是中期声速 ,F是辐射
40、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）其中d是厘米，khz是千赫， 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心 。 （6）L是测试表面最小的距离。对应的散热器直径 （7）（7）作为从均衡器（ 6 ）及（ 7 ） ，“声振”现场最小直径，最高要求散热器直径距离不得少于2.自然的
41、，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， 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的必要性在这种情况下被用词组的形式表示出来。 （8）在这里是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
42、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： （9）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LminR，必要的单向散热器的直径d的必要性可以从公式找到 （10）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ymax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 1-3 中给出了空气中关于测量超声波振动
43、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 已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0.3 d B/m。吸收系数B，温度25 ，湿度为37 时的数据显示在 2 表1中吸收系数取决于相对湿度.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升至中期+30，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 min= 0.15 m-1,max= 0.5 m-1 ;在频率为200khz 时min= 0.6 m-1,max = 2 m-1。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Moscow(1957).Moscow(1960).
