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1、毕业设计(论文) 外文文献翻译文献、资料中文题目:在空气中超声测距文献、资料英文题目:文献、资料来源: 文献、资料发表(出版)日期:院(部):专 业: 班 级:姓 名:学 号:指导教师:翻译日期:2017. 02. 14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 measur
2、ement of distances in the order of 0.2 to 10 m in air.such a problem occurs,for instance,when measuring the relativethre edimensional position of separate machine members or structural units.interesting possibilities for its solution are opened up by utilizing ultrasonic vibrations as an information
3、 carrier.the physical properties of air,in which the measurements are made,permit vibrations to be employed at 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 di
4、stances in air is somewhat different from other problems in the a -pplication of ultrasound. although the possibility 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 de
5、velopments using this method that are suitable for practical purposes.the main difficulty here is in providing a reliable acoustic three-dimensional contact with the test object during severe changes in the airs characteristic.practically all acoustic arrangements presently known for checking distan
6、ces use a method of measuring the propagation time for certain information samples from the radiator to the reflecting member and back.the unmodulated acoustic(ultrasonic)vibrations radiated by a transducer are not in themselves a source of information.in order to transmit some informational communi
7、cation that can then be selected at the receiving end after reflection from the test member,the radiated vibrations must be modulated.in this case the ultrasonicvibrations are the carrier of the information which lies in the modulation signal,i.e.,they are the means for establishing the spatial cont
8、act between the measuring instrument and the object being measured.this conclusion,however,does not mean that the 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 c
9、oding method for the informational communication,with the passband of the receiving and radiating elements in the 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 rang
10、ing in air,namely:on the choice of a carrier frequency and the amount of acoustic power received.an analysis shows 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 obsta
11、cle,the amount of acoustic power arriving at the receiving area pr for the case of reflection from an ideal plane surface located at right angles to the acoustic axis of the transducer comes to2pr4ltgad1where prad is the amount of acoustic power radiated,b is the absorption coefficient for a plane w
12、ave in the medium,l is the distance between the electroacoustic transducer and the test me mber,d is the diameter of the radiator(receiver),assuming they are equal,and cis the angle of the directivitydiagram for the electroacoustic transducer in the radiator.fia 9.ymln (200 khz)hg. 3both in eq.(l)an
13、d below,the absorption coefficient is dependent on the amplitude and not on the intensity as in some worksl,and therefore we think it necessary to stress this difference.in the various problems of sound ranging on the test members of machines and structures,the relationship between the signal attenu
14、ations due to the absorption of a planewave and due to the geometrical properties of the sound beam are,as a rule,quite different.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 s
15、patial distortion relative to some average position.let us consider in more detail the relationship betweenthe geometric and the 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
16、of a circular piston vibratingin an infinite baffle is a function of the ratio of the pistons diameter to the wavelength d/x as found from the following expression:sma70:ltsin a(2)where j1 is a bessel function of the first order and a is the angle between a normal to the piston and a line projected
17、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 to sound pressure will occur at the angle0.76 义6r0 5 = arcsinfor angles a<20.eq.(3)can be simplified to0.76ca)5«f
18、dwhere 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 a specified angle of the directivity diagram at the0.5 level of pressure taken with res
19、pect to the axis can befound to be 1400(5)where disincmf is in khz,and ot is in degrees of angle.curves are shown in fig.l plotted from eq.(5)for six angles of a radiators directivity diagram.the directivity diagrm needed for a radiator is dictated by the maximum distance to be measured and by the s
20、patial 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 angle of divergence for the sound beam and,as far as possibles small-diameter radiat
21、or.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 controlled by two variables,namely:the diameter of the radiator and the divergence a
22、ngle of the sound beam.in the general case the minimum diameter of thensonicatedf,spot dmin on a plane surface normally disposed to the radiators axis is given byd-=min6cl(6)where l is the least distance to the test surface.the specified value of dmin corresponds to a radiator with a diameter .5cl(7
23、)d =as seen from eqs.(,6)and(7),thelinimum diameter of thensonieated"spot at the maximum required distancecannot be less than two radiator diameters.naturally.withshorter distances to the obstacle the size of themsonicatedn surface is less.let us consider the case of sound ranging on a cylindri
24、cally 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 angleaof the radiators directivity diagram isr + lmin(8)given in this case by th
25、e expressiona > arcsinwherea 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 reflecting surface measured along the straig
26、ht 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,thef,runningntime of the information signal is controlled by the length of the path in a direction normal to the cylinders surface,or in other words,the measure distance is alw
27、ays 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:d =(9)yin the particular case where the sound ranging takes place in air having c=33o m/s
28、ec,and on the asstunption that l min«r,the necessary diameter of aunidirectional piston radiator d can be found from the fomula25 r(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 cylinders ra
29、dius 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 minimum distance to radius.the ultrasonic absorption in air is the second factor in determining the resolutionof ul
30、trasonic ranging devices and their range of action.the results of physical investigations concerning the measurement 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 fo
31、r ultrasonic vibrations in air.thus,for frequencies in the order of 50 to 60 khz at a temperature of+25°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 freq
32、uency for a temperature of+25°cand 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 occurs at 20%humidity3,and at 40%
33、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 appreciable effect on the ultra
34、sonic absorption 1 .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 absorption coefficient:at a fre
35、quency of 60 khz /3min=0.15 m"1 andmaxzo.sat a frequency of 200 khz/min=0.6 m1 and bmax=2 m'1.the relationships 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 radiators directivity dia
36、gram,where(11)thevaluesfortheminimum minandrnaxil-nummaxntransmittancencoefficients were obtained 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 ove
37、rall value of thentransmittanceuis obtained by multiplying the values of g and 0 for given values of l,f,and d.literaturecited1 .l.bergman,ultrasonicsrussian translation jzd.inostr.lit.?moscow(l 957).2. v.a.krasilnikov,sonic and ultrasonic wavesin russian,f i z m a t g i z?moscow(1960).3. m.mokhtar
38、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. rudashevski 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
39、赫,或当与障碍物之间修正距离延仲达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丁其他的问题。虽然能否利用声波修正 测距的可行性己经研宄了很长一段时间,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。几乎所有的目前己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
40、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。<v14ltga(1)在pfad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 器方向性阁的角
41、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,我们认为有必耍强调这种差异。d. cm图2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。7id . sin a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/ x为下列表达式基础:2j'w =(2)从均衡器(2
42、 )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aq5 = arcsin0.76ad(3)表1fdkhz10203040506080100150200300500p()db/m1.522.63.546916400.76cld(4)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阁上是必耍的1400(4(5)其中d是厘米,khz是千赫,(x是度角。在阁1中显示的曲线阁是均衡器(5 )中6个角度散热器的方向性阁。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。min(6)l是测试表面最小的距离。对应的散热器直径d =(7)作为从均衡器(6 )及(7 ), “声振”现场最小直径,最高耍求 散热器直径距离不得少于2.自然的,以短距离的障碍的大小,“声振“表面
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