畢業(yè)論文外文翻譯-在空氣中超聲測(cè)距

1、附錄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).附錄b中文翻譯在空氣中超聲測(cè)距g. e. rudashevsk

38、i and a. a. gorbatovudc 534,321.9:531.71.083.7在儀器技術(shù)中遠(yuǎn)程是最重要的一個(gè)問(wèn)題。在空氣中，從0.2米至10米非接 觸式測(cè)量距離時(shí)，涉及到了這個(gè)問(wèn)題，例如，在測(cè)量時(shí)個(gè)別機(jī)件或結(jié)構(gòu)單位的相 對(duì)三維位置。有趣的是，是利用超聲振動(dòng)作為信息運(yùn)輸工具，開(kāi)啟了解決辦法的 可能性在空氣這個(gè)自然道具中，進(jìn)行測(cè)量的是雇用成員和傳感器之間距離0.5 米的時(shí)候，允許振動(dòng)頻率高達(dá)500千赫，或當(dāng)與障礙物之間修止距離延仲達(dá)10 米時(shí)候，振動(dòng)頻率高達(dá)60千赫茲。應(yīng)用超聲波在空氣中測(cè)量距離不同于其他的問(wèn)題。雖然能否利用聲波修止 測(cè)距的可行性已經(jīng)研究了很長(zhǎng)一段時(shí)間，乍一看似乎很簡(jiǎn)

39、單，但是目前只有為數(shù) 不多的新發(fā)明使用這種適合實(shí)際目的方法，主耍困難是在有嚴(yán)重特有變化的空氣 中提供一個(gè)可靠試驗(yàn)對(duì)象去接觸三維聲波。幾乎所有的目前已知用來(lái)校驗(yàn)距離使用的，都是為了某些來(lái)自用來(lái)反射成員 和后面的散熱器信息樣本，測(cè)量傳播時(shí)間解決聲音的辦法。該未解調(diào)的聲（超聲）振動(dòng)由傳感器輻射的，本身并不是一個(gè)信息來(lái)源.在接收 端，來(lái)自測(cè)試會(huì)員反射后，為了傳遞一些情報(bào)信息，因而被選定后，輻射振動(dòng)一 定會(huì)被調(diào)制。在這種情況下，超聲波振動(dòng)是在于調(diào)制信號(hào)的信息的承運(yùn)人，即他 們就是在測(cè)量?jī)x器和測(cè)量穩(wěn)定的對(duì)象之間建立了空間三維接觸的手段。這一結(jié)論，但是，并不意味著分析和選擇的參數(shù)承運(yùn)人振動(dòng)重要性小止相 反，

40、承運(yùn)人振動(dòng)頻率與信息溝通編碼方法，與接收通頻帶和儀器中的輻射元素, 與超聲波空間特有的溝通渠道，以及測(cè)量精度是具有非常密切的聯(lián)系方式。 讓我們談具有普遍意義的空氣中超聲波測(cè)距問(wèn)題，即：載波頻率和的被普遍認(rèn)為 標(biāo)準(zhǔn)的聲音數(shù)額的選擇。p. = p”在pad輻射聲功率，b是平面波在介質(zhì)中吸收系數(shù)為，l是聲電傳感器和 測(cè)試箱之間的距離，d是散熱器（接收）的直徑，c是的電聲換能器的散熱 器方向性圖的角度。在均衡器（1 ）及以下，和作品1一樣，吸收系數(shù)依賴于振幅和而不是 強(qiáng)度，因此，我們認(rèn)為有必要強(qiáng)調(diào)這種差異。d. cm圖1圖2圖3在聲音的各種問(wèn)題上，包括成員測(cè)試設(shè)備和結(jié)構(gòu)的關(guān)系，由于信號(hào)衰減吸收 的平面

41、和適當(dāng)?shù)膸缀涡再|(zhì)的聲束是，作為一項(xiàng)規(guī)則，一定是相差甚遠(yuǎn)的需要指 岀的是，選擇的實(shí)際情況中光束具休的兒何參數(shù)，是基于形狀的反射面和空間的 一些失真相對(duì)平均排布。讓我們考慮一下更詳細(xì)的兒何關(guān)系和聲束的動(dòng)力參數(shù)這個(gè)最常見(jiàn)包括平面 和圓柱結(jié)構(gòu)的成員情況。眾所周知，定向特性瓦的一個(gè)圓形活塞振動(dòng)無(wú)限擋板是一個(gè)活塞比例函數(shù),d/入為下列表達(dá)式基礎(chǔ):2j,7td . smaa7hl sinza(2)從均衡器（2 ）中很容易發(fā)現(xiàn)，在減少兩到一個(gè)敏感性散熱器方面，聲壓級(jí)角度將會(huì)引起注意。0.762°05=arcsin dfokhz10203040506080100150200300500卩 odb/m0

42、.5().71.21.522.63.54691640表1對(duì)角可以簡(jiǎn)化為(x < 2o.eq.°0.50.76c(4)fd其中c是中期聲速，f是輻射震動(dòng)的頻率它遵循均衡器（4 ）,當(dāng)輻射到空中，其中c = 300米/秒，在0.5級(jí)的壓力面，散熱器為采取的軸的直徑用于指定角度的方向性圖上是必要的(5)71400a =其中d是厘米，khz是千赫，a是度角。在圖1中顯示的曲線圖是均衡器（5 ）中6個(gè)角度散熱器的方向性圖。事實(shí)上，直徑的“超聲波降解標(biāo)本”現(xiàn)場(chǎng)控制的兩個(gè)變量，即：直徑的散熱 器和發(fā)散角的聲音束一般情況下，最小直徑的“超聲波降解標(biāo)本”在現(xiàn)場(chǎng)飛機(jī) 表面處理，通常傾向于散熱器的軸

43、心。對(duì)應(yīng)的散熱器直徑l是測(cè)試表面最小的距離。7(6)(7)（7）作為從均衡器（6 ）及（）,“聲振”現(xiàn)場(chǎng)最小直徑，最高要求散熱器直徑距離不得少丁 2.自然的,以短距離的障礙的大小，“聲振“表面的更少。其中d是厘米，khz的在千赫,a是度角讓我們考慮在半徑為r的中聲波測(cè)距的情況。問(wèn)題是在x和y中坐標(biāo)軸上衡量從聲電傳感器的到圓柱形物體側(cè)表面的距離缸 其各種可能的位移沿x和y軸，散熱器的方向性圖角度a的必耍性在這種情況下被用詞組的形式表示岀來(lái)。y maxa > arcsinr + 厶 nin(8)在這里是a的價(jià)值角度的方向性圖，ymax是聲學(xué)軸中心最大位移氣瓶，lmin 是從中央電傳感器的反射

44、面測(cè)量沿直線連接的中心與中心會(huì)員的傳感器之間最 短距離很顯然，當(dāng)測(cè)量距離，在信息信號(hào)“運(yùn)行”時(shí)，對(duì)于在圓柱體表面來(lái)說(shuō)在一 個(gè)標(biāo)準(zhǔn)方向上，軌跡的長(zhǎng)度是受控制的?；蛘邠Q句話說(shuō)，始終衡量距離是最短的一個(gè)。對(duì)于所有來(lái)自測(cè)試表面一次性 往復(fù)震動(dòng)鏡面反射情況這個(gè)聲明都是正確的。當(dāng)w = 0.5時(shí)決均衡器（2 ）及（8 ）的連立解有下面的表達(dá)式： =0.76久依+厶訕）（9）y max在特定情況下發(fā)生的各種聲音在空氣中傳播有速度是? = 300米/秒，并假定 lmin«r,必要的單向散熱器的直徑d的必要性可以從公式找到心空（10）仇ax其中d的單位是厘米,f的單位是千赫。在圖2中曲線圖顯示，以確定

45、以來(lái)自最大位移的四輻射頻率軸的圓柱形直徑 作為散熱器比例函數(shù)的必要性.,這個(gè)數(shù)字是方向性圖角的函數(shù)r與yn林四個(gè)比 率為半徑最小距離也在其中顯示。在空氣中超聲的吸收是在決心解決超聲波測(cè)距裝置及其一系列功能的第二 個(gè)因素.在13中給岀了空氣中關(guān)于測(cè)量超聲波振動(dòng)物理調(diào)查結(jié)果。到目前為 止，在空氣中吸收超聲波振動(dòng)結(jié)果實(shí)驗(yàn)在理論解釋和實(shí)驗(yàn)之間己有沒(méi)有明確的 的差異，因此，對(duì)于頻率為50至60千赫，在溫度的25°c和相對(duì)濕度37 %時(shí)， 平面波能量吸收系數(shù)為2.5db/m,與此同時(shí)理論值為0.3db/mo吸收系數(shù)b,溫 度25 °c,濕度為37 %時(shí)的數(shù)據(jù)顯示在2表1中吸收系數(shù)取決于

46、相對(duì)濕度因此，為了得到吸收系數(shù)最高價(jià)值為10到20khz, 發(fā)生在濕度3 時(shí)為20 %，并在吸收濕度減少約二分之一時(shí)為40 %。對(duì)于最 大吸收頻率為60千赫的情況，在30°c時(shí)濕度下降，結(jié)果會(huì)提高到98 %或下降 到10 %,其系數(shù)約為四比一?？諝鉁囟瘸曃找灿忻黠@的影響1 。當(dāng)溫度從+10°c升至中期+30°c, 吸收的頻率在30至50千赫期間增加了約三分之一。所有因素考慮進(jìn)來(lái)我們獲得了如下近似值：吸聲系數(shù)：在頻率為60khz時(shí) pmin= 0.15 m1,pmax= 0.5 m_1 ;在頻率為 200khz 時(shí) pmin= 0.6 m",卩max

47、= 2 m1 o正在審議的關(guān)系，生動(dòng)地顯示在圖3中。在上部曲線圖的g = f (l)中將散熱器的方向性總角度的價(jià)值分為五個(gè)，在那里(11)參考文獻(xiàn)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

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