【正文】 s center from the acoustic axis, and L min 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 number with the center of the transducer.It is clear that when measuring distance, the running time of the information signal is controlled by the length of the path in a direction normal to the cylinder39。s axis is given by （6）where L is the least distance to the test surface.The specified value of D min corresponds to a radiator with a diameter （7）As seen from Eqs.(6)and(7), the minimum diameter of the sonieated spot at the maximum required distance cannot be less than two radiator diameters. Naturally, with shorter distances to the obstacle the size of the sonicated 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 cylinder with its various possible displacements along the X and Y axes. The necessary angleαof the radiator39。s directivity diagram.The directivity 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 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 possible, a smalldiameter radiator. These two requirements are mutually inconsistent since for a given radiation frequency a reduction of the beam39。s 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 back.The acoustic (ultrasonic) vibrations radiated by a transducer are not in themselves a source of information. In order to transmit some informational munication 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 ultrasonic vibrations are the carrier of the information which lies in the modulation signal, and 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 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 munication, with the pass band of the receiving and radiating elements in the apparatus, with the spatial characteristics of the ultrasonic munication channel, and with the measuring accuracy.Let us dwell on the questions of general importance for ultrasonic ranging in air, name: 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 obstacle, the amount of acoustic power arriving at the receiving area for the case of reflection from an ideal plane surface located at right angles to the acoustic axis of the transducer es to （1）where 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, d is the diameter of the radiator (receiver), assuming they are equal, and c is 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 works [1], 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 attenuations due to the absorption of a plane wave and due to the geometrical properties of the sound beam are, as a rule, quite different. It 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 position.Let us consider in more detail the relationship between the geometric and the power parameters of acoustic beams for the most mon 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 piston39。最后，衷心感謝在百忙之中抽出時(shí)間審閱本論文的專家教授。在課題設(shè)計(jì)過程中還得到了徐穎俊、王柏淵同學(xué)的幫助，正是在各位老師的大力支持和各位同學(xué)的通力協(xié)助下，我才得以順利完成學(xué)位論文，在此一并表示深深的謝意。他嚴(yán)肅的科學(xué)態(tài)度，嚴(yán)謹(jǐn)?shù)闹螌W(xué)精神，精益求精的工作作風(fēng)，深深地感染和激勵(lì)著我。本設(shè)計(jì)是在我的導(dǎo)師蔣暢江老師的親切關(guān)懷和悉心指導(dǎo)下完成的，從課題的選擇到論文的最終完成，老師都始終給予我細(xì)心的指導(dǎo)和不懈的支持。致 謝歲月荏苒，四年的大學(xué)生活即將結(jié)束，站在畢業(yè)的門檻上，回首往昔，汗水和淚水成為絲絲的記憶，酸酸的甜甜的一直回蕩。② 由于受實(shí)驗(yàn)條件的限制，本設(shè)計(jì)未能進(jìn)行現(xiàn)場(chǎng)實(shí)驗(yàn)數(shù)據(jù)的采集，所有實(shí)驗(yàn)僅局限于實(shí)驗(yàn)室，這與實(shí)際測(cè)量有一定差距。由于個(gè)人能力及試驗(yàn)條件有限，我的設(shè)計(jì)還有很多不足之處，系統(tǒng)雖然能實(shí)現(xiàn)基本的功能，但投入使用時(shí)仍需要對(duì)系統(tǒng)作進(jìn)一步的完善和提高：① 超聲波的測(cè)量距離與環(huán)境直接相關(guān)，由于本設(shè)計(jì)中所用設(shè)定溫度為常溫，故應(yīng)用范圍相對(duì)較小。② 設(shè)計(jì)了以STC89C52單片機(jī)為核心的超聲波測(cè)距系統(tǒng)，該系統(tǒng)具有低成本、高精度、微型化數(shù)字顯示的特點(diǎn)。針對(duì)附加功能的要求，提出了鎖定、存儲(chǔ)、查詢功能的超聲波測(cè)距系統(tǒng)，并在軟件和硬件上實(shí)現(xiàn)了該系統(tǒng)。本設(shè)計(jì)的超聲波測(cè)距儀，可以對(duì)不同距離進(jìn)行測(cè)試，并可以進(jìn)行一定的誤差分析。結(jié) 論隨著社會(huì)的發(fā)展，人們對(duì)距離或長度測(cè)量的要求越來越高。第二節(jié) 本章小結(jié)本次設(shè)計(jì)的超聲波測(cè)距系統(tǒng)所測(cè)距離與實(shí)際距離基本相同，但是如果所測(cè)距離較遠(yuǎn)，由于模塊信號(hào)衰減等問題會(huì)造成誤差，但都在可接受范圍之內(nèi)。硬件電路引起的時(shí)間誤差由于收發(fā)電路對(duì)信號(hào)的處理會(huì)對(duì)回聲時(shí)間產(chǎn)生y個(gè)固定的延遲時(shí)間從而引出一定的測(cè)量誤差. 另外，在測(cè)量過程中測(cè)量的起始位置與探頭的壓電晶片所在位置之間一定的距離，也對(duì)測(cè)量結(jié)果造成一定的誤差，但是這種誤差不隨測(cè)量環(huán)境距離的變化而變化，屬于固定誤差。根據(jù)不同的環(huán)境溫度確定聲速，以提高測(cè)距的穩(wěn)定性和準(zhǔn)確性。在系統(tǒng)加入溫度傳感器來監(jiān)測(cè)環(huán)境溫度，可進(jìn)行溫度補(bǔ)償。如果測(cè)距精度要求很高，則應(yīng)通過溫度補(bǔ)償?shù)姆椒右孕Ｕ?。若超聲波?0℃的環(huán)境下以0℃的聲速測(cè)量100m距離所引起的測(cè)量誤差將達(dá)到5m，測(cè)