1、1.,Chapter 3 Sound Wave,2.,3.,4.,5.,6.,3.To know Ultrasonic wave and its applications to medical science.,7.,波的产生和传播,8.,Chapter 4 Sound Wave,Section 1 basic characters of sound wave,Section 2 Intensity level 、Loudness level,Section 3 Doppler effect,Section 4 the application of Ultrasonic wave,9.,. d
2、efinition of sound wave,. Speed of sound,. intensity of sound,. sound pressure and acoustic impedance,. Range of ones hearing,Section 1 basic characters of sound wave,10.,Between 20Hz 20000Hz,Sound wave,Less than 20Hz,Infrasonic wave,higher than 20,000Hz,Ultrasonic wave,Frequency,propagablemedia,声波,
3、1. definition of sound wave,Solid 、gas and liquid,The longitudinal mechanical waves in the frequency range from 20Hz to 20,000Hz strike the human ear ,and give rise to the Sensation of sound we call the mechanical waves in such frequency range as sound waves.,机械波, 需要传播媒质,11.,声波,sound wave,10-4 100 1
4、04 108 1012 ,次声波,地震海啸核爆炸,可闻声波,超声波,特超声波,语言音乐自然界,老鼠蝙蝠海豚,分子热振动,返回,12.,电磁波,可在真空中传播,10-5 10-3 10-1 10 103 104 109 1011 1012 1013 1015 (nm),13.,2. Speed of sound,In the liquid and gas,In the solid,The speed of sound wave propagating throughAn elastic medium depends only on the properties of the medium .,M
5、- molar mass ,R universal gas constant ,T kelvin temperature ,r ratio of the heat capacity =cp/cv,In the air,14.,15.,声波,3. sound pressure,Sound wave is a longitudinal wave. When it is traveling in a medium, the density of the medium changes recurrently. The medium is compressed and expanded periodic
6、ally. The region compressed has higher pressure and the area expanded in the medium has lower pressure.,16.,Sound pressure P is the pressure difference between the actual pressure Pi (sound propagating) and the normal atmospheric pressure P0(no sound propagating) at any point .,sound pressure,简谐波,so
7、und wave equation,17.,s,18.,19.,sound pressure,由此可知：声压波比位移波在位移上落后/2,声波,sound pressure ( to force),Pm is the amplitude of the sound pressure.,20.,几种声波的声压值,声压,声波,21.,声波,4. acoustic impedance,acoustic impedance,Suppose that the amplitude of the vibrational velocity is vm， then we have vm = A. The acous
8、tic impedance is defined as,Where is the density of the medium and u is the propagating velocity of wave in the medium.,pressure amplitude,22.,Values of 、u and Z for some materials,声波,23.,24.,声强,6. intensity of sound (to energy),Unit : (w/m2) 或 J/(m2.s),The sound intensity is defined as the average
9、power transported per time per unit area which is perpendicular to the direction of propagation.,25.,声强,Eg:,The sound source is considered to be a point one and the wave sent out will be spherical .The energy propagates in all direction,The intensity of a spherical wave varies inversely as the squar
10、e of its distance from the source,26.,exercise,The pressure amplitude Pm of a sound wave that is tolerable to a human ear is about 28Pa ,(1) what fraction is Pm of normal atmospheric pressure? (2) What intensity of sound does Pm correspond to in air at room temperature?,27.,声强,7. reflection and refr
11、action,the law of reflection and refraction is obeyed,the energy is changed in the reflection and refraction,强度反射系数Reflection coefficient of Intensity,强度透射系数refraction coefficient of Intensity,Sound wave will reflect （反射） or refract （折射）at the boundary of two different mediums.,28.,声强,Application :
12、reflection and refraction,Eg: ultrasound scanners,29.,声波,Ear is sensitive to,Frequency Intensity,threshold of hearing ：the min intensity level which can cause ones hearing .If the frequency of sound waves ,the threshold of hearing is different .,Eg: normal person 1000Hz -听阈值 10-12W/m2,100Hz- -听阈值 10
13、-9W/m2,Sensitive range of human is 3000Hz-5000Hz,8. Auditory region (听觉区域）,30.,31.,声波,Threshold of pain ：the min intensity level which can make ones ear feel pain.If the frequency of sound waves ,the threshold of hearing is different ,but the changes arent obvious .,Eg: normal person 1000Hz -痛阈值 1W/
14、m2,100Hz-听阈值 1W/m2左右,The maximum intensity which the ear can tolerate,Range of ones hearing,32.,标准声强 I0 :An arbitrary reference intensity taken as 10-12w/m2 corresponding roughly to the faintest sound which can be heard : the threshold of hearing of 1000Hz sound wave.,听觉区域Auditory region ：the range
15、between threshold of hearing and threshold of pain.,33.,. Intensity level,. Loudness level,section 2 intensity level,34.,because of the large range of the intensities over which the ear is sensitive ,a logarithmic rather than an arithmetic intensity scale is convenient .,人耳对声音的主观感觉到的强弱更接近于和声强的对数成正比。
16、,单位:贝尔bel(B),以1000 Hz 时的声强作为基准声强 I0=10-12Wm-2,单位:分贝(dB),声波,intensity level,Intensity level,decibel (分贝), denoted by dB.,35.,intensity level -eg,Select 1000Hz sound wave :,Intensity level,听阈值 I=10-12 W/m2,痛阈值 I=1 W/m2,L=0 dB,L=120 dB,Conclusion: an intensity level of 120 dB between the minimum intens
17、ity and the maximum intensity,36.,Intensity level and intensity of some common sounds,37.,exercise,If the average intensity level of each of two radios is 45dB, what is the average intensity level when both radios are on ?,Assume the intensity one radio is I1,intensity level is L1,When both radios a
18、re on ,the intensity is 2I1,38.,Loudness and loudness level,Ones reflection to Sound wave,Intensity,Frequency,The term loudness refers to the listeners subjective perception of the magnitude of a sound sensation,Subjective Loudness Level口方,声波,Theory :Intensity level dB,0 方 响度,120 方 响度,0dB,120dB,39.,
19、正常人的听阈曲线,听力衰减者的听阈曲线,loudness level.,声波,40.,exercise,The distance is 10m between the point and the source of sound.the intensity level of this point is 20dB, if we dont consider the absorption of energy (1) what is the intensity level if the distance is 5.0m,(2) how far can we not hear the sound at l
20、east?,26dB100m,41.,Section 3 Doppler effect,Phenomena,Quantitative analysis,Application in medicine,42.,当声源与接收者之间有相对运动发生时, 接收者接收到的声音频率与声源的振动频率不同.,Phenomena,when a source of sound .or an observer .or both ,are in motion relative to the medium ,the pitch of the sound , As heard by the observer , is in
21、 genera not the same as when source and observer are at rest . The most common example is that the pitch of the whistle of locomotive is higher when the source is approaching the observer than when it has passed and is receding . This phenomenon is called Doppler effect .,43.,44.,声源和接收者都静止,45.,Sourc
22、e of sound : motion speed of source vs,observer : motion speed vo , frequency Sound speed u ,wavelength,多谱勒效应,Quantitative analysis,medium: sound speed u ;frequency ,46.,1、Source of sound and observer all rest in the medium vs=0, vo=0声源与接受者相对于媒质都静止,47.,声源不动接受者动,48.,49.,50.,声源动接受者不动,波面被压缩,51.,52.,53.
23、,Doppler effect,Conclusion,54.,The difference of the generating and receiving frequencies is Doppler frequency displacement:,The speed of blood flow could be calculated using above formula.,55.,解释马赫锥(快拖),56.,马赫锥 :为何有时飞机过后,才听见震耳隆隆声,当飞机作超音速飞行时,飞行中这个运动的波源将在空气中引起扰动,并按球面波向外传播,这一系列球面波的包络面是圆锥面.圆锥面以外,没有声波传播
24、,这个圆锥称为马赫锥.这时多普勒频率公式失去作用.,57.,证明: 马赫锥,令 t=0 时点波源(飞机)在x=0 处, t=t 时 在A 处,设在O 和t 之间任意t 时刻由A点发出球面波,该波在t 时刻的波面,上式对t求偏微分,得,58.,代入原方程得下式,移动坐标原点,令,以 A为顶点, x 轴为对称轴的圆锥面,即马赫锥,59.,称作马赫角, 称作马赫数,计算圆锥的半顶角,实际中,测得高速飞行炮弹的马赫数,可以相当准确的计算炮弹的飞行速度,因为声波引起空气疏密的变化,对光的折射率改变了,可以拍摄马赫锥照片.,60.,超音速火焰,61.,Section 4 Ultrasound and it
25、s application in medicine,The properties of Ultrasound,Generation and detection of Ultrasound,Application in medicine,62.,Ultrasonic wave (超声波) and applications,In this section, we would like to introduce the the features and applications of ultrasonic wave. It is really not my job to introduce all
26、details about the productions of ultrasonic waves and the principles of all ultrasonic machines. Students who are interested in this part could get more information from our Chinese text book.Wave length: 16.6cm 0.6710-7m in air74.0cm 0.30 10-6m in water,63.,The properties of ultrasonic waves The fr
27、equency of ultrasonic waves is between 2104 and 5109 Hz. Ultrasonic waves not only have the features of sound wave but also possess the characteristics of high frequencies or short waves and other properties:Directionality (方向性) : Since high frequency corresponding to short wavelength， high frequenc
28、y waves hardly (几乎不) diffract (衍射: deviation of a wave line at the edge of an obstacle (障碍物) and propagate in line.,64.,2. High transmission (高透射本领): This property is very important as it can penetrate high density materials like water, fat, muscle (肌肉) , soft tissue (软组织) , bone, lung (肺) tissues a
29、nd so on but not air. Using these property, the ultrasonic wave can be used to the medical treatments. 3. Reflection (反射): Ultrasonic waves will reflect at the boundary (边界) of medium. Only if the dimension (尺度) of the object is a few times of the wavelength, can the ultrasonic waves be reflected.,6
30、5.,Due to the short wavelength of the ultrasonic waves, a pretty small object can cause reflection, such as an air bubble (气泡) in steel, lesion (损伤/li: n/) in biological tissue (生物组织). Echo (回声) generates the ultrasonic image.Ultrasonic waves has become a very useful tool for diagnosis and detection
31、. When high intensity ultrasound propagates through a medium, it generates series special actions such as mechanical action, cavitation and thermal (or heat) action.,66.,1. mechanical action,2. Heat action,3. Cavitations,4. Chemical action,Special function s to material,频率高，强度大，在固、液体中传播时衰减很小在强大的声压下，
32、液体被拉断而出现微小空腔,超声波,The properties of Ultrasound,超声波在人体中传播时的振动和压力会对细胞和组织结构产生直接的效应.,分子振动和转动能量可逆转性增加,使介质温度上升,超声空化可以定义为充有气体或水蒸气的空腔在超声场作用下发生震荡的各种现象.,67.,Piezoelectric effect:,certain materials have the property that the application of an electric field cause a change in its thickness d ,and vice versa. Thi
33、s phenomenon is know as the piezoelectric effect . Many crystals have this properties .,超声波,Generation and detection of Ultrasound,逆压电效应,压电效应,Quartz crystal,68.,超声波,Generation and detection of Ultrasound,高频电发生器,压电晶体,69.,超声波探测,70.,超声波产生,71.,Applications of ultrasound to medicineUltrasound is widely u
34、sed for diagnosis and treatment, especially diagnosis. Most ultrasound images came from the boundary reflection in the human body. We can diagnose pathological (病理的) changes in tissue.,超声诊断成像的基本原理以三个物理假定为前提：,（1）声束在介质中以直线传播;（2）在各种介质中声速均匀一致;（3）在各种介质中介质的吸收系数均匀一致.,72.,A型显示是最基本的超声显示方式,属于幅度调制,即回波的脉冲大小决定显示
35、器中脉冲的幅度.脉冲之间的距离正比于反射界面之间的距离(深度).A超主要用于颅脑的占位性病变的诊断.一维信号,1. A-type ultrasonic diagnosing instrument (A型超声诊断仪)This sort of instrument can only get one dimension signal. You cannot see the shape of lesions (损伤) or pathological changes.,73.,M型超声诊断仪是在A超基础上发展起来的,适用于观察心脏的运动状况,又称超声心动仪.(一维随时间波动信号),M超与A超相比具有如下
36、特点：（1）改幅度显示为亮度显示;（2）频率很低的帧扫描则实现了时间展开.,2. M-type ultrasonic diagnosing instrument (M型超声诊断仪)Using this instrument, the function of heart can be detected and the heartbeat image (心动图) can be obtained.,74.,深度-时间,75.,3. B-type ultrasonic diagnosing instrument (B型超声诊断仪)This sort of instrument can form two
37、-dimensional tomography (层析x-射线摄影法) image (图象) of human internal organs (内脏器官) and the lesions in tissue. This will greatly help doctors to make a correct diagnosis. 辉度调制：回波不再以一定幅度的脉冲显示，而是将回波信号经放大处理后加于示波管的控制栅极，改变栅极与阴极之间的电位差，从而改变辉度。回波以不同辉度的光点显示。屏上光点的位置表示相应反射界面的位置，光点的辉度与回波的强度成正比。显示断层声像 :,76.,4. Ultras
38、onic Doppler blood-flow instrument (血流仪) -D型超声Ultrasonic Doppler blood-flow instrument is based on the Doppler effect. The probe of this instrument consists of two crystals, one is transmitter and the other is receiver. The velocity of bloodcell (血细胞) flow can be obtained by this instrument.D型超声全名为超
39、声多普勒血流测量技术,它是利用多普勒效应研究和应用超声波由运动物体反射或散射,从而获得心脏、血管、血流及胎儿心率等信息的一种技术.,77.,5. Color Doppler ultrasonic blood-flow imaging instrument (彩超)This is the most advanced instrument to diagnose(诊断) heart diseases. If you would like to know what it can do and what you can get from it.,彩色多普勒血流现象仪(简称“彩超”)多采用脉冲超声多蹼勒
40、成像系统.其原理是：利用多道选通技术可在同一时间内获得多个采样容积的回波信号进行频谱或自相关处理,获得速度大小、方向及方差信息,同时滤去迟缓部位的低频信号,再将提取的信号转变为红色、蓝色、绿色的色彩显示.,78.,超声成像原理图,79.,彩超的主要特点,用同一个高速相控阵扫描探头来实现彩色血流 显像与B型图象信息的重合.,广泛采用自相关技术作信号处理.,血流图象叠加在B型图象上的, B型图象以黑白显示,血流必须以彩色才能与脏器区分开.（彩色处理器）,80.,血流彩色显示,频率色彩编码器,彩色,B型黑白图象,叠加,采用红、蓝、绿三种基本颜色,其他颜色由其混合而成,红色：表示正向血流,即朝探头的流动,蓝色：表示反向流,即背向探头的流动,绿色及其亮度表示方差的大小（血流速度分布分散程度）,红色与蓝色的亮度分别表示正向流与反向流速速的大小,三种颜色混合方差越大,则绿色混合程度越大,湍流,81.,summary,3.To know Ultrasonic wave and its applications to medical science.,
