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1、Chapter 3 Sound Wave123451.To master: (1)The concepts of Sound pressure , Acoustic impedance (2)Sound intensity (3)Intensity level . (4)Doppler effect and applications 2.To understand (1)loudness level (2)Ultrasonic wave (超声波) 3.To know Ultrasonic wave and its applications to medical science. 6波的产生和
2、传播7波线和波面8波在介质中的传播9Chapter 3 Sound WaveSection 1 basic characters of sound waveSection 2 Intensity level 、Loudness levelSection 3 Doppler effect Section 4 the application of Ultrasonic wave 10. definition of sound wave . Speed of sound . intensity of sound. sound pressure and acoustic impedance . Ran
3、ge of ones hearing Section 1 basic characters of sound wave11Between 20Hz 20000HzSound wave Less than 20Hz Infrasonic wavehigher than 20,000HzUltrasonic waveFrequency propagable media 声 波1. definition of sound wave Solid 、gas and liquidThe longitudinal mechanical waves in the frequency range from 20
4、Hz 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.12 The vibrations which have the mechanical frequencies from 20Hz (Hertz) to 20,000Hz are called sound vibration. The longitudinal wave caused by sound vib
5、ration is called Sound Wave. Ultrasonic (超声的) wave is defined as the sound wave whose frequency is higher than 20,000Hz. Infrasonic (次声的) waves frequency is less than 20Hz. 13声 波sound wave 10-4 100 104 108 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142. Speed of sound In the liquid and gasI
6、n the solid The speed of sound wave propagating through An elastic medium depends only on the properties of the medium .M- molar mass ,R universal gas constant ,T kelvin temperature ,r ratio of the heat capacity =cp/cvIn the air 1516声 波3. sound pressureSound wave is a longitudinal wave. When it is t
7、raveling in a medium, the density of the medium changes recurrently. The medium is compressed and expanded periodically. The region compressed has higher pressure and the area expanded in the medium has lower pressure. 17Sound pressure P is the pressure difference between the actual pressure Pi (sou
8、nd propagating) and the normal atmospheric pressure P0(no sound propagating) at any point .sound pressure简谐波sound wave equation18PP+dpdxxs1920sound 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.Where is the density of the medium and u is the prop
9、agating velocity of wave in the medium.21几种声波的声压值声压 声 波Sound waveSound pressure 1000HZ声音的可闻 阈210-5微风吹动树叶声210-4在房间里高声谈话0.05 0.1交响乐演奏声0.3飞机发动机声102Sound pressure 22声阻抗声 波声阻4. acoustic impedance Suppose that the amplitude of the vibrational velocity is vm， then we have vm = A. The acoustic impedance is
10、defined as声压幅值Where is the density of the medium and u is the propagating velocity of wave in the medium.23Values of 、u and Z for some materials声 波媒质声速(ms-1)密度(kgm-3)声阻抗(kgm-2s-1)空气3.32102 (0C) 3.44102 (20C)1.29 1.214.28102 4.16102 水14.8102 (20C)988.21.48106 脂肪14.01029701.36106脑15.310210201.56106肌肉1
11、5.710210401.63106密质骨36.010217006.12106 钢50.5102780039.410624介质名称 密度（103kgm-3） 速度（ms-1） 声阻抗(106 Nsm-3) 血液 1.055 1 570 1.656 血浆 1.027 _ _ 大脑 1.038 1 540 1.599 小脑 1.030 1 470 1.514 脂肪 0.955 1 476 1.410 软组织 （平均值） 1.016 1 500 1.542 肌肉（平均值） 1.074 1 568 1.684 肝 1.050 1 570 1.648 肾 _ 1 560 _ 脑积 液 1.000 1 522 1.522 颅骨 1.658 3 860 5.571 甲状腺 _ _ 1.6201660 胎体 1.023 1 505 1.540 羊水 1.013 1 474 1.493 胎盘 _ 1 541 _ 角膜 _ 1 550 _ 水晶体 1.136 1 650 1.874 前房水 0.9921.012 1 495 1.4861.513 玻璃体 0.9921.010 1 495 1.4831.510 巩膜 _ 1 630
