科技英语阅读—多普勒效应简介.ppt

1、,Doppler effect Yuan Maoyang NO.20105893,What is Doppler effect?,1.the wavelength of the radiation from an object due to the relative movement of the wave source and the observers produce changes. In motion in front of the source of waves, the waves are compressed, the wavelength becomes shorter, th

2、e frequency becomes higher (blue shift Blue Shift) 2.When movement Boyuan behind will have the opposite effect. The wavelength becomes longer, the frequency becomes lower (redshift red shift);,The Doppler effect is named for the honor of the Austrian physicist and mathematician Christian John Dopple

3、r (Christian Johann Doppler). In 1842, he first proposed this theory, mainly as follows:,3. Boyuan the speed is higher, the greater the effect produced. According to wave the degree of shift in the red (blue), can calculate the the Boyuan follow the speed of movement of the direction of observation.

4、 Stellar the displacement of the spectral lines to display the speed of movement of sun follow the direction of observation, unless the the Boyuan speed very close to the speed of light, or the extent of the Doppler shift is usually very small. All the fluctuation phenomena exist Doppler effect.,Wha

5、t is Doppler effect?,How it was found?,In 1842, Austria, a mathematician called Doppler physicist. One day, he was passing the railway at the intersection, coincides with a train from his side Chiguo, he found that the whistle louder tone sharpened train from far and near, and the whistle of the tra

6、in from near and far weaker, tone becomes low. He felt on the physical phenomena of great interest and research. Found that this is due to the existence of relative movement between the vibration source and the observer, so that the viewer to hear the sound of the frequency is different from the loc

7、al oscillator frequency of the phenomenon. This is the frequency shift phenomenon. Because the sound source in motion relative to the observer, the observer will hear the voice of change. When the sound source from the observer away, the increase in the wavelength of the acoustic wave, tone becomes

8、low, when the sound source close to the observer, the wavelength of the sound decreases, the pitch becomes high. Related to the ratio of the change in pitch simultaneous relative speed between the source and the observer, and sonic velocity. The greater the ratio, the more significant the change, th

9、e descendants called the Doppler effect.,Principle,Doppler effect noted that the wave the Boyuan toward the observer when the reception frequency becomes high, and the reception frequency becomes lower when Boyuan away from the observer. When the observer moves to get to the same conclusion. However

10、, due to the lack of laboratory equipment, Doppler was not verified by experiment, a few years later was invited a team of trumpeter playing on a flatbed truck, home music ear trained to identify the change in pitch, in order to verify the effect. An often used example is the whistle of the train, w

11、hen the train approaches the observer, the vapor song is more strident than usual. Train passed, you can hear the shrill sound changes. Same: the sound of the siren of the police car and racing engines.,Principle,the completion of the sound source is a full vibration sent out one wavelength of the w

12、ave, the frequency representation of the completed within the unit time the number of vibrations, and therefore the Boyuan the frequency is equal to the number of unit time Boyuan issued full wave, the observerhear the sound of the tone, the frequency received by the observer, i.e. completely the nu

13、mber of waves received by the unit time of the decision. When the relative movement in the wave source and the observer, the observer received frequency will change. Within a unit time, the number of observer receives full wave number, i.e. the received frequency is increased. The same token, when t

14、he observer away from the wave source, the reduced completely the number of waves received by the observer within a unit time, i.e. the received frequency is reduced.,The application of the Doppler effect,Medical applications Color Doppler ultrasound,Color Doppler ultrasound is generally used since

15、the related art Doppler signal processing, the blood flow signal from the Doppler effect of the related art 5 is obtained after color-coded real time is superimposed on the two-dimensional image, i.e. forming a color DopplerLe ultrasound blood flow images. This shows that color Doppler ultrasound (i

16、e ultrasound) has both the advantages of the two-dimensional ultrasound structural image, while providing a wealth of information for hemodynamic practical applications have been widely appreciated and welcome, is hailed in the clinical as a non-invasive angiography. Transportation Applications Traffic Police emission of the ultrasonic frequency is known to the moving vehicle and simultaneously measuring the frequency of the reflected wave, will be able to know how much th