Doppler shift

Doppler effect is a memorial to Christian Johann Doppler, named after the, he in 1842 firstly put forward this theory. Main contents: the wavelength of the light source object radiation because the observer and the relative motion changes. In the movement of the waves, wave front compressed, wavelength becomes shorter, frequency becomes higher (blueshift blue shift); When moving in waves behind, can produce adverse effect. Wavelength becomes longer, frequency become low (redshift ep-red shift). The higher the speed of the waves, the effects of refuse. According to the light red (blue) move degree, can calculate waves followed the observation direction movement speed

The cause

1842 Austria named doppler mathematician and physicist. One day, he was passing by railway crossing zero at a train from his side est, he found the train from far and close the whistle variable ring, tones, but the train variable pointed from far and near when the whistle slacken, tone become low. He knew the physical phenomenon felt great interest, and studied. Find this is due to vibration sources and observers exists between the relative motion, make the observer audible voice frequency different YuZhenYuan frequency phenomenon. This is frequency shift. Because, sound relative to the observer is moving, observers have heard the voices will change. When sound from the observer, acoustic wavelength increases, tones descended, when sound sources close to the observer, acoustic wavelength decreases, and tone become tall. With sound and tones of change of the relative speed between the observer and sound velocity ratio of relevant. This ratio is larger, the more significant change, the posterity is called it "the doppler effect".

The acoustic as regular interval emitted pulses can imagine if you each step, they launched a pulse, so before you each pulse is bigger than you stood motionless when closer to you. And behind you sound is than the original fixed when far step. Or, before you become the pulse frequency than usual after you high, while the pulse frequency are lower than usual.

So-called doppler effect is when its source and receiving body exists between the relative motion, receiving body receives its source emission information frequency and its source launch the frequency of information are not identical, this phenomenon is called doppler effect, receive frequency and transmit frequency difference is called the doppler frequency. The spread of voice also exist doppler effect, when the source and receiving between body have relative motion, receiving body receiving acoustic frequency f 'and noise resource frequency f exist doppler frequency shift Δ f (doppler shift) namely

Δ f = f '- f

When receiving body and sound near each other, receive frequency f 'greater than the transmit frequency f namely

Δ f > 0

When receiving body and sound going away from each other, receive frequency f 'less than transmit frequency namely:

Δ f < 0

Can proof if receiving body and sound near each other or going away from each other for v, the speed of sound velocity for c, then receive body receiving sound wave doppler frequency for:

F '= f. (v) / c + + v) (c -

Parentheses molecules and denominator upline operations and descending computing respectively to "close" and "from" meaning.

Application examples

Doppler effect not only applicable to sound waves, it also apply to all types of wave, including wavelengths. Edwin Hubble scientists using doppler effect that the universe is expanding conclusion. He found that distant galactic light frequency in become low, namely to move to the red end of the spectrum. This is red the doppler frequency, or called redshift. If the galaxy is moving towards the blue end, the light will become blue shift.

In mobile satellite communications, when the plane moving towards the satellite, frequency becomes tall, far from satellite, frequency become low, and because of the speed of an airplane is very quickly, so we in mobile satellite communications should be fully considered "dopplereffect". On the other hand, because the geosynchronous satellites itself also have high speed, so now mainly use geosynchronous satellites and airplanes to communicate, and to avoid this kind of influence and cause us problems in communication, we have to be different considerations in technology. Also increases the complexity of mobile satellite communication.

Sound wave doppler effect also can be used in medical diagnosis, namely we ordinary sufficiency. Color dopplar ultrasound simply means high definition of black and white b-sonography plus color doppler, first say super audio move diagnostics, namely D super, in this application doppler effect principle, when the source and receiving body (namely probe and reflector) between the relative motion, the echo of frequency changing, this frequency changes called doppler-shift, D super including pulsed doppler, continuous doppler and color doppler images. Color doppler ultrasound is commonly use the relevant technology doppler signal processing, the autocorrelation technology for blood signal by color coding after real-time overlay on 2-d image, it forms of color doppler ultrasound image blood flow. Thus, color doppler ultrasound (i.e. color dopplar ultrasound) has both the advantages of structure of two-dimensional ultrasound images, and also provides hemodynamic of the rich information, practical applications received wide attention and welcome, in clinical is known as "nontraumatic angiography".