# Ultrasound machine

## Main Question or Discussion Point

how does ultrasound machine detects the reflected wave?

i have read a bit of information and unfortunately Im still unsure how they detect the wave.

"The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward. Conversely, when sound or pressure waves hit the crystals, they emit electrical currents. Therefore, the same crystals can be used to send and receive sound waves."

I dont understand how the change in electric field can be related to the detection of the wave. plz help

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Homework Helper
The speaker and microphone are the same thing.
If you put a voltage across the piezo crystal it changes shape and emits a sound, if you change it's shape, by a sound hitting it, it generates a voltage.

This is true of most microphones/speakers

The speaker and microphone are the same thing.
If you put a voltage across the piezo crystal it changes shape and emits a sound, if you change it's shape, by a sound hitting it, it generates a voltage.

This is true of most microphones/speakers
So when this happens this is the reverse of the piezoelectric effect? (from mechanical energy to electrical energy.)

And the transducer receives sound wave because of this reverse piezoelectric effect?

also there is the other bit that i dont understand

"the crystal will be changed in the same way as when crystal the crystal was generating ultrasound. In this case the changing crystal will cause a changing electric field to be produced across the crystal"

to be honest, I have no idea what they talk about at all. :(

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Oscillation of sound to produce an image. Instead of using gamma rays to produce material densities, you use sound to reflect surfaces. When sound is produced by a device and interpreted in a certain way, it can produce images.

Oscillation of sound to produce an image. Instead of using gamma rays to produce material densities, you use sound to reflect surfaces. When sound is produced by a device and interpreted in a certain way, it can produce images.
yes it calculates the time that takes to travel back to the transducer to produce an image.

but i dont really get this staement below "the crystal will be changed in the same way as when crystal the crystal was generating ultrasound. In this case the changing crystal will cause a changing electric field to be produced across the crystal"

The crystal is a sensor, it creates vibrations and interprets vibrations. the change from sound to an electric signal is in the circuitry of the machine. The crystal interprets sound to be transmitted over the circuit.

The crystal is a sensor, it creates vibrations and interprets vibrations. the change from sound to an electric signal is in the circuitry of the machine. The crystal interprets sound to be transmitted over the circuit.
oops sorry i understand now thx!

just wondering, would the change in amplitude (voltage) has any effect on this?

yes???

hey here is another question :S

When the frequency of the wave is too high it will be absorbed easily? I don't understand why. Is it because of the increase in wavelength?