ultrasound (1 Viewer)

[mystify]

i was hoping that sum1 mite be able to help me... are ultrasounds produced due to the reflection of the waves which a transducer picks up or refraction of the waves thru the medium?

my phyzix teacher claims that its due to refraction but some notes say that a transducer picks up the reflected waves and produces an electrical impulse which a computer uses to produce an image.

thnx in advance

 

[wahashtini]

ur welcome

 

[kheir]

its due to reflection when ultrasound moves from one interface to another ie experience a large change in acoustic impedence it is reflected this reflection causes scattreing of the ultrasound

 

[the_archduke]

I think Ultrasounds are caused by both reflection and refraction; it all depends on the angle. Whenever the wave from the transducer reaches an interface in a perpendicular orientation the wave is reflected back in the exact same line as the initial wave (with less energy though). If a wave hits an interface at an angle the wave changes direction and may or may not return to the transducer.

 

[Shimtek]

piezoelectric effect anyone?

"2. The piezoelectric effect is when a special crystal expands and contracts when an alternating voltage is applied across it, producing sound waves. This is due to the dipoles in the crystal which rotates due to the AC. Electrical energy is converted into the ultrasound pressure wave. A commonly used crystal is lead zirconatetitanate (PZT). Each crystal transducer has its own natural resonant frequency which depends on the crystal thickness. The electrical voltage driving the transducer should match the natural vibrational frequency of the transducer to maximise the conversion of the electrical energy into ultrasound energy. The frequency the crystal produces is dependant only on the thickness of the crystal, with the wavelength produced usually being twice the length of the crystal"