TB - Transducer (Chp 2) Flashcards
How does thickness of the tx/crystal relate to frequency?
thicker beam produces a lower freq
What is the formula for the frequency of the TX for pulsed-wave operation?
Operating Freq = c/ (thickness X 2)
The operating frequency is also about 1/2 of what?
the wavelength
Define depth ambiguity?
This is an artifact that occurs when the tx. sends out a pulse before the previous one has returned. and it therefore cant figure out where it originated to display it correctly
What is Huygens Princuple
The sound beam starts out as small wavelets at tx face –> these form a sounds beam while traveling perpendicular to the wave front
What does the housing of the transducer do?
provides insulation and protection from electrical shock
What are the advantages of the damping/backing materal?
decreases number of cycles in a pulse (ringing period), decreases SPL, increases axial res
What is the backing material made of?
epoxy resin and tungsten
What are the side effects/disadvantages of dampening?
- decreases sensitivity and increases BW
- reduces QF
What is the Quality Factor?
term to quantify the purity of the beam
operating freq/bandwidth
What is the process of phasing to steer?
Changing the timing of shocking the elements in order to shape/steer the beam
What else is the technique of phasing used for?
focusing by firing the peripheral elements first
What is a CW transducer?
1 element to continuously transmit sound and one that continuously receives sound - produces no image
How can we decrease the SPL?
- decreasing wavelength by increasing the frequency
- decreasing the number of pulses per SL by increasing damping material
Do we want a high number of axial resolution or low?
the lower the number = the closer the objects can be - which is what we want
What is the SPL formula?
SPL = wavelength x n
What is the wavelength formula?
c/f
What type of resolution is usually better in transducers, axial or lateral?
axial resolution
What can a 1.5D array tx do that a 1D cant?
it can focus the beam in the elevational plane
What minimun FR needs to be obtained or else the image will flicjer?
atleast a FR of 15 Hz
What is the FR formula?
FR = PRF/LPF (lines per frame)
What is dropout
occurs on an image as. a black line when tx is damaged
Which is the type of transducer that utilizes elements arranged in a concentric pattern?
Annular Array
Which transducer has moving parts?
mechanical array
What happens to the diameter of the sound beam in the fresnel zone?
it decreases
How can you increase the NZL?
increase the aperture and the frequency
What will decrease beam divergence in the far field?
Increase the aperture and frequency
What is angular resolution another name for?
lateral resolution
What happens to the frequnecy with a thin crystal element?
it will give a higher frequency
