• Support PF! Buy your school textbooks, materials and every day products Here!

Why does piezoelectric need amplifying?

  • #1
125
5

Homework Statement


Descibe[/B] in detail the contruction of a piezoelectric device (ultrasound machiene) and how it works. And explain why the singal from that device need amplification

graphic4.png


Homework Equations




The Attempt at a Solution


Electrical current passes to the piezoelectric crystal (non-conductive material, no charge in any arrangement) and electrical pressure is experienced. The pressure causes the crystals to contarct/expand and virbate which causes the molecules to move causing an imbalance of charge making one electrode more positive then the other producing soundwaves. These soundwaves reflex from organs etc and are recieved by the transducer probe. The pressure from the waves casue the molecules in the crystals to move causing an imbalance in charge making one metal plate positively charged and the other negitively charged creating a potential difference producing a current which flows down the cable.

Amplification is used to increase the size of the electrical pulses coming from the transducer after an echo is received. This is becasue the electrical signal is too small to produce a detailed image

(I am really struglying with why the signal needs amplifying as I can't find an explanation)
 

Attachments

Last edited:

Answers and Replies

  • #2
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,714
5,030
Electrical current passes to the piezoelectric crystal (
As you say, it is non conducting, so it's a matter of potential, not current.
electrical pressure is experienced.
What is electrical pressure? Do you mean potential?
causes the crystals to contarct/expand and virbate
Yes, apart from the typos.
which causes the molecules to move causing an imbalance of charge making one electrode more positive
You have correctly described going from electric impulses to vibration, but now you seem to be going back the other way. Delete this.
creating a potential difference producing a current which flows down the cable.
Again, it is more a matter of potential than current.
This is becasue the electrical signal is too small to produce a detailed image
Not so much a question of detail, just too small to produce any image.
 
  • #3
tnich
Homework Helper
1,048
336
Amplification is used to increase the size of the electrical pulses coming from the transducer after an echo is received. This is becasue the electrical signal is too small to produce a detailed image
I think that is a good start. Why is the signal too small to produce an image? (And please note @haruspex comment - it's not the detail that is the problem.) What kind of device are you using to display an image?

Is it analog? If so, what range of values of the input signal does the display device respond to?

Is the image a bitmap? What is the display's threshold level?

Is it a digital representation in which each pixel has a range of potential values? What is the range of inputs of the A/D converter?

How does the output level of the piezoelectric crystal compare to the input level(s) of the display device?
 
  • #4
125
5
As you say, it is non conducting, so it's a matter of potential, not current.
Could I say voltage is passed to the crystals?
What is electrical pressure? Do you mean potential?
Yes
You have correctly described going from electric impulses to vibration, but now you seem to be going back the other way. Delete this
I read somewhere that the crystals are non conductive and they have a neutral charge because the charges of the molecules cancel each other out. And when pressure was put on this material it caused the molecules to move making one plate positively charge and the other negatively charged creating a potential difference . (link to video: ).


Another website put it saying as the material got hit, squeezed etc it increasing or decreasing the space between the atoms by squeezing, hitting, or bending the crystal can cause the electrons to redistribute themselves and cause electrons to leave the crystal, or create room for electrons to enter the crystal. A physical force on the crystal creates the electromotive force that moves charges around a circuit. (link: https://www.allaboutcircuits.com/technical-articles/how-piezoelectric-speakers-work/)
creating a potential difference producing a current which flows down the cable. //
Again, it is more a matter of potential than current.
So could I say voltage?
 
Last edited:
  • #5
125
5
I think that is a good start. Why is the signal too small to produce an image? (And please note @haruspex comment - it's not the detail that is the problem.) What kind of device are you using to display an image?
The signal is to weak to produce an image because the echoes recieved by the transducer has less energy as the sound wave diminishes as it propagates through the body and when it is reflected therefore only produces small electrical impulses.
I am using the ultrasound machine display.

Is it analog? If so, what range of values of the input signal does the display device respond to?
I have wrote that it is digital but other than that I couldn't find anything else.

Is the image a bitmap? What is the display's threshold level?
I don't know what that is, will do some research

Is it a digital representation in which each pixel has a range of potential values? What is the range of inputs of the A/D converter?
How does the output level of the piezoelectric crystal compare to the input level(s) of the display device?
The output is larger than the imput because the waves diminish
 
Last edited:
  • #6
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,714
5,030
I read somewhere that the crystals are non conductive and they have a neutral charge because the charges of the molecules cancel each other out. And when pressure was put on this material it caused the molecules to move making one plate positively charge and the other negatively charged creating a potential difference . (link to video: ).

Another website put it saying as the material got hit, squeezed etc it increasing or decreasing the space between the atoms by squeezing, hitting, or bending the crystal can cause the electrons to redistribute themselves and cause electrons to leave the crystal, or create room for electrons to enter the crystal. A physical force on the crystal creates the electromotive force that moves charges around a circuit. (link: https://www.allaboutcircuits.com/technical-articles/how-piezoelectric-speakers-work/)
Yes, but in what you wrote you confused the two directions of the effect.
When a voltage is applied, it causes the crystal to expand or to contract. This is the effect the device uses to create the ultrasound.
Conversely, when the crystal is stretched or compressed it generates a voltage. This is the effect used to detect the reflected ultrasound.
Because the voltage generated by the reflection is much smaller than the one used to drive the vibration, some clever electronics disables the detection circuit during the driving phase.

Note also that if applying a positive voltage to one side causes contraction then compressing the material will cause a negative voltage on that side. This 'reversal' is common to many reactive processes. E.g. in electromagnetism.
 

Related Threads on Why does piezoelectric need amplifying?

Replies
7
Views
2K
Replies
2
Views
2K
  • Last Post
Replies
14
Views
1K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
13
Views
2K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
6
Views
640
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
13
Views
7K
Top