Friends,A doubt in piezoelectricity. I heard that when pressure is

[Raama]

Friends,

A doubt in piezoelectricity. I heard that when pressure is applied in a quartz crystals(or other similar items), a high voltage is produced and this is called piezoelectricity. My question is, is it necessary a pressure cycle should go on? i.e. first a high pressure, then low, then high is needed to produce it or simply a constant high pressure is enough for it.

Please answer me.

 

[Bill_K]

Not pressure but stress, e.g. compression along one axis. It causes a charge separation in the crystal and therefore an electric dipole moment. Attach leads to opposite sides and you'll see a small voltage difference, which goes away when the stress is removed.

 

[Raama]

I can understand. Is there any equation to find the potential difference between them or any other like that. If so, please give me explain it to me so that I can understand.

 

[BrockLee]

I believe that this coined phrase piezo refers to tha man who found the range of frequency response from a naturally occurring mineral. And that this equation your looking for is actually varying on the material in question which happens to be in the periodic table's ordered model of subatomic interaction. Something like Capacitance Medium is on one end of the scale and the Induction is on the other, which is going to give you:
frequency=capacitance*resistance;
frequency=inductance/resistance;
But expect to pay much for the oscilliscope to find out if you have the inductance and capacitance values correct for your test circuit.

 

[DrFurious]

I'll also add that for such crystals the opposite is true: when a voltage is applied they expand.

 

[pallidin]

For more info, please see here:

http://en.wikipedia.org/wiki/Piezoelectricity

 

[Raama]

I'll also add that for such crystals the opposite is true: when a voltage is applied they expand.

For more info, please see here:

http://en.wikipedia.org/wiki/Piezoelectricity

@DrFurious: I know that but any way thanks for ur reply.

@pallidin: Hey, I asked the question only after reading the article. I can't understand the equation given there. Please explain it to me.

 

[pallidin]

@pallidin: Hey, I asked the question only after reading the article. I can't understand the equation given there. Please explain it to me.

OK, gotcha, perhaps someone more knowlegable than I on this subject can assist you.

 

[kaelibw]

@pallidin: Hey, I asked the question only after reading the article. I can't understand the equation given there. Please explain it to me.

If you are referring to the matrix, please send me a message if you figure it out. Thats something i can't understand either

 

[nasu]

The matrix equations look so complicated because they are given for a general case.
The second one in the link:

$$\begin{bmatrix} D_1 \\ D_2 \\ D_3 \end{bmatrix} = \begin{bmatrix} 0 & 0 & 0 & 0 & d_{15} & 0 \\ 0 & 0 & 0 & d_{24} & 0 & 0 \\ d_{31} & d_{32} & d_{33} & 0 & 0 & 0 \end{bmatrix} \begin{bmatrix} T_1 \\ T_2 \\ T_3 \\ T_4 \\ T_5 \\ T_6 \end{bmatrix} + \begin{bmatrix} {\varepsilon}_{11} & 0 & 0 \\ 0 & {\varepsilon}_{22} & 0 \\ 0 & 0 & {\varepsilon}_{33} \end{bmatrix} \begin{bmatrix} E_1 \\ E_2 \\ E_3 \end{bmatrix}$$

gives the components of the electric induction D but for the case when you apply pressure on the piezoelectric (T) AND and external field (E).
For the question in the OP you can discard the second part in the right hand side and you will have just the field components due to stress (T). Here 1,2,3 for D and E means x,y,z components. For stress (T) is a little more complicated. Each index (1,2,3...) means two indices (see stress tensor).

For example, if you apply a compression stress along the x-axis (for example applying pressure), the stress component describing this will be Txx=T1.
The effect will be a field component along the z axis:
D3=d31*T1

In general, what the matrix equation means is a set of three algebraic equations:
D1=d15*T2
D2=d24*T4
D3=D31*T1+d32*T2+d33*T3

The coefficients dij are provided by the manufacturer of the piezoelectric device or material.

 

[kaelibw]

Yeah...I don't even know what half of that meant. I have never used a matrix in my life. Probably should have said that first.