Re: ATM Yet another interesting thought

[Aplanatic@aol.com]

Hi Mel,

You asked about the cost of piezoelectric actuators.  In unit quantities, a 2.85" X 2.85" sheet, 10 mils thick, of the best material for our applications is US$100.  That is either high or low depending on your point of view.  See:

>http://www.piezo.com/

Here's a summary for material PSI-5H-S4-ENH:

Composition: Lead Zirconate Titanate  
Material Designation: PSI-5H-S4-ENH
Strain Coefficient: 650 x 10^-12 meters/Volt 
Voltage Coefficient: 19.0 x 10^-3 Volt-meters/Newton 
Polarization Field: 1.5 x 10^6 Volts/meter 
Initial Depolarization Field: 3.0 x 10^5 Volts/meter

Assume that we place three actuators on a 1.5" diameter circle.  If we use a single thickness of this material, then we can apply a maximum voltage across it of about 80 volts (Initial Depolarization Field X thickness).  We then get a total strain of 52 nm (Strain Coeff X voltage).  Over a 1" moment arm, with one actuator energized the mirror rotates 2 microradians (52 nm / 1") or 0.42 arcseconds.  Using all three actuators, we can rotate the mirror 0.84 arcseconds and the image moves 1.68 arcseconds.  Not bad, but not enough.  So, we should use a stack of four of these devices to achieve an image movement of about 7 arcseconds.  This is enough to remove most seeing and mount vibration effects.  In practice, we can drive the PZT about 2 times the initial depolarization field and still be fairly linear.

We can use a very small diameter actuator.  A 1/2" square is way more than enough.  So, we cut the (nearly) 3" X 3" sheet into 36 pieces and we have enough for several complete experiments.

With a four-stack, we need to generate about 300 volts to drive the actuators, but 600 would be better.

Dave Rowe