Technical Background for mK Setups
power dissipation and leakage currents
Power Dissipation
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The power dissipation of the capacitive piezoelement is another source of
generated heat at ultra-low temperatures. A Piezo dissipates the power
P = f CU² tanδ with the total power P, maximum voltage U, piezo capacitance C,
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For example, with C = 200 nF, f = 10 Hz, U = 70 V, and tanδ ≈ 4% the heat
generated calculates to P = 490 μW. In case of a rotator, this number gets dou-
bled because there are two piezoelements used to drive these positioner types.
signal repetition rate f, and loss angle δ of the dissipated electrical power.
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P = fCU² tanδ
with
C = 800 nF
tanδ = 0.019
500
0
0
50
100
150
frequency [Hz]
200
Comparison between calculated and measured power dissipation.
Leakage Currents
Piezoelements typically have GΩ resistances. Even with e.g. 1 GΩ
resistance, the heating due to leakage currents at 100 V static voltage
is order of P = U²/R = 10 μW. This leakage current can only be reduced by
using elements with higher ohmic resistances. attocube ensures a reduced
leakage current by hand-selecting the piezoelements for dedicated mK
positioners.
250