david seebacher, aec’09, cern, switzerland
Post on 22-Feb-2016
56 Views
Preview:
DESCRIPTION
TRANSCRIPT
1
David Seebacher, AEC’09, CERN, Switzerland
13.10.2009
Impedance of Coatings
Outline
Motivation
Method
Results
13.10.2009 2David Seebacher, AEC’09, CERN, Switzerland
Motivation
Electromagnetic Properties of NEG coatings different statements about the influence of
NEG coatings on the impedance of machines exist
to check possible influences of the coatings, the impedance in the microwave range was measured
additionally carbon coatings were tested
13.10.2009 3David Seebacher, AEC’09, CERN, Switzerland
Cavity Perturbation Method
Cavity perturbation method was used to measure the properties
a frequency range of 2-4Ghz was chosen
13.10.2009 4David Seebacher, AEC’09, CERN, Switzerland
5
Glass rods with a 4mm diameter were chosen as „sample holders“
a non conducting material eases the determination of electromagnetic properties
coatings with different thicknesses were measured
13.10.2009
Samples
David Seebacher, AEC’09, CERN, Switzerland
Cavity Perturbation Method
permittivity and permeability can be determined in the microwave range
magnetic and/or electric field in the resonator, influenced by the insertion of a sample
NEG measurement sample was inserted horizontally in
the center of the resonator therefore it only interacts with the
odd resonance peaks and the electric field
13.10.2009 6David Seebacher, AEC’09, CERN, Switzerland
inserted sample detunes the cavity the permittivity and the sample size
determine the amount of detuning
Cavity Perturbation Method
dielectric
conductor
losses
13.10.2009 7David Seebacher, AEC’09, CERN, Switzerland
8
The upward shifted and damped odd peaks of NEG show resistive behavior as cross check a brass rod of the same size was measured and simulated The results of the brass rod are very similar to the of NEG this is due to
similar thickness/skindepth and conductivity13.10.2009
Results NEG Coating
David Seebacher, AEC’09, CERN, Switzerland
913.10.2009
Results Carbon Coating
no significant changes in frequency and only slight damping of the peaks Such small changes in frequency can also be caused by temperature
dependence of the resonator conductivity was determined by the difference of the Q-factors
David Seebacher, AEC’09, CERN, Switzerland
1013.10.2009
Results Carbon Coating average square conductivity is
~4000S/m (~1kΩ/square for a 0,25µm coating) at DC
conductivity of ~600S/m (~6.6kΩ/square) was measured within the variation of different coatings
~1E5 smaller than copper
The variation of the conductance is caused by reaching the validity of the method (it has to be a small sample)
David Seebacher, AEC’09, CERN, Switzerland
Results Glass Rods all odd peaks up to the 9th
resonance have been considered
relative large deviation between the different resonance peaks
sample is not a „small“ perturbation any more (condition for the evaluation formulas)
imaginary part shows negative values, corresponding to negative losses!
13.10.2009 11David Seebacher, AEC’09, CERN, Switzerland
Measurement Results
both coatings show resistive behaviormajor impact on the impedance can be
excluded
dielectric constant can’t be determinedchanges were too small detuning already highly influenced by temperature
at such small changes
the measured data was cross checked with simulations
13.10.2009 12David Seebacher, AEC’09, CERN, Switzerland
top related