Alpha-A
analyzer
Broad frequency range 3.10-5
.. 2.107 Hz including low frequencies for
characterization of dielectric relaxations and electrochemical effects
Most impedance analyzers start at frequencies higher than some 10 Hz. This is sufficient for many technical applications as the impedance at low frequency is often constant at low frequencies and therefore does not yield new information.
On the other hand many material samples show strong frequency dependence at very low frequencies down to the mHz range or even lower. The low frequency response contains a lot of additional information unavailable from the "high frequency" spectra above 10 Hz. This especially applies to dielectric materials, electrochemical systems and generally all high impedance samples.
Dielectric Materials
The main
effect measured in dielectric materials is the relaxation dynamics of
polar molecules. Relaxation times are from some pico seconds to
practically infinite (like e.g. years). This corresponds to frequencies
from 100 GHz to nHz. The entire frequency range contains important
information. It should therefore be as broad as possible. Dielectric
samples require in addition high phase accuracy
and wide impedance range.
Measurement examples: Broadband Dielectric Spectra of PVDF measured with Alpha analyzer.
Electrochemical Systems
In these systems charge transport is often governed by more or less free ions. The ion conductivity by itself is frequency independent up the GHz range. In practice, technical systems with e.g. electrolyte to metal, electrolyte to membrane or electrolyte to insulator systems for batteries, fuel cells, paints or corrosion analysis are important. At the electrolyte borders, interface polarization effects are created due to ion accumulation involving slow processes. This results in low frequency dependence of the measured system impedance related to the structure of the interface region and corresponding charge transport processes.
High Impedance Samples
As a general electrical property, all systems with sufficient high resistance show low frequency dependence. This is because any insulating system can be modeled in good approximation by an equivalent circuit of a frequency dependent resistance R and capacity C. The capacity is at least a stray capacity in the pF range. This circuit behaves like a Debye relaxator with an relaxation frequency of fr=1 / 6.28 * R*C. E.g. for C=1 pF and R=1 TΩ fr = 0.15 Hz and the impedance spectrum will show strong low frequency dependence down to the mHz range. Therefore, low frequency characterization for high impedance samples is always required.
Measurement examples: High impedance materials and components measured with Alpha analyzer