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Keysight Technologies
Materials Measurement:
Liquid Materials
Application Brief
02 | Keysight | Materials Measurement: Liquid Materials - Application Brief
Overview Problem
There are increasing demands for the electrical measurement to For scientists who are not familiar with the electrical measure-
investigate the properties of liquid materials that is characterized ment, it is not easy to understand the electrical model of liquid
by permittivity and conductivity. materials.
Permittivity, also called as dielectric constant is related to the Complex permittivity measurement is done by measuring the
electric polarization and conductivity is the measure of a mate- electrical impedance of the material using LCR meters or imped-
rial's ability to conduct electric current when applied an electri- ance analyzers. Although they are accepted as standard instru-
cal field. Dielectric spectroscopy, also known as electrochemical ments in evaluating electronic components and materials, special
impedance spectroscopy (EIS) measures permittivity and conduc- devices will be required when applying to liquid materials.
tivity as a function of frequency. Complex permittivity measure-
ment enables not only to evaluate electrical property but also Dielectric spectroscopy is suited for in-situ characterization of
to analyze the composition, the structure of the heterogeneous colloidal dispersion or molecular dynamics however it requires
system and the interaction of the molecules in the liquid. accurate measurement system over a wide frequency range.
The electrical measurement is fast, non-destructive, non-invasive
and cost effective method and also allows continuous monitor-
ing of liquid material without any pretreatment. It can be applied
Solution
to liquid, emulsion and colloidal suspension including chemical
Impedance analyzers are the best instruments for the evaluation
materials, crude oil, cosmetics, wine or whiskey brewing as well
of electronic components and materials. The Keysight Technolo-
as blood and biological cell.
gies, Inc. 16452A liquid test fixture is designed to be used with
the Keysight E4990A impedance analyzer for the permittivity
Complex permittivity can be derived from the electrical imped-
measurement of liquid materials. Their four-terminal-pair con-
ance of the liquid, which can be measured using impedance
figuration effectively eliminates the errors due to the cables. The
analyzers with appropriate fixtures.
16452A adopts parallel plate capacitance method covering the
frequency range from 20 Hz to 30 MHz and has liquid container
between two electrodes that form a capacitor filled with the liquid
material. The distance of the electrodes is variable by changing
spacers and it requires sample of less than 10 mL.
03 | Keysight | Materials Measurement: Liquid Materials - Application Brief
Figure 3. Relative permittivity of water/ethanol mixture
Figure 1. Impedance analyzer with liquid test fixture
Figure 2. Parallel plate capacitance method
Complex relative permittivity is derived by comparing the ca-
pacitance of the 16452A fixture with and without the liquid mate- Figure 4. Permittivity change by volume fraction
rial filled in it, which provides accurate measurement regardless
the size of the fixture.
The 16452A is suited for the measurement of liquid materials with
C G low permittivity and low conductivity. It provides accurate meas-
* = '- j " = P - j
C urement eliminating the errors due to the fringe capacitance by
0 C0 the guard electrode.
where * : complex permittivity
0 : permittivity of free space If sample contains electrolyte, problem occurs below 10 kHz
because of the electrode polarization, which is shown in the
CP : measured capacitance graph above and is more serious when applying to bio materials.
G : measured conductance Although there is no established method to eliminate or to correct
this effect, platinized platinum electrodes (platinum black coated
C0 : air capacitance platinum electrode) properly reduce it.
: angular frequency
The following is an example of a hand-made measurement cell
Shown below is an example in which mixtures of purified water (fixture) with the platinized platinum electrodes. The system con-
and anhydrous ethanol with different mixing ratio were mea- sists with the E4990A impedance analyzer, the 42942A terminal
sured with the 16452A and the E4990A. The volume ratio of the adapter, the 16092A spring clip fixture and the measurement cell.
water is 0/25/50/75/100%, respectively. The relative permittivity
increases when increasing the mixing ratio of water. At 0% and
100%, the values are consistent with the permittivity of ethanol
(24.3 at 25