Biomedical Engineering Reference
In-Depth Information
labeled A1 through A5 and placed in water-filled baggies to keep them hydrated.
Each sample was tested in the impedance analyzer by manually sweeping through
a range of frequencies and measuring the magnitude and phase of the impedance at
each frequency.
The impedance of the samples was on the order of 2-5
Ω
. The impedance of
the test fixture was on the order of 1
; therefore, the measured data were corrected
to account for the impedance of the fixture. Assuming that the sample was in series
with the fixture, the data were corrected by first transforming the measured data into
real and imaginary components through the expressions:
Ω
(
)
=
(
)
Re
Z
Z
cos
∠
Z
meas
meas
meas
(7.19)
(
)
=
(
)
Im
Z
Z
si
n
∠
Z
meas
meas
meas
The data were corrected by subtracting the impedance of the fixture from the
measured impedance of the actuator, and transforming back into magnitude and
phase.
(
)
(
)
=
(
)
−
Re
Z
Re
Z
Re
Z
corr
meas
fixture
(7.20)
(
)
=
(
)
−
(
)
Im
Z
I
m
Z
Im
Z
corr
meas
fixture
Figures 7.35 and 7.36 are the magnitude and phase plots for the corrected data.
The impedance magnitude varies between 1.1 and 2.4
over the frequency range
of 5 Hz to 1 kHz. The reactive component of the impedance is approximately equal
to the active component below approximately 10 Hz.
Ω
3.00
2.80
2.60
2.40
2.20
2.00
Sample A1
Sample A2
Sample A3
Sample A4
Sample A5
1.80
1.60
1.40
1.20
1.00
0.001
0.010
Frequency (kHz)
0.100
1.000
FIGURE 7.35
Measured impedance at an input voltage of 0.5 V.
