Biomedical Engineering Reference
In-Depth Information
through the impedance head and transformed into the frequency domain using a Fast
Fourier Transformation (FFT) routine. This transformation is very useful because from the
inspection of the frequency response of the measurement it is possible to identify a
characteristic resonance frequency for the sample.
Load
Cell
Stack of
Piezoelectric
Crystals
I
mpedan
ce
Head
Oscillati
n
g
Plate
Sample
Fixe
d
Plate
Fig. 8. Schematic of the OSF testing apparatus
Since the samples are considered viscoelastic they can be represented by a combination of
elastic component, with a stiffness
S
, and viscous components with a damping
R
. A
schematic of the elastic-viscous system used for analysis of the measurements is illustrated
in Figure 9. For the testing, the sample is placed between the oscillating plate and a fixed
plate. The oscillating plate is then brought down to touch the sample and the gap between
O
scilla
ting
Plate
s
h
o
R
Rigid
Surface
Fig. 9. Schematic of the spring-dashpot system, used for the analysis of the data.
h
o
,
R
, and
S
are the height, the viscous resistance (damping), and the stiffness of the sample respectively.
