The Q factor was calculated by fitting the measured data with
the envelope of Eq. (27). The measurements were carried out 20
times and the averaged value was selected as the Q factor of the
polymer at a certain strain.
Fig. 12 shows the Q factors measured by the impact testing
method. The natural frequencies of the 100-, 150-, and 200-mmlong
polymer-based bars were approximately 0.18, 0.08, and
0.05 kHz, respectively. In the range of 0.005–0.010%, the Q factor
of the PPS-based cantilever was approximately 580, which was
twice as high as that in the range of 0.035–0.040%. The Q factor
of the PEEK-based cantilever was 150 in the range of 0.005–
0.010% and decreased to 90 as the strain increased to 0.040%. The
experimental results also demonstrate that the Q factor is independent
of frequency in the range of 0.050–0.180 kHz.
The Q factors of the PPS- and PEEK-based bars at 0.08 kHz measured
using the impact tested method are shown in Fig. 10. They
are in accordance with the frequency- and strain-dependences of
the Q factor measured by the devised method described above.
However, these Q factors are lower than the values extrapolated
from the results obtained by the devised method. This may be
attributed to the mechanical loss generated on the contacting surface
between the cantilever and the plates. In the devised method
(Fig. 5), the energy loss is distributed in the transducer, contacting
surface, and polymer-based bar. Since the active vibration power
flowing across a cross-section is calculated, the dissipated energy,
which reflects the energy loss generated on a certain part, can be
estimated. In contrast, using the impact testing method (Fig. 11),
it is difficult to separate the energy loss generated on the bar from
that on the contacting surface between the plate and the polymerbased
bar. In the impact testing method, the energy loss in the
vibration system is used as the dissipated energy in calculations,
which yields a smaller Q factor than that obtained by the devised
method.