Biomedical Engineering Reference
In-Depth Information
zero at the
A
f
temperature of 370 K and 430 K for the Ti-Ni M-phase microactuator and
the Ti-Ni-Pd microactuator, respectively. The Ti-Ni-Pd microactuator exhibits almost the
same displacement as the Ti-Ni M-phase microactuator.
M
s
of the Ti-Ni-Pd microactuator
is about 70 K higher than that of the Ti-Ni M-phase microactuator. Also, it is noted that the
transformation temperature hysteresis of the Ti-Ni-Pd microactuator is smaller than that
of the Ti-Ni M-phase microactuator (Miyazaki et al., 2009).
Microdiaphragm Using M-Phase of Ti-Ni-Cu
Figure 9.57a shows temperature dependence of
h
(height at the center of the diaphragm)
during cooling and heating in the microactuator employing a Ti-38.0Ni-10.0Cu thin film
that was heat-treated at 973 K for 0.6 ks (Miyazaki et al., 2009). Data obtained during the
cooling and heating processes are denoted by open and closed circles, respectively. Upon
cooling,
h
starts to increase at
M
s
and finishes at
M
f
, whereas
h
starts to decrease at
A
s
and
finishes at
A
f
upon heating. The increase and decrease in
h
are due to the forward and
reverse transformations, respectively, in the Ti-Ni-Cu layer of the microactuator. Therefore,
the microactuator utilizing the Ti-Ni-Cu thin film is expected to exhibit a higher actuation
speed than that utilizing the Ti-Ni binary thin film.
Figure 9.57b shows current amplitude dependence of the displacement at each working
frequency (Miyazaki et al., 2009). As shown in the displacement-current curve for the
working frequency of 10 Hz, the displacement increases with increasing current ampli-
tude reaching a maximum, then becomes almost constant. When the current amplitude is
small, the temperature of the Ti-Ni-Cu layer does not increase up to
A
f
, resulting in small
displacement due to incomplete reverse transformation. By increasing the current ampli-
tude, the temperature approaches
A
f
, leading to increase in displacement. The current
amplitude necessary for generating a maximum displacement increases with increasing
working frequency. This is because each heating time decreases with increasing working
frequency under a fixed duty ratio condition.
(a)
(b)
10
20
8
M
f
15
A
s
6
10
∆
H
M
Heating
4
Cooling
10 Hz
20 Hz
40 Hz
60 Hz
80 Hz
100 Hz
5
A
f
2
M
s
0
0
300
320
340
360
380
400
0
0.5
1
1.5
2
2.5
3
Temperature (K)
Current (A)
FIGURE 9.57
(a) Temperature dependence of height of a microactuator utilizing the Ti38.0Ni10.0Cu thin film that was heat-
treated at 973 K for 0.6 ks; displacement as a function of current amplitude for each working frequency. (From
Miyazaki, S., in Miyazaki et al., eds.,
Thin Film Shape Memory Alloys: Fundamentals and Device Applications
,
Cambridge University Press, UK, 2009, reproduced with permission from Cambridge University Press.)
