Biomedical Engineering Reference
In-Depth Information
The maximum displacement at each working frequency is plotted in Figure 9.58
(Miyazaki et al., 2009). For comparison, the result of the microactuator utilizing the Ti-Ni
thin film is also included. The microactuator utilizing the Ti-Ni and Ti-Ni-Cu thin films
are abbreviated to Ti-Ni microactuator and Ti-Ni-Cu microactuator, respectively. The dis-
placement of the Ti-Ni microactuator is almost the same as that of the Ti-Ni-Cu micro-
actuator at working frequency below 20 Hz. However, it decreases by increasing working
frequency up to 50 Hz. The displacement of the Ti-Ni-Cu microactuator does not decrease
until the working frequency reaches 60 Hz. Above 60 Hz of working frequency, it gradu-
ally decreases. However, the microactuator operates even at 100 Hz. As shown in Figure
9.58, the displacement of the Ti-Ni-Cu microactuator is even larger than that of the micro-
actuator using the M-phase transformation within the working frequency range from 1 Hz
to 100 Hz. Thus, a high-speed microactuator with large displacement was successfully fab-
ricated by utilizing the Ti-Ni-Cu thin film.
The working frequency of the microactuators utilizing the Ti-Ni-Pd and Ti-Ni-Cu
thin films reached 100 Hz and that of the microactuator using the R-phase transformation
reached 125 Hz. Because the Ti-Ni-Pd and Ti-Ni-Cu show the shape memory behavior
associated with the martensitic transformation, the displacements of the microactuators
utilizing these two alloy films are almost equal to that of the Ti-Ni M-phase microactuator.
However, the displacement of the Ti-Ni R-phase microactuator is one-third of that of the
Ti-Ni M-phase microactuator. We can choose either of the microactuators depending on
the requirements of response speed and magnitude of displacement.
Microgrippers
Wireless capsule endoscope (WCE) is a new diagnostic tool in searching for the cause
of obscure gastrointestinal bleeding. A WCE contains video imaging, self-illumination,
image transmission modules, and a battery (Iddan et al., 2000; Waye, 2003). The indwell-
ing camera takes images and uses wireless radio transmission to send the images to a
receiving recorder device that the patient wears around the waist. However, there are two
drawbacks in the current WCE: (1) lack of ability for biopsy; and (2) difficulty in identifying
10
8
6
4
2
Ti-Ni
Ti-Ni-Cu
0
0
20
40
60
80
100
120
Working frequency (Hz)
FIGURE 9.58
Comparison of maximum displacements expressed as a function of working frequency for two types of micro-
actuators. (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.)
