Aluminum nitride (AlN) is a promising Acoustic Emission (AE) sensor element for
high-temperature environments such as gas turbines and other plants because AlN maintains its
piezoelectricity up to 1200°C. Highly c-axis-oriented AlN thin-film sensor elements were prepared
on silicon single crystals by rf magnetron sputtering. Both ordinary-temperature AE sensors and
high-temperature AE sensors have been developed using these elements. In this paper, to study effects
of d33 and thickness of AlN elements on sensor sensitivity, AlN elements with d33 from 2 to 7 pm/V
and thickness from 3 to 9 /m were prepared. It is confirmed that the AE sensor sensitivity increased
with d33 and thickness of AlN elements. The sensitivity of the high-temperature AE sensor was also
improved by a design of the sensor structure. The sensor characteristics were evaluated at elevated
temperatures from 200 to 600°C. It was confirmed that the AE sensor works well at 600°C and does
not deteriorate.
In
this study, we attempted to expand the applicability of the
mechanism for arranging diamagnetic particles in a modulated magnetic
field. A Halbach array magnet was prototyped as a portable device
for generating a high magnetic field. Despite the magnet being palm-size
with dimensions of 50 × 50 × 20 mm, the magnetic field is
1.31 T at 1 mm from the surface. Additionally, an Si substrate on
which an Fe thin film is formed and patterned to be compatible with
the integrated circuit (IC)—utilizing the microelectromechanical
systems process technology—is prototyped as a tool to generate
a modulated magnetic field. Regarding the deposition condition of
the Fe thin film, holes with diameters of 30 μm are arranged
in an array at intervals of 60 μm, and the thickness is approximately
0.5 μm. Finally, a particle magnetic-adsorption experiment was
conducted using the prototypes. The diamagnetic particles (diameter:
25 μm) dispersed in the paramagnetic surrounding medium were
observed to be arranged in the hole portions. This result indicates
that the microparticles are absorbed in their arbitrary positions
by the modulated magnetic field. In the end, we succeeded in achieving
the portability and implementation on IC for the particle arrangement
magnetic mechanism.
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