Research Express@NCKU - Articles Digest
Research Express@NCKU Volume 21 Issue 7 - March 2, 2012
[ http://research.ncku.edu.tw/re/articles/e/20120302/1.html ]
Plastic Chips by Hot Embossing Methods and Their
Applications for DNA Separation and Detection
Gwobin Lee
1,*
,Shu-Hui Chen
2
, Guan-Ruey Huang
1
, Wang-Chou Sung
2
, Yen-Heng Lin
1
1
Department of Engineering Science,
2
Department of Chemistry, National Cheng Kung University,
Tainan, Taiwan, 701
gwobin@mail.ncku.edu.tw
SENSOR ACTUATOR B-CHEM 75 (1-2): 142-148 APR 30 2001
Times Cited: 161
Design and fabrication of microfluidic devices on polymethylmethacrylate (PMMA)
substrates for analytical chemistry and biomedical-related applications using novel
microfabrication methods are described. The image of microstructures is transferred from
quartz master templates possessing the inverse image of the devices to plastic plates by
using hot embossing methods. The micro channels on quartz master templates are formed
by the combination of metal etch mask and wet chemical etching of a photomask blank.
The micromachined quartz templates can be used repeatedly to replicate cheap and
disposable plastic devices. The reproducibility of the hot embossing method is evaluated using 10 channels on
different PMMA plastics (Fig. 1). The relative standard deviation of the channel profile on the plastic chips is less
than 1 %. In this study, the PMMA microfluidic chips have been demonstrated as a micro capillary electrophoresis
(μ-CE) device for DNA separation and detection. The capability of the fabricated chip for electrophoretic
injection and separation is characterized via the analysis of DNA fragments
Φ
X-174-RF Hae III digest.
Experimental results indicate that all of the 11 DNA fragments of the size marker could be identified in less than 2
minutes with relative standard deviations less than 0.4 % and 8 % for migration time and peak area, respectively.
Moreover, with the use of a near IR dye, fluorescence signals of the higher molecular weight fragments (> 603 bp
in length) could be detected at total DNA concentrations as low as 0.1 μg/mL. In addition to DNA fragments
Φ
X174-RF Hae III digest, DNA sizing of hepatitis C viral (HCV) amplicon is also achieved using microchip
electrophoresis on PMMA substrates.
Fig. 1 Picture of a micro electrophoresis chip fabricated by the hot embossing method.
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Research Express@NCKU - Articles Digest
Research Express@NCKU Volume 21 Issue 7 - March 2, 2012
[ http://research.ncku.edu.tw/re/articles/e/20120302/2.html ]
Design of Large Power Surface-Mounted Permanent-
Magnet Motors Using Post-Assembly Magnetization
Min-Fu Hsieh
*
, You-Chiuan Hsu and David Dorrell
Department of System and Naval Mechatronic Engineering, College of Engineering, National Cheng
Kung University
mfhsieh@mail.ncku.edu.tw
IEEE Transactions on Industrial Electronics, vol. 57, no. 10, pp. 3376-3384, 2010.
Rare-earth permanent-magnet (PM) brushless motors possess the advantages of high
efficiency, high torque/power density and low maintenance. They are usually assembled
with the magnets pre-magnetized. However, as the motor size and output power increase,
the handling of the pre-magnetized components can be difficult. These increase the
manufacturing cost
[1-2]
. Hence, the “post-assembly magnetization” (PAM) represents a
potential solution. Fig. 1(a) presents the conventional manufacture process for rare-earth
PM motors while Fig. 1(b) illustrates the process with PAM. Problems occur in the steps of magnet insertion and
rotor assembly (Fig. 1(a)), and this makes it difficult to produce large PM motors with high power. With PAM, the
motor is fully assembled before the magnets are magnetized by applying a current pulse to the motor windings
(this is commonly used for cheaper and smaller ferrite magnet machines). Fig. 1(b) shows that magnetization is
performed in the last step and the assembly of the machine is more straightforward.
Fig. 1 Manufacturing processes for brushless PM machines (a) Conventional manufacture (b) Post-assembly
magnetization
This paper presents the design of rare-earth surface-mounted PM (SPM) motors for manufacture with PAM. In the
design procedure, magnetic circuit modeling is used in conjunction with a process for addressing the PAM. In this
magnetization, a large current impulse is required to fully magnetize the magnets, and such current usually creates
a large magnetic field that saturates the stator core material. The relative permeability becomes almost unity at the
instant of magnetization. This paper makes use of this phenomenon in the design derivation for PAM. A 6 kW
SPM motor was designed to demonstrate the proposed method. The design was then simulated using finite element
analysis. To experimentally verify the proposed process, a 400 W SPM prototype was designed and magnetized.
Derivation of Design Process
Post-assembly or in-situ magnetization techniques have been investigated
[1-6]
but no systematic design so far is
proposed. The process derived in this paper is detailed in the following.
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Research Express@NCKU - Articles Digest
Material Permeability at Large Magnetizing Currents
The magnetizing current required for full PAM is approximately 3-4 times the coercivity current for NdFeB
magnet material
[5]
, although
[4]
find that 2-2.5 times is sufficient.
Design Process
The design process considers both the “parameter design for motor operation” and the “magnetizing current for
PAM”. As can be seen in Fig. 2, at Point A of the machine geometry, there is a filamentary conductor with the
same number of turns as the belt of magnetizing coil sides (distributed over several slots) so that it represents the
MMF center for the magnetization. The winding layout for one phase and the connection of the two phases for
magnetization are shown in Fig. 3. The magnetizing terminal current or phase current I
ph
is 2I
mag
because there are
two parallel connections in a phase winding.
Fig. 2 MMF center and flux density for magnetization.
The relationship between I
mag
, R
o
and r
o
for the required magnetizing flux density can be used to calculate the
required current for magnetization. The slot-fill factor is a critical factor for design with PAM. This is because the
conditions for both magnetization and motoring operation should both be satisfied.
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Research Express@NCKU - Articles Digest
Fig. 3. Coil arrangement and orientation of one phase (2 parallel paths formed from 2 series coils) and
magnetization connections. Phase B could be used, or Phases A and C, as used in the simulation and experimental
work.
To summarize, in the proposed design process, R
o
and r
o
are first calculated from the motor specification (e.g., the
slot-fill factor and back EMF constant). For a calculated R
o
and r
o
combination, the magnetizing current can be
determined to satisfy the design. A computer program has been developed using this method to calculate the
magnetizing current.
Design Results and Simulation
Initial Design Specification
A 4-pole 18-slot 6 kW machine is studied. The curves in Fig. 4 show the relationships between r
o
and R
o
for the
defined back EMF constant. The solid curves represent I
mag
from 500 A to 2 kA for various r
o
and R
o
combinations under the prescribed field intensity at Point C of Fig. 2. In Fig. 4, at the design point, 1.8 kA should
be sufficient to produce the magnetic field (2.5 times the magnet coercivity) required to fully magnetize the motor.
This can be considered as the lower bound.
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Research Express@NCKU - Articles Digest
Fig. 4. Relationship of I
mag
, r
o
and R
o
. 1800 A is sufficient to supply 2.5 times the magnet coercivity at the design
point for full magnetization.
Magnetization Validation
Fig. 5(a) shows a flux plot for an applied magnetizing pulse on the designed SPM motor. The winding layout of
one phase is shown in Fig. 3. This simulation was carried out using ANSOFT finite element software. The winding
current generates a magnetic flux which correctly magnetizes the four-pole rotor. The flux pattern illustrates that
there is high saturation since there appears to be only little material boundary. Also, the field intensities in different
locations shown in Fig. 5(b) are sufficient to magnetize the magnets.
Fig. 5. Simulation results: (a) SPM motor with magnetization flux (2 kA coil current) and (b) Magnet field
intensities at different parts of the magnet during magnetization (with 2 kA coil current) - sufficient to magnetize
the motor. The unit of M is 10
6
A/m.
Experimental Study
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