Online proceedings - EDA Publishing Association

device consisted of a bimorph cantilever with a permanent
magnet located at the cantilever tip. The size of the bimorph
and the permanent magnet is 28 × 13.4 × 9 (mm 3 ) and 5 × 5
× 2 (m 3 ), respectively. The remanence magnetization B r is
assumed as 1.2 T. Fig. 5 shows a simple measurement set-up
for preliminary demonstration by the macro-scale device. The
output voltage, arising from the direct current supplied by a DC
power supply (AND Co. AD-8735A, JPN), is measured by an
oscilloscope (Tektronix Co. TDS2014, USA). The applied
direct current is measured by a current probe (Tektronix Co.
TCP312, USA). The output voltage and the applied direct
current were measured with a 2msec sampling interval.
However, the center of the permanent magnet is located at 25.5
mm from the base of cantilever and 4.1 mm from the center of
the appliance cord.
11-13 May 2011, Aix-en-Provence, France
impulse signal and the applied DC current. The sensitivities of
the macro-scale device were derived as around 7 mV/A and 5
mV/A for the cases of turning on and turning off the DC power
supply, respectively.
Fig. 6. A typical measurement showing the output voltage impulses when a
direct current of 2A was applied to a two-wire appliance cord (ON), and when
the applied current was discontinued (OFF), respectively, as shown in Fig. 5.
The output voltage from the current probe was also drawn for comparison.
Fig. 4. A macro-scale prototype DC current sensor with a permanent magnet
on the tip of the piezoelectric bimorph cantilever was fabricated
for demonstration measurements.
Fig. 7. The peak values (in error bar) of the output voltage impulse as a function
of the applied direct current, as measured in Fig. 6.
V. DESIGN OF MEMS-SCALE DC SENSOR DEVICES
Fig. 5. Measurement set-up for demonstration measurements by the fabricated
macro-scale device shown in Fig. 4.
As a result, we succeeded in measuring the impulsive values
of the output voltage by the macro-scale device for the first time.
Fig. 6 typically shows that the output voltage impulse signal was
clearly detected out when 2A was applied to a two-wire
appliance cord. The peak value was measured as -10 mV when
turning on the DC power supply, while that was measured as 17
mV when turning off the DC power supply. The output voltage
impulse signal converged to zero within 0.07 sec. Such
measurement can be conducted from a lower applied current of
0.5 A to a higher one of 3 A. Fig. 7 shows a linear relation
between the absolute peak values (in error bar) of output voltage
A. StructuralDesign with An Applicable Approach
We assume that the measurement system for the
MEMS-scale DC sensor employ a microcomputer built-in A/D
converter with the resolution capability of 12 bit and the
reference voltage of 3 V. In the case of future DC houses, it is
also reasonable to further assume that a direct current supplied
to the home electrical appliance is in the range of 0.04 A to 10
A. It is therefore very crucial to carry on such kind of a
structural design to make the MEMS-scale DC sensor not only
measure a detectable impulse signal of over 0.74 mV even
when a very lower direct current of 0.04A is applied, but also be
able to bear off the stronger bending when a higher direct
current of 10 A is applied. Generally, the piezoelectric sensors
work with a charge amplifier driven by an electrical power. It is
thus necessary to design a novel sensor device which can
generate enough high voltage by itself so as to meet our future
powerless working requirement.
Fig.8 gives a schematic showing such kind of design
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