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11-13 May 2011, Aix-en-Provence, France Developing MEMS DC Electric Current Sensor for End-use Monitoring of DC Power Supply Kohei Isagawa 1 , Dong F. Wang 1 , Takeshi Kobayashi 2 , Toshihiro Itoh 2 and Ryutaro Maeda 2 1 Micro Engineering & Micro Systems Laboratory, Ibaraki University (College of Eng.), Hitachi, Ibaraki 316-8511 Japan (Tel: +81-294-38-5024; Fax: +81-294-38-5047; E-mail: dfwang@mx.ibaraki.ac.jp) 2 Ubiquitous MEMS and Micro Engineering Research Center (UMEMSME), AIST, Tsukuba, Ibaraki 305-8564, Japan Abstract- A non-drive, non-contact MEMS DC electric current sensor to satisfy the increasing needs of DC power supply for monitoring the electricity consumption by either one-wire or two-wire appliance cord has been proposed. A micro magnet is integrated into the MEMS-scale DC sensor and the appropriate position for locating the micro magnet has been theoretically pinpointed. A macro-scale prototype DC sensor was therefore fabricated, and an impulse piezoelectric voltage output can be clearly detected out when a DC electric current was applied to a two-wire electrical appliance cord. A linear relationship between the detected peak value of the impulse output voltage and the applied DC electric current was further obtained based on the empirical measurements. After the demonstration of the macro-scale prototype DC sensor, the MEMS-scale DC sensor has been then theoretically designed from the view point of reasonable output voltage measurements, and preliminarily micro-fabricated for further characterizations. Keywords- MEMS DC sensor; Electricity end-use monitoring; DC power supply; PZT; Non-drive; Non-contact; Two-wire cord I. INTRODUCTION The energy consumption by factories, automobiles and even human’s daily life make the increase of CO 2 exhaust, which subsequently aggravates the green-house effect. The total amount of CO 2 exhaust in Japan in 2008 was 1.21 billion ton, and about one of thirds was caused by residential section and commercial section. About 40% of the amount of CO 2 is caused by electrical consumption of household equipment and Information and Communication Technology (ICT) devices. Moreover, in Japan, the electricity consumption of ICT devices will increase by about 4.2 times by the year of 2025. The electricity consumption of internet data center (IDC) is also rapidly increasing with the increasing amount of the data traffic on the internet. It is estimated to grow by two order of its present value by the year of 2025 [1]. In addition, IDC have been anticipated to achieve a decrease in AC to DC conversion loss. Something similar is being conducted at DC houses consisting of a solar battery or a storage cell. Therefore, it is essential to monitoring the DC electricity consumption so as to establish an effective electricity management system. Although Hall element based direct current sensor is the main stream at the present day. However, since the household equipment and ICT device use two-wire appliance cord, the Hall element based direct current sensors can not be applied directly without a line separator to first separate the two-wire appliance so as to measure the current. In addition, a drive voltage is physically necessary for the Hall element based sensors, which is inconvenient to monitor electrical consumption at anytime and anywhere without a power supply. In this work, a novel MEMS DC sensor, which is self-driven and applicable to both one-wire and two-wire appliance cord, has been proposed, designed, and preliminarily investigated. The proposed MEMS DC sensor is believed to be very useful to various kinds of DC systems in the near future. II. PORPOSING MEMS-SCALE DC SENSOR AND ITS APPLICATION TO TWO-WIRE ELECTRICAL APPLICANCE CORD The proposed MEMS DC sensor, as shown in Fig. 1, is expected to be utilized for monitoring the electricity consumption by one-wire or two-wire appliance cord. The critical component, which is encapsulated in the green shell, is a cantilever made up of piezoelectric film and a permanent micro-magnet fixed on the end. When a direct current from DC power supply is flowed via a two-wire appliance cord, the piezoelectric film coated cantilever is bended by the created magnetic force acted on the micro magnet, and the output voltage is generated by the piezoelectric film and the applied DC current is therefore detected out. Fig. 1. A newly proposed non-drive and non-contact MEMS DC sensor for end-use monitoring of DC power supply. 231
Compared with commercially available current sensors, the proposed MEMS DC electric current sensor has several advantages such as non-drive, non-contact, and capability in sensing one-wire to two-wire appliance cord. In this study, a macro-scale prototype DC sensor was also fabricated and demonstrated to confirm whether the impulse (momentary) output voltage signal from DC current could be clearly detected out or not. III. MAGNET’S POSITION WITH A RESPECT TO THE GENERATED MAGNETIC FILED The magnetic force on a permanent magnet in a magnetic field is proportional to the integral of the field gradient over the magnet’s volume [2 - 4]. If the magnet comes close to a long current-carrying cord, the magnetic forces in the plane normal to the wire can be described by Equation (1). ( ) 11-13 May 2011, Aix-en-Provence, France pervious study [5]. d d = BF ry ∫ d = BF VH ( ) dy ∫ d (1) rz VH dz dH z dz ⎛ ⎜ π ⎝ ( − ) a + ⎞ + yi ay )( ⎟ (4) +− zay ))( ++ zay ⎠ ( −= 222 ))( 222 Fig. 3 plots the z-direction gradient of the y-component of the magnetic field surrounding a two-wire appliance cord. The dash lines in Figs. 2 and 3 mean the maximum value of the z-direction gradient of the z-component of the magnetic field for a single wire or a two-wire appliance cord, respectively. In the above Equation, y and z are horizontal and vertical direction, respectively, F is the magnetic force on the magnet, H y and H z are horizontal and vertical components of magnetic field in amperes pre meter, B r is the remanence of permanent magnet in Tesla, and V is the magnet’s volume. Assuming that the remanence of the permanent magnet is uniform and aligned in the positive z-direction. In order to analyze the magnetic field gradient all around an electric power cord, the magnetic field surrounding a single current-carrying cord should be considered and is described by Equation (2). Fig. 2. Plot of the magnitude of the vertical component of z-direction magnetic field gradient around a single wire, 10 A current assumed. i H = (2) 2πr H is the magnetic field in amperes per meter, i is the current in wire (A), and r is radial distance from the wire to point of interest. The direction of H is determined using the ‘right-hand rule’, aligning the thumb of the right hand with direction of flowing current. Equation (3) can thus be inducted from Equation (2) for z-direction gradient of the z-component of the magnetic field surrounding a single wire. dH z iyz −= (3) dz π + zy 222 )( Fig. 2 plots the y-direction gradient of the y-component of the magnetic field surrounding a single wire. In case of a two wire appliance cord, we define a as the distance between the center of the appliance cord and the center of right cord or lift one. Then, we induct the z-direction gradient of the y-component of the magnetic field surrounding a two-wire appliance cord by Equation (4) which reported in our Fig. 3. Plot of the magnitude of the vertical component of z-direction magnetic field gradient around a two-wire appliance cord, 10 A current assumed. IV. DEMONSTRATION MEASUREMENTS BY USING A MACRO-SCALE DC SENSOR DEVICE Generally speaking, when a direct current is applied to the appliance cord, the output signal from the proposed cantilever based MEMS DC sensor is supposed to be very impulsive. Therefore a macro-scale device, as shown in Fig. 4, has been fabricated to demonstrate whether the output signal arising from direct current can be measured or not. The macro-scale 232
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COLLECTION OF PAPERS PRESENTED AT T
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Table of Contents Wednesday 11 May
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PANEL DISCUSSION TEXTILE MICROSYSTE
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Friday 13 May SESSION C4: APPLICATI
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SPECIAL SESSION OF BIO-MEMS/NEMS a
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suspended membrane can be pulled to
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that detectors may measure the diff
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2) Cavity width effect To verify th
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Fig.9. Capacitive sensor output, Va
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! TABLE 3 SUMMARY OF SELECTIVITIES
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The fabrication of optical Cap-Wafe
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the glass is polished down in a cos
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Fig. 14. Time history of the envelo
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Y X Fig. 1. Scanning electron mic
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10 3 11-13 May 2011, Aix-en-Proven
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Intenstiy (counts/second) Fig. 1. X
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piezoelectric displacement transduc
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Figure 7 Displacement conditions of
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A. Continuous domain Starting from
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700 11-13 May 2011, Aix-en-Provenc
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o o o o o o o o Check applicability
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C. Identification Results The ident
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teen wire segments of a coil, as in
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B. Implemented die overview A die c
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IN CLK OUT Fig. 16. Probe setup for
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adhesive material with 30μm thickn
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B. Dynamics of Energy Flows For a l
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80˚C. Additionally, we looked into
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The XRD shows a peak above the 2θ
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fibers which define the electric co
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Figure 15. Key board input system.
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ρ = h 2∆α∆T + + E 1h 3 1 +E 2
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In recent years, the pipe flow moni
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inches silicon wafers which have th
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samples tested in different vacuum
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l c 11-13 May 2011, Aix-en-Provence
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Vp (V) 3,5 3,0 2,5 2,0 1,5 1,0 0,5
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II. MATHEMATICAL MODEL AND NUMERICA
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fluids travel along a curved channe
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measured mixing indices are depicte
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length, which enables them to focus
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Page 230 and 231: electrocardiogram. • The heart be
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followed by titanium (Ti) which sho
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exposure dose, post exposure bake t
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B. Energy Applications Society is f
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Presently, the microfabrication pro
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[6] C. Richard, A. Renaudin, V. Aim
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NA sinθ c 11-13 May 2011, Aix-en-
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the waveguide on the fused silica,
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microphone diaphragm. The chosen CM
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TABLE V MICROPHONE CHARACTERISTICS
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Figure 7b shows the effect of a par
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over the temperature range (i.e. th
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given. This allows a CTM model to b
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the magic-Tee, and the coherent sig
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After analyzing the two conditions
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IV. MICRO FABRICATION For fabricati
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IV. A. Simulation and Sensitivity A
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grown to sub-confluence were washed
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Clamps rotation [21] Clamps transla
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Layout Total dimensions of the grip
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focusing increased both as the stre
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Time of diffusion (hr) 1200 1000 80
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Chip Magnet Light source Hot plate
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This phenomenon is now reaching the
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The VerilogA block code is : 11-13
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Author Index Abi-Saab D. 81 Aimez V
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Nussbaum Dominic 273 O’Hara T. 35
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