Abstract:
Disclosed herein is a low-power proximity AC current sensor. A low-power proximity AC current sensor according to the present invention includes a magnetic material having a location that changes depending on the intensity of a magnetic field formed outside the magnetic material; a piezoelectric film disposed at a location adjacent to the magnetic material and configured to generate electric charge due to a change in location of the magnetic material; and a substrate for securing the piezoelectric film. Another low-power proximity AC current sensor according to the present invention includes a magnetic material having a location that changes depending on the intensity of a magnetic field formed outside the magnetic material; corresponding electrodes disposed at a location adjacent to the magnetic material and configured to vary capacitance depending on a change in location of the magnetic material; and a substrate for securing the piezoelectric film.

Description:
[0001]     Pursuant to 35 U.S.C. § 119(a), this application claims the benefit of earlier filing date and right of priority to Korean Patent Application No. 10-2004-0091066 and 10-2004-0103821, filed on Nov. 9, 2004 and Dec. 9, 2004, the content of which is hereby incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The document relates to a low-power proximity Alternating Current (AC) current sensor.  
         [0004]     2. Description of the Related Art  
         [0005]     In general, AC current sensors are classified into ampere meter-type sensors that detect current using electromagnetic force generated between current flowing through a coil and a magnet, hall sensors that use the Hall effect, and Great Magneto-Resistance (GMR)-type current sensors that detect variation in magneto-resistance.  
         [0006]      FIG. 1  is a schematic diagram illustrating the construction of a typical ampere meter and the arrangement of the components thereof. The ampere meter is generally connected in series to a conducting line through which current flows, and measures the amount of current in the conducting line using the electromagnetic force that is generated between a magnetic field generated by current flowing through a movable coil wound on a soft iron core, and a permanent magnet mounted in the ampere meter.  
         [0007]     However, the ampere meter-type current sensors are difficult to install because they are directly connected to conducting lines through which current flows, and are disadvantageous in that they have many movable components and are large, thus being expensive. Meanwhile, the hall sensors and the GMR-type current sensors have advantages in size and ease of installation over the ampere meter-type current sensors, but are disadvantageous in that power is consumed because power is supplied to the sensors and the sensors are operated using the power. These types of sensors are unsuitable for use in sensor networks because of their size, price and power consumption.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a low-power proximity AC current sensor that measures the amount of AC current flowing through a conducting line using electromagnetic force that is applied to a magnetic material, which is attached to the sensor, by a magnetic field induced by the current flowing through the conducting line.  
         [0009]     In order to accomplish the above object, the present invention provides a low-power proximity AC current sensor, including a magnetic material having a location that changes depending on the intensity of a magnetic field formed outside the magnetic material; a piezoelectric film disposed at a location adjacent to the magnetic material and configured to generate electric charge due to a change in location of the magnetic material; and a substrate for securing the piezoelectric film.  
         [0010]     Furthermore, the present invention provides a low-power proximity AC current sensor, including a magnetic material having a location that changes depending on the intensity of a magnetic field formed outside the magnetic material; corresponding electrodes disposed at a location adjacent to the magnetic material and configured to vary capacitance depending on a change in location of the magnetic material; and a substrate for securing the piezoelectric film.  
         [0011]     In order to implement a low-power sensor, the present invention uses a method of detecting a piezoelectric effect varying depending on current and a method of detecting variation in capacitance. Furthermore, the present invention provides a low-power proximity AC current sensor that can detect the amount of current only by causing the sensor to approach a conducting line through which the current flows, without an electrical connection, unlike an existing current sensor that is connected to the interior of an electrical circuit formed by a conducting line for which the amount of current is detected.  
         [0012]     The low-power proximity AC current sensor according to the present invention basically includes a cantilever, a bridge, a membrane movable structure, and a magnetic material and a sensing part provided in the movable structure. The magnetic material of the proximity current sensor according to the present invention is subjected to force due to an induced magnetic field generated by AC current around the conducting line, therefore the movable structure is moved, thus resulting in the deformation and displacement thereof. Such deformation or displacement is detected using a piezoelectric effect or variation in capacitance.  
         [0013]     In particular, the AC current sensor according to the present invention can detect current only by being attached to a predetermined location, such as a covering part, that is adjacent to the conducting line through which the AC current flows. Since the piezoelectric effect and variation in capacitance are generated due to the movement of the movable structure, power consumption can be considerably reduced. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0015]      FIG. 1  is a perspective view illustrating the internal structure of a typical ampere meter;  
         [0016]      FIG. 2  is a perspective view of a low-power proximity AC current sensor according to an embodiment of the present invention;  
         [0017]      FIGS. 3A  to  3 F are perspective views showing various examples of low-power proximity AC current sensors according to embodiments of the present invention;  
         [0018]      FIG. 4  is a perspective view showing an example of the mounting of the low-power proximity AC current sensor according to the embodiment of the present invention;  
         [0019]      FIG. 5  is a conceptual view illustrating the operational principle of the low-power proximity AC current sensor according to the embodiment of the present invention;  
         [0020]      FIGS. 6A and 6B  are perspective views of a low-power proximity AC current sensor having an additional external noise removal function according to an embodiment of the present invention;  
         [0021]      FIG. 7  is a perspective view of a capacitance detection-type low-power proximity AC current sensor according to an embodiment of the present invention;  
         [0022]      FIGS. 8A  to  8 F show various examples of the capacitance detection-type low-power proximity AC current sensor according to an embodiment of the present invention;  
         [0023]      FIG. 9  shows an example the mounting of the capacitance detection-type low-power proximity AC current sensor according to the embodiment of the present invention;  
         [0024]      FIG. 10  is a conceptual view illustrating the operating principle of the capacitance detection-type low-power proximity AC current sensor according to an embodiment of the present invention; and  
         [0025]      FIGS. 11A and 11B  are perspective views of a capacitance detection-type low-power proximity AC current sensor having an external noise removal function according to an embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.  
         [0027]      FIG. 2  is a perspective view of a low-power proximity AC current sensor  20  according to an embodiment of the present invention.  
         [0028]     In this embodiment, the low-power proximity AC current sensor  20  includes a magnetic material  21 , a piezoelectric thin film  22 , an upper plate wire  23 , a lower plate wire  24  and a substrate  25 .  
         [0029]     In  FIG. 2 , a structure in which the low power AC current sensor  20  is formed of the piezoelectric film  22  is schematically illustrated.  
         [0030]     Referring to  FIG. 2 , a depression  26  is formed in the substrate  25  at a location that is slightly biased from the center thereof to one side. The piezoelectric film  22  is formed over the depression  26 . The location of the depression  26  is not limited to the one described above, but can be any location on the substrate  25  as long as the piezoelectric film  22  is allowed to move freely.  
         [0031]     The magnetic material  21  is layered on the piezoelectric film  22 . A pair of electrode wires  23  and  24  is formed at one side of the piezoelectric film  22 . The upper plate wire  23  is brought into contact with the upper surface of the piezoelectric film  22 , while the lower plate wire  24  is connected to the lower surface of the piezoelectric film  22 . In the above-described embodiment, the piezoelectric film  22  has a cantilever shape. The piezoelectric film  22  may have various shapes. A method of forming the piezoelectric film  22  will be described in detail below with reference to  FIG. 3 .  
         [0032]     The piezoelectric film  22  generates electric charge by the deformation thereof. It is preferred that Rochelle salt or barium titanate, having a high piezoelectric effect, be used as the material of the piezoelectric film  22 .  
         [0033]     The piezoelectric film  22  is deformed by the movement of the magnetic material  21 . If a magnetic field is formed around the piezoelectric film  22  and the magnetic material  21  formed on the piezoelectric film  22  moves, the piezoelectric film  22  is deformed accordingly. The change in location of the magnetic material is proportional to the magnitude of the surrounding magnetic field.  
         [0034]     The electrode wires  23  and  24  function to guide the electric charge, which is generated in the piezoelectric film  22 , to a predetermined measuring device (not shown) in order to measure the amount of charge generated in the piezoelectric film  22 .  
         [0035]     In summary, when AC current is formed in a typical conducting line, a magnetic field is formed around the conducting line in proportion to the amount of current, the location of the magnetic material  21  changes in proportion to the magnitude of the magnetic field, and the amount of electric charge formed in the piezoelectric film  22  changes depending on the change in location of the magnetic material  21 , so that the amount of current can be measured.  
         [0036]      FIGS. 3A  to  3 F show various examples of a low-power proximity AC current sensor according to embodiments of the present invention.  
         [0037]      FIG. 3A  shows a cantilever-shaped low-power proximity AC current sensor in which a magnetic material  31   a  is deposited on the entire surface of a piezoelectric film  32   b .  FIG. 3B  shows a bridge-shaped low-power proximity AC current sensor in which a magnetic material  31   b  is deposited on part of a piezoelectric film  32   b .  FIG. 3C  shows a bridge-shaped low-power proximity AC current sensor in which a magnetic material  31   c  is deposited on the entire surface of a piezoelectric film  32   c .  FIG. 3D  shows a thin film-type low-power proximity AC current sensor in which a magnetic material  31   d  is deposited on the entire surface of a piezoelectric film  32   d .  FIG. 3E  shows a thin film-type low-power proximity AC current sensor in which a magnetic material  31   e  is deposited on part of a piezoelectric film  32   e .  FIG. 3F  shows an AC sensor from which the magnetic material of the thin film type AC sensor shown in  FIG. 3D  or  3 E is removed. It is preferred that a depression  32   f  formed in the substrate of the AC sensor having the thin film shape be larger than those formed in the AC sensors having the cantilever and bridge shapes.  
         [0038]      FIG. 4  shows an example of the mounting of the low-power proximity AC current sensor according to the embodiment of the present invention.  FIG. 5  is a conceptual view illustrating the operational principle of a low-power proximity AC current sensor  20  according to the embodiment of the present invention.  
         [0039]     Referring to  FIG. 5 , a concentric circle-shaped magnetic field is generated around a conducting line  41  due to current flowing through the conducting line  41 . The low-power current sensor  20 , including a piezoelectric film to which a magnetic material is attached, is moved by the magnetic field. As shown in  FIG. 5 , in the case of the piezoelectric film made of a piezoelectric material, an electric charge is generated by the movement of the piezoelectric film, the voltage or current of which can be measured.  
         [0040]      FIGS. 6A and 6B  are perspective views of a low-power proximity AC current sensor package having an additional external noise removal function according to an embodiment of the present invention.  
         [0041]     In this embodiment, in the low-power proximity AC current sensor package, a reference sensor  61  is further included in the low-power proximity AC current sensor  20  shown in  FIG. 2 .  
         [0042]     In  FIGS. 6A and 6B , the shape of the reference sensor  61  is schematically illustrated.  
         [0043]     Referring to  FIG. 6A , the reference sensor  61  has the same construction as the current sensor shown in  FIG. 2  except that a depression is not formed in the portion of a substrate  25  where the reference sensor  61  is formed. In general, noise components as well as a signal generated from current always exist around a conducting line through which the current flows. In order to remove the external noise components, the reference sensor  61  may additionally be used. For the same current input, the reference sensor  61  generates only noise components in which the movement of a corresponding electrode is not included. Therefore, when the two signals are subtracted from each other, a pure signal generated by the current can be detected.  
         [0044]     The method of measuring current depending on variation in the amount of charge, which is generated in the piezoelectric film depending on variation in a surrounding magnetic field, has been described above. A sensor for measuring current by measuring variation in capacitance, not by using the piezoelectric effect, will be described below.  
         [0045]      FIG. 7  is a perspective view of a capacitance detection-type low-power proximity AC current sensor according to an embodiment of the present invention.  
         [0046]     In the above embodiment, the low-power proximity AC current sensor includes a magnetic material  71 , corresponding electrodes  72  and  73 , a support  74 , electrode wires  75  and  76 , and a substrate  77 .  
         [0047]     In  FIG. 7 , a structure in which the corresponding electrodes  72  and  73  are formed on the substrate  77  is schematically illustrated.  
         [0048]     Referring to  FIG. 7 , the corresponding electrodes  72  and  73  are formed on the top of the substrate  77 . The magnetic material  71  is layered on the top of the corresponding electrodes  72 . The corresponding electrodes  72  and  73  are formed such that the upper plate  72  and the lower plate  73  face each other and have a predetermined gap therebetween. It is preferred that the predetermined gap between the upper plate  72  and the lower plate  73  be achieved by layering the support  74  having a predetermined thickness on one side of the lower plate  73  and layering the upper plate  72  on the support  74 .  
         [0049]     The electrode wires  75  and  76  are brought into contact with first sides of the upper plate  72  and the lower plate  73  that are in contact with the support  74 . It is preferred that the upper plate wire  75  be connected to the upper surface of a first side of the upper plate  72  and the lower plate wire  76  be connected to the lower surface of a first side of the lower plate  73 . In this embodiment, the current sensor may be formed in a cantilever shape. The corresponding electrodes  72  and  73  may be formed in various shapes. A method of forming corresponding electrodes will be described in detail below with reference to  FIG. 8 .  
         [0050]     The upper plate  72  is deformed by the movement of the magnetic material  71 . When the magnetic material  71  formed on the upper plate  72  is moved by a magnetic field formed around the upper plate  72 , the upper plate  72  is deformed. The location of the magnetic material  71  changes in proportion to the magnitude of a surrounding magnetic field. As the upper plate  72  is deformed, the distance between the upper plate  72  and the lower plate  73  varies. This variation changes the capacitance between the two electrodes  72  and  73 . Therefore, the capacitance changes in proportion to the amount of the magnetic field formed around the conducting line, so that the magnitude of a magnetic field can be easily measured.  
         [0051]     The electrode wires  75  and  76  function to guide the electric charge, which is formed by the upper and lower plates  72  and  73 , to a predetermined measuring device (not shown) in order to measure an electrical signal depending on the capacitance formed between the corresponding electrodes  72  and  73 .  
         [0052]     In summary, when AC current is formed in a typical conducting line, a magnetic field is formed around the conducting line in proportion to the amount of the current, the location of the magnetic material  71  changes in proportion to the magnetic field, the upper plate  72  of the corresponding electrodes is deformed depending on the change in location of the magnetic material  71 , and the distance between the upper plate  72  and the lower plate  73  of the current sensor varies depending on the change. Therefore, the amount of capacitance formed by the upper plate  72  and the lower plate  73  varies, so that the amount of current can be measured.  
         [0053]      FIGS. 8A  to  8 F show various examples of a capacitance detection-type low-power proximity AC current sensor according to an embodiment of the present invention.  
         [0054]      FIG. 8A  shows a cantilever-shaped capacitance detection-type low-power proximity AC current sensor in which a magnetic material  81   a  is formed on the entire upper surface of an upper plate  82   a . The structure of this embodiment is almost the same as that shown in  FIG. 7 . However, the magnetic material provided in the capacitance detection-type low-power proximity AC current sensor shown in  FIG. 7  is layered on part of the upper plate, whereas the magnetic material in this embodiment is layered on the entire surface of the upper plate  82   a . The sensor has a support  83   a  disposed between the first sides of the corresponding electrodes  82   a  and  84   a , thus forming a gap.  
         [0055]      FIG. 8B  shows a capacitance detection-type low-power proximity AC current sensor in which a magnetic material  81   b  is formed on part of an upper plate  82   b . The structure of this embodiment is the same as that shown in  FIG. 7  except that the magnetic material  81   b  is layered at the center of the upper plate  82   b , but not on one side of the upper plate  82   b . In addition, supports  83   b  are formed not only on first sides of the corresponding electrodes  82   a  and  84   a  but also on second sides thereof. Therefore, a gap is formed between the upper and lower plates  82   b  and  84   b  by the supports  83   b . In the present embodiment, the distance between the central portions of the corresponding electrodes  82   b  and  84   b  varies depending on variation in an external magnetic field, thus resulting in variation in capacitance.  
         [0056]      FIG. 8C  shows a capacitance detection-type low-power proximity AC current sensor in which a magnetic material  81   c  is formed on the entire surface of the upper plate  82   c  of the current sensor. The structure of the present embodiment is the same as that of  FIG. 8B  except that the magnetic material  81   c  is formed on the entire surface of the upper plate  82   c . The sensor also has supports  83   c  formed on both sides of corresponding electrodes  82   c  and  84   c.    
         [0057]      FIG. 8D  shows a thin film-shaped capacitance detection-type low-power proximity AC current sensor in which a magnetic material is formed on the entire upper surface of the current sensor. The structure of the present embodiment is the same as that of  FIG. 8C  except that the shapes of corresponding electrodes  82   d  and  84   d  have thin film shapes that extend over the entire substrate of the sensor.  
         [0058]      FIG. 8E  shows a thin film-shaped capacitance detection-type low-power proximity AC current sensor in which a magnetic material is formed on part of the upper surface of a corresponding electrode. The structure of the present embodiment is almost the same as that of  FIG. 8   d  except that a magnetic material  81   e  layered on the upper surface of an upper plate  82   e  is formed at the center portion of the current sensor.  
         [0059]      FIG. 8F  is a sectional view of the low-power proximity sensor shown in  FIG. 8E . A gap is also formed between corresponding electrodes  82   e  and  84   e.    
         [0060]      FIGS. 9 and 10  show a state where the capacitance detection-type low-power proximity AC current sensor  70  according to the embodiment of the present invention is attached to a conducting line  90 .  
         [0061]     Referring to  FIG. 9 , the capacitance detection-type low-power proximity AC current sensor  70  operates at a location that is adjacent to the conducting line  90 . The operation of the sensor  70  will be described with reference to  FIG. 10 . A concentric circle-shaped magnetic field is generated around the conducting line  90  due to current flowing through the conducting line  90 , and an upper plate to which a magnetic material is attached is moved by the magnetic field. As shown in  FIG. 10 , the capacitance type low-power proximity AC current sensor  70 , including the corresponding electrode to which the magnetic material is attached, has varying capacitance depending on the movement of the upper plate, and, thus, can detect the varying capacitance as an electrical signal.  
         [0062]      FIGS. 11A and 11B  are perspective views of a capacitance detection-type low-power proximity AC current sensor having an external noise removal function according to an embodiment of the present invention.  
         [0063]     In the present embodiment, the low-power proximity AC current sensor further includes a reference sensor  100 .  
         [0064]     Referring to  FIGS. 11A and 11B , the reference sensor  100  includes a single electrode  102 , and a magnetic material  101  is layered on the upper surface of the electrode  102 . It is preferred that the plate  102  of the reference sensor be the same as an upper plate  74  and the magnetic material  101  of the reference sensor  100  be the same as the magnetic material  71  of a current sensor. Noise components as well as a signal generated from current always exist around a conducting line through which the current flows. In order to remove the external noise components, the reference sensor  100  may be additionally provided. For the same current input, the reference sensor  61  generates only noise components from which the influence of the movement of corresponding electrodes  72  and  73  is excluded. Therefore, when the two signals are subtracted from each other, a pure signal generated by the current can be detected.  
         [0065]     As described above, in accordance with the present invention, the low-power proximity current sensor of the present invention, which can be fabricated using micro-machine technology and a semiconductor process, can be integrated with a semiconductor circuit, thus implementing an integrated micro-miniature proximity current sensor.  
         [0066]     Furthermore, the AC current sensor employs a method of detecting variation in capacitance, so that the AC current sensor has low power consumption and can be used for applications that require low power and micro-sized sensors, such as a sensor network.  
         [0067]     In addition, the AC current sensor can measure current simply by being mounted on a conducting line through which the current flows, so that it has an advantage in that the installation thereof is easier than that of existing current sensors.  
         [0068]     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.