WO2014067462A1 - 一种验钞磁头 - Google Patents

一种验钞磁头 Download PDF

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Publication number
WO2014067462A1
WO2014067462A1 PCT/CN2013/086245 CN2013086245W WO2014067462A1 WO 2014067462 A1 WO2014067462 A1 WO 2014067462A1 CN 2013086245 W CN2013086245 W CN 2013086245W WO 2014067462 A1 WO2014067462 A1 WO 2014067462A1
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WO
WIPO (PCT)
Prior art keywords
magnetic
money
magnetic head
detecting
sensor chip
Prior art date
Application number
PCT/CN2013/086245
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English (en)
French (fr)
Inventor
迪克詹姆斯·G
刘明峰
白建明
诸敏
Original Assignee
江苏多维科技有限公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
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Application filed by 江苏多维科技有限公司 filed Critical 江苏多维科技有限公司
Priority to EP13851737.0A priority Critical patent/EP2916295B1/en
Priority to JP2015538279A priority patent/JP6276283B2/ja
Priority to US14/439,981 priority patent/US9721415B2/en
Publication of WO2014067462A1 publication Critical patent/WO2014067462A1/zh

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    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/04—Testing magnetic properties of the materials thereof, e.g. by detection of magnetic imprint
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
    • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
    • G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
    • G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
    • G01R15/20—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using galvano-magnetic devices, e.g. Hall-effect devices, i.e. measuring a magnetic field via the interaction between a current and a magnetic field, e.g. magneto resistive or Hall effect devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/028—Electrodynamic magnetometers
    • G01R33/0283—Electrodynamic magnetometers in which a current or voltage is generated due to relative movement of conductor and magnetic field
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
    • G01R33/09—Magnetoresistive devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
    • G01R33/09—Magnetoresistive devices
    • G01R33/091—Constructional adaptation of the sensor to specific applications
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C19/00—Digital stores in which the information is moved stepwise, e.g. shift registers
    • G11C19/02—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements
    • G11C19/08—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure
    • G11C19/085—Generating magnetic fields therefor, e.g. uniform magnetic field for magnetic domain stabilisation

Definitions

  • the invention relates to the technical field of magnetoresistive sensors, and in particular to a magnetic resistance counterfeit magnetic head.
  • the application of money detectors is very extensive, such as vending machines, money counters, and banknote inspection equipment.
  • the magnetic properties of the banknote are very weak, and therefore, the money-detecting magnetic head for recognizing the magnetic properties of the banknote needs to have characteristics of high sensitivity, low noise, and high signal-to-noise ratio.
  • Fig. 1 shows a prior art money detector magnetic head in which a sensor element detects a magnetic field component perpendicular to a head detecting surface which is generated by magnetic ink on a banknote.
  • the material used for such sensor elements is indium antimonide.
  • a money detector magnetic head composed of such a sensor element has the following disadvantages:
  • Indium antimonide sensors are affected by temperature and require complex temperature compensation circuits
  • the intrinsic noise of the indium antimonide sensor is relatively large, so the magnetic biasing element is required to provide a large bias signal to improve the signal-to-noise ratio, thereby causing a large volume of the magnetic biasing element, thereby causing a large volume of the money detecting head;
  • the present invention provides a magnetoresistive banknote magnetic head.
  • the magnetoresistive sensor used in the present invention can measure the magnetic field component generated by the object to be measured parallel to the detecting surface, and the magnetoresistive sensor can be a tunnel magnetoresistive sensor, a giant magnetoresistive sensor, or an anisotropic magnetoresistive sensor. .
  • a money detector magnetic head comprising:
  • a magnetoresistive sensor chip comprising a bridge circuit having a bridge arm having a magnetosensitive element, the sensitive direction of the magnetosensitive element being parallel to a detection surface of the money detector head;
  • a magnetic biasing unit located on a side of the magnetoresistive sensor chip remote from the detecting surface of the sound detecting magnetic head and spaced apart from the magnetoresistive sensor chip, the magnetic biasing unit having a recessed structure, the recessed structure being disposed such that The magnetic field generated by the magnetic biasing unit is small in a component parallel to the direction of the detecting surface such that the magnetic sensing element operates in a linear region.
  • the magnetic biasing unit includes a permanent magnet having a recess on a side facing the magnetoresistive sensor chip.
  • the magnetic biasing unit comprises a rectangular permanent magnet having a rectangular groove or a dimple perpendicular to the detecting surface on a side facing the magnetoresistive sensor chip.
  • the magnetic biasing unit comprises a rectangular permanent magnet and at least one pole piece having a rectangular recessed surface formed of a high magnetic permeability magnetic material.
  • the magnetic biasing unit comprises a rectangular permanent magnet and a rectangular annular pole piece composed of a high magnetic permeability magnetic material.
  • the magnetic biasing unit comprises two rectangular permanent magnets placed separately.
  • a non-magnetic material or a soft ferromagnetic material is placed between the two separately placed rectangular permanent magnets.
  • the magnetic bias unit generates a magnetic field having a component in the sensitive direction of the magnetosensitive element that is less than 25 Gauss.
  • the magnetic sensing element is a tunnel magnetoresistance (TMR) element, a giant magnetoresistance (GMR) element or an anisotropic magnetoresistive (AMR) element.
  • TMR tunnel magnetoresistance
  • GMR giant magnetoresistance
  • AMR anisotropic magnetoresistive
  • the magnetosensitive elements are TMR elements connected in series and / or in parallel, GMR elements connected in series and / or in parallel, or AMR elements connected in series and / or in parallel.
  • the magnetic head further includes a metal case accommodating the magnetoresistive sensor chip and the magnetic bias unit, the metal case having an opening on an opposite side of the head detecting face.
  • the magnetic head further includes a metal casing accommodating the magnetoresistive sensor chip and the magnetic biasing unit, the metal casing being provided with a grounding end.
  • the metal casing is filled with an injection molded body for fixing.
  • the money detecting magnetic head according to the present invention is suitable for identifying a banknote made of a hard magnetic material and for identifying a banknote made of a soft magnetic material;
  • the money detecting magnetic head according to the present invention adopts a magnetoresistive sensor including a magnetic sensing element such as a tunnel magnetoresistive TMR element, a giant magnetoresistive GMR element or an anisotropic magnetoresistive AMR element, and an indium antimonide Hall element
  • a magnetic sensing element such as a tunnel magnetoresistive TMR element, a giant magnetoresistive GMR element or an anisotropic magnetoresistive AMR element, and an indium antimonide Hall element
  • the sensitivity and signal-to-noise ratio of the above-mentioned magnetic sensing element are relatively high, so the money-detecting magnetic head of the present invention has higher sensitivity and signal-to-noise ratio;
  • the magnetic field generated by the concave magnetic biasing element has a small or close component to the sensitive direction of the magnetic sensitive element, so that the magnetic sensitive element can operate In the linear zone, it can ensure that the money detector head can work normally;
  • the magnetoresistive sensor chip of the money detecting magnetic head adopts a bridge structure, the money detecting magnetic head can effectively suppress interference from a common mode magnetic field other than the money detecting magnetic head;
  • the money detector magnetic head of the present invention can be used for both a money detector and a cash register;
  • the money detecting magnetic head according to the present invention uses a flexible wiring board to connect the printed wiring board and the output lead pin, and the flexible wiring board does not restrict the outer shape of the permanent magnet, which is advantageous for the design of the permanent magnet.
  • FIG. 1 is a schematic view of a money detector magnetic head of Comparative Example 1 of the prior art
  • FIG. 2(A) is a magnetic line distribution diagram of a magnetic field generated by a rectangular permanent magnet in the magnetic head shown in FIG. 1;
  • 2(B) is a magnetic field intensity distribution generated by a rectangular permanent magnet in the magnetic head shown in FIG. 1;
  • 3(A) is a magnetic line distribution diagram of a magnetic field generated by a rectangular permanent magnet in the magnetic head of Comparative Example 2 of the prior art;
  • 3(B) is a magnetic field intensity distribution generated by a rectangular permanent magnet in the magnetic head of Comparative Example 2 of the prior art
  • FIG. 4 is a schematic view of a money detector magnetic head according to an embodiment of the present invention.
  • FIG. 5 is a top plan view showing a money detector magnetic head according to an embodiment of the present invention.
  • Figure 6 (A) is a magnetic line distribution diagram of a magnetic field generated by a magnetic bias unit in a magnetic head according to Example 1 of the present invention
  • 6(B) is a magnetic field intensity distribution generated by a magnetic bias unit in a magnetic head according to Example 1 of the present invention
  • Example 7(A) is a magnetic line distribution diagram of a magnetic field generated by a magnetic bias unit in the magnetic head of Example 2;
  • Example 7(B) is a magnetic field intensity distribution generated by a magnetic bias unit in the magnetic head of Example 2;
  • Figure 7 (C) is a perspective view of a pole piece in the magnetic bias unit of Example 2.
  • Example 8(A) is a magnetic line distribution diagram of a magnetic field generated by a magnetic bias unit in the magnetic head of Example 3;
  • Example 8(B) is a magnetic field intensity distribution generated by a magnetic bias unit in the magnetic head of Example 3;
  • Figure 8 (C) is a perspective view of the magnetic bias unit in the magnetic head of Example 3.
  • 9(A) is a magnetic line distribution diagram of a magnetic field generated by a magnetic bias unit in the magnetic head of Example 4.
  • Fig. 9(B) is a magnetic field intensity distribution generated by the magnetic bias unit in the magnetic head of Example 4.
  • the money detector magnetic head includes a sensor chip 11, a printed wiring board (PCB) 12, an input/output pin 13, a metal case 14, a permanent magnet 15, and an injection molded body (not shown).
  • An opening of the metal casing 14 on a side away from the detecting surface is provided for assembly and extraction of the input and output pins.
  • the sensor chip 11 is mounted close to the detecting surface of the metal casing 14, and its magnetic sensitivity direction is perpendicular to the head detecting surface.
  • the sensor chip 11 and the permanent magnets 15 are respectively disposed on both sides of the printed wiring board 12.
  • the magnetization direction of the permanent magnet 15 is as shown in FIG. There is no direct contact between the printed wiring board 12 and the permanent magnets 15.
  • the input and output ends of the sensor chip 11 are soldered to respective terminals on the printed wiring board 12, respectively, so that the printed wiring board 12 can support and fix the sensor chip 11.
  • One end of the input/output pin 13 is soldered to the corresponding terminal of the printed wiring board 12, so that the input/output pin 13 is electrically connected to the input terminal and the output terminal of the sensor chip 11.
  • the other end of the input/output pin 13 serves as an output end of the money detecting head.
  • the sensor chip 11 employs an indium telluride Hall element, and the sensitive direction 17 of the indium antimonide Hall element is perpendicular to the detection surface of the magnetic head.
  • a ground pin 16 is provided on the metal casing 14.
  • a metal casing 14 provided with a ground pin 16 is used to shield electromagnetic interference from outside the metal casing 14 and to eliminate static electricity.
  • the shape of the permanent magnet 15 may be a rectangular parallelepiped.
  • the shape and size of the injection molded body are matched with the shape and size of the metal casing 14, the printed wiring board 12, and the permanent magnet 15, respectively, for fixing the metal casing 14, the printed wiring board 12, and the permanent magnet 15, and realizing the printed wiring board 12 and permanent Electrical isolation of the magnet 15.
  • the sensor chip of the money detecting magnetic head of Comparative Example 1 employs an indium telluride Hall element, and the sensitivity and signal-to-noise ratio of the money detecting magnetic head are very low. Since the manufacturing process of the indium telluride Hall element is complicated, and the influence of temperature and stress is very obvious, the yield is low, which results in a complicated processing method and a high cost of the money detecting head of the comparative example. On the other hand, since the end of the money-receiving head output pin of the comparative example is directly fixed on the printed circuit board, and the output pin cannot directly pass through the permanent magnet, the position of the output pin restricts the size of the permanent magnet and increases the design. Difficulty.
  • the permanent magnet of the money detecting magnetic head of Comparative Example 1 is a rectangular parallelepiped
  • the magnetic field generated by the rectangular permanent magnet has a large component along the sensitive direction of the MTJ element, causing the working point of the MTJ element to deviate from its linear operation.
  • the area even causes the resistance of the MTJ component to saturate the magnetic field, thereby affecting the performance of the money detector head and even causing the money detector head to malfunction.
  • Fig. 2(A) is a magnetic line distribution diagram of a magnetic field generated by a rectangular magnet in the money detecting magnetic head shown in Fig. 1.
  • the magnetization direction of the permanent magnet 15 having a rectangular cross-sectional structure in the drawing is perpendicular to the detecting surface 40, and the detecting surface is indicated by "AA” in the drawing.
  • the magnetoresistive sensor element 41 is located below the detection surface 40 and is placed in the "BB" direction in the drawing.
  • the magnetic lines of force of the magnetic field generated by the permanent magnet 15 are shown by the thin solid line 23 in the figure.
  • FIG. 2(B) shows a component 28 of the magnetic field generated by the permanent magnet 15 at the detecting surface parallel to the direction of the detecting surface and a component 27 perpendicular to the direction of the detecting surface, and the horizontal axis 29 indicates the offset of the position in the "AA" direction.
  • the sensor detects only the magnetic field component 27 perpendicular to the direction of the detection surface, so that the magnetic field component 28 parallel to the direction of the detection surface does not have any influence on the operation of the money verification magnetic head.
  • the biasing magnet must be modified to reduce the influence of the magnetic field generated by the permanent magnet parallel to the detecting surface on the sensor sensing signal.
  • 3(A) and 3(B) are magnetic field line distribution maps and magnetic field intensity distribution diagrams of magnetic fields generated by rectangular permanent magnets in the magnetic head of Comparative Example 2 of the prior art, respectively. Comparing Fig. 3(A) with Fig. 2(A), it can be seen that the biasing magnet 35 has a significantly increased area on the side adjacent to the sensor element 41. As can be seen from Fig. 3(A), the magnetization direction 21 of the permanent magnet 35 is perpendicular to the detection surface 40, and the detection direction is "AA" in the figure. The magnetoresistive sensor element 41 is located below the detection surface 40 and is placed in the "BB" direction in the drawing.
  • Fig. 3(B) shows a component 28 in which the magnetic field generated by the permanent magnet 35 is parallel to the direction of the detecting surface at the detecting surface and a component 27 perpendicular to the direction of the detecting surface, and the horizontal axis 29 indicates the offset of the position in the "AA" direction.
  • the magnetic field component 28 of the comparative example 2 parallel to the direction of the detecting surface is significantly smaller than the magnetic field component of the comparative example 1 of Fig. 2(B) parallel to the direction of the detecting surface.
  • Fig. 4 is a view showing the money detecting magnetic head of the embodiment of the present invention.
  • the magnetoresistive banknote magnetic head of the present invention comprises a magnetoresistive sensor chip 41, a printed wiring board 42, an input/output pin 43, a metal casing 44, a magnetic biasing unit 45 formed with a recessed structure, for example, a permanent magnet having a recess, a flexible wiring board (FPC) 46.
  • the first injection molded body 47 and the second injection molded body 50 have a detection surface 40.
  • the magnetic biasing unit formed with the recess is, for example, a permanent magnet having a rectangular groove on one side or a permanent magnet having a rectangular pit on one side.
  • the metal outer casing 44 is made of a non-magnetic wear resistant material and has an opening on a side away from the detecting surface 40.
  • the magnetoresistive sensor chip 41 is mounted in the metal casing 44 near the detecting surface 40.
  • the distance between the outer surface of the outer surface of the detecting surface 40 and the upper surface of the magnetoresistive sensor chip is less than or equal to 0.2 mm.
  • the magnetoresistive sensor chip 41 and the magnetic bias unit 45 are respectively located on both sides of the printed wiring board 42, and the recessed portion of the magnetic bias unit 45 faces the printed wiring board 42.
  • the magnetization direction of the magnetic bias unit 45 is perpendicular to the detection surface 40 as shown in FIG.
  • the second molded body 50 is, for example, located between the printed wiring board 42 and the magnetic bias unit 45 for isolating the printed wiring board 42 from the magnetic bias unit 45.
  • the input and output ends of the sensor chip 41 are respectively connected to corresponding terminals on the printed wiring board 42, for example by soldering, so that the printed wiring board 42 can support and fix the sensor chip 41.
  • the first injection molded body 47 is located on the side of the magnetic bias unit 45 opposite to the recessed portion.
  • the input/output pin 43 is fixed by the first injection molded body 47.
  • the magnetoresistive sensor chip 41 comprises at least one bridge circuit, the bridge circuit comprising at least one bridge arm, preferably each bridge arm can comprise at least one such as a tunnel magnetoresistive TMR element, a giant magnetoresistive GMR element or an anisotropic magnetic A magnetic sensing element that blocks an AMR element.
  • each bridge arm may comprise a tunnel magnetoresistive TMR element connected in series and / or in parallel, a giant magnetoresistive GMR element connected in series and / or in parallel, or an anisotropic magnetoresistive AMR connected in series and / or in parallel element.
  • the magnetoresistive sensor chip 41 has a full bridge structure, and each of the bridge arms includes at least one magnetosensitive element.
  • the sensitive direction 49 of the magnetic sensing element is parallel to the detecting surface of the money detecting magnetic head, and the sensitive direction 49 of the magnetic sensitive element is perpendicular to the concave direction of the magnetic biasing unit 45.
  • the metal casing 44 is provided with a ground pin 48 for shielding electromagnetic interference from outside the metal casing 44 and for eliminating static electricity.
  • the shape and size of the second molded body 50 are matched with the shape and size of the metal casing 44, the printed wiring board 42, and the magnetic bias unit 45, respectively, for fixing the printed wiring board 42 and the magnetic bias unit 45 to the metal casing 44. in.
  • the first injection molded body 47 and the second injection molded body 50 can be engaged.
  • Fig. 5 is a top plan view showing the money detecting magnetic head of the magnetoresistive sensor chip having the full bridge structure of the present invention.
  • the magnetoresistive sensor chip 41 is located above the recessed structure of the magnetic bias unit 45.
  • the magnetic induction generated by the permanent magnet 45 parallel to the detection surface 40 is less than 25 Gauss, and the magnetic bias unit 45 does not have magnetic sensitivity in the area.
  • Element 91 is magnetized to saturation. Therefore, it is possible to ensure that the magnetic sensing element whose magnetic sensitivity direction is parallel to the detecting surface in the detection area operates in the linear region.
  • the detection region 90 has a size ranging, for example, from 1 mm to 10 mm in a direction parallel to the sensitive direction 49 of the magnetosensitive element.
  • the banknote When the magnetic resistance counterfeit magnetic head is used, the banknote is brought close to the detecting surface of the magnetoresistive counterfeit magnetic head, and is moved relative to the detecting surface, and the magnetoresistive sensor chip detects the magnetic change of the bill and passes the output lead pin. The relevant signals are output to realize the magnetic recognition of the banknotes.
  • the magnetoresistive banknote magnetic head is suitable for both recognizing the magnetic properties of banknotes made of a hard magnetic material and for identifying the magnetic properties of banknotes made of a soft magnetic material.
  • the magnetoresistive banknote magnetic head preferably uses a magnetic sensing element whose sensing direction is parallel to the detecting surface of the money detecting magnetic head, such as a TMR element, a giant magnetoresistive GMR element or an anisotropic magnetoresistive AMR element.
  • a magnetic sensing element whose sensing direction is parallel to the detecting surface of the money detecting magnetic head, such as a TMR element, a giant magnetoresistive GMR element or an anisotropic magnetoresistive AMR element.
  • the sensitivity and signal-to-noise ratio of these magneto-sensitive elements are higher, so the sensitivity and signal-to-noise ratio of the magnetoresistive banknote magnetic head are relatively high.
  • the manufacturing process of these magnetic sensing elements is relatively simple, and is not easily affected by temperature and stress, and the yield is high. Therefore, the processing technology of the magnetic resistance counterfeit magnetic head is simple and the cost is low. Since the magnetic resistance coin-detecting magnetic head uses a flexible circuit board to connect the printed circuit board and the input/output pin, the flexible circuit board does not limit the shape of the permanent magnet, which is advantageous for the design of the permanent magnet. Since the permanent magnet of the magnetic resistance counterfeit magnetic head has a concave structure, the magnetic field generated by the permanent magnet having the concave structure is small or close to zero in the sensitive direction of the magnetic sensitive element, so that the magnetic sensitive element is in its linear working area, thereby being able to It is guaranteed that the magnetic resistance counterfeit magnetic head works normally.
  • the magnetoresistive sensor chip of the magnetic resistance counterfeit magnetic head adopts the magnetic sensitive element of the bridge circuit structure, the magnetic resistance counterfeit magnetic head can effectively suppress the interference of the common mode magnetic field from the magnetic reluctance magnetic detecting head.
  • the magnetoresistive banknote magnetic head can be used for both a money detector and a cash register.
  • magnetic bias unit 45 there are many design methods for realizing the above-described magnetic bias unit 45, and for example, it may be a magnet element having a concave structure as described above, or a magnet-pole piece combination type element, or a rectangular magnet combination type element.
  • the magnetic biasing units of these structures are listed as having the advantage of being easy to produce and low in cost.
  • Various examples of magnetic biasing units will be described in detail below with reference to the accompanying drawings.
  • Fig. 6(A) is a magnetic line distribution diagram of a magnetic field generated by a rectangular permanent magnet having a concave structure in a magnetic head according to Example 1 of the present invention.
  • the permanent magnet 55 has a groove 52 on the surface close to the detecting surface 40, and the groove depth direction is perpendicular to the surface on which the permanent magnet 55 is formed with a groove.
  • the magnetization direction 51 of the permanent magnet 55 is perpendicular to the detection surface 40.
  • the magnetic field 53 generated by the permanent magnet 55 having the groove 52 It is perpendicular to the detecting surface 40, thus eliminating the horizontal magnetic field component at the magnetoresistive sensor chip 41 such as the TMR element.
  • FIG. 6(B) is a magnetic field intensity distribution diagram along the detecting surface 40, wherein the broken line 57 is a magnetic field intensity component perpendicular to the detecting surface 40, the thin solid line 58 is a magnetic field strength component parallel to the detecting surface 40, and the vertical axis 56 is The magnetic induction intensity, the horizontal axis is the distance from the center point of the detection surface 40.
  • the intensity component of the magnetic field parallel to the detecting surface 40 above the groove 55 is small, and the value of the magnetic field strength in this direction is significantly smaller than that of the conventional structure of Figs. 2 and 3.
  • the magnetic biasing unit having the recessed structure may also be a rectangular permanent magnet having a dimple.
  • Fig. 7(A) is a magnetic line distribution diagram of a magnetic field generated by a magnetic biasing element in the magnetic head of Example 2.
  • a permanent magnet having a rectangular cross section 65 is covered with a soft magnetic alloy piece, also referred to as a "pole piece" 64, for adjusting the magnetic field distribution parallel to the detecting surface 40.
  • the pole piece 64 is typically made of a soft magnetic alloy such as permalloy.
  • the magnetization direction 61 of the permanent magnet 65 is perpendicular to the detection surface 40, and the magnetization direction of the pole piece 64 is determined by the magnetization direction of the permanent magnet 65.
  • the grooves 62 of the pole pieces are used to reduce the strength of the magnetic field in a direction parallel to the detection surface 40.
  • Fig. 7(B) is a magnetic field intensity distribution diagram of Example 2 along the detecting surface 40, wherein the broken line 67 is a magnetic field intensity component perpendicular to the detecting surface 40, and the thin solid line 68 is a magnetic field intensity component parallel to the detecting surface 40, the vertical axis 66 is the magnetic induction intensity, and the horizontal axis is the offset distance along the detection surface 40.
  • the strength of the magnetic field parallel to the detecting surface 40 above the pole piece groove 64 is small, and the value of the magnetic field strength in this direction is significantly smaller than that of the conventional structure in Figs. 2 and 3.
  • Figure 6 (C) is a perspective view of the pole piece 64 of Example 2, wherein the groove structure 62 can be realized by die casting, stamping, cutting, and the like.
  • Fig. 8(A) is a magnetic line distribution diagram of a magnetic field generated by a magnetic biasing element in the magnetic head of Example 3.
  • a permanent magnet having a rectangular section 75 is covered with a soft magnetic alloy sheet, also referred to as a pole piece 74, for adjusting the magnetic field distribution of the permanent magnet parallel to the detecting surface 40.
  • the pole piece 74 is typically made of a soft magnetic alloy such as permalloy.
  • the magnetization direction 71 of the permanent magnet 75 is perpendicular to the detection surface 40, and the magnetization direction of the pole piece 74 is determined by the magnetization direction of the permanent magnet 75.
  • the opening 72 in the pole piece 74 serves to reduce the strength of the magnetic field parallel to the sensing surface 40.
  • Figure 8 Is the magnetic field intensity distribution along the detecting surface 40, wherein the broken line 77 is the magnetic field intensity component perpendicular to the detecting surface 40, the thin solid line 78 is the magnetic field strength component parallel to the detecting surface 40, and the vertical axis 76 is the magnetic induction intensity, the horizontal axis It is the distance from the neutral point of the detection surface 40.
  • the strength of the magnetic field parallel to the detecting surface 40 above the opening of the pole piece 74 is small, and the value of the magnetic field strength in this direction is significantly smaller than that of the conventional structure of Figs. 2 and 3.
  • Figure 8 (C) is a perspective view of the pole piece 64 of Example 3, wherein the structure of the opening 72 can be achieved by die casting, stamping, cutting, and the like.
  • Fig. 9(A) is a magnetic line distribution diagram of a magnetic field generated by a magnetic bias unit in the magnetic head of Example 4.
  • the material in the isolation region 84 may be a non-magnetic metal material, a non-magnetic plastic material, a non-magnetic ceramic material, or Soft ferromagnetic materials, etc.
  • the magnetization direction of the permanent magnet 85 is perpendicular to the detection surface 40, and above the isolation region 84, the magnetic field strength parallel to the detection surface 40 is zero.
  • Figure 9 (B) Is a magnetic field intensity distribution along the detecting surface 40 in the magnetic flux of Embodiment 4, wherein the broken line 87 is a magnetic field intensity component perpendicular to the detecting surface 40, and the thin solid line 88 is a magnetic field intensity component parallel to the detecting surface 40, the vertical axis 86 is the magnetic induction intensity, and the horizontal axis is the offset distance along the detection surface 40.
  • the strength of the magnetic field parallel to the detection surface 40 above the isolation region 84 is small, and the value of the magnetic field strength in this direction is significantly smaller than in the case of the conventional structure in Figs. 2 and 3.

Abstract

一种验钞磁头，包括：磁阻传感器芯片（41），以及在所述磁阻传感器芯片（41）远离验钞磁头检测面（40）一侧与所述磁阻传感器芯片（41）分开放置的磁偏置单元（45），其特征在于，该磁阻传感器芯片（41）包括桥臂具有磁敏元件的桥式电路，该磁敏元件的敏感方向（49）平行于所述验钞磁头的检测面（40），以及所述磁偏置单元（45）具有凹陷结构，该凹陷结构被设置为使得所述磁偏置单元（45）产生的磁场在平行于检测面（40）方向的分量小到使得所述磁敏元件工作在线性区。该验钞磁头具有更高的灵敏度和信噪比。

Description

[根据细则37.2由ISA制定的发明名称]　一种验钞磁头
技术领域
本发明涉及磁阻传感器技术领域，特别涉及一种磁阻验钞磁头。
背景技术
日常生活中，验钞磁头的应用非常广泛，例如自动售货机、点钞机，以及纸币检验设备等。通常，纸币的磁性非常弱，因此，用于识别纸币磁性的验钞磁头需要具有高灵敏度、低噪声和高信噪比的特性。
图1示出了一种现有技术的验钞磁头，该验钞磁头中的传感器元件检测的是与磁头检测面垂直的磁场分量，该磁场由纸币上的磁性油墨产生。通常情况下，这种传感器元件所用材料为锑化铟。由这种传感器元件构成的验钞磁头具有如下缺点：
(1) 锑化铟霍尔元件的灵敏度和信噪比非常低，导致该种验钞磁头的灵敏度和信噪比非常低；
(2) 锑化铟传感器且受温度的影响非常明显，需要复杂的温度补偿电路；
(3) 锑化铟传感器固有噪声比较大，因此需要磁偏置元件提供很大的偏置信号，以提高信噪比，由此导致磁偏置元件的体积较大，进而导致验钞磁头体积较大；
(4)在磁头检测面附近存在磁偏置元件的一个平面磁极，这个磁极产生与检测面平行的磁场分量。由于这个磁场分量的存在，导致很难精确测量被测物体产生磁场的大小。
因此，需要一种能够精确测量被测物体磁场大小的验钞机头。
发明内容
为了解决上述的问题，本发明提供了一种磁阻验钞磁头。本发明中所用的磁阻传感器可以测量被测物体产生的平行于检测面的磁场分量，磁阻传感器可以是隧道磁阻传感器，或者是巨磁阻传感器，或者是各向异性磁阻传感器等等。
根据本发明的一个方面，提供一种验钞磁头，该验钞磁头包括：
磁阻传感器芯片，该磁阻传感器芯片包括桥臂具有磁敏元件的桥式电路，该磁敏元件的敏感方向平行于所述验钞磁头的检测面；和
位于所述磁阻传感器芯片的远离验钞磁头检测面的一侧并与所述磁阻传感器芯片分开放置的磁偏置单元，所述磁偏置单元具有凹陷结构，该凹陷结构被设置为使得所述磁偏置单元产生的磁场在平行于检测面方向的分量小到使得所述磁敏元件工作在线性区。
优选地，所述磁偏置单元包括一永磁体，该永磁体在朝向所述磁阻传感器芯片一侧具有凹陷。
优选地，所述磁偏置单元包括矩形永磁体，该矩形永磁体在朝向所述磁阻传感器芯片一侧具有垂直于检测面的矩形凹槽或凹坑。
优选地，所述磁偏置单元包括矩形永磁体和至少一个由高导磁率磁性材料构成的表面具有矩形凹陷的磁极片。
优选地，所述磁偏置单元包括矩形永磁体和由高导磁率磁性材料构成的矩形环状磁极片。
优选地，所述磁偏置单元包括两个分开放置的矩形永磁体。
更优选地，所述两个分开放置的矩形永磁体之间放置有非磁性材料或软铁磁性材料。
优选地，所述磁偏置单元产生的磁场在所述磁敏元件敏感方向的分量小于25高斯。
优选地，所述磁敏元件为隧道磁阻（TMR）元件、巨磁阻（GMR）元件或各向异性磁阻（AMR）元件。
优选地，所述磁敏元件为串联和/或并联连接的TMR元件，串联和/或并联连接的GMR元件，或串联和/或并联连接的AMR元件。
优选地，该磁头进一步包括容纳所述磁阻传感器芯片和所述磁偏置单元的金属外壳，该金属外壳在磁头检测面相对侧上具有开口。
优选地，该磁头进一步包括容纳所述磁阻传感器芯片和所述磁偏置单元的金属外壳，该金属外壳设置有接地端。
优选地，所述金属外壳填充有用于固定的注塑体。
本发明具有如下有益效果：
（1）本发明所述的验钞磁头，既适用于识别由硬磁性材料制成的纸币，又适用于识别由软磁性材料制成的纸币；
（2）本发明所述的验钞磁头采用包括如隧道磁阻TMR元件、巨磁阻GMR元件或各向异性磁阻AMR元件等磁敏元件的磁阻传感器，与锑化铟霍尔元件相比，上述磁敏元件的灵敏度和信噪比较高，因此本发明的验钞磁头具有更高的灵敏度和信噪比；
（3）由于上述磁敏元件的制作工艺较简单，且不易受环境温度和应力的影响，成品率高，因此根据本发明的验钞磁头的加工工艺较简单，成本较低；
（4）通过将验钞磁头的磁偏置元件形成凹陷，具有凹陷的磁偏置元件产生的磁场在上述磁敏元件敏感方向的分量很小或趋近于零，使得磁敏元件元件能够工作在线性区，从而能够保证验钞磁头能够正常工作；
（5）由于验钞磁头的磁阻传感器芯片采用桥式结构，使得验钞磁头能够有效抑制来自所述验钞磁头之外的共模磁场的干扰；
（7）本发明的验钞磁头既可以用于验钞机，又可以用于收银机；
（8）根据本发明的验钞磁头采用柔性线路板连接印刷线路板和输出引针，而柔性线路板不会对永磁体的外形产生限制，有利于永磁体的设计。
附图说明
图1为现有技术比较例1的验钞磁头的示意图；
图2(A)为图1所示磁头中矩形永磁体产生的磁场的磁力线分布图；
图2(B)为图1所示磁头中矩形永磁体产生的磁场强度分布；
图3(A)为现有技术比较例2的磁头中矩形永磁体产生的磁场的磁力线分布图；
图3(B)为现有技术比较例2的磁头中矩形永磁体产生的磁场强度分布；
图4为根据本发明实施例的验钞磁头的示意图；
图5示出根据本发明实施例的验钞磁头的俯视示意图；
图6(A)为根据本发明实例1的磁头中磁偏置单元产生的磁场的磁力线分布图；
图6(B)为根据本发明实例1的磁头中磁偏置单元产生的磁场强度分布；
图7(A)为实例2的磁头中磁偏置单元产生的磁场的磁力线分布图；
图7(B)为实例2的磁头中磁偏置单元产生的磁场强度分布；
图7(C)为实例2的磁偏置单元中磁极片的透视图；
图8(A)为实例3的磁头中磁偏置单元产生的磁场的磁力线分布图；
图8(B)为实例3的磁头中磁偏置单元产生的磁场强度分布；
图8(C)为实例3的磁头中磁偏置单元的透视图；
图9(A)为实例4的磁头中磁偏置单元产生的磁场的磁力线分布图；
图9(B)为实例4的磁头中磁偏置单元产生的磁场强度分布。
具体实施方式
下面将参考附图并结合实施例，来详细说明本发明的技术方案。在具体实施方式中，相似的附图标记表示相似的特征或元件。
现有技术比较例1
图1示出比较例1的验钞磁头的示意图。该验钞磁头包括传感器芯片11、印刷线路板(PCB)12、输入输出引针13、金属外壳14、永磁体15和注塑体(图中未示出)。金属外壳14的远离检测面的一个面上有开口，用于装配以及输入输出引针的引出。传感器芯片11靠近金属外壳14的检测面安装，其磁敏方向垂直于磁头检测面。传感器芯片11和永磁体15分别设于印刷线路板12的两侧。永磁体15的充磁方向如图1所示。印刷线路板12与永磁体15之间不直接接触。传感器芯片11的输入端和输出端分别与印刷线路板12上的相应接线端焊接，使得印刷线路板12能够支撑和固定传感器芯片11。输入输出引针13的一端与印刷线路板12的相应接线端焊接，使得输入输出引针13与传感器芯片11的输入端和输出端导通。输入输出引针13的另一端作为验钞磁头的输出端。传感器芯片11采用锑化铟霍尔元件，且锑化铟霍尔元件的敏感方向17垂直于磁头的检测面。金属外壳14上设有接地引针16。设有接地引针16的金属外壳14用于屏蔽来自金属外壳14之外的电磁干扰，并消除静电。永磁体15的形状可以是长方体。注塑体的形状和尺寸分别与金属外壳14、印刷线路板12和永磁体15的形状和尺寸匹配，用于固定金属外壳14、印刷线路板12和永磁体15，并实现印刷线路板12和永磁体15的电气隔离。
该比较例1中验钞磁头的传感器芯片采用锑化铟霍尔元件，所述验钞磁头的灵敏度和信噪比非常低。由于锑化铟霍尔元件的制作工艺复杂，且受温度和应力的影响非常明显，成品率低，导致比较例的验钞磁头的加工工艺复杂，成本高。另一方面，由于比较例的验钞磁头输出引针的一端直接固定在印刷线路板上，且输出引针不能直接穿过永磁体，因此输出引针的位置限制了永磁体的尺寸，增加设计的难度。另外，由于比较例1的验钞磁头的永磁体为长方体，当传感器芯片采用MTJ元件时，矩形永磁体产生的磁场沿MTJ元件敏感方向的分量很大，导致MTJ元件的工作点偏离其线性工作区，甚至导致MTJ元件的电阻对磁场的响应达到饱和，从而影响验钞磁头的性能，甚至导致验钞磁头无法正常工作。
图2(A)是图1所示验钞磁头中，矩形磁体产生的磁场的磁力线分布图。图中具有矩形截面结构的永磁体15的磁化方向垂直于检测面40，检测面用图中的“AA”表示。磁阻传感器元件41位于检测面40的下方，沿着图中的“BB”方向放置。永磁体15产生的磁场的磁力线如图中的细实线23所示。图2(B)展示了永磁体15产生的磁场在检测面处平行于检测面方向的分量28和垂直于检测面方向的分量27，横轴29表示在“AA”方向上位置的偏移量。在传统的霍尔效应验钞磁头中，传感器仅检测垂直于检测面方向的磁场分量27，因此平行于检测面方向的磁场分量28不会对验钞磁头的工作产生任何影响。
若磁阻传感器的感应方向平行于检测面40时，必须对偏置磁体进行改进，以减小永磁体产生的平行于检测面的磁场对传感器感应信号的影响。
现有技术比较例2
增加偏置磁体与传感器元件的体积比是解决上述问题的一种有效方法。图3(A)和3(B)分别为现有技术比较例2的磁头中矩形永磁体产生的磁场的磁力线分布图和磁场强度分布图。比较图3（A）和图2（A）可以看出，偏置磁体35邻近传感器元件41一面具有显著增加的面积。从图3（A）中可以看出，永磁体35的磁化方向21垂直于检测面40，检测方向是图中的“AA”。磁阻传感器元件41位于检测面40的下方，沿着图中的“BB”方向放置。永磁体35产生的磁场的磁力线如图中的实线23所示。图3(B)展示了永磁体35产生的磁场在检测面处平行于检测面方向的分量28和垂直于检测面方向的分量27，横轴29表示在“AA”方向上位置的偏移量。从图3(B)可以看出，比较例2平行于检测面方向的磁场分量28明显小于图2(B)中比较例1的平行于检测面方向的磁场分量。
但是比较例2中，较大的永磁体体积会增加验钞磁头的体积，进而增加其在验钞机中安装的难度。进一步，增加永磁体和磁头的体积意味着产品成本的增加，进而增加验钞机的成本。
本发明的优选实施例
图4示出本发明实施例的验钞磁头示意图。本发明的磁阻验钞磁头包括磁阻传感器芯片41、印刷线路板42、输入输出引针43、金属外壳44、形成有凹陷结构的磁偏置单元45例如具有凹陷的永磁体、柔性线路板(FPC) 46、第一注塑体47和第二注塑体50，并具有检测面40。该形成有凹陷的磁偏置单元例如是在一侧具有矩形凹槽的永磁体，或在一侧具有矩形凹坑的永磁体。金属外壳44采用非磁性耐磨材料，且其在远离检测面40的一侧有开口。磁阻传感器芯片41在金属外壳44内靠近检测面40安装。检测面40侧外壳外表面距离磁阻传感器芯片上表面之间的距离小于或等于0.2mm。磁阻传感器芯片41和磁偏置单元45分别位于印刷线路板42的两侧，磁偏置单元45的凹陷部分朝向印刷线路板42。磁偏置单元45的充磁方向垂直于检测面40，如图4所示。第二注塑体50例如位于印刷线路板42与磁偏置单元45之间，用于将印刷线路板42和磁偏置单元45隔离。传感器芯片41的输入端和输出端分别与印刷线路板42上的相应接线端例如通过焊接连接，使得印刷线路板42能够支撑和固定传感器芯片41。第一注塑体47位于磁偏置单元45的与凹陷部分相反的一侧。输入输出引针43通过第一注塑体47固定。柔性线路板46的一端与印刷线路板42的相应接线端电连接，柔性线路板46的另一端与输入输出引针43的一端电连接，使得输入输出引针43分别与磁阻传感器芯片41的输入端和输出端导通。输入输出引针43的另一端作为验钞磁头的输入输出端。磁阻传感器芯片41至少包含一个桥式电路，该桥式电路至少包含一个桥臂，优选地，每个桥臂可至少包含一个例如隧道磁阻TMR元件，巨磁阻GMR元件或各向异性磁阻AMR元件的磁敏元件。更优选地，每个桥臂可包含串联和/或并联连接的隧道磁阻TMR元件，串联和/或并联连接的巨磁阻GMR元件，或串联和/或并联连接的各向异性磁阻AMR元件。在本实施例中，磁阻传感器芯片41具有全桥结构，该全桥结构中的每一个桥臂至少包含一个磁敏元件。磁敏元件的敏感方向49与验钞磁头的检测面平行，且磁敏元件的敏感方向49与磁偏置单元45的凹陷方向垂直。优选地，金属外壳44上设有接地引针48，接地的金属外壳用于屏蔽来自金属外壳44之外的电磁干扰，并用于消除静电。第二注塑体50的形状和尺寸分别与金属外壳44、印刷线路板42和磁偏置单元45的形状和尺寸相匹配，用于将印刷线路板42和磁偏置单元45固定在金属外壳44中。优选地，第一注塑体47与第二注塑体50能够扣合。
图5示出本发明具有全桥结构的磁阻传感器芯片的验钞磁头的俯视示意图。如图所示，磁阻传感器芯片41位于磁偏置单元45凹陷结构的上方。在磁阻传感器芯片41内存在一个检测区域90，在这个区域内，永磁体45产生的平行于检测面40的磁感应强度小于25高斯，磁偏置单元45不会将该区域内的各磁敏元件91磁化到饱和。因此，可以确保处于检测区域内其磁敏方向平行于检测面的磁敏元件工作在线性区。在平行于磁敏元件敏感方向49的方向，检测区域90的尺寸范围例如是1mm到10mm。
使用磁阻验钞磁头时，将纸币靠近所述磁阻验钞磁头的检测面，且使其相对于该检测面进行运动，磁阻传感器芯片将会检测到纸币的磁性变化并通过输出引针输出相关信号，从而实现对纸币磁性的识别。
根据本发明优选实施例的磁阻验钞磁头既适用于识别由硬磁性材料制成的纸币的磁性，又适用于识别由软磁性材料制成的纸币的磁性。磁阻验钞磁头优选采用其敏感方向平行于验钞磁头的检测面的磁敏元件，例如TMR元件，巨磁阻GMR元件或各向异性磁阻AMR元件。与锑化铟霍尔元件相比，这些磁敏元件的灵敏度和信噪比更高，因此此磁阻验钞磁头的灵敏度和信噪比较高。这些磁敏元件的制作工艺较简单，且不易受温度和应力的影响，成品率高，因此该磁阻验钞磁头的加工工艺较简单，成本较低。由于磁阻验钞磁头采用柔性线路板连接印刷线路板和输入输出引针，而柔性线路板不会对永磁体的外形产生限制，有利于永磁体的设计。由于磁阻验钞磁头的永磁体具有凹陷结构，具有凹陷结构的永磁体产生的磁场沿磁敏元件敏感方向的分量很小或趋近于零，使得磁敏元件在其线性工作区，从而能够保证所述磁阻验钞磁头正常工作。由于该磁阻验钞磁头的磁阻传感器芯片采用桥式电路结构的磁敏元件，使得磁阻验钞磁头能够有效抑制来自该磁阻验钞磁头之外的共模磁场的干扰。该磁阻验钞磁头既可以用于验钞机，又可以用于收银机。
用于实现上述磁偏置单元45的设计方法较多，例如可以是如上所述的具有凹陷结构的磁体元件，或者磁体-磁极片组合型元件，或者是矩形磁体组合型元件。所列这些结构的磁偏置单元都具有易于生产、成本较低的优势。下面将参照附图分别对磁偏置单元的各种实例进行详细阐述。
实例1
图6(A)为根据本发明实例1的磁头中具有凹陷结构的矩形永磁体产生的磁场的磁力线分布图。如图6(A)所示，永磁体55在接近检测面40的表面上开有凹槽52，凹槽深度方向垂直于永磁体55形成有凹槽的表面。 永磁体55的磁化方向51垂直于检测面40。在检测面40的中心处，具有凹槽52的永磁体55产生的磁场53 垂直于检测面40，因此消除了在例如TMR元件的磁阻传感器芯片41处的水平磁场分量。
图6(B)是沿着检测面40的磁场强度分布图，其中虚线57是垂直于检测面40的磁场强度分量，细实线58是平行于检测面40的磁场强度分量，纵轴56是磁感应强度，横轴是距检测面40中心点偏移的距离。从图中可以看出，凹槽55上方的平行于检测面40的磁场强度分量较小，该方向的磁场强度的数值明显小于图2和图3中的传统结构的情形。
可以理解，具有凹陷结构的磁偏置单元也可以是具有凹坑的矩形永磁体。
实例2
图7(A)为实例2的磁头中磁偏置元件产生的磁场的磁力线分布图。如图7(A)，具有矩形截面65的永磁体上方覆盖了一个软磁合金片，也称为“磁极片”64，用来调整平行于检测面40的磁场分布。磁极片64通常是由软磁合金制成的，比如坡莫合金。永磁体65的磁化方向61垂直于检测面40，磁极片64的磁化方向由永磁体65的磁化方向决定。磁极片的凹槽62用来减小磁场在平行于检测面40方向的磁场强度。
图7(B)是实例2沿着检测面40的磁场强度分布图，其中虚线67是垂直于检测面40的磁场强度分量，细实线68是平行于检测面40的磁场强度分量，纵轴66是磁感应强度，横轴是沿检测面40的偏移距离。从图中可以看出，在磁极片凹槽64上方的平行于检测面40的磁场强度较小，该方向的磁场强度的数值明显小于图2和图3中的传统结构的情形。
图6(C)是实例2磁极片64的透视图，其中凹槽结构62可以通过压铸、冲压、切割等方法实现。
实例3
图8(A)为实例3的磁头中磁偏置元件产生的磁场的磁力线分布图。如图8(A)所示，具有矩形截面75的永磁体上方覆盖了一个软磁合金片，也称之为磁极片74，用来调整永磁体在平行于检测面40的磁场分布。磁极片74通常是由软磁合金制成的，比如坡莫合金。永磁体75的磁化方向71垂直于检测面40，磁极片74的磁化方向由永磁体75的磁化方向决定。磁极片74上的开孔72用来减小平行于检测面40的磁场的强度。
图8(B) 是沿着检测面40的磁场强度分布图，其中虚线77是垂直于检测面40的磁场强度分量，细实线78是平行于检测面40的磁场强度分量，纵轴76是磁感应强度，横轴是距检测面40中性点偏移的距离。从图中可以看出，在磁极片74开孔上方的平行于检测面40的磁场强度较小，该方向的磁场强度的数值明显小于图2和图3中的传统结构的情形。
图8(C)是实例3磁极片64的透视图，其中开孔72的结构可以通过压铸、冲压，切割等方法实现。
实例4
图9(A)为实例4的磁头中磁偏置单元产生的磁场的磁力线分布图。在此设计中，有两个具有矩形截面85的永磁体，且两个永磁体之间存在隔离区域84，隔离区域84内的材料可以是非磁性金属材料、非磁性塑料、非磁性陶瓷材料，或者软铁磁性材料等。永磁体85的磁化方向垂直于检测面40，在所述隔离区域84上方，平行于检测面40的磁场强度为零。
图9(B) 是实施例4的磁通中沿着检测面40的磁场强度分布图，其中虚线87是垂直于检测面40的磁场强度分量，细实线88是平行于检测面40的磁场强度分量，纵轴86是磁感应强度，横轴是沿检测面40的偏移距离。从图中可以看出，在隔离区域84上方的平行于检测面40的磁场强度较小，该方向的磁场强度的数值明显小于图2和图3中的传统结构的情形。
以上所述仅为本发明的优选实施例而已，并不用于限制本发明，对于本领域的技术人员来说，本发明可以有各种更改和变化。凡在本发明的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (13)

1．一种验钞磁头，包括：
磁阻传感器芯片，和
位于所述磁阻传感器芯片远离验钞磁头检测面的一侧并与所述磁阻传感器芯片分开放置的磁偏置单元，
其特征在于，
所述磁阻传感器芯片包括桥臂具有磁敏元件的桥式电路，所述磁敏元件的敏感方向平行于所述验钞磁头的检测面，
所述磁偏置单元具有凹陷结构，所述凹陷结构被设置为使得所述磁偏置单元产生的磁场在平行于检测面方向的分量小到使得所述磁敏元件工作在线性区。
2．如权利要求1所述的验钞磁头，其特征在于，所述磁偏置单元包括永磁体，所述永磁体在朝向所述磁阻传感器芯片的一侧具有凹陷。
3．如权利要求1所述的验钞磁头，其特征在于，所述磁偏置单元包括矩形永磁体，所述矩形永磁体在朝向所述磁阻传感器芯片的一侧具有垂直于检测面的矩形凹槽或凹坑。
4．如权利要求1所述的验钞磁头，其特征在于，所述磁偏置单元包括矩形永磁体和至少一个由高导磁率磁性材料构成的表面具有矩形凹陷的磁极片。
5．如权利要求1所述的验钞磁头，其特征在于，所述磁偏置单元包括矩形永磁体和由高导磁率磁性材料构成的矩形环状磁极片。
6．如权利要求1所述的验钞磁头，其特征在于，所述磁偏置单元包括两个分开放置的矩形永磁体。
7．如权利要求6所述的验钞磁头，其特征在于，所述两个分开放置的矩形永磁体之间放置有非磁性材料或软铁磁性材料。
8．如权利要求1所述的验钞磁头，其特征在于，所述磁偏置单元产生的磁场在所述磁敏元件敏感方向的分量小于25高斯。
9．如权利要求1所述的验钞磁头，其特征在于，所述磁敏元件为隧道磁阻TMR元件、巨磁阻GMR元件或各向异性磁阻AMR元件。
10．如权利要求1所述的验钞磁头，其特征在于，所述磁敏元件为串联和/或并联连接的TMR元件，串联和/或并联连接的GMR元件，或串联和/或并联连接的AMR元件。
11．如权利要求1所述的验钞磁头，其特征在于，所述验钞磁头进一步包括容纳所述磁阻传感器芯片和所述磁偏置单元的金属外壳，所述金属外壳在所述验钞磁头检测面相对侧上具有开口。
12．如权利要求1所述的验钞磁头，其特征在于，所述验钞磁头进一步包括容纳所述磁阻传感器芯片和所述磁偏置单元的金属外壳，所述金属外壳设置有接地端。
13．如权利要求11或12所述的验钞磁头，其特征在于，所述金属外壳中填充有用于固定的注塑体。
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