Abstract:
A device has magnetic sensors and magnets in an array on a flexible substrate. Each magnetic sensor is sensitive to immediately proximate magnets. At least one controller evaluates magnetic sensor signals from the magnetic sensors produced in response to deformation of the flexible substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 62/053,076, filed Sep. 19, 2014, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to analyzing surface shape. More particularly, this invention relates to techniques for magnetic sensor based surface shape analysis. 
       BACKGROUND OF THE INVENTION 
       [0003]    Sensors play a crucial role in modern technology as they have become an essential part of millions of products that we use every day. Sensors can be found in every imaginable type of product from consumer and industrial products, to communications, automotive and biomedical products. The same is true for magnetic sensors that are used widely in consumer, communications, computer, industrial, automotive, biomedical and precision instrumentation products. 
         [0004]    A variety of sensor devices have been used for surface position and shape sensing including optical sensors and stress sensors, such as piezoresistive sensors and piezoelectric sensors. These solutions experience system complexity, high cost and poor performance. Accordingly, it would be desirable to provide new techniques for surface position and shape sensing. 
       SUMMARY OF THE INVENTION 
       [0005]    A device for surface shape analysis includes a flexible substrate supporting magnetic sensors and magnets or current conductors operative as a magnetic field source. One or more controller circuits receive magnetic sensor signals from the magnetic sensors. The one or more controllers collect reference magnetic sensor signals when the flexible substrate is flat, first polarity magnetic sensor signals in response to position change of the flexible substrate in a first direction and second polarity magnetic sensor signals in response to position change of the flexible substrate in a second direction.  
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]    The invention is more fully appreciated in connection with the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0007]      FIG. 1  illustrates a magnetic sensor surface shape analysis system configured in accordance with an embodiment of the invention. 
           [0008]      FIG. 2  is a side view of a single magnetic sensor and accompanying magnet on a flat surface that results in a reference signal from the magnetic sensor. 
           [0009]      FIG. 3  is a side view of a downwardly deformed surface that causes the magnetic sensor to generate a signal with a first polarity. 
           [0010]      FIG. 4  is a side view of an upwardly deformed surface that causes the magnetic sensor to generate a signal with a second polarity. 
           [0011]      FIG. 5  is a top view of a matrix of magnetic sensors and magnets. 
           [0012]      FIG. 6  is a schematic view of upward and downward surface deformations evaluated in accordance with an embodiment of the invention. 
           [0013]      FIG. 7  illustrates processing operations to construct a system in accordance with an embodiment of the invention. 
           [0014]      FIG. 8  illustrates a substrate processed in accordance with an embodiment of the invention. 
           [0015]      FIG. 9  illustrates ferrite deposition performed in accordance with an embodiment of the invention. 
           [0016]      FIG. 10  illustrates magnetic sensor positioning performed in accordance with an embodiment of the invention. 
           [0017]      FIGS. 11-12  illustrate a magnetic sensor and magnet configuration in accordance with an embodiment of the invention. 
           [0018]      FIGS. 13-14  illustrate a magnetic sensor and magnet configuration in accordance with another embodiment of the invention. 
           [0019]      FIGS. 15-16  illustrate a magnetic sensor and magnet configuration in accordance with still another embodiment of the invention. 
           [0020]      FIG. 17  illustrates a magnetic sensor surface shape analysis system configured in accordance with another embodiment of the invention. 
           [0021]      FIG. 18  illustrates processing operations to construct the system of  FIG. 17 . 
       
    
    
       [0022]    Like reference numerals refer to corresponding parts throughout the several views of the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1  illustrates a magnetic sensor surface shape analysis system  100  configured in accordance with an embodiment of the invention. The system  100  includes a set of magnetic sensors  102 _ 1  through  102 _N and a set of accompanying magnets  104 _ 1  through  104 _N positioned on a flexible substrate  106  (e.g., polyimide or similar material). Each magnetic sensor  102  is identical and has an axis of sensitivity oriented in a direction defined by a predetermined pattern used to cover the surface  106 . Each magnet has the same strength of magnetic field. 
         [0024]    Each sensor  102  has a link  107  to an X-axis controller  108  and a link  109  to a Y-axis controller  110 . The controllers  108  and  110  may be positioned on or outside of the flexible substrate  106 . The controllers  108  and  110  may be combined into a single controller. 
         [0025]    Link  107  is shown as a dashed line to suggest that it might be on a different plane of the substrate  106  (i.e., the substrate  106  may have multiple conductive layers). The matrix configuration of  FIG. 1  is exemplary. As discussed below, other sensor and magnet configurations are utilized in accordance with embodiments of the invention. 
         [0026]    Each magnetic sensor  102  may be any type of magnetic sensor, such as a Hall device, Anisotropic Magnetic Resistance (AMR) sensor, Giant Magnetic Resistance (GMR) sensor and/or magnetic logic unit (MLU) sensor. In one embodiment, an MLU sensor of the type described in U.S. Ser. No. 13/787,585 (the &#39;585 application), filed Mar. 6, 2013, is used. The &#39;585 application is owned by the owner of this patent application and is incorporated herein by reference. 
         [0027]    By way of overview, the MLU sensor disclosed in the &#39;585 application has circuits, where each circuit includes multiple magnetic tunnel junctions, and each magnetic tunnel junction includes a storage layer having a storage magnetization direction and a sense layer having a sense magnetization direction. A field line is configured to generate a magnetic field based on an input. The sense magnetization direction of each magnetic tunnel junction is configured based on the magnetic field. Each magnetic tunnel junction is configured such that the sense magnetization direction and a resistance of the magnetic tunnel junction vary based on an external magnetic field. A sensing module is configured to determine a parameter of each of the circuits. The parameter is selected from impedance, voltage and current. The parameter of each of the circuits varies based on the resistances of the multiple magnetic tunnel junctions included in each of the circuits. A magnetic field direction determination module is configured to determine an angular orientation of the apparatus relative to the external magnetic field based on the parameter of each of the  circuits. The magnetic field direction determination module is implemented in at least one of a memory or a processing device. 
         [0028]    An advantage of the MLU sensor disclosed in the &#39;585 application is that the sensor may be placed 1-5 cm from a small magnet and still register a signal. Many comparable magnetic sensors need to be within 1 mm of a small magnet to register a signal. Accordingly, an embodiment of the invention has high sensitivity. This allows for larger sensor spacing, which reduces cost and preserves high flexibility in the substrate  106 . The sensor of the &#39;585 application has a desirable frequency response. Another advantage of the magnetic sensor of the &#39;585 application is that it allows for positive and negative sense signaling, as discussed below. 
         [0029]      FIG. 2  is a side view of a magnetic sensor  102  and an adjacent magnet  104 . In this instance, the substrate  106  is flat. The magnet  104  produces a magnetic field that is orthogonal to the flat surface. The magnetic sensor  102  is positioned to receive an orthogonal magnetic field and therefore generates a reference output (i.e., zero or below some minimum threshold). 
         [0030]    In  FIG. 3 , the surface  106  is deformed in a downward direction. As a result, the magnetic sensor  102  receives a non-orthogonal magnetic field, which induces a first polarity magnetic sensor signal.  FIG. 3  illustrates an angle Θ produced by the deformation of the surface  106 . The angle characterizes the deformation of the flexible substrate  106 . The first polarity magnetic sensor signal may be characterized as the sine function of the angle Θ. That is, the first polarity magnetic sensor signal may be expressed as Ao×Sin(Θ), where Ao is the absolute value of the vector of magnetic induction. 
         [0031]      FIG. 4  illustrates the surface  106  deformed in an upward direction. As a result, the magnetic sensor  102  receives a non-orthogonal magnetic field, which induces a second polarity magnetic sensor signal. The second polarity sensor signal may be characterized as the negative sine function of the angle Θ. 
         [0032]    Thus, it can be appreciated that obtaining information from all sensors distributed over the surface  106  provides precise information on the shape of the surface. Consider the positional schema of  FIG. 5 , which corresponds to the structure of the system  100  of  FIG. 1 . A simplified equation of the near range sensor interactions for sensor Δi,j may be expressed as: Δi,j=Ao×[Sin(Θij,ij-1)+Sin(Θij,ij+1)+Sin(Θij,i-1j)+Sin(Θij,i+1j)]. In one embodiment, the system is configured such that only adjacent magnets induce a deviation different than the reference signal if the bending is along the x-axis or the y-axis. The physical position of each sensor is known. Therefore, the position can be   correlated with the magnetic sensor signal to develop a shape profile for each position on the surface  106 . 
         [0033]      FIG. 6  illustrates a situation where the surface  106  is bent along two diagonals. In particular, there is an upward diagonal force  600  producing positive deviations  602  and there is a downward diagonal force  604  producing negative deviations  606 . 
         [0034]    Returning to  FIG. 1 , it can be appreciated that the X-axis controller  108  samples magnetic sensor signals to identify movement along the X-axis, while the Y-axis controller samples magnetic sensor signals to identify movement along the Y-axis. Various sampling techniques may be used. For example, in a quiescent state a first sampling rate may be used across the entire surface  106 . Upon detection of movement within a region of the surface, the sampling rate may be increased in the subject region. The controllers  108  and  110  may track the rate of change over time. Accordingly, surface profiles over time may be produced. 
         [0035]      FIG. 7  illustrates processing operations associated with the fabrication of the disclosed device. Initially, a substrate with sensor connection lines is supplied  700 .  FIG. 8  illustrates an exemplary substrate  800  with sensor connection lines  802 . There are regions  804  for locating magnetic sensors  804  and regions  806  for locating magnets. The substrate  800  is a flexible material, such as polyimide. 
         [0036]    Returning to  FIG. 7 , the next processing operation is to inject a ferrite paste  702 .  FIG. 9  illustrates a ferrite paste  900  being injected in regions  806 . The next operation is to planarize the ferrite paste  704 . The ferrite paste may be planarized through chemical and/or mechanical polishing. 
         [0037]    Next, the substrate is annealed  706 . The ferrites are then magnetized  708 . Magnetic sensor chips are then connected  710 .  FIG. 10  illustrates a wafer  1000  with a plurality of magnetic sensors. Magnetic sensors, such as magnetic sensor  102 _ 1 , are positioned in regions  804 . The substrate is then annealed once again  712 . A final protective coating is then applied  714 . 
         [0038]    The techniques of the invention may be used to create any number of magnetic sensor and magnet configurations.  FIG. 11  illustrates a system where a magnet is surrounded by four magnetic sensors. In  FIG. 11  each magnet is designated by an M and each sensor is designated by an S.  FIG. 12  illustrates a single magnet  104  and four associated sensors  102 _ 1 ,  102 _ 2 ,  102 _ 3  and  102 _ 4 . 
         [0039]      FIG. 13  illustrates a honeycomb system where a magnet is surrounded by six magnetic sensors. In  FIG. 13  each magnet is designated by an M and each sensor is  designated by an S.  FIG. 14  illustrates a single magnet  104  and six associated sensors  102 _ 1 ,  102 _ 2 ,  102 _ 3 ,  102 _ 4 ,  102 _ 5  and  102 _ 6 . 
         [0040]      FIG. 15  illustrates a system where a magnet is surrounded by three magnetic sensors. In  FIG. 15  each magnet is designated by an M and each sensor is designated by an S.  FIG. 16  illustrates a single magnet  104  and three associated sensors  102 _ 1 ,  102 _ 2  and  102 _ 3 . Alternate embodiments include circles and other geometric patterns. 
         [0041]      FIG. 17  illustrates an alternate system  1700  configured in accordance with an embodiment of the invention. Substrate  1701  hosts a set of magnetic sensors  102 _ 1  through  102  N. This system omits magnets. Instead, magnetic interactions are induced by currents driven through X-axis current paths  1702  and Y-axis current paths  1704 . An X-axis controller  1706  drives the current on X-axis current path  1702 . The X-axis controller  1706  also senses an X-axis magnetic sensor signal from line  1710 . Similarly, the Y-axis controller  1708  drives the current on Y-axis current path  1704 , while sensing a Y-axis magnetic sensor signal from line  1712 . Maxwell&#39;s equations may be used to compute an induced magnetic field as a function of current, deformation of the flexible substrate and distance between the magnetic sensor and the current path. 
         [0042]      FIG. 18  illustrates processing operations associated with the fabrication of the substrate of  FIG. 17 . A substrate is supplied with sensor connection lines and magnetization lines (i.e., X-axis current paths and Y-axis current paths)  1800 . Magnetic sensor chips are connected  1802 . A final protective coating is then applied  1804 . 
         [0043]    Thus, magnetic sensors are disclosed for surface shape analysis. The disclosed magnetic sensors may be incorporated into any number of devices for shape analysis, such as game controllers, physical movement analyzers, airplane wing force analyzers and devices for measuring deformations of solids and liquids. The output of such devices may be used in any number of ways. For example, the disclosed flexible substrate and associated magnetic sensors may be applied to a display (e.g., a television display, computer display, wearable device display) to analyze surface distortion and then make corrective image projection adjustments. 
         [0044]    The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that specific details are not required in order to practice the invention. Thus, the foregoing descriptions of specific embodiments of the invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed; obviously, many modifications and  variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, they thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the invention.