Abstract:
A device has a flexible substrate supporting an array of magnetic sensors exposed to a uniform external magnetic field. One or more controllers receive magnetic sensor signals from the magnetic sensors. The one or more controllers collect reference magnetic sensor signals when the flexible substrate is aligned with the uniform external magnetic field. The one or more controllers collect first polarity magnetic sensor signals in response to deformation of the flexible substrate in a first direction. The one or more controllers collect second polarity magnetic sensor signals in response to deformation of the flexible substrate in a second direction. The magnetic sensor signals establish a profile of the orientation of the flexible substrate with respect to the uniform external magnetic field.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/059,138, filed Oct. 2, 2014, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to analyzing surface shape and spatial positioning. More particularly, this invention relates to techniques for magnetic sensor based surface shape analysis. 
     BACKGROUND OF THE INVENTION 
     Sensors play a crucial role in modern technology as they have become an essential part of millions of products used 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. 
     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 
     A device has a flexible substrate supporting an array of magnetic sensors exposed to a uniform external magnetic field. One or more controllers receive magnetic sensor signals from the magnetic sensors. The one or more controllers collect reference magnetic sensor signals when the flexible substrate is aligned with the uniform external magnetic field. The one or more controllers collect first polarity magnetic sensor signals in response to deformation of the flexible substrate in a first direction. The one or more controllers collect second polarity magnetic sensor signals in response to deformation of the flexible substrate in a second direction. The magnetic sensor signals establish a profile of the orientation of the flexible substrate with respect to the uniform external magnetic field. 
     The disclosed techniques may be combined with other shape sensing methods. The disclosed techniques may be used for rotation sensing and may be applied to three dimensional objects. The earth&#39;s magnetic field may be supplemented by a fixed externally generated magnetic field. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention is more fully appreciated in connection with the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a magnetic sensor surface shape analysis system configured in accordance with an embodiment of the invention. 
         FIG. 2  is a side view of two magnetic sensors in a uniform magnetic field. 
         FIG. 3  illustrates magnetic sensor orientation in three axes relative to a uniform magnetic field. 
         FIG. 4  illustrates a deformed substrate and resultant magnetic sensor vector signals. 
     
    
    
     Like reference numerals refer to corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a magnetic sensor surface shape and spatial positioning analysis system  100 , which is configured in accordance with an embodiment of the invention. The system  100  includes a set of magnetic sensors  102 _ 1  through  102 _N positioned on a flexible substrate  106  (e.g., polyimide or similar material). Each magnetic sensor  102  is identical and is sensitive to an external magnetic field along three dimensions of space. In one embodiment, each magnetic sensor has an axis of sensitivity oriented in a direction defined by a predetermined pattern used to cover the surface  106 . 
     Each sensor  102  has a link  107  to an X-axis controller  108 , a link  109  to a Y-axis controller  110  and a link  111  to a Z-axis controller  112 . The controllers may be positioned on or outside of the flexible substrate  106 . The controllers may be combined into a single controller. 
     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. Various uniform and non-uniform spacing paradigms may be used. 
     Each magnetic sensor  102  must have sufficient sensitivity to measure the magnitude and orientation of the earth&#39;s magnetic field, which is substantially uniform in any local area. In one embodiment, MLU sensors of the type described in European Patent Application 2013EP-290244 (CROCUS-63-EP) filed Nov. 10, 2013, and European Patent Application 2013EP-290243 (CROCUS-65-EP) filed Nov. 10, 2013, are used. These applications are owned by the owner of this patent application and are incorporated herein by reference. 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. 
     By way of overview, the MLU sensors disclosed in the referenced applications include a magnetic tunnel junction with a reference layer that has a reference magnetization oriented substantially parallel to the plane of the reference layer. A sense layer has a sense magnetization. A tunnel barrier layer is positioned between the sense and reference layers. A magnetic device provides a sense magnetic field adapted for aligning the sense magnetization. The sense layer magnetization may be oriented between a direction parallel to the plane of the sense layer and a direction perpendicular to the plane of the sense layer when the sense magnetic field is provided. The sense layer magnetization may be oriented with a magnitude of an external magnetic field being below 150 Oe. 
     An external magnetic field has an in-plane component oriented parallel to the plane of the sense layer and an out-of-plane component perpendicular to the plane of the sense layer. The out-of-plane component and the in-plane component are sensed by the sense layer. 
       FIG. 2  is a side view of two magnetic sensors  102 _ 1  and  102 _ 2  in a uniform magnetic field  104  (e.g., the earth&#39;s magnetic field). In this instance, the substrate  106  is flat. The magnetic field  104  is orthogonal to the flat surface. The magnetic sensor  102  is positioned to receive an orthogonal magnetic field and therefore generates a reference output. 
       FIG. 3  illustrates magnetic sensor orientation in three axes relative to a uniform magnetic field. The figure also illustrates associated angles for a vector mapped to X, Y and Z values. 
       FIG. 4  illustrates the surface  106  with a flat section  400 , which will receive a signal corresponding to the orientation of the reference field (e.g., earth field). Section  402  is deformed upwards, while section  404  is deformed downwards. As a result, the sensors on sections  402  and  404  detect different signals corresponding to the same reference field. The different signals are indicative of respective orientations of sections  402  and  404 . 
     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. 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 . 
     Returning to  FIG. 1 , it can be appreciated that the X-axis controller  108  samples magnetic sensor signals to identify rotation along the Y-axis and Z-axis, while the Y-axis controller  110  samples magnetic sensor signals to identify rotation along the X-axis and Z-axis and the Z-axis controller  112  samples magnetic sensor signals to identify rotation along the X-axis and 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 rotation within a region of the surface, the sampling rate may be increased in the subject region. The controllers  108 ,  110  and  112  may track the rate of change over time. Accordingly, surface profiles and spatial orientation over time may be produced. This can be used for sensing rotation, thereby operating as a gyroscope. 
     Observe that for any particular sensor, the signal collected allows one to deduce the magnitude of the reference field and the orientation of the sensor with respect to the reference field. Since the reference field is fixed, uniform and identical for all sensors, information from sensors enables one to deduce the relative orientation of any sensor with respect to any other sensor. The earth&#39;s magnetic field provides a fixed magnetic field of approximately 0.5 Oersted, which is sufficient for a sensor. However, for certain applications, a stronger externally generated magnetic field (e.g., 200 Oersted) may be utilized for increased sensitivity and accuracy. The externally generated magnetic field may be produced by a proximately positioned magnet. Alternately, the externally generated magnetic field may be produced by lines that carry currents and thereby induce a magnetic field. 
     An assembly of sensors on a flexible substrate may be used to cover an object or be positioned within the object. Taking known positions on the surface or within the object and relative orientation of sensors to each other enables one to deduce the shape of the object. The knowledge of sensor orientation with respect to the reference field allows one to deduce the orientation of the object itself with respect to the reference field. Since the measurement of position and shape is not dependent on the proximity to a local source of magnetic field, the sensors can be freely arranged at long distances from one another to effectively cover very large objects, such as a bridge or building to monitor movement, position, oscillatory modes and so forth. 
     Embodiments of the invention can be used for body motion capture with applications in fields as varied as film making (e.g., motion capture) or medical applications (respiratory monitoring). In such cases the sensors may be inserted in a three dimensional body to deliver additional information on the local variations within the object. 
     Techniques of the invention may be used with other shape and spatial position sensors for increased accuracy and sensitivity. Elastic deformation may be sensed when localized magnets are used to generate magnetic fields on each sensor. When a membrane is stretched, the magnet and sensor separation increases so the detected magnetic field is reduced independently of any bending. 
     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.