CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit under 35 U.S.C. § 119 of the filing date of

Norwegian patent application no. 20140653 filed May 27, 2014, the disclosure of which is incorporated herein by reference.

FIELD OF THE DISCLOSURE

[0002] This disclosure relates to a biometric sensor device for measuring structures and properties of an object of organic tissue, especially a fingerprint sensor.

BACKGROUND

[0003] There are, in general, two types of fingerprint sensors, swipe/sweep sensors and area/placement sensor. Swipe sensors can be manufactured at lower cost than placement sensors as the sensing area of a swipe sensor is smaller than that of a placement sensor. Fewer interconnects, smaller sensor substrates, smaller ASIC (application-specific integrated circuit), etc. contribute to the lower cost of swipe sensors relative to placement sensors. Swipe sensors, however, are considered less user-friendly than placement sensors. This is mainly due to the fact that some training of the user on how to swipe the finger across the swipe sensor is necessary. For a placement sensor, on the other hand, the finger is simply laid over, or placed on, the sensor, which might be more intuitive to the user. The downside of placement sensors is the need for more complex electronics due to the many more sensing elements, leading to larger ASICS and more complex interconnects, and hence higher cost.

[0004] European Patent Publication EP1353294 and U.S. Patent No. 7,190,816 describe a system utilizing a sweep fingerprint sensor where the finger is registered in the system in the normal

l way, by making a full finger swipe. The swipe sensor can thereafter be used in a strict

authentication mode and an easy authentication mode. In the strict authentication mode the finger needs to perform a full swipe to fulfill the authentication, while in the easy authentication mode the finger might lay still on the swipe sensor and an image of only a small part of the fingerprint is generated. The small image is used to authenticate the user with a lower security level, suitable for releasing a dial lock or other low-security level activity.

[0005] U.S. Patent No. 7,369,684 describes a system using multiple sweep sensors in which each sweep sensor has multiple linear sensing arrays. The linear sensing arrays of the first sweep sensor have a first regular spacing, the linear sensing arrays of the second sweep sensor have second regular spacing, which may be identical to the first regular spacing, and the multiple sweep sensors are spaced apart such that the spacing between them is other than an integer multiple of the first known spacing. The idea of this patent is to use multiple sweep sensor to increase the resolution of the image, hence the importance of the non-integer multiple of the spacing between them. Each sweep sensor of this application is a multi-line sweep sensor, as would be required for image stitching as described therein.

[0006] U.S. Patent No. 7,734,074 describes using a plurality of linear finger sensing arrays in order to generate a respective plurality of finger image data sets, determining the movement of the finger based upon the finger image set, generating a resampled finger image data set based on the finger movement by arranging the plurality of finger image data sets into a single array to generate a supersampled finger image data array having a resolution greater than a resolution of each finger image data set, and then downsampling the supersampled finger image data array to generate a downsampled finger image data array having a resolution lower than the resolution of the supersampled finger image data array and thereby defining the resampled finger image data set. The patent states that this is in contrast to approaches that use various types of finger speed sensors to control the sampling rate or discard repeated data, such as disclosed, for example, in U.S. Patent No. 6,002,815, or use cross-correlation between partially overlapped image frames to eliminate redundant data and stitch the data together into a single global image, such as disclosed in U.S. Patent No. 6,289,114.

[0007] Based on the discussion above a benefit may be achieved by providing a sensor system that combines the low cost of the swipe sensor system with the user friendliness of the placement sensor. This is obtained as stated in the accompanying claims.

[0008] The invention will be described more in detail below with reference to the accompanying drawings, illustrating the invention by way of examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic view of an exemplary sensor as described herein.

[0010] FIG. 2 is a fingerprint as measured by a sensor as described herein.

DETAILED DESCRIPTION

[0011] As illustrated in FIG. 1 the present invention relates to a biometric sensor device 10 with a limited number of swipe sensor arrays ai-a _n , where n corresponds to the number of swipe sensor arrays or linear sensing arrays, typically in the range of 4-12 arrays. These arrays ai-a„ are spaced a few millimeters d apart such that the arrays cover a typical fingerprint placement sensor area, e.g., 6x6 mm ² , 8x8 mm ² , 10x10 mm ² or 10x12 mm ² . The arrays may be arranged in a rectangular configuration as shown or in other shapes beneficial to the particular application. The distance d is typically larger than a typical feature of an organic tissue to be measured, typically less than 5 mm, preferably less than 2 mm. Though the sensor anays ai-a„ are shown as equidistant, the distance d between two arrays may in an alternative embodiment vary between the different pairs of sensor arrays. One exemplary configuration as illustrated in FIG. 1 comprises eight sensor arrays separated by a distance d = 1.5 mm.

[0012] Each of the individual swipe sensor arrays ai-a _n may be of any suitable type already known by the person skilled in the art. Each swipe sensor array may comprise a single sensor line or may comprise multiple sensor lines. A swipe sensor array, e.g., as described in EP0988614, would typically have one or two sensor lines per swipe sensor array, while a sensor array, e.g., as described in U.S. Patent No. 6,289,114 and U.S. Patent No. 7,864,992, typically would have more than three sensor lines per swipe sensor array. At least one of the sensor arrays of the biometric sensor device may be provided with means for measuring the velocity, i.e., speed and direction, of the organic tissue over the sensor as either an integral part of the sensor array, e.g., as described in EP0988614, or the sensor array may comprise separate velocity measurement sensors.

[0013] In the following description, the object of organic tissues is described as a finger surface or finger. The biometric sensor device 10 is not, however, limited to sensing fingerprints, but all organic tissues that could be measured by the biometric sensor device, such as palm print, knuckle print, ear pattern, etc.

[0014] In an exemplary embodiment, to use the biometric sensor device 10, the user places the finger on the sensor array and performs a very short swipe in the direction essentially perpendicular to the individual sensor array, typically only a few millimeters, depending on the distance d. The distance of the finger movement necessary to cover a desired portion of the fingerprint thus corresponds to the distance d between the swipe sensor arrays. In the case of the alternative embodiment where the distances d between the swipe sensor arrays were not equidistant, the necessary finger movement would be similar to the largest distance d.

[0015] Each sensor array generates a plurality of measurement data, preferably at a predetermined sampling rate, as the finger is swiped over the swipe sensor array. The sampling rate may in one exemplary embodiment be specified so as to obtain a desired image resolution for a predetermined maximum velocity of finger swiped over the swipe sensor arrays.

[0016] In a first step, a processor 12, e.g. in an ASIC, generates a set of first images of the finger from each of the plurality of measurement data. This first step of generating a first set of images might be performed using any suitable method. One such method is to calculate or measure the velocity of the finger to determine the relative positioning of the plurality of measurement data to form a two-dimensional image of the finger. Another such method is to use overlapping parts of the plurality of measurement data to form the two dimensional image of the finger. As the finger performed a very short swipe, the images from the first set of images would not contain a complete fingerprint. Hence, the first set of images consists of a set of partial images of the fingerprint surface. In a next step, the processor 12 combines the partial images generated from each of the plurality of measurement data to generate a complete image of the finger surface, where the complete image of the finger surface is larger than each of the partial images, typically a factor of n larger than the size of the partial images. In this way, the complete image of the organic tissue may be obtained based on a sliding movement n times smaller than the dimension of the complete image.

[0017] FIG. 2 illustrates a finger surface measured by a biometric sensor device as described herein, where ai-a„ illustrates the positions of the sensor arrays in relation to the respective partial images di-d _» measured by the sensor array.

[0018] In order to reduce the processing needs of the biometric sensor device it would be preferable only to scan each part the finger once. By measuring the velocity of the finger the scanning may be stopped when the finger has moved a distance substantially corresponding to the distance between the scanning lines. Alternatively, the sensor may be provided with means for detecting when the finger has moved a certain distance. Accordingly, the scanning rate and/or period may be adjusted according to the velocity of the finger relative to the sensors. Alternatively, the measurements may continue but only the data scanned during the distance dj-d _n between the lines ai-a„ are used.

[0019] As the user may swipe the finger slightly off axis relative to the scanning direction the system may include measuring means for measuring the direction, thus providing means for correcting the sampled data. This may be performed as described in EP1328919 by combining and correlating the signals from sensors on a two dimensional surface.

[0020] While the invention has been illustrated and described in detail in the drawings and forgoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive and is not intended to limit the invention to the disclosed embodiments. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used advantageously. Any reference signs in the claims should not be construed as limiting the scope of the invention..