Ultrasonic fingerprint sensing
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Products |
Ultrascan > 2013 > Qualcomm |
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"It's practically impossible to try to predict what types of patterns will be available or what types of covers," Katouzian said. "We are constantly buying different covers and different materials to make sure the algorithm can tell the difference between a legitimate fingerprint and a spoof." |
Qualcomm 3D Sonic Sensor Gen 1 was 4x9mm (surface area 36mm2). Gen 2 will debut with a sensor that is 8x8 (64mm2). This is not the very large 20x30mm sensor: likely too expensive. |
CrossMatch >> Sonavation"Authorizer prototype": 64x64 pixels @126 micron pitch (announced @250dpi, but this is 200 dpi). |
The key imaging component of the sensor is the ceramic Micro-Electro Mechanical System (MEMS) piezoelectric transducer array that is made from a ceramic composite material. When this piezoelectric material is formed into a pillar 1/10th the diameter of a human hair, it has a unique set of properties that enable it to mechanically oscillate when an electric field is applied or create an electrical voltage when mechanically vibrated. The piezoelectric pillar is electrically vibrated at its natural ultrasonic resonant frequency. If a fingerprint ridge is directly above the pillar, much of the ultrasonic energy is absorbed by the skin and the signal impedance of the pillar is very high. If a valley is directly above the pillar, very little energy is absorbed and the impedance is very low. By arranging the pillars in a matrix of several thousand elements a two-dimensional image of a fingerprint can be created. The imaging ASIC electrically controls the pillar oscillation, imaging of the fingerprint and data management of the fingerprint information. |
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UC Berkeley Swarm lab >> Invensense |
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Looks to work more or less like the Optel sensor. |
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Reseach & Development |
Optel |
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Cornell University + Intel / Geegah / A*STARlinear array 64 pixels ultrasonic (AlN) |
single transducer. AlN on CMOS 180 nm chip, ultrasonic waves through the silicon. Transmit & receive transducers are 50x50 microns. |
Tsinghua university |
North Carolina State University / GoodixOne pixel moving / 500 dpi demonstrated. Based on PZT-5H. Detect a vessel @ 1 mm depth. Curiously, no real fingerprint image displayed ! |
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Design and fabrication of a cMUT probe for ultrasound imaging of fingerprints / A. Savoia & als. Nicola Lambertia, Giosue Caliano, Antonio Iula, Alessandro Stuart Savoia |