Fake finger detection using ridge features

An ultrasonic fingerprint sensor device comprising:

• a two-dimensional array of ultrasonic transducers;
• and
• a processor, wherein the processor is configured to:
• capture a first image of a fingerprint pattern at an ultrasonic fingerprint sensor, wherein the first image is based on ultrasonic signals corresponding to a first time of flight range;
• capture a second image of the fingerprint pattern at the ultrasonic fingerprint sensor, wherein the second image is based on ultrasonic signals corresponding to a second time of flight range, the second time of flight range being delayed compared to the first time of flight range;
• quantify a difference in a width of ridges of the fingerprint pattern in the first image compared to the width of ridges of the fingerprint pattern in the second image;
• and
• based on the quantification of the difference, determine a probability whether the finger is a real finger.

A non-transitory computer readable storage medium having computer readable program code stored thereon for causing a computer system to perform a method for determining whether a finger is a real finger at a fingerprint sensor, the method comprising:

• capturing a first image of a fingerprint pattern at an ultrasonic fingerprint sensor, wherein the first image is based on ultrasonic signals corresponding to a first time of flight range;
• capturing a second image of the fingerprint pattern at the ultrasonic fingerprint sensor, wherein the second image is based on ultrasonic signals corresponding to a second time of flight range, the second time of flight range being delayed compared to the first time of flight range;
• quantifying a difference in a width of ridges of the fingerprint pattern in the first image compared to the width of ridges of the fingerprint pattern in the second image;
• and
• based on the quantification of the difference, determining a probability whether the finger is a real finger.