Ultrasonic fingerprint sensor with a contact layer of non-uniform thickness

A method for generating an image at an ultrasonic sensor, the method comprising:

• performing an imaging operation at an ultrasonic sensor comprising an array of ultrasonic transducers and a contact layer having a non-uniform thickness overlying the array of ultrasonic transducers, such that a thickness of the contact layer is non-uniform over a surface of the array of ultrasonic transducers, comprising:
• controlling a transmission frequency of activated ultrasonic transducers during the imaging operation, wherein a plurality of transmission frequencies are used during the imaging operation;
• and
• capturing a plurality of portions of a fingerprint image using the plurality of transmission frequencies such that each portion of the plurality of portions of the fingerprint image is captured using one transmission frequency of the plurality of transmission frequencies.

A non-transitory computer readable storage medium having computer readable program code stored thereon for causing a computer system to perform a method for generating an image at an ultrasonic sensor, the method comprising:

• performing an imaging operation at an ultrasonic sensor comprising an array of ultrasonic transducers and a contact layer having a non-uniform thickness overlying the array of ultrasonic transducers, such that a thickness of the contact layer is non-uniform over a surface of the array of ultrasonic transducers, comprising:
• controlling a transmission frequency of activated ultrasonic transducers during the imaging operation, wherein a plurality of transmission frequencies are used during the imaging operation;
• and
• capturing a plurality of portions of a fingerprint image using the plurality of transmission frequencies such that each portion of the plurality of portions of the fingerprint image is captured using one transmission frequency of the plurality of transmission frequencies.