FIG. 8 illustrates an example graph 800 of transmission versus contact layer thickness of an ultrasonic fingerprint sensor for different frequencies, according to embodiments. Graph 800 illustrates that for different contact layer thicknesses, different transmission frequencies result in constructive or destructive interference. For example, at a transmission frequency of 40 MHz, a contact layer thickness of approximately 35 micrometers (μm) results in maximal constructive interference as indicated by the peak transmission signal. Similarly, at 20 MHz, a contact layer thickness of approximately 70 μm results in maximal constructive interference as indicated by the peak transmission signal. However, a contact layer thickness of approximately 70 μm results in maximal destructive interference for a transmission frequency of 40 MHz, as indicated by the minimum transmission signal.
