Average of 250 measurements of the switch-on \(U_{on}\left(t\right)\)  and switch-off \(U_{off}\left(t\right)=-U_{on}\left(t-l\right)\) response of the sensor at the maximum transmitted power, and the average of 50 measurements of an individual pyroelectric pulse generated using a 6 ms ultrasound burst at maximum power. The switch-off response has been inverted and shifted by -τ so that its amplitude can be compared with that of the switch-on response.