A system (100) uses a pyroelectric membrane (122) and an ultrasound absorber (123) to measure the amount of ultrasonic energy received from a transmitter (105) through a sample (110). The thermal response of the pyroelectric membrane (122) is sensitive to ultrasound time-averaged intensity but is insensitive to the phase of the ultrasound. A waveform (200) shows rising (210), peak (220) and decaying (230) portions of a signal from the pyroelectric membrane (122) in response to on/off transitions of the transmitter (105). A system (300) uses a peak detector (333) to automatically turn the transmitter (105) on/off. A system (400) has background removal circuitry (444) to remove unwanted accelerometer-induced noise or electrical noise. A multi-element ultrasonic sensor (520) has cavities (555) so that a dummy sensor (521b) can be used to compensate for unwanted accelerometer sensitivity of a sensor element (521a). A sensor (620) has ultrasound absorbing (or reflective) regions (660) to compensate for unwanted accelerometer sensitivity. A system (900) has a low frequency path (909) sensitive to the pyroelectric effect, and a high frequency path (919) sensitive to the acoustic pressure amplitude, of a signal from a sensor (920). A sensor (1020) uses a pyroelectric material (1022) with poled regions (1099) separated by a non-poled region (1098).
