Abstract: A sensor or receiver array includes first and second pyroelectrically active electrodes formed of polyvinylidene difluoride and separated by a spacer layer that acts to electrically separate the pyroelectric layers while keeping them close enough such that they see effectively the same vibration or background acoustic excitation while maintaining sufficient separation to ensure that they generate significant differences in their pyroelectric responses. The structure provides two distinct signals (at separate timestamps), the difference between which provides a more accurate signal. An ultrasound detection system includes the tri-laminar sensor, disposed within a detection zone in which a test element can be positioned. The apparatus includes a processing unit, which comprises a detector unit coupled to the first and second pyroelectric elements and configured to derive a differential signal from the first and second pyroelectric elements.

Abstract: A sensor or receiver array includes first and second pyroelectrically active electrodes formed of polyvinylidene difluoride and separated by a spacer layer that acts to electrically separate the pyroelectric layers while keeping them close enough such that they see effectively the same vibration or background acoustic excitation while maintaining sufficient separation to ensure that they generate significant differences in their pyroelectric responses. The structure provides two distinct signals (at separate timestamps), the difference between which provides a more accurate signal. An ultrasound detection system includes the tri-laminar sensor, disposed within a detection zone in which a test element can be positioned. The apparatus includes a processing unit, which comprises a detector unit coupled to the first and second pyroelectric elements and configured to derive a differential signal from the first and second pyroelectric elements.

Abstract: There is disclosed an apparatus and method for detecting cavitation in fluid machines, for example pumps (100). In one embodiment a piezoelectric gasket (102) is used as a sensor to sense cavitation. In some embodiments highpass filters (302), (501) are used to detect ultrasonic acoustic signals in about the MHz range. If the energy in the MHz range is excessive then cavitation is deemed to be occurring and the speed of a motor (110) may be reduced in proportion to the degree of cavitation deemed to be occurring. In another embodiment (FIG. 5) the energy in the MHz range is normalized against the energy in the kHz range. Other sensors (600, 701) are also disclosed.

Abstract: 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 (521 b) can be used to compensate for unwanted accelerometer sensitivity of a sensor element (521 a).

Abstract: 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 (521 b) can be used to compensate for unwanted accelerometer sensitivity of a sensor element (521 a).

Abstract: There is disclosed an apparatus and method for detecting cavitation in fluid machines, for example pumps (100). In one embodiment a piezoelectric gasket (102) is used as a sensor to sense cavitation. In some embodiments highpass filters (302), (501) are used to detect ultrasonic acoustic signals in about the MHz range. If the energy in the MHz range is excessive then cavitation is deemed to be occurring and the speed of a motor (110) may be reduced in proportion to the degree of cavitation deemed to be occurring. In another embodiment (FIG. 5) the energy in the MHz range is normalised against the energy in the kHz range. Other sensors (600, 701) are also disclosed.

Abstract: A cavitation sensor includes an ultrasonically absorbent coating (20) disposed around a piezoelectric element (30) and a conduit (25). The conduit (25) includes a boundary delimited by the piezoelectric element (30), while the ultrasonically absorbent coating (20) is substantially transparent to acoustic driving field frequencies. The sensor is more accurate than prior art sensors.