High-frequency calibration of piezoelectric displacement sensors using elastic waves induced by light pressure/Visokofrekvencna umeritev piezoelektricnega senzorja pomikov z uporabo elasticnih valov vzbujenih s svetlobnim tlakom

In the study of ultrasound propagation In matter, displacement sensors are Indispensable and of these, the most sensitive are piezoelectric sensors. In order to eliminate the intrinsic effects of the sensor from the measurements, the sensor has to be properly calibrated, which means that its transfer function has to be evaluated from a known sensor input signal and a measured sensor output signal. This has usually been done by comparing the sensor response signal to a known input signal, namely, an ultrasonic waveform, which can be theoretically calculated using mathematical models and numerical algorithms. Until now, the point-source-point-sensor model has been primarily used, while ultrasonic waves were induced mechanically either by a dropped ball or a capillary fracture. In this paper, a real-source-real-sensor model is presented. It provides a more faithful waveform construction and it enables the removal of the aperture effect from the calculated sensor transfer function, thus giving correct and universal sensor response characteristics. This was corroborated by high- frequency calibration measurements of the output signal of a Glaser-type conical sensor in two positions on both surfaces of a glass plate, while ultrasonic waves were induced by the radiation pressure of a nanosecond laser pulse. Keywords: absolute sensor calibration, piezoelectric sensor, laser pulse, aperture effect, elastic waves in a plate, optodynamics, Green's function V prispevku je predstavljena kalibracija piezoelektricnega senzorja majhnih pomikov z ultrazvocnimi valovi, ki jih vzbudi svetlobni tlak laserskega bliska na povrsini steklene plosce. S primerjavo meritev in matematicnega modela sirjenja ultrazvoka v trdni snovi je dolocena frekvencna karakteristika senzorja pri visjih frekvencah kot doslej. Merjenje majhnih pomikov snovi je nepogresljivo pri proucevanju sirjenja mehanskega valovanja v snovi. Med vsemi senzorji so najbolj obcutljivi tisti, ki delujejo z izkoriscanjem piezoelektricnega pojava, in so zato najbolj primerni za merjenje valovanj z majhno amplitudo pomika. Taksni senzorji so tako v uporabi v strojnistvu, pri testiranjih ter v razvoju in raziskavah. Uporabljajo se pri meritveh akusticne emisije in pri neporusnih preiskavah snovi, v mikroseizmologiji ter pri mnogih drugih aplikacijah ultrazvoka v snovi. Cilj umeritve senzorja je dolocitev njegove prenosne funkcije. Z njo se lahko iz izhodnih signalov senzorja izlusci pomike merjenega mehanskega valovanja.