Accurate detection of mechanical vibrations having very high frequencies and extremely small amplitudes, has significant importance in many scientific areas. Among the practical applications of this kind of detection are sub-nanometric characterization of piezo actuators, and the characterizations of Surface Acoustic Wave (SAW) based RF filters, in order to determine their propagation losses. In this master thesis, already existing optics have been extended to measure amplitude of mechanical vibrations on the surface of SAW based RF filter. To achieve this goal, necessary electronics are developed, which take electrical signals from the photodetector of optical interferometer and then extract vibration amplitude information from it.
At the beginning, a study is conducted to get in depth knowledge of SAW devices and already developed optical interferometry set-up. The requirements of electronic detection system are specified, according to the specification of the photodetector. In the next stage a basic concept is developed, to build this system based upon a comparative study of different RF receiver architectures. This concept named Low-IF receiver architecture acts as a baseline for the next design phase, in which this receiver is going to be a major part of complete electronic detection system. The design process included finalization of the overall structure of the receiver chain, and selection of all hardware and software components.
Additionally this structure and components are analyzed according to the requirements. The hardware and software implementations are done in different stages. Initially, receiver chain and components are analyzed theoretically using software tools like ADISimRF, diamond plots and spread sheets. In the next stage the circuit implementation on hardware is tested using signal generators, spectrum analyzer and NI supported modules. The complete system incorporating both optics and electronics is then tested, using LabView based software, with specific tests defined exclusively for critical analysis of this application. Finally, test results prove that, the RF receiver can measure signal amplitudes in the complete required range of -80 dBm to -140 dBm , with an accuracy close to 100%. Also the precision in measuring vibration amplitudes is in acceptable limits and the electronic detection system can easily support measurements as low as 1 pm.
The overall system has proved to be fast enough to satisfy the million measurements per day requirement, by completing a single measurement in less than 86 msec. Because of LabView, the system also supports automation for the upcoming task of moving the SAW surface, to characterize multiple points