LOW-COST OPEN-LOOP VIBRATING REED MECHANICAL SPECTROMETER USING PULSE-TRAIN EXCITATION AND CAPACITIVE CURRENT DETECTION

A new, low cost, vibrating reed mechanical spectrometer has been devel oped. The setup consists of a pulse train generation system for capaci tive excitation of the specimen in one of its flexural vibration modes and of a capacitive current measuring and amplification circuit for d etection of the specimen oscillation. The used detection method is con venient for low damping levels (internal friction, Q(-1) less than or equal to 0.02) and low vibration amplitudes (less than or equal to 0.1 mu m) only. The resonance frequency and the mechanical energy dissipa tion are derived by numerical analysis of the measured freely decaying vibrations. In terms of experimental performance several such analysi s methods (Hilbert transformation method, zero-transition method, nonl inear fitting) are evaluated. The system's performance is illustrated with some informative examples.