Microelements vibration measurement using quasi-heterodyning method and smart-pixel camera

Rapid increase of M(O)EMSs production with the focus on highly responsible elements requires 100% quality control of the products and therefore also development of the suitable measurement methods with high accuracy and high speed. Vibration measurements play an important role in the micromechanical object characterization especially during reliability testing, objects functionality testing, material properties derivation and also defect detection. Optical characterization methods suits well this requirements. Among different optical measurement methods interferometric techniques are of the main interest due to their noncontact and non contaminating character as well as high measurement precision. Laser Doppler Vibrometry (LDV) [1] is considered to be the most accurate method for determination of resonance frequencies as well as determination of vibration amplitude distribution over an object under test. However as a point method, for the second task it requires a 2D scanning, which elongates the measurement time considerably. For fast measurement full field optical methods are preferable. The most widely used are the time-averaging and stroboscopic interferometry [2]. Unfortunately both methods require the vibration amplitude of at least 0.19λ to be able to detect resonant frequency of an object. That limitation puts strong constrain on the excitation method and a type of an element to be tested. An interesting method allowing measurement of small vibration amplitudes with high accuracy is so called heterodyning time-averaging interferometry [3]. It requires, however, more complex measurement