Two-dimensional vibration measurement by using a quadrant position sensor

A new method for measuring vibrations using a quadrant position sensor has been developed. It allows non-contact measurement of natural frequencies of objects which are small or light and transparent. The natural frequencies in two dimensions can be received at the same time. The system consists of a laser light source, a quadrant position sensor and spectrum analyzer. The object is illuminated by divergence laser rays coming from a microscope objective. The vibration amplitudes are magnified and detected by the position sensor. By adjusting the distance between object and microscope objective or detector, the sensitivity and linearity of the system can be changed. The natural frequencies of a plastic plate were measured by this method. The experimental results agreed well with the calculation results according to the theory of material mechanics. This method is very useful in the research field of millibioflight. The natural frequencies of the dragonfly wing, which is lighter than 0.1 mg, has been measured by this method. We can determine the natural frequencies of bending and torsional deformation by using the information of two dimensions.