Modal Analysis

When an object is set into motion, higher order bending modes often result in complex vibrational patterns, a phenomenon which is of critical importance in the design of sensors and actuators. For a full modal analysis of such devices, the measurement laser of the PICOSCALE Vibrometer is scanned over the sample and vibrations are measured at each pixel. From the recorded data a vibration image can be reconstructed.

Working Principle

The vibrations are measured with a tightly focused laser beam of a Michelson interferometer, thus employing the same measurement principle as the PICOSCALE Interferometer. The recorded displacements at each pixel can be analysed in the time or frequency domain. In addition, the instrument is equipped with a lock-in amplifier which allows for the direct imaging of bending modes without the need of post-processing the data.

The scanning of the measurement laser over the sample is performed by a 3D SmarAct positioning system that makes it possible to image structures with sizes from just a few µm up to 20 mm. Because closed loop piezo positioners with nm resolution are used, the positioning of the laser beam is highly reproducible.

In order to excite the sample, vibrations can be either induced by the advanced piezo-based shaker stage or directly with an electrical signal that is generated by the PICOSCALE Vibrometer.

A unique feature of the PICOSCALE Vibrometer is that the interferometer laser beam is used simultaneously to record a microscopy image of the sample. This microscopy image is thus intrinsically aligned with the vibration measurements and a separate microscope imaging system is not required.

Specifications

Vibration Measurements
 
Vibration Resolution in Single Point Mode [pm] 1
Vibration Resolution in Imaging Mode [nm] < 1
Frequency Range [MHz] Up to 2.5*
Optical Microscope
 
Optical Lateral Resolution [μm] 2 ... 7**
Working Distance [mm] 1.5 ... 10**
Maximum Image Size [mm] 20 x 20
Minimum Pixel Size [μm] 1
Maximum Number of Pixels 1000 x 1000
Dimensions
 
Controller 2 units of each 33 x 27 x 7.2 cm (W x L x H), combined
weight 7.6 kg
Scanning Stage 5.5 x 11.0 x 7.5 cm (W x L x H), weight 0.25 kg
Scanning Mount Granite stone 15 x 20 x 4 cm (W x L x H) with stainless steel post 2.5 x 15 cm (Ø x H), combined weight 4.3 kg
Shaker Stage Stainless steel 8 x 1.5 cm (Ø x H), weight 0.5 kg

*lowest frequency in imaging mode is 250 Hz

**depending on sensor head