Scanning Vibrometry

The PICOSCALE Vibrometer is a turnkey solution to measure vibrations of micromechanical structures with sizes that range from just a few µm to multiple cm. Applications include the testing of MEMS, sensors, miniature loudspeakers but also bearings and actuators. Because the instrument is equipped with an integrated microscope and can measure up to 1 million pixels, it is excellently suited to visualize vibrational modes at high spatial and temporal resolution.

• Contactless measurements with light
• Scanning laser interferometer to measure out-of-plane motion (in the direction of the laser beam)
• Measurement bandwidth up to 2.5 MHz (10 MHz sample rate) with a resolution under 1 pm
• Integrated infrared confocal microscope with an optical resolution down to 2 µm
• Modal analysis of encapsulated MEMS
• Stroboscopic imaging of in-plane motion (perpendicular to the direction of the laser beam)
• Turn-key instrument complete with shaker stage

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.

SmarAct offers also a non-scanning vibrometer to measure vibrations and motion at up to 3 points, an ideal solution to track the dynamics of motion systems in 3D but also to identify noise sources in machines.

Application Examples

For an overview of all application notes click here.

Measuring vibration of encapsulated MEMS

When MEMS are packaged in a silicon enclosure it is impossible to use conventional optical measurement methods to evaluate their dynamic performance without opening them up. The PICOSCALE Vibrometer utilizes an infrared measurement laser with a confocal detection scheme which opens the way to analyze the dynamics of a motion sensor through its enclosure of silicon.

We thank InvenSense, a TDK Group Company, for their support with this application example.

Measuring lateral vibrations within all-silicon loudspeakers

Beyond the interferometric measurement of out-of-plane vibrations, the PICOSCALE Vibrometer allows the imaging of in-plane vibrations of encapsulated devices with infrared confocal microscopy. Here, we tested an innovative MEMS loudspeaker design in which sound pressure is generated by multiple electrostatic bending actuators that move laterally.

We thank the Fraunhofer Institute for Photonic Microsystems for the sample and their support with this application note.

Identifying unsound resonances of smartphone loudspeakers

Characterizing the dynamic response of loudspeakers is essential to optimize their performance in a wide range of appliances. Here, we used SmarAct’s PICOSCALE Vibrometer to analyze the response of two smartphone loudspeakers from different manufacturers. The ability of the instrument to directly image vibrational modes of mechanical structures allows to attribute discontinuities in the amplitude spectra to specific resonances of the loudspeaker diaphragm or housing.

Testing ultrasonic transducers with vibrometry

The performance of ultrasonic transducers can be evaluated by measuring the mechanical motion that is induced by an electrical pulse. The PICOSCALE Vibrometer allows precise measurements of sub-nanometer motions of the transducer surface by interferometry.

We thank Vallen Systeme GmbH for their support with this application example.

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 for data post-processing.

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.

Key Specifications

For each of the Components of the PICOSCALE vibrometer, a detailed specification sheet is available at the download section.

¹ When analyzing displacements in the frequency domain

² Sampling rate is 10 MHz

³ Depending on the selected sensor head