Experimental studies on extremely small scale vibrations of micro-scale mechanical and biological structures

Abstract

Experimental vibration analysis of mechanical structures is a well-established field, with extensive literature on macro-scale structures in civil, mechanical, and aerospace engineering. However, the study of vibrations in micro-scale structures such as MEMS devices, liquid droplets, and biological cells is relatively new.

At these scales, vibration amplitudes are typically in the nanometer or sub-nanometer range, while frequencies lie in the kHz-MHz range depending on the dimensions. In this study, a scanning Laser Doppler Vibrometer (LDV) was used to measure vibrations of micro-scale objects, with frequency response up to 24 MHz and picometer displacement resolution.

MEMS Electrothermal Actuator A 2-D micromechanical MEMS electrothermal actuator was fabricated using the SOI MUMPs process.

LDV experiments captured up to 50 out-of-plane vibration modes with a single excitation - an unprecedented achievement.

FEM simulations confirmed experimental results, with measured frequencies within 5% of theoretical predictions.

Micro Droplet Dynamics Studied the dynamics of 3-D mercury microdroplets on different substrates.

Adhesion properties, determined by wettability/contact angle, modulated the natural frequency.

LDV captured 10 vibration modes, with measured frequencies within 6% of analytical predictions.

Demonstrated a novel method: using pairs of natural frequencies to calculate surface tension and contact angle, enabling adhesion measurement on unknown surfaces.

Biological Cells Muscle Fibers (Drosophila)

Fibers studied in fixed-fixed and cantilever configurations.

Diseased fibers showed significant reduction in natural frequency.

Myopathies classified into nemaline and cardiac types based on frequency signatures.

Elastic modulus, dictating frequency, correlated with myosin expression levels.

Cancer Cells

Natural frequencies of normal vs. cancerous cells were measured.

Cancerous cells exhibited frequencies approximately half those of normal cells.

Differentiated epithelial vs. mesenchymal cancer cells by frequency values.

Induction of EMT in epithelial cells reduced natural frequency, corroborating biochemical assays (Western blots, PCR).

Established vibration-based mechanical assay as a novel mechano-diagnostic tool.