Geometry and thickness dependant anomalous mechanical behavior of fabricated SU-8 thin film micro-cantilevers

SU-8 micro-cantilever arrays consisting of V- and M-shaped structures fabricated using a simplified single hard mask step. Bending tests were performed under similar peak loads (ranging 2–10 µN), with thickness ranging between micron (3.5 µm) and sub-micron (0.2 µm) scales. Various mechanical properties such as stiffness and hysteresis are determined from the load versus deflection curves. When the thickness of the V-shaped beam is decreased from 2 µm to 0.2 µm, the stiffness increases by a factor of 2.7, which is in contradiction with the classical beam theory according to which the stiffness for 0.2 µm beam should be three orders of magnitude less than that of 2 µm beam. Micropolar elasticity theory with a variable-intrinsic length scale (thickness dependant) is used to explain such an anomalous response. Experimentally obtained stiffness of two M-shaped beams of thickness 2 µm and 0.2 µm are almost identical. Reason behind this contradictory result is that the thicker beam has a residual strain with a large plastic deformation which usually increases the cross-linking network density, leading to increase in elastic modulus, hardness and thus stiffness of polymers. But the thinner beam has undergone an elastic deformation. The size effect of V- and M-shaped cantilever beams is discussed.

Actuation of Higher Harmonics in Large Arrays of Micromechanical Cantilevers for Expanded Resonant Peak Separation

A large array of elastically coupled micro cantilevers of variable length is studied experimentally and numerically. Full-scale finite element (FE) modal analysis is implemented to determine the spectral behavior of the array and to extract a global coupling matrix. A compact reduced-order (RO) model is used for numerical investigation of the array's dynamic response. Our model results show that at a given excitation frequency within a propagation band, only a finite number of beams respond. Spectral characteristics of individual cantilevers, inertially excited by an external piezoelectric actuator, were measured in vacuum using laser interferometry. The theoretical and experimental results collectively show that the resonant peaks corresponding to individual beams are clearly separated when operating in vacuum at the third harmonic. Distinct resonant peak separation, coupled with the spatially confined modal response, make higher harmonic operation of tailored, variable-length cantilever arrays well suited for a variety of resonant-based sensing applications.

Towards personalised rapid label free miRNA detection for cancer and liver injury diagnostics in cell lysates and blood based samples

Label free nanomechanical miRNA detection from biological samples utilising cantilever arrays in an automated diagnostic platform.