A MEMS (Micro-Electro-Mechanical Systems) microcantilever is a tiny mechanical structure commonly used for sensing and detecting various physical or chemical changes in its environment. It operates based on the principles of mechanical deflection and piezoresistive or piezoelectric sensing.
Here's a step-by-step description of the operation of a MEMS microcantilever for sensing:
Structure: A microcantilever is a thin, beam-like structure usually made of a semiconductor material such as silicon. It is anchored at one end and free to move at the other end, resembling a diving board. The cantilever's dimensions can vary, but they are typically on the order of micrometers.
Coating: The sensing surface of the cantilever is often functionalized with a specific material or coating that interacts with the target substance to be detected. This coating could be sensitive to changes in mass, stress, or surface interactions, depending on the intended sensing application.
Mechanical Deflection: When the target substance (such as gas molecules, biomolecules, or particles) comes into contact with the coated surface of the cantilever, it causes a change in the mechanical properties of the cantilever. This change might be due to adsorption, absorption, or other interactions between the coating and the target substance.
Bending and Stress: The interaction between the coating and the target substance causes the cantilever to bend or deflect. This bending induces stress and strain within the cantilever structure, leading to a measurable change in its mechanical properties. The amount of deflection is directly proportional to the magnitude of the interaction, which in turn is related to the concentration or presence of the target substance.
Piezoresistive/Piezoelectric Sensing: The deflection of the cantilever can be detected using either piezoresistive or piezoelectric elements integrated into the cantilever structure. In piezoresistive sensing, changes in stress alter the electrical resistance of specific regions on the cantilever, which can be measured using Wheatstone bridge circuits. In piezoelectric sensing, the mechanical deformation generates a voltage difference across the cantilever due to the piezoelectric effect.
Signal Amplification and Processing: The electrical signals from the piezoresistive or piezoelectric sensors are amplified and processed using electronic circuits. The output signal is typically converted into a digital format for further analysis.
Data Analysis: The output signal is analyzed to determine the presence, concentration, or other relevant characteristics of the target substance. This analysis might involve comparing the signal to a calibration curve or a known reference, allowing for quantification of the sensed parameter.
MEMS microcantilevers find applications in various fields, including chemical and gas sensing, biosensing, environmental monitoring, and medical diagnostics, due to their small size, sensitivity, and compatibility with microfabrication techniques.