Doubling the quality factor of cantilevers in liquid through fluid coupling-based actuation

Abstract

Dynamic-mode cantilevers are a promising tool for real-time biosensing applications due to their high sensitivity and ability to perform label-free measurements. However, operating dynamic-mode cantilevers in liquid is challenging since viscous damping greatly reduces their quality factor and thus limit of detection. We reasoned through physical analysis that if the motion of the surrounding fluid is driven by an external force and not by the sensing cantilever itself, then the dissipative fluid force on the cantilever could be reduced and the quality factor of the cantilever could be increased. Here we demonstrate a new fluid coupling-based actuation method where one piezoelectric cantilever (directly excited) is used to excite another closely located cantilever (indirectly excited) through vibrations transferred through the surrounding medium. We performed measurements in several mediums, including air, water, ethanol, and acetone and observed that the viscosity of the medium influences the effectiveness of fluid coupling-based actuation. We also observed that fluid coupling-based actuation is more effective for the first bending mode of the cantilever, likely since fluid motion decays with distance from the tip of the directly excited cantilever. A significant result is that the indirectly excited cantilever has a quality factor that is double that of the directly excited one for the first bending mode in water. This method could improve the performance of dynamic-mode cantilevers operated in liquid.

Stochastic resonance induced performance enhancement of MEMS cantilever biosensors

“…The reliability of the sensor model under hydrodynamic influences is established by comparing the predictions from equations ( 7) and ( 8) with the available experimental results as shown by the examples in tables 1 and 2 and figure 1. There is a 3-4 times reduction in the cantilever resonance frequency in water from the lossless vacuum state to the liquid immersed state for different conditions on the gap-to-width ratio (H ≈ 0.3 − 1.0) [28,62,69]. The major contribution to this reduction comes from the added mass effect; table 2.…”

“…In some studies, damping nonlinearity under large amplitude oscillation conditions and driving cantilever above resonance have been exploited for improving Q-factor [25][26][27]. Leahy and Lai [28] reported that instead of actuating directly, if the cantilever is actuated via liquid coupling the quality factor is improved by a factor of 2. In a recent review, Miller et al [29] summarized research on a variety of pumping mechanisms (including electrical feedback oscillators) for controlling Q-factor of MEMS oscillators.…”

Thermal Fluctuations and Dynamic Modeling of a dAFM Cantilever

“…However, to achieve a good AFM resolution, noise sources must be reduced as much as possible, since the lowest signal level that can be considered as a valid information must be not mixed up with external noise. In spite of this, the cantilever thermal motion is also utilized to calibrate the cantilever's spring constant and to extract the resonance frequencies and quality factors of its resonances as well . Indeed, although novel methods are being developed, most of the times the AFM cantilever calibration is made by means of the thermal noise spectrum method.…”