An overview of micro-force sensing techniques

Yuzhang Wei, Qingsong Xu

Due to the trend of miniaturization of devices, micromanipulation has been a hot topic in the last two decades. Unlike the macro world, the micro object is easy to be damaged if the contact force is not reliably detected and controlled. Hence, micro-force sensing is of great importance in micromanipulation, microassembly, medical applications, biomedical applications, materials science, dimension measurements and MEMS/NEMS for protecting micro-parts and micro-gripper from being damaged and ensuring the success of the manipulation process. This paper presents a survey of the recent methods of micro-force sensing. The working principle, detection accuracy, advantage and disadvantage of seven widely used force sensing methods are presented. Typical applications of each method in micro-assembly and micromanipulation are discussed. In addition, the comparisons among different kinds of force sensing approaches have been addressed. Moreover, another five promising micro-force sensing methods, which are confined to special component measurements or not widely used, are briefly introduced. Furthermore, two popular types of commercial micro-force sensors are listed to provide a guideline of selection for a specific application. The presented state-of-the-art overview is helpful to those engaged in micro-force sensing area to know the recent development and research tendency on micro-force sensing.

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Particles nanomanipulation by the enhanced evanescent field through a near-field scanning optical microscopy probe

B.H. Liu, L.J. Yang, Y. Wang and J.L. Cui

A near-field scanning optical microscopy (NSOM) probe and a polarized semiconductor laser (808 nm, cw) were applied to push the trapping resolution down to 120 nm on near-field optical manipulation. A multi-circular shape with a minimum size of 400 nm consisting of 120 nm polystyrene particles can be obtained. They are at a resolution of d (d: NSOM probe tip diameter) and λ/7 (λ: laser wavelength), respectively. It is proved that sample concentration and laser power can affect feature size of trapping patterns. In this paper, the effect of trapping forces acted on a nanoparticle along three axis directions on trapping positions is studied, and different trapping positions are generated: the aperture edge in polarization direction and center surface of the probe tip. The result indicates that the single mode NSOM fiber probe is able to trap nanoparticles in a circular shape with lower laser intensity than that required by conventional optical tweezers. The simulated trapping positions around the probe tip based on the conservation law of momentum are found to agree well with experimental results.

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Control of micro-cantilever using passive optical feedback for force microscopy

Hao Fu, Yong Liu, Jian Chen and Gengyu Cao

We demonstrate the use of bolometric force backaction in lever-based miniature Fabry–Pérot (FP) optical cavity for micro-cantilever control. In our experiment, low finesse FP microcavity is formed by polished fiber end and mass loaded micro-cantilever. We show that the dynamics of micro-cantilever can be deeply modified when photon intensity stored in the FP microcavity is sufficiently large. For blue microcavity detuning, we confirm this control mechanism can optimize the dynamics of micro-cantilever and dramatically reduce its Brownian motion amplitude without deteriorating force resolution. This effective and low-cost control method can be simply realized in most optical detection force microscopes.

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