General Active Q-Control of Electromechanical Quartz Resonator
- PDF / 372,693 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 32 Downloads / 210 Views
1232-OO07-04
General Active Q-Control of Electromechanical Quartz Resonator J. Jahng1, 2, M. LEE1, and W. Jhe1 1 Center for Nano Liquid, Department of Physics and Astronomy, Seoul National University, Seoul, KOREA 2Condensed Matte Research Institute, Seoul National University, Seoul, KOREA. ABSTRACT We present generalized theoretical analysis and experimental realization of active quality factor control for the self-oscillating quartz tuning-fork (QTF). The quality factor Q and resonance frequency can be controlled by adding a phase shifted signal of proper gain with respect to the QTF motion. The reliable technique can be extended to other quartz resonators which are analyzed by an equivalent circuit-a combination of a parallel circuit of an harmonic L-R-C and a stray capacitance C0. Finally, we suggest the prospect of several applications by using the active Q control of QTF such as increasing force sensitivity, reducing scanning time in scanning probe microscopy, and feedback cooling of electromechanical resonator. INTRODUCTION The quartz tuning-fork (QTF) is widely used as an imaging sensor in scanning probe microscopy (SPM), such as near-field scanning optical microscopy [1, 2], atomic force microscopy (AFM) [3, 4], electrostatic force microscopy [5], and magnetic force microscopy [6]. Recently, the QTF is regarded as an alternative imaging probe due to its high sensitivity and self-oscillationdetection characteristic: The high quality factor Q resulted in high sensitivity can increase an image resolution in SPM. Moreover, the feature of self-oscillation and self-detection helps minimize the instrumental finesses of SPM such as an additional mechanical vibrator and a laser detection skim. Unfortunately, the benefit of high sensitivity is limited in some special conditions. When the QTF is used in liquid as a force sensor or an image sensor [7], the quality factor Q as well as the detection sensitivity are drastically deteriorated. On the other hand, the Q-factor is too increased in vacuum or at low temperature to scan a sample. Because high Q results in slow response in feedback control [8, 9], or even being too sensitive to approach the sample. Therefore, it is very crucial to properly control the Q-factor, which is the main subject of the so-called Q-control [10-15]. Despite its importance, the general Q-control scheme which included the resonance shift has not been analytically treated in the QTF-based AFM. In this Letter, we suggest a general Q-control technique of electromechanical QTF by employing the QTF's equivalent circuit model [16]. Our result shows that the Q value can be varied by adding a signal of proper phase lag with respect to the drive signal. In particular, It is shown that even a simple follower (inverter) [19] without the external phase shifter to increase (decrease) the Q-factor. Then, we show the results can be extended other electromechanical quartz resonators.
THEORY The total induced current of QTF in a self-excitation is generally considered as the sum of a mechanical harmonic mot
Data Loading...
