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Proceedings Paper

A closed-loop system for frequency tracking of piezoresistive cantilever sensors
Author(s): Hutomo Suryo Wasisto; Qing Zhang ; Stephan Merzsch ; Andreas Waag ; Erwin Peiner
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Paper Abstract

A closed loop circuit capable of tracking resonant frequencies for MEMS-based piezoresistive cantilever resonators is developed in this work. The proposed closed-loop system is mainly based on a phase locked loop (PLL) circuit. In order to lock onto the resonant frequency of the resonator, an actuation signal generated from a voltage-controlled oscillator (VCO) is locked to the phase of the input reference signal of the cantilever sensor. In addition to the PLL component, an instrumentation amplifier and an active low pass filter (LPF) are connected to the system for gaining the amplitude and reducing the noise of the cantilever output signals. The LPF can transform a rectangular signal into a sinusoidal signal with voltage amplitudes ranging from 5 to 10 V which are sufficient for a piezoactuator input (i.e., maintaining a large output signal of the cantilever sensor). To demonstrate the functionality of the system, a self-sensing silicon cantilever resonator with a built-in piezoresistive Wheatstone bridge is fabricated and integrated with the circuit. A piezoactuator is utilized for actuating the cantilever into resonance. Implementation of this closed loop system is used to track the resonant frequency of a silicon cantilever-based sensor resonating at 9.4 kHz under a cross-sensitivity test of ambient temperature. The changes of the resonant frequency are interpreted using a frequency counter connected to the system. From the experimental results, the temperature sensitivity and coefficient of the employed sensor are 0.3 Hz/°C and 32.8 ppm/°C, respectively. The frequency stability of the system can reach up to 0.08 Hz. The development of this system will enable real-time nanoparticle monitoring systems and provide a miniaturization of the instrumentation modules for cantilever-based nanoparticle detectors.

Paper Details

Date Published: 17 May 2013
PDF: 8 pages
Proc. SPIE 8763, Smart Sensors, Actuators, and MEMS VI, 876337 (17 May 2013); doi: 10.1117/12.2017009
Show Author Affiliations
Hutomo Suryo Wasisto, Braunschweig Univ. of Technology (Germany)
Qing Zhang , Braunschweig Univ. of Technology (Germany)
Stephan Merzsch , Braunschweig Univ. of Technology (Germany)
Andreas Waag , Braunschweig Univ. of Technology (Germany)
Erwin Peiner , Braunschweig Univ. of Technology (Germany)

Published in SPIE Proceedings Vol. 8763:
Smart Sensors, Actuators, and MEMS VI
Ulrich Schmid; José Luis Sánchez de Rojas Aldavero; Monika Leester-Schaedel, Editor(s)

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