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Chemosensors 2019, 7(1), 2; https://doi.org/10.3390/chemosensors7010002

Real-Time Frequency Tracking of an Electro-Thermal Piezoresistive Cantilever Resonator with ZnO Nanorods for Chemical Sensing

1
Institute of Semiconductor Technology (IHT) and Laboratory for Emerging Nanometrology (LENA), Technische Universität Braunschweig, D-38106 Braunschweig, Germany
2
Research Centre for Physics, Indonesia Institute of Sciences (LIPI), Tangerang Selatan 15314, Indonesia
3
Department of Metrology, Kenya Bureau of Standards (KEBS), Nairobi 00200, Kenya
*
Author to whom correspondence should be addressed.
Received: 29 October 2018 / Revised: 21 December 2018 / Accepted: 24 December 2018 / Published: 3 January 2019
(This article belongs to the Special Issue Nanotechnology Efforts for Chemical Sensors)
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Abstract

The asymmetric resonance response in electro-thermal piezoresistive cantilever resonators causes a need of an optimization treatment for taking parasitic actuation-sensing effects into account. An electronic reference circuit for signal subtraction, integrated with the cantilever resonator has the capability to reduce the effect of parasitic coupling. Measurement results demonstrated that a symmetric amplitude shape (Lorentzian) and an optimized phase characteristic (i.e., monotonically decreasing) were successfully extracted from an asymmetric resonance response. With the monotonic phase response, real-time frequency tracking can be easier to implement using a phase-locked loop (PLL) system. In this work, an electro-thermal piezoresistive cantilever resonator functionalized with self-assembled monolayers of chitosan-covered ZnO nanorod arrays as sensitive layers has been investigated under different relative humidity (rH) levels. Enhancement of resonance phase response has been demonstrated by implementing the reference signal subtraction. Subsequently, a lock-in amplifier integrated with PLL system (MFLI, Zurich Instruments, Zurich, Switzerland) was then employed for continuously tracking the resonant frequency. As a result, we find a good correlation of frequency shift (∆f0) with change in rH monitored using a commercial reference sensor. View Full-Text
Keywords: phase optimization; phase-locked loop (PLL); electro-thermal cantilever; resonant MEMS sensor; environmental monitoring phase optimization; phase-locked loop (PLL); electro-thermal cantilever; resonant MEMS sensor; environmental monitoring
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Setiono, A.; Xu, J.; Fahrbach, M.; Bertke, M.; Nyang’au, W.O.; Wasisto, H.S.; Peiner, E. Real-Time Frequency Tracking of an Electro-Thermal Piezoresistive Cantilever Resonator with ZnO Nanorods for Chemical Sensing. Chemosensors 2019, 7, 2.

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