Harmonic Detection of Resonance: A Review

Electromechanical resonators in the micro (MEMS) and nano (NEMS) regimes have emerged as promising tools for use in such diverse applications as ultrasensitive physical, chemical, and biological sensors, with detection limits as low as a single molecule. The advent of state-of-the-art micro-fabrication techniques has enabled a high throughput platform for commercialization. However, the sensitivity and reliability of such devices are highly dependent on the employed detection technique. This article summarizes the popularly implemented actuation and detection methods, and presents a review of the patented highly useful yet simple electrical detection schemes, the Harmonic Detection of Resonance (HDR) method and the pulsed ring-down method. The prominent HDR features are elucidated, and their advantages are highlighted with respect to other techniques. A theoretical model of the system is presented, and the origin of harmonics in the signal is explained. The applications of HDR range from using microcantilevers as sensors to probing mechanical properties in nano-cantilever systems. Finally, the technique based on the ring-down phenomenon is introduced as an alternative to HDR, and its effectiveness is illustrated in gas sensing applications.