A Mechatronic Lock-In Amplifier: Integrating Demodulation in Sensor Electronics for Measuring Mechanical Oscillations

The demodulation of mechanical oscillations is essential for the operation of micro- and nanometer-scale transducer systems, such as resonant MEMS mirrors and cantilever-based sensors. The use of external demodulators, such as lock-in amplifiers and spectrum analyzers is not always desired due to their large size, complexity, and cost. The method presented in this article enables simplified demodulation of the oscillation of mechanical oscillators with integrated deflection sensors. By configuring two deflection sensors in separate bridge circuits, which are supplied with in-phase and quadrature sinusoidal signals, the amplitude, and phase of the mechanical oscillation can directly be measured without additional demodulation. The method is implemented and experimentally verified by demodulating the oscillation of a self-sensing Atomic Force Microscopy cantilever with integrated piezoresistive elements.

I. Introduction

Mechanical oscillators are crucial components in micro- and nanometer-scale transducer applications. For instance, resonant MEMS mirrors enable high-speed laser beam steering, which is essential for modern optical scanning systems, such as light detection and ranging (LIDAR) [1], photoacoustic imaging [2], and optical endoscopy [3]. Micromachined cantilevers are used in a variety of sensor applications, such as biosensing [4], chemical and environmental detection [5], as well as the local measurement of surface properties by Atomic Force Microscopy (AFM) [6].