Analytic Optimization of Cantilevers for Photoacoustic Gas Sensor with Capacitive Transduction

Abstract

We propose a new concept of photoacoustic gas sensing based on capacitive transduction which allows full integration while conserving the required characteristics of the sensor. For the sensor’s performance optimization, trial and error method is not feasible due to economic and time constrains. Therefore, we focus on a theoretical optimization of the sensor reinforced by computational methods implemented in a Python programming environment. We present an analytic model to optimize the geometry of a cantilever used as a capacitive transducer in photoacoustic spectroscopy. We describe all the physical parameters which have to be considered for this optimization (photoacoustic force, damping, mechanical susceptibility, capacitive transduction, etc.). These parameters are characterized by opposite trends. They are studied and compared to obtain geometric values for which the signal output and signal-to-noise ratio are maximized.

Highly Sensitive Capacitive MEMS for Photoacoustic Gas Trace Detection

“…To enhance the collection of the photoacoustic energy, the structure size should be selected to resonate at a frequency which corresponds to the maximum acoustic pressure generated by the target gas. This maximum pressure is related to the target gas vibrational–transitional relaxation rate by means of the heat production rate, expressed in [ 10 ]. The wide central part is devised to overlap with the acoustic wave and thus increase the applied force, as the wider the surface, the higher the force will be.…”

“…Knowing that the acoustic wavelength at the resonance λ a ∼3.4 cm ( λ a = , where is the speed of sound = 343 m/s and is the frequency = 10 kHz), this reduced gap together with the resonator thickness (~75 µm) allows the pressure difference between the upper and back sides of the mechanical resonator to increase. Thus, the applied force is increased, as illustrated in [ 10 ].…”

“…However, the performance achieved by the first prototype we developed was far from the state of the art [ 8 ]. This can be explained by the capacitive transduction mechanism, based on gap reduction, which generates an important viscous squeeze film effect due to the proximity between the two electrodes as described in [ 10 ]. This effect reduces the mechanical resonator displacement; thus, the capacitance variations is limited and, therefore, its sensitivity.…”

Cantilever-enhanced photoacoustic spectroscopy for gas sensing: A comparison of different displacement detection methods

“…However, small gap will cause great viscous damping called squeeze film effect [70] . In CEPAS, capacitive cantilever should be carefully designed to achieve a good performance [71] . Therefore, in the following, some capacitive resonators that are not in the traditional cantilever form will be introduced.…”

Impacts of Length Scale Parameter on Material Dependent Thermoelastic Damping in Micro/nanoplates Applying Modified Coupled Stress Theory

“…Quality factor (QF) decides the sensitivity and resolution of micro-/nano systems when used in sensor industry [35,36]. As far as communication systems in micron ranges are concerned, enhanced quality factors increase signal to noise ratio and reduce phase noise [37,38]. A high quality factor in resonators is achieved by reducing the dominant energy dissipation mechanisms which can be classified as extrinsic and intrinsic ones .The extrinsic losses like anchor damping [39,40]and squeeze film damping [41,42] can be diminished by proper geometric design.…”