Abstract
We present a mode localized mass sensor prototype based on a hybrid system excited at a fixed frequency slightly below the resonances. Indeed, we show, both theoretically and experimentally, that this condition yields higher sensitivities and similar sensitivity ranges than that of resonance peak tracking while being less time consuming than a classical open-loop configuration due to the absence of frequency sweep. The system is made of a quartz resonator and a hardware that includes a resonator and the coupling. The digital aspect allows maximum sensitivity to be achieved with a fine tuning of the different parameters and the implementation of a coupling, regardless of the physical resonator geometry. This allows the generation of mode localization on shear waves resonant structures such as the quartz cristal microbalance widely used in biosensing. This solution has been successfully implemented using resin micro balls depositions. The sensitivities reach almost their maximum theoretical values which means this fixed frequency method has the potential to reach lower limit of detection than the open loop frequency tracking method.
Highlights
The last two decades saw the development of sensors that were based on arrays of weakly coupled resonators
The values of the different parameters are entered in the field programmable gate array (FPGA)
This is due to the fact that with the transfer function from Equation (9), mode aliasing occurs for higher coupling values because the frequency of the second mode is located between series and parallel resonances
Summary
The last two decades saw the development of sensors that were based on arrays of weakly coupled resonators. The output parameter of mode localized sensors is the vibration amplitude shift, whether for evaluating a change in eigenvectors or amplitude ratios at resonance. This is a major difference from mechanical resonant sensors that measure a change in resonant frequency (RtF). While the resolution of such sensors is rather good, the normalized sensitivity (NS), defined as the relative output over input shifts, is limited to the constant value of 12 [2]. The theoretical NS of mode-localized sensors can be two to three orders of magnitude higher than this value. It seems appropriate to work with high quality factor resonators to achieve the highest possible NS
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