Time-domain chemical vapour mass sensor using a functionalized subordinate array

Abstract

This work describes a chemical vapour detection scheme based on observing changes in the time-domain impulse response of a single structure to which an array of smaller cantilevers is attached. The distribution of properties of the cantilevers in the array is chosen to transfer vibration energy to the array and confine it there for a specified duration . Accumulation of added mass on the cantilevers changes the array properties, altering the duration for which energy is confined. When every second cantilever is functionalized to adsorb mass, a portion of the vibration energy returns to the primary structure in half the original time. The amount of added mass can be estimated by comparing the vibration energy in the primary structure to the total energy in the array at the return time . Numerical analysis is used to investigate the performance of the proposed detection scheme. It is shown that increasing the number of sensing elements reduces errors in mass predictions due to mass adsorption variability and increases mass sensitivity. However, reducing the number of sensing elements improves the signal-to-noise ratio. These opposing effects require consideration for a specific sensing application. Experimental results using a centimetre scale prototype demonstrate feasibility of this interferometric approach for MEMS-scale implementation.