A Ferrofluid-Based Tuning Strategy for Flexible Accelerometers

In this article, a novel methodology to tune parameters of a resonant accelerometer realized by a flexible structure is presented. A model describing the behavior of the tuning mechanism has been proposed and experimentally validated as well as a suitable design flow is presented through case studies. The device under test, whose dimensions are in the mesoscale, adopts a resistive sensing readout strategy implemented through strain gauges, directly inkjet printed on the flexures (springs) supporting the central membrane. The tuning mechanism, which exploits the interaction between an external magnetic field and a magnetic fluid (ferrofluid) embedded in the device's springs, has been experimentally investigated by using a lab-scale prototype. The procedure for the optimal design of the sensor has also been addressed. The prototype shows a responsivity of 721.0 mu strain/m/s2 at the resonance frequency of 30.5 Hz and a noise floor of 7.5e - 5 { ext {m/}} ext {s}^{{2}} {/}sqrt { ext {Hz}} estimated in a bandwidth of 500 Hz. Responsivities of 657.0∼mu strain/m/s2 and 580.0∼mu strain/m/s2 as well as noise floor of 8.7e - 5 { ext {m/}} ext {s}^{{2}} {/}sqrt { ext {Hz}} and 10.9e - 5 { ext {m/}} ext {s}^{{2}} {/}sqrt { ext {Hz}} have been estimated in case of the tuning magnetic fields of H =6.8 ext{e}-3 T and H =11.4 ext{e}-3 T, respectively, showing resonance frequencies of 31.0 and 32.5 Hz. The main novelty of the proposed approach arises from the tuning strategy that is important for many real applications requiring a fine-tuning of the sensor parameters while the use of a cheap inkjet printing technology for the device realization represents a substantial advantage in terms of costs and to enable the rapid prototyping of customizable devices on flexible substrates.