Periodic Reporting for period 1 - MARS (Versatile mass and rheological sensing platform)
Período documentado: 2020-09-01 hasta 2022-08-31
The sensors and smart-sensors global markets are evaluated at > 200 Billion USD (2025) and 58 Billion USD (2022), respectively, and expected to grow at a Compound Annual Growth Rate (CAGR) of 18.1%. These growths are fomented by end-markets in the Industrial, Automotive, Consumer and Medical Sectors, and mostly driven by new paradigms such as the Fourth Industrial Revolution (Industry 4.0) Autonomous Cars, Smart Cities/Homes, Internet of Things (IoT) and Diagnostics.
MEMS-based sensors have been widely utilized in electronics, automotive and aerospace systems, biophysics, environmental monitoring and medical diagnosis sectors. These sensors are often based on the interaction between a micrometric mechanical device and its surrounding medium, where the mechanical device responds to changes in some environmental property, such as, for example, temperature, pressure, flow, density, viscosity, or the presence of some analytes of interest. The current trend to miniaturize is driven by the need of minimizing the footprint and power-consumption of these devices, but also by the need of probing smaller space and time scales, allowing measurements of physical phenomena in real-time at the micro- and nano-scale.
Fluids play a key role for many of the sensing applications, being either the substance to be tested (e.g. blood or saliva) or the support environment used to keep the substance of interest in its physiological state (e. g. proteins, DNA or analytes in solution). Therefore, measuring the mass of analytes with extremely high – potentially single molecule – accuracy, or understanding the rheology of simple and complex fluids play a critical role in a wide variety of applications, from the food and process industry, to environmental monitoring, to healthcare, to microfluidics. Several of these problems do not currently have an adequate solution, as many of the current sensing technologies only allow for bulk measurements of fluid properties, have poor limits of detection and limited accuracy/reliability when using extremely small samples.
The MARS project aimed at developing a proof-of-concept platform with new capabilities for sensing mass and rheological properties of Newtonian and non-Newtonian fluids with unprecedented sensitivity and reliability.
MEMS-based sensors have been widely utilized in electronics, automotive and aerospace systems, biophysics, environmental monitoring and medical diagnosis sectors. These sensors are often based on the interaction between a micrometric mechanical device and its surrounding medium, where the mechanical device responds to changes in some environmental property, such as, for example, temperature, pressure, flow, density, viscosity, or the presence of some analytes of interest. The current trend to miniaturize is driven by the need of minimizing the footprint and power-consumption of these devices, but also by the need of probing smaller space and time scales, allowing measurements of physical phenomena in real-time at the micro- and nano-scale.
Fluids play a key role for many of the sensing applications, being either the substance to be tested (e.g. blood or saliva) or the support environment used to keep the substance of interest in its physiological state (e. g. proteins, DNA or analytes in solution). Therefore, measuring the mass of analytes with extremely high – potentially single molecule – accuracy, or understanding the rheology of simple and complex fluids play a critical role in a wide variety of applications, from the food and process industry, to environmental monitoring, to healthcare, to microfluidics. Several of these problems do not currently have an adequate solution, as many of the current sensing technologies only allow for bulk measurements of fluid properties, have poor limits of detection and limited accuracy/reliability when using extremely small samples.
The MARS project aimed at developing a proof-of-concept platform with new capabilities for sensing mass and rheological properties of Newtonian and non-Newtonian fluids with unprecedented sensitivity and reliability.
The new sensing platform was firstly developed. The microcantilever was placed in a closed cell, where it could oscillate immersed in a viscous medium. Its motion can be excited either by a dither piezo (in experiments in gas) or by a modulated blue laser (in experiments in liquid), while its deflection was optically read by reflecting a red laser to a four-quadrant detector.
The deflection of the cantilever was analysed by a customized digital circuit (developed in collaboration with Elbatch srl), which allowed to read the oscillation frequency in real-time. Any interaction of the cantilever with the surrounding environment, such as a change of its mass, or a change of the rheological properties of the surrounding fluid, can then be detected in real-time and with very low noise as small shifts of frequency.
The behaviour of the platform was analytically modelled and validated with two major sets of experiments. In the first, different gases and tiny variations of their density were detected, allowing to demonstrate the best physical gas density sensor to date.
In the second set of experiments, the platform was used to detect the viscosity of Newtonian solutions of water and glycerol with very high sensitivity. Subsequently, the platform was used to detect the elastic and viscous modulus of non-Newtonian solutions of polyacrylamide (PAM) with different concentrations.
A second electronic circuit (custom made by Elbatech srl) was added to the platform. This second circuit is used to implement parametric excitation: an excitation mechanism which modulates the spring constant of the cantilever at a fixed phase and frequency, and allows to controllably change the phase, frequency and amplitude responses of the cantilever. The dynamical response of the cantilever when using this excitation mechanism was analytically modelled and its sensing capabilities analysed in detail.
The deflection of the cantilever was analysed by a customized digital circuit (developed in collaboration with Elbatch srl), which allowed to read the oscillation frequency in real-time. Any interaction of the cantilever with the surrounding environment, such as a change of its mass, or a change of the rheological properties of the surrounding fluid, can then be detected in real-time and with very low noise as small shifts of frequency.
The behaviour of the platform was analytically modelled and validated with two major sets of experiments. In the first, different gases and tiny variations of their density were detected, allowing to demonstrate the best physical gas density sensor to date.
In the second set of experiments, the platform was used to detect the viscosity of Newtonian solutions of water and glycerol with very high sensitivity. Subsequently, the platform was used to detect the elastic and viscous modulus of non-Newtonian solutions of polyacrylamide (PAM) with different concentrations.
A second electronic circuit (custom made by Elbatech srl) was added to the platform. This second circuit is used to implement parametric excitation: an excitation mechanism which modulates the spring constant of the cantilever at a fixed phase and frequency, and allows to controllably change the phase, frequency and amplitude responses of the cantilever. The dynamical response of the cantilever when using this excitation mechanism was analytically modelled and its sensing capabilities analysed in detail.
The developed customized digital circuit was shown to be exceptionally stable and with very low noise. Therefore, it allows to detect very small shifts of frequency induced by changes of the gaseous medium surrounding the cantilever, enough to decrease the limit of detection of the platform to the best values reported to date.
The developed analytical model and experiments with the new platform showed that the cantilever sensor is more sensitive to both density and viscosity when working at frequencies/phases below the resonance, contrarily to the generally accepted idea that the resonator should work at the resonance frequency. This result can be readily implemented in analogous systems and increase their sensitivity by around 50%.
Experiments using the parametric amplification excitation mechanism showed very conclusively that it does not seem useful in sensing applications requiring detecting frequency shifts. The reason is the general increase of noise (phase and frequency) that prevents detecting small shifts of frequency and, therefore, hinders the attainable limits of detection.
However, there is also evidence that parametric excitation can still be useful in a sensing platform to, for example, control the amplitude of the oscillation in dissipative media or obtain faster transient responses.
These new findings can be readily adopted when developing new topologies of resonant sensors and easily implemented in future commercial sensors. These can be used for detecting and discriminating the presence of different gas molecules in environmental monitoring, or to monitor and control industrial and chemical processes, with very high sensitivity, a fast response time and a low achievable limit of detection.
The developed analytical model and experiments with the new platform showed that the cantilever sensor is more sensitive to both density and viscosity when working at frequencies/phases below the resonance, contrarily to the generally accepted idea that the resonator should work at the resonance frequency. This result can be readily implemented in analogous systems and increase their sensitivity by around 50%.
Experiments using the parametric amplification excitation mechanism showed very conclusively that it does not seem useful in sensing applications requiring detecting frequency shifts. The reason is the general increase of noise (phase and frequency) that prevents detecting small shifts of frequency and, therefore, hinders the attainable limits of detection.
However, there is also evidence that parametric excitation can still be useful in a sensing platform to, for example, control the amplitude of the oscillation in dissipative media or obtain faster transient responses.
These new findings can be readily adopted when developing new topologies of resonant sensors and easily implemented in future commercial sensors. These can be used for detecting and discriminating the presence of different gas molecules in environmental monitoring, or to monitor and control industrial and chemical processes, with very high sensitivity, a fast response time and a low achievable limit of detection.