This research investigates the feasibility of mass sensing in piezoresistive MEMS devices based on catastrophic bifurcation and sensitivity enhancement due to the orientation adjustment of the device with respect to the crystallographic orientation of the silicon wafer. The model studied is a cantilever microbeam at the end of which an electrostatically actuated tip mass is attached. The piezoresistive layers are bonded to the vicinity of the clamped end of the cantilever and the device is set to operate in the resonance regime by means of harmonic electrostatic excitation. The nonlinearities due to curvature, shortening and electrostatic excitation have been considered in the modelling process. It is shown that once the mass is deposited on the tip mass, the system undergoes a cyclic fold bifurcation in the frequency domain, which yields a sudden jump in the output voltage of the piezoresistive layers; this bifurcation is attributed to the nonlinearities governing the dynamics of the response. The partial differential equations of the motion are derived and discretized to give a finite degree of freedom model based on the Galerkin method, and the limit cycles are captured in the frequency domain by using the shooting method. The effect of the orientation of the device with respect to the crystallographic coordinates of the silicon and the effect of the orientation of the piezoresistive layers with respect to the microbeam length on the sensitivity of the device is also investigated. Thanks to the nonlinearity and the orientation adjustment of the device and piezoresistive layers, a twofold sensitivity enhancement due to the added mass was achieved. This achievement is due to the combined amplification of the sensitivity in the vicinity of the bifurcation point, which is attributed to the nonlinearity and maximizing the sensitivity by orientation adjustment of the anisotropic piezoresistive coefficients.

In part I, we identified encapsulation, contamination suppression, and virus elimination as our three governing strategies for developing surfaces to combat the transmission and spread of COVID-19. We showed that our recent superhydrophobic nanocomposites has the potential of encapsulating and suppressing the virus so as to limit its transmission and spread. In this study, we examine the durability of the newly developed surfaces when subjected to elevated temperature, chemical attack and mechanical damage in the form of abrasion and compressive load. Extensive tests were conducted to reveal the effect of these parameters on the surface performance. Three aspects of the work were accordingly examined. The first was concerned with controlled thermal stability tests in which the surfaces were subjected to elevated temperatures approaching 350 °C for silicone-based nanocomposites and 150 °C for epoxy-based nanocomposites. The second was concerned with subjecting the surfaces to alkaline and acidic solutions with pH concentrations ranging between 1 and 13. Finally, the third involved surface damage by abrasion tests. Our results show clearly that the newly developed superhydrophobic surfaces are capable of resisting the adverse effects of thermal and chemical attacks as well as mechanical abrasion owing to the excellent structural stability and mechanical properties of the constituents of the nanocomposite. Moreover, our superhydrophobic monolith demonstrated exceptional regenerative capabilities even after being subjected to damaging compressive stresses of up to 10 MPa.

According to the World Health Organisation, one of the main concerns of COVID-19 virus is its tenacity to spread from droplets that either land directly on a surface or are transmitted to a surface by an infected person. In this study, we report the potential of using superhydrophobic surfaces to combat the transmission and spread of fomites infected by COVID-19 virus strand. Fomites include clothes, utensils, furniture, regularly touched objects and personal protective equipment used by Health Care Workers to act as barriers against fluid transmission and/or fluid penetration. In this effort, we propose three strategies to combat the transmission and the spread of the virus: encapsulation, contamination suppression, and elimination. We believe that this can be achieved by the use of our recently developed superhydrophobic coating and regenerative monolith to encapsulate and suppress the virus. The newly developed superhydrophobic coating and monolith are scalable, economical, and facile with the monolith capable of regeneration. The elimination of the virus will be through the use of antiviral and antibacterial copper nanoparticles or dedicated copper surfaces.

Superhydrophobicity and icephobicity are governed by surface chemistry and surface structure. These two features signify a potential advance in surface engineering and have recently garnered significant attention from the research community. This review aims to simulate further research in the development of superhydrophobic and icephobic surfaces in order to achieve their wide-spread adoption in practical applications. The review begins by establishing the fundamentals of the wetting phenomenon and wettability parameters. This is followed by the recent advances in modeling and simulations of the response of superhydrophobic surfaces to static and dynamic droplets contact and impingement, respectively. In view of their versatility and multifunctionality, a special attention is given to the development of these surfaces using nanocomposites. Furthermore, the review considers advances in icephobicity, its comprehensive characterization and its relation to superhydrophobicity. The review also includes the importance of the use of superhydrophobic surface to combat viral and bacterial contamination that exist in fomites.

Emerging manufacturing technologies, including 3D printing and additive layer manufacturing, offer scope for making slender heterogeneous structures with complex geometry. Modern applications include tapered sandwich beams employed in the aeronautical industry, wind turbine blades and concrete beams used in construction. It is noteworthy that state-of-the-art closed form solutions for stresses are often excessively simple to be representative of real laminated tapered beams. For example, centroidal variation with respect to the neutral axis is neglected, and the transverse direct stress component is disregarded. Also, non-classical terms arise due to interactions between stiffness and external load distributions. Another drawback is that the external load is assumed to react uniformly through the cross-section in classical beam formulations, which is an inaccurate assumption for slender structures loaded on only a sub-section of the entire cross-section. To address these limitations, a simple and efficient yet accurate analytical stress recovery method is presented for laminated non-prismatic beams with arbitrary cross-sectional shapes under layerwise body forces and traction loads. Moreover, closed-form solutions are deduced for rectangular cross-sections. The proposed method invokes Cauchy stress equilibrium followed by implementing appropriate interfacial boundary conditions. The main novelties comprise the 2D transverse stress field recovery considering centroidal variation with respect to the neutral axis, application of layerwise external loads, and consideration of effects where stiffness and external load distributions differ. A state of plane stress under small linear-elastic strains is assumed, for cases where beam thickness taper is restricted to . The model is validated by comparison with finite element analysis and relevant analytical formulations.