In the prevailing era, an influential shape memory alloy (SMA) nitinol has emerged as a potentially viable and economically affordable material that is capable of playing a significant role in both existing and emerging technological applications spanning the domains of aircraft and aerospace, biomaterials in bioengineering, sensors in health monitoring, advanced manufacturing, and microelectromechanical systems (MEMS), to name a few. A high strain recovering capability coupled with superelasticity are two key and essential characteristics of a “smart” material that distinguish it easily from its conventional counterparts. The phase transformation behavior shown by nitinol (NiTi) was found to be governed by intrinsic variations in temperature. In order to obtain the desired application-based functionality of this high performing material, potentially viable approaches include the following: (i) an alteration of its chemical composition, (ii) the addition of ternary elements and quaternary elements, and (iii) the use different processing treatments. These approaches are being constantly studied, carefully and systematically examined and frequently reported in the published literature. In this manuscript, an effort is made to present and discuss several of the recent advances specific to the NiTi-based shape memory alloy applications and its phase transformation behaviour when subject to processing treatments. The influence of compositional variation of the NiTi-based shape memory alloys (SMAs) and even its ternary variants and quaternary variants, coupled with the role and/or influence of different processing treatments on both macroscopic properties and microscopic properties is the focus. The emphasis on increasing the suitability of shape memory alloys (SMSs) for selection and use in a spectrum of sensing-related or sensing specific applications is highlighted and briefly discussed.

Fabrication of micro-fractals in lifting plate Hele-Shaw cell for bio-mimicking and micro-level applications has been gaining popularity in recent years. Instability in the interface between the two distinctly viscous fluids due to the Saffman-Taylor instability phenomenon leads to this spontaneous fabrication. Micro-fractals have already been developed on flat surfaces in lifting plate Hele-Shaw cell at the primary level and validated by its numerical simulation. Developed micro-fractals mimic different ordered patterns found in nature. This paper presents the experimental characterization of the micro-fractals formed on conical surfaces. The fractal formation process is experimented on lifting plate Hele-Shaw cell apparatus. A Bingham plastic fluid (toothpaste) is used as a high-viscosity fluid, and air as a low-viscosity fluid. Variations are observed in the micro-fractals pattern obtained by varying process controlling parameters, viz. initial thickness of the high-viscosity fluid, velocity of lifting plate and semi-cone angle. Characterization of the formed fractals results in optimum process control parameters that can lead to desired micro-fractal formation for various micro-applications in the future.

Lifting plate Hele-Shaw cell involves a high viscous fluid sandwiched between two parallel plates. The low viscosity fluid (air) enters from the periphery when one of the plates is lifted away from another plate. The air penetrates a high viscous fluid at various points from the periphery. This penetration causes the formation of a tree-branch-like structure called viscous fingering. Due to this insertion, sandwiched fluid changes its structure. This structural change is known as instability. The viscous fingers generated through this flow are highly random and unstable. This study presents methods to control the instabilities. The study reports control techniques by providing anisotropies (holes and slots) on any one of the plates. The study further presents the effect of size, position, and the orientation of these holes and slots on the viscous fingering exhaustively. Deployment of these control techniques leads to the emergence of new fabrication techniques with the potential to develop meso-sized finger patterns spontaneously without expensive setup as otherwise required in the lithography process. To demonstrate the capability of this proposed fabrication technique, various net-shaped patterns available in nature are mimicked. These developed miniature patterns can be used in various applications such as micro-mixers, micro-heat exchangers, etc.

Recently various control methodology has been demonstrated by researchers to fabricate the spontaneously multiscale fractal-like structure. These multiscale fractal structures mimic different living structures available in nature, such as a leaf, vascular systems in the animal kingdom etc. This paper presents the design methodology for the development of the system to fabricate these multiscale fractal structures spontaneously with the flexibility to vary the control parameters on a wide range. Various components require in the system are a system of two plates arresting fluid in between them. One plate out of two is fixed while the other is allowed to move. The primary attributes for the generation of fractal structures are the separation distance between plates, the volume of fluid trapped in the plates, the separation velocity, and the provision for lift orientation. The paper discusses a cost-effective way to develop a setup embodying different processing parameters and finally yielding precise fabrication of micro-fractals. The designed experimental setup can be used to successfully fabricate micro-fractals with different process parameters.

Shape memory alloys (SMAs) are smart materials having an ability to remember the original shape when deformed at the temperatures below martensite finish (Mf), which can be recovered up to certain extent by heating these alloys to temperatures above austenite finish (Af). SMAs find wide applicability in engineering sectors including automotive, aerospace, and biomedical. Prior to fabrication of any sensors and actuators using SMA, it is recommended to have an extensive simulation study that requires material properties as a prime input to the software. Scattered literature on SMA’s material properties make this challenging for new researchers. This paper presents a review of binary, ternary and quaternary alloys exhibit shape memory effect and their comparison in terms of transformation temperatures and mechanical properties. It also comments on effects in their properties due to addition of ternary and quaternary elements. Impact of thermomechanical treatments to enhance the mechanical properties and shape recovery characteristics of SMAs is reviewed. The study concludes with signifying the use of processing techniques in enhancing mechanical properties of SMAs for their utilization in possible sensing applications.

Bio-mimicking is the process of mimicking the various patterns, models, and systems of nature to take inspiration and solve human problems. The fractal-like patterns are seen in the leaves, tree branches, veins and arteries of the human body, etc. Imitation of these structures is a complex process. This can be achieved using lifting plate Hele-Shaw cell (LPHSC). In LPHSC, non-Newtonian fluid is placed between the two flat plates separated by a minimal distance. The lower plate is kept fixed, and the upper plate is lifted precisely. This leads to the formation of Saffman-Taylor instability or uncontrolled viscous fingering. When a low viscous fluid interacts with high viscous fluid, it tries to displace high viscous fluid, resulting in fractal-like structures. This paper investigates fractal formation in Hele-Shaw cell on different polygonal surfaces such as triangular, square, pentagonal, and hexagonal plates. The authors studied the effect of the sides and corners of the polygons and controlled the instabilities using a gap between plates and the lifting velocity of the upper plate. The entire process of fractal formation is simulated in ANSYS software, and experimental and simulated results hold good agreement. This proposed method will be used to fabricate microstructures.

Use of shape memory alloy (SMA) has been extensively increased to fabricate sensors and actuators. It is because of its inherently unique properties such as pseudo-elasticity and shape memory effect. Among various SMA’s, Ni–Ti SMA has received a prime interest in various applications. However, Ni–Ti SMA-based sensors suffer from the Joule heating effect as their performance is impacted due to an increase in the temperature. This work presents a finite element analysis approach to estimate a rise in temperature in Ni–Ti SMA sensors. A numerical model was developed in COMSOL, considering a Ni–Ti with Cu segment. Electro-thermal boundary conditions were set to assess the thermal response of the segmented wire. Multiple simulation runs were carried out by varying material and geometric characteristics of segmented wire. The results are validated against the literature and quantitative estimation of thermal characteristics through physics driven analytical model. Simulation results show that the Joule heating effect has a significant effect on the properties of the material which can be considered while designing and selecting the sensor application. This study further brought a few mitigation actions which can minimize the Joule heating effect without hindering the performance of Ni–Ti SMA-based sensors.

The paper presents design, analysis and fabrication of a 1.71 Kg. quadruped robot which incorporates four bar chain leg mechanism as its locomotion element. The main objectives of this paper are mechanical design, gait analysis and fabrication of quadruped robot. Quadruped robot designed and fabricated here involves 8 degrees of freedom which are controlled by servomotors and it walks on flat terrain using symmetrical gaits viz. trot and pace. Its locomotion is controlled by controlling angular rotation of servomotors.