Towards Smart Materials

Smart materials are at the cutting edge of modern engineering. Their ability to respond dynamically to changes in the environment enables adaptive and efficient systems. The need in the aerospace industry for lighter, energy-efficient, and highly adaptive materials has driven further development and integration of smart materials into aircraft, spacecraft, and satellite structures. These materials have been applied to the development of morphing wings, vibration control systems, deployable components, and structural health monitoring and have greatly contributed to flight efficiency and reliability. However, they are not widely applied because of limitations, such as temperature sensitivity, fatigue resistance, low actuation force, and scalability issues in large-scale aerospace applications. The solution to these challenges is crucial for ensuring the long-term durability and safety of smart materials under extreme conditions in the aerospace industry. This study focuses on the development, mechanism application, and future development of the following three popular smart materials: Shape Memory Alloys, Piezoelectric Materials, and Electroactive Polymers. The strength of each material will be discussed together with its limitations and how it is being used in the transformation of engineering within the aerospace sector. It highlights how smart materials have increasingly become active players in providing adaptive, sustainable, and high-performance aerospace systems, and critically reviews challenges from smart materials that are faced by real-world aerospace applications, with their potential solution and long-term viability.

This article presents a review of recent-important developments in the field of intelligent material and fluid systems. Intelligent material and fluid systems, sometimes referred to as smart materials and fluids, can adjust their behavior to changes of external or internal parameters analogously to biological systems. In these systems, sensors, actuators and controllers are seamlessly integrated with structural materials at the macroscopic or mesoscopic level. In general, sensors and actuators are made of functional materials and fluids such as piezoelectric materials, magnetostrictive materials, shape memory alloys, polymer hydrogels, electro- and magneto-rheological fluids and so on. This article is specifically focused on the design of intelligent material and fluid systems used to control the deformation, vibration and fracture of composite materials and structures.

In many dynamic systems such as robot and aerospace areas, flexible structures have been extremely employed to satisfy various requirements for large scale, light weight and high speed in dynamic motion. However, these flexible structures are readily susceptible to the internal/external disturbances (or excitations). Therefore, vibration control schemes should be exerted to achieve high performance and stability of flexible structure systems. Recently, in order to successfully achieve vibration control for flexible structures smart materials such as piezoelectric materials [1-2], shape memory alloys [3-4], electrorheological (ER) fluids [5-6] and magnetorheological (MR) fluids [7] are being widely utilized. Among these smart materials, ER or MR fluid exhibits reversible changes in material characteristics when sub‐ jected to electric or magnetic field. The vibration control of flexible structures using the smart ER or MR fluid can be achieved from two different methods. The first approach is to replace conventional viscoelastic materials by the ER or MR fluid. This method is very effec‐ tive for shape control of flexible structures such as plate [5]. The second approach is to de‐ vise dampers or mounts and apply to vibration control of the flexible structures. This method is very useful to isolate vibration of large structural systems subjected to external excitations [6-7]. In this work, a new type of MR mount is proposed and applied to vibration control of the flexible structures.

In recent years, increasing research efforts have been devoted to the development of new controllable dampers, in the aim of mitigating vibration of mechanical equipment, automobile, civil construction and so on. Most of the new controllable dampers are made with special performance of smart materials, such as MR/ER fluid, piezoelectric ceramic and shape memory alloy. Although has similar smart performance such as rapid response time, low power requirement and large driving force with those smart materials, magnetostrictive material, especially magnetostrictive composite material is only got attention by a few researchers. In this paper, by analysis character of magnetosrtrictive effect, the possible applications of magnetosrtrictive composite material in area of vibration control are discussed; several new dampers, made with magnetosrtrictive composite material, such as smart friction or viscous dampers are presented.

Recent advancements in smart materials have ushered in a new era of adaptive, efficient, and sustainable technologies1. Smart materials possess intrinsic capabilities to respond dynamically to external stimuli—such as temperature, pressure, moisture, and electromagnetic fields—enabling their integration into responsive systems across multiple industries. This paper presents a comprehensive review of innovations in smart materials with an interdisciplinary focus, incorporating recent breakthroughs in shape memory alloys, piezoelectric materials, smart polymers, and nanostructured composites. In particular, the study includes a novel data-driven analysis of bio-inspired smart materials modelled after the natural hygromorphic behaviour of pine cones. Experimental data demonstrates controlled, reversible defor-mation under ambient humidity fluctuations (30–90% RH), with a response time averaging 15–30 minutes and displacement amplitudes up to 12 mm5.

Abstract: This chapter explores the engineering of adaptive structures using smart materials with programmable mechanical and optical properties, offering a pathway to innovation in fields such as aerospace, architecture, and biomedical engineering. These materials, including shape-memory alloys, electroactive polymers, and photonic crystals, can alter their stiffness, elasticity, transparency, and light transmission in response to external stimuli like heat, electricity, and light. The chapter covers the design principles, fabrication techniques, and computational modeling tools used to develop these materials, highlighting real-world applications in aerospace shape-shifting components, self-healing medical implants, and dynamic building façades. Future trends such as AI-driven material optimization and biocompatible smart materials for regenerative medicine are also discussed. Keywords: smart materials, adaptive structures, programmable properties, shape-memory alloys, electroactive polymers, photonic crystals, mechanical properties, optical properties, self-healing, computational modeling, AI-driven material design, aerospace, biomedical engineering, regenerative medicine, dynamic façades, sustainability.

Smart actuators, made of smart materials, are becoming more attractive in many applications because smart materials are not subjected to wear and does not require lubrication during services. Piezoelectric materials are a group of the many attractive smart materials that are being investigated for many applications today. Piezoelectric materials show fast responses, high efficiency/accuracy and operate on a large bandwidth. Composite materials are of interest because of their design flexibility and because they are lighter than other materials commonly used in aircraft and other applications. For the research reported here, a piezoelectric material was embedded in a composite material to form a piezoelectric composite actuator. This research was conducted to expand our knowledge of piezoelectric composite material actuators, and originated from the need to control air flow separation over an airfoil. There is a need to build a profound knowledge about such actuators before they can be implemented in an airfoil, and to understand which parameters influence the behaviour of piezoelectric composite material actuators under static and dynamic operating conditions. The actuators were manufactured and tested under static and dynamic conditions and the experimental results were compared to the finite element models. The models were incorporated with piezoelectric material properties that were determined experimentally. The results showed that a piezoelectric material’s response to an input stimulant, e.g. electric voltage and frequency, influences the actuator’s behaviour.

Ag-TiNx electrodes deposited on piezoelectric poly(vinylidene fluoride) for biomedical sensor applications

Smart materials, which respond to external stimuli such as temperature, light, stress, or magnetic fields, have gained significant prominence in civil engineering. This paper examines the development of smart materials and their applications in construction, with a focus on Shape Memory Alloys (SMAs), Piezoelectric Materials, Self-Healing Concrete, Shape-Shifting Polymers, Smart Sensors, Magnetorheological Fluids, Photochromic and Thermochromic Materials, and Carbon Fiber Reinforced Polymers (CFRPs). The paper explains, • The temperature-dependent phases of SMAs and their stress-temperature relationship. • The types, advantages, and limitations of piezoelectric materials, emphasizing their diverse applications in construction. • Applications, advantages, and disadvantages of self-healing concrete in various construction scenarios. • Applications of Shape Memory Polymers (SMPs)in adaptive architecture for self-regulating systems, emphasizing their properties, applications, and limitations. • Applications of smart sensors in construction, highlighting their role in real-time monitoring, safety, and resource utilization. • Potential of Photochromic and Thermochromic Materials in architectural applications for dynamic light and temperature control. • Properties, applications, advantages, and limitations of CFRPs in enhancing structural robustness. This comprehensive overview aims to provide insights into the diverse applications of smart materials in civil engineering, paving the way for innovative and resilient construction practices

A smart structure involves distributed actuators and sensors, and one or more microprocessors that analyze the responses from the sensors and use distributed-parameter control theory to command the actuators to apply localized strains to minimize system response. A smart structure has the capability to respond to a changing external environment (such as loads or shape change) as well as to a changing internal environment (such as damage or failure). It incorporates smart actuators that allow the alteration of system characteristics (such as stiffness or damping) as well as of system response (such as strain or shape) in a controlled manner. Many types of actuators and sensors are being considered, such as piezoelectric materials, shape memory alloys, electrostrictive materials, magnetostrictive materials, electro- rheological fluids and fiber optics. These can be integrated with main load-carrying structures by surface bonding or embedding without causing any significant changes in the mass or structural stiffness of the system. Numerous applications of smart structures technology to various physical systems are evolving to actively control vibration, noise, aeroelastic stability, damping, shape and stress distribution. Applications range from space systems, fixed-wing and rotary-wing aircraft, automotive, civil structures and machine tools. Much of the early development of smart structures methodology was driven by space applications such as vibration and shape control of large flexible space structures, but now wider applications are envisaged for aeronautical and other systems. Embedded or surface-bonded smart actuators on an airplane wing or helicopter blade will induce alteration of twist/camber of airfoil (shape change), that in turn will cause variation of lift distribution and may help to control static and dynamic aeroelastic problems. Applications of smart structures technology to aerospace and other systems are expanding rapidly. Major barriers are: actuator stroke, reliable data base of smart material characteristics, non-availability of robust distributed parameter control strategies, and non-existent mathematical modeling of smart systems. The objective of this paper is to review the state-of-the-art of smart actuators and sensors and integrated systems and point out the needs for future research.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Smart materials are a class of materials that can respond to external stimuli, such as temperature, light, pressure, and electric or magnetic fields. Chemical engineers play a crucial role in the development, optimization, and scalability of smart materials, which have applications in a wide range of industries, including aerospace, automotive, healthcare, and construction. This article discusses the role of chemical engineering in the design and synthesis of smart materials, focusing on the development of polymers, composites, and nanomaterials that exhibit responsive behaviors. The paper also explores the challenges, innovations, and future directions in smart material technology, highlighting the interdisciplinary nature of chemical engineering in advancing this field.

This study explores an innovative energy harvesting technique for biomedical implants in alignment with the United Nations Sustainable Development Goals, focusing on good health and well-being (Goal 3). The study promotes sustainable healthcare solutions by analysing mechanically deformed materials, surface charges, and electric fields. This review research delves into the advancements and potential of piezoelectric materials and their integration with other energy-harvesting technologies, such as thermoelectrics, to create innovative hybrid systems for sustainable energy production and biomedical applications. The study highlights the development of stretchable, self-healing, and biodegradable piezoelectric materials enabled by nano-fillers, structural engineering, and various fabrication techniques. Integrating piezoelectric and thermoelectric materials in hybrid Energy Harvesters (EH) has led to devices capable of simultaneously harnessing thermal and mechanical energy, ensuring continuous and efficient energy production. The research on self-healing piezoelectric crystals explores the possibility of creating durable and resilient EH that can withstand repeated mechanical stress. The novelty and potential of this research lie in developing adaptive, high-performance, and environmentally friendly piezoelectric materials and devices. By combining piezoelectrics with other disciplines and exploring new designs, materials, and techniques, this review aims to inspire future research and innovation in sustainable energy solutions.

Film Bulk Acoustic Wave Resonators (FBARs) are fundamental electronic components in modern radio frequency (RF) wireless communication systems. They use thin-film piezoelectric materials to generate and filter high-frequency acoustic waves. However, FBARs with conventional piezoelectric materials are facing a challenge to increase their resonant frequencies beyond several GHz because conventional piezoelectric materials are hard to maintain high piezoelectricity with their thickness below sub-micron. Recent advancement in two dimensional (2D) piezoelectric materials creates new opportunities in this aspect. Several 2D piezoelectric materials exhibit strong piezoelectricity with even a single atomic layer. The research carried out in this PhD project has been focused onto the pioneering studies of several typical 2D piezoelectric materials for novel FBARs, which show better performances than those counterpart devices based on conventional piezoelectric materials. 3R (3 Rhombohedral) MoS2, a transitional metal dichalcogenide, has been theoretically predicted and experimentally confirmed to possess strong piezoelectricity regardless of the numbers of the atomic layers involved. The atomic layers are bound through van der Waals (vdWs) force and are easily exfoliated into single or few layer flakes with atomically flat and defect-free surfaces, very promising for acoustic wave device application. In this PhD project, the out-of-plane piezoelectricity of 3R-MoS2 flakes has been characterized by Piezo-response Force Microscope (PFM) technique. 3R-MoS2 based solid mounted resonators (SMRs), a category of FBARs, have been designed, fabricated and characterized. Ultrahigh resonant frequencies up to 27.5 GHz have been achieved with SMRs with ~200 nm thick 3R-MoS2. To the best of our knowledge, those devices are the first bench of FBARs based on 2D piezoelectric materials in the world. With the development of the 5/6G industry, communication band has become wider and more crowded. Compared to the static FBARs, dynamic FBARs whose resonant frequencies can be tuned corresponding to the requirements become increasingly attractive. In this PhD project, we have systematically studied the out-of-plane piezoelectricity and room-temperature ferroelectricity of 2D α phase In2Se3 and found that the domains of the α-In2Se3 flakes can be switched by a direct current (DC) electric field. This unique characteristic makes α-In2Se3 very promising for dynamic FBARs. To avoid the challenge of the matching between the Bragg mirror and α-In2Se3 flakes, we have adopted the air gap structure and successfully fabricated and characterized α-In2Se3 based tunable and switchable FBARs. High tuning efficiency of 4.3 MHz/V (0.05% tuning/V at the resonant frequency of 8.60 GHz) has been achieved with 160 nm thick α-In2Se3 flake. The device is at the on-state under zero bias and can be switched off under a small bias voltage of - 4 V. To the best of our knowledge, it is the first dynamic FBARs based on 2D ferroelectric materials that could work beyond the sub-6G band, with a high tuning efficiency and a very small switched-off voltage.

To unlock the lock of futuristic developments, nowadays shape memory alloys (SMAs) are acting as key by outnumbering the existing smart materials in view of new design competence, innovative techniques, enhanced technologies, and meeting the dire need according to the demand of ongoing scientific and industrial progress. Undoubtedly, it can be worthy to associate SMAs with the term polymorphism, as they possess unique capability to encapsulate multitudinous inherent characteristics under their name. Shape memory effect, superelasticity, and damping are there to name a few among many others, as prime indicators. The exhibition of these characteristics of SMAs is due to the transformation that takes place between austenite phase and martensite phase which is achieved either by temperature or stress variation. The fascinating characteristics they possess enable them to attract researchers and designers toward their potential applications in diverse domain as smart and multi-functional materials. The present work focuses on the review of research works accomplished in the recent 5 years pertaining to modeling and applications of shape memory alloys in distinct domains. Under the topic of modeling, a look into the research carried out on a variety of SMA structures—like functionally graded SMAs, SMA springs, porous SMAs, novel SMA actuators—is presented. In addition to this, the work carried out to represent SMAs with large strains and large rotations and to model polycrystalline SMAs is also covered. This is supplemented by application-oriented domains, each of which disseminates the attributes of SMAs that are self-sufficient to express what factors make SMAs more prominent. It is believed that the foregoing works comprehensively detailed in this review article will certainly lay a solid platform for the future investigations that are going to take place in time to come.

With the rapid development of smart material technology, piezoelectric materials have become a hot topic in driver research due to their superior performance in fast response and high precision. Compared with other smart materials, such as shape memory alloys and electro-deformable materials, piezoelectric materials exhibit significant advantages in small displacement and high-frequency vibration applications, enabling more precise control and higher response frequencies. Additionally, piezoelectric actuators are small and lightweight, making them particularly suitable as driving units for high-precision linear motion mechanisms. This article develops a threaded piezoelectric actuator based on the principle of the inverse piezoelectric effect of piezoelectric materials. The working frequency and mode are determined through dynamic simulation analysis, and a prototype is constructed. The working principle is verified through vibration characteristic testing. Finally, a linear platform driven by a threaded piezoelectric actuator is designed, and step characteristic experiments are conducted. The results show that its step resolution can reach 0.2 μm.