Advances In Electrostrictive, Magnetostrictive, And Ionic Polymer-Metal Composites For Micro-Robotics Essay.

Electrostrictive Smart Materials

Inspired by biological systems such as human body systems, scientists have widened their innovations in the application of smart materials in the design and manufacturing of intelligent systems. According to the research (Meinzer, 2017, pp.1-1), smart materials can respond to the changes in their environments by detecting the changes through the sensors and responding to the changes using the actuators. The discovery of these smart materials has had a huge impact on micro-robotics innovations since it enhanced the functionalities and capabilities of micro-robots through intelligence, cooperation, propulsion, biocompatibility, and intelligence (Soto et al., 2021). Smart materials have allowed the construction of micro-robots made up of new sensing, actuation, control, self-protective, self-detection, and self-controlled smart systems. The smart materials are made up of different distinct properties, hence used to develop different smart systems. Therefore, depending on the nature of the materials and their properties, the smart materials are divided into two major groups; polymeric and non-polymeric smart materials (Greco and Mattoli, 2012, pp. 1-27). The non-polymeric materials are further subdivided into electrostrictive, magnetostrictors smart materials. The polymeric smart materials are subdivided into ionic polymer metal composites, conductive polymer, and ionic polymer gels.

This study describes the advances of such smart materials as electrostrictive, Magnetostrictive, and ionic polymer-metal composites about their classifications, their applications, recent developments, and prospects in micro-robotics.

The electrostrictive smart materials utilize the electrostriction effect through the mechanical displacement in response to the external electric field changes in the environment (QADER et al., 2019, pp. 755-788). According to research by (You et al., 2019, p. 3780), the electrostrictive material responds to the external changes through its ions. The positive ions are displaced in respect to the external electric field as the negative ions relocate to the opposite direction of the field. The research further states that the displacement of the ions in the material to a specific area thus allows them to accumulate in the area resulting in elongation in the direction of the external electric field, thus responding to the external changes in the environment forming a perfect actuator. The induced strain on the electrostrictive material depends on the magnitude of the exposed electric field; hence the length of the elongation can be controlled using the amount of external electric field exposed to it. The findings from the research (Ask et al., 2012, pp.9-21) on the electrostriction in electro-viscoelastic polymers show that the combination of the controlled elongation in the material with the non-contact induction makes the electrostrictive materials perfect actuators in the micro-robotics.

With the rising need for smart materials to be used in the advancing technology, researchers (Jin et al., 2018, pp. 21816-21824) conducted extensive research to determine electrostrictive properties. Their findings show that the effects of the electrostrictive materials can be maximized by doing the material to give more superior powers that have a fast response to the external stimuli. Additionally, the study (Tohluebaji et al., 2019, p. 1817) shows that electrostrictive properties can be utilized in the construction of electrostrictive polymers to create stronger dielectric properties and crystallinity to provide improved electrostriction behavior due to the dielectric permittivity hence improving the response time for the micro robots' actuators. Large strain response with fatigue-free behavior of the micro-robotic actuators can be constructed using electrostrictive materials added with lead-free ceramics. This is in accordance to the research study (Hao et al., 2016, pp.4003-4014). The findings from the study further state that the materials had a high and pure electrostrictive effect with a large electrostrictive coefficient, thus ensuring high precisions positioning of the micro-robotics actuators

Magnetostrictive Smart Materials

Over the years, there have been numerous advancements in the use of electrostrictive material to develop an intelligent system that is responsive to changes in the environment. Based on the research by (Xiao et al., 2016) on the use of electrostrictive material to construct a fish-like robot that can respond to such external stimuli as heat, pressure, electricity, and light. Additionally, the researchers (Ganet et al., 2015, pp.1-12) on the use of electrostrictive polymer to develop a smart guidewire used in robotic surgery found out in their research that electrostrictive materials could be used to guide x-ray fluoroscopic imaging hence enhancing the accurate surgical process. However, the study concludes that ionic polymer composite materials are better than electrostrictive material since they can generate large displacements at a low electrical field and moderate speeds compared to the electrostrictive material.

According to the research (Jacquemin et al., 2019) on the application of the electrostrictive material on the multilayer polymer actuator in the modeling of the continuum robotic snake, electrostrictive material help in micro-robotics to improve the design of the robot in its compact design, high strain, and low cost. Moreover, in the study (Ahmed and Billah, 2016, p.89) the electrostrictive material was used to design a flexible snake as the material could easily respond to the changes in external stimuli thus allowing easy bending.

As various scholars described their properties and how they can respond to external stimuli, the electrostrictive materials are perfect material to be used in the design of micro-robot’s actuators since they have quick response time and higher displacement of ions hence offers good productivity. However, there are challenges associated with the material that might limit the operation of the designed actuators. The challenges include the lack of bidirectional respond to the stimuli hence lacks flexibility. Moreover, electrical breakdown of the actuators might happen when the electric field applied in the poling directing exceeds the dielectric strength of the material. the

Magnetostrictive smart materials can alter their shapes and dimensions in response to the influence of the magnetic field and mechanical stress that allows them to exhibit a change in their magnetization (Elhajjar et al., 2018, pp. 204-229). The domains of the magnetostrictive materials are randomly arranged in nature; however, when the material is magnetized, these domains are arranged parallel to each other, thus magnetizing the material, and any interaction with the external magnetic field would result in the magnetostrictive effect (Krishnan, 2016). The magnetostrictive effect; the ability to change its shape and dimension due to the influence of the magnetic field is useful in the design and building of microrobots. According to the study (Muller et al., 2019, p. 045113), improvements have been made on the magnetostrictive materials through deformations to ensure that the materials are highly responsive to the external stimuli by developing a non-contact torque sensor. Additionally, the findings from the study (Zhang et al., 2012, p.055014) on the magnetostrictive actuators show that the actuators designed using the magnetostrictive materials have high precision and fast response that is beyond the traditional actuators. Based on the results of the study (Carlson, 2013, p.1808), the bidirectional response of the magnetostrictive materials and their ability to be controlled by the strength applied of the magnetic field makes it the perfect material for the design and building of micro-robotics.

Ionic Polymer-Metal Composites

The bidirectional, magnetostrictive effect and fast response of the magnetostrictive materials have largely been applied in micro-robotics to create advanced actuators for the microrobots. The bidirectional property of the magnetostrictive materials allows it to be used for sensing the changes in the external stimuli and responding accordingly. In the study (Jing and Cappelleri, 2013, pp. 81-100) on towards functional mobile magnetic micro-robots, the study shows the application of the magnetostrictive material in building microrobots. The study uses the magnetostrictive effect to design a crawling microrobot that exhibits tumbling and crawling locomotion mechanisms. The microrobot body was fitted with magnetic sensors to respond to mechanical stimuli to allow it to move in the specified direction through micro-force sensing. In the study (Adam et al., 2019, p. 69) on functional mobile micro-robotic systems, the research findings show that when using magnetic actuation in the micro-robotic systems, the microrobots can be wirelessly and accurately controlled. However, according to the study, it is impossible for an individual to accurately control multiple magnetic microrobots. In an attempt to answer the research, question the study concludes that a local magnetic field system to foster magnetostrictive effect on multiple microrobots allows an individual to have central independent control of multiple magnetic microrobots.

More advanced development and progress have been made in the medical field using microrobots in several medication operations such as imagining and surgical operations. In the study on medical imaging of microrobots, the researchers (Aziz et al., 2020, pp. 10865-10893) found out that due to its low precision and its ability to manually control, the microrobots with magnetostrictive actuators offer the best solution in medical imaging since the microrobots are easily controlled to the desired location in the patient’s body. Additionally, the microrobots can be easily controlled to enter the narrowest parts of the human body to ensure effective drug delivery.

According to research (Karnaushenko et al., 2020. P. 1902994), although the magnetostrictive materials are more effective than other smart materials such as electrostrictive materials, the design of the microrobots using these materials proves to be difficult since, for maximum actuation effect, there is need to the solenoid and magnetic circuit thus making the microrobot larger and bulkier compared to that made using the electrostrictive material. Therefore, this implementation issue restricts the use of the magnetostrictive material in the design of the microrobots that will be used in areas where the weight of the robot is not a problem.  

This is a unique smart material whose structure is made up of properties that allow it to operate as an actuator and a sensor (Jo et al., 2013, pp.1037-1066). This is because the material can convert the acquired electrical stimuli to the mechanical movement (actuator) and convert the mechanical parts to detect changes in its environment (Shahinpoor, 2015). The ionic polymer-metal composites (IPMC) are made up of two ions; the cations and the anions. The cations are mobile while the anions are fixed. The rearrangement and redistribution of these ions give the material the smart properties to react to the changes in the external stimuli. Naturally, the ions are equally distributed in the material; however, in response to such forces as electrical, osmotic, and elastic interaction forces, the ions are redistributed with the external force (Amirkhani and Bakhtiarpour, 2015). Based on the findings of the study (Farajollahi et al., 2016, pp.45-46), such properties as low activation voltage, biocompatibility, its ability to operate in wet and dry conditions, large bending strain, and its ease to miniaturize, the ionic polymer-metal composite material makes it a perfect material build microrobots. The microrobots designed and built using the IPMC smart material are gaining significant attention in such fields as medicine, aerospace, and the automotive industry. Therefore, there has been advanced development in various fields where microrobots are used to solve various problems.    

Applications in Micro-Robotics

Due to the property of IPMC smart materials to be useful in both the dry and wet areas, marine engineers have developed underwater microrobots designed using the IPMC materials. According to recent research (Shi et al., 2012, pp.415-420) on modeling of IPMC actuators, the underwater micro-robots were designed to detect changes in the ocean currents, pollution, study animal migration, and measurement of depths. According to the study, the IPMC material ensured the design of a multi-functional, flexible, and high-precision underwater microrobot with a compact structure.  

A study on the swimming microrobots (Boerefijn, 2017) found that autonomous microrobots created using IPMC smart material could swim through the body fluids to the desired location. This is due to its properties, such as operating in wet conditions and biocompatibility. The study further suggests that the microrobots could be used in medicine and surgery to deliver the drugs, perform implants, and remote sensing. Furthermore, due to such properties as being light-weight, multi-directional, and ability to give a significant bending under low voltage, the study (Guo et al., 2012, pp. 1472-1483) shows autonomous micro-robotic diaphragms have been developed to be used during surgery.

Although the IPMC smart material has aided in designing and manufacturing effective microrobots applied in various fields, the study (Annabestani, 2018) shows that the IPMC microrobot has not met the desired outcome features to solve other complex problems. The study points out such drawbacks as the back relaxation effect in the IPMC microrobots that hinder it from attaining stable and constant bending response to the external stimuli. Therefore, the IPMC microrobots need advanced research on the modeling, identification, application, and control.

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