Flexible pressure sensors are pivotal in advancing artificial intelligence, the Internet of Things (IoT), and wearable technologies. While microstructuring the functional layer of these sensors effectively enhances their performance, current fabrication methods often require complex equipment and time-consuming processes. Herein, we present a novel magnetization-induced self-assembly method to develop a magnetically grown microneedle array as a dielectric layer for flexible capacitive pressure sensors. By precisely controlling the magnetic particle concentration and dynamic magnetic field strength, we achieve a tunable microneedle morphology. The resulting sensor exhibits high sensitivity (4.11 kPa-1), an ultrafast response time (20 ms), excellent cyclic stability (≈1700 cycles), and flexibility. We demonstrate real-time monitoring of various physiological signals including pulse, grip force, breathing rate, and head motion. This study introduces a promising approach for fabricating high-performance flexible sensors, potentially enabling more intuitive and effective human-machine interactions.

Magnesium-based implants are highly valued in the biomedical field for biocompatibility and biodegradability, though their inherent low strength in body fluids is a limitation. This study addresses this by alloying magnesium with zinc and titanium to enhance its properties. Mechanical alloying was used to synthesize binary (Mg-Zn, Mg-Ti) and ternary (Mg-Zn-Ti) alloys, which were then compacted and sintered. The alloy powders, composed of 10 wt% Zn and 5 wt% Ti, were milled at 360 rpm for 10 h. Microstructural analysis revealed uniformly dispersed particles, with SEM confirming spherical and fine particles alongside laminates. XRD identified intermetallic compound formation. The ternary alloy demonstrated superior micro-hardness and Young's modulus similar to human bone, making it particularly promising for biomedical applications. Incorporating zinc and titanium into the magnesium matrix resulted in a ternary alloy that outperformed its binary counterparts.

Flexible dual mode strain-temperature sensors that mimic human skin functions are highly desired for wearable devices and intelligent robots. However, integrating dual sensing characteristics into a single sensor for simultaneous and decoupled strain-temperature detection still remains a challenge. Herein, we report a flexible dual-modal sensor that uses a "neutral surface" structural design technique to integrate an independently prepared temperature sensing layer (TSL) and strain sensing layer (SSL), for simultaneous monitoring of strain and temperature, in a decoupled manner. The TSL consists of a PDMS/BaTiO3 based dielectric layer whose dielectric constant and thickness change in response to temperature fluctuations. The SSL consists of a resistive type Ni80Cr20 film whose resistance changes in response to external strain. After optimizing the temperature and strain sensing characteristics of the TSL and SSL, the obtained dual-modal flexible sensor has shown a broad temperature sensing range (30 to 200 degrees C), with high temperature sensitivity (-160.90 fF degrees C-1), excellent linearity (0.998), and highly discernible temperature resolution (0.1 degrees C). Additionally, the sensor has also exhibited a wide strain monitoring range (20 to 1000 mu epsilon), good strain resolution (20 mu epsilon or 0.002%), and a fast strain response time (54 ms). When practically demonstrated, our sensor has successfully shown independent perception of strain and temperature, which highlights its promising application potential in the fields of smart robotics and intelligent prosthetics. The neutral surface in the structural design enables a flexible dual modal strain sensor with strain-temperature decoupling. At the same time, material selection ensures stable sensing of temperature and strain over a wide temperature range.

Flexible electronic devices extended abilities of humans to perceive their environment conveniently and comfortably. Among them, flexible magnetic field sensors are crucial to detect changes in the external magnetic field. State-of-the-art flexible magnetoelectronics do not exhibit low detection limit and large working range simultaneously, which limits their application potential. Herein, a flexible magnetic field sensor possessing a low detection limit of 22 nT and wide sensing range from 22 nT up to 400 mT is reported. With the detection range of seven orders of magnitude in magnetic field sensor constitutes at least one order of magnitude improvement over current flexible magnetic field sensor technologies. The sensor is designed as a cantilever beam structure accommodating a flexible permanent magnetic composite and an amorphous magnetic wire enabling sensitivity to low magnetic fields. To detect high fields, the anisotropy of the giant magnetoimpedance effect of amorphous magnetic wires to the magnetic field direction is explored. Benefiting from mechanical flexibility of sensor and its broad detection range, its application potential for smart wearables targeting geomagnetic navigation, touchless interactivity, rehabilitation appliances, and safety interfaces providing warnings of exposure to high magnetic fields are explored.

Smart skins and smart textiles equipped with strain sensors for motion detection are of prime significance for personalized health monitoring, lifestyle and fitness applications. Yet, the dependence of these devices on wired power supplies and rigid batteries limits their use in everyday settings. Here, we report self-powered and highly elastic strain sensors withstanding stretching to 200% for monitoring the human motion. The sensor is based on a torsional-spring-shaped coil of liquid metal wound around an elastomeric tubing and equipped with a tiny piece of a magnetic ring. The energy is harvested from the body motion relying on the Faraday's law of electromagnetic induction when the coil is exposed to a time-varying magnetic field of the magnetic ring upon the mechanical deformation of the strain sensor. The max short-circuit current is 2 mA, which is much higher than previous work, and the peak power of our device is 20 mu W, sufficiently high to drive conventional low-power electronics. We demonstrate the application potential of our sensor for wearable electronics for monitoring the motion of arms and legs during fitness workout and riding bicycle. The sensor can measure motion of fingers and wrist for health applications and establish wireless control of robotic hands.

Flexible strain sensors play vital role in human–machine interaction. Despite their vast development, a strain sensor having broad strain sensing range, ultralow detection limit, and negligible hysteresis still remains a challenge. Herein, a liquid metal (LM)‐based stretchable resistive strain sensor, prepared by selective wetting and transferring process to attain improved compatibility between LM and polydimethylsiloxane substrate, is reported. This sensor exhibits broad strain sensing range (105%), with ultralow detection limit (0.05%), minimal hysteresis, fast response time (58 ms), and excellent repeatability. When practically demonstrated, this sensor successfully monitored various human activities, such as blink motion monitoring, voice intensity differentiation, heartbeat and wrist pulse monitoring. Moreover, when the current sensor is used in the form of smart kneecap and smart glove, it efficiently detected various human gestures, which confirms its great application potential in the fields of human health and motion monitoring, human–machine interface, and virtual reality applications.

The multi-mode pain-perceptual system (MMPPS) is essential for the human body to perceive noxious stimuli in all circumstances and make an appropriate reaction. Based on the central sensitization mechanism, the MMPPS can switch between different working modes and thus offers a smarter protection mechanism to human body. Accordingly, before injury MMPPS can offer warning of excessive pressure with normal pressure threshold. After injury, extra care on the periphery of damage will be activated by decreasing the pressure threshold. Furthermore, the MMPPS will gradually recover back to a normal state as damage heals. Although current devices can realize basic functions like damage localization and nociceptor signal imitating, the development of a human-like MMPPS is still a great challenge. Here, a bio-inspired MMPPS is developed for prosthetics protection, in which all working modes is realized and controlled by mimicking the central sensitization mechanism. Accordingly, the system warns one of a potential injury, identifies the damaged area, and subsequently offers extra care. The proposed system can open new avenues for designing next-generation prosthetics, especially make other smart sensing systems operate under complete protection against injuries.

Stretchable strain sensors are important components of soft robotics, rehabilitation assistance, and human health monitoring systems. However, strain sensors capable of wide‐range force detection with adjustable modulus facilities are highly desirable to obtain mechanical feedback in various scenarios. Herein, a stretchable capacitive strain sensor capable of adjustable modulus and wide‐range force detection is reported. The sensor consists of two liquid metals (LMs) filled thermoplastic elastomer (TPE) tubes encapsulated in flexible silicone. The adjustable modulus capability of the sensor is attained by mounting the sensor with springs of different elastic coefficients. During electromechanical tests, the elastic coefficient‐dependent adjustable modulus is obtained in the range of 0.78–10.3 MPa. After optimizing the performance, a sensor capable of wide force‐sensing range (0.07–74 N), high cyclic stability (>3500 cycles), with low hysteresis, good linearity, and fast response time (<50 ms) is achieved. Finally, a digital display system is developed to display the amount of detected force during the loading of the sensor, which confirms the great capability of the sensor to be applied in joint rehabilitation and soft robotic fields.

Surface electromyography (sEMG) sensors are widely used in the fields of ergonomics, sports science, and medical research. However, current sEMG sensors cannot recognize the various exercise intensities efficiently because of the strain interference, low conductivity, and poor skin-conformability of their electrodes. Here, we present a highly conductive, strain-insensitive, and low electrode–skin impedance elastic sEMG electrode, which consists of a three-layered structure (polydimethylsiloxane/galinstan + polydimethylsiloxane/silver-coated nickel + polydimethylsiloxane). The bottom layer of the electrode consists of vertically conductive magnetic particle paths, which are insensitive to stretching strain, collect sEMG charge from human skin, and finally transfer it to processing circuits via an intermediate layer. Our skin-friendly electrode exhibits high conductivity (0.237 and 1.635 mΩ·cm resistivities in transverse and longitudinal directions, respectively), low electrode–skin impedance (47.23 kΩ at 150 Hz), excellent strain-insensitivity (10% change of electrode–skin impedance within the 0–25% strain range), high fatigue resistance (>1500 cycles), and good conformability with skin. During various exercise intensities, the signal-to-noise ratio (SNR) of our electrode increased by 22.53 dB, which is 206% and 330% more than that of traditional Ag/AgCl and copper electrode, respectively. The ability of our electrode to efficiently recognize various exercise intensities confirms its great application potential for the field of sports health.

Flexible pressure sensors are highly desirable in artificial intelligence, health monitoring, and soft robotics. Microstructuring of dielectrics is the common strategy employed to improve the performance of capacitive type pressure sensors. Herein, a novel, low-cost, large-area compatible, and mold-free technique is reported in which magnetically grown microneedles are self-assembled from a film of curable magnetorheological fluid (CMRF) under the influence of a vertical curing magnetic field (B-curing). After optimizing the microneedles' fabrication parameters, i.e., magnetic particles' (MPs') concentration and B-curing intensity, piezocapacitive sensors capable of wide range pressure sensing (0-145 kPa) with ultrafast response time (50 ms), high cyclic stability (>9000 cycles), as well as very low detection limit (1.9 Pa) are obtained. Sensor properties are found dependent on microneedles' fabrication parameters that are controllable, produce variable-sized microneedles, and allow to govern sensing properties according to desired applications. Finally, the sensor is employed in holding a bottle with different weights, human breath, and motion monitoring, which demonstrate its great potential for the applications of human-machine interaction, human health monitoring, and intelligent soft robotics.

Wearable sensors are gradually enabling decentralized healthcare systems. However, these sensors need to be closely attached to skin, which is unsuitable for long-term dynamic health monitoring of the patients, such as infants or persons with burn injuries. Here, a wearable capacitive sensor based on the capacitively coupled effect for healthcare monitoring in noncontact mode is reported. It consists of a ring-shaped top electrode, a disk-shaped bottom electrode, and a porous dielectric layer with low permittivity. This unique design enhanced the capacitively coupled effect of the sensor, which enables a high noncontact detectivity of capacitance change. When an object approaches the sensor, its capacitance change (ΔC/C i = -38.7%) is 3-5 times higher than that of previously reported sensors. Meanwhile, the sensor is insensitive to the stretching strain and pressure (ΔC/C i < 5%) due to the unique ring-shaped electrode and the incompressible closed cells of the porous dielectric material, respectively. Finally, various human physiological signals (pulse and respiratory) are recorded in noncontact mode, where a person wears loose and soft clothes implanted with the sensor. Thus, it is promising to build smart healthcare clothes based on it to develop wearable decentralized healthcare systems.

The Editor-in-Chief has retracted this article [1] because Figures 11 and 12 appear to be identical with Figures 3 and 4 respectively from a previously published article [2].

Piezoelectric materials have wide applications in the field of mechanical, aerospace and civil engineering because of its voltage dependent actuation. Piezoelectric material goes through voltage generation whenever deflection is induced in it and vice versa. Piezoelectric bimorph beam has been widely used for sensing and actuating. In the actuation mode, an electric field is applied across the beam thickness, one layer contracts while the other expands. This results in the bending of the entire structure and tip deflection. In the sensing mode, the bimorph is used to measure an external load by monitoring the piezoelectric induced electrode voltages. In this research work, a 2D bimorph piezoelectric actuator model having two layers made of polyvinylidene fluoride (PVDF) material was developed to examine the inverse piezoelectric effect. Finite element analysis (FEA) was carried out on specially designed actuator model by using MATLAB Partial Differential Equation (PDE) Toolbox™. Theoretical analysis has been carried out to measure the tip deflection under applied electric field. The laboratory test was performed to investigate the deformation behavior of piezoelectric actuator. It is observed that, more the electric field applied, more the material would be deformed in a particular direction. The experimental results are in good agreement with numerical results.

Joint motion is a very common activity which involves tensile or compressive bending motions. Distinguishing and monitoring of joint motions are important for an interactive human-machine interface or rehabilitation of human joints. Here, we present an asymmetric structure based, liquid metal embedded, resistive strain sensor, which is prepared by a stereolithography-based 3D printing process. Electromechanical characterization results of sensors confirm that the current sensor can monitor the angle and direction of joints even if the angle amplitude remains the same. The sensor exhibits good mechanical stability and minimum resolution angle of 1 degrees, ranging from 70 degrees to -70 degrees. Sensor performance is enhanced with the increase of its thickness, which is due to an additional deviation produced at the center. This deviation causes the resistance of the sensor to change greatly during both compressive and tensile bending. Finally, a sensor's capability is practically demonstrated by the monitoring the motion of index of the finger, wrist, and neck joints under various human activities. Our sensor paves a way for real-time continuous monitoring of human or artificial robot joint motions.

Recent achievements in the field of electronic skin have provided promising technology for prosthetic systems. However, the development of a bionic tactile-perception system that exhibits integrated stimuli sensing and neuron-like information-processing functionalities in a low-pressure regime remains a challenge. Here, we demonstrate a tactile sensor for smart prosthetics based on giant magneto-impedance (GMI) material embedded with an air gap. The sensor exhibits a high sensitivity of 120 newton(-1) (or 4.4 kilopascal(-1)) and a very low detection limit of 10 micronewtons (or 0.3 pascals). The integration of the tactile sensor with an inductance-capacitance (LC) oscillation circuit enabled direct transduction of force stimuli into digital-frequency signals. The frequency increased with the force stimuli, consistent with the relationship between stimuli and human responses. The minimum loading of 50 micronewtons (or 1.25 pascals), which is less than the sensing threshold value of human skin, was also encoded into the frequency, similar to the pulse waveform of humans. The proposed tactile sensor not only showed desirable sensitivity and low detection limit but also exhibited transduction of digital-frequency signals like human stimuli responses. These features of the GMI-based tactile sensor show potential for its applications in smart prosthetics, especially prosthetic limbs that can functionally replace natural limbs.

Carbon fiber reinforced aluminum laminates (CARALL) are one of the aluminum based Fiber metal laminates (FMLs) which, due to their high strength to weight ratio and good impact resistance are greatly replacing aluminum alloys in aircraft structures. In this research work, interlaminate shear strength of Vacuum assisted resin transfer molding (VARTM) manufactured CARALL has been investigated. Numerical simulation model incorporated with real time material data has been developed to predict the delamination behavior of CARALL laminates. Standard CARALL specimens with different surface morphologies were prepared by electric discharge machining, mechanical, chemical and electrochemical surface treatments. T-peel tests were carried out according to standard ASTM D1876-08 to find out inter laminate shear strength. FMLs made out of mechanically, chemically and electrochemically cleaned metal sheets depicted high interlaminate shear strength. SEM micrographs of failed surfaces verify the high adhesive strength of epoxy. Developed numerical simulation model accurately predicts the delamination behavior of CARALL as observed during experimentation.

Fibre metal laminates (FMLs) are being used to manufacture many structural components in aerospace industry because of their very high strength to weight ratios, yet the exact model for estimating fatigue crack propagation in FMLs cannot be developed because of many variable parameters affecting it. In this research, tensile strength, fatigue life and fracture toughness values of 2/1 configuration carbon reinforced aluminium laminate (CARALL), aramid reinforced aluminium laminate and glass laminate aluminium reinforced epoxy specimens have been investigated. Mechanical, chemical and electrochemical surface treatments were applied to AA 1050 face sheets to improve the adhesive properties of the laminates. The specimens were prepared using vacuum assisted resin transfer moulding technique and were cut to desired shapes. Fatigue tests were conducted on centre notched specimens according to ASTM Standard E399. Real time material data and properties of adhesive were used in definition of numerical simulation model to obtain the values of stress intensity factor at different crack lengths. It was observed that CARALL shows very superior tensile and fatigue strength because of stress distribution during failure. Numerical simulation model developed in this research accurately predicts fracture toughness of aramid reinforced aluminium laminate, CARALL and glass laminate aluminium reinforced epoxy with less than 2% error. An empirical analytical model using experimental data obtained during research was developed which accurately predicts the trend of FMLs fatigue life.

Fatigue crack initiation behaviors of casting aluminum alloys are viewed mainly on the basis of experimental results. Fatigue strength and crack initiation of the representative AA320 (UNS#03200) are also summarized with respect to surface temperature effects. Cumulative damage data is used to identify the two different regimes named as initiation and propagation. Load sequence effect is successfully applied to notify initiation phase life. Crack initiation at notch root and fatigue life is calculated under single step mechanical loading (ML) in phase I experiments and multistep ML and combined thermal cycling (CTC) is applied respectively in phase II & III experiments. From a comprehensive experimental details of each phase, the S-N curves are plotted and a comparison is made between crack lips segregation (initiation + stage I propagation) & propagation leading to failure under different ML with & without thermal loading (TL). [Rana Atta-ur-Rahman, M. Ali Nasir, Mudaser Ullah, Riffat Asim Pasha, Nazeer Ahmad Anjum, Shahid Mehmood, M. Muddassar, Ilyas Farooqi, Waqas Asghar, M.Imran. Demarcation of Fatigue Crack Cumulative Damage (Initiation + stage I) of Aluminum Alloy under Combined Loading. Life Sci J 2013; 10(12s):678-683] (ISSN: 1097-8135). http://www.lifesciencesite.com. 109

Fatigue life of aluminum alloys are reviewed mainly on the basis of experimental results. Fatigue strength and failure history of the representative AA5052-H32 are summarized with respect to surface temperature effects during the welding process. In oxy acetylene welding three different zones named as welded zone (WZ), heat affected zone (HAZ) and base metal (BM) are formed having totally varying properties depending on their specific grain structure. Fatigue life and hardness of these different zones are determined in three successive phases of experiments. It is viewed that the grains are shifted from large rough round to elongated oval shaped from WZ to HAZ and relatively small and fine in BM respectively. Depending on grain configuration the fatigue strength increases from WZ to BM due to concentration of grain boundaries, a hindrance in fatigue crack propagation.