The outstanding properties of graphene have initiated myriads of research and development; yet, its economic impact is hampered by the difficulties encountered in production and practical application. Recently discovered laser-induced graphene is generated by a simple printing process on flexible and lightweight polyimide films. Exploiting the electrical features and mechanical pliability of LIG on polyimide, we developed wearable resistive bending sensors that pave the way for many cost-effective measurement systems. The versatile sensors we describe can be utilized in a wide range of configurations, including measurement of force, deflection, and curvature. The deflection induced by different forces and speeds is effectively sensed through a resistance measurement, exploiting the piezoresistance of the printed graphene electrodes. The LIG sensors possess an outstanding range for strain measurements reaching >10% A double-sided electrode concept was developed by printing the same electrodes on both sides of the film and employing difference measurements. This provided a large bidirectional bending response combined with temperature compensation. Versatility in geometry and a simple fabrication process enable the detection of a wide range of flow speeds, forces, and deflections. The sensor response can be easily tuned by geometrical parameters of the bending sensors and the LIG electrodes. As a wearable device, LIG bending sensors were used for tracking body movements. For underwater operation, PDMS-coated LIG bending sensors were integrated with ultra-low power aquatic tags and utilized in underwater animal speed monitoring applications, and a recording of the surface current velocity on a coral reef in the Red Sea.npj Flexible Electronics (2019) 3:15 ; https://doi.
Physical sensors form the fundamental building blocks of a multitude of advanced applications that detect and monitor the surroundings and communicate the acquired physical data. The everlasting need for more compliant, low-cost, and energy-efficient sensor solutions has led to considerable interest in enhancing their features and operation limits even further. While graphene has emerged as a promising candidate material, due to its outstanding electrical and mechanical properties, it is still not available in large volumes for practical applications. Meanwhile, Laser-Induced Graphene has opened new perspectives for a versatile, durable, printed physical sensing platform capable of detecting various physical parameters across a range of conditions and subjects. In this review, LIG physical sensors were categorized into four broad types based on their transduction mechanism: mechanical, thermal, magnetic, and electromagnetic. We summaries various design strategies established for preparing reliable physical sensors without the involvement of chemical treatments, synthesis, and multi-step fabrication processes. The review considers the effects of laser choice, lasing environment, and parameters on graphene properties. We also discuss a broad spectrum of applications of LIG physical sensors in fields ranging from healthcare, tactile sensing, environmental monitoring, energy harvesting, and soft robotics to desalination and THz modulation.
Flexible and wearable magnetoelectronics add intriguing new functionalities to our natural perception. Of particular interest regarding these artificial skins are wireless sensing and touchless interactions. Biocompatibility and imperceptibility are the most significant features of wearable devices attached to our bodies. In this work, a biocompatible magnetic skin is introduced. It offers extreme flexibility, stretchability (>300%), and lightweight while maintaining a remanent magnetization up to 360 mT. The magnetic skin is comfortable to wear, can be realized in any desired shape or color, and adds tunable permanent magnetic properties to the surface it is applied to. It provides remote control functions and combined with magnetic sensors; it implements a complete wearable magnetic system. For example, eye tracking is realized by attaching the magnetic skin to the eyelid. The advantage that it does not require any wiring makes it an extremely viable solution for soft robotics and human-machine interactions. Wearing the magnetic skin on a finger or integrated
While the outstanding properties of graphene have attracted a lot of attention, one of the major bottlenecks of its widespread usage is its availability in large volumes. Laser printing graphene on polyimide films is an efficient single‐step fabrication process that can remedy this issue. A laser‐printed, flexible pressure sensor is developed utilizing the piezoresistive effect of 3D porous graphene. The pressure sensors performance can be easily adjusted via the geometrical parameters. They have a sensitivity in the range of 1.23 × 10−3 kPa and feature a high resolution with a detection limit of 10 Pa in combination with an extremely wide dynamic range of at least 20 MPa. They also provide excellent long‐term stability of at least 15 000 cycles. The biocompatibility of laser‐induced graphene is also evaluated by cytotoxicity assays and fluorescent staining, which show an insignificant drop in viability. Polymethyl methacrylate coating is particularly useful for underwater applications, protecting the sensors from biofouling and shunt currents, and enable operation at a depth of 2 km in highly saline Red Sea water. Due to its features, the sensors are a prime choice for multiple healthcare applications; for example, they are used for heart rate monitoring, plantar pressure measurements, and tactile sensing.
Tunable, Flexible composite magnets for marine monitoring applications**
Salinity is one of the most relevant parameters in oceanography used to study properties of the oceans as well as the effects of climate change. Salinity measurements are challenging, due to the harsh environment that leads to corrosion and biofouling. In the context of animal monitors, salinity sensors should also be minimally intrusive and have a long lifetime. Here, a conductivity cell for salinity sensing is presented based on a single-step laser irradiation process on flexible polyimide substrate. The sensors are characterized by lightweight, flexibility, low power consumption and low fabrication costs. A two-electrode cell is used to measure the impedance, and thereby the conductivity, of the water in the MHz frequency range. It offers an accuracy of ±0.5 psu, which is not affected by sensor deformation.Deployment of the sensors in the Red Sea revealed that the materials are corrosion resistant and can withstand the harsh environment. While biofouling is strongly affecting commonly employed low frequency conductivity measurements, in the MHz frequency range, it acts like a short-circuited capacitance. Hence, biofouling independent salinity sensing can be achieved using a two-electrode impedance measurement at a frequency of 1 MHz.Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff)) Published online: ((will be filled in by the editorial staff))
Graphene has shown considerable potential for sensing magnetic fields based on the Hall Effect, due to its high carrier mobility, low sheet carrier density, and low-temperature dependence. However, the cost of graphene in comparison to conventional materials has meant that its uptake in electronic manufacturing has been slow. To lower technological barriers and bring more widespread adoption of graphene Hall sensors, we are using a one-step laser scribing process that does not rely on multiple steps, toxic chemicals, and subsequent treatments. Laser-scribed graphene Hall sensors offer a linear response to magnetic fields with a normalized sensitivity of ~1.12 V/AT. They also exhibit a low constant noise voltage floor of ~ 50 nV/$$\sqrt {{\mathrm{Hz}}}$$ Hz for a bias current of 100 µA at room temperature, which is comparable with state-of-the-art low-noise Hall sensors. The sensors combine a high bendability, come with high robustness and operating temperatures up to 400 °C. They enable device ideas in various areas, for instance, soft robotics. As an example, we combined a laser-scribed graphene sensor with a deformable elastomer and flexible magnet to realize low-cost, compliant, and customizable tactile sensors.
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