Flexible sensors have the potential to be seamlessly applied to soft and irregularly shaped surfaces such as the human skin or textile fabrics. This benefits conformability dependant applications including smart tattoos, artificial skins and soft robotics. Consequently, materials and structures for innovative flexible sensors, as well as their integration into systems, continue to be in the spotlight of research. This review outlines the current state of flexible sensor technologies and the impact of material developments on this field. Special attention is given to strain, temperature, chemical, light and electropotential sensors, as well as their respective applications.

Textiles enhanced with thin-film flexible sensors are well-suited for unobtrusive monitoring of skin parameters due to the sensors' high conformability. These sensors can be damaged if they are attached to the surface of the textile, also affecting the textiles' aesthetics and feel. We investigate the effect of embedding flexible temperature sensors within textile yarns, which adds a layer of protection to the sensor. Industrial yarn manufacturing techniques including knit braiding, braiding, and double covering were utilised to identify an appropriate incorporation technique. The thermal time constants recorded by all three sensing yarns was <10 s. Simultaneously, effective sensitivity only decreased by a maximum of 14% compared to the uncovered sensor. This is due to the sensor being positioned within the yarn instead of being in direct contact with the measured surface. These sensor yarns were not affected by bending and produced repeatable measurements. The double covering method was observed to have the least impact on the sensors' performance due to the yarn's smaller dimensions. Finally, a sensing yarn was incorporated in an armband and used to measure changes in skin temperature. The demonstrated textile integration techniques for flexible sensors using industrial yarn manufacturing processes enable large-scale smart textile fabrication.

Thanks to the extraordinary advances flexible electronics have experienced over the last decades, applications such as conformable active-matrix displays, ubiquitously integrated disposable flexible sensor nodes, wearable or textile-integrated systems, as well as imperceptible and transient implants are now reachable. To enable these applications, specialized analog circuits able to transmit and receive data, condition sensors' parameters, drive actuators or control powering devices are required. High-performance sensor conditioning, driving and transceiver circuits on a wide range of flexible substrates are therefore extremely important to develop. However, the currently available materials and processes compatible with mechanically flexible substrates impose massive limitations in terms of large-area uniformity, device dimensions' shrinkability and circuit design, challenging the realization of flexible analog systems. Among state-of-the-art technologies employing low-temperature fabrication processes, thin-film transistors (TFTs) based on metal oxide semiconductors represent the potentially best compromise in terms of prize, performance, technology maturity and capacity to realize complex systems. This is why metal oxide TFTs are nowadays widely used for flexible, light-weight, transparent, stretchable and bio-degradable analog circuits and systems. Here, we review the current trends of flexible metal oxide TFTs for analog applications. First, an introduction is given, where current challenges and requirements related to the realization of flexible analog circuits and systems are analysed. Additionally, TFT performance parameters and configurations are briefly revised. Then, the recent advances in the field of flexible metal oxide TFTs for analog applications are summarized. In particular, all reported approaches to reduce the channel length and improve the AC performance are shown. Next, the current state of flexible metal oxide TFT-based analog circuits is shown, discussing n-type only and complementary circuit configurations. The last topic of the review covers systems based on flexible metal oxide analog circuits. Finally, a conclusion is drawn and an outlook over the field is provided.

Efficient stunning is essential for the welfare of animals destined for slaughter. Several studies have dictated certain signs as reliable for the assessment of stunning efficiency in cattle. However, there is still a lack of data concerning the viability of these signs. The aim of the following study was to assess stunning efficiency at a slaughterhouse, studying the relationship between age, sex and breed of cattle and the efficiency of stunning and determining the feasibility of the following signs in assessing stunning efficiency: immediate collapse, muscle spasms, rhythmic breathing, rotation of the eyeballs, painful response to ear or nose pinch, vocalisation and muscle tone of the ears. Cattle were observed immediately after stunning and hoisting onto the bleed rail. Results showed that stunning efficiency decreased with age, was greater in females than males (for animals greater than 12 months of age) and was superior in ‘dairy’ compared to ‘beef’ cattle at all age ranges. Presence of ear muscle tone, absence of muscular spasms, presence of rhythmic breathing, and vocalisation were the most common signs of inefficient stunning recorded in the present study. Recognition of the most frequently occurring signs associated with inefficient stunning will point out the need for re-stunning, preventing animals from regaining sensibility.

A biocompatible inexpensive strain sensor constituting of an elastomer filled with natural coconut oil (CNO) and carbon black (CB) is presented here. Strain sensors are widely utilized for applications in human activity recognition, health monitoring, and soft robotics. Given that these sensors are envisioned to be present in a plethora of fields, it is important that they are low cost, reliable, biocompatible, and eco‐friendly. This work demonstrates that CNO can be used to create conductive percolation network in elastomers, without the necessity for harmful chemicals or expensive machinery. The sensor has a gauge factor of 0.77 ± 0.01, and the sensing material has a porous morphology filled with an oily suspension formed of CNO and CB. Results indicate that the liquid filled porous structure can improve the reliability of these resistive strain sensors in comparison to sensors fabricated utilizing commonly used non‐polar solvents such as heptane. Consequently, the sensor demonstrates a hysteresis of only 2.41% at 200% strain over 250 stretch/release cycles. Finally, to demonstrate the potential of this fabrication technique, a functionalized glove is developed and used to detect wrist motion. These easily manufacturable and cost‐effective sensors enable wearable on‐skin ergonomic intervention systems with minimal impact on the environment.

Abstract-In this letter, the direct fabrication of amorphous Indium-Gallium-Zinc-Oxide thin-film transistors (TFTs) and circuits on a commercial carbon fiber reinforced polymer (CFRP) substrate is demonstrated. The CFRP is encapsulated with a ≈10.6 µm thick resin layer, although the surface roughness and temperature sensitivity of the substrate are not ideal for the fabrication of electronic devices, we present depletion mode TFTs exhibiting a field effect mobility of 18.3 cm 2 V −1 s −1 , and a common source amplifier, providing a voltage gain of 8 dB and a −3 dB cutoff frequency of 11.5 kHz. The amplifier does not require any input bias voltage and can hence be directly used to condition signals originating from various transducers e.g. piezoelectric strain sensors used to monitor the structural integrity of CFRP elements. This opens the way to the fabrication of smart mechanical CFRP parts with integrated structural integrity monitoring systems.

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An inexpensive biocompatible strain sensor constituting of an elastomer filled with natural coconut oil and carbon black is shown by Pasindu Lugoda and co‐workers in article number 2000780. The easily manufacturable and eco‐friendly fabrication technique enables the creation of strain sensors in environments where standard electronic/chemical fabrication facilities are unavailable, like in schools and developing countries. These devices stretch to 1035% and are utilized for smart textile applications.