This paper presents poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate polymer microchannel (diameter ≈175 µm) based stretchable strain sensor developed inside polydimethylsiloxane substrate. The microchannel diameter changes when subjected to various strains, leading to change in the resistance of strain sensor. The sensor exhibits about three order (ΔR/R0 ≈ 1200) increase in the resistance (R) for 10% applied strain (ΔL/L, L = length of the sensor). This leads to a gauge factor (GF Δ (ΔR/R0)/(ΔL/L) of ≈12 000, which is about ≈400 times higher than most of the reported polymer‐based strain sensors. The sensor is evaluated up to a maximum strain of 30%, which is the standard strain limit associated with human body parts such as fingers and wrists. The sensor exhibits a considerably good average degree of hysteresis (<9%). Further, the sensor is also studied for bending and twisting experiments. A response of (ΔR/R0 ≈ 250) and (ΔR/R0 ≈ 300) is recorded for 90° bending and 150° twisting, respectively. The sensor shows an electrical resolution of ≈150% per degree of free bending and ≈12k% per percentage of stretching. Finally, the potential application of presented sensor in robotics and wearable systems is demonstrated by using sensor feedback from human hand to remotely control the robotic hand movements.
This article presents a smart bandage with wireless strain and temperature sensors and a batteryless near-field communication (NFC) tag. Both sensors are based on conductive poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) polymer. The highly sensitive strain sensor consists of a microfluidic channel filled with PEDOT:PSS in Polydimethylsiloxane (PDMS) substrate. The strain sensor shows 3 order (∼1250) increase in the resistance for 10% strain and considerably high gauge factor (GF) of ∼12 500. The sensor was tested for ∼30% strain, which is more than typical stretching of human skin or body parts such as chest expansion during respiration. The strain sensor was also tested for different bending and the electrical resolution was ∼150% per degree of free bending and ∼12k% per percentage of stretching. The resistive temperature sensor, fabricated on a Polyvinyl Chloride (PVC) substrate, showed a ∼60% decrease in resistance when the temperature changed from 25 • C to 85 • C and a sensitivity of ∼1% per • C. As a proof of concept, the sensors and NFC tag were integrated on wound dressing to obtain wearable systems with smart bandage form factor. The sensors can be operated and read from distance of 25 mm with a user-friendly smartphone application developed for powering the system as well as realtime acquisition of sensors data. Finally, we demonstrate the potential use of smart bandage in healthcare applications such as assessment of wound status or respiratory diseases, such as asthma and COVID-19, where monitoring via wearable strain (e.g., respiratory volume) and temperature sensors is critical.
Electronic skin (eSkin) with various types of sensors over large conformable substrates has received considerable interest in robotics. The continuous operation of large number of sensors and the readout electronics make it challenging to meet the energy requirements of eSkin. In this article, we present the first energy generating eSkin with intrinsic tactile sensing without any touch sensor. The eSkin comprises a distributed array of miniaturized solar cells and infrared light emitting diodes (IRLEDs) on soft elastomeric substrate. By innovatively reading the variations in the energy output of the solar cells and IRLEDs, the eSkin could sense multiple parameters (proximity, object location, edge detection, etc.). As a proof of concept, the eSkin has been attached to a 3-D-printed hand. With an energy surplus of 383.6 mW from the palm area alone, the eSkin could generate more than 100 W if present over the whole body (area ∼1.5 m 2 ). Further, with an industrial robot arm, the presented eSkin is shown to enable safe human−robot interaction. The novel paradigm presented in this article for the development of a flexible eSkin extends the application of solar cell from energy generation alone to simultaneously acting as touch sensors.Index Terms-Electronic skin (eSkin), energy harvesting, human−robot interaction (HRI), proximity sensing, solar cell, touch sensing. I. INTRODUCTIONElectronic skin or "eSkin" has recently emerged as a novel platform for advances in robotics, prosthesis, health diagnostics, therapeutics, and monitoring [1]. It allows robots and prosthetic limbs to gather tactile information from large area contacts and to exploit the same to operate in unstructured environment or to improve human−robot interaction (HRI) [2]-[6]. Likewise, eSkin has been explored for measurement of vital health parameters and to provide reliable, effective, and, sometimes, life-saving functions [7]-[9]. With increasing number and type of sensors (pressure, temperature, texture, proximity, etc.) and electronics associated with them on large area eSkin [10]-[13], a stable power supply is critical for practical usage [11], [14]. Thus, a realistic and accessible power source is urgently needed for a next-generation of smart, stand-alone, always-on eSkins. This is a challenge as the continuous power supply through batteries is not practical because they add weight, are not flexible, and may require redesigning of robotics platform [15], [16]. Likewise, for applications requiring intimate integration of eSkin
In this work we present a full-passive flexible multigas sensing tag for the determination of oxygen, carbon dioxide, ammonia, and relative humidity readable by a smartphone. This tag is based on near field communication (NFC) technology for energy harvesting and data transmission to a smartphone. The gas sensors show an optic response that is read through high-resolution digital color detectors. A white LED is used as the common optical excitation source for all the sensors. Only a reduced electronics with very low power consumption is required for the reading of the optical responses and data transmission to a remote user. An application for the Android operating system has been developed for the power supplying and data reception from the tag. The responses of the sensors have been calibrated and fitted to simple functions, allowing a fast prediction of the gases concentration. Cross-sensitivity has also been evaluated, finding that in most of the cases it is negligible or easily correctable using the rest of the readings. The election of the target gases has been due to their importance in the monitoring of modified atmosphere packaging. The resolutions and limits of detection measured are suitable for such kinds of applications.
Herein, a novel tactile sensing device (SensAct) with a soft touch/pressure sensor seamlessly integrated on a flexible actuator is presented. The squishy touch sensor is developed with custom‐made graphite paste on a tiny permanent magnet, encapsulated in Sil‐Poxy, and the actuator (15 μ‐thick coil) is fabricated on polyimide by Lithographie Galvanoformung Abformung (LIGA) micromolding method. The actuator can operate in two modes (expansion and contraction/squeeze) and two states (vibration and nonvibration). The sensor was tested with up to 12 N applied forces and exhibited ≈70% average relative resistance variation (ΔR/Ro), ≈0.346 kPa−1 sensitivity, and ≈49 ms response time with excellent repeatability (≈12.7% coefficient of variation) at 5 N. During simultaneous sensing and actuation, the modulation of coil current, due to ΔR/Ro (≈14% at 2 N force) in the sensor, allows the close loop control (ΔI/Io ≈385%) of expansion/contraction (≈69.8 μm expansion in nonvibration state and ≈111.5 μm peak‐to‐peak in the vibration state). Finally, the soft sensor is embedded in the 3D‐printed fingertip of a robotic hand to demonstrate its use for pressure mapping along with remote vibrotactile stimulation using SensAct device. The self‐controllable actuation of SensAct could provide eSkin the ability to tune stiffness and the vibration states could be utilized for controlled haptic feedback.
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