Abstract

Analysis of foot pressure, also known as plantar pressure analysis, plays a pivotal role in biomedical assessments related to posture and gait analysis. Extensive research has been conducted on leveraging this technique for clinical purposes, leading to the development of flexible pressure sensors. In this letter, we present the use of in-shoe flexible pressure sensor array for determining the nature of the walking surface. The sensor system is fabricated using eight low-cost and robust, in-shoe pressure sensors that leverage the piezoresistivity of velostat. The sensor array was characterized for four different surface types. Random Forest (RF) algorithm was used to classify the surfaces with 86% accuracy. Based on this analysis, we propose a novel method for analyzing various surfaces based on their attributes such as firmness, rigidity, and penetrability. Such a device can be used for ascertaining surface characteristics after construction, or playing surfaces in a stadium.

Abstract

Electrically conductive fibers are attracting attention because of the newly emerging areas of interactive textiles and smart fabrics. In this paper, we present the fabrication and characterization of a flexible conductive cotton fabric (CCF) of size 20 cm×20 cm coated with polypyrrole synthesized using in-situ chemical oxidative polymerization. This is the largest area reported in the literature for a polypyrrole-coated conducting fabric. The characteristics of the conducting fabric were investigated at 25 points by sandwiching it between the electrodes in the form of a 5×5 array. To test its reliability, the CCF was washed with distilled water 10 times, and its response was measured after every wash. We observed that there was a change in the resistance after the first four washes, however, the response stabilized thereafter. The average deviation in resistance until first four washes was found to be 27.45%, whereas for washes 6 to 10, it was 5.11%.

Abstract

Street lights are ubiquitous public infrastructure in urban areas that can be leveraged for smart city applications. In this paper, we present an electric vehicle charging station (EVCS) that communicates using Wi-SUN network integrated on a network of streetlights, and using oneM2M middleware. The proposed architecture follows the level 2 charging standards and the open charge point protocol (OCPP), ensuring compatibility and interoperability across diverse charging infrastructures. By seamlessly incorporating Wi-SUN network and oneM2M middleware, our architecture enables efficient communication and interaction with a wide array of devices and services. The utilization of the oneM2M platform further enhances the integration by establishing a seamless connection between the EVCS and the broader smart city infrastructure. We have fabricated a proof-of-concept system that consists of the EVCS connected to a Wi-SUN network integrated with the streetlight network in the institute campus. The performance of our solution was evaluated by measuring the latency associated with authentication and billing for EV users. We report the average latency observed over several iterations of charging to be 0.7±0.2 s (excluding the time required for charging). We also measured the Wi-SUN communication range in the campus environment with trees and buildings and found the maximum range to be around 370 m.

Abstract

There is an emerging consensus that the future of intelligent and energy efficient homes is automation and cloud control. This paper presents a novel infrastructural concept using smart ceiling tiles and an energy-harvesting Bluetooth Low Energy (BLE) switch to control home appliances. The switch location is determined using trilateration of the signals received by the tiles installed in different rooms. In this paper, we localized the switch among three rooms separated by a brick wall by analyzing the received signal strength indicator (RSSI) values captured by three tiles located in three rooms. The tiles are powered with DC power using the support rails, thus minimizing wiring for power delivery. We used different machine learning classification algorithms with the received RSSI values as features for predicting the location of the switch accurately. Through experimentation, we achieved high accuracy of 93% in classifying the switch position among the rooms. The integration of smart tiles in the false ceiling along with the use of an energy-harvesting BLE switch offers numerous advantages, such as reducing wiring complexity, enhancing user convenience, and aesthetic design.

Abstract

The scalability of remote Internet of Things (IoT) deployments into verticals of smart cities relies primarily on the communication protocols and data platforms employed. Accordingly, the adoption of LoRaWAN, Sigfox, NB-IoT, etc. has risen in recent years. These protocols have been created to cater to the low power and long range requirements of IoT. In this paper, we evaluate one such protocol, Wi-SUN (Wireless Smart Ubiquitous Network), that additionally offers excellent redundancy owing to its use of a mesh topology. Wi-SUN is based on the IEEE 802.15.4g standard and uses license-free sub-GHz bands. However, IoT networks using any communication protocol require a knowledge of signal propagation and attenuation in real-world scenarios. Thus, we evaluated the path loss of WiSUN transmissions by analysing the RSSI values inside a typical city building and an urban outdoor habitat

Abstract

Crosstalk, in a sensor matrix, is the unwanted signal obtained at a sensor pixel that is not directly related to the stimulus. This paper presents a novel approach towards quantifying the crosstalk characteristics of a sensor matrix. The method involves obtaining the normalized sum of all the neighbouring pixel readings, weighted by their distance from the stimulated pixel. We have used this methodology to characterise the crosstalk for a 5×5 velostat-based flexible pressure sensing matrix that uses a crossbar electrode architecture. The measure thus obtained is a dimensionless value between 0 to 1, 0 indicating no crosstalk and 1 indicating the maximum possible crosstalk. We characterized sensor matrices with three different pitch lengths: 3mm, 4mm, and 5mm. We observe the crosstalk values to lie between 0.032 to 0.17 across different weights and pitches, which indicates a low measure of crosstalk. The 5 mm pitch matrix displayed the least crosstalk, which was expected due to the larger spacing between the pixels. We also characterised the crosstalk for all 25 pixels of a 4 mm pitch matrix and found the mean to be 0.081±0.002 , within the range from 0.0071 to 0.1656.

Abstract

Polymer-based piezoresistive pressure sensors that possess flexibility and stretchability have received increased recognition in wearable sensing systems. In this paper, we present a flexible pressure sensor designed using polypyrrole-coated cotton (PCC) that was synthesized using in-situ chemical oxidative liquid polymerization. The sensor shows high sensitivity at low-pressure ranges and can measure pressures in the range 160 Pa to 16 kPa. The response time of the sensor was found to be 463 ms. It also exhibits excellent repeatability during continuous loading-unloading for over 1000 cycles. The performance of the sensor was evaluated in terms of resistance change as a function of tensile strain, by applying repeated compression and expansion strains. We report the gauge factor of the resistive sensor to be 0.32 for applied compressive strains from 0% to 99.6%. Such a large compressive strain range can be achieved with cotton because of its fibrous nature. It was observed that there is no change in conductivity, at a given strain, on repeated expansion and compression of the polymer for 20 cycles.

Abstract

Regular plantar pressure monitoring is required for diabetic, wheelchair-bound and bed-ridden individuals. It has been shown that peak plantar pressure for diabetics increases significantly and progressively, and requires regular monitoring for early detection and intervention. Sensor matrices of capacitative, resistive, and piezoelectric transducers are most commonly used for measuring areal pressure. Calibration for such medical devices is crucial for reliability and repeatable results. In this work, we elaborate on the calibration challenges of a 32×32 velostat-based sensor matrix, and demonstrate calibration strategies suitable for a manufactured product. We show that 2N parameters can be used to calibrate an N×N sensor matrix instead of 2N2 . We observe the accuracy of calibration of a 32×32 sensor matrix by comparing the total detected weight of 35 participants at a static load with their reported weight, with 4.2% mean error and 3.1% median error. For participants in the 50–85 kg weight range, the difference was always within ±5%. Further, upon drawing contour plots and using the pressure distribution information, we were able to distinguish participants with possible foot ulcers and flat feet.

Abstract

Bio-inspired structures provide several new possibilities in the area of robotics due to their superiority and diversity in execution. Researchers have been developing various robotic applications with the combination of soft materials such as silicone and various 3D printed materials. These kinds of soft robots can be useful for various human-robotic interactions such as search and rescue, medical surgery and so on. In this work, we present the fabrication and characterization of a small caterpillar-like soft robot (7 cm ×3.5 cm ×3 cm) powered using PneuNet actuation. Due to the limitations of traditional robotics, we believe that such soft material-based robots can be effective in various applications. The fabricated silicone-based PneuNet soft robot, which moves like a caterpillar, has also been embedded with an ESP camera module and LED light to enable applications such as surveillance and search-and-rescue. This soft robotic actuator can also perform tasks on various types of terrains, including ice and water surface. We find that the normalized distance travelled per actuation cycle on gravel to be 0.23 BL.

Abstract

Pressure sensors are subjected to continuous force and stress that may affect the operation of the sensor in the long run. Reliability is a crucial factor that must be considered when designing and fabricating any sensor. It is essential to test the material used in the sensor to assess the reliability of the complete product. In this work, we report the long-term reliability of a flexible pressure sensor mat using a carbon-impregnated polymer, velostat, which is a flexible, light, and thin polymer composite material with piezoresistive properties. We focus on the analysis of the performance of a flexible pressure sensor array under long-term and repeated loading. Tests were performed every fortnight for 210 days. We have observed that the material characteristics of the velostat material change on repeated application of pressure up to a certain time frame. For a given loading, once the material settles, the change in resistance of the material becomes consistent for a given application of pressure. We have also analyzed the changes in the parameters associated with the 2-parameter model, and have analyzed the effect of crosstalk on the sensor matrix for different pitch lengths to select the best pitch that will give us the minimum crosstalk. We have observed that the error rate of the sensor pixels decreased by 53 percentage points in 210 days. The results obtained from the experimental tests for reliability reveal a practical possibility of implementing velostat-based pressure sensors in wearable and healthcare devices and provide steps to take while calibrating an as-fabricated velostat-based sensor.