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.

Abstract

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Abstract

Biomimetic technologies are an important part of the soft robotics research area because of their ability to replicate naturally occurring structures. Researchers have been developing and improving many such technologies ranging from prosthetics to artificial skin. In this work, we present the fabrication and characterization of an artificial muscle flapping wing using dielectric elastomer actuators (DEAs). The actuator was fabricated using a urethane acrylate polymer elastomer with carbon nanotube (CNT) based electrodes. The 40 mm × 20 mm rectangular actuator was powered through two electrodes at the top. It was subjected to different voltages in the range of 500 - 2500 V and the displacement of the bottom edge was observed. We report the actuator edge displacement to be 20 mm, i.e., 0.5 body lengths (BL) at static 2.5 kV. The dynamic behavior of the device was also analyzed by actuating it with a square wave of various frequencies (0 to 10 Hz). We report the resonant frequency of the actuator to be 4 Hz, with a sub-harmonic at 2 Hz

Abstract

Digital multimedia tools are becoming increasingly important as the world slowly shifts to an online mode. In this work, we present a low-cost, flexible writing pad that uses a 16×16 pressure sensing matrix based on the piezoresistive thin film of velostat. The writing area is 5 cm×5 cm with an effective pixel area of 0.06 mm2. A read out circuit is designed to detect the change in resistance of the velostat pixel using a voltage divider. A microprocessor raster scans through the sensor pixel matrix to obtain a data frame of 256 integers. This data is processed using techniques like squaring and normalising (S&N), Gaussian blurring, and adaptive thresholding to generate a more readable output. The writing pad is able to resolve characters larger than 2 cm in length. The flexible writing pad produces legible output while flexed at bending radius of upto 4 cm. Such flexibility promises to enhance the usability and portability of the writing pad significantly.

Abstract

Plantar pressure or foot pressure analysis is a predominant tool for biomedical assessment of posture, gait, and other activities. The distribution and magnitude of pressure can provide fruitful information to diagnose or predict any risk of foot disorders or impairments. This paper presents the design and fabrication of a low-cost, flexible pressure sensor (FLEPS) mat for assessing plantar pressure variations. We have designed a 32× 32 velostat-based piezoresistive pressure sensor array with dimensions of 330 mm × 330 mm and an active sensing area of 284 mm × 284 mm. Each sensor pixel is of size 5 mm × 5 mm with a pitch of 4 mm. To enhance the resolution and the visual quality of the heat map obtained, we have used different interpolation techniques like the nearest neighbor, bilinear, and bicubic for the received data and transformed the 32× 32 array to a 100× 100-pixel array. It was observed that the bicubic interpolation technique gives a better image quality but takes more computation time than the other two interpolation techniques.

Abstract

Micropumps are one of the most widely used components in lab-on-a-chip devices and other biomedical applications as they can manipulate fluid flow in a very small footprint. In this study, a flexible nozzle-diffuser planar micropump was fabricated using polydimethylsiloxane (PDMS). The pump was fabricated using a two layer structure: bottom layer with molded channels and chamber encapsulated by a planar top layer. The use of PDMS as the structural material for both layers imparts flexibility and transparency to the complete pump assembly. The micropump was characterized by counting the number of compression cycles required for a known volume of fluid, here water, to flow from the inlet to the outlet. A similar characterization was performed while bending the pump at bending radii of 71 cm and 45 cm. The pump produced a flow rate per compression cycle of 5.53 μ1 on flat surface and that of 4μ1,3.6μ1 when placed on surfaces of bending radii of 71cm and 45 cm respectively. The transparency of the pump and biocompatability of PDMS make it an excellent material for biomedical and colorimetric applications.