Liquid Polymer/Metallic Salt-Based Stretchable Strain Sensor to Evaluate Fruit Growth

Abstract

Conventional methods for measuring the various dimensions of a fruit vary from vernier calipers to machine vision systems. This accounts for system bulkiness, high installation charges, and miscellaneous difficulties in continuous and precise monitoring. Considering the limitations, this paper reveals an inventive liquid-state stretchable strain sensor by incorporating poly(ethylene glycol) (PEG) and silver nitrate into an indigenous transparent polymer band. The combination of poly-(dimethylsiloxane) (PDMS) and Ecoflex having an optimal mixing ratio (20:80) realized the equilibrium between a large strain, low stress, and less stickiness. The inclusion of a liquid polymer promoted high viscosity and chemical stability, while the addition of a metallic salt enhanced the electrical conductivity of the sensor. The correlation between strain and resistance showed high sensitivity and good repeatability of the PEG−silver nitrate composite. Linear resistance changes were noted with high coefficients of determination (R 2 > 0.99) at least up to the strain of 30%. The performance test as a dendrometer on fruits of two different species demonstrated excellent stability of the sensor with increasing ratios from 1.7 to 3.9 kΩ/mm. This tunable elastic band sensor opened up a route toward long-term evaluation-targeted versatile applications such as fruit growth monitoring.

Antenna-Shaped Biomimetic Tactile Sensor Using Elastomers and Conductive Liquid

“…In addition to confirming the chemical bonds using FTIR, we also conducted size measurements to observe the distribution of silver particles in the mixture of PEG and silver nitrate (Figure ). In this mixture shown in Figure d-ii, silver nitrate is reduced into silver particles whose size mainly depends on heating temperature . The result obtained from the particle size analyzer (Figure d-i) shows that most of the silver particles in the nonheated liquid composite sample were located in the range of 0 to 1 μm, while those in the liquid composite sample heated at 70 °C for 2 and 4 h were in the range of 1 to 7 μm.…”

“…In this mixture shown in Figure 5d-ii, silver nitrate is reduced into silver particles whose size mainly depends on heating temperature. 15 The result obtained from the particle size analyzer (Figure 5d-i) shows that most of the silver particles in the nonheated liquid composite sample were located in the range of 0 to 1 μm, while those in the liquid composite sample heated at 70 °C for 2 and 4 h were in the range of 1 to 7 μm. The size measurement of silver particles elucidated the chemical transition of the mixture of PEG and silver nitrate before and after being transformed into the liquid composite.…”

“…It was reported that, when PEG and silver nitrate are mixed, the functional group of PEG is transformed into the aldehyde group. 15 Fourier transform infrared spectroscopy (FTIR) is often used to identify specific functional groups through molecular vibrations with thermal energy. For example, the interaction between silver nanoparticles and PEG was confirmed using this technique.…”

“…Compared to the solid materials, the use of flexible material to represent the lymph space of the insect sensilla facilitates larger deformations . The conductive liquid used in the sensor is a composite of polyethylene glycol (PEG) and silver nitrate, which was reported to be stable for months. , A piezoresistive strain sensor was also developed with this composite to measure fruit growth . The structure of the sensor was designed using three-dimensional (3D) printing techniques and then completed with a mixture of two distinct elastomers to form an elastic structure and a less sticky surface for the sensor.…”

“…13,14 A piezoresistive strain sensor was also developed with this composite to measure fruit growth. 15 The structure of the sensor was designed using three-dimensional (3D) printing techniques and then completed with a mixture of two distinct elastomers to form an elastic structure and a less sticky surface for the sensor. A miniaturized and flexible structure is adapted to a biomimetic robot with an artificial tactile sensing system, which can be applied in military operations in the case of a malfunction of optical sensors.…”