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.

Water potential measurement is an essential factor in determining water consumption management and recycling in the agricultural field. We report the development of a continuous water potential measurement system using sensors for water stress analysis in tomato plants with better irrigation plan feedback. The water potential sensor uses the capacitive sensing principle which measures humidity inside an anodic aluminum oxide (AAO) layer. An analog to digital converter with a wireless communication module system records the capacitance data of the sensing system. Calibration data of sensors derived from superabsorbent polymer (SP) and deionized water (DIW) mixtures can represent their water potential value. The method showed good matching of capacitance and water potential values above −7 MPa, matching the result obtained in tomato stem. The measurements were conducted for a few days with the sap flow and water potential sensors connected in series on a tomato stem. When sunlight is sufficient, sap flow increases; meanwhile, water potential decreases. The opposite phenomenon could be observed during the nighttime. With irrigation restricting conditions, both sap flow and water potential signal decrease, triggering the emergency watering signals. This continuous water potential sensing system can quantitatively monitor the plant stem's water stress and set irrigation schedules to achieve high-quality products in the agricultural field.

The antenna of an insect has inspired researchers to develop various types of antenna-mimicking tactile sensors. We suggest a conductive liquid-based biomimetic tactile covered with elastomers, focusing on imitating its anatomical features. The polyethylene glycol (PEG) and silver nitrate composite proved its compatibility with elastomers and its reliability as a conductive material. The working mechanism of the sensor established from the conductive liquid and wires was investigated. A three-dimensional (3D) printer-driven fabrication process facilitated the applicability of the sensor to an integrated biomimetic robot for military purposes. Wall scanning tests using multiple sensors and walls with various geographical features showed a linear relationship between bending angles and resistance with outstanding coefficients of determination up to 0.9889. Especially, wall scanning experiments at a fixed distance led to their geographical reconstruction with high accuracy. Our antenna-shaped tactile sensor was made with alternative elements, a simple fabrication process, and an alternative working mechanism. It also demonstrated high repeatability on the basis of bending angles and showed the possibility to be used for 3D image reconstruction.

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