Optical sensors for monitoring water uptake in plants

Abstract

The monitoring of water uptake in plants is becoming increasingly important. Optical sensors offer considerable advantages over conventional methods and several sensors have been developed including an optical potometer that monitors water uptake from individual roots, the detection of xylem cavitation using audio acoustic emissions with an interferometric force feedback microphone, and an optical fiber displacement transducer that detects changes in leaf thickness in relation to leaf-water potential.

Measurements of leaf water content using terahertz radiation

“…More recently, the employment of optical techniques and, in particular, of optical fibers [7] in measuring leaf thickness using a reflectance-typeamplitude modulated displacement transducer have shown considerable advantages over conventional LVDT's, in that they do not introduce errors by applying pressure to the leaf during the measurement and do not require compensation for the leaf temperature. Furthermore, the optimization of the emitting and receiving angles of the fibers (a technique that has been developed in our laboratory) [8] has shown two orders of magnitude improvement in responsivity and improved resolution over conventional optical techniques. However, errors can still arise in the determination of leaf water content from measurements of leaf thickness alone.…”

Measurement and control of emergent phenomena emulated by resistive-capacitive networks, using fractional-order internal model control and external adaptive control

“…The system in ( 7) displays a damped oscillatory response, which is typical of many feedback-controlled transduction processes encountered in cantilever positioning in atomic force microscopy, 93 optical force feedback microphones, [94][95][96] or the control of complex deexcitation lifetimes encountered in many types of spectroscopies, e.g., nuclear magnetic, 97 electron-spin, 98,99 microwave, [100][101][102] and multiphoton fluorescence, e.g., Förster resonance, 103 and in lock-in applications 104 or in other control and identification schemes. 105 The desired closed-loop dynamics are specified in the form (6) with aD = bD = 0.5, which corresponds to a first-order transfer function with a time constant of 2 s. All the simulations were carried out by using the Matlab ® /Simulink ® software and the FOTF code 106 for fractional-order systems available within the FOMCON toolbox (www.fomcon.net).…”

On the Interpretation of Responses from Hydrogel Based Distributed Microbend Fibre Optic Sensors

“…This type of sensor has been used for monitoring the drying process in cement [5,6], and has applications in smart structures [7,8], because it can also provide a warning signal to changes in the pH in the vicinity of the fibre [9][10][11], which is of particular interest for corrosion monitoring. Furthermore, this type of sensor has potential uses in the development of 'smart fields' for agriculture [12,13], by enabling continuous monitoring of water in soils, complementing other optical [14] or terahertz (THz) sensing modalities [15][16][17] for the field.…”