## 2 Impedance Spectroscopy
### Scopes of Application
#### 2.1.2 Is Applied in Forest and Agriculture Management
Leaves are an essential part of plants--once through them, carbohydrates are assimilated by photosynthesis and they help to regulate water flow during evapotranspiration. [PERSON] et al. [61] proposed to evaluate plant water status; they utilized EleIS to model the relative water content of canola, corn, wheat, and soybean leaves (impedance spectroscopy measurements were made employing a four-points setup for operating frequencies in the range 5-100 kHz, and a 2 Vp-p AC voltage amplitude). Recently, [PERSON] and his team [62] pursued their research into ageing using EleIS (a 2 Vp-p AC voltage amplitude was applied while varying the frequency in a range from 5 to 15 kHz for a four-points measuring setup) and evaluated the nitrogen content of the leaves of those same crops (canola, corn, wheat, and soybean); they observed a strong connection between the leaves' impedance and their water availability. [PERSON] and co-workers [63] demonstrated that the incidence of solar light on plant leaves is reflected in their impedance spectra; they conducted their EleIS experiments under dark conditions at 23 \({}^{\circ}\)C while applying a 20 mV AC signal possessing frequencies ranging from 10 Hz to 10 MHz, using a four-points measuring setup. Still in the domain of plants, the evaluation of fruits, particularly those that contain seeds required for reproduction, is of great commercial interest. EleIS measurements allowing for the evaluation of fruit maturity and firmness were performed by [PERSON] and colleagues [64] (impedances were measured using a four-points configuration, applying an AC voltage with 500 mV of amplitude and possessing a frequency of 10 kHz). The experimental results showed a significant correlation between impedance and firmness (the more mature the fruit was, the lower the impedance was). The results allowed them to conclude that the measured impedances could be used to predict fruit firmness when combined with machine learning models. EleIS has also been applied to evaluate the effects of some agricultural products' processing procedures, such as drying and freeze-thawing. [PERSON] et al. [65] performed such evaluation on eggplant pulp; the impedance, resistance, and reactance of the samples were obtained over the frequency range of 42 Hz-5 MHz under an AC voltage with an amplitude of 1 V, utilizing a four-points measuring setup. [PERSON] et al. [66] extracted a feature from the Nyquist plots (length of the impedance vector, Ztop, where the circular arc in the Nyquist plot reaches its zenith) and proposed it to assess damage in biological tissue during the processing of agricultural products. They conducted the study in Japanese pears after drop tests, and the results showed that the resistance of the protoplasm of the injured tissues increased slightly; in contrast, the capacitance of cell membranes and the resistance of apoplast fluids (apoplast is the continuous space external to the plasma membranes existent throughout the plants that facilitate the transport of water and solutes) significantly decreased (the Nyquist's were obtained at a 25 \({}^{\circ}\)C temperature, for frequencies in the interval 42 Hz to 1 MHz, possessing an AC voltage amplitude of 1.0 V, using a four-points measurement setup). 2.1.3. IS in Materials Science and Applied Technologies  
Impedance Spectroscopy is an essential analysis tool in several areas of Materials Science, being capable of providing important information about the electrical properties of materials, which are directly related to the rates at which chemical reactions occur, their dielectric characteristics, corrosion potential, microstructure, and types of conduction mechanism [67; 68; 69; 70]. The electrical response determined by IS has been widely used as a signature of phenomena experienced by materials based on their interaction with the environment and/or other materials.