Design and Validation of a Portable AD5933–Based Impedance Analyzer for Smart Agriculture

Abstract

This paper presents a portable impedance analyzer based on the AD5933 integrated circuit, specifically designed for fruit quality monitoring throughout its entire supply chain. The custom designed system allows to flexibly tune the parameters (i.e. excitation voltage, feedback resistor, settling time) for each AD5933 frequency range from 10 Hz to 100 kHz, leading to a precise system calibration and consequently, measurement. FruitMeter runs MicroPython on an STM32 microcontroller, allowing ease of development, advanced low-power mode, and both on-demand and scheduled measurements. The system employs Low-Energy Bluetooth and USB communication with a micro SD data storage which, together with its small size (7.5 × 2 × 4 cm in volume) and the 300 mAh rechargeable battery with USB recharge, increases the system portability and connectivity, critical for smart agriculture on-field applications. The developed portable system is validated by comparing its performance with a benchtop impedance analyzer with both passive components and fruit samples (apple, avocado, banana, mango and tomato). The comparison resulted in an average Root Mean Square Error (RMSE) of 1.0 % and 4.3 % for the passive components and of 1.36 % and 6.8 % for the fruit samples, for impedance magnitude and phase, respectively. We finally validated the system for a real use-case regarding the evaluation of banana aging evolution.

PanelTM: Two- And Three-Way Dynamic Panel Threshold Regression Model for Change Point Detection

“…Bioimpedance is typically measured by using a bioimpedance analyzer, an instrument specifically designed for this purpose. In the experiment on fruit ripening, two bioimpedance analyzers have been used: a bench-top EIS device called "impedance analyzer" (IA) that is a marketed equipment, and an innovative portable custom-made device called "FruitMeter" (FM) (Ibba et al, 2021). Bench-top EIS devices are typically unwieldy and more powerful than a portable EIS device and, therefore, are generally more expensive and require more maintenance and expertise to operate.…”

Laser‐Induced, Green and Biocompatible Paper‐Based Devices for Circular Electronics

“…Although the mechanical conditions during the experiment (bending radius for apple ≈4 cm, and for banana ≈2 cm), our paper electrodes show good correlation with the impedance response previously reported for apples and bananas. [74][75][76][77] For both fruits, the magnitude difference at low frequencies between the commercial and paper types electrodes is mainly due to the following reasons: 1) at the fruit-electrode interface, while the highly porous nature of the banana skin (skin roughness ranging from 2.5 µm in unripe cases, to 6.6 µm for ripe ones [78] ) provides a good electrode adhesion, the smoother apple skin (roughness ≈1.43 µm [79] ) has an opposite effect, rendering the adhesion, and thus the electrical contact, less stable; 2) on the other electrode end, the non-uniformity of the laser-induced carbon is responsible for a non-ideal interface with crocodile clips and wires; 3) wetting effect, due to the use of conductive gel, making the system calibration unreliable over time.…”

Toward noninvasive monitoring of plant leaf water content by electrical impedance spectroscopy

“…For benchtop studies, the necessary frequency range will usually go from approximately 10 Hz to 1 MHz, although some studies report promising results with lower frequency ranges. This is the case for our own-built portable impedance analyzers based on commercially available integrated circuits such as the AD5933 (Analog Devices, Inc.) used to detect fruit ripening (Ibba et al, 2021). That same device was used in another study (Jamaludin et al, 2015), but the results were inconclusive, as the impedance spectrum exhibited low frequency values exceeding the AD5933 specifications and showed significant interferences, preventing the fit to an equivalent circuit.…”