Electrical Capacitance Characteristics of Wood Chips at Low Frequency Ranges: A Cheap Tool for Quality Assessment

Abstract

Moisture content is one of the most important parameters related to the quality of wood chips that affects both the calorific and economic value of fuel chips. For industrial applications, moisture content needs to be detected quickly. For this purpose, various indirect moisture content measurement methods (e.g., capacitance, NIR, microwave, ECT, X-ray CT, and nuclear MR) have been investigated with different results in the past. Nevertheless, determining wood chip moisture content in real time is still a challenge. The main aim of this article was therefore to analyze the dielectric properties of wood chips at low frequencies (10 kHz–5 MHz) and to examine the possibility of using these properties to predict wood chip moisture content and porosity. A container-type probe was developed for this purpose. The electrical capacitance and dissipation factor of wood chips with different moisture content was measured by an LCR meter at 10 kHz, 50 kHz, 100 kHz, 500 kHz, 1 MHz, and 5 MHz frequencies. Wood chip porosity was also measured using a gas displacement method. Linear models for moisture content and porosity prediction were determined by backward stepwise linear regression. Mathematical model was developed to better understand the physical relationships between moisture content, porosity, and electrical capacitance. These models were able to predict the moisture content of observed quantities of wood chips with the required accuracy (R2 = 0.9−0.99). This finding opens another path to measuring the moisture content and porosity of wood chips in a relatively cheap and fast way and with adequate precision. In addition, principal component analysis showed that it is also possible to distinguish between individual wood chip fraction sizes from the information obtained.

A comprehensive review on wood chip moisture content assessment and prediction

“…2. Operates destructively, i.e., the properties of the samples are irreversibly altered, making them not reusable [9]. 3.…”

“…However, the existing widely used method of determining the MC (oven drying) is timeconsuming [8], causing vehicles to wait in line. Moreover, oven drying is prone to sampling errors and cannot be used in real-time [9]. Additional MC checks are performed while the wood chips are on the conveyor waiting to enter into the subsequent manufacturing operations.…”

Effect of pore characteristics on the dielectric constant of wood: considering the Moisture content and Frequency change

“…In 2021, Jakub proved the feasibility of dielectric properties to predict the MC and porosity of wood chips. He modeled the prediction of MC and porosity of wood chips in the frequency range of 10 KHz − 5 MHz, with R 2 in the range of 0.9-0.99 (Lev J et al 2021). However, the study did not specify whether the pores measured were those of the wood itself or those between the chips.…”

Electrical Properties at Multi-Frequencies for Analysis of Physical and Anatomical Properties of Fast-Growing Standing Teak Trees at Various Ages

“…Quality prediction using the electrical potential approach in wood has been carried out in several studies on small wood samples, showing that the use of electrical capacitance sensors to determine the dielectric properties of wood samples, especially capacitance, in the low-frequency range has a high correlation with hardness and specific gravity [16,17]. The same method has been shown to have a high correlation for predicting the moisture content (MC) of wood chips [18,19]. Understanding the electrical properties of wood and the electrical potential of trees is still an evolving area of research that requires further investigation.…”

“…However, the prediction model for trees can be challenging because of fresh conditions with a moisture content above 100%. Some studies have shown that fresh wood affects the signal, causing inaccuracies in quality prediction [19][20][21].…”