A Novel Handheld Device for Intact Corn Ear Moisture Content Measurement

Kernel moisture content is an important factor in mechanized corn harvesting. However, the rapid and nondestructive in situ detection of the kernel moisture content within an intact corn ear in the field remains challenging. In this work, we designed a novel handheld device with a double-ring sensing probe for nondestructive and convenient kernel moisture detection in intact corn ears based on an active reflection bridge operating in the radio frequency range. By proposing an equivalent first-order resistor–capacitor impedance model for a load composed of a corn ear and the double-ring sensing probe, we found that the reflection coefficient’s phase angle $\theta $ was monotonic with the moisture content and also found that the measurement signal frequency affected the corn grain moisture measurement sensitivity. Before using the handheld device in the field, we investigated its optimal signal frequency range and the effects of temperature variations on the measurement results. In the frequency range of 140–165 MHz, the measured voltages from the device showed a good linear relationship and high sensitivity with respect to both the dielectric constants and the corn ear temperature (9 °C–22 °C). Using this device at a signal frequency of 160 MHz, we conducted corn ear moisture measurements in a total of 73 samples and then established a linear model. The results showed that, for corn ear moisture contents in the range of 15.7%–31.5%, the R values of the training set and the prediction set were 0.7027 and 0.8317, respectively, with a prediction error of 3.54% at the 95% confidence interval.