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. 2016 Dec 20;16(12):2196.
doi: 10.3390/s16122196.

Nondestructive In Situ Measurement Method for Kernel Moisture Content in Corn Ear

Han-Lin Zhang  1   2 , Qin Ma  3   4 , Li-Feng Fan  5   6 , Peng-Fei Zhao  7   8 , Jian-Xu Wang  9   10 , Xiao-Dong Zhang  11   12 , De-Hai Zhu  13   14 , Lan Huang  15   16 , Dong-Jie Zhao  17   18 , Zhong-Yi Wang  19   20   21
Affiliations

Nondestructive In Situ Measurement Method for Kernel Moisture Content in Corn Ear

Han-Lin Zhang et al. Sensors (Basel). .

Abstract

Moisture content is an important factor in corn breeding and cultivation. A corn breed with low moisture at harvest is beneficial for mechanical operations, reduces drying and storage costs after harvesting and, thus, reduces energy consumption. Nondestructive measurement of kernel moisture in an intact corn ear allows us to select corn varieties with seeds that have high dehydration speeds in the mature period. We designed a sensor using a ring electrode pair for nondestructive measurement of the kernel moisture in a corn ear based on a high-frequency detection circuit. Through experiments using the effective scope of the electrodes' electric field, we confirmed that the moisture in the corn cob has little effect on corn kernel moisture measurement. Before the sensor was applied in practice, we investigated temperature and conductivity effects on the output impedance. Results showed that the temperature was linearly related to the output impedance (both real and imaginary parts) of the measurement electrodes and the detection circuit's output voltage. However, the conductivity has a non-monotonic dependence on the output impedance (both real and imaginary parts) of the measurement electrodes and the output voltage of the high-frequency detection circuit. Therefore, we reduced the effect of conductivity on the measurement results through measurement frequency selection. Corn moisture measurement results showed a quadric regression between corn ear moisture and the imaginary part of the output impedance, and there is also a quadric regression between corn kernel moisture and the high-frequency detection circuit output voltage at 100 MHz. In this study, two corn breeds were measured using our sensor and gave R² values for the quadric regression equation of 0.7853 and 0.8496.

Keywords: corn ear; high-frequency detection; impedance; moisture; nondestructive measurement.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Experimental setup for in situ measurement of corn kernels in a corn ear. (a) The device prototype with the sensor; a high-frequency detection circuit is connected to the measurement electrodes of the sensor; (b) a VNA is connected to the measurement electrode, where the electrode’s output impedance values (R and X) are shown on the computer screen; and (c) the appearance of corn ear.
Figure 2
Figure 2
Corn ear moisture measurement sensor structure, including circuit and electrodes.
Figure 3
Figure 3
Simulation results for the measurement electrodes. (a) Horizontal electric field distribution of the electrode; (b) vertical electric field distribution of the electrode; (c) electric field intensity distribution curve in the horizontal diameter direction along the electrodes; (d) electric field intensity distribution curve in the electrode’s vertical direction; (e) electric field distribution histogram in the horizontal diameter direction along the electrode produced by the 5 mm piecewise integral accumulator; and (f) electric field distribution histogram in the vertical diameter direction along the electrode produced by the 5 mm piecewise integral accumulator.
Figure 4
Figure 4
Operation to measure the effective scope of the electrode’s electric field. (a) Level influence depth experiment device; (b) vertical impact experiment device; (c) level influence depth experiments, based on water injection outside introversion; and (d) level influence depth experiments, based on outside-in water injection.
Figure 5
Figure 5
Rapid nondestructive process for measurement of the moisture content of the kernels of a corn ear.
Figure 6
Figure 6
Results of horizontal effective depth measurement of the electrode’s electric field. (a,b) show the imaginary part of the electrode’s output impedance versus injected DD water in the PP tubes from the first ring to the fifth ring; (c,d) show the imaginary part of the electrode’s output impedance versus DD water injection into the PP tubes from the fifth ring to the first ring.
Figure 6
Figure 6
Results of horizontal effective depth measurement of the electrode’s electric field. (a,b) show the imaginary part of the electrode’s output impedance versus injected DD water in the PP tubes from the first ring to the fifth ring; (c,d) show the imaginary part of the electrode’s output impedance versus DD water injection into the PP tubes from the fifth ring to the first ring.
Figure 7
Figure 7
Results of measurement of the vertical effective depth of the electrode’s electric field.
Figure 8
Figure 8
Results of experiments on temperature variation effects. (a) The relationship between temperature and differential output voltage from the detection circuit at a frequency of 100 MHz; (b) The relationship between temperature and output impedance from the VNA at a frequency of 100 MHz; (c) coefficients of determination R2 in the frequency range from 300 kHz to 300 MHz; and (d) standard deviations in the frequency range from 300 kHz to300 MHz.
Figure 9
Figure 9
Results of experiments on conductivity variation effects. (a) The relationship between conductivity and the differential output voltage from detection circuit at frequency of 100 MHz; (b) the relationship between conductivity and output impedance from the VNA at a frequency of 100 MHz; and (c) standard deviations at various frequencies ranging from 300 kHz to 300 MHz.
Figure 10
Figure 10
Output voltage of the sensor’s detector circuit versus absolute moisture of the corn under test.
Figure 11
Figure 11
R2 of the quadratic polynomial fitting over the sweep frequency range. (a) Corn: JINDAO111; and (b) corn: JH1303.
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