The frequency of excitation signal is an important factor that affects performance of high-frequency capacitive soil moisture sensor.A series of tested dielectric solution whose equivalent soil volumetric water content is 0.9 %

51.8 %

is prepared by deionized water mixing with 2—isoproxyethanol or dioxane

instead of soil sample to test performance of soil water content sensor.Performance test and analysis are carried out from two aspects which are the relationship with soil water content and temperature variability with seven sensors whose excitation frequency is 40

50

60

70

80

90

100 MHz.The results show that the output voltage of sev

en kinds of frequency of sensor has linear negative correlation with volumetric soil moisture

and the coefficient of correlation R2is greater than 0.94

and the temperature variability of output voltage of the sensors is not affected by excitation signal frequency

the temperature difference is the main factor that affects temperature variability

and the maximum variation is less than 4 %.The test results can provide guidance for choosing the frequency of excitation signal when designing a high-frequency capacitive soil water content sensor.