SOIL MOISTURE SENSOR BASED ON ELECTROSTATIC SENSING
A soil sensor includes a signal generator, and a transmitter coupled to the signal generator, the transmitter configured to transmit a signal from the signal generator, the signal having a fixed frequency, the transmitter including a transmit electrode embedded within a first dielectric material. The soil sensor includes a receiver, the receiver being configured to electrostatically couple to the transmitter through a channel including soil, the receiver including a charge variation (QVAR) electrode embedded within a second dielectric material. The soil sensor includes a charge variation (QVAR) sensor coupled to the QVAR electrode, the QVAR sensor configured to detect a variation in charge detected at the QVAR electrode in response to the signal from the signal generator and output a digital signal including the charge detected. And the soil sensor further includes a processing circuit coupled to the QVAR sensor and configured to determine a level of moisture in the channel based on the digital signal.
1 . A soil sensor comprising:
a signal generator;
a transmitter coupled to the signal generator, the transmitter configured to transmit a signal from the signal generator, the signal having a fixed frequency, the transmitter comprising a transmit electrode embedded within a first dielectric material;
a receiver, the receiver being configured to electrostatically couple to the transmitter through a channel comprising soil, the receiver comprising a charge variation (QVAR) electrode embedded within a second dielectric material;
a charge variation (QVAR) sensor coupled to the QVAR electrode, the QVAR sensor configured to detect a variation in charge detected at the QVAR electrode in response to the signal from the signal generator and output a digital signal comprising the charge detected; and
a processing circuit coupled to the QVAR sensor and configured to determine a level of moisture in the channel based on the digital signal.
2 . The soil sensor of claim 1 , further comprising a power supply to power the processing circuit.
3 . The soil sensor of claim 1 , further comprising a transceiver to transmit the determined level of moisture in the channel, and to receive instructions for operation of the signal generator.
4 . The soil sensor of claim 1 , wherein the processing circuit and the signal generator are disposed within a common water-proof casing.
5 . The soil sensor of claim 1 , wherein the processing circuit and the signal generator are enclosed in separate water-proof casings and coupled to each other through water-proof cables.
6 . The soil sensor of claim 1 , wherein the first dielectric material and the second dielectric material comprise the same dielectric material.
7 . The soil sensor of claim 6 , wherein the first dielectric material and the second dielectric material comprise polytetrafluoroethylene, polyimide, glass, polyester, or metal oxides.
8 . The soil sensor of claim 1 , wherein the first dielectric material and the second dielectric material provide a water-proof seal around the respective transmit and QVAR electrodes.
9 . The soil sensor of claim 1 , wherein the QVAR and transmit electrodes comprise regions of metal on a PCB.
10 . The soil sensor of claim 1 , further comprising a filter to remove noise from the detected signal at the receiver.
11 . A soil moisture detection method comprising:
having a transmitter and a receiver of a soil sensor in a patch of soil;
transmitting an output signal from a signal generator through the transmitter;
detecting the output signal at the receiver;
sensing the detected output signal at a charge variation (QVAR) sensor as QVAR signal; and
processing the digital signal from the QVAR sensor to obtain a moisture content of the patch of soil.
12 . The soil moisture detection method of claim 11 , further comprising filtering the digital signal using a filter.
13 . The soil moisture detection method of claim 12 , wherein the filtering comprises removing noise generated from transmission of power.
14 . The soil moisture detection method of claim 11 , further comprising transmitting the moisture content of the patch of soil.
15 . The soil moisture detection method of claim 11 ,
wherein the transmitter comprises a transmit electrode embedded within a first dielectric material; and
wherein the receiver comprises a charge variation (QVAR) electrode embedded within a second dielectric material.
16 . The soil moisture detection method of claim 15 , wherein the first dielectric material and the second dielectric material provide a water-proof seal around the respective transmit and QVAR electrodes.
17 . The soil moisture detection method of claim 15 , wherein the first dielectric material and the second dielectric material comprise polytetrafluoroethylene, polyimide, glass, polyester, or metal oxides.
18 . A soil sensor calibration method comprising:
placing a transmitter and a receiver of a soil sensor in a first patch of soil;
generating a first soil moisture measurement using the soil sensor;
after generating the first soil moisture measurement, adding a known volume of water to the patch of soil;
after adding the water, generating a second soil moisture measurement using the soil sensor; and
determining a moisture content calibration table for the soil based on the first and the second moisture measurements.
19 . The method of claim 18 , further comprising:
placing a transmitter and a receiver of a soil sensor in a second patch of soil;
generating a third soil moisture measurement using the soil sensor; and
determining a moisture content of the second patch based on the third soil moisture measurement and the moisture content calibration table.
20 . The method of claim 19 , wherein the first patch and the second patch are from a same sample of the soil.