Soil moisture sensor based on electrostatic sensing

Abstract

The invention relates to a 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 configured to be electrostatically coupled to the transmitter through a channel including soil, the receiver including a charge change (QVAR) electrode embedded within a second dielectric material. The soil sensor includes a charge change (QVAR) sensor coupled to the QVAR electrode, the QVAR sensor configured to detect a change in charge detected at the QVAR electrode in response to a signal from the signal generator, and output a digital signal including the detected charge. And the soil sensor further comprises processing circuitry coupled to the QVAR sensor and configured to determine a moisture level in the channel based on the digital signal.

Description

Technical Field

[0001] The present invention relates generally to soil moisture sensing and, in particular embodiments, to soil moisture sensors based on electrostatic sensing. Background Art

[0002] Soil moisture sensing plays a vital role in optimizing irrigation practices, managing crop health, and conserving water resources. Over time, many electronic soil moisture sensors have been developed and employ various principles such as resistance, capacitance, or time domain reflectometry (TDR) to measure the moisture content of a patch of soil.

[0003] Resistive soil moisture sensors operate on the principle that the resistance of the soil changes with its moisture content. While these sensors are relatively simple and inexpensive, they are susceptible to interference from changes in soil salinity, temperature, and conductivity, resulting in reduced accuracy and reliability. The electrodes of a typical soil moisture sensor are in direct contact with the soil and, as a result, corrode due to exposure to water.

[0004] Capacitive soil moisture sensors use the dielectric properties of soil, which vary with moisture content, to estimate soil moisture levels. These sensors measure the capacitance between electrodes embedded in the soil. While capacitive sensors offer improved accuracy and reduced sensitivity to soil salinity compared to resistive sensors, they still face challenges in accurately determining soil moisture levels under different soil types and environmental conditions.

[0005] Time domain reflectometry (TDR) sensors transmit electromagnetic pulses into the soil and measure the time it takes for the pulses to reflect back. This measurement is related to the dielectric constant of the soil, which in turn is related to the soil moisture content. TDR sensors provide accurate and reliable soil moisture measurements, but are relatively expensive and may require a complex calibration process.

[0006] Traditional soil moisture measurement methods, such as gravimetric techniques and tensiometers, have limitations in terms of being labor-intensive, limited spatial coverage, and not providing real-time data. Current sensors are expensive to purchase and have high maintenance costs (due to the sensors operating in wet environments). Summary of the invention

[0007] According to an embodiment of the present invention, a soil sensor includes a signal generator. The soil sensor also includes a transmitter coupled to the signal generator, the transmitter being configured to transmit a signal from the signal generator having a fixed frequency, the transmitter including a transmitting electrode embedded in a first dielectric material. The soil sensor also includes a receiver, the receiver being configured to be electrostatically coupled to the transmitter through a channel including soil, the receiver including a charge change (QVAR) electrode embedded in a second dielectric material. The soil sensor also includes a charge change (QVAR) sensor coupled to the QVAR electrode, the QVAR sensor being configured to detect a change in charge detected at the QVAR electrode in response to a signal from the signal generator, and outputting a digital signal including the detected charge. And the soil sensor also includes a processing circuit, the processing circuit being coupled to the QVAR sensor and being configured to determine the moisture level in the channel based on the digital signal.

[0008] One embodiment of a soil moisture detection method includes placing a transmitter and a receiver of a soil sensor in a piece of soil. The soil moisture detection method also includes transmitting an output signal from a signal generator through the transmitter. The soil moisture detection method also includes detecting the output signal at a receiver. The soil moisture detection method also includes detecting the output signal at a charge variation (QVAR) sensor as a QVAR signal. And the soil moisture detection method also includes processing a digital signal from the QVAR sensor to obtain the moisture content of the soil block.

[0009] The soil sensor calibration method of an embodiment includes placing a transmitter and a receiver of a soil sensor in a first soil mass. The soil sensor calibration method also includes generating a first soil moisture measurement using the soil sensor. The soil sensor calibration method also includes adding a known volume of water to the soil mass after generating the first soil moisture measurement. The soil sensor calibration method also includes generating a second soil moisture measurement using the soil sensor after adding the water. The soil sensor calibration method also includes determining a moisture content calibration table of the soil based on the first and second moisture measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0011] Figure 1 is a schematic diagram of components of an electronic device according to some embodiments;

[0012] Figure 2 Two graphs depicting two types of waveforms that may be output by a signal generator are shown;

[0013] Figure 3is a flow chart of a soil moisture testing method capable of determining the moisture level of a piece of soil;

[0014] Figure 4 is a graph showing the output of a soil moisture sensor that has been placed in a piece of soil and to which different amounts of water have been added;

[0015] Figure 5A - Figure 5B are flow charts of two different methods of calibrating a soil moisture sensor according to some embodiments;

[0016] Figure 6 is a diagram of a dielectric housing for covering electrodes of a soil moisture sensor in an embodiment;

[0017] Figure 7 is a schematic diagram of an analog front end circuit (AFE) and an analog-to-digital converter (ADC) of a charge change (QVAR) sensor in an embodiment;

[0018] Figure 8 is a schematic diagram of the elements of a QVAR sensor in an embodiment;

[0019] Fig.9A - Fig. 9B is a diagram showing polarization of water molecules between electrodes of a soil sensor in an embodiment; and

[0020] Fig. 10A - Fig. 10B is a diagram showing the polarization of water molecules between electrodes of a soil sensor at different amounts of water in the soil. DETAILED DESCRIPTION

[0021] Soil sensors detect and monitor the moisture level of the soil. Over time, soil sensors have become an essential tool in the agricultural and agro-industry to improve the efficiency of their operations. Soil sensors provide these industries with accurate, real-time data about soil conditions, leading to improved decision-making, optimization of resources, and increased productivity. Specifically, soil sensors help farmers optimize their irrigation practices by providing real-time data about soil moisture levels. This information allows farmers to determine the precise amount and timing of water required for their crops, thereby minimizing water waste and reducing the risk of over- or under-irrigation.

[0022] There are many types of soil sensors on the market that detect moisture levels, each using different technologies to measure soil moisture content. The various commonly used types of soil sensors for moisture detection include: capacitive sensors, tensiometers, time domain reflectometry (TDR) sensors, frequency domain reflectometry (FDR) sensors, and resistive sensors.

[0023] Capacitive sensors measure soil moisture by evaluating the capacitance between two or more electrodes inserted into the soil. The moisture content affects the dielectric constant of the soil, which in turn changes the capacitance. By measuring this change, the capacitive sensor estimates the moisture level in the soil.

[0024] Tensiometers measure soil water tension, also known as soil water potential. These sensors consist of a porous ceramic cup filled with water. When the soil dries, water is drawn out of the cup, creating negative pressure. The tension in the water is measured using a manometer, providing an indication of the soil's water status.

[0025] Time Domain Reflectometry (TDR) sensors determine soil moisture by measuring the propagation time of an electromagnetic pulse through the soil. These sensors have two electrodes inserted into the soil and emit a pulse of electromagnetic energy between them. The time it takes for the pulse to propagate reflects the dielectric properties of the soil, which is related to the moisture content.

[0026] Frequency Domain Reflectometry (FDR) sensors analyze the dielectric properties of soil to estimate moisture levels. These sensors transmit electromagnetic waves of varying frequencies and measure the reflected signal. The frequency of the reflected signal changes in an indication of soil moisture content.

[0027] The resistance sensor consists of a porous block that absorbs and releases water based on soil conditions. The resistance of the block changes with the moisture content, and this change is used to estimate the soil moisture level.

[0028] All of the above sensors can be connected to data loggers or integrated into automatic irrigation systems, allowing farmers to monitor soil moisture levels and make informed decisions about irrigation schedules and water management practices.

[0029] Although soil sensors are extremely useful, current sensors are expensive to purchase and have high maintenance costs (due to the sensors operating in wet environments). Innovations are needed to reduce the cost of soil sensors, and there is a need to improve the robustness of the sensors. An effective and robust system and method is needed that provides protection from the environment and reduces the cost of soil moisture sensors.

[0030] In various embodiments, the soil sensor of the present disclosure incorporates an electrostatic sensor to measure the soil moisture content of a piece of soil, which is different from currently used technologies (such as capacitance or resistance technologies). Embodiments of the present disclosure describe a new type of electrostatic soil sensor for moisture detection. In one embodiment, the present disclosure uses a new type of electrostatic sensor called a charge change (QVAR) sensor. Various aspects of the present invention include a QVAR sensor coupled to a passive electrode. Although the QVAR sensor has a single differential input including two input pins (which can be coupled to two or more electrodes), the present invention details the case where only a single input pin of the differential input is used and the remaining input pins are left floating.

[0031] In an embodiment, a change in the electric field near an active (receiver or QVAR) electrode of a QVAR sensor induces a charge polarization on the active electrode. This charge polarization is equivalent to a voltage that is proportional to the change in the electric field. In order to generate a changing electric field near a receiver electrode connected to a QVAR sensor, a signal generator is connected to a transmitter electrode, and the transmitter electrode is placed at a fixed distance from the receiver electrode. In one embodiment, the signal generator generates a signal output by the transmitter electrode having a fixed assignment, a frequency (within a range consistent with quasi-static phenomena, such as 0.01 Hz-20 Hz), and a waveform output by the transmitter electrode. This changing electric field emitted by the transmitter electrode induces a polarization or voltage on the receiver electrode connected to the QVAR sensor. When both the receiver and transmitter electrodes of the device are placed in a piece of soil, the amount of polarization of the receiver electrode changes based on the moisture content of the piece of soil, which enables this new type of soil sensor to detect and monitor soil moisture levels. This can be used in a soil sensor that is used Figure 1 One or more embodiments of the soil sensor shown are implemented.

[0032] Figure 1 is a schematic diagram of components of an electronic device according to some embodiments. In the illustrated embodiment, the electronic device is a soil sensor.

[0033] Figure 1 A soil sensor 100 is shown that is capable of measuring the moisture level of a patch of soil 113. The soil sensor 100 includes an RX-side waterproof housing 101 that protects a power supply 102, a memory 103, a processor 104, a transceiver 105, and an optional filter 107. The components protected by the RX-side waterproof housing 101 are coupled to a charge variation (QVAR) sensor 106.

[0034] The components of the RX-side waterproof housing 101 are connected to the components of the TX-side waterproof housing 108 that protects the signal generator 110. The QVAR sensor 106 is coupled to the receiver electrode 112a. The receiver electrode 112a is encapsulated in a housing 111a, which is composed of a dielectric material to protect the receiver electrode from directly contacting the soil mass 113. The components disposed within the TX-side waterproof housing 108 are connected to the transmitter electrode 112b. The transmitter electrode 112b is encapsulated in a housing 111b, which is composed of a dielectric material to protect the transmitter electrode from directly contacting the soil mass 113.

[0035] The signal generator 110 is a type of electronic device capable of generating an electrical signal with a set amplitude, frequency, and waveform characteristics. The signal generator 110 can be any suitable device that generates an electrical signal with a set amplitude, frequency, and waveform characteristics, such as an arbitrary waveform generator (AWG), a pulse generator, or a function generator. After receiving a set of pulse instructions at the transceiver 105, the signal generator 110 generates an electrical signal based on these instructions. The set of pulse instructions includes the amplitude, frequency, and waveform (e.g., 5Vpp amplitude, 10Hz frequency, and a sine waveform) to be output by the signal generator.

[0036] Once the electrical signal is generated by the signal generator 110, the electrical signal is transmitted by the transmitter electrode 112b through the soil block 113. The transmitter electrode 112b can be of any shape and made of any material suitable for transmitting the electrical signal generated by the signal generator. In one embodiment, the shape is a cylindrical metal rod, which is encapsulated in a housing 111b of a suitable dielectric material to protect the transmitter electrode 112b from direct contact with the soil block 113. In another embodiment, the shape of the transmitter electrode 112b can be a rectangular thin metal strip on a printed circuit board (PCB). In the case of using a rectangular thin metal strip as a transmitter electrode, the transmitter electrode is coated with a suitable dielectric material (the coating is used for the same purpose as the housing 111b) to protect the transmitter electrode 112b from direct contact with the soil block 113.

[0037] After the transmission signal passes through the soil block 113, the transmission signal is detected at the receiver electrode 112a at a set distance from the transmitter electrode 112b. The receiver electrode 112a is a passive element having an electric potential induced thereon by an external environmental electrostatic field (e.g., an electrostatic field transmitted by the transmitter electrode 112b through the soil). The receiver electrode 112a can be of any shape and made of any material suitable for detecting the electrical signal transmitted by the transmitter electrode 112b. In one embodiment, the shape is a cylindrical metal rod, which is encapsulated in a housing 111a of a suitable dielectric material to protect the receiver electrode 112a from direct contact with the soil block 113. In another embodiment, the shape of the receiver electrode 112a can be a rectangular thin metal strip on a printed circuit board (PCB). In the case of using a rectangular thin metal strip as a receiving electrode, the receiving electrode is coated in a suitable dielectric material (the coating is used for the same purpose as the housing 111a) to protect the receiving electrode 112a from direct contact with the soil block 113.

[0038] The receiver electrode 112a receives the transmitted signal, and the received signal is detected by the QVAR sensor 106. The charge change (QVAR) sensor 106 is coupled to the receiver electrode 112a. The QVAR sensor 106 has a differential input (a differential input includes two input pins), which will allow one receiver electrode to be coupled to the QVAR sensor 106. In this embodiment, the QVAR sensor 106 has only one input pin connected to the differential input of the receiver electrode 112a. This configuration is advantageous when operating an electrostatic sensor (such as the QVAR sensor 106) for soil moisture detection. Compared to other types of moisture sensors, this configuration results in lower power consumption due to how the electrostatic sensor works. Electrostatic sensors do not sense by using current flowing through the soil and therefore do not consume as much power.

[0039] The QVAR sensor works by detecting the difference in charge between the input pins of the differential input. The change in the external electric field induces a charge polarization of the electrodes connected to the input pins of the differential input, which induces a potential on the input pins of the differential input. The induced potential depends on the proximity of the electric field source and the electrical characteristics of the material between the source of the changing electric field and the electrodes connected to the differential input. The differential input of the QVAR sensor is compared to a common mode reference, and the potential difference between the input pins of the differential input will induce a current in the circuit of the QVAR sensor. This current can then be used to detect the presence of material, and quantify the amount of material present.

[0040] As previously described in various embodiments, only one of the input pins of the differential input is used, and the other input pin of the differential input is kept floating at a common mode reference, the common mode signal is not eliminated, and the differential potential difference induced on the connected input pins of the differential input is compared to the common mode reference without loss of amplitude.

[0041] It should be noted that there are significant differences between soil moisture sensors that use capacitive sensors and soil moisture sensors that use electrostatic sensors (such as the QVAR sensor of the present disclosure). Soil moisture sensors based on QVAR sensors measure the soil moisture content of a soil block by quantifying the potential difference induced between the two input pins of the differential input of the QVAR sensor and correlating the measured potential difference with the amount of polarization of the soil block. The polarization of the soil block between the electrodes is a result of the polar properties of water (which are polar molecules), and the applied electric field polarizes the water molecules, causing their dipoles to point in the direction of the induced electric field. The QVAR sensor measures the moisture content of the soil block by measuring the change in polarization.

[0042] Soil moisture sensors that use capacitive sensors to measure the soil moisture content of a piece of soil use frequency measurement to determine the change in capacitance of a capacitor (by measuring the potential difference between the plates of the capacitor). For example, a high frequency voltage signal can be applied across the plates of a capacitor to determine the change in frequency at which the capacitor resonates. Alternatively, the change in frequency of a clock coupled to a capacitor placed in the soil can be measured. The change in frequency is the result of the dielectric between the plates of the capacitor changing due to the different water (or moisture) content between the plates. The change in capacitance caused by the change in the dielectric can be used to quantify the moisture content of the soil block.

[0043] Furthermore, soil moisture sensors employing capacitive sensors evaluate the capacitance between two or more electrodes inserted into the soil, whereas electrostatic sensors deal directly with charge. In the case of a capacitive sensor, the phenomenon occurring is related to the potential difference between the plates (i.e., electrodes) of the capacitor, ΔV=Vplate2-Vplate1. In the case of a QVAR sensor, the two electrodes do not involve a common potential with each other (one electrode generates the potential, while the other electrode can be connected to the QVAR sensor for sensing). Also, when a QVAR sensor is used (such as in the present disclosure), the dielectric protection used to protect the electrodes from direct contact with the soil and water prevents any parasitic currents between the electrodes (this is not the case with a capacitive sensor).

[0044] In summary, the QVAR sensor measures the potential difference between the input pins of the differential input to quantify the soil moisture content of the soil mass based on the polarization of the water molecules. In contrast, a capacitive sensor measures the frequency change caused by the water content in the soil changing the dielectric between the capacitor plates (which changes the capacitance of the capacitor). A capacitive sensor measures the potential difference between the capacitor plates (between the electrodes). In contrast to a capacitive sensor, a QVAR sensor implements low frequencies and measures the polarization changes of the water molecules in the soil (measuring the potential difference between its input pins instead of the electrodes). In a QVAR sensor, the sensor is in an electrostatic configuration (no current), while a capacitive sensor is in an electrodynamic configuration (current).

[0045] The advantage of using the QVAR sensor 106 for soil moisture sensing in the soil sensor 100 is that there is no direct connection between the transmitter electrode 112b and the receiver electrode 112a (or the connection has a very large resistance because the connection is the soil between the two dielectric shells 111a-b). Due to the isolation of the two electrodes, there is actually no current flow between the two electrodes. Therefore, because there is actually no current flow between the electrodes, the power consumption of the soil sensor 100 is minimal, and the soil sensor 100 is more energy-efficient than other types of soil sensors.

[0046] The QVAR sensor 106 is coupled to a filter 107, which is connected to the processor 104 of the soil sensor 100. Any sensed information obtained by the QVAR sensor passes through the filter 107 and then through the processor 104 to determine the moisture level of the soil mass 113. In one embodiment, the sensed information obtained by the QVAR sensor 106 is an alternating signal. In this case, an analog-to-digital converter (ADC) within the QVAR sensor 106 can be used to convert the analog signal to a digital signal to pass through the filter 107 and then reach the processor 104.

[0047] The detection signal from the QVAR sensor 106 then passes through a filter 107, which filters out unwanted electrical noise that may be present in the detection signal. The filter 107 may be any suitable type of filter that passes the frequency of the detected signal to the processor 104 and suppresses electrical noise, such as a low-pass filter or a band-pass filter. Using a low-pass filter, low-frequency signals emitted from the receiver electrode 112a and detected by the QVAR sensor 106 may be allowed to pass, while attenuating or reducing the amplitude of higher-frequency signals. In other words, the low-pass filter allows detection signals from the QVAR sensor 106 having frequencies below a certain cutoff frequency to pass, while blocking or attenuating signals above the frequency. For example, the cutoff frequency may be 50 Hz to avoid signals from a nearby power grid, which typically runs at 60 Hz. In another embodiment, a band-pass filter may be used to allow signals having a specific frequency range (called a passband) detected by the QVAR sensor 106 to pass, while attenuating or blocking frequencies outside the range. In other words, the band-pass filter selectively allows signals within a specific frequency range to pass, while suppressing or attenuating signals below and above the range. In another embodiment, the filter 107 may be an algorithm implemented in software. After the signal detected by the QVAR sensor 106 has been filtered by the filter 107 , the filtered signal is passed to the processor 104 to extract the soil moisture content of the soil mass 113 .

[0048] In some embodiments, the processor 104 of the soil sensor 100 executes instructions stored in the memory 103 of the device. These instructions tell the processor 104 how to process the signal detected by the QVAR sensor 106. The processor processes the signal to extract the soil moisture content of the soil block 113, and then the soil moisture content information can be stored in the memory 103 together with a timestamp. In other embodiments, the transceiver 105 can be used to actively transmit the soil moisture content to an external receiver for real-time display and monitoring of the soil moisture content. The processor 104 can be any component or collection of components suitable for performing calculations or other processing-related tasks related to the methods disclosed herein. The processor 104 can be, for example, a microprocessor, a microcontroller, a control circuit, a digital signal processor, a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), a system on a chip (SOC), or a combination thereof.

[0049] The memory 103 may be any component or collection of components suitable for storing programs, event information, or instructions executed by the processor 104. In one embodiment, the memory 103 includes non-transitory computer-readable media. Non-transitory computer-readable media include all types of computer-readable media, including magnetic storage media, optical storage media, flash memory media, and solid-state storage media.

[0050] It should be understood that the software can be installed in the soil sensor 100 and sold with the soil sensor 100. Alternatively, the software can be obtained and loaded into the soil sensor 100, including obtaining the software through physical media or distribution systems, including, for example, obtaining the software from a server owned by the creator of the software or from a server that the creator of the software does not own but uses. For example, the software can be stored on a server for distribution over the Internet.

[0051] In various embodiments, the memory 103 is a dedicated non-transitory memory for storing instructions or data specific to determining soil moisture level. In other embodiments, the memory 103 may refer to an existing storage device to store soil moisture level measurements made by a soil sensor. In other embodiments, the memory 103 may have the functionality of the previous two embodiments. The memory 103 may include a non-volatile memory, a read-only memory, or a random access memory.

[0052] The transceiver 105 may be any device suitable for use as a transmitter and receiver for the soil sensor 100, such as an RF transceiver or a radio transceiver. In various embodiments, the transceiver 105 may be integrated with or separate from the QVAR sensor 106. A transceiver is a device that combines both transmitter and receiver functions, allowing for bidirectional communication. The transceiver 105 is used as a receiver to receive configuration instructions for the signal generator, to receive instructions to transmit soil moisture information stored in the memory 103, and to receive instructions to start or end data acquisition for the soil sensor 100. The transceiver 105 is used as a transmitter to transmit the status of the soil sensor (e.g., the sensor is operational, or actively acquiring data), and to transmit soil moisture information when interrogated, or to transmit soil moisture information in real time (depending on the configuration of the soil sensor having received operating instructions). In some embodiments, the receiver and transmitter functions of the transceiver 105 may also be implemented independently.

[0053] The power supply 102 provides power for the operation of all electronic components enclosed in the RX side waterproof housing 101. The power supply 102 can be any suitable electronic device, such as a battery power supply, a linear power supply, a switch mode power supply (SMPS), an uninterruptible power supply, a solar power supply or a combination thereof.

[0054] The RX side and TX side waterproof housings 101 and 108 protect their respective electronic components from water in the soil sensor operating environment. The housing can be made of any suitable material that will prevent water from penetrating into the electronic components. In various embodiments, the RX side waterproof housing 101 and the TX side waterproof housing 108 may include polycarbonate, thermoplastic elastomer (TPE), thermoplastic polyurethane (TPU), silicone or other waterproof plastics. In addition, the RX side waterproof housing 101 and the TX side waterproof housing 108 can be sealed with gaskets, O-rings, etc. to ensure and prevent water from penetrating through the joint. In certain embodiments, the RX side waterproof housing 101 and the TX side waterproof housing 108 can be sealed to industrial standards such as IP55, IP56 and IP65. In various embodiments, the RX side waterproof housing 101 and the TX side waterproof housing 108 can be sealed to prevent dust and moisture from penetrating. In various embodiments, the RX side waterproof housing 101 and the TX side waterproof housing 108 can be sealed to have an IP rating of IPxy, where x is greater than 3 and y is greater than 2. In various embodiments, the RX-side waterproof housing 101 and the TX-side waterproof housing 108 may hermetically seal the components therein.

[0055] In another embodiment, a single waterproof housing protecting all the electronics of the soil sensor can be used instead of having two waterproof housings. Such an integrated housing can be formed to have similar properties as described above.

[0056] In various embodiments, the electrodes of the soil sensor include at least two layers. The first layer provides an external interface to the environment surrounding the soil sensor 100, and the soil sensor 100 is polarized in response to an external electrostatic field. The first layer includes a dielectric material (or a dielectric shell 111a-b) characterized as a good insulator with a good relative permittivity. For example, the first layer can be polytetrafluoroethylene, polyimide, glass, polyester, metal oxide, etc. The second layer includes a conductive material that senses the potential of the first layer and forms a main electrode (e.g., a receiver electrode 112a or a transmitter electrode 112b). For example, the second layer can be a metal (e.g., copper), a metal alloy, etc.

[0057] The potential induced at the receiver electrode 112a varies depending on, for example, the size, geometry, and arrangement of the electrodes 112a - b relative to each other and the soil sensor 100 .

[0058] The receiver electrode 112a and any other input pin of the differential input of the QVAR sensor 106 have a common reference, and the changing electric field transmitted by the transmitter electrode 112b through the soil mass 113 induces a potential at the receiver electrode 112a. Because the receiver electrode 112a and the other input pin of the differential input of the QVAR sensor 106 have a common reference, the distance difference between the receiver electrode 112a and the transmitter electrode 112b provides a detectable differential potential between the receiver electrode 112a and the other input pin of the differential input of the QVAR sensor 106, which remains floating at each moment.

[0059] Figure 2 Two different types of signals that a signal generator can output are shown. As described above, the signal generator outputs an electrical signal characterized by amplitude, frequency, and waveform. Both graphs show a waveform having a peak-to-peak voltage Vpp and an oscillation period T. The vertical axis of the graph is voltage and the horizontal axis of the graph is time. The peak-to-peak voltage is related to the amplitude of the waveform. The oscillation period is inversely proportional to the frequency of the waveform.

[0060] In one embodiment, the signal generator may receive instructions to output a signal similar to Figure 2 The waveform shown in the top curve of is a sine wave. For example, the waveform may be a waveform of 5 Vpp amplitude, 10 Hz frequency (which is 0.1 s oscillation period) and a sine wave.

[0061] In another embodiment, the signal generator may receive instructions to output a signal similar to Figure 2 The waveform depicted in the bottom curve of is a square wave. For example, the waveform may be a waveform of 5 Vpp amplitude, 10 Hz frequency (which is 0.1 s oscillation period) and a square wave.

[0062] Although they are not Figure 2 , but the signal generator can output more wave types than sine waves or square waves. For example, the signal generator can output triangle waves, pulse waves, cardiac pattern waves, Gaussian pulse waves, and arbitrary waves, as well as sine waves and square waves. In some embodiments, the wave may include a pulse sequence with only positive pulses.

[0063] In various embodiments, the frequency is selected to minimize interference from other noise sources in the area. For example, if the soil sensor is placed near an electric utility or a cable carrying electricity, the frequency is designed to be below 60 Hz. Similarly, if the location is close to other equipment that causes electromagnetic pulse noise, the frequency can be modified to minimize interference.

[0064] Figure 3 The flowchart of FIG. 1 shows a method for operating the soil sensor 100 to determine the soil moisture level of a piece of soil. This exemplary method assumes that the soil sensor 100 has been calibrated for a particular soil. The method for calibrating the soil sensor 100 is described in Figure 5A and Figure 5B and discussed later in this document.

[0065] The method begins at box 302, where the soil sensor 100 is initially placed. The transmitter electrode (isolated in its dielectric housing) and the receiver electrode (isolated in its dielectric housing) of the soil sensor 100 can be placed in a piece of soil. Because the two electrodes are in their respective dielectric housings, they are not in direct contact with the soil. The separation distance between the receiver and transmitter electrodes is in the range of 1-5 cm.

[0066] Once the receiver and transmitter electrodes have been placed in the soil, the method moves to box 304. In box 304, an output signal is generated by the signal generator and output into the soil through the transmitter electrode. The output signal is the time-varying potential induced on the transmitter electrode by the signal generator. The time-varying potential causes a time-varying electric field through the soil. The soil and any water between the receiver and transmitter electrodes are polarized by the time-varying electric field.

[0067] After the output signal has been generated and output by the transmitter electrode into the soil, the method moves to block 306. The polarization of the material between the transmitter and receiver electrodes can be detected by the receiver electrode. In block 306, the polarization of the material between the receiver and transmitter electrodes induces a potential on the receiver electrode. In other words, the receiver electrode is connected to the QVAR sensor, which detects the transmitted signal on the receiver electrode. The potential induced on the receiver electrode is sensed by the QVAR sensor 106. As in Figure 1As mentioned in the detailed description, this results in a potential difference between the input pins of the QVAR sensor's differential inputs connected to the receiver electrodes and the common mode reference of the QVAR sensor. This potential difference causes current to flow in the device, and this information can be processed to extract soil moisture content.

[0068] The signal detected by the QVAR sensor at the receiver electrode may be filtered to remove any erroneous noise from the environment (block 308). After moving to block 308, the method removes any noise in the detected signal by using a filter. The filter may be any type of filter that does not remove the detected signal, such as a low pass filter, a band pass filter, a high pass filter, and other filters that may have multiple pass bands. In one embodiment, the transmitted signal has a frequency of 10 Hz. Therefore, the filter may allow the 10 Hz signal to pass through to the processor.

[0069] In block 310, processor 104 processes the digital signal output from the QVAR sensor using instructions from memory 103 to extract the moisture level of the material between the receiver electrode and the transmitter electrode. This may be performed by applying a benchmark function or looking up a calibration table and comparing the value of the digital signal from the QVAR sensor to the value in the calibration table. Figure 4 , Figure 5A and Figure 5B Other embodiments described describe calibration tables.After the moisture level is reached, the information can be stored in the soil sensor, or transmitted to a device for further analysis, or a combination of both.

[0070] Figure 3 The method shown in the flow chart of can operate in different ways. In one embodiment, the method can be a continuous reading process, where the moisture level is constantly monitored. In other embodiments, the method can be instructed to take readings over a configurable time frame. In other embodiments, the method is used to provide readings when the soil sensor 100 has been connected to an irrigation control system. Example outputs of the soil sensor 100 will now be discussed.

[0071] Figure 4 is a graph schematically illustrating the output of the soil sensor 100, which is the moisture level over time. The vertical axis corresponds to the moisture level of the soil block and the horizontal axis corresponds to time. The graph shows the output of the soil sensor in one embodiment, where the soil sensor is activated in a dry soil block and a known volume of water is added to the soil at three specific times. The volume of water added to the soil is the same all three times (e.g., one cup of water is added to the soil every 45 seconds).

[0072] exist Figure 4The beginning of the curve of 401 shows the baseline moisture level of the soil block. This baseline 401 is an initial measurement of the soil moisture level of the soil block before a known volume of water (e.g., a single cup) is added to the soil block. After this baseline 401 measurement is taken, a single cup of water is added to the soil block. The addition of water causes the level of the soil sensor 100 reading to rise sharply to the new moisture level 402 of the soil.

[0073] After the single cup of water is added to the soil block, there is a relatively short period of time (approximately 45 seconds) of pause to allow the water added to the soil block to saturate and give a stable reading at the soil block's new moisture level 402. After the short period of time has passed, a second cup of water is added to the soil block, which corresponds to a sharp rise in the new moisture level to a new soil moisture level 403 for the soil block.

[0074] Once the second cup of water is added to the soil block, there is a pause of the same time frame (approximately 45 seconds) to allow the water added to the soil block to saturate and give a stable reading at the new soil moisture level 403. Figure 4 It is evident from the curve that at the new soil moisture level 403, the patch of soil has not reached the same stable moisture level reading as the previously measured level. This is a result of the large amount of water now present in the soil patch. The amount of water that is present will take longer to move around and find areas of the soil patch that are not yet fully saturated. The water moves from the area where the water was added (between the two electrodes of the soil sensor) to the areas of the soil patch that are not yet saturated. This behavior is evidenced by the slow drop in moisture level depicted in the soil moisture level 403.

[0075] Again, after waiting the same time frame (approximately 45 seconds), another single cup of water (making a total of three cups of water) is added to the soil mass. The final addition of water raises the soil moisture level 403 to a new soil moisture level 404. As the saturation level of the soil mass increases, the water will move around to find areas in the soil that are not fully saturated. This movement of water from the area between the two electrodes of the soil sensor results in Figure 4 A slow decrease in moisture level is observed at soil moisture level 404 in the graph of FIG. Figure 4 The moisture level determination capability of the soil sensor of the present disclosure is shown.

[0076] In order to detect the moisture level of a patch of soil with the highest accuracy, the soil sensor of the present invention can be calibrated to the environment in which it will operate. Figure 5A and Figure 5B Two different methods of calibrating a soil sensor are shown in the flow chart of FIG.

[0077] Figure 5AThe flowchart shown describes a calibration method for a soil sensor that uses a separate (calibrated) soil sensor as a calibration reference to serve as a benchmark for the soil sensor of the present disclosure. Figure 5A The individual soil sensor calibration method of the present invention begins in block 500. At block 500, a reference soil sensor that has been calibrated is placed in a block of soil. It should be understood that the reference soil sensor does not necessarily have to be the same type of soil sensor described in the present disclosure. The reference soil sensor can be any type of soil sensor that has soil moisture level readings comparable to the soil sensors of the present disclosure. Once the reference soil sensor is placed in the block of soil, multiple soil moisture level readings are determined, for example, at different moisture contents or even without changing the moisture content of the soil.

[0078] After recording a plurality of soil moisture readings obtained using the already calibrated soil sensor, the individual soil sensor calibration method proceeds to block 501. In block 501, a soil sensor of the same type as the present disclosure that needs to be calibrated is placed in the same soil patch where the previously calibrated soil sensor is located. Once the soil sensor that needs to be calibrated is in the same patch of soil, a plurality of soil moisture level readings are determined under the same conditions as the reference soil sensor.

[0079] Next, referring to box 502, the soil moisture level readings of the soil sensor of the same type as the present disclosure are compared to the soil moisture level readings from the reference soil sensor. Because the moisture readings of the reference soil sensor correspond to a known moisture, the soil moisture readings of the same type of soil sensor as the present disclosure can be benchmarked to the same soil moisture value. Once this benchmark is formed between the two soil sensors, the soil sensor of the same type as the present disclosure is calibrated. In one or more embodiments, the difference between the sensors can be stored as a benchmark function, which can be easily applied to the output of the soil sensor being calibrated or to look up a calibration table.

[0080] Figure 5B An illustration of a flow chart of a soil sensor calibration method that requires only the soil sensor that needs calibration rather than two soil sensors (one already calibrated and the other needing calibration) is shown. Figure 5B The calibration method is relative to Figure 5A The main advantage of the calibration method shown is that Figure 5B The calibration method uses only a single soil sensor. Figure 5B The calibration method is better than Figure 5A The calibration method requires more steps. Figure 5B The calibration method uses a moisture content calibration table to calibrate the soil sensor.

[0081] Figure 5BThe calibration method of begins at block 510. In block 510, the soil sensor to be calibrated is placed in a patch of soil and soil moisture level readings are recorded. Once the soil moisture level readings are recorded, the calibration method proceeds to block 511.

[0082] once Figure 5B In block 511, a known volume of water is added to the soil block. A new soil moisture level reading corresponding to the new soil moisture level is then recorded using the soil sensor. The process of block 511 is repeated multiple times, adding a known volume of water each time. This repetition is performed to collect multiple data points at a known volume of water level in the soil block.

[0083] After taking a plurality of moisture level readings as discussed above as part of block 511, the calibration method moves to block 512. In block 512, the data collected in blocks 510-511 are analyzed to determine changes in the soil moisture level / known water volume ratio. This ratio can then be used to form a moisture content calibration table.

[0084] After determining the ratio of block 512, Figure 5B The calibration method proceeds to block 513. In block 513, a moisture content calibration table is constructed using the ratios determined in block 512. The moisture content calibration table is then used as a calibration tool to convert the soil sensor readings to actual soil moisture level values. Once the moisture content calibration table has been constructed, the soil sensor has been calibrated and can be used to make accurate soil moisture level readings.

[0085] In one embodiment, Figure 6 A dielectric condition is shown that may be used to isolate the transmitter electrode 112b or the receiver electrode 112a from the soil mass 113 that they occupy. Figure 6 The dielectric box shown in can be used as Figure 1 As described above, the dielectric housing may be constructed of any material that provides adequate protection from the soil mass in which the soil sensor is placed, such as polytetrafluoroethylene, polyimide, glass, polyester, metal oxides, and the like.

[0086] exist Figure 6 In one embodiment, the top of dielectric housing 601 and the bottom of dielectric housing 602 are both made of the same material and assembled with the electrode placed inside hole 603. In another embodiment, the top of dielectric box 601 and the bottom of dielectric box 602 can be made of different materials.

[0087] The top of dielectric housing 601 and the bottom of dielectric housing 602 can be assembled around the electrodes by gluing or epoxying the two halves together to form a watertight seal. Once assembled together, holes 603 are sealed around the connections from the electrodes (inside the dielectric housing) to the appropriate circuitry corresponding to each electrode. This is done to prevent any water from entering the interior of the dielectric housing and contacting the electrodes. The dielectric housing can be constructed using typical machining processes, molding, or even 3D printing techniques.

[0088] An advantage of using a waterproof dielectric material to cover the electrodes is that the metal electrodes are not in direct contact with the soil mass in which the soil sensor is placed. As a result, the electrodes are protected from corrosion-causing elements present in the soil. Thus, unlike many other types of soil sensors currently on the market, the electrodes of the soil sensor 100 of the present invention will not corrode over time.

[0089] Figure 7 An analog front end (AFE) circuit 705 and ADC 708 of a QVAR sensor 106 that may be installed in a soil sensor 100 are shown. As shown, the AFE 705 includes operational amplifiers 702a-b, a bias stage 704, R1, R2, and R3 resistors 706a-c, and an analog-to-digital converter (ADC) 708. The input electrode pair - the receiver electrode 112a and the floating input 701 represent the input pins to the differential input of the QVAR sensor 106 and are coupled to the AFE 705, where in this embodiment, the floating input 701 remains floating. The potential difference between the receiver electrode 112a and the floating input 701 is shown as a voltage Vd. The bias stage 704 (i.e., a buffer stage) biases the AFE 705 at a common mode voltage Vcm.

[0090] The inverting terminals of the operational amplifiers 702a-b are connected through R2 resistor 706b. The potential difference between the receiver electrode 112a and the floating input 701 generates a current I=Vd / R2 through resistor 706b. This current passes through R1, R2 and R3 resistors 706a-c, and assuming R1=R3, generates an output voltage Vd' at the input of the ADC 708, given by Vd'=I(2R1+R2) or equivalently Vd(2(R1 / R2)+1).

[0091] A differential potential Vd' proportional to the differential potential Vd is provided to the input of ADC 708. ADC 708 converts the analog voltage into a digital charge change signal Sq, which is then transmitted to processor 104. It should be understood that the overall gain of QVAR sensor 106 depends primarily on R2 resistor 706b and can therefore be adjusted by appropriately selecting the value of R2 resistor 706b.

[0092] In one embodiment, the charge change signal Sq is a high resolution (16-bit or 24-bit) digital stream. ADC 708 is optional, as processor 104 may be configured to operate directly on analog signals, or may itself include an analog-to-digital converter suitable for converting signal Vd'.

[0093] Figure 8 1 is a schematic diagram of a QVAR sensor 106 in one embodiment. In one embodiment, the QVAR sensor 106 includes an analog front end circuit (AFE) 705, an analog-to-digital converter (ADC) 708, a digital processing unit 802, and a communication interface 804. The receiver electrode 112a and the floating input 701 are coupled to the input pins of the differential input and coupled to Figure 7 AFE705 is described in Figure 7 AFE705 detects the analog signal (e.g. Figure 7 Vd' in is transmitted to ADC708.

[0094] ADC 708 converts the detected analog signal from AFE 705 into a digital charge change signal (eg Figure 7 Sq) for processing by the digital processing unit 802. In one embodiment, there is no ADC 708 in the QVAR sensor 106, but there is an ADC in the soil sensor 100.

[0095] The digital processing unit 802 may be any processor that processes the digital charge change signal from the ADC 708 to quantify the QVAR signal detected by the QVAR sensor 106. After processing the digital charge change signal from the ADC 708, the digital processing unit 802 communicates the processed charge change signal by transmitting the processed charge change signal via the communication interface 804.

[0096] The communication interface 804 may be any communication interface capable of transmitting the processed charge change signal from the QVAR sensor 106 to other components including the soil sensor 100. For example, the communication interface may be in I2C or SPI format.

[0097] Fig.9A9B is a diagram illustrating the polarization of water molecules 902 in a soil mass 113 caused by the operation of the soil sensor 100 of the present invention. The soil sensor 100 shows a receiver electrode 112a in a receiver dielectric housing 111a and a transmitter electrode 112b in a transmitter dielectric housing 111b, which are placed a fixed distance apart in the soil mass 113. Between the two electrodes is the soil mass 113, which has water molecules 902 present in the soil. The water molecules 902 (H=O=H) are polar molecules and are illustrated with their two hydrogen atoms 902a bonded to their single oxygen atom 902b. Since the hydrogen atoms 902a are distributed around the more positively charged core of the oxygen atom 902b (which causes one end of the molecule to be more positive and the other end to be more negative), an electric dipole is naturally formed. Molecules that are more positive at one end and more negative at the other end form a dipole and are called polar molecules. When exposed to an external electric field, polar molecules align with their dipoles pointing in the direction of the field.

[0098] Fig.9A 1 is a diagram of the random configuration of water molecules 902 when the signal generator has no signal output through the transmitting electrode 112b. The water molecules 902 are randomly oriented and their dipoles are not aligned with any external electric field. Fig.9A In the random orientation shown, the water molecules 902 are not polarized. When the signal generator does not output a signal, the water molecules 902 will remain in the random orientation and the soil mass 113 (which includes the soil and water molecules 902) is in electrostatic equilibrium (ie, they are at the same potential).

[0099] Fig. 9B The structure of the water molecule 902 after the signal generator is activated is shown. The water molecule 902 is aligned with the electric field output by the signal generator. The dipoles of the water molecule 902 are aligned in the direction of the electric field. As a result, the water molecules are aligned, which is called polarization. The polarized water molecule 902 has a hydrogen atom 902a on the transmitter electrode 112b side and an oxygen atom 902b on the receiver electrode 112a side. Although the water molecule 902 is polarized, there is no charge movement between the electrodes of the soil sensor 100. Therefore, the soil sensor 100 operates in an electrostatic manner (no current flows between the electrodes).

[0100] Once the QVAR of the soil sensor 100 is turned on, the QVAR will measure the change in charge present in the soil mass 113 due to the polarization effect. In other words, the QVAR detects the potential difference between the input pins of its differential input, which is generated by inducing a signal on the receiver electrode 112a due to the polarization of the water molecules 902 present in the soil mass 113. Due to the polarization of the water molecules 902 in the soil mass 113, the induced signal on the receiver electrode 112a is different from the output signal of the transmitter electrode 112b.

[0101] Fig. 10A - Fig. 10B The structures of water molecules 902 are shown with different amounts of water present in a soil mass 113. The figures show the varying amounts of water in a soil mass 113. The polarization of the water molecules 902 is a result of the operation of a soil sensor 100 having a receiver electrode 112a located in a receiver dielectric housing 111a at a fixed distance from a transmitter electrode 112b in a transmitter dielectric housing 111b. Fig. 10A - Fig. 10B Different numbers of polarized water molecules 902 in the soil mass 113 are shown. Fig. 10A A small number of water molecules 902 are shown, Fig. 10B A number of water molecules 902 are shown. Fig. 10A - Fig. 10B The water molecules 902 in are all polarized.

[0102] Fig. 10A The moisture content level is shown as an initial measurement level. In one embodiment, as an example, Fig. 10A The amount of water molecules 902 in the soil mass 113 is shown, which can be related to Figure 4 The moisture content level shown at the mid-baseline 401 soil moisture level is consistent. The measurements made by the soil sensor 100 can output Figure 4 The baseline 401 soil moisture level shown is consistent with the soil moisture level.

[0103] Fig. 10B The moisture content level is shown, which is the fully saturated level of the soil block 113. In one embodiment, as another example, Fig. 10B The amount of water molecules 902 in the soil mass 113 is shown, which can be related to Figure 4 The measurement made by the soil sensor 100 can output the same moisture content level as shown at the soil moisture level 404 in FIG. Figure 4 Soil moisture level 404 is shown as a consistent soil moisture level.

[0104] Example embodiments of the present invention are described below. Other embodiments may also be understood from the overall description and claims filed herein.

[0105] Example 1. A soil sensor includes a signal generator. The soil sensor also includes 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 transmitting electrode embedded in a first dielectric material. The soil sensor also includes a receiver configured to be electrostatically coupled to the transmitter through a channel including soil, the receiver including a charge change (QVAR) electrode embedded in a second dielectric material. The soil sensor also includes a charge change (QVAR) sensor coupled to the QVAR electrode, the QVAR sensor configured to detect a change in charge detected at the QVAR electrode in response to a signal from the signal generator, and output a digital signal including the detected charge. And the soil sensor also includes a processing circuit coupled to the QVAR sensor and configured to determine a moisture level in the channel based on the digital signal.

[0106] Example 2. The soil sensor according to Example 1, further comprising a power supply for supplying power to the processing circuit.

[0107] Example 3. The soil sensor according to one of examples 1 or 2, further comprising a transceiver for transmitting the determined moisture level in the channel and receiving an operation instruction of the signal generator.

[0108] Example 4. The soil sensor according to any one of examples 1 to 3, wherein the processing circuit and the signal generator are disposed in a common waterproof housing.

[0109] Example 5. The soil sensor according to any one of Examples 1 to 4, wherein the processing circuit and the signal generator are packaged in separate waterproof housings and coupled to each other through a waterproof cable.

[0110] Example 6. The soil sensor according to any one of Examples 1 to 5, wherein the first dielectric material and the second dielectric material comprise the same dielectric material.

[0111] Example 7. The soil sensor according to any one of Examples 1 to 6, wherein the first dielectric material and the second dielectric material include polytetrafluoroethylene, polyimide, glass, polyester, or metal oxide.

[0112] Example 8. The soil sensor according to any one of Examples 1 to 7, wherein the first dielectric material and the second dielectric material provide a waterproof seal around the corresponding transmitter electrode and QVAR electrode.

[0113] Example 9. The soil sensor of any one of Examples 1 to 8, wherein the receiver and transmitter electrodes comprise metal areas on a PCB.

[0114] Example 10. The soil sensor of any one of Examples 1 to 9 further comprises a filter for removing noise from a signal detected at the receiver.

[0115] Example 11. A soil moisture detection method includes a transmitter and a receiver of a soil sensor disposed in a soil block. The soil moisture detection method also includes transmitting an output signal from a signal generator through the transmitter. The soil moisture detection method also includes detecting the output signal at a receiver. The soil moisture detection method also includes detecting the output signal at a charge change (QVAR) sensor as a QVAR signal. And the soil moisture detection method also includes processing a digital signal from the QVAR sensor to obtain the moisture content of the soil block.

[0116] Example 12. The soil moisture detection method of Example 11 further includes filtering the digital signal using a filter.

[0117] Example 13. The soil moisture detection method according to one of Examples 11 or 12, wherein the filtering includes removing noise generated by power transmission.

[0118] Example 14. The soil moisture detection method according to any one of Examples 11 to 13 further comprises transmitting the moisture content of the soil block.

[0119] Example 15. The soil moisture detection method according to any one of Examples 11-14, wherein the transmitter comprises a transmitting electrode embedded in a first dielectric material, and the receiver comprises a charge change (QVAR) electrode embedded in a second dielectric material.

[0120] Example 16. The soil moisture detection method according to any one of Examples 11-15, wherein the first dielectric material and the second dielectric material provide a waterproof seal around the respective transmitting electrode and QVAR electrode.

[0121] Example 17. The soil moisture detection method according to any one of Examples 11-16, wherein the first dielectric material and the second dielectric material include polytetrafluoroethylene, polyimide, glass, polyester or metal oxide.

[0122] Example 18. A soil sensor calibration method includes placing a transmitter and a receiver of a soil sensor in a first soil mass. The soil sensor calibration method also includes generating a first soil moisture measurement using the soil sensor. The soil sensor calibration method also includes adding a known volume of water to the soil mass after generating the first soil moisture measurement. The soil sensor calibration method also includes generating a second soil moisture measurement using the soil sensor after adding the water. The soil sensor calibration method also includes determining a moisture content calibration table for the soil based on the first and second moisture measurements.

[0123] Example 19. The method of Example 18 further includes placing a transmitter and a receiver of a soil sensor in a second soil block. The soil sensor calibration method further includes generating a third soil moisture measurement using the soil sensor. And the soil sensor calibration method further includes determining the moisture content of the second block based on the third soil moisture measurement and the moisture content calibration table.

[0124] Example 20. The method of one of examples 18 or 19, wherein the first block and the second block are from the same soil sample.

[0125] Although the present invention has been described with reference to illustrative examples, this description is not intended to be interpreted in a limiting sense. Various modifications and combinations of the illustrative examples and other embodiments of the present invention will be apparent to those skilled in the art, based on the reference specification. Therefore, the appended claims are intended to cover any such modifications or embodiments.

Claims

1. A soil sensor, comprising: 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 transmitting electrode embedded in a first dielectric material; a receiver configured to electrostatically couple to the transmitter through a passage including soil, the receiver comprising a charge change QVAR electrode embedded in a second dielectric material; a charge change QVAR sensor coupled to the QVAR electrode, the QVAR sensor configured to detect a change in charge detected at the QVAR electrode in response to a signal from the signal generator and to output a digital signal including the detected charge; as well as A processing circuit is coupled to the QVAR sensor and is configured to determine a moisture level in the channel based on the digital signal.

2. The soil sensor according to claim 1, further comprising: A power supply is provided to supply power to the processing circuit.

3. The soil sensor according to claim 1, further comprising: A transceiver for transmitting the determined moisture level in the channel and receiving 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 waterproof housing.

5. The soil sensor according to claim 1, wherein the processing circuit and the signal generator are packaged in separate waterproof housings and are connected to each other through a waterproof cable.

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 according to claim 6, wherein the first dielectric material and the second dielectric material include polytetrafluoroethylene, polyimide, glass, polyester or metal oxide.

8. A soil sensor according to claim 1, wherein the first dielectric material and the second dielectric material provide a waterproof seal around the corresponding transmitting electrode and QVAR electrode.

9. The soil sensor of claim 1, wherein the QVAR electrode and the transmitting electrode comprise metal areas on a PCB.

10. The soil sensor according to claim 1, further comprising: A filter is provided for removing noise from a signal detected at the receiver.

11. A soil moisture detection method, comprising: Setting up a soil sensor transmitter and receiver in a patch of soil; transmitting an output signal from a signal generator via the transmitter; detecting the output signal at the receiver; sensing the detected output signal at the charge change QVAR sensor as a QVAR signal; as well as The digital signal from the QVAR sensor is processed to obtain the moisture content of the soil mass.

12. The soil moisture detection method according to claim 11, further comprising: The digital signal is filtered using a filter.

13. The soil moisture detection method according to claim 12, wherein the filtering includes removing noise generated from transmission of electric power.

14. The soil moisture detection method according to claim 11, further comprising transmitting the moisture content of the soil block.

15. The soil moisture detection method according to claim 11, wherein the transmitter comprises a transmitting electrode embedded in a first dielectric material; and Wherein the receiver comprises a charge change QVAR electrode embedded in 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 waterproof seal around the corresponding emitter electrode and the QVAR electrode. 17 . The soil moisture detection method according to claim 15 , wherein the first dielectric material and the second dielectric material comprise polytetrafluoroethylene, polyimide, glass, polyester or metal oxide.

18. A soil sensor calibration method, comprising: placing a transmitter and a receiver of a soil sensor in a first soil mass; generating a first soil moisture measurement using the soil sensor; adding a known volume of water to the soil mass after generating the first soil moisture measurement; generating a second soil moisture measurement using the soil sensor after adding the water; and A moisture content calibration table for the soil is determined based on the first moisture measurement and the second moisture measurement.

19. The method according to claim 18, further comprising: placing a transmitter and a receiver of a soil sensor in a second soil mass; generating a third soil moisture measurement using the soil sensor; as well as The moisture content of the second block is determined based on the third soil moisture measurement and the moisture content calibration table.

20. The method of claim 19, wherein the first block and the second block are from the same soil sample.

Images