WO2019037081A1

WO2019037081A1 - Moisture sensing device

Info

Publication number: WO2019037081A1
Application number: PCT/CN2017/099039
Authority: WO
Inventors: Jing Tian Xi; Chi Lun Mak
Original assignee: Sang Eco System Limited
Priority date: 2017-08-25
Filing date: 2017-08-25
Publication date: 2019-02-28

Abstract

A moisture sensing device (100) comprises a moisture sensing element (102) arranged to detect moisture on a surface of or within a substrate, wherein the moisture sensing element (102) is connected to a communication interface (104) positioned to be in a distal position from the moisture sensing element (102).

Description

MOISTURE SENSING DEVICE

TECHNICAL FIELD

The invention relates to a moisture sensing device and particularly, although not exclusively, to a radio-frequency identification (RFID) -based moisture sensing device operable to determine moisture level in soil.

BACKGROUND

Water is essential for nurturing and growing plants as it is necessary for plants to carry out photosynthesis. However, too much water or too little water could be detrimental to plant growth.

Overwatering of plants, which leads to waterlogged soil, would cut off air supply to the roots of the plants, as well as to the microorganisms in the soil for maintaining the health of the plants. The roots would be damaged, resulting in poor nutrients and water supply to the plants, and eventually would lead to death of the plants. On the other hand, insufficient water to plants prevents the plants from carrying out necessary photosynthesis for creating food. In the absence of adequate nutrients, the plants would no longer be able to grow healthily.

For this reason, it is important to water the plants such that the moisture level in the soil is always at a suitable amount.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided a moisture sensing device comprising a moisture sensing element arranged to detect moisture on a surface of or within a substrate, wherein the moisture sensing element is connected to a communication interface positioned to be in a distal position from the moisture sensing element.

In an embodiment of the first aspect, the moisture sensing element is connected to the communication interface via a transmission channel.

In an embodiment of the first aspect, the moisture sensing element includes a capacitive arrangement wherein a capacitance of the capacitive arrangement is arranged to vary according to a moisture level proximate to the capacitive arrangement.

In an embodiment of the first aspect, the capacitive arrangement includes a pair of capacitively-coupled conductors.

In an embodiment of the first aspect, the capacitive arrangement comprises an interdigital capacitor.

In an embodiment of the first aspect, the interdigital capacitor comprises conductive fingers arranged opposite to each other.

In an embodiment of the first aspect, the transmission channel is arranged to transmit a signal indicative of a capacitance of the capacitive arrangement to the communication interface.

In an embodiment of the first aspect, a change in the capacitance of the capacitive arrangement is arranged to cause a change in input impedance at the communication interface.

In an embodiment of the first aspect, the communication interface includes: a communication circuit arranged to interface with the moisture sensing element； and an antenna arranged to communicate with an external electronic reader.

In an embodiment of the first aspect, the communication interface is arranged to communicate with the external electronic reader through radio-frequency waves. In an embodiment of the first aspect, the antenna is arranged to communicate with the external electronic reader through radio-frequency waves.

In an embodiment of the first aspect, the communication circuit is arranged to communicate a signal indicative of a capacitance of the capacitive arrangement to the external electronic reader.

In an embodiment of the first aspect, the capacitance is measured by monitoring a resonant frequency at the communication interface.

In an embodiment of the first aspect, the resonant frequency is arranged to vary with a change in input impedance at the communication interface.

In an embodiment of the first aspect, the resonant frequency is arranged to vary with a capacitance of the capacitive arrangement.

In an embodiment of the first aspect, the antenna comprises a patch antenna having a patch radiator and a ground plane.

In an embodiment of the first aspect, the patch radiator is comprises an array of vias at one end, and is arranged to connect with the communication circuit at the other end.

In an embodiment of the first aspect, the antenna comprises a T-match dipole.

In an embodiment of the first aspect, the T-match dipole comprises a dipole and an embedded T-match structure.

In an embodiment of the first aspect, the communication interface is arranged to be energized by the external electronic reader.

In an embodiment of the first aspect, the communication interface is arranged to generate a backscattered signal when energized.

In an embodiment of the first aspect, the resonant frequency, signal strength, and read range can be measured from the backscattered signal for moisture level detection.

In an embodiment of the first aspect, the backscattered signal is arranged to be received by the external electronic reader.

In accordance with a second aspect of the invention, there is provided a moisture sensing device comprising: a moisture sensing element operable to determine a moisture level of a substrate； a transmission element operably connected with the moisture sensing element； and a communication interface operably connected with the moisture sensing element through the transmission element, the communication interface being arranged for communication of a signal indicative of a moisture level of the substrate to an external electronic reader. The moisture sensing element may be operable to provide a measurement indicative of the moisture level of the substrate. The communication interface may directly communicate the measurement to the external electronic reader, or alternatively, may process the measurement and generate a signal indicative of the measurement to be provided to the external electronic reader.

In one embodiment of the second aspect, the moisture sensing element is arranged to be at least partly embedded in the substrate.

In one embodiment of the second aspect, the moisture sensing element is arranged to provide a measurement indicative of the moisture level of the substrate. Preferably, the measurement is arranged to vary linearly with the detected moisture level.

In one embodiment of the second aspect, the moisture sensing element comprises a capacitive arrangement operable to provide a capacitance value indicative of the moisture level of the substrate.

In one embodiment of the second aspect, the capacitive arrangement comprises an interdigital capacitor.

In one embodiment of the second aspect, the transmission element comprises a shielded transmission line.

In one embodiment of the second aspect, the transmission element comprises a planar transmission line.

In one embodiment of the second aspect, the communication interface comprises a wireless communication interface.

In one embodiment of the second aspect, the communication interface comprises an RFID tag with an antenna and a circuit chip.

In one embodiment of the second aspect, the RFID tag is a passive RFID tag.

In one embodiment of the second aspect, the antenna comprises a T-match dipole.

In another embodiment of the second aspect, the antenna comprises a patch antenna. Preferably, the patch antenna comprises an array of vias at one end.

In one embodiment of the second aspect, the moisture sensing device is arranged to receive a signal from the external electronic reader for activation to transmit a backscattered signal to the external electronic reader, the backscattered signal including the signal indicative of the moisture level of the substrate.

In one embodiment of the second aspect, the external electronic reader is arranged to determine a moisture level of the substrate based on at least one of: resonant frequency, signal strength, and read range of the signal received from the communication interface such as the RFID tag.

In one embodiment of the second aspect, the substrate comprises soil.

In accordance with a third aspect of the invention, there is provided a plant watering system comprising the moisture sensing device of the first aspect.

In accordance with a fourth aspect of the invention, there is provided a plant watering system comprising the moisture sensing device of the second aspect.

In accordance with a fifth aspect of the invention, there is provided a moisture sensing system comprising the moisture sensing device of the first aspect and an external electronic reader arranged to communicate with the moisture sensing device.

In accordance with a sixth aspect of the invention, there is provided a moisture sensing system comprising the moisture sensing device of the second aspect and an external electronic reader arranged to communicate with the moisture sensing device.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a functional block diagram of a system including a moisture sensing device in accordance with one embodiment of the invention and an associated electronic reader；

Figure 2 is a schematic diagram of the moisture sensing device in accordance with one embodiment of the invention and an associated electronic reader；

Figure 3 is a schematic diagram of a capacitive coupling in the moisture sensing element of Figure 2；

Figure 4 illustrates an exemplary application of a moisture sensing device in accordance with one embodiment of the invention for measuring moisture level in the soil of a plant；

Figure 5A is a top view of a prototype of the moisture sensing device of Figure 2；

Figure 5B is an enlarged view of the moisture sensing element of Figure 5A；

Figure 6A is a top view of a second prototype of the moisture sensing device with a patch antenna.

Figure 6B is a bottom view of the moisture sensing device of Figure 6A.

Figure 7A is an experimental setup in which the moisture sensing device of Figure 5A is used for measuring moisture level of soil in a plant；

Figure 7B is an enlarged view of the moisture sensing device of Figure 6A；

Figure 8 is a graph showing a relationship between a forward read range of the moisture sensing device of Figure 6A and the frequency for different amount of water in the soil (nth pouring, n ＝ 0 (before) , 1, 2, 3, 4) obtained from an experiment performed using the setup in Figure 6A； and

Figure 9 is a graph showing a relationship between a forward read range of the moisture sensing device of Figure 6A and the frequency for different amount of water in the soil (nth pouring, n ＝ 4, 5, 6, 7, 8, 9) obtained from an experiment performed using the setup in Figure 6A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Figure 1, there is shown a functional block diagram of a moisture sensing device 100 comprising a moisture sensing element 102 arranged to detect moisture on a surface of a substrate or within the substrate, wherein the moisture sensing element 102 is connected to a communication interface 104 positioned to be in a distal position from the moisture sensing element 102. Preferably, the moisture sensing element 102 is connected to the communication interface 104 via a transmission channel 110. The transmission channel is arranged to further transmit a signal indicative of the moisture level measured at the moisture sensing element 102 to the communication interface 104.

In this embodiment, the communication interface 104 includes a communication circuit 106 and an antenna 108. The communication circuit 106 may be a circuit chip, and it is arranged to interface with the moisture sensing element 102. The antenna 108 may be arranged to communicate, actively or passively, with an external electronic reader 112. The communication is preferably to be wireless, but may also be wired. In one embodiment, the communication interface 104 is arranged to communicate with the external electronic reader 112 using radio-frequency waves. In alternative embodiments, the communication interface 104 may communicate with the external electronic reader 112 using electromagnetic waves of other frequency ranges.

In operation, the external electronic reader 112 radiates radio-frequency signals towards the antenna 108. The antenna 108 then extracts energy from the radio-frequency waves emitted by the external electronic reader 112. The energy received by the antenna 108 further energises the communication circuit 106, which generates a signal that is subsequently transmitted back to the antenna 108. The signal contains information related to the detected moisture level. The signal is then transmitted from the antenna 108 to the external electronic reader 112, using radio-frequency waves. In this way, a signal indicative of the moisture level can be transmitted to the external electronic reader 112.

In one exemplary application, the user can insert the moisture sensing element 102 of the moisture sensing device 100 into a substrate so that the moisture sensing element 102 at least partly contacts the substrate, and the communication interface 104 is exposed to the environment, without contacting the substrate, for receiving and transmitting signals. An external electronic reader 112 can then be brought near the moisture sensing device 100 to radiate radio-frequency waves towards the moisture sensing device 100 for energizing the moisture sensing device 100. When energized, the moisture sensing device 100 detects the moisture level, then generates and transmits a signal indicative of the detected moisture level to the external electronic reader 112. The external electronic reader 112 may then process the signal to determine the moisture level and optionally perform further analysis.

Referring now to Figure 2 and 3, there is shown a moisture sensing device 200 in one embodiment of the invention. The moisture sensing device 200 includes a moisture sensing element 202 for detecting moisture level, a transmission channel 212 for transmitting signals from the moisture sensing element 202, and a communication interface 206 for communicating with an external electronic device 214. The moisture sensing element 202 is substantially rectangular, but it may be shaped differently in other embodiments. For example, in other embodiments, the moisture sensing element 202 may be trapezoidal, triangular, circular, elliptical, polygonal, etc. The moisture sensing element 202 may be surrounded by a casing that is arranged such that various electronic components of the moisture sensing device 200 are isolated from the substrate and other outside environment in which liquid may be present, to protect the moisture sensing device 200 against water and dust which may induce error when measuring moisture level.

The moisture sensing element 202 further includes a

capacitive arrangement

204, 300. The capacitance of the

capacitive arrangement

204, 300 is dependent on a moisture level proximal to the

capacitive arrangement

204, 300. The

capacitive arrangement

204, 300 comprises microstrip lines, preferably formed by a pair of capacitively-coupled conductors 302. The capacitance of the

capacitive arrangement

204, 300 is changed based on a moisture level of the substrate in contact with the moisture sensing element 202. In other words, by determining the capacitance, the moisture level can be determined. Preferably, the changes are proportional or vary linearly with each other.

In one embodiment, the

capacitive arrangement

204, 300 may comprise a interdigital capacitor, formed by a pair of

conductors

302A, 302B (e.g., microstrip lines) comprising

conductive fingers

304A, 304B arranged opposite to each other. A first electrode with a first polarity is connected to one of the conductor 302A； a second electrode with a second, opposite polarity is connected to another conductor 302B. The conductive fingers 304A of the conductor 302A complement the conductive fingers 304B of the conductor 302B, with the

conductive fingers

304A, 304B arranged adjacently. In one embodiment, the conductor 302A comprises four conductive fingers 304A and the conductor 302B comprises three conductive fingers 304B. Each finger 304B of the conductor 302B is respectively interposed between adjacent fingers 304A of the conductor 302A. A narrow gap is arranged between every two

adjacent fingers

304A, 304B. In other embodiments, the number of conductors and/or the number of fingers may vary. For example, there may be two conductive fingers 304A in the conductor 302A and one conductive finger 304B in the conductor 302B； three conductive fingers 304 in the conductor 302A and two conductive fingers 304 in the conductor 302B； etc. Typically, the width of the gap between adjacent fingers is largely the same. The conducting

fingers

304A, 304B implement capacitive coupling through the gaps. This configuration is advantageous in that in a compact planar footprint, the effective capacitance and the sensitivity of the moisture sensing device 200 are increased.

Referring back to Figure 2, the transmission channel 212 connects the moisture sensing element 202 with the communication interface 206, and it is further arranged to transmit a signal indicative of the capacitance at the moisture sensing element 202 to the communication interface 206. Preferably, the transmission channel 212 is shielded such that it transmits a signal indicative of only the capacitance at the moisture sensing element 202 but not anywhere else. This ensures that the detected moisture level is at the targeted area. It is also advantageous in that the electronic components in the transmission channel 212 can be protected against water and dust. In one embodiment, the transmission channel 212 may be a transmission line in the form of a coaxial cable. The coaxial cable may comprise of four layers: an innermost layer of a thin conducting wire for transmitting signals without interference, a second, dielectric layer made of an insulating material surrounding the conducting wire, a third, shield layer made of metal foil or braided copper mesh surrounding the dielectric layer, and an outer insulating jacket. In some other embodiments, any shielded transmission channel could be used, and the inner layer may be an optical fibre, a copper wire, etc.

In a preferred embodiment, the communication interface 206 comprises a radio-frequency identification (RFID) tag. Preferably, the RFID tag is a passive RFID tag that does not have a local power source and is arranged to receive energy from an external electronic reader in the form of electromagnetic energy. The use of passive RFID is advantageous in that it is cheap and requires less maintenance such as changing battery. In alternative embodiment, an active RFID tag may also be used.

As shown in Figure 2 and 3, the communication interface 206 includes a communication circuit 208 and an antenna 210. The communication circuit 208 is arranged to interface with the moisture sensing element 202. In one embodiment, the communication circuit is arranged to transmit a signal indicative of the capacitance of the capacitive arrangement (and hence the detected moisture level proximate to the capacitive arrangement) . The capacitance of the moisture sensing element 202 may be related to the input impedance of the communication circuit 208 such that when the capacitance is changed the input impedance is accordingly changed. In one example, by detecting the input impedance at the communication circuit 208, the capacitance of the moisture sensing element 202 (and hence the detected moisture level proximate to the capacitive arrangement) can be determined.

The antenna 210 may be arranged to receive and transmit signals for communication with an external electronic reader 214. In one embodiment, the antenna 210 comprises a T-match dipole. The T-match dipole comprises a dipole and an embedded T-match structure implemented by striplines or microstrip lines. In another embodiment, the antenna may be a patch antenna comprising a patch radiator and a ground plane. Other types of antenna can also be used in other embodiments. In some applications, a T-match dipole can adopt to an effective wavelength change when the moisture sensing device 200 is used to measure moisture level in objects made of different materials. Such change results in a better readability and higher sensitivity in some applications.

The communication interface 206 is arranged to communicate with the external electronic reader 214 through radio-frequency waves. The external electronic reader 214 radiates signals towards the antenna 210, which then extracts energy from the radio-frequency waves. The energy received by the antenna 210 energises the communication circuit 208, which subsequently generates and transmits a signal back to the antenna 210. The signal generated by the communication circuit 208 is a backscattered signal. The backscattered signal preferably includes a signal indicative of the detected moisture level. The backscattered signal is then transmitted by the antenna 210 to the external electronic reader 214 for moisture level detection. The backscattered signal may comprise one or more of the following parameters and information: resonance frequency, signal strength, and read range. The resonance frequency varies with the input impedance at the communication interface 206, which varies in proportion to the capacitance at the moisture sensing element 202. In other words, the resonance frequency varies with the capacitance at the moisture sensing element 202. Therefore, by measuring the resonant frequency from the backscattered signal, the detected moisture level can be determined.

In some applications, a user may wish to implement intelligent plant watering systems to increase yields and quality of crops and plants. In these cases, it is necessary to detect the moisture level of the soil efficiently and accurately. Three requirements are particularly important for a moisture sensing device suitable for this purpose. The first requirement is data accuracy. In some cases, the sensing element measures moisture level outside of the targeted area due to the configuration of the device, or it may wrongly interpret the raw data. These can lead to error. The second requirement is the use of wireless communication. Receiving and transferring information and data wirelessly enables faster deployment and easier management. The third requirement is cost. A low production cost of moisture sensing device is desired as this makes employing the moisture sensing device economical for both industrial use and domestic use. These three requirements are of paramount importance in the development of a moisture sensing device.

Figure 4 shows an exemplary application in which a moisture sensing device 400 is used to measure the moisture level of the soil in a flower pot. In this example, the transmission channel 406 is a shielded transmission line, which allows the signal indicative of the capacitance of the moisture sensing element 402 to be transmitted to the communication interface 404 with minimal loss and interference. The moisture sensing element 402 can be inserted into any target sensing area at any desired depth for pinpoint sensing. In this example, the moisture sensing element 402 is inserted to the targeted sensing area near the root of a plant, in order to measure the moisture level at that particular area.

In this embodiment, the moisture sensing device 400 is a passive RFID device, and it relies on an external energy source for activation. After placing the moisture sensing element 402 at the targeted sensing area, an external electronic reader 408 is brought near to the moisture sensing device 400. The external electronic reader 408 transmits radio-frequency waves to the communication interface 404 of the moisture sensing device 400, and the moisture sensing device 400 is energised upon receiving the radio-frequency waves. A signal indicative of the capacitance at the moisture sensing element 402 is transmitted along the transmission channel 406 to the communication interface 404 to change the input impedance at the communication interface 404. The change in the input impedance leads to change in the parameters of the backscattered signal transmitted at the communication interface 404 to the reader 408. The backscattered signal is then received by the external electronic reader 408, which then analyses the parameters of the backscattered signal to determine the detected moisture level of the soil at the targeted sensing area.

Figure 5A and 5B show a prototype of a moisture sensing device 500 in one embodiment of the invention. The moisture sensing element 502 is connected to the communication interface 506 via a transmission channel 512. Specifically, the moisture sensing element 502 is connected to the communication circuit 508 at the communication interface 506. In this embodiment, the moisture sensing element 502 is rectangular, and is 1.3cm in length and 1.9cm in width. A capacitive arrangement 504 is arranged to be part of the moisture sensing element 502. The capacitive arrangement 504 comprises an interdigital capacitor, with conducting fingers arranged adjacently in turn with a narrow gap in between. This arrangement provides a larger surface contact area with the substrate, thus increasing the effective capacitance and sensitivity of the device. The outer layer of the moisture sensing element 502 may be made of plastic or other insulating material, such that moisture is only in contact with the capacitive arrangement, and the electronic components inside the moisture sensing element 502 is protected against water and dust. The transmission channel 512 comprises a shielded coaxial cable for transmitting a signal indicative of a capacitance at the moisture sensing element 502 to the communication interface 506. The communication interface 506 comprises a communication circuit 508 and an antenna 510. The antenna 510 is a T-match dipole comprising a dipole and an embedded T-match structure.

Figure 6A and 6B show another prototype of a moisture sensing device 600. In this preferred embodiment, the moisture sensing device 600 is elongated with a moisture sensing element 602 at one end, and a communication interface 606 at the other end, connected by a transmission channel 612 in between. The moisture sensing element 602 is trapezoidal, with a capacitive arrangement 604 for detecting moisture level at a targeted area. The capacitive arrangement 604 comprises an interdigital capacitor, with conducting fingers arranged adjacently in turn with a narrow gap in between. The capacitive arrangement 604 is positioned at the end of the moisture sensing element 602, and is disposed away from the communication interface 606, such that the capacitive arrangement 604 is readily available to be in contact with the surrounding substrate for detecting moisture level.

The moisture sensing element 602 can be inserted into a substrate, such as soil, for detecting its moisture level. The transmission channel 612 connecting the moisture sensing element 602 and the communication interface 606 transmits a signal indicative of the detected signals to the communication interface 606. The communication interface 606 then further communicates a signal indicative of the detected moisture level to an external electronic reader, for example, for data collection and analysis. In this embodiment, the transmission channel 612 is a shielded channel with an outer insulating layer. The outer insulating layer ensures that signals can be transmitted from the moisture sensing element 602 to the communication interface 606 with minimal loss and interference.

In this embodiment, the communication interface 606 comprises a communication circuit 608, in the form of a circuit chip, and an antenna 610. The antenna 610 is a patch antenna, which in this example, is substantially rectangular. In some other examples, the patch antenna may be squared, circular, elliptical, etc. The patch antenna includes a patch radiator and a ground plane. The patch radiator includes a flat sheet or “patch” of conductor or transmission line arranged on the ground plane. An array of vias is arranged at one end of the patch radiator such that the patch radiator can be shorted to a quarter wavelength in length. The other end of the patch radiator is connected to a communication circuit 608. This arrangement of the patch antenna is advantageous in that the overall length of the device can be reduced. Also, influence of the substrate on the sensing performance can be minimized, such that the antenna does not have to be elevated from the substrate surface by a large extent.

Figure 7A and 7B show an experimental setup whereby the moisture sensing device 700 is used to measure the moisture level of the soil in a pot. As shown in the Figures, the pot is placed above a spacer, whereas an external electronic reader 706 is placed below the spacer. A moisture sensing device 700 is inserted into the soil of the pot, with the moisture sensing element (not shown) being placed at the targeted sensing area, while the communication interface 702 and at least part of the transmission channel 704 are above the soil, exposed to the external environment. After being energised by the external electronic reader 706, the moisture sensing device 700 can be used for moisture level measurement.

In the experiment, water was poured into the pot several times, adding a fixed amount of water each time. The capacitance of the capacitive arrangement of the moisture sensing element varied proportionally with the moisture level in the soil. A signal indicative of the capacitance was transmitted along the shielded transmission channel 704 to the communication interface 702. The input impedance changes according to the change in capacitance. The change in capacitance also causes changes in the resonance frequency in the backscattered signal. By measuring the backscattered signal emitted from the communication interface 702, moisture level can be determined.

Figure 8 and 9 show experimental results of a water-pouring experiment. Initially, before any pouring, the peak resonate frequency was at 912Hz and the forward read range was 9.8m. When more water was poured into the pot, a decreasing trend in resonant frequency was observed, with a leftward shift of the read range curves, up to the 4^th pour (of water) as a result of a change in capacitance (i.e., a change in moisture level detected at the targeted sensing area) . The forward read range also dropped slightly from 9.8m to 7.2m. This was due to signal power attenuation as the soil-and-water compromises the power transfer and the radiation efficiency. After the 4^th pour, further pours only resulted in a drop in the forward read range. This may be caused by the saturation of the capacitive arrangement of the moisture sensing element. The forward read range from the 4^th pour to the 9^th pour decreased from 7.2m to 3.5m, while the resonant frequency remained unchanged (or changed insignificantly) .

Accordingly, the data from the moisture sensing device can be analysed for determining moisture level of the substrate. Specifically, the shift in resonant frequency as observed reflected a change in capacitance of the moisture sensing element. After the 4^th pour, the capacitors were saturated, and a change in moisture level was reflected by the drop in forward read range. Preferably, the moisture sensing device is calibrated according to the application for more accurate moisture level detection.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.

Claims

A moisture sensing device comprising:

a moisture sensing element arranged to detect moisture on a surface of or within a substrate, wherein the moisture sensing element is connected to a communication interface positioned to be in a distal position from the moisture sensing element.
The moisture sensing device in accordance with claim 1, wherein the moisture sensing element is connected to the communication interface via a transmission channel.
The moisture sensing device in accordance with claim 1 or 2, wherein the moisture sensing element includes a capacitive arrangement, wherein a capacitance of the capacitive arrangement is arranged to vary according to a moisture level proximate to the capacitive arrangement.
The moisture sensing device in accordance with claim 3, wherein the capacitive arrangement includes a pair of capacitively-coupled conductors.
The moisture sensing device in accordance with claim 3 or 4, wherein the capacitive arrangement is an interdigital capacitor.
The moisture sensing device in accordance with claim 5, wherein the interdigital capacitor comprises conductive fingers arranged opposite to each other.
The moisture sensing device in accordance with claim 3, wherein the transmission channel is arranged to transmit a signal indicative of a capacitance of the capacitive arrangement to the communication interface.
The moisture sensing device in accordance with claim 7, wherein a change in the capacitance of the capacitive arrangement is arranged to cause a change in input impedance at the communication interface.
The moisture sensing device in accordance with any one of the preceding claims, wherein the communication interface includes:

a communication circuit arranged to interface with the moisture sensing element； and

an antenna arranged to communicate with an external electronic reader.
The moisture sensing device in accordance with claim 9, wherein the antenna is arranged to communicate with the external electronic reader through radio-frequency waves.
The moisture sensing device in accordance with claim 9, wherein the communication circuit is arranged to communicate a signal indicative of a capacitance of the capacitive arrangement to the external electronic reader.
The moisture sensing device in accordance with claim 11, wherein the capacitance is measured by monitoring a resonant frequency at the communication interface.
The moisture sensing device in accordance with claim 12, wherein the resonant frequency is arranged to vary with an input impedance at the communication interface.
The moisture sensing device in accordance with claim 12, wherein the resonant frequency is arranged to vary with a capacitance of the capacitive arrangement.
The moisture sensing device in accordance with claim 9, wherein the antenna comprises a patch antenna having a patch radiator and a ground plane.
The moisture sensing device in accordance with claim 15, wherein the patch radiator comprises an array of vias at one end, and is arranged to connect with the communication circuit at the other end.
The moisture sensing device in accordance with claim 9, wherein the antenna comprises a T-match dipole.
The moisture sensing device in accordance with claim 17, wherein the T-match dipole comprises a dipole and an embedded T-match structure.
The moisture sensing device in accordance with any one of the preceding claims, wherein the communication interface is arranged to be energized by an external electronic reader for generation of a backscattered signal to be received by the external electronic reader.
The moisture sensing device in accordance with claim 19, wherein resonant frequency, signal strength, and read range can be determined from the backscattered signal for moisture level detection.