DETECTION DEVICE AND READER FOR MEASURING THE AMOUNT OF WATER CONTENT IN BUILDING STRUCTURES

Abstract

The apparatus for detecting moisture in a building structure comprises at least one inductance element; at least one fixed capacitance element configured not to have a change in capacitance although the moisture is present in the building structure; and

Description

TECHNICAL FIELD

The present invention relates to a technique for measuring wetness contained in a building structure. The present invention relates to a technology for measuring wetness in a building material and informing a user of the measurement result in order to determine whether the strength of a cement-based building material is properly maintained.

BACKGROUND ART

Cement is widely used as a building material because it is inexpensive and has excellent compressive strength. cement-based building materials include, for example, cement paste (cement and water), cement mortar (cement and fine aggregate (sand)), concrete (cement and gravel), depending on the formulation. Chemical or non-chemical additives such as fibers may be added to improve the properties of cement-based materials.

While this specification describes concrete, for example, the present invention applies equally to all materials based on cement as well as concrete.

The amount of moisture and strength of the concrete are changed by the hydration reaction of the cement. If we know the amount of moisture in the concrete by using the relation between the compressive strength and the amount of moisture, we can accurately estimate the compressive strength of the concrete.

Since the hydration reaction of cement generates heat, the compressive strength of concrete can be estimated indirectly by measuring the temperature of the concrete. However, when the ambient temperature is low, the speed of the hydration reaction may be slowed, and the measured temperature of concrete is directly affected by the ambient temperature. In addition, the measured value of temperature varies depending on the measurement location, therefore, it is difficult to accurately estimate the compressive strength of concrete using temperature.

Another method used in many construction sites defines and uses a target of concrete curing strength (ex) 7-days concrete curing strength, 28-days concrete curing strength). When concrete is placed, test specimens are made, and the time it takes for the strength of the specimen to reach the target of concrete curing strength is estimated. In the case of using such a method, a problem occurs in that the estimated value of the time to reach the target of concrete curing strength is incorrect due to changes in weather, etc.

In addition, it is possible to estimate the compressive strength of concrete using the speed at which the S-wave and P-wave of sound waves are transmitted within the concrete, and the ratio at which S- and P-waves are attenuated in the concrete, but the generation and measurement of sound waves is difficult.

As will be described in detail below, embodiments of the present invention have the advantage of not being greatly affected by changes in surrounding environment and location.

DETAILED DESCRIPTION OF THE INVENTION

Technical Problem

This invention can reduce the size of the device and reduce the manufacturing cost by supplying wireless power without its own power to measure the amount of moisture in the building structure.

This invention provides a device with a relatively simple structure without a switch structure because it determines a change in resonance frequency based on a change in capacitance of a capacitor due to moisture in a building structure.

Embodiments of the inventive concept may provide a detection device which has a structure that allows a narrow frequency sweep range for resonant frequency detection, and an a detection reader usable together with the moisture detection device.

Technical Solution

According to an exemplary embodiment, a moisture detection device may include at least one inductance element, at least one fixed capacitance element configured not to have a change in capacitance although the moisture is present in the building structure, and at least one variable capacitance element configured to be electrically connected with the at least one fixed capacitance element and have a change in capacitance when the moisture is present in the building structure. At least one first resonant frequency may be determined based on the at least one inductance element, the at least one fixed capacitance element, and the at least one variable capacitance element.

The at least one variable capacitance element may include an absorber that absorbs the moisture to change a capacitance of the at least one variable capacitance element and conductors separated by the absorber in between the conductors.

In addition, the at least one variable capacitance element may further include at least one insulating layer between the absorber and the at least one conductor to prevent the conductors from being directly exposed to the moisture absorbed by the absorber. In this case, the insulating layer may be present irrespective of whether the absorber is present or how the absorber is arranged.

The at least one variable capacitance element may have a change in capacitance, when the moisture is present in the building structure. At least one second resonant frequency may be determined based on the at least one inductance element, the at least one fixed capacitance element, and the at least one variable capacitance element, the capacitance of which is changed. The at least one first resonant frequency and the at least one second resonant frequency may be different from each other.

The moisture detection device may further include at least one terminal configured to be exposed to the outside of the building structure; wherein the first resonance frequency and the second resonance frequency are measured through the at least one terminal.

The moisture detection device may further include at least one inductor configured to be induction-coupled to at least one of the inductance element; wherein the at least one terminal is electrically wired with the at least one inductor.

According to an exemplary embodiment, a moisture detection reader may include a power supply unit that generates a first alternating magnetic field, a frequency of which is changed to induce an electric current in the moisture detection device, a sensor unit that senses a parameter associated with a second alternating magnetic field generated by the induced electric current in the moisture detection device, a control unit that determines whether moisture is present, based on the parameter associated with the second alternating magnetic field, the parameter being sensed by the sensor unit, and an output unit that notifies a user whether the moisture is present.

The power supply unit may generate the first alternating magnetic field, the frequency of which is changed within a frequency band including at least one first resonant frequency and at least one second resonant frequency.

The parameter may be the amplitude of an induced current for each frequency, the amplitude of or an induced voltage for each frequency, or impedance for each frequency.

The control unit may determine a resonant frequency based on the value of the parameter and may compare the resonant frequency with at least one first resonant frequency or at least one second resonant frequency to determine whether the moisture is present.

The control unit may determine at least one resonant frequency before the moisture is present and at least one resonant frequency after the moisture is present, based on a value of the parameter, and may determine whether the moisture is present, based on the at least one resonant frequency before the moisture is present and the at least one resonant frequency after the moisture is present.

The moisture detection reader may further include a connector configured to be connected to at least one terminal included in the moisture detection device.

Advantageous Effects of the Invention

The moisture detection device according to the inventive concept may receive wireless power without the necessity of having its own power supply to have a small size and have low unit cost of manufacture.

The moisture detection device according to the inventive concept may determine a change in resonant frequency before and after discharge of moisture based on a change in capacitance of a capacitor (particularly a variable capacitor) due to moisture in the building structure to have a relatively simple structure without a switch structure.

The moisture detection device according to the inventive concept and the moisture detection reader usable together with the moisture detection device may have a structure capable of narrowing a frequency sweep range for measuring a resonant frequency.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing illustrating a moisture detection device and a moisture detection reader according to an embodiment;

FIG. 2 is an example of a graph illustrating a parameter value sensed by a sensor unit of a moisture detection reader,

FIG. 3 is a drawing illustrating a conventional moisture detection device;

FIG. 4 is an example illustrating a moisture detection device according to an embodiment;

FIG. 5 is another example illustrating a moisture detection device according to an embodiment;

FIG. 6 is another example illustrating a moisture detection device according to an embodiment;

FIGS. 7 to 13 are drawings illustrating the structures of capacitance elements;

FIG. 14 illustrates an embodiment of using an interdigital capacitor shown in FIG. 13 as a variable capacitance element;

FIG. 15 illustrates an equivalent circuit for an embodiment shown in FIG. 14;

FIG. 16 illustrates an embodiment of using parasitic capacitance of an inductor as a variable capacitance element; and

FIG. 17 illustrates an equivalent circuit for an embodiment shown in FIG. 16.

FIG. 18 illustrates a moisture content measuring device and a moisture content measuring reader including a wire to measure the resonance frequency of the moisture content measuring device.

BEST MODE

Hereinafter, a description will be given in detail of a specific embodiment among various embodiments of the inventive concept with reference to the accompanying drawings. However, this specific embodiment is restricted or limited to the inventive concept. Like reference numerals indicates like components without regard to denotations of the drawings, and a duplicated description will be omitted.

Embodiments of the inventive concept are applicable to technologies of detecting moisture present in a building structure and are not always limited to such technologies. In this case, those skilled in the art may easily derive technologies of detecting various materials from the technical scope of the inventive concept. For example, embodiments of the inventive concept are applicable to detecting whether any material having various forms, such as a liquid, a gas, and a solid, is present. Hereinafter, an embodiment of the inventive concept is exemplified as a target material is moisture present in the building structure.

FIG. 1 is a drawing illustrating a moisture detection device and a moisture detection reader according to an embodiment.

Referring to FIG. 1, a moisture detection device 100 may include a resonant circuit 110. The a moisture detection device 100 may be inserted into a building structure such as concrete formed of cement or the like. The resonant circuit 110 may include an inductance element 131, a fixed capacitance element 132, and a variable capacitance element 133.

When moisture is present in a building structure, the variable capacitance element 133 may have a change in capacitance. To this end, an absorber (not shown) which absorbs the moisture may be present between two conductors. That the absorber is present between the two conductors may mean that the absorber is located in a place where the absorber has an influence on the capacitance formed by the two conductors. In other words, that the absorber is present between the two conductors may include when the absorber is present around each conductor and is able to have an influence on the capacitance as well as when the absorber is present in a space between the conductors.

When the inductance element 131 is implemented in practice, a capacitance component (e.g., a parasitic capacitance element) is present in the inductance element 131. Because permeability which has an influence on an inductance of the inductance element 131 is a variable which is relatively less affected by moisture, although moisture is located near the inductance element, the inductance changes relatively less, but a capacitance of a capacitance component changes to the point of being unable to ignore it as permittivity is changed when the moisture is present near the capacitance component. To take advantage of the fact, instead of regarding the variable capacitance component that occurs in practical implementation of an inductance element 131 (e.g., a parasitic capacitance component) as an extra element in the design/arrangement, the variable capacitance component can be allowed to play a role as a variable capacitance element 133.

In this case, in a process of designing a specific element, an embodiment of the inventive concept may allow the element to have desired capacitance and inductance. For example, by intentionally structuring a conductor included in the specific element, an embodiment of the inventive concept may allow the element to have desired capacitance and inductance.

In the specification, the variable capacitance element 133 is defined as the term including a parasitic capacitance component in such a design.

Although the fixed capacitance element 132 is designed to be disposed on a location which is nearly unaffected by moisture and have a structure for minimizing an influence of moisture, or is waterproofed or disposed to be nearly unaffected by moisture, the capacitance of the fixed capacitance element may change minutely due to surrounding environments such as human fluid, humidity, and even moisture. Herein, in the specification, for convenience of description, it is described that a subtle change in capacitance of the fixed capacitance element is excluded and that the fixed capacitance element does not have a change in capacitance due to moisture.

The number of inductance elements and capacitance elements may be different from that shown in FIG. 1. Because there can be a variety of combinations of inductance elements and capacitance elements to obtain a desired resonant frequency, the number of inductance elements and capacitance elements may be varied according to a design.

The moisture detection reader 140 may include a power supply unit 150, a sensor unit 160, a control unit 170, and an output unit 180. It is shown that the moisture detection reader 140 shown in FIG. 1 includes the power supply unit 150, the sensor unit 160, the control unit 170, and the output unit 180, but at least one of the power supply unit 150, the sensor unit 160, the control unit 170, and the output unit 180 may be separated as a separate module. For example, the power supply unit 150 may be configured as a module separated from the sensor unit 160, the control unit 170, and the output unit 180.

The power supply unit 150 may allow an electric current to flow in a coil to generate a first alternating magnetic field 191 having a specific frequency band. The frequency band may be set to a band including a resonant frequency of the resonant circuit 110. The alternating magnetic field is a magnetic field produced by an alternating current (AC) that flows in a coil, and the magnitude and the direction change in time. A sinusoidal wave may flow in a coil to generate an alternating magnetic field.

The first alternating magnetic field 191 creates a time varying magnetic flux linkage that affects the inductance element 131 of the resonant circuit 110 and induces electric current in the resonant circuit 110. When the induced current flows in the resonant circuit 110, the inductance element 131 produces a second alternating magnetic field 192 different from the first alternating magnetic field 191.

Although the amplitude of the first alternating magnetic field 191 is constant in the frequency band, because the impedance of the resonant circuit 110 is varied for each frequency, the amplitude of the induced current is also varied for each frequency, and, as a result, the amplitude of the second alternating magnetic field 192 is not constant. Furthermore, the amplitude of the induced current is the highest at the resonant frequencies of the resonant circuit 110, and thus the second alternating magnetic field 192 generated by the induced current has the highest amplitude at the resonant frequencies of the resonant circuit. In other words, when the amplitude of the first alternating magnetic field 191 is constant in the frequency band, and when the frequency of the first alternating magnetic field 191 is swept in the frequency band and the second alternating magnetic field 191 is sensed, it may be verified that the second alternating magnetic field 192 has the highest amplitude at the resonant frequencies.

In this case, when a change in the amplitude of the second alternating magnetic field 192 is measured to determine the resonant frequency, the amplitude of the first alternating magnetic field 191, which is an input, may be kept constant. Furthermore, by making the quality factor (Q factor) of the resonant circuit 110 high, the characteristics that the amplitude of the second alternating magnetic field 192 changes near the resonant frequency may be clearly observed.

The coil of the sensor unit 160 may detect the second alternating magnetic field 192, and an electric current may be induced in the sensor unit 160 by the second alternating magnetic field 192. When the amplitude of the first alternating magnetic field 191 is constant, because it is possible to find the resonant frequency of the resonant circuit 110 using the amplitude of the second alternating magnetic field 192, the resonant frequency of the resonant circuit 110 may be determined when the current induced by the second alternating magnetic field 192 is analyzed. A description will be given of a detailed embodiment with reference to FIG. 2. Voltage, impedance, or the like as well as current may be used as a parameter for determining the resonant frequencies.

For the convenience of description, the coils of the power supply unit 150 and the sensor unit 160 are represented as being different from each other, but the power supply unit 150 and the sensor unit 160 may share the same coil.

In the specification, the ‘first resonant frequency’ may be a reference frequency indicating that there is no moisture and there may be one or more first resonant frequencies. When there is no moisture, the first resonant frequency may be a resonant frequency value determined theoretically or experimentally based on the inductance of an inductance element, the capacitance of a variable capacitance element, or the capacitance of a fixed capacitance element. In an example, the first resonant frequency may be determined by a manufacturer based on the values of the elements that comprise a moisture detection device or a moisture detection reader. In another example, a user may determine the first resonant frequency by directly entering a frequency value into the moisture detection reader or may determine the first resonant frequency through an action of pushing a ‘no moisture’ button and measuring a resonant frequency.

There may be one or more ‘second resonant frequencies’. The second resonant frequency may be a reference frequency indicating that moisture is present. When moisture is present, the second resonant frequency may be a resonant frequency value determined theoretically or experimentally based on the inductance of an inductance element, the capacitance of a variable capacitance element, or the capacitance of a fixed capacitance element.

In an embodiment, when a resonant circuit, a capacitance of the variable capacitance element 133 of which is not changed because moisture is not present in a building structure, is called a first resonant circuit, a first resonant frequency of the first resonant circuit may be determined by the inductance element 131, the fixed capacitance element 132, and the variable capacitance element 133. In this case, when the power supply unit 150 generates the first alternating magnetic field 191, the resonant circuit 110 may generate the second alternating magnetic field 192 in response to it and the sensor unit 160 may sense the second alternating magnetic field 192. The control unit 170 may measure a resonant frequency at this time and may determine that the measured resonant frequency is the same as the first resonant frequency within a margin of error to determine that there is no moisture in the building structure.

When a resonant circuit, a capacitance of the variable capacitance element 133 of which is changed due to moisture present in the building structure, is call a second resonant circuit, because a second resonant frequency of the second resonant circuit is determined based on the inductance element 131, the fixed capacitance element 132, and the variable capacitance element 133, the capacitance of which is changed, the second resonant frequency may be different from the first resonant frequency.

The control unit 170 may measure the changed resonant frequency using information received from the sensor unit 160 and may determine that the measured resonant frequency is the same as the second resonant frequency within a margin of error to determine that there is moisture in the building structure. The control unit 170 may allow the output unit 180 to provide a moisture detection alarm to a user.

To decide whether the measured resonant frequency is identical to the first resonant frequency or to the second resonant frequency within a margin of error, the frequency band of the first alternating magnetic field 191 may be determined to include the first resonant frequency and the second resonant frequency.

Because the variable capacitance element 133 needs to change its capacitance when it is exposed to moisture, it may be located in a place where the moisture will be discharged. When a variable capacitance element portion except for an absorber and a resonant circuit portion except for the absorber come into direct contact with moisture, because the direct contact may lead to an unexpected change in capacitance or inductance or introduce a parasitic resistance component, the variable capacitance element portion except for the absorber and the resonant circuit portion except for the absorber may be insulated or waterproofed.

It is shown in FIG. 1 that conductors (metal plates) separated from each other are planar plates substantially parallel to each other, but an embodiment of the inventive concept may include any structure of separated metal plates capable of having capacitance. For the convenience of description, a description will be given of an inventive concept using planar plates parallel to each other. Herein, the “conductor” or “metal plate” is not necessarily limited to having a planar structure and refers to an object or circuit made of a conductive material having any structure. For example, it should be understood that a circuit manufactured with a conductive ink or a circuit formed of a conducive material through etching are included in the category of the ‘conductor’ or “metal plate” used in the specification.

FIG. 2 is an example of a graph illustrating a parameter value sensed by a sensor unit of a moisture detection reader.

In detail, a graph 210 of a parameter value of a first resonant circuit sensed by a sensor unit 160 and a graph 220 of a parameter value of a second resonant circuit sensed by the sensor unit 160 are shown.

In the graph 210 of the parameter value of the first resonant circuit sensed by the sensor unit 160, it may be observed that the rate of change in the parameter value at f₁ in a specific frequency band B is closest to 0. A control unit 170 may obtain the frequency where the rate of change in the parameter value is closest to 0. Because a point where the rate of change in the parameter value is closest to 0 represents a local minimum value in the graph shown in FIG. 2, the control unit 170 may determine a frequency at the point as a resonant frequency. As shown in FIG. 2, the control unit 170 may obtain f₁ before the hydration reaction of the cement proceeds and may obtain f₁ when moisture content changes as the hydration reaction of cement proceeds.

In an example, when the measured resonant frequency f₁ and the resonant frequency f₂ measured later have a difference greater than a threshold, the control unit 170 may determine that the moisture content reaches the predetermined threshold. For example, when a user measures a resonant frequency of a moisture detection device using a moisture detection reader to obtain 1 MHz and then measures a resonant frequency of the moisture detection device to obtain 2 MHz, because the difference between the measurements are greater than or equal to 0.5 MHz which is a predetermined threshold, the control unit 170 may determine that the moisture content reaches the predetermined threshold.

The user may make sure that the moisture content reaches the predetermined threshold in a building structure (for example, concrete) and measure the resonant frequency so that the control unit 170 obtains f₁. For example, the user may enter ‘no moisture’ via an input unit (not shown) of the moisture detection reader and may measure a resonant frequency, so that f₁ becomes a resonant frequency when moisture is not present. Thereafter, when the user measures a resonant frequency when the moisture content reaches the predetermined threshold in the building structure using the moisture detection reader, the control unit 170 may obtain f₂ and may compare f₂ with f₁ to determine whether the moisture content reaches the predetermined threshold.

In an example, the control unit 170 may determine that f₁ which is the measured resonant frequency is the same as a first resonant frequency of the designed first resonant circuit within a predetermined margin of error to determine that the moisture content reaches the predetermined threshold in the building structure. For example, when the first resonant frequency is 1 MHz and when f₁ measured by the moisture detection reader is 1.02 MHz, the control unit 170 may determine that the first resonant frequency and f₁ are the same as each other within a predetermined margin of error 2% to determine that the moisture content does not reach the predetermined threshold in the building structure. Likewise, the control unit 170 may determine that f₂ which is the measured resonant frequency is the same as the expected second resonant frequency when variable capacitance is changed by moisture within a predetermined margin of error to determine that the moisture content reaches the predetermined threshold in the building structure. For example, when the expected second resonant frequency is 3 MHz and when f₂ measured by the moisture detection reader is 3.03 MHz, the control unit 170 may determine that the second resonant frequency and f₂ are the same as each other within a predetermined margin of error 1% to determine that the moisture content reaches the predetermined threshold in the building structure.

In an embodiment, the control unit 170 may determine a resonant frequency measured after the user pushes, for example, a ‘no moisture’ button in a desired time as the first resonant frequency, other than determining a resonant frequency theoretically calculated based on a theoretical element value or a real element value of a variable capacitance element, a fixed capacitance element, or an inductance element as the first resonant frequency or the second resonant frequency.

In an example, the control unit 170 may determine the frequency where a rate of change in parameter value is closest to 0 and may compare the frequency with a frequency threshold preset to determine whether the moisture content reaches the predetermined threshold. For example, the control unit 170 may determine that f₁ measured as 1 MHz is greater than a predetermined frequency threshold 0.9 MHz to determine that the moisture content reaches the predetermined threshold.

In an example, the control unit 170 may determine whether f₁ is within a predetermined frequency threshold range to determine that the moisture content reaches the predetermined threshold. For example, the control unit 170 may determine that f₁ measured as 1 MHz is greater than 0.9 MHz and is less than 1.2 MHz, which is a predetermined frequency range, to determine that the moisture content does not reach the predetermined threshold.

An output unit 180 may provide information indicating that that the moisture content does not reach the predetermined threshold to the user using a display, a sound, or the like.

It is shown in FIG. 2 that f₁>f₂, but it is possible that f₁<f₂ depending on a design of a resonant circuit. An embodiment of measuring a resonant frequency using a parameter value and determining whether the moisture content does not reach the predetermined threshold, for example, a method for determining a frequency where there is the highest rate of change in parameter value as a resonant frequency, a method for determining a frequency that generates a smallest parameter value as a resonant frequency, or a method for determining a frequency that generates a highest parameter value as a resonant frequency, other than a method for determining a frequency at which the rate of change in parameter value is closest to 0 in a method for finding the resonant frequency, may correspond to an embodiment of the inventive concept.

In an embodiment, the moisture detection reader may measure several resonant frequencies in each of states of hydration reaction of cement using the fact that one circuit may have several resonant frequencies depending on the structure of the resonant circuit and may compare the difference between the several resonant frequencies with a predetermined threshold to determine whether the building structure is in each of states of hydration reaction of cement.

As an example, when the first resonant circuit generates two resonant frequencies, the moisture detection reader may measure the two resonant frequencies of the first resonant circuit and may compare the difference between the two resonant frequencies with a predetermined threshold to determine that the hydration reaction of cement proceeds. In the same method, the moisture detection reader may compare the difference between at least two resonant frequencies of the second resonant circuit with a predetermined threshold to determine that the hydration reaction of cement proceeds in the building structure.

When a physical external force is applied to a resonant circuit, an inductance element, a capacitance element, or the like, which has an influence on each of two resonant frequencies in common may be physically deformed. In this case, each of the several resonant frequencies in the first resonant circuit or the second resonant circuit may have a large change in value by the deformation of the inductance element, the capacitance element, or the like, whereas the difference between each of the several resonant frequencies may have a small change in value making it possible to detect moisture more reliably.

Furthermore, embodiments of the inventive concept may be modified in more various manners. For example, as in the case that there are two resonant frequencies before the hydration reaction of cement proceeds but there is one resonant frequency while the hydration reaction of cement proceeds, the number of resonant frequencies may change. An embodiment of the inventive concept may detect a change in the number of resonant frequencies. On the other band, the case where there is one resonant frequency before the hydration reaction of cement proceeds but there are two resonant frequencies when the hydration reaction of cement proceeds is an embodiment of the inventive concept.

In addition, frequency shift of a resonant frequency as well as a change in the number of resonant frequencies may be detected. For example, two resonant frequencies before the hydration reaction of cement proceeds may be decreased or increased while the interval between the two resonant frequencies is maintained when the hydration reaction of cement proceeds, and an embodiment of the inventive concept is applicable to such a case.

FIG. 3 is a drawing illustrating a conventional moisture detection device.

Referring to FIG. 3, a conventional moisture detection device 310 may include a resonant circuit 320. The resonant circuit 320 may include an inductor 330 and a variable capacitor 340. The variable capacitor 340 may include an absorber, permittivity of which is changed when exposed to moisture. The variable capacitor 340 may have a change in capacitance by a change in permittivity. When the capacitance of the variable capacitor 340 changes, a resonant frequency determined by the inductor 330 and the variable capacitor 340 may change. A moisture detection reader 350 may measure the changed resonant frequency of the resonant circuit 320 and may determine the moisture content in a building structure. For example, when permittivity in the variable capacitor 340 increases by a factor of 100 due to moisture, the capacitance of the variable capacitor 340 increases by a factor of 100 according to Equation 1 below.

C _v =εS/d  [Equation 1]

a denotes permittivity of the material between the metal plates, d denotes the distance between the metal plates, and S denotes the area of the metal plate. In this case, because the resonant frequency is represented as Equation 2 below, when capacitance increases by a factor of 100, the resonant frequency decreases by a factor of 1/10 due to moisture.

f _r=1/{2π(LC_v)^1/2}  [Equation 2]

For example, when an inductance of the inductor 330 is 1 mH and when a capacitance of the variable capacitor 340 before the hydration reaction of cement proceeds is 1 μF, the resonant frequency is 5033 Hz by Equation 2 above. When the capacitance of the variable capacitor 340 increases by a factor of 100 because moisture content is changed in the building structure, the resonant frequency is 503.3 Hz by Equation 2 above.

In general, when a dielectric which has an influence on capacitance is affected by moisture and changes in permittivity, because it is possible that the permittivity can increase dozens of times, the resonant frequency may greatly decrease. The moisture detection reader 350 may measure both of a first resonant frequency when the hydration reaction of cement does not proceed in the building structure and a second resonant frequency when the hydration reaction of cement proceeds in the building structure. Thus, the moisture detection reader 350 should perform a frequency sweep in a frequency range that includes the first resonant frequency and the second resonant frequency. In this case, when the resonant frequency greatly decreases as the permittivity increases dozens of times, the frequency range to be swept may become excessively wide and it will not only make the implementation of the moisture detection reader 350 complicated but also make the moisture detection speed slow.

FIG. 4 is an example illustrating a moisture detection device according to an embodiment.

Referring to FIG. 4, a moisture detection device 410 according to an embodiment of the inventive concept may include a resonant circuit 420. The resonant circuit 420 may include an inductance element 430, a fixed capacitance element 440, and a variable capacitance element 450. For the convenience of description, one inductance element 430, one fixed capacitance element 440, and one variable capacitance element 450 are shown in FIG. 4, but the resonant circuit 420 may include one or more elements of each type. The resonant circuit may be designed through a parallel connection, a serial connection, or a combination thereof using one or more elements of each type, but a description will be given of an embodiment of the inventive concept using a resonant circuit 410 where the elements are connected in parallel for convenience of description.

The resonant frequency of a resonant circuit 420 may be determined by the inductance element 430, the fixed capacitance element 440, and the variable capacitance element 450 according to Equation 3 below.

f _r=1/{2π(LC_f+C_v)^1/2}  [Equation 3]

For example, when the inductance is 1 mH, when the capacitance of the fixed capacitance element 440 is 1 μF, and when the capacitance of the variable capacitance element 450 is 100 nF, the first resonance frequency before the hydration reaction of cement proceeds will be about 4799 Hz.

Although the hydration reaction of cement proceeds in a building structure, the fixed capacitance element 440 has no change in capacitance. Thus, when the hydration reaction of cement proceeds in the building structure, because only the capacitance of the variable capacitance element 450 is changed, compared with a conventional moisture detection device, the change of the resonant frequency by moisture may be reduced.

For example, when permittivity of the dielectric material around the variable capacitance element 450 reduced to 1/10 because the hydration reaction of cement proceeds in the building structure, because the capacitance of the variable capacitance element 450 reduced to 1/10 to be 10 nF, the resonant frequency when the hydration reaction of cement proceeds in the building structure may be about 5008 Hz by Equation 1 above. When the capacitance of the variable capacitance element 450 reduced to 1/10 due to moisture, the resonant frequency of the conventional moisture detection device may decrease by 316%, whereas the resonant frequency of the moisture detection device 410 according to an embodiment of the inventive concept may decrease by 4.35% thanks to the fixed capacitance element 440. Thus, discharge of moisture because it is possible to measure the resonant frequencies before and after discharge of moisture with a small frequency sweep range, the moisture detection speed may be enhanced.

As described above, by making the magnitude of the capacitance of the variable capacitance element 450 significantly less than that of the capacitance of the fixed capacitance element 440, the fixed capacitance element 440 may be used to determine the first resonant frequency and the variable capacitance element 450 may be used to determine the second resonant frequency.

The moisture detection reader 460 may be a separate device for detecting moisture but may also be a mobile device, such as a smartphone, a PDA, or a tablet PC, having the above-mentioned functions.

FIG. 5 is another example illustrating a moisture detection device according to an embodiment.

Referring to FIG. 5, a variable capacitance element 550 may further include an absorber 510 for absorbing moisture. The absorber 510 may be located between the parallel metal plates of the variable capacitance element 550.

The ‘separated metal plates’ in the inventive concept may include metal plates which are substantially parallel to each other and may also include any form of metal plates capable of having capacitance such as coaxial cylindrical metal plates parallel to each other, metal plates that are separated from each other and are arranged in the form of rolls, and metal plates of any shape that are parallel to each other, as well as the plane-shaped metal plates parallel to each other.

That there is an absorber between two metal plates may mean that the absorber is located in a place where the absorber may have an influence on the capacitance formed by the two metal plates. In other words, that there is an absorber between two metal plates may mean that the absorber located in the space between the metal plates, but it may also mean that the absorber is present around the metal plates and is able to have an influence on the capacitance.

The absorber 510 may be extended to the outside of parallel metal plates to make it absorb the moisture in the building structure more efficiently. For example, even when the moisture is not located in the vicinity of the variable capacitance element 550, the moisture absorbed by the absorber portion extended to the outside of the parallel metal plates may soak through the absorber and reach the absorber portion between the parallel metal plates and change its permittivity.

Because the variable capacitance element 550 is is supposed to be affected by moisture, it may be exposed to moisture without an insulator.

In an example, when moisture comes into a direct contact with the variable capacitance element 550, because the conductive property of the moisture may lead to an unexpected change in parasitic capacitance or inductance, or introduce a parasitic resistance component, the parallel metal plate may be insulated or waterproofed to prevent it.

In an example, at least a part of the resonant circuit except for the absorber 510 may be insulated or waterproofed to prevent the at least a part of the resonant circuit except for the absorber 510 (the concrete of the building) from being affected by moisture. As shown in FIG. 5, the fixed capacitance element 540 may be in the form of being integrally connected with the variable capacitance element 550. In this case, when the absorber 510(the concrete of the building) between the variable capacitance elements 550 absorbs moisture, because permittivity of the fixed capacitance element 540 should not be changed, there may be a wall separating the fixed capacitance element 540 and the variable capacitance element 550. In other words, reliability of the permittivity of the fixed capacitance element 540 may be maintained through the separating wall 520.

If the volume of the absorber 510(the concrete of the building) expands by absorbing moisture, the distance between the metal plates parallel to each other is increased, and the capacitance of the variable capacitance element 550 may be decreased according to Equation 1. The distance between the metal plates may be increased by the expansion of the absorber 510(the concrete of the building), and the amount of increase in the distance between the metal plates may depend on the expansion rate of the absorber, the moisture absorption rate of the absorber, or the resistance of the two metal plates parallel to each other to the expansion of the absorber 510(the concrete of the building). For example, even when the distance between the metal plates is increased by a factor of 2, if the permittivity increases dozens of times, the capacitance increases.

There is actually a dielectric between the parallel metal plates of the fixed capacitance element 540, but the dielectric of the fixed capacitance element 540 is omitted in FIG. 5 to emphasize that the portion where permittivity is changed is only in the variable capacitance element 550 in the inventive concept.

FIG. 6 is another example illustrating a moisture detection device according to an embodiment.

Referring to FIG. 6, a fixed capacitance element 540 and a variable capacitance element 550 may be electrically connected to each other by a connection portion 610. When the fixed capacitance element 540 and the variable capacitance element 550 are located within a short distance, contrary to the intention that only the variable capacitance element 550 is allowed to change its permittivity as the absorber 510(the concrete of the building) absorbs moisture, the fixed capacitance element 540 within a short distance may also be affected by the moisture and its permittivity may be changed. To prevent this from happening, the inductance element 530 and the fixed capacitance element 540 may be located away from the variable capacitance element 530 and from the location where moisture is discharged so that the inductance element 530 and the fixed capacitance element 540 are not affected by the moisture. In an example, at least a part of the resonant circuit except for the absorber 510(the concrete of the building) may be waterproofed to prevent the at least a part of the resonant circuit portion except for the absorber 510(the concrete of the building) from being affected by moisture.

FIGS. 7 to 13 are drawings illustrating the structures of capacitance elements.

FIG. 7 illustrates the structure of a capacitance element where cylindrical plates are arranged in parallel to each other. Referring to FIG. 7, two cylindrical plates 710 and 720, each of which has a different diameter, may be arranged in parallel to each other.

FIG. 8 illustrates the structure of a capacitance element in the form of a roll. Referring to FIG. 8, at least two plates 810 and 820 may have a form where they are wound alternatively.

FIG. 9 illustrates the structure of a capacitance element where metal plates 910 and 920, each of which having an arbitrary curved surface shape, are arranged in parallel to each other. FIG. 10 is a drawing illustrating the structure of a capacitance element that consists of two bent parallel plates 1010 and 1020. FIG. 11 is a drawing illustrating the structure of a capacitance element that consists of a thick conductive plate 1110 and a bent conductive plate 1120. FIG. 12 is a drawing illustrating the structure of a capacitance element that consists of a thin conductive plate 1210 and a bent conductive plate 1220. FIG. 13 is a drawing illustrating the structure of a printable capacitance element that consists of conductive plates of a concave and convex shape.

FIG. 13 is a drawing illustrating a capacitance element of a concave and convex shape (a finger shape). The capacitance may be controlled by using gap G, end gap (Ge), width W, length L, and the number of fingers as variables. The capacitance element of a concave and convex shape shown in FIG. 13 is called an interdigital capacitor.

FIG. 14 illustrates an embodiment of using an interdigital capacitor shown in FIG. 13 as a variable capacitance element.

Referring to FIG. 14, a moisture detector of the inventive concept does not include a separate absorber. When the moisture content changes due to the hydration reaction of the cement in the concrete (1410, 1420) of the building structure, there may occur a change in permittivity of the absorbers 1410 and 1420 of the building structure. The change in permittivity of the concrete (1410, 1420) of the building structure results in a change of the capacitance of the interdigital capacitor 1430 used as a variable capacitor. The moisture detector of the inventive concept may detect the changed capacitance of the interdigital capacitor 1430.

FIG. 15 illustrates an equivalent circuit of the embodiment shown in FIG. 14. Referring to FIG. 15, the interdigital capacitor 1430 may be represented equivalently as a variable capacitor 1510 in FIG. 15. Absorbers 1410 and 1420(the concrete of the building structure) may be represented as a dielectric 1520 of the variable capacitor 1510 in the equivalent circuit. Thus, a change in permittivity of the 1410 and 1420(the concrete of the building structure) may be represented by a change in permittivity of the dielectric 1520 of the variable capacitor 1510 of the equivalent circuit.

FIG. 16 illustrates an embodiment of using parasitic capacitance of an inductor as a variable capacitance element.

Referring to FIG. 16, a moisture detector of the inventive concept does not include a separate absorber. When moisture is absorbed by absorbers 1610 and 1620 of a building structure, there may occur a change in permittivity of the absorbers 1610 and 1620 (the concrete of the building structure). The change in permittivity of the absorbers 1610 and 1620 (the concrete of the building structure) results in a change of the parasitic capacitance of the inductor 1630 used as a variable capacitor. The moisture detector of the inventive concept may detect the changed capacitance of the parasitic capacitance of the inductor 1630.

FIG. 17 illustrates an equivalent circuit of the embodiment shown in FIG. 16. Referring to FIG. 17, the parasitic capacitance of inductor 1630 may be represented equivalently as a variable capacitor 1710 in FIG. 17. Absorbers 1610 and 1620 (the concrete of the building structure) may be represented as a dielectric 1720 of the variable capacitor 1710 in the equivalent circuit. Thus, a change in permittivity of the absorbers 1610 and 1620 (the concrete of the building structure) may be represented by a change in permittivity of the dielectric 1720 of the variable capacitor 1710.

FIG. 18 illustrates a moisture content measuring device and a moisture content measuring reader including a wire to measure the resonance frequency of the moisture content measuring device.

It may not be easy to measure the moisture content in the building structure by approaching the moisture content measurement reader to the building structure. For example, in the case of structures (e.g., bridges) constructed over rivers or seas, it is assumed that a moisture content measuring device is inserted in a portion located below the surface of the pier. In this case, it is not easy to approach the moisture content measuring reader at a distance sufficiently close to the moisture content measuring device. Accordingly, the moisture content measuring apparatus may include a wire for measuring a resonance frequency of the moisture content measuring apparatus. Referring to FIG. 18, the moisture content measuring apparatus includes wires 134 and 135 for measuring a resonance frequency of the moisture content measuring apparatus. In this case, the wire for measuring the resonance frequency of the moisture content measuring device consists of terminals (136, 137, 138, 139) connected to inductors (134, 135), and inductors (134, 135) of the moisture content measuring device, and terminals (136, 137, 138, 139) are exposed to the outside of concrete. The moisture content measurement reader may measure a change in a resonance frequency (a first resonance frequency and a second resonance frequency) through the terminal.

In FIG. 18, wires 134, 136, 137 connected to the power supply part of the moisture content measuring reader and wires 135, 138, 139 connected to the sensor part are expressed differently, but wires 134, 136, 137 and 139, may be the same.

In addition, although not explicitly shown in FIG. 18, the moisture content measuring reader may include a connector to enable connection with terminals 136, 137, 138, and 139. Here, the connector can be implemented as a separate device to facilitate electrical connection, as well as in the form of a simple wire for electrical connection.

MODE FOR INVENTION

Although the inventive concept is given in detail of the limited embodiment, the inventive concept is not limited to the above-mentioned embodiment. Those skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and spirit of the inventive concept as disclosed in the accompanying claims.

Claims

1. An apparatus for detecting moisture in a building structure, the apparatus comprising: at least one inductance element;at least one fixed capacitance element configured not to have a change in capacitance although the moisture is present in the building structure; andat least one variable capacitance element configured to be electrically connected with the at least one fixed capacitance element and have a change in capacitance when the moisture is present in the building structure,wherein at least one first resonant frequency is determined based on the at least one inductance element, the at least one fixed capacitance element, and the at least one variable capacitance element.

2. The apparatus of claim 1, wherein the at least one variable capacitance element includes: an absorber configured to absorb the moisture to change a capacitance of the at least one variable capacitance element; andat least one conductor separated by the absorber in between the at least one conductor.

3. The apparatus of claim 2, wherein the at least one variable capacitance element further includes: at least one insulating layer between the absorber and the at least one conductor to prevent the at least one conductor from being directly exposed to the moisture absorbed by the absorber.

4. The apparatus of claim 1, wherein the at least one variable capacitance element has a change in capacitance, when the moisture is present in the building structure, wherein at least one second resonant frequency is determined based on the at least one inductance element, the at least one fixed capacitance element, and the at least one variable capacitance element, the capacitance of which is changed, andwherein the at least one first resonant frequency and the at least one second resonant frequency are different from each other.

5. A moisture detection reader, comprising: a power supply unit configured to generate a first alternating magnetic field, a frequency of which is changed to induce an electric current in a moisture detection device according to claim 1;a sensor unit configured to sense a parameter associated with a second alternating magnetic field generated by the induced electric current in the moisture detection device;a control unit configured to determine whether moisture is present, based on the parameter associated with the second alternating magnetic field, the parameter being sensed by the sensor unit; andan output unit configured to notify a user whether the moisture is present.

6. The moisture detection reader of claim 5, wherein the power supply unit generates the first alternating magnetic field, the frequency of which is changed within a frequency band including at least one first resonant frequency and at least one second resonant frequency.

7. The moisture detection reader of claim 5, wherein the parameter is the amplitude of an induced current for each frequency, the amplitude of an induced voltage for each frequency, or impedance for each frequency.

8. The moisture detection reader of claim 5, wherein the control unit determines a resonant frequency based on a value of the parameter and compares the resonant frequency with at least one first resonant frequency or at least one second resonant frequency to determine whether the moisture is present.

9. The moisture detection reader of claim 5, wherein the control unit determines at least one resonant frequency before the moisture is present and at least one resonant frequency after the moisture is present, based on a value of the parameter, and determines whether the moisture is present, based on the at least one resonant frequency before the moisture is present and the at least one resonant frequency after the moisture is present.

10. The apparatus of claim 4, further comprising: at least one terminal configured to be exposed to the outside of the building structure;wherein the first resonance frequency and the second resonance frequency are measured through the at least one terminal.

11. The apparatus of claim 10, further comprising: at least one inductor configured to be induction-coupled to at least one of the inductance element;wherein the at least one terminal is electrically wired with the at least one inductor.

12. The moisture detection reader of claim 5, further comprising: a connector configured to be connected to at least one terminal included in the moisture detection device.