JP2016173253A - Moisture content estimation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a moisture content estimation system that excels in the accuracy of estimating a moisture content.SOLUTION: Provided is a moisture content estimation system comprising a plurality of wireless tags Tag1, Tag2 mutually differing in resonance frequency and secured to the same lumber 20 and a tag reader capable of communicating with the plurality of wireless tags, the system estimating the moisture content of the lumber 20 on the basis of the comparison of reception levels that are the signal levels of received signals that the tag reader has received from each of the plurality of wireless tags, wherein the plurality of wireless tags are secured to the lumber 20 in such a way that each wireless tag intersects at center of the other wireless tag. This makes it possible to equalize the distance between each wireless tag and the tag reader while keeping antenna tips having a strong electric field and contributing significantly to radio wave radiation in each wireless tag separated from each other. Thus, as it is possible to equalize the distance between each wireless tag and the tag reader while reducing the mutual interference of each wireless tag, the accuracy of estimating a moisture content is improved.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a moisture content estimation system that estimates a moisture content of a measurement object based on communication between a wireless tag and a tag reader.

  Patent Document 1 discloses a moisture content estimation system that estimates the moisture content of a measurement object based on communication between a wireless tag and a tag reader. The moisture content estimation system disclosed in Patent Document 1 includes a plurality of wireless tags that have resonance frequencies set to different frequencies and are fixed to the same measurement object. And the moisture content of a measurement object is estimated based on the comparison of the reception level which is the signal level of the received signal which each tag reader received from the some radio | wireless tag.

  The reception level received from the wireless tag not only changes depending on the moisture content of the measurement object, but also changes depending on the distance between the wireless tag and the tag reader. Therefore, in Patent Document 1, two wireless tags are attached at positions close to each other.

JP 2014-190857 A

  When a plurality of wireless tags are arranged at positions close to each other, radio waves transmitted by the plurality of wireless tags interfere with each other and are received by the tag reader. Due to this interference, the reception level is different from that when the wireless tag is attached alone, and as a result, the estimation accuracy of the moisture content is lowered.

  Here, if a plurality of wireless tags are arranged apart from each other, interference is reduced. However, if a plurality of wireless tags are arranged apart from each other, the degree to which the distance between each wireless tag and the tag reader differs between wireless tags increases, and the reception level changes due to this distance difference. Accuracy is reduced. Therefore, even if the distance between the plurality of wireless tags is increased, the estimation accuracy of the moisture content is not improved.

  The present invention has been made based on this situation, and an object of the present invention is to provide a moisture content estimation system with good moisture content estimation accuracy.

  The above object is achieved by a combination of the features described in the independent claims, and the subclaims define further advantageous embodiments of the invention. Reference numerals in parentheses described in the claims indicate a correspondence relationship with specific means described in the embodiments described later as one aspect, and do not limit the technical scope of the present invention. .

  In order to achieve the above object, the present invention provides a plurality of wireless tags (Tag) having different resonance frequencies and fixed to the same measurement object (20), and a tag reader (R) capable of communicating with the plurality of wireless tags. A moisture content estimation system for estimating a moisture content of a measurement object based on a comparison of reception levels, which are signal levels of received signals respectively received by a tag reader from a plurality of wireless tags, A plurality of wireless tags are fixed to the measurement object such that other wireless tags intersect at the center.

  In this way, it is possible to separate the antenna tip portions having a strong electric field that contribute to radiation of radio waves in each wireless tag and having a strong electric field while keeping the distance between each wireless tag and the tag reader the same. Therefore, since the mutual interference of each wireless tag can be reduced while making the distance between each wireless tag and the tag reader the same, the estimation accuracy of the moisture content is improved.

  When two wireless tags are crossed with each other, the tips of the wireless tags are farthest from each other when the crossing angle is 90 degrees. Therefore, it is best when the crossing angle is 90 °. As a result of experiments to be described later, it was found that if the crossing angle is 90 ° ± 30 °, the difference in reception level is not so great from that in the case of 90 °. Therefore, it is preferable to provide two wireless tags whose crossing angle is within 90 ° ± 30 °, as in claim 2.

  When the object to be measured is wood, the reception level also changes depending on the angle with respect to the grain of wood. Therefore, when there are two wireless tags, it is preferable that the two wireless tags have the same angle with respect to the grain of wood. However, even if the angles of the two wireless tags with respect to the grain are not completely the same, the estimation accuracy is not so lowered as long as it is within a certain range. When this range was determined based on experiments, it was found that the difference between the absolute values of the angles of the two wireless tags with respect to the grain was preferably within 40 °.

  Therefore, as described in claim 3, as a plurality of wireless tags, the difference between the absolute value of the angle of one wireless tag with respect to the wood grain and the absolute value of the angle with respect to the grain of the other wireless tag is within 40 °. It is preferable to include two wireless tags.

  In order to estimate the moisture content, as in claim 4, one of the plurality of wireless tags is used as a reference wireless tag, the other one of the plurality of wireless tags is used as a measurement wireless tag, and the measurement wireless tag is used. A reception level difference calculation unit that calculates a difference between a reception level of a signal received from the reference radio tag and a reception level of a signal received from a reference wireless tag, a preset relationship in which a moisture content is determined from the difference in reception level, and a reception level A moisture content determining unit that determines the moisture content of the measurement object from the difference in the reception level calculated by the difference calculating unit can be provided.

  In this case, as described in claim 5, the reference wireless tag has a relative permittivity capable of ignoring the influence of the change in the moisture content of the measurement object, and the measurement wireless tag includes the measurement object. It is preferable to provide a relative dielectric constant in which the response power changes due to a change in the moisture content.

  In this way, since the difference in reception level becomes larger, the estimation accuracy of the moisture content based on the difference in reception level is improved.

It is an appearance perspective view of tag reader R with which the moisture content presumption system of an embodiment is provided. 2 is a block diagram showing an internal configuration of a tag reader R. FIG. It is a figure which shows the use condition of two radio | wireless tags Tag1 and Tag2 with which the moisture content estimation system of embodiment is provided. It is a graph which shows the relationship between the moisture content Wt and response electric power. It is a figure explaining angle (theta) 1 in FIG. It is a figure which shows the change of the response electric power when changing the angle with respect to the grain of a radio | wireless tag Tag. It is a figure which shows that response electric power difference (DELTA) p changes with the moisture content Wt. FIG. 4 is a diagram for explaining an angle θ2 obtained by changing the inclinations of two wireless tags Tag1 and Tag2 from the state of FIG. It is a figure which shows the change of the response power difference (DELTA) p when changing (theta) 2. It is a figure which shows the change of the gain with respect to the change of angle (theta) 1 of the radio | wireless tag Tag with respect to a grain. It is a figure explaining the relationship between angle (theta) 1 and (theta) 3. FIG. It is a figure which shows the response electric power difference (DELTA) p when radio | wireless tag Tag2 is made into the tag for a reference. 3 is a diagram showing a state where three wireless tags Tag1, Tag2, and Tag3 are attached to a wood 20. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view of the tag reader R. FIG. The moisture content estimation system of this embodiment includes the tag reader R shown in FIG. 1 and the two wireless tags Tag1 and Tag2 shown in FIG. When the two wireless tags Tag1 and Tag2 are not distinguished, they are described as wireless tags Tag.

(Configuration of tag reader R)
As shown in FIG. 1, the tag reader R is a handy type and includes a handle portion 12 and a display portion 14. The handle portion 12 is also provided with input keys for performing various inputs to the tag reader R. The display unit 14 displays a result of communication with the wireless tag Tag.

  FIG. 2 is a block diagram mainly showing the internal configuration of the tag reader R. As shown in FIG. As shown in FIG. 2, the tag reader R includes an antenna 102, an antenna duplexer 104, an IQ demodulator 106, a reception level measurement unit 108, a decoding unit 110, a control unit 120, a storage device 130, a coding unit 132, a modulator 134, A local oscillator 136, a variable gain amplifier 138, and a power amplifier 140 are provided.

  The antenna 102 is used for both transmission and reception. The frequency transmitted and received by the antenna 102 is around 915 MHz in the present embodiment. The antenna duplexer 104 is a device for connecting a transmitting device and a receiving device to the same antenna 102, and outputs a signal from the power amplifier 140 to the antenna 102, while the signal from the antenna 102 is IQ demodulated. Output to the device 106.

  A local oscillation signal generated by the local oscillator 136 is input to the IQ demodulator 106. The IQ demodulator 106 separates the received signal input from the antenna 102 via the antenna duplexer 104 into an in-phase component I and a quadrature component Q using this local oscillation signal. Then, the in-phase component I and the quadrature component Q are input to the reception level measuring unit 108 and the decoding unit 110, respectively.

  The reception level measurement unit 108 measures reception response power (hereinafter simply referred to as response power) from the magnitude of the in-phase component I and the vector length of the quadrature component Q. This response power means the reception level of the response signal that is generated by the wireless tag Tag and generated by the power transmitted by the tag reader R. The reception level measurement unit 108 outputs the measured response power to the control unit 120.

  The decoding unit 110 performs decoding based on the magnitude of the in-phase component I and the angle of the quadrature component Q, and reads the tag ID included in the response signal transmitted by the wireless tag Tag. Then, the read tag ID is output to the control unit 120.

  A writable storage device 130 is connected to the control unit 120. The control unit 120 stores the response power and the tag ID in the storage device 130. Then, the moisture content Wt is estimated from the stored contents of the storage device 130.

  In order to estimate the moisture content Wt, the control unit 120 includes a reception level difference calculation unit 121 and a moisture content determination unit 122. The processing of the reception level difference calculation unit 121 and the moisture content determination unit 122 will be described later with reference to FIG.

  The coding unit 132 encodes the signal output from the control unit 120 and outputs the encoded signal to the modulator 134. The signal output from the control unit 120 to the coding unit 132 includes, for example, a response request signal for requesting the wireless tag Tag to transmit a response signal.

  The modulator 134 receives a local oscillation signal from the local oscillator 136 and modulates the signal input from the coding unit 132 using the local oscillation signal. Then, the modulated signal is output to the variable gain amplifier 138.

  Variable gain amplifier 138 amplifies the signal input from modulator 134 and outputs the amplified signal to power amplifier 140. The control unit 120 controls the gain of the variable gain amplifier 138.

  The power amplifier 140 amplifies the signal input from the variable gain amplifier 138 with a constant gain and outputs the amplified signal. The signal output from the power amplifier 140 is input to the antenna 102 via the antenna duplexer 104 and transmitted as a radio wave from the antenna 102.

(Description of wireless tag Tag)
As shown in FIG. 3, two wireless tags Tag 1 and Tag 2 are attached to the surface of the same wood 20. In the present embodiment, the wood 20 is a measurement object for measuring the moisture content Wt. Both of these two wireless tags Tag1 and Tag2 have the same configuration as a known passive tag.

  As shown in FIG. 3, each of the wireless tag Tag1 and the wireless tag Tag2 has a longitudinal shape, and intersects with the other wireless tags Tag2 and Tag1 at the center in the longitudinal direction. The operation of crossing the wireless tags Tag1 and Tag2 is performed by a human hand.

  Each of the wireless tags Tag1 and Tag2 includes a circuit unit 30 and an antenna 31. 3 shows the circuit unit 30 only for the wireless tag Tag2, and the circuit unit 30 is not shown for the wireless tag Tag1 on which Tag2 is superimposed. Each of the wireless tags Tag1 and Tag2 includes a dielectric on the back surface that is the surface on the wood 20 side. This dielectric has different relative permittivity between the radio tags Tag1 and Tag2. Since the resonance frequency varies depending on the relative dielectric constant, the resonance frequency differs when the relative dielectric constants are different from each other. The relative permittivity of the wireless tags Tag1 and Tag2 is set so that the resonance frequency becomes a predetermined frequency.

  The circuit unit 30 has a known configuration including an encoding unit, a transmission unit, a reception unit, a decoding unit, and the like inside (not shown). The antenna 31 has a rod shape and is provided as a pair. The pair of antennas 31 protrude from the circuit unit 30 to the opposite sides. In the present embodiment, the antennas 31 of the wireless tags Tag1 and Tag2 have the same length. However, since the relative permittivity of the dielectric provided on the back surface is different between the wireless tags Tag1 and Tag2, the wireless tags Tag1 and Tag2 have different resonance frequencies. Similar to Patent Document 1, the resonance frequencies may be made different from each other by making the lengths of the antennas 31 different from each other.

  As shown in FIG. 3, the two wireless tags Tag1 and Tag2 each have an angle θ1 with respect to the grain of 45 °, and thus the crossing angle with each other is 90 °. The reason why the crossing angle is 90 ° will be described.

(Explanation of crossing angle)
FIG. 4 is a graph showing the relationship between the water content Wt and the magnitude of the response signal power received by the tag reader R from the wireless tag Tag, that is, the response power. In FIG. 4, rhombus marks are response powers measured by attaching only one wireless tag Tag 1 to the wood 20. On the other hand, the square mark is the response power of the wireless tag Tag1 when the wireless tags Tag1 and Tag2 are attached to the wood 20 in parallel and close to each other, unlike the arrangement of FIG.

  As can be seen from FIG. 4, when only the wireless tag Tag1 is attached to the wood 20, the response power changes according to the moisture content Wt. On the other hand, when the wireless tags Tag1 and Tag2 are attached to the wood 20 in parallel with each other and close to each other, the correlation between the moisture content Wt and the response power is not known.

  With only the response power from one radio tag Tag, the response power changes not only with the moisture content Wt but also with the distance between the radio tag Tag and the tag reader R. Therefore, it is necessary to remove the influence of distance by receiving response power from a plurality of wireless tags Tag.

  However, as can be seen from FIG. 4, when the two wireless tags Tag1 and Tag2 are attached to the wood 20 in parallel and close to each other, the change in the moisture content Wt is not reflected in the response power.

  The reason why the change in the moisture content Wt is not reflected in the response power is the radio wave interference of the wireless tag Tag. The portion where the electric field is strong in the wireless tag Tag is the tip of the antenna 31. Therefore, the closer the tip of the antenna 31 of one radio tag Tag is to the tip of the antenna 31 of the other radio tag Tag, the greater the radio wave interference. In other words, the interference decreases as the tips of the two wireless tags Tag1 and Tag2 are separated from each other.

  When two radio tags Tag1 and Tag2 are crossed, a total of four tips existing in the radio tags Tag1 and Tag2 are most distant from each other. Is 90 degrees. Therefore, in the present embodiment, the two wireless tags Tag1 and Tag2 intersect each other at the center, and the intersection angle is 90 °.

(Influence of angle on the grain)
Further, in the present embodiment, the wireless tags Tag1 and Tag2 are inclined by 45 ° with respect to the grain. Next, the reason will be described.

  As shown in FIG. 5, the response power was measured by changing the angle θ1 with respect to the grain of the wireless tag Tag1. The result is shown in FIG. As can be seen from FIG. 6, when the angle θ1 with respect to the grain changes, the response power changes. When using two wireless tags Tag1 and Tag2 to remove the influence of a change in response power due to a change in the distance between the tag reader R and the wireless tag Tag, the response power does not change depending on differences other than the distance. Is preferred.

  Assuming that the crossing angle is 90 °, as shown in FIG. 3, only when the inclination of the two wireless tags Tag1 and Tag2 with respect to the grain is 45 °, the two wireless tags Tag1 and Tag2 The inclination with respect to the grain becomes equal. Therefore, in the present embodiment, the inclination of the two wireless tags Tag1 and Tag2 with respect to the grain is 45 °.

  When two wireless tags Tag1 and Tag2 having different resonance frequencies are attached to the wood 20 in the state shown in FIG. 3, the response power of each of the wireless tags Tag1 and Tag2 is shown in accordance with the moisture content Wt of the wood 20. 7 as shown.

  The response power difference Δp in FIG. 7 is the difference between the response power received by the tag reader R from the wireless tag Tag1 and the response power received from the wireless tag Tag2 in the state shown in FIG. As can be seen from FIG. 7, the response power difference Δp changes according to the moisture content Wt. On the other hand, since the response power is measured in the state shown in FIG. 3, the distances from the tag reader R to the two wireless tags Tag1 and Tag2 are equal. Also, the effect of angle on the grain is equal. Therefore, it is considered that the value of the response power difference Δp changes mainly according to the moisture content Wt of the wood 20.

  In this embodiment, the correspondence between the response power difference Δp and the moisture content Wt is determined in advance based on experiments. This correspondence is assumed to be stored in the storage device 130 here.

  The reception level difference calculation unit 121 of the control unit 120 calculates the difference between the response power for the wireless tag Tag1 output from the reception level measurement unit 108 and the response power for the wireless tag Tag2, that is, the response power difference Δp. The response power difference Δp may be on either side, but here, the response power for the wireless tag Tag1 is subtracted from the response power for the wireless tag Tag2.

  The reason for calculating the difference between the two response powers in this way is to remove the influence of the response power fluctuation due to the fluctuation of the distance to the tag reader R, as already described. Either one of the wireless tags Tag functions as a measurement wireless tag that measures response power according to the moisture content Wt. The other wireless tag Tag functions as a reference wireless tag that measures response power for removing the effect of fluctuations in response power due to fluctuations in the distance to the tag reader R.

  The moisture content determination unit 122 estimates the moisture content Wt of the wood 20 from the correspondence relationship stored in the storage device 130 and the response power difference Δp calculated by the reception level difference calculation unit 121.

(Acceptable range of angle difference with the grain)
The grain is not a perfect straight line, and the radio tags Tag1 and Tag2 are attached to the wood 20 by a human hand. Therefore, it is difficult to set the angle of the two wireless tags Tag1 and Tag2 to exactly 45 degrees.

  Therefore, the allowable angle with respect to the grain was examined. In this examination, as shown in FIG. 8, the angle at which the wireless tag Tag2 is inclined 45 ° with respect to the grain is set to 0 °. Then, the response power difference Δp was measured while changing the angle θ2 of the wireless tag Tag2 with reference to 0 °, while maintaining the crossing angle of the two wireless tags Tag1 and Tag2 at 90 °. The measurement results are shown in FIG. Since this measurement is for the purpose of confirming the influence of the angle difference between the two wireless tags Tag1 and Tag2 with respect to the grain on the response power difference Δp, the wireless tag Tag2 is the same as the wireless tag Tag1.

  Here, if the error of the response power difference Δp is about ± 1 dB, it is assumed that the tolerance is acceptable. This permissible range is determined based on the required estimation accuracy of the moisture content Wt. When the error of the response power difference Δp is within ± 1 dB, it can be said from FIG. 9 that it is within the allowable range if −20 ° ≦ θ2 ≦ 20 °.

  Here, when θ2 = −20 °, the wireless tag Tag2 is at an angle of 25 ° with respect to the grain. At this time, the angle of the wireless tag Tag1 with respect to the grain is −65 °. In FIG. 8, the minus sign means the angle between the wireless tag Tag and the wireless tag Tag when the wireless tag Tag is rotated clockwise from the position along the grain. For the wood grain, the angle of the wireless tag Tag2 is 25 °, and the angle of the wireless tag Tag1 is −65 °. Therefore, the absolute values of the angles of the two wireless tags Tag1 and Tag2 with respect to the wood grain are 25 respectively. The angle difference is 40 °. This angle difference is also an absolute value.

  When θ2 = −15 °, the wireless tag Tag2 is closer to the 45 ° line shown in FIG. 8 by 5 ° than when θ2 = −20 °. Therefore, the angle with respect to the grain is θ2 = −20 °. It will be 5 ° larger than sometimes. That is, when θ2 = −15 °, the wireless tag Tag2 is at an angle of 30 ° with respect to the grain. At this time, the angle with respect to the grain of the wireless tag Tag1 is −60 °. Therefore, when θ2 = −15 °, the absolute values of the angles with respect to the grain of the two wireless tags Tag1 and Tag2 are 30 ° and 60 °, respectively, and the angle difference is 30 °.

  When θ2 = 0 °, that is, when the wireless tag Tag2 is along the line of 45 ° shown in FIG. 8, the angle of the wireless tag Tag2 with respect to the grain is 45 °. At this time, the angle with respect to the grain of the wireless tag Tag1 is −45 °. Therefore, when θ2 = 0 °, the absolute values of the angles with respect to the grain of the two wireless tags Tag1 and Tag2 are both 45 °, and the angle difference is 0 °.

  Considering the same as when θ2 = −20, when θ2 = 20 °, the absolute values of the angles of the two wireless tags Tag1 and Tag2 with respect to the grain are 65 ° and 25 °, respectively. The difference is 40 °.

  Therefore, on the basis of the grain, it can be said that it is an allowable range if the difference between the absolute values of the angles of the two wireless tags Tag1 and Tag2 is within 40 °.

(Acceptable range of crossing angle)
Next, the allowable range of the crossing angle between the two wireless tags Tag1 and Tag2 will be considered. FIG. 10 is a graph showing the relationship between the angle θ1 shown in FIG. 3 and the gain of the wireless tag Tag1. In FIG. 10, a square mark is a gain measured by attaching the wireless tag Tag1 to the wood 20 and changing the angle θ1. The circle mark is the gain of the wireless tag Tag1 measured while simultaneously changing the angle θ1 with respect to the grain of the two wireless tags Tag1 and Tag2.

  Note that this measurement is for the purpose of confirming the allowable range of the crossing angle of the two wireless tags Tag1 and Tag2, in other words, the allowable range of the influence of interference. Therefore, the wireless tag Tag2 is the same as the wireless tag Tag1. Was used.

  As can be seen from FIG. 10, when the angle θ1 is 45 °, the wireless tag Tag1 intersecting with the wireless tag Tag2 has the same gain as the single wireless tag Tag1. If the gain is within ± 1 dB with reference to this 45 °, 30 ° ≦ θ1 ≦ 60 ° is within the allowable range. That is, if θ1 = 45 ° ± 15 ° or less, it is within the allowable range.

  The measurement of FIG. 10 includes the influence of the angle on the grain in addition to the change of the influence of the interference due to the change of the crossing angle. However, if the angle with respect to the wood grain changes from 0 ° to 90 °, the change tendency of the gain due to the change of the angle with respect to the wood grain is monotonously decreasing or monotonically increasing. Therefore, by changing θ1, not only the influence of interference but also the influence of the angle on the grain, the influence of the angle on the grain is the maximum of either θ1 = 30 ° or 60 °, and the other is Is the smallest.

  In addition, when θ1 = 30 °, the angle θ3 = 60 ° shown in FIG. 11 is obtained. When θ1 = 60 °, θ3 = 30 °. That is, regarding the influence of interference, θ1 = 30 ° and θ1 = 60 ° are the same.

  Regarding the influence of interference, θ1 = 30 ° and θ1 = 60 ° are the same, and the influence of the angle on the grain is θ1 = 30 ° or 60 °, one of which is maximum and the other is minimum. Therefore, it can be said that the allowable range is 30 ° ≦ θ1 ≦ 60 °.

  Since the angle θ1 is half of the crossing angle, the allowable range of the crossing angle is 60 ° to 120 °, that is, 90 ° ± 30 °.

(Summary of embodiment)
In the present embodiment described above, as shown in FIG. 3, the two wireless tags Tag1 and Tag2 fixed to the wood 20 as the measurement object are set to have a crossing angle of 90 ° at the center in the longitudinal direction. Overlapping.

  By crossing in this way, the distance between the radio tags Tag1 and Tag2 and the tag reader R is made the same, and the antenna tips having strong electric fields that contribute to radio wave radiation at the radio tags Tag1 and Tag2 are mutually connected. Can be released. As a result, mutual interference between the wireless tags Tag1 and Tag2 can be reduced while keeping the distance between the wireless tags Tag1 and Tag2 and the tag reader R the same, so that the estimation accuracy of the moisture content Wt is improved.

  Further, since the two wireless tags Tag1 and Tag2 are crossed, the pasting area can be reduced as compared with the case where the two wireless tags Tag1 and Tag2 are arranged so as not to overlap. Therefore, there are many cases where the moisture content Wt can be estimated even if the place to be pasted is limited.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, The following embodiment is also contained in the technical scope of this invention, and also the summary other than the following is also included. Various modifications can be made without departing from the scope.

<Modification 1>
For example, in the above-described embodiment, both of the two wireless tags Tag1 and Tag2 have characteristics that the response power varies depending on the moisture content Wt. However, the characteristics of the wireless tag Tag on the side used as the reference wireless tag may be characteristics that can ignore the influence of the change in the moisture content Wt on the response power. In order to achieve this characteristic, the relative dielectric constant may be increased. In order to increase the dielectric constant, for example, a dielectric having a high relative dielectric constant may be used as a dielectric provided on the back surface portion of the wireless tag Tag.

  FIG. 12 shows the relationship between the moisture content Wt and the response power when the wireless tag Tag2 has a high relative dielectric constant. When the relative permittivity of the wireless tag Tag2 is increased, the response power becomes substantially constant even when the moisture content Wt changes, as shown in FIG. As a result, the response power difference Δp increases. If the response power difference Δp is increased, the range of the response power difference Δp corresponding to the same range of the moisture content Wt is widened, so that the estimation accuracy of the moisture content Wt based on the response power difference Δp is improved.

<Modification 2>
In the above-described embodiment, the two wireless tags Tag1 and Tag2 each intersect the other wireless tags Tag2 and Tag1 at the center in the longitudinal direction, but it is not always necessary to intersect at the center. The purpose of intersecting the two wireless tags Tag1 and Tag2 at the center in the longitudinal direction is to keep the distance between the two wireless tags Tag1 and Tag2 to the tag reader R and to separate the tips of the two wireless tags Tag1 and Tag2 as much as possible. This is to make it happen.

  Even if the crossing portion is slightly shifted in the longitudinal direction, the purpose of making the crossing instantly cannot be achieved. Therefore, the wireless tags Tag1 and Tag2 only need to intersect the other wireless tags Tag2 and Tag1 at the center. The central portion means a range in which the intersecting purpose can be achieved. For example, the central portion is a central portion when the wireless tag Tag is equally divided into three in the longitudinal direction.

<Modification 3>
Although the above-described embodiment includes two wireless tags Tag, the number of wireless tags Tag may be three or more. FIG. 13 shows an arrangement example of the three wireless tags Tag when three wireless tags Tag are provided. In FIG. 13, the crossing angle of the wireless tag Tag1 and the wireless tag Tag2 is 90 °. On the other hand, the wireless tag Tag3 is arranged so as to intersect the two wireless tags Tag1 and Tag2 at an equal angle.

  As shown in FIG. 13, in the case of providing three wireless tags Tag, when any one wireless tag Tag is used as the reference wireless tag shown in the first modification, the wireless tag Tag3 is used as the reference wireless tag. It is preferable that In this way, the tips of the wireless tag Tag1 and the wireless tag Tag2 that are measurement wireless tags can be separated.

<Modification 4>
Further, the method of estimating the moisture content Wt based on the response power of the plurality of wireless tags Tag is not limited to the method described in the above embodiment. For example, the method disclosed in the first embodiment of Patent Document 1 may be used. That is, the tag reader R determines whether or not information can be read from the wireless tag Tag while sequentially changing the transmission power, corrects the reception power at the time of reading with the transmission power at that time, and after the correction The moisture content Wt may be estimated based on the received power.

<Modification 5>
Further, the wireless tag Tag in the above-described embodiment is a passive tag, but even an active tag is affected by the relative permittivity of the measurement object (in other words, the influence of the moisture content Wt of the measurement object). That is the same as passive tags. Therefore, the wireless tag in the moisture content estimation system of the present invention may be an active tag.

12: handle part, 14: display part, 20: wood, 30: circuit part, 31: antenna, 102: antenna, 104: antenna duplexer, 106: IQ demodulator, 108: reception level measuring part, 110: decoding , 120: control unit, 121: reception level difference calculation unit, 122: moisture content determination unit, 130: storage device, 132: coding unit, 134: modulator, 136: local oscillator, 138: variable gain amplifier, 140: Power amplifier, R: Tag reader, Tag: Wireless tag

Claims (5)

A plurality of wireless tags (Tags) that have different resonance frequencies and are fixed to the same measurement object (20);
A tag reader (R) capable of communicating with the plurality of wireless tags;
A moisture content estimation system that estimates the moisture content of the measurement object based on a comparison of reception levels that are signal levels of reception signals received from the plurality of wireless tags by the tag reader,
The moisture content estimation system, wherein the plurality of wireless tags are fixed to the measurement object such that another wireless tag intersects at the center of each wireless tag. In claim 1,
The moisture content estimation system comprising two wireless tags whose crossing angles are within 90 ° ± 30 ° as the plurality of wireless tags. In claim 1 or 2,
The measurement object is wood;
As the plurality of wireless tags, two wireless tags in which a difference between an absolute value of an angle of one wireless tag with respect to the wood grain and an absolute value of an angle of the other wireless tag with respect to the wood grain is within 40 ° A moisture content estimation system comprising: In any one of Claims 1-3,
One of the plurality of wireless tags as a reference wireless tag,
Another one of the plurality of wireless tags is a measurement wireless tag,
A reception level difference calculation unit (121) for calculating a difference between a reception level of the signal received from the measurement wireless tag and a reception level of the signal received from the reference wireless tag;
A moisture content determination unit (122) that determines the moisture content of the measurement object based on a preset relationship in which the moisture content is determined from the difference in the reception level and the difference in the reception level calculated by the reception level difference calculation unit. And a moisture content estimation system. In claim 4,
The wireless tag for reference includes a relative permittivity capable of ignoring an influence due to a change in moisture content of the measurement object,
The moisture content estimation system, wherein the measurement wireless tag includes a relative permittivity in which response power changes due to a change in moisture content of the measurement object.

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