JP6787834B2 - Permittivity measurement systems, equipment and methods - Google Patents

Description

The present invention relates to a permittivity measuring system, apparatus and method for measuring the relative permittivity of an object using electromagnetic waves.

In recent years, product inspection has become more important in article manufacturers. In particular, food manufacturers may be in a situation where their business performance is tight due to the contamination of processed foods with foreign substances, such as deterioration of company reliability and suspension of shipment. At the stage of product shipment inspection, it is desirable to detect foreign matter mixed in the product and prevent the product containing foreign matter from being shipped. However, although the imaging device, which is an existing detection device, can detect metals, there is a problem that it cannot detect organic substances such as insects and foods different from products with high accuracy.

On the other hand, if the relative permittivity of an object can be obtained, it becomes possible to detect the inclusion of foreign matter in the object. Conventionally, a dual frequency CW (Continuous Wave) method has been proposed as a method for measuring the relative permittivity of an object using electromagnetic waves (see Non-Patent Document 1). The measurement is performed when there is no object to be measured between the electromagnetic wave radiator 100 and the detector 101 as shown in FIG. 10 (A) and when there is an object to be measured 102 as shown in FIG. 10 (B). Do it times.

First, in the configuration of FIG. 10A, the phases θ ₁ _ _air and θ ₂ _ _air after _two electromagnetic waves of different frequencies f ₁ and f ₂ have passed through the _air are measured. Next, to measure the phase theta ₁ _ _sample and theta ₂ _ _sample after two different electromagnetic waves frequencies f ₁ and f ₂ are transmitted through the DUT 102 in the configuration of FIG. 10 (B), the object to be measured 102 Calculate the phase change with the measurement result when there is no θ ₁ = θ ₁ _ _sample − θ ₁ _ _air , θ ₂ = θ ₂ _ _sample − θ ₂ _ _air . These phase changes theta _1, the phase difference theta ₂ - [theta] ₁ is the difference between the theta ₂ is represented by the formula (1). The relative permittivity ε _r of the object to be measured 102 can be calculated by this equation (1). In the formula (1), L is the thickness of the object to be measured 102, and c is the speed of light.

However, in reality, since the phase fluctuation occurs due to the reflected wave generated inside the object to be measured, there is an error in the measured phase change. In order to perform highly accurate permittivity measurement by the conventional method disclosed in Non-Patent Document 1, it is necessary to widen the interval Δf = f ₂ −f ₁ between two frequencies as much as possible.

In FIG. 11A, the permittivity measurement error (calculation error of the relative permittivity ε _r ) decreases by 1 / Δf as the interval Δf between the two frequencies increases, but increases sharply when the upper limit of Δf is reached. Indicates to do. FIG. 11B shows a case where the interval Δf between the two frequencies is narrow, and since the phase of the observed electromagnetic wave has a turbulence affected by the measurement environment and the like, this turbulence becomes a phase error and the permittivity. It shows that the measurement error becomes large. On the other hand, when the interval Δf between the two frequencies is widened as shown in FIG. 11C, the influence of the phase error is reduced and the error in the permittivity measurement is reduced, but the position between the two frequencies is reduced as shown in FIG. 11D. If the phase difference changes by 2π or more, measurement becomes impossible (upper limit of Δf in FIG. 11A). As described above, the method disclosed in Non-Patent Document 1 has a problem that the relative permittivity of an object cannot be measured with high accuracy because there is an upper limit to the interval Δf between two frequencies.

As a method for solving such a problem, the inventors have proposed a method for performing phase connection at a plurality of frequencies (see Non-Patent Document 2). In non-patent disclosed in reference 2 a dielectric constant measuring method, to measure the electromagnetic wave of the phase after the interval f _s between adjacent frequency is transmitted through the DUT with electromagnetic waves of a plurality of frequencies satisfy the formula (2) , Phase connection is performed for each measured phase to compensate for the phase discontinuity (FIG. 12).

Epsilon _eff _ _max of the formula (2) is the maximum value of the effective dielectric constant of the object to be measured can take. The phase connection (unwrap) calculates the difference between the phases θ _n and θ _{n + 1} of electromagnetic waves of two adjacent frequencies, and if the calculated difference is 0 or more, all the phases after θ _{n + 1} 0 is added to, and if the difference is negative, 2π is added to all the phases after θ _{n + 1} . Point 120 in FIG. 12 indicates a phase sampling point (phase measurement point), point 121 indicates a point after phase connection, and a straight line 122 indicates a true value of the phase inclination.

In the method disclosed in Non-Patent Document 2, after the phase connection is performed, the phase inclination as shown by the straight line 123 in FIG. 12 is calculated from the first phase sampling point and the last phase-connected point. The relative permittivity of the object to be measured is calculated using the formula (1). In this way, in the method disclosed in Non-Patent Document 2, the bifrequency interval Δf can be widened, and the measurement error of the relative permittivity can be reduced.

However, in reality, the band of the transmitting / receiving device (for example, an amplifier, an oscillator, etc.) used for measurement is limited. Generally, the band of a device near the center frequency of 300 GHz is about 30 GHz, which is 10% of 300 GHz. Therefore, the method disclosed in Non-Patent Document 2 cannot extend the two-frequency interval Δf beyond the band of the transmission / reception device used for measurement, and has a problem that it is difficult to further reduce the measurement error.

Liangliang Zhang, et al., “Terahertz multiwavelength phase imaging without 2π ambiguity”, Optics letters, Vol.31, Issue 24, pp.3668-3670, 2006 T.Jyo, et al., “THz Permittivity Imaging Using Multi-tone Unwrapped Phase Slope method”, IRMMW 2016

The present invention has been made to solve the above problems, and an object of the present invention is to further reduce the measurement error of the relative permittivity of an object in a dielectric constant measuring method using electromagnetic waves of a plurality of frequencies.

The permittivity measurement system of the present invention includes a transmitter that irradiates an object to be measured with electromagnetic waves having frequencies f ₁ , f ₂ , ..., F _m of m (m is an integer of 3 or more), and the object to be measured. The transmitter includes a receiver that detects an electromagnetic wave transmitted through the object and calculates the relative permittivity of the object to be measured, and the transmitter sets the assumed maximum relative permittivity of the object to be measured to ε _eff _ _max . When the known thickness of the object to be measured is L and the speed of light is c, the interval f _s between two adjacent frequencies f _n and f _{n + 1} (n is an integer greater than or equal to 1 (m-1)) is
The m frequency f ₁ satisfying, f _2, · · ·, and emitting an electromagnetic wave of f _m to the measured object, wherein the receiver is the m frequency f ₁ which has transmitted through the DUT, f ₂ , ..., an antenna for receiving an electromagnetic wave of f _m, the frequency f ₁ of m received by the antenna, f _2,..., a phase measurement section for measuring a respective phase of the electromagnetic wave of f _m , The phase difference calculation unit that calculates the phase difference of electromagnetic waves of two adjacent frequencies f _n and f _{n + 1} based on the measurement result of this phase difference measurement unit, and the phase difference calculated by this phase difference calculation unit are negative. In the case of, an update processing unit that repeats the process of adding 2π to each of the phases of electromagnetic waves of each frequency after f _{n + 1} and updating from n = 1 to n = m-1, and m frequencies f ₁ , F ₂ , ..., The phase of the electromagnetic wave of the lowest frequency f ₁ of f _m and the phase of the electromagnetic wave of m-1 frequencies f ₂ , ..., f _m excluding f ₁ are updated as described above. The relative dielectric constant of the measured object is calculated from the approximated portion that linearly approximates the phase after being updated by the processing unit, the inclination of the approximated straight line obtained by this approximated portion, and the thickness L of the measured object. It is characterized in that it is composed of a specific dielectric constant calculation unit.

Further, in one configuration example of the dielectric constant measuring system of the present invention, the phase measuring unit is in a state where there is only a background material between the transmitter and the antenna of the receiver and there is no object to be measured. The phase is measured once for each of the background material and the object to be measured, and the phase difference calculation unit measures the electromagnetic wave with only the background material and no object to be measured. The phase change, which is the difference between the phase of the above and the phase of the electromagnetic wave measured in a certain state between the background material and the object to be measured, is calculated for each frequency, and the electromagnetic waves of two adjacent frequencies f _n and f _{n + 1} are calculated. The difference between the phase change θ _n and θ _{n + 1} of the above is taken as the phase difference of the electromagnetic waves having these frequencies f _n and f _{n + 1} , and the phase difference calculated by the phase difference calculation unit is negative in the update processing unit. In the case of, the process of adding 2π to each of the phase changes θ _{n + 1} , θ _{n + 2} , ···, and θ _m of the electromagnetic waves of each frequency after f _{n + 1} and updating is performed from n = 1 to n. Repeating up to = m-1, the approximation part is the phase change θ ₁ of the electromagnetic wave of the lowest frequency f ₁ among _m frequencies f ₁ , f ₂ , ..., F _m , and m excluding f _1. -1 frequency f _2,..., the phase theta ₂ of the electromagnetic wave of f _m, ..., theta _m the update processing unit phase change phi ₂ after updating by, ..., and phi _m It is characterized by linear approximation.

Further, the permittivity measuring device of the present invention includes an antenna that receives electromagnetic waves of frequencies f ₁ , f ₂ , ..., F _m transmitted through an object to be measured (m is an integer of 3 or more). A phase measuring unit that measures the phase of each of the _m electromagnetic waves of frequencies f ₁ , f ₂ , ..., And fm received by the antenna, and two adjacent frequencies based on the measurement results of this phase measuring unit. When the phase difference calculation unit that calculates the phase difference of electromagnetic waves of f _n and f _{n + 1} (n is an integer of 1 or more (m-1) or less) and the phase difference calculated by this phase difference calculation unit are negative. An update processing unit that repeats the process of adding 2π to each of the phases of electromagnetic waves of each frequency after f _{n + 1} and updating from n = 1 to n = m-1, and m frequencies f ₁ , f. _The update processing unit updates the phase of the electromagnetic wave having the lowest frequency f ₁ of ₂ , ..., F _m and the phase of the electromagnetic wave having m-1 frequencies f ₂ , ..., f _m excluding f _1. The relative permittivity of the object to be measured is calculated from the approximation portion that linearly approximates the phase after updating by, the inclination of the approximation straight line obtained by this approximation portion, and the known thickness L of the object to be measured. The electromagnetic wave of the _m frequencies f ₁ , f ₂ , ..., F _m is provided with a relative permittivity calculation unit, and the expected maximum relative permittivity of the object to be measured is ε _eff _ _max , and the light velocity. When c is, the interval f _s between two adjacent frequencies f _n and f _{n + 1} is
It is characterized by satisfying.

Further, the dielectric constant measuring method of the present invention, when the maximum dielectric constant of epsilon _eff _ _max envisaged of the object to be measured, a known thickness of said object to be measured was L, and speed of light is c, two adjacent The interval f _s between the frequencies f _n and f _{n + 1}
The object to be measured is irradiated with electromagnetic waves having frequencies f ₁ , f ₂ , ..., F _m of m (m is an integer of 3 or more, n is an integer of 1 or more (m-1) or less) that satisfies the above conditions. The first step, the second step of receiving the electromagnetic waves of _m frequencies f ₁ , f ₂ , ..., F _m transmitted through the object to be measured, and the m received in this second step. A third step of measuring the phases of electromagnetic waves of frequencies f ₁ , f ₂ , ..., F _m , and two adjacent frequencies f _n , f _{n +} based on the measurement results of this third step. _When the fourth step of calculating the phase difference of the electromagnetic wave of ₁ and the phase difference calculated in this fourth step are negative, add 2π to each of the phases of the electromagnetic waves of each frequency after f _{n + 1.} The fifth step of repeating the updating process from n = 1 to n = m-1, and the phase of the electromagnetic wave having the lowest frequency f ₁ among the _m frequencies f ₁ , f ₂ , ..., F _m. When, m-1 pieces of frequency f ₂ with the exception of f _1, · · ·, a sixth step of linearly approximating a phase after the electromagnetic wave of the phase of the f _m was updated by the fifth step, the first It is characterized by including a seventh step of calculating the relative dielectric constant of the object to be measured from the inclination of the approximate straight line obtained in step 6 and the thickness L of the object to be measured.

According to the present invention, by receiving electromagnetic waves of two adjacent m number of electromagnetic waves with a frequency appropriate set the interval f _s frequency is irradiated to the measurement object, the m frequencies transmitted through the DUT , Each phase of the electromagnetic wave is measured, and the phase difference of the electromagnetic waves of two adjacent frequencies f _n and f _{n + 1} is calculated based on the measurement result, and when the calculated phase difference is negative, f _{n + 1} The process of adding 2π to each of the phases of the electromagnetic waves of each subsequent frequency and updating is repeated from n = 1 to n = m-1, and the phase of the electromagnetic wave having the lowest frequency f ₁ among the m frequencies is used. , m-1 pieces of frequency f ₂ with the exception of f _1, · · ·, linear approximation the phase after the electromagnetic wave updates f _m, and a thickness L of the slope and the object to be measured of the approximate straight line, to be measured By calculating the specific dielectric constant of an object, the specific dielectric constant of the object to be measured can be detected with higher accuracy than before within the range of the frequency interval Δf = f _m −f ₁ limited by the transmitting / receiving device. ..

FIG. 1 is a diagram illustrating a dielectric constant measuring method of the present invention. FIG. 2 is a diagram for explaining the phase fluctuation of the electromagnetic wave due to the reflected wave generated inside the object to be measured. FIG. 3 is a diagram showing the phase fluctuation of the electromagnetic wave when only the fundamental wave and the twice reflected wave are present. FIG. 4 is a block diagram showing a configuration of a permittivity measurement system according to an embodiment of the present invention. FIG. 5 is a flowchart illustrating the operation of the permittivity measurement system according to the embodiment of the present invention. FIG. 6 is a diagram illustrating an example of an object to be measured to be measured according to an embodiment of the present invention. FIG. 7 is a diagram showing the results of calculating the permittivity measurement error in the conventional permittivity measurement method and the permittivity measurement method according to the embodiment of the present invention. FIG. 8 is a diagram illustrating another example of the object to be measured to be measured according to the embodiment of the present invention. FIG. 9 is a diagram showing the results of measuring the relative permittivity of the object to be measured by the conventional permittivity measuring method and the permittivity measuring method according to the embodiment of the present invention. FIG. 10 is a diagram illustrating a configuration of an optical system used in a conventional dielectric constant measuring method. FIG. 11 is a diagram illustrating a problem of the conventional dielectric constant measuring method. FIG. 12 is a diagram illustrating another conventional method for measuring a permittivity.

[Principle of invention]
In the present invention, as shown in FIG. 1, a plurality of frequencies f ₁ , f ₂ , ..., f _n , f in which the intervals f _s = f _{n + 1} −f _n of adjacent frequencies satisfy the following equation (3). Measure the phase of the electromagnetic wave after it has passed through the object to be measured by the electromagnetic waves of _{n + 1} , ..., f _m-1 , f _m (m is an integer of 3 or more, n is 1 or more (m-1) or less). Integer). At this time, let θ _n be the phase detected at the frequency f _n of the electromagnetic wave (the phase change when there is no object to be measured and when there is an object to be measured). The white circles in FIG. 1 indicate the phase sampling points (phase measurement points).

In the formula (3), L is the thickness of the object to be measured, c is the speed of light, and ε _{eff _max} is the maximum value of the effective relative permittivity that the object to be measured can take. When the permittivity is measured according to the present invention, a preset fixed value is used for ε _eff _ _max .

Next, a phase connection is made for each phase measured in the same manner as in the conventional case. Specifically, the difference between the phases θ _n and θ _{n + 1} of electromagnetic waves of two adjacent frequencies f _n and f _{n + 1} is calculated, and if the calculated difference is negative, θ _{n + 1} or later. 2π is added to all of the phases θ _{n + 1} , θ _{n + 2} , ···, θ _m of to update. When the difference is 0 or more, 0 may be added to all of the phases θ _{n + 1} , θ _{n + 2} , ..., θ _m . That is, when the difference is 0 or more, it is not necessary to update the value.

The above update step is repeated from n = 1 to n = m-1. After the update step up to n = m-1, the phases θ _{n + 1} , θ _{n + 2} , ···, θ _m are changed to φ _{n + 1} , φ _{n + 2} , ···, φ _m . To do. The black circles in FIG. 1 indicate the points after the phase connection. Since the phase theta ₁ of the electromagnetic wave of frequency f ₁ is not subject to update, without phi _1, is set to remain theta _1.

Subsequently, a linear approximation is performed by the least squares method for each phase θ ₁ , φ ₂ , ···, φ _n , φ _{n + 1} , ···, φ _m after phase connection. Finally, the relative permittivity ε _r of the object to be measured is calculated from the slope α of the approximate straight line using Eq. (4).

The straight line 50 in FIG. 1 shows a straight line obtained by the conventional phase connection, the straight line 51 shows the straight line obtained by the straight line approximation of the present invention, and the straight line 52 shows the true value of the phase inclination.
According to the present invention, it is possible to average the error due to the phase fluctuation of the electromagnetic wave caused by the reflected wave in the object to be measured, and further reduce the measurement error within the range of Δf limited by the transmission / reception device.

Next, the derivation of the equation (3) will be described. The fluctuations of the phases θ ₁ , θ ₂ , ···, θ _n , θ _{n + 1} , ···, θ _m on the frequency axis shown in FIG. 1 are the fundamental wave (wave transmitted without reflection) and the reflected wave. It is caused by the interference with and the interference between the reflected waves. The phase fluctuation is composed of the overlap of periodic functions according to the difference in propagation length of each interference wave. Therefore, by sampling one cycle or more at a frequency interval finer than 1/2 cycle of the phase fluctuation and linearly approximating the phase fluctuation, the phase fluctuation can be averaged and its influence can be reduced.

For the sake of explanation, consider an object 10 having a relative permittivity ε ₂ = 3 and a thickness L = 30 mm, as shown in FIG. 2, surrounded by air (relative permittivity ε ₁ = 1). .. It is assumed that only the fundamental wave and the double reflected wave exist in the object 10 to be measured. In FIG. 2, for the sake of clarity, the fundamental wave and the double reflected wave are described so as to be separated from each other in position, but in reality, the fundamental wave and the double reflected wave are at the same position. It is a wave generated by overlapping with.

The propagation length difference D between the fundamental wave and the double reflected wave is expressed by Eq. (5).

Further, the period CY of the phase fluctuation of the electromagnetic wave due to the fundamental wave and the twice reflected wave is expressed by the equation (6) (FIG. 3).

That is, the larger the propagation length difference D between the fundamental wave and the twice reflected wave, the finer the period CY of the fluctuation of the phase θ on the frequency axis of FIG. As a reflected wave in the object to be measured 10 twice when only the reflected wave is present, the electromagnetic waves after passing through the object to be measured 10 for more than one period of the phase swing at a frequency interval f _s shown in Equation (7) Phase By measuring θ and obtaining an approximate straight line from each phase θ, the influence of the fluctuation of the phase θ is reduced, and a desired phase gradient can be obtained.

On the other hand, in the actual object 10 to be measured, infinite reflections occur, such as two reflections, four reflections, and so on. In order to cancel the influence of all reflected waves, it is necessary to measure the phase θ with electromagnetic waves with infinitely fine frequency intervals. However, the energy E of the reflected wave is attenuated as in the equation (8) according to the number of reflections n of the electromagnetic wave in the object to be measured 10.

That is, since the energy of the reflected wave after the fourth reflection is greatly attenuated, the second reflected wave has the greatest influence on the fluctuation of the phase θ. Therefore, when the propagation length difference D between the fundamental wave in two reflection longest to fit (if shaking of the phase θ is the most fine), to choose the interval f _s of the frequency of electromagnetic waves used for the measurement desirable.
When the maximum value of the effective permittivity of the object 10 to be measured is ε _eff _ _max , the largest propagation length difference D _{max from the} fundamental wave among the two reflections is expressed by Eq. (9).

Therefore, the phase θ is measured by electromagnetic waves of a plurality of frequencies whose frequency interval f _s satisfies the equation (3) over a frequency range of one cycle or more of the fluctuation of the phase θ, and a linear approximation is performed for each phase θ. , The influence of the fluctuation of the phase θ due to the propagation length difference D _max and the influence of the fluctuation of the phase θ due to the propagation length difference D shorter than D _max can be reduced.

[Example]
Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 4 is a block diagram showing a configuration of a permittivity measurement system according to an embodiment of the present invention. The permittivity measurement system uses a transmitter 1 that irradiates the object 10 with electromagnetic waves of frequencies f ₁ , f ₂ , ..., F _m of m (m is an integer of 3 or more) and the object 10 to be measured. It is composed of a receiver 2 (permittivity measuring device) that detects the transmitted electromagnetic wave and calculates the relative permittivity ε _r of the object 10 to be measured.
The receiver 2 includes an antenna 20, a phase measurement unit 21, a phase difference calculation unit 22, an update processing unit 23, an approximation unit 24, a relative permittivity calculation unit 25, and a calculation result output unit 26. There is.

FIG. 5 is a flowchart illustrating the operation of the permittivity measurement system of this embodiment. First, the relative dielectric constant ε transmitter 1 ₁ in the absence of the object to be measured 10 when there is only known background material 11 (e.g., air), m pieces of frequency _{f 1, f 2, ···,} f m The background material 11 is irradiated with the electromagnetic waves of (FIG. 5, step S100).

As described above, the distance f _s = f _{n + 1} −f _n between two adjacent frequencies satisfies the equation (3). In this embodiment, it is assumed the use of such contamination detection in food, for the maximum value epsilon _eff _ _max of the effective dielectric constant, in consideration of the maximum dielectric constant of the foreign matter, the possible values Should be set in advance. Further, in this embodiment, the thickness L of the object to be measured 10 in the direction from the transmitter 1 to the antenna 20 is a known value. The transmitter 1 may be any one capable of irradiating an object with electromagnetic waves having a plurality of frequencies on the order of GHz, for example.

Antenna 20 of the receiver 2, m pieces of frequency f ₁ that has passed through the background material 11, f _2, ···, receives an electromagnetic wave of f _m (Fig. 5 step S101).
The phase measuring unit 21 of the receiver ₂ measures the phases of the electromagnetic waves of _m frequencies f ₁ , f ₂ , ..., And fm received by the antenna 20 (step S102 in FIG. 5). A technique for measuring the phase of an electromagnetic wave (to be exact, the amount of change in the phase of a signal received by the receiver 2 with respect to a reference signal on the transmitter 1 side) is an existing technique such as a network analyzer (VNA). It is a well-known technique that can be realized using a measuring instrument.

Next, the user who uses the permittivity measurement system places the object 10 to be measured having a known thickness L and an unknown relative permittivity ε _r inside or above the background substance 11.
With the object 10 to be measured arranged in this way, the transmitter 1 irradiates the background substance 11 and the object 10 to be measured with electromagnetic waves having frequencies f ₁ , f ₂ , ..., F _m ( _m ). FIG. 5 step S103).

Antenna 20 of the receiver 2, the background material 11 and the m frequency f ₁ which has transmitted through the DUT 10, f _2, · · ·, receives an electromagnetic wave of f _m (Fig. 5 step S104).
The phase measuring unit 21 of the receiver ₂ measures the phases of the electromagnetic waves of _m frequencies f ₁ , f ₂ , ..., And fm received by the antenna 20 (step S105 in FIG. 5).

Subsequently, the phase difference calculation unit 22 of the receiver 2 calculates the phase change θ, which is the difference between the phase of the electromagnetic wave obtained in step S102 and the phase of the electromagnetic wave obtained in step S105, for each frequency of the electromagnetic wave. two adjacent frequencies f _n, the f n _{+ 1} (n is 1 or more (m-1) an integer) difference θ _{n + 1} -θ _n of the phase change theta _n and theta _{n + 1} of an electromagnetic wave, Let the phase difference Δθ of electromagnetic waves having two frequencies f _n and f _{n + 1} (step S106 in FIG. 5). As described above, in this embodiment, the net phase change due to the object 10 to be measured obtained by taking the difference between the two phase measurement results is defined as θ. The phase difference calculation unit 22 calculates the phase difference Δθ as described above for each of n = 1 to n = m-1.

Next, the update processing unit 23 of the receiver 2 determines whether or not the phase difference Δθ of the electromagnetic waves of two adjacent frequencies f _n and f _{n + 1} is negative (step S108 in FIG. 5), and the phase difference Δθ is negative. in the case of, θ _{n + 1} and subsequent phase change _{θ n + 1, θ n +} 2, ···, and updates by adding 2π to each theta _m (Fig. 5 step S109). As described above, when the phase difference Δθ is 0 or more, 0 is added to each of the phase changes θ _{n + 1} , θ _{n + 2} , ..., θ _m , so that the phase difference Δθ is 0. In the above cases, it is not necessary to update the phase change. Such an update step is repeated starting from n = 1 and increasing n by 1 (steps S107 to S110 in FIG. 5), and when the processing is completed up to n = m-1 (in step S111 in FIG. 5). YES), the operation of the update processing unit 23 ends. As described above, the phase changes θ _{n + 1} , θ _{n + 2} , ..., θ _m after the update step up to n = m-1 is completed, φ _{n + 1} , φ _{n + 2} , ...・, Φ _m .

By repeating the process of step S109, the phase changes θ _{n + 1} , θ _{n + 2} , ..., θ _m increase, but even after the process of step S109, the two adjacent frequencies f _n , The phase difference Δθ of the electromagnetic wave of f _{n + 1} does not change. Therefore, it is not necessary to recalculate the phase difference Δθ each time the process of step S109 is performed, and the determination process of step S108 may be performed based on the calculation result of the phase difference calculation unit 22.

The approximation part 24 of the receiver 2 has m-1 pieces excluding the phase changes θ ₁ and f ₁ of the electromagnetic wave having the lowest frequency f ₁ among _m frequencies f ₁ , f ₂ , ..., F _m . The phase change φ ₂ , ..., φ _m after the update of the electromagnetic wave of the frequencies f ₂ , ..., F _m is linearly approximated by the minimum square method (step S112 in FIG. 5).

The relative permittivity calculation unit 25 of the receiver 2 uses the slope α of the approximate straight line obtained by the approximate unit 24 and the known thickness L of the object 10 to be measured, and the object 10 to be measured according to the equation (4). The relative permittivity ε _{r of} is calculated (FIG. 5, step S113).

The calculation result output unit 26 of the receiver 2 outputs the calculation result of the relative permittivity calculation unit 25 (step S114 of FIG. 5). Specifically, the calculation result output unit 26, and transmits for example, specific to view the relative dielectric constant epsilon _r of the object to be measured 10 a dielectric constant calculator 25 has calculated, the information of the relative permittivity epsilon _r to the outside To do. As described above, the operation of the permittivity measurement system of this embodiment is completed.

In this embodiment, for comparison with the conventional case, as an example, the relative permittivity ε _r = 10 in the background material 11 having a relative permittivity ε ₁ = 3 and a thickness L ₁ = 30 mm as shown in FIG. The effect of this embodiment will be described when the object to be measured 10 having a thickness L = 2 to 10 mm is contained. Under this condition, the maximum value of the effective permittivity ε _{eff _max} is 4.88. Is calculated from equation (3), the frequency interval f _s required in the present embodiment is required to be 1.2GHz smaller value.

FIG. 7 shows a simulation result of a permittivity measurement error (calculation error of relative permittivity ε _r ) when two frequencies of f ₁ = 300 GHz and f ₂ = 308 GHz are used in the conventional method disclosed in Non-Patent Document 1. Shown in. In this case, the interval between the two frequencies is 8 GHz. The dotted line 70 in FIG. 7 shows an error when the relative permittivity ε _r of the object to be measured 10 is calculated by the method disclosed in Non-Patent Document 1. The maximum error was 14.5%.

The alternate long and short dash line 71 in FIG. 7 shows an error when the relative permittivity ε _r of the object to be measured 10 is calculated by the conventional method disclosed in Non-Patent Document 2. Here, the frequency interval Δf between the lowest frequency and the highest frequency of the electromagnetic wave is extended to 30 GHz by using five frequencies of f ₁ = 300 GHz, f ₂ = 308 GHz, f ₃ = 316 GHz, f ₄ = 324 GHz, and f ₅ = 330 GHz. did. The maximum error for this method was 3.7%.

On the other hand, the solid line 72 in FIG. 7 shows an error when the relative permittivity ε _r of the object to be measured 11 is calculated by the method of this embodiment. In this example, 31 frequencies at 1 GHz intervals from f ₁ = 300 GHz to f ₃₁ = 330 GHz were used. As a result of the simulation, it was found that the maximum error can be reduced to 0.86%.

Next, as another example of the object to be measured 10, as shown in FIG. 8, the case of the object 10 to be measured in which a foreign substance 10b made of a synthetic resin is contained in chocolate 10a having a length and width of 50 mm and a thickness of L = 21 mm is described. The effect of the embodiment will be described.

FIG. 9 (A) is a diagram showing the result of measuring the relative permittivity ε _r of the object to be measured 10 of FIG. 8 by the method disclosed in Non-Patent Document 1, and FIG. 9 (B) is disclosed in Non-Patent Document 2. shows the results of measuring the relative dielectric constant epsilon _r of the object to be measured 10 by methods, shows the FIG. 9 (C) is the result of the measurement of the relative dielectric constant epsilon _r of the object to be measured 10 by the method of the present embodiment Is. 9 (A), 9 (B), and 9 (C) show the distribution of the relative permittivity ε _r in the plane of the object to be measured 10 in different colors. Here, as for the method disclosed in Non-Patent Document 1, two frequencies of f ₁ = 280 GHz and f ₂ = 288 GHz were used. For Non-Patent Document 2 and the method of this example, 6 frequencies at 6 GHz intervals from f ₁ = 280 GHz to f ₆ = 310 GHz were used.

9 (D), 9 (E), and 9 (F) show the relative permittivity ε _r at the position of the straight line A in FIGS. 9 (A), 9 (B), and 9 (C), respectively. Is. 90 in FIGS. 9 (D), 9 (E), and 9 (F) shows the theoretical value of the relative permittivity ε _r , 91 shows the measurement result by the method disclosed in Non-Patent Document 1, and 92 shows the measurement result by the method disclosed in Non-Patent Document 1. The measurement result by the method disclosed in Non-Patent Document 2 is shown, and 93 shows the measurement result by the method of this Example. The measurement error of the relative permittivity ε _r at the position of the foreign matter 10b is 3.6% in the case of the method disclosed in Non-Patent Document 1 and 1.3% in the case of the method disclosed in Non-Patent Document 2. In the case of the method of the example, it was 0.29%.

The phase measurement unit 21, the phase difference calculation unit 22, the update processing unit 23, the approximation unit 24, the relative permittivity calculation unit 25, and the calculation result output unit 26 described in this embodiment are a CPU (Central Processing Unit) and a storage device. It can be realized by a computer equipped with an interface and a program that controls these hardware resources. The program for realizing the permittivity measuring method of the present invention is provided in a state of being recorded on a recording medium such as a flexible disk, a CD-ROM, a DVD-ROM, or a memory card, and is stored in a storage device. The CPU of the computer executes the process described in this embodiment according to the program stored in the storage device.

The present invention can be applied to a technique for measuring the relative permittivity of an object using electromagnetic waves.

1 ... Transmitter, 2 ... Receiver, 10 ... Object to be measured, 11 ... Background material, 20 ... Antenna, 21 ... Phase measurement unit, 22 ... Phase difference calculation unit, 23 ... Update processing unit, 24 ... Approximation unit, 25 ... Relative permittivity calculation unit, 26 ... Calculation result output unit.

Claims (6)

A transmitter that irradiates an object to be measured with electromagnetic waves of frequencies f ₁ , f ₂ , ..., F _m of m (m is an integer of 3 or more).
It is equipped with a receiver that detects electromagnetic waves transmitted through the object to be measured and calculates the relative permittivity of the object to be measured.
The transmitter has a maximum dielectric constant of epsilon _eff _ _max envisaged of the object to be measured, said known thickness of the object to be measured L, when the speed of light is c, the two adjacent frequency f _n, The interval f _{s of} f _{n + 1} (n is an integer greater than or equal to 1 (m-1)) is
The object to be measured is irradiated with electromagnetic waves having _m frequencies f ₁ , f ₂ , ..., F _m that satisfy the conditions.
The receiver
An antenna that receives electromagnetic waves of _m frequencies f ₁ , f ₂ , ..., F _m that have passed through the object to be measured, and
A phase measuring unit that measures the phase of each of the _m electromagnetic waves of frequencies f ₁ , f ₂ , ..., F _m received by this antenna, and
A phase difference calculation unit that calculates the phase difference between two adjacent electromagnetic waves of frequencies f _n and f _{n + 1} based on the measurement results of this phase measurement unit.
When the phase difference calculated by the phase difference calculation unit is negative, the process of adding 2π to each of the phases of the electromagnetic waves of each frequency after f _{n + 1} and updating is performed from n = 1 to n = m-1. Update processing unit that repeats up to
The phase of the electromagnetic wave of the lowest frequency f ₁ of _m frequencies f ₁ , f ₂ , ..., F _m , and m-1 frequencies f ₂ , ..., f _m excluding f ₁ . An approximation unit that linearly approximates the phase of the electromagnetic wave after it has been updated by the update processing unit, and
A dielectric characterized by being composed of a relative permittivity calculation unit that calculates the relative permittivity of the object to be measured from the slope of the approximate straight line obtained by the approximate unit and the thickness L of the object to be measured. Permittivity measurement system. In the dielectric constant measuring system according to claim 1,
The phase measuring unit is 1 in each of a state where there is only a background material between the transmitter and the antenna of the receiver and there is no object to be measured, and there is a background material and the object to be measured. The phase is measured one time at a time.
The phase difference calculation unit determines the phase of the electromagnetic wave measured in the state where there is only the background material and the object to be measured, and the phase of the electromagnetic wave measured in the state where the background material and the object to be measured are present. The phase change, which is the difference, is calculated for each frequency, and the difference between the phase changes θ _n and θ _{n + 1} of the electromagnetic waves of two adjacent frequencies f _n , f _{n + 1} is calculated by these frequencies f _n , f _{n + 1.} The phase difference of the electromagnetic waves of
When the phase difference calculated by the phase difference calculation unit is negative, the update processing unit changes the phase of the electromagnetic wave of each frequency after f _{n + 1,} θ _{n + 1} , θ _{n + 2} , ..., θ. _The process of adding 2π to each of _m and updating is repeated from n = 1 to n = m-1.
The approximation part is the phase change θ ₁ of the electromagnetic wave of the lowest frequency f ₁ among _m frequencies f ₁ , f ₂ , ..., F _m , and m-1 frequencies f ₂ excluding f _1. a feature., phase theta ₂ of the electromagnetic wave of f _m, ..., theta phase change after the _m updated by the update processing unit phi _2, ..., to linear approximation and phi _m Dielectric constant measurement system. An antenna that receives electromagnetic waves of frequencies f ₁ , f ₂ , ..., F _m that have passed through the object to be measured and have m (m is an integer of 3 or more).
A phase measuring unit that measures the phase of each of the _m electromagnetic waves of frequencies f ₁ , f ₂ , ..., F _m received by this antenna, and
A phase difference calculation unit that calculates the phase difference of electromagnetic waves of two adjacent frequencies f _n and f _{n + 1} (n is an integer of 1 or more (m-1) or less) based on the measurement result of this phase measurement unit.
When the phase difference calculated by the phase difference calculation unit is negative, the process of adding 2π to each of the phases of the electromagnetic waves of each frequency after f _{n + 1} and updating is performed from n = 1 to n = m-1. Update processing unit that repeats up to
The phase of the electromagnetic wave of the lowest frequency f ₁ of _m frequencies f ₁ , f ₂ , ..., F _m , and m-1 frequencies f ₂ , ..., f _m excluding f ₁ . An approximation unit that linearly approximates the phase of the electromagnetic wave after it has been updated by the update processing unit, and
A relative permittivity calculation unit for calculating the relative permittivity of the object to be measured is provided from the slope of the approximate straight line obtained by the approximate section and the known thickness L of the object to be measured.
The electromagnetic waves of the _m frequencies f ₁ , f ₂ , ..., F _m are two adjacent ones when the assumed maximum relative permittivity of the object to be measured is ε _eff _ _max and the speed of light is c. The interval f _s between the frequencies f _n and f _{n + 1}
A permittivity measuring device characterized by satisfying. In the dielectric constant measuring apparatus according to claim 3,
The phase measuring unit measures the phase once in each of a state where there is only a background substance in the direction of arrival of the electromagnetic wave and there is no object to be measured and a state where the background substance and the object to be measured are present. Do,
The phase difference calculation unit determines the phase of the electromagnetic wave measured in the state where there is only the background material and the object to be measured, and the phase of the electromagnetic wave measured in the state where the background material and the object to be measured are present. The phase change, which is the difference, is calculated for each frequency, and the difference between the phase changes θ _n and θ _{n + 1} of the electromagnetic waves of two adjacent frequencies f _n , f _{n + 1} is calculated by these frequencies f _n , f _{n + 1.} The phase difference of the electromagnetic waves of
When the phase difference calculated by the phase difference calculation unit is negative, the update processing unit changes the phase of the electromagnetic wave of each frequency after f _{n + 1,} θ _{n + 1} , θ _{n + 2} , ..., θ. _The process of adding 2π to each of _m and updating is repeated from n = 1 to n = m-1.
The approximation part is the phase change θ ₁ of the electromagnetic wave of the lowest frequency f ₁ among _m frequencies f ₁ , f ₂ , ..., F _m , and m-1 frequencies f ₂ excluding f _1. a feature., phase theta ₂ of the electromagnetic wave of f _m, ..., theta phase change after the _m updated by the update processing unit phi _2, ..., to linear approximation and phi _m Dielectric constant measuring device. When the assumed maximum relative permittivity of the object to be measured is ε _eff _ _max , the known thickness of the object to be measured is L, and the speed of light is c, the interval between two adjacent frequencies f _n and f _{n + 1} . f _s
The object to be measured is irradiated with electromagnetic waves having frequencies f ₁ , f ₂ , ..., F _m of m (m is an integer of 3 or more, n is an integer of 1 or more (m-1) or less) that satisfies the above conditions. Step 1 and
The second step of receiving electromagnetic waves of _m frequencies f ₁ , f ₂ , ..., F _m transmitted through the object to be measured, and
The third step of measuring the phases of the electromagnetic waves of _m frequencies f ₁ , f ₂ , ..., And f _m received in this second step, and
Based on the measurement results of this third step, the fourth step of calculating the phase difference between the electromagnetic waves of two adjacent frequencies f _n and f _{n + 1} and
When the phase difference calculated in the fourth step is negative, the process of adding 2π to each of the phases of the electromagnetic waves of each frequency after f _{n + 1} and updating is performed from n = 1 to n = m-1. The fifth step to repeat and
The phase of the electromagnetic wave of the lowest frequency f ₁ of _m frequencies f ₁ , f ₂ , ..., F _m , and m-1 frequencies f ₂ , ..., f _m excluding f ₁ . A sixth step of linearly approximating the phase of the electromagnetic wave after updating the phase in the fifth step, and
The permittivity includes a seventh step of calculating the relative permittivity of the object to be measured from the slope of the approximate straight line obtained by the sixth step and the thickness L of the object to be measured. Measuring method. In the dielectric constant measuring method according to claim 5,
The third step is performed once for each of the state where there is only the background substance and there is no object to be measured and the state where there is the background substance and the object to be measured.
In the fourth step, the phase of the electromagnetic wave measured with only the background material and the object to be measured and the phase of the electromagnetic wave measured with the background material and the object to be measured are set. The phase change, which is the difference, is calculated for each frequency, and the difference between the phase changes θ _n and θ _{n + 1} of the electromagnetic waves of two adjacent frequencies f _n , f _{n + 1} is calculated by these frequencies f _n , f _{n + 1.} Including the step of making the phase difference of the electromagnetic wave of
In the fifth step, when the phase difference calculated in the fourth step is negative, the phase change of the electromagnetic wave of each frequency after f _{n + 1 is} θ _{n + 1} , θ _{n + 2} , ..., θ. _The process of adding 2π to each of _m and updating it includes a step of repeating from n = 1 to n = m-1.
In the sixth step, the phase change θ ₁ of the electromagnetic wave having the lowest frequency f ₁ among _m frequencies f ₁ , f ₂ , ..., F _m , and m-1 frequencies excluding f ₁ step f _2, ···, phase theta ₂ of the electromagnetic wave of f _m, ···, phase change after updating theta _m by the fifth step φ _2, ···, linear approximation and phi _m A method for measuring a dielectric constant, which comprises.