JP2018179663A - Permittivity measurement system, device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce measurement errors of relative permittivity of an object.SOLUTION: A permittivity measurement system comprises: a transmitter 1 that irradiates a measured object 10 with m pieces of electromagnetic waves of frequencies f, f, ..., f; a phase measurement unit 21 that measures phases of received m pieces of electromagnetic waves of frequencies f, f, ..., f; a phase difference calculation unit 22 that calculates a phase difference between adjacent two electromagnetic waves of frequencies fand fon the basis of a measurement result; an update processing unit 23 that, when the phase difference is negative, repeats processing for adding 2π to each phase of the electromagnetic wave of each frequency following f, and updating the phase of the electromagnetic wave from n=1 to n=m-1; an approximation unit 24 that linearly approximates a phase of the electromagnetic wave of a frequency fand post-updated phases of m-1-pieces of electromagnetic waves of frequencies f, ..., fexcluding f; and a relative permittivity calculation unit 25 that calculates a relative permittivity of the measured object 10 from a tilt of an approximate linear and a thickness L of the measured object 10.SELECTED DRAWING: Figure 4

Description

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

  In recent years, the importance of product inspection has increased in the manufacture of articles. In particular, in the case of food manufacturers, contamination of processed food with foreign substances may lead to a situation in which the company's reliability may decline or shipping may be halted, resulting in tight performance. It is desirable to detect contamination of the product at the product inspection stage to prevent shipment of the product contaminated with contamination. However, although the imaging apparatus which is the existing detection apparatus can detect metals, it has a problem that it can not detect organic substances such as insects and food different from products with high accuracy.

  On the other hand, if the relative permittivity of the object can be determined, it is possible to detect the entry of foreign matter into the object. Conventionally, a two-frequency CW (Continuous Wave) method has been proposed as a method of measuring the relative dielectric constant of an object using an electromagnetic wave (see Non-Patent Document 1). In the measurement, as shown in FIG. 10A, there is no object to be measured between the electromagnetic wave emitter 100 and the detector 101, and in the case where the object to be measured 102 is present as shown in FIG. 10B. Do it

First, in the configuration of FIG. 10A, the phases θ ₁ _ _air and θ _{2 _air} after electromagnetic waves of _two different frequencies f ₁ and f ₂ pass through _air are measured. Next, the phases θ ₁ _ _sample and θ ₂ _ _sample after the electromagnetic waves of _two different frequencies f ₁ and f ₂ pass through the object to be measured 102 in the configuration of FIG. The phase change θ ₁ = θ ₁ _ _sample −θ ₁ _ _air , θ ₂ = θ ₂ _ _sample −θ ₂ _ _air with respect to the measurement result when there is not is calculated. The phase difference θ ₂ −θ _{1 which} is the difference between the phase changes θ ₁ and θ ₂ is expressed by equation (1). The relative dielectric constant ε _r of the object to be measured 102 can be calculated by this equation (1). In the equation (1), L is the thickness of the object to be measured 102 and c is the speed of light.

However, in practice, there is an error in the measured phase change because the phase fluctuation occurs due to the reflected wave generated inside the object to be measured. In order to perform high-precision dielectric constant 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 error of the dielectric constant measurement (calculation error of the relative dielectric constant ε _r ) decreases by 1 / Δf with the increase of the interval Δf of two frequencies, but increases rapidly when the upper limit of Δf is reached. It shows that you do. FIG. 11 (B) shows the case where the interval Δf between the two frequencies is narrow, and the disturbance of the phase of the observed electromagnetic wave is affected by the measurement environment etc., so this disturbance becomes a phase error, and the dielectric constant It shows that the error of measurement becomes large. On the other hand, if the interval Δf of the two frequencies widens as shown in FIG. 11C, the influence of the phase error becomes smaller and the error of the dielectric constant measurement becomes smaller. However, as shown in FIG. When 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 dielectric constant of an object can not be measured with high accuracy because there is an upper limit to the two-frequency interval Δf.

As a method of solving such a problem, the inventors proposed a method of 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 of the measured phases to compensate for phase discontinuity (FIG. 12).

In the equation (2), 式_eff _ _max is the maximum value of the effective relative permittivity that can be taken by the object to be measured. The phase connection (unwrap) calculates the difference between the phases θ _n and θ _{n + 1} of electromagnetic waves of two adjacent frequencies, and when the calculated difference is 0 or more, all phases after θ _{n + 1} Is a process of adding 0 to all the phases after θ _{n + 1} and adding 2π if the difference is negative. A point 120 in FIG. 12 indicates a phase sampling point (phase measurement point), a point 121 indicates a point after phase connection, and a straight line 122 indicates the true value of the phase slope.

  In the method disclosed in Non-Patent Document 2, after phase connection is performed, the inclination of the phase as shown by a straight line 123 in FIG. 12 is calculated from the first phase sampling point and the last point connected in phase; The relative dielectric constant of the object to be measured is calculated using equation (1). Thus, the method disclosed in Non-Patent Document 2 can widen the two-frequency interval Δf and can reduce the measurement error of the relative dielectric constant.

  However, in practice, there is a limit to the band of the transmission / reception device (eg, amplifier, oscillator, etc.) used for measurement. Generally, the bandwidth of the device around the center frequency of 300 GHz is about 30 GHz of 10% of 300 GHz. Therefore, the method disclosed in Non-Patent Document 2 can not widen 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. 3686-3670, 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-mentioned problems, and it is an object of the present invention to further reduce the measurement error of the relative permittivity of an object in comparison with the conventional method in a permittivity measurement method using electromagnetic waves of a plurality of frequencies.

The dielectric constant measurement system of the present invention comprises a transmitter for irradiating an electromagnetic wave of _m (m is an integer of 3 or more) frequencies f ₁ , f ₂ ,..., F _{m to} the object to be measured, and the object to be measured And a receiver for detecting the electromagnetic wave that has passed through to calculate the relative dielectric constant of the device under test, and the transmitter is configured to estimate the maximum relative dielectric constant of the device under test by ε _eff _ _max , When the known thickness of the object is L and the speed of light is c, the distance f _s between two adjacent frequencies f _n and f _{n + 1} (n is an integer of 1 or more and (m-1) or less) is
The electromagnetic wave of _m frequencies f ₁ , f ₂ ,..., F _m satisfying the above is applied to the object to be measured, and the receiver transmits m frequencies f ₁ and f ₂ transmitted through the object to be measured. ,..., F _m, an antenna for receiving the electromagnetic waves, and a phase measurement unit for measuring the phase of each of the _m frequencies f ₁ , f ₂ ,. A phase difference calculation unit that calculates the phase difference between two adjacent electromagnetic waves having frequencies f _n and f _{n + 1} based on the measurement result of the phase measurement unit; and the phase difference calculated by the phase difference calculation unit is negative. In the case of f _{n + 1,} an update processing unit that adds 2π to each of the phases of the electromagnetic wave of each frequency after f _{n + 1} to update, repeats n = 1 to n = m−1, and m frequencies f ₁ , F ₂ ,..., F _m , the phase of the electromagnetic wave of the lowest frequency f ₁ , and m−1 frequencies f ₂ , excluding f ₁ ..., an approximation unit which linearly approximates the phase of the electromagnetic wave of f _m after updating by the update processing unit, the inclination of the approximation straight line obtained by the approximation unit, and the thickness L of the object to be measured And a relative dielectric constant calculation unit for calculating the relative dielectric constant of the object to be measured.

In one configuration example of the dielectric constant measurement system according to the present invention, the phase measurement unit includes only the background material between the transmitter and the antenna of the receiver and does not have the object to be measured. The phase measurement is performed once in each of the background substance and the object under measurement, and the phase difference calculation unit measures only the background substance and the electromagnetic wave measured without the object under measurement. Phase change, which is the difference between the phase of the electromagnetic wave measured in the presence of the background material and the object under test, is calculated for each frequency, and electromagnetic waves of two adjacent frequencies f _n and f _{n + 1} are calculated. The difference between the phase changes θ _n and θ _{n + 1} is the phase difference of the electromagnetic waves of these frequencies f _n and f _{n + 1} , and the update processing unit has a negative phase difference calculated by the phase difference calculator. f _{n + 1} subsequent phase change theta _{n + 1} of the electromagnetic wave of each frequency in the case of, θ _{n + 2,} ·· , Theta a process of updating by adding 2π to each _m, repeat from n = 1 to n = m-1, the approximate unit, m pieces of frequency f _1, f _2, ···, of f _m the lowest electromagnetic wave phase shift theta ₁ of frequency f ₁ of out, m-1 pieces of frequency f ₂ with the exception of f _1, · · ·, phase theta ₂ of the electromagnetic wave of f _m, ···, a theta _m It is characterized in that the phase changes φ ₂ ,..., Φ _m after being updated by the update processing unit are linearly approximated.

The dielectric constant measuring apparatus according to the present invention is an antenna for receiving _m electromagnetic waves (m is an integer of 3 or more) of frequencies f ₁ , f ₂ ,. A phase measurement unit that measures the phase of each of the _m electromagnetic waves having frequencies f ₁ , f ₂ ,..., F _m received by the antenna, and two adjacent frequencies based on the measurement result of the phase measurement unit A phase difference calculation unit that calculates the phase difference of electromagnetic waves f _n and f _{n + 1} (n is an integer of 1 or more and (m−1) or less) and the phase difference calculated by the phase difference calculation unit is negative And an update processing unit that repeats the process of adding 2π to the phase of the electromagnetic wave of each frequency after f _{n + 1} and updating it from n = 1 to n = m−1, m frequencies f ₁ , f _2, ..., and the phase of the lowest of the electromagnetic wave of the frequency f ₁ of the f _m, m-1 pieces of frequency f ₂ with the exception of f _1, ... from a phase after updating by the update processing unit an electromagnetic wave of the phase of f _m and approximation unit for linear approximation, the known thickness L of inclination as the object to be measured of the approximation straight line obtained by the approximation unit A relative dielectric constant calculating unit for calculating a relative dielectric constant of the object to be measured, and the _m electromagnetic waves having frequencies f ₁ , f ₂ ,..., F _m are assumed to be the object to be measured _Assuming that the maximum relative permittivity is ε _eff _ _max and the speed of light is c, the distance f _s between two adjacent frequencies f _n and f _{n + 1} is
It is characterized by satisfying.

In the dielectric constant measurement method of the present invention, assuming that the assumed maximum relative dielectric constant 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, 2 adjacent Interval f _{s of} two frequencies f _n and f _{n + 1}
The object to be measured is irradiated with electromagnetic waves of frequencies f ₁ , f ₂ ,..., F _m where m is an integer (m is an integer of 3 or more and n is an integer of 1 or more (m-1) or less) 1 step, a second step of receiving the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m transmitted through the object to be measured, and m pieces received in the second step The third step of measuring the phase of each of the electromagnetic waves of the frequencies f ₁ , f ₂ ,..., F _m , and two adjacent frequencies f _n , f _{n +} based on the measurement result of the third step Is added to each of the phases of the electromagnetic waves of each frequency after f _{n + 1} when the fourth step of calculating the phase difference of ₁ and the phase difference calculated in the fourth step is negative. A fifth step of repeating the process of updating from n = 1 to n = m-1, and m frequencies f ₁ , f ₂ ,. and the lowest frequency f ₁ of the electromagnetic wave of the phase of the _m, m-1 pieces of frequency f ₂ with the exception of f _1, · · ·, after the electromagnetic wave of the phase of the f _m is updated by said fifth step phase And the seventh step of calculating the relative dielectric constant of the object to be measured from the inclination of the approximate straight line obtained by the sixth step and the thickness L of the object to be measured. And a step.

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 The phase of each of the electromagnetic waves is measured, and the phase difference between the adjacent electromagnetic waves of the 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} A process of adding 2π to each of the phases of the electromagnetic waves of each frequency and updating the same is repeated from n = 1 to n = m−1, and the phase of the electromagnetic wave of the lowest frequency f ₁ among m frequencies and , F ₁ , m-1 pieces of the frequency of the electromagnetic wave of frequency f ₂ , ..., f _m after update are linearly approximated, and from the inclination of the approximate straight line and the thickness L of the object to be measured, Of the frequency interval Δf = f _m −f ₁ limited by the transmitting and receiving device by calculating the relative Within the range, the relative dielectric constant of the object to be measured can be detected with higher accuracy than in the past.

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

[Principle of the invention]
In the present invention, as shown in FIG. 1, a plurality of frequencies f ₁ , f ₂ ,..., F _n , f _where the spacing between adjacent frequencies f _s = f _{n +1} −f _n satisfies the following equation (3) _{n + 1, ···, f m} -1, an electromagnetic wave of f _m to measure the electromagnetic wave of the phase after transmission through the object to be measured (m is an integer of 3 or more, n represents 1 or (m-1) or less Integer). At this time, it is assumed that the phase detected at the frequency f _n of the electromagnetic wave (phase change when there is no object and when there is an object) is θ _n . The white circles in FIG. 1 indicate sampling points (phase measurement points) of the phase.

In the equation (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 performing the dielectric constant measurement according to the present invention, a fixed value set in advance is used for ε _eff _ _max .

Next, phase connection is performed for each phase measured 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 phase _{θ n + 1, θ n +} 2, ···, updated by adding 2π to all theta _m. When the difference is equal to or larger than 0, the phase _{θ n + 1, θ n +} 2, ···, it may be added to 0 for all theta _m. That is, when the difference is 0 or more, updating of the value is unnecessary.

The above update steps are repeated from n = 1 to n = m-1. n = the phase theta _{n + 1} after the updating step has been completed up to _{m-1, θ n + 2} , ···, a _{θ m, φ n + 1,} φ n + 2, ···, and phi _m Do. The black circles in FIG. 1 indicate points after phase connection. Since the phase θ ₁ of the electromagnetic wave of the frequency f ₁ is not a target of updating, the phase θ ₁ is not set to φ ₁ and remains θ ₁ .

Subsequently, the linear fit according to the least square method the phase theta ₁ after phase _{unwrapping, φ 2, ···, φ n} , φ n + 1, ···, against phi _m. Finally, the relative dielectric constant ε _r of the object to be measured is calculated from the slope α of the approximate straight line using the equation (4).

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

Next, derivation of equation (3) will be described. The oscillations of the phases θ ₁ , θ ₂ ,..., Θ _n , θ _{n +1} ,..., Θ _m on the frequency axis shown in FIG. 1 are fundamental waves (waves transmitted without reflection) and reflected waves And interference with reflected waves, and interference between reflected waves. The phase fluctuation is formed by the overlap of periodic functions according to the propagation length difference of each interference wave. Therefore, by sampling one line or more at a frequency interval finer than a half cycle of the phase fluctuation and performing linear approximation, the phase fluctuation can be averaged and the influence thereof can be reduced.

For the purpose of explanation, consider an DUT 10 having a relative dielectric constant ε ₂ = 3 and a thickness L = 30 mm surrounded by air (relative dielectric constant ε ₁ = 1) as shown in FIG. 2 as an example . It is assumed that only the fundamental wave and the twice reflected wave exist in the DUT 10. In FIG. 2, although the fundamental wave and the twice reflected wave are described as being separated in position in order to make the description easy to understand, in practice, the fundamental wave and the twice reflected wave are the same position It is a wave generated by overlapping in

  The propagation length difference D between the fundamental wave and the twice reflected wave is expressed by equation (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, as the propagation length difference D between the fundamental wave and the twice reflected wave is larger, the period CY of the swing of the phase θ on the frequency axis in FIG. 3 becomes finer. 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 can be reduced and a desired phase inclination can be obtained.

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

That is, since the energy of the reflected wave after the four reflections is greatly attenuated, the two reflection waves most affect the fluctuation of the phase θ. Therefore, the interval f _s of the frequency of the electromagnetic wave used for measurement should be selected according to the case where the propagation length difference D with the fundamental wave is the longest among the two reflections (when the fluctuation of the phase θ is the smallest) desirable.
When the maximum value of the effective dielectric constant of the device under test 10 is ε _eff _ _max , the largest propagation length difference D _{max from the} fundamental wave in the double reflection is expressed by equation (9).

Therefore, by measuring the phase θ with electromagnetic waves of a plurality of frequencies at which the frequency interval f _s satisfies the equation (3) over the frequency range of one period or more of the fluctuation of the phase θ, 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, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a block diagram showing the configuration of a dielectric constant measurement system according to an embodiment of the present invention. The dielectric constant measurement system includes a transmitter 1 for irradiating the electromagnetic wave of _m (m is an integer of 3 or more) frequencies f ₁ , f ₂ ,. It comprises the receiver 2 (dielectric constant measuring device) which detects the transmitted electromagnetic waves and calculates the relative dielectric constant ε _r of the device under test 10.
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 dielectric constant calculation unit 25, and a calculation result output unit 26. There is.

FIG. 5 is a flow chart for explaining the operation of the dielectric constant measurement system of this embodiment. First, in the state where there is only the background material 11 (for example, air) whose relative dielectric constant ε ₁ is known (for example, air) and the DUT 10 is not present, the transmitter 1 has m frequencies f ₁ , f _{2 ,.} The electromagnetic wave of is applied to the background material 11 (step S100 in FIG. 5).

As described above, the interval f _s = f _{n + 1} -f _n between two adjacent frequencies satisfies the equation (3). In this embodiment, applications such as detection of foreign matter contamination in food are assumed. Therefore, regarding the effective dielectric constant maximum value ε _eff _ _max , an estimated value taking into consideration the maximum dielectric constant of foreign matter. Should be set in advance. In the present embodiment, the thickness L of the device under test 10 in the direction from the transmitter 1 to the antenna 20 is a known value. In addition, the transmitter 1 should just be what can irradiate the electromagnetic wave of the several frequency of GHz order to an object, for example.

The antenna 20 of the receiver 2 receives the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m transmitted through the background material 11 (step S101 in FIG. 5).
The phase measurement unit 21 of the receiver ₂ measures the phases of the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m received by the antenna 20 (step S102 in FIG. 5). The technique for measuring the phase of the electromagnetic wave (more precisely, the amount of change in the phase of the signal received by the receiver 2 with respect to the reference signal on the transmitter 1 side) is, for example, an existing network analyzer (VNA). It is a known technique that can be realized using a measuring instrument.

Next, a user who uses the dielectric constant measurement system places the DUT 10 having a known thickness L and an unknown relative dielectric constant ε _r inside or on the background material 11.
The transmitter 1 irradiates the background material 11 and the object 10 with electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _{m while} the object 10 is disposed in this manner ( FIG. 5 step S103).

The antenna 20 of the receiver 2 receives the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m transmitted through the background material 11 and the object to be measured 10 (step S104 in FIG. 5).
The phase measurement unit 21 of the receiver ₂ measures the phases of the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m received by the antenna 20 (step S105 in FIG. 5).

Subsequently, the phase difference calculation unit 22 of the receiver 2 calculates, for each frequency of the electromagnetic wave, the phase change θ that 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. 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, The phase difference Δθ between electromagnetic waves of two frequencies f _n and f _{n + 1} is obtained (step S106 in FIG. 5). As described above, in this embodiment, the net phase change due to the DUT 10 obtained by taking the difference between the measurement results of the phase twice is assumed to be 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 two adjacent electromagnetic waves of the 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 [Delta] [theta] of 0 or more, the phase change _{θ n + 1, θ n +} 2, ···, it means that adds 0 to the respective theta _m, the phase difference [Delta] [theta] 0 In the above case, updating of the phase change is not necessary. Such an update step is repeated starting from n = 1 and incrementing n one by one (FIG. 5, steps S107 to S110), and when processing is completed up to n = m-1 (FIG. 5, step S111). 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 steps up to n = m−1 are completed are φ _{n + 1} , φ _{n + 2} ,. ·, Φ _m .

Although the phase changes θ _{n + 1} , θ _{n +2} ,..., Θ _m increase by repeating the process of step S109, the two adjacent frequencies f _n also after the process of step S109. , F _{n + 1} do not change. Therefore, it is not necessary to recalculate the phase difference Δθ every time the process of step S109 is performed once, and the determination process of step S108 may be performed based on the calculation result of the phase difference calculation unit 22.

The approximation unit 24 of the receiver 2 has m-1 pieces of phase changes θ ₁ and f ₁ excluding the electromagnetic wave with the lowest frequency f ₁ among the _m frequencies f ₁ , f ₂ ,. frequency f _2, ···, phase change phi ₂ after update of an electromagnetic wave f _m, ···, and phi _m is linearly approximated by the least squares method (Fig. 5 step S112).

The relative dielectric constant calculation unit 25 of the receiver 2 uses the slope α of the approximate straight line obtained by the approximation unit 24 and the known thickness L of the device under test 10 to obtain the device under test 10 according to equation (4). The relative dielectric constant ε _{r of} is calculated (step S113 in FIG. 5).

The calculation result output unit 26 of the receiver 2 outputs the calculation result of the relative dielectric constant calculation unit 25 (step S114 in 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 Do. As described above, the operation of the dielectric constant measurement system of the present embodiment is completed.

In the present embodiment, for comparison with the prior art, the relative dielectric constant ε _r = 10 in the background material 11 having a relative dielectric constant ε ₁ = 3 and a thickness L ₁ = 30 mm as shown in FIG. 6 as an example The effect of the present embodiment will be described for the case where the object to be measured 10 in the range of thickness L = 2 to 10 mm is contained. Under this condition, the maximum value of effective dielectric constant ε _eff _ _max is 4.88. The frequency interval f _s required in the present embodiment, which is calculated from the equation (3), needs to be a value smaller than 1.2 GHz.

In the conventional method disclosed in Non-Patent Document 1, the simulation result of the dielectric constant measurement error (calculation error of the relative dielectric constant ε _r ) when using two frequencies of f ₁ = 300 GHz and f ₂ = 308 GHz is shown in FIG. Shown in. In this case, the interval between two frequencies is 8 GHz. A dotted line 70 in FIG. 7 indicates an error when the relative dielectric constant ε _r of the DUT 10 is calculated by the method disclosed in Non-Patent Document 1. The maximum error was 14.5%.

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

On the other hand, a solid line 72 in FIG. 7 indicates an error when the relative dielectric constant ε _r of the object to be measured 11 is calculated by the method of the present embodiment. In this example, 31 frequencies at 1 GHz intervals from f ₁ = 300 GHz to f ₃₁ = 330 GHz were used. Simulation results show 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, in the case of the object to be measured 10 in which the foreign object 10b made of a synthetic resin is contained in chocolate 10a of 50 mm in length and width L = 21 mm. The effects of the embodiment will be described.

FIG. 9 (A) shows the result of measuring the relative dielectric constant ε _r of the device under test 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 It is. In FIG. 9A, FIG. 9B, and FIG. 9C, the distribution of the relative dielectric constant ε _r in the plane of the device under test 10 is shown by color coding. Here, as the method disclosed in Non-Patent Document 1, two frequencies of f ₁ = 280 GHz and f ₂ = 288 GHz were used. For the method of Non-Patent Document 2 and this example, six 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 dielectric constant ε _r at the position of the straight line A in FIGS. 9 (A), 9 (B) and 9 (C) respectively. It is. In FIG. 9 (D), FIG. 9 (E), and FIG. 9 (F), 90 indicates the theoretical value of the relative dielectric constant ε _r , 91 indicates the measurement result by the method disclosed in Non-Patent Document 1, and 92 indicates The measurement result by the method disclosed by the nonpatent literature 2 is shown, 93 shows the measurement result by the method of a present Example. The measurement error of the relative dielectric constant ε _r at the position of the foreign object 10 b is 3.6% in the case of the method disclosed in Non-patent document 1, 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 dielectric constant calculation unit 25, and the calculation result output unit 26 described in this embodiment are a central processing unit (CPU) and a storage device. And an interface, and a program for controlling these hardware resources. A program for realizing the dielectric constant measurement method of the present invention is provided in the state of being recorded on a recording medium such as a flexible disk, a CD-ROM, a DVD-ROM, a memory card, and stored in a storage device. The CPU of the computer executes the processing described in the present embodiment in accordance with 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 an electromagnetic wave.

  DESCRIPTION OF SYMBOLS 1 ... Transmitter, 2 ... Receiver, 10 ... Object to be measured, 11 ... Background material, 20 ... Antenna, 21 ... Phase measurement part, 22 ... Phase difference calculation part, 23 ... Update processing part, 24 ... Approximate part, 25 ... relative permittivity calculation unit, 26 ... calculation result output unit.

Claims (6)

and m pieces (m is an integer of 3 or more) transmitters irradiating frequency f _1, f ₂ of, ..., an electromagnetic wave of f _m to the measurement object,
A receiver for detecting an electromagnetic wave transmitted through the object to be measured to calculate a relative dielectric constant of the object to be measured;
The transmitter sets the assumed maximum relative dielectric constant of the object to be measured as ε _eff _ _max , the known thickness of the object to be measured as L, and the speed of light as c, two adjacent frequencies f _n , The interval f _{s of} f _{n + 1} (n is an integer of 1 or more and (m−1) or less) is
The object to be measured is irradiated with electromagnetic waves of _m frequencies f ₁ , f ₂ ,.
The receiver is
An antenna for receiving the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m transmitted through the object to be measured;
A phase measurement unit that measures the phase of each of the _m electromagnetic waves of frequencies f ₁ , f ₂ ,..., F _m received by the antenna;
A phase difference calculating unit that calculates a phase difference between two adjacent electromagnetic waves having frequencies f _n and f _{n + 1} based on the measurement result of the phase measuring 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 wave of each frequency after f _{n + 1} and updating is performed, n = 1 to n = m−1 The update processing unit that repeats up to
m pieces of frequency f _1, f _2, ···, and the phase of the lowest of the electromagnetic waves of frequency f ₁ of the f _{m, m-1} pieces of frequency f ₂ with the exception of f _1, ···, of f _m An approximation unit that linearly approximates the phase of the electromagnetic wave after being updated by the update processing unit;
A dielectric comprising: a relative dielectric constant calculation unit for calculating a relative dielectric constant of the object to be measured from the inclination of the approximate line obtained by the approximation unit and the thickness L of the object to be measured Rate measurement system. In the dielectric constant measurement system according to claim 1,
The phase measurement unit has only the background material between the transmitter and the antenna of the receiver and does not have the object under measurement, and the phase material has one or more of the background material and the object under measurement. Measure the phase several times
The phase difference calculation unit may be configured such that the phase of the electromagnetic wave measured in the state where there is only the background material and there is no object under measurement, and the phase of the electromagnetic wave measured in the state where the background material and the object under measurement exist. 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} two adjacent electromagnetic waves having frequencies f _n and f _{n + 1} can be calculated as these frequencies f _n and f _{n + 1} And the phase difference of the
The update processing unit is configured to adjust the phase change θ _{n + 1} , θ _{n + 2} ,..., Θ of the electromagnetic wave of each frequency after f _{n + 1} when the phase difference calculated by the phase difference calculation unit is negative. _The process of updating by adding 2π to each of _m is repeated from n = 1 to n = m−1,
The approximating unit includes a phase change θ ₁ of the electromagnetic wave of the lowest frequency f ₁ among the _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 for receiving _m electromagnetic waves (m is an integer of 3 or more) at frequencies f ₁ , f ₂ ,.
A phase measurement unit that measures the phase of each of the _m electromagnetic waves of frequencies f ₁ , f ₂ ,..., F _m received by the antenna;
A phase difference calculation unit that calculates the phase difference between two adjacent electromagnetic waves having frequencies f _n and f _{n + 1} (n is an integer of 1 or more and (m−1) or less) based on the measurement result of the 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 wave of each frequency after f _{n + 1} and updating is performed, n = 1 to n = m−1 The update processing unit that repeats up to
m pieces of frequency f _1, f _2, ···, and the phase of the lowest of the electromagnetic waves of frequency f ₁ of the f _{m, m-1} pieces of frequency f ₂ with the exception of f _1, ···, of f _m An approximation unit that linearly approximates the phase of the electromagnetic wave after being updated by the update processing unit;
A relative dielectric constant calculation unit that calculates the relative dielectric constant of the object to be measured from the slope of the approximate straight line obtained by the approximation unit and the known thickness L of the object to be measured;
The electromagnetic waves having _m frequencies f ₁ , f ₂ ,..., F _m are adjacent to each other when the maximum relative permittivity assumed for 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} is
A dielectric constant measuring device characterized by satisfying. In the dielectric constant measurement device according to claim 3,
The phase measurement unit measures the phase once in each of a state in which only the background material is present in the incoming direction of the electromagnetic wave and the object is not present, and a state in which the background material and the object are present. Do,
The phase difference calculation unit may be configured such that the phase of the electromagnetic wave measured in the state where there is only the background material and there is no object under measurement, and the phase of the electromagnetic wave measured in the state where the background material and the object under measurement exist. 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} two adjacent electromagnetic waves having frequencies f _n and f _{n + 1} can be calculated as these frequencies f _n and f _{n + 1} And the phase difference of the
The update processing unit is configured to adjust the phase change θ _{n + 1} , θ _{n + 2} ,..., Θ of the electromagnetic wave of each frequency after f _{n + 1} when the phase difference calculated by the phase difference calculation unit is negative. _The process of updating by adding 2π to each of _m is repeated from n = 1 to n = m−1,
The approximating unit includes a phase change θ ₁ of the electromagnetic wave of the lowest frequency f ₁ among the _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. Assuming that the assumed maximum relative dielectric constant 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 distance between two adjacent frequencies f _n and f _{n + 1} f _s is
The object to be measured is irradiated with electromagnetic waves of frequencies f ₁ , f ₂ ,..., F _m where m satisfies m (m is an integer of 3 or more and n is an integer of 1 or more (m-1) or less) Step 1 and
A second step of receiving the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m transmitted through the object to be measured;
A third step of measuring the phase of each of the _m electromagnetic waves of frequencies f ₁ , f ₂ ,..., F _m received in the _second step;
A fourth step of calculating the phase difference between two adjacent electromagnetic waves of frequencies f _n and f _{n + 1} based on the measurement result of the third step;
A process of adding 2π to each of the phases of electromagnetic waves of frequencies after f _{n + 1} and updating the phase when the phase difference calculated in the fourth step is negative, from n = 1 to n = m-1 The fifth step to repeat
m pieces of frequency f _1, f _2, ···, and the phase of the lowest of the electromagnetic waves of frequency f ₁ of the f _{m, m-1} pieces of frequency f ₂ with the exception of f _1, ···, of f _m A sixth step of linearly approximating the phase of the electromagnetic wave after the phase of the electromagnetic wave is updated by the fifth step;
And a seventh step of calculating the relative dielectric constant of the object to be measured from the slope of the approximate line obtained in the sixth step and the thickness L of the object to be measured. Measuring method. In the dielectric constant measurement method according to claim 5,
Performing the third step once each in a state in which there is only the background material and there is no said object, and in a state in which the background material and the object are present,
In the fourth step, the phase of the electromagnetic wave measured with the background material alone and without the object to be measured, and the phase of the electromagnetic wave measured with the background material and the object to be measured 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} two adjacent electromagnetic waves having frequencies f _n and f _{n + 1} can be calculated as these frequencies f _n and f _{n + 1} Step of phase difference of the electromagnetic waves of
The fifth step, the f _{n + 1} subsequent phase change theta _{n + 1} of the electromagnetic wave of the frequency when the phase difference calculated by the fourth step is _{negative, θ n + 2, ···,} θ including the step of repeating the process of adding 2π to each of _m and updating, from n = 1 to n = m−1,
In the sixth step, the phase change θ ₁ of the electromagnetic wave of the lowest frequency f ₁ among the _m frequencies f ₁ , f ₂ ,..., F _m and m−1 frequencies excluding f ₁ f _2, ..., the phase theta ₂ of the electromagnetic wave of f _m, ..., theta phase change phi ₂ after updating the _m by the update processing unit, ..., the step of linearly approximating the phi _m A method of measuring dielectric constant, comprising: