JP6533187B2 - Dielectric constant evaluation method - Google Patents

Description

  The present invention relates to a dielectric constant evaluation method for measuring the relative dielectric constant of an object using electromagnetic waves of a plurality of frequencies.

  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.

  The dielectric constant evaluation method for acquiring the value of the relative dielectric constant of an object calculates the relative dielectric constant of an object based on the frequency of an electromagnetic wave passing through the object and information of the measured phase. If the relative dielectric constant can be determined, it is possible to detect the entry of foreign matter into the object. On the other hand, if the phase of the electromagnetic wave transmitted through the object is observed, it is possible to obtain the optical path length in the object from the phase and the frequency of the electromagnetic wave. The optical path length in the object is a parameter consisting of the thickness of the object and the relative permittivity of the object, and if the thickness of the object is known, the relative permittivity can be determined.

  In the conventional dielectric constant evaluation method, two electromagnetic waves with known frequencies are irradiated from the electromagnetic wave emitter to the object to be measured, the electromagnetic wave transmitted through the object to be measured is detected by the detector, and the phase of the electromagnetic waves is measured. (See Non-Patent Document 1). In the measurement, as shown in FIG. 7A, 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. 7B. Do it

First, measuring the phase theta ₁ _ _air and theta ₂ _ _air after the two different electromagnetic waves frequencies f ₁ and f ₂ are transmitted through the air in the configuration of FIG. 7 (A). 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 DUT 102 in the configuration of FIG. 7B are measured, and the DUT 102 is measured. 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.

  As shown in FIG. 8, the phase change θ of the measured electromagnetic wave increases in proportion to the frequency f of the electromagnetic wave, but the actual measuring instrument can measure the phase only in the range of 0 to 2π. Also, the amount of actual phase change can not be calculated.

Liangliang Zhang, et al., “Terahertz multiwavelength phase imaging without 2π ambiguity”, Optics letters, Vol. 31, Issue 24, pp. 3686-3670, 2006

Since a phase error due to reflection or the like exists in an actual measurement environment, it is necessary to widen the interval Δf = f ₂ −f ₁ between two frequencies as much as possible in order to perform highly accurate dielectric constant evaluation. In FIG. 9A, the error of the dielectric constant evaluation (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. 9 (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 evaluation becomes large. On the other hand, if the interval Δf between the two frequencies is broadened as shown in FIG. 9C, the influence of the phase error becomes smaller and the error in the dielectric constant evaluation 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. 9A). As described above, in the conventional dielectric constant evaluation method, there is a problem that the relative dielectric constant of the object can not be detected with high accuracy because the upper limit exists in the interval Δf between the two frequencies.

  The present invention has been made to solve the above-described problems, and has an object of detecting the relative dielectric constant of an object with high accuracy in a dielectric constant evaluation method using electromagnetic waves of a plurality of frequencies.

In the dielectric constant evaluation method of the present invention, the maximum phase error assumed at each frequency is θ _noise , the assumed maximum relative dielectric constant of the object to be measured is ε _eff _ _max , the thickness of the object to be measured is L, the speed of light Where c is the interval Δf between two adjacent frequencies f _n and f _{n + 1}
Of the electromagnetic waves having frequencies f ₁ , f ₂ ,..., F _m with m (m is an integer of 3 or more and n is an integer of 1 or more (m-1) or less) satisfying the above An irradiation step, an electromagnetic wave detection step of detecting an electromagnetic wave transmitted through the object to be measured, a phase detection step of detecting a phase change of each of the electromagnetic waves of m frequencies, and two adjacent frequencies f _n and f _n Is added to each of the phase change of the electromagnetic waves of each frequency after f _{n +1} when the phase difference calculation step of calculating the phase difference of the ₊₁ electromagnetic wave and the phase difference calculated in this phase difference calculation step is negative. , And an update step of repeating the process of updating from n = 1 to n = m−1, and the lowest frequency f ₁ and frequency f ₁ among _m frequencies f ₁ , f ₂ ,. phase change and the m frequency f _1, f ₂ of the electromagnetic wave, ..., a f _m Chino from the highest frequency f _m and the frequency f of the known thickness of the electromagnetic wave phase shift between the object to be measured after the update of the _m L, the relative dielectric constant calculation step of calculating a relative dielectric constant epsilon _r of the object to be measured And is included.

In one configuration example of the dielectric constant evaluation method of the present invention, the phase is once in each of the state in which there is only the background material and there is no such object, and the state in which the background material and the object are present. The detection step is performed, and the phase difference calculation step is measured in a state in which there is the phase of the electromagnetic wave measured in the state where there is only the background material and there is no object to be measured, the background material and the object to be measured the phase change is the difference between the phase of the electromagnetic wave is calculated for each frequency, two adjacent frequencies f _n, the difference between the phase change theta _n and theta _{n + 1} of an electromagnetic wave f n _{+ 1,} these frequencies f _n , F _{n + 1} as the phase difference of the electromagnetic wave, and the updating step is a phase change θ of the electromagnetic wave of each frequency after f _{n + 1} if the phase difference calculated in the phase difference calculating step is negative. _{n + 1, θ n + 2} , ···, and updates by adding 2π to each theta _m The management includes the step of repeating the n = 1 to n = m-1, the relative dielectric constant calculation step, an electromagnetic wave of frequency f ₁ and the frequency phase change of the electromagnetic wave of f ₁ theta ₁ and the frequency f _m and the frequency f _m And calculating the relative dielectric constant ε _r of the object to be measured from the phase change φ _m after updating and the known thickness L of the object to be measured.

According to the present invention, it is possible to extend the upper limit of the frequency interval by performing phase connection on electromagnetic waves of m frequencies, and to detect the relative dielectric constant ε _r of the object to be measured with high accuracy It becomes.

It is a figure explaining the phase change measurement by multiple frequencies of this invention. It is a figure explaining the phase connection process of this invention. It is a block diagram which shows the structure of the dielectric constant evaluation apparatus based on embodiment of this invention. It is a flowchart explaining operation | movement of the dielectric constant evaluation apparatus which concerns on embodiment of this invention. It is a figure explaining one example of the to-be-measured object used as the measuring object of embodiment of this invention. It is a figure which shows the result of having calculated the dielectric constant evaluation error in the conventional dielectric constant evaluation method and the dielectric constant evaluation method which concerns on embodiment of this invention. It is a figure explaining the composition of the optical system used with the conventional dielectric constant evaluation method. It is a figure which shows the relationship of the frequency and phase change of electromagnetic waves in the conventional dielectric constant evaluation method. It is a figure explaining the problem of the conventional dielectric constant evaluation method.

[Principle of the invention]
In the conventional dielectric constant evaluation method, the upper limit of the two-frequency interval Δf is due to the presence of a discontinuity due to the phase jump. Therefore, by connecting these discontinuities, it is possible to extend the upper limit of the two-frequency interval Δf. In the present invention, m frequencies f ₁ , f ₂ ,..., F _n , f _where the interval Δf = f _{n + 1} −f _n of adjacent frequencies satisfies the following equation (2) as shown in FIG. Phase change detection is performed by _{n + 1} ,..., f _m-1 and f _m (m is an integer of 3 or more, n is an integer of 1 or more and (m-1) or less). At this time, the phase change detected at the frequency f _n of the electromagnetic wave is taken as θ _n . Circles in FIG. 1 indicate sampling points of phase change (phase change measuring points).

Similarly to the above, L is the thickness of the object to be measured, c is the speed of light, and θ _noise is the estimated maximum phase error at each frequency. Equation (2) shows the condition for not changing the phase difference between adjacent frequencies by 2π or more when the maximum phase error θ _noise is taken into consideration. ε _eff _ _max is the maximum value of the effective relative permittivity that can be taken by the object to be measured. When performing the dielectric constant evaluation according to the present invention, fixed values set in advance are used for θ _noise and ε _eff _ _max .

Next, the difference between the phase changes θ _n and θ _{n + 1 of} two adjacent electromagnetic waves of frequencies f _n and f _{n + 1} is calculated, and if the calculated difference is negative, θ _{n + 1} or later The phase change θ _{n + 1} , θ _{n + 2} ,..., Θ _m is updated by adding 2π. When the difference is equal to or larger than 0, the phase change _{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. phase change theta _{n + 1} after the n = update step to m-1 is completed, θ _{n + 2,} ···, a _{θ m, φ n + 1,} φ n + 2, ···, φ m I assume. The relationship between the frequency after update and the phase change is shown in FIG. The phase change theta ₁ of the electromagnetic wave of frequency f ₁ since not subject to update, without phi _1, it is set to remain theta _1. By performing the updating step in this manner, as shown in FIG. 2, the characteristic that the phase change linearly increases in proportion to the frequency of the electromagnetic wave is referred to as phase connection in the present invention.

Next, after the phase connection is completed, the lowest frequency f ₁ of _m frequencies f ₁ , f ₂ ,..., F _m , the phase change θ ₁ of the electromagnetic wave of frequency f ₁ , and m Using the highest frequency f _{m of the} frequencies f ₁ , f ₂ ,..., F _m and the phase change φ _m after the update of the electromagnetic wave of the frequency f _m , measurement is made according to the following equation (3) The relative dielectric constant ε _r of the object is calculated.

Thus, according to the present invention, by performing phase connection with respect to electromagnetic waves of a plurality of frequencies, it is possible to extend the upper limit of the two-frequency interval Δf, and to detect the relative dielectric constant ε _r of the object to be measured with high accuracy. Is possible.

Embodiment
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 3 is a block diagram showing the configuration of the dielectric constant evaluation device according to the embodiment of the present invention. The dielectric constant evaluation apparatus according to the present embodiment includes an electromagnetic wave emitter 1 that irradiates the object 11 with electromagnetic waves of _m (m is an integer of 3 or more) frequencies f ₁ , f ₂ ,. A detector 2 for detecting an electromagnetic wave transmitted through the object to be measured 11 and a relative dielectric constant evaluation unit 3 for calculating the relative dielectric constant ε _r of the object to be measured 11 based on the detection result of the detector 2 .
The relative dielectric constant evaluation unit 3 includes a phase detection unit 30, a phase difference calculation unit 31, an update processing unit 32, a relative dielectric constant calculation unit 33, and a calculation result output unit 34.

FIG. 4 is a flow chart for explaining the operation of the dielectric constant evaluation device of the present embodiment. First, the ratio electromagnetic radiator 1 dielectric constant epsilon ₁ is in the absence of the measurement object 11 if there is only known background material 10, m pieces of frequency f _1, f _2, · · ·, the electromagnetic wave of f _m The background material 10 is irradiated (FIG. 4 step S100).

As described above, the interval between adjacent two frequencies Δf = f _{n + 1} −f _n satisfies the equation (2). At this time, with regard to the maximum phase error θ _noise at each frequency, an estimated value may be set in advance in consideration of the disturbance affected by the measurement environment or the like. Further, 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, contemplated The value to be set may be set in advance. Further, in the present embodiment, the thickness L of the object to be measured 11 is a known value.

The detector 2 detects the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m transmitted through the background material 10 (step S101 in FIG. 4).
The phase detection unit 30 of the relative dielectric constant evaluation unit 3 detects the phases of the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m from the detection result of the detector 2 in step S101 ( FIG. 4 step S102). In addition, the technique which detects the phase of electromagnetic waves is a well-known technique which can be implement | achieved using the existing measuring device.

Next, a user who uses the dielectric constant evaluation apparatus has a known thickness L and an unknown relative dielectric constant ε _{r on} the top of the background material 10 (or inside the background material 10) whose relative dielectric constant ε ₁ is known The object to be measured 11 is placed.
The electromagnetic wave emitter 1 radiates electromagnetic waves of m frequencies f ₁ , f ₂ ,..., F _{m to} the background material 10 and the object 11 under the condition that the object 11 is disposed as described above. (FIG. 4 step S103).

The detector 2 detects the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m transmitted through the background substance 10 and the object to be measured 11 (step S104 in FIG. 4).
The phase detection unit 30 of the relative dielectric constant evaluation unit 3 detects the phases of the electromagnetic waves of _m frequencies f ₁ , f ₂ ,..., F _m from the detection result of the detector 2 in step S104 ( FIG. 4 step S105).

Subsequently, the phase difference calculation unit 31 of the relative dielectric constant evaluation unit 3 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. calculated, two adjacent frequencies _{f n, f n + 1 (} n is 1 or more (m-1) an integer) the difference between the phase change theta _n and theta _{n + 1} of an electromagnetic wave theta _{n + 1} - [theta] _{Let n be} the phase difference Δθ of electromagnetic waves of two frequencies f _n and f _{n + 1} (step S106 in FIG. 4). As described above, in the present embodiment, the net phase change due to the DUT 11 obtained by taking the difference between the measurement results of the phase twice is assumed to be θ. The phase difference calculation unit 31 calculates the phase difference Δθ as described above for each of n = 1 to n = m−1.

Next, the update processing unit 32 of the relative dielectric constant evaluation unit 3 determines whether or not the phase difference Δθ between the two adjacent electromagnetic waves of the frequencies f _n and f _{n + 1} is negative (step S108 in FIG. 4). Δθ is in the case of negative, θ _{n + 1} and subsequent phase change _{θ n + 1, θ n +} 2, ···, and updates by adding 2π to each theta _m (Fig. 4 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 updating step is repeated starting from n = 1 and incrementing n one by one (FIG. 4 steps S107 to S110), and when processing is completed up to n = m-1 (FIG. 4 step S111 YES), the operation of the update processing unit 32 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 31.

The relative permittivity calculation unit 33 of the relative permittivity evaluation unit 3 calculates the lowest frequency f ₁ of the _m frequencies f ₁ , f ₂ ,..., F _m and the frequency calculated by the phase difference calculation unit 31. an electromagnetic wave phase shift theta ₁ of f _1, m pieces of frequency f _1, f _2, ···, and the highest frequency f _m of f _m, of the electromagnetic wave of the frequency f _m of the update processing unit 32 is calculated Using the phase change φ _m after the update and the known thickness L of the device under test 11, the relative dielectric constant ε _r of the device under test 11 is calculated according to equation (3) (step S112 in FIG. 4).

The calculation result output unit 34 of the relative dielectric constant evaluation unit 3 outputs the calculation result of the relative dielectric constant calculation unit 33 (step S113 in FIG. 4). Specifically, the calculation result output unit 34, and transmits for example, to display the relative dielectric constant epsilon _r of the measurement object 11 to the dielectric constant calculator 33 has calculated, the information of the relative permittivity epsilon _r to the outside Do. As described above, the operation of the dielectric constant evaluation device 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 10 having a relative dielectric constant ε ₁ = 3 and a thickness L ₁ = 30 mm as shown in FIG. 5 as an example. The effect of the present embodiment will be described for the case where the object to be measured 11 in the range of thickness L = 1 to 10 mm is contained. Under this condition, the maximum value of effective dielectric constant ε _eff _ _max is 4.88. Further, assuming that the maximum phase error θ _noise generated by the reflection at the dielectric boundary is 0.1 radian, the maximum value of the interval Δf between two adjacent frequencies is calculated to be 8 GHz using the equation (2).

In the conventional dielectric constant evaluation method using equation (1), the simulation result of the dielectric constant evaluation error (calculation error of the relative dielectric constant ε _r ) in the case of using two frequencies of f ₁ = 300 GHz and f ₂ = 308 GHz is shown. It is shown in 6. In this case, the interval Δf between the two frequencies is 8 GHz. The dotted line 60 in FIG. 6 shows an error when the relative dielectric constant ε _r of the device under test 11 is calculated by the conventional dielectric constant evaluation method. The maximum error was 14.5%.

On the other hand, a solid line 61 in FIG. 6 indicates an error when the relative dielectric constant ε _r of the device under test 11 is calculated by the dielectric constant evaluation method of the present embodiment. Here, the frequency interval between the lowest frequency and the highest frequency of the electromagnetic wave is extended to 30 GHz using five frequencies f ₁ = 300 GHz, f ₂ = 308 GHz, f ₃ = 316 GHz, f ₄ = 324 GHz, f ₅ = 330 GHz . According to FIG. 6, it can be seen that the maximum error can be reduced to 3.7%.

  The relative dielectric constant evaluation unit 3 described in the present embodiment can be realized by a computer provided with a central processing unit (CPU), a storage device, and an interface, and a program for controlling these hardware resources. 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 ... electromagnetic wave radiator, 2 ... detector, 3 ... relative dielectric constant evaluation part, 10 ... background material, 11 ... thing to be measured, 30 ... phase detection part, 31 ... phase difference calculation part, 32 ... update process part, 33 ... relative permittivity calculation unit, 34 ... calculation result output unit.

Claims (2)

Assuming that the maximum phase error assumed at each frequency is θ _noise , the assumed maximum relative dielectric constant of the object to be measured is ε _eff _ _max , the thickness of the object to be measured is L, and the speed of light is c, 2 adjacent Of two frequencies f _n and f _{n + 1}
Of the electromagnetic waves having frequencies f ₁ , f ₂ ,..., F _m with m (m is an integer of 3 or more and n is an integer of 1 or more (m-1) or less) satisfying the above Irradiation step,
An electromagnetic wave detection step of detecting an electromagnetic wave transmitted through the object to be measured;
A phase detection step of detecting a phase change of each of the m frequency electromagnetic waves;
A phase difference calculating step of calculating a phase difference between electromagnetic waves of two adjacent frequencies f _n and f _{n + 1} ;
When the phase difference calculated in this phase difference calculation step is negative, the process of adding 2π to each of the phase change of the electromagnetic wave of each frequency after f _{n + 1} and updating is performed, n = 1 to n = m−1 Update step to repeat up to
The phase change of the electromagnetic wave with the lowest frequency f ₁ and the frequency f ₁ among the _m frequencies f ₁ , f ₂ ,..., f _m and the m frequencies f ₁ , f _{2 ,.} Relative permittivity _{r r} of the object to be measured from the phase change after updating of the electromagnetic wave of the highest frequency f _m and frequency f _m and the known thickness L of the object to be measured And a calculation step. In the dielectric constant evaluation method according to claim 1,
The phase detection step is performed once in each of a state in which there is only the background material and there is no such object, and a state in which there is the background material and the object.
In the phase difference calculating step, a phase of an electromagnetic wave measured in a state where there is only the background material and there is no object to be measured, and a phase of an electromagnetic wave measured in a 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} 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
In the updating step, when the phase difference calculated in the phase difference calculating step is negative, the phase change θ _{n + 1} , θ _{n + 2} ,..., Θ _m of the electromagnetic wave of each frequency after f _{n + 1} Including the step of repeating the process of updating by adding 2π to each, from n = 1 to n = m−1,
Known thickness of the dielectric constant calculation step, the frequency f ₁ and an electromagnetic wave phase shift theta ₁ and the frequency f _m and the phase change phi _m and the object to be measured after the electromagnetic wave of the update frequency f _m of frequency f ₁ Calculating the relative dielectric constant ε _r of the device under test from L and L.