JP6662798B2 - Dielectric constant measurement system, apparatus and method - Google Patents

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 been increasing in article manufacturers. In particular, for food manufacturers, there is a case where business performance becomes tight due to foreign matters mixed into processed foods, such as a decrease in company reliability or a suspension of shipment. It is desirable to detect foreign matter in the product at the stage of product shipping inspection and prevent the product containing the foreign material from being shipped. However, the existing imaging apparatus, which is an imaging apparatus, can detect metals, but cannot detect organic substances such as insects and foods different from products with high accuracy.

  On the other hand, if the relative permittivity of the object can be obtained, it becomes possible to detect the intrusion of the foreign object into the object. Conventionally, as a method for measuring the relative permittivity of an object, there is a method using a phase gradient between two different frequencies (see Non-Patent Document 1). FIG. 13 is a block diagram showing a configuration of a conventional dielectric constant measurement system. The dielectric constant measurement system includes a transmitter 100 and a receiver 101.

  The transmitter 100 uses a voltage controlled oscillator (VCO) 1000 to time-sweep the frequency of a radio frequency signal (hereinafter, RF signal) as shown in FIG. Send out.

The receiver 101 receives the RF signal transmitted through the object 102 with the antenna 1010. The mixer 1011 converts the RF signal into an intermediate frequency signal (hereinafter, IF signal) by mixing the received RF signal with a local signal for a receiver (hereinafter, LO signal). Assuming that the frequency of the RF signal is f ₁ and f ₂ and the frequency of the LO signal is f _lo , the frequencies of the IF signal are f ₁ -f _lo and f ₂ -f _lo as shown in FIG.

An AD converter (ADC: Analog to Digital Converter) 1012 converts an IF signal into a digital signal. The phase measuring unit 1013 measures the phases θ ₁ and θ ₂ at the two frequencies f ₁ -f _lo and f ₂ -f _lo of the IF signal. The phase difference calculator 1014 calculates the phase difference θ ₁ −θ ₂ . Then, the dielectric constant calculator 103 calculates the dielectric constant epsilon _r of the object 102 from the phase difference θ ₁ -θ _2.

  As the transmitter 10, the antenna 1010, the mixer 1011, the AD converter 1012, and the phase measurement unit 1013 of the receiver 101, a network analyzer (VNA) is used. The VNA is disclosed in Non-Patent Document 2, for example.

However, the conventional permittivity measurement system has a problem that the measurement time is long mainly for the following two reasons.
(I) The first reason is that the frequency of the RF signal is time-swept. In a conventional dielectric constant measurement system, RF signals of two frequencies are sequentially generated and irradiated on an object, and the phases of signals transmitted through the object are separately measured.
(II) The second reason is that when switching the frequency of the RF signal by the VCO, a settling time is required until the desired frequency is settled, and it takes time to switch the frequency. According to Non-Patent Document 3, the settling time is generally several ms.

  As described above, when inspecting for contamination of food, it is necessary to inspect the food flowing on the production line in a short time, and therefore it is desirable that the measurement time is short. Therefore, there is a need for an improvement in the measurement time of the dielectric constant measurement system.

T. Jyo, et al., “THz Permittivity Imaging Using Multi-tone Unwrapped Phase Slope method”, IRMMW 2016 "Basics of Measurement Seminar RF / Microwave Course Basics of Network Analyzer", Agilent Technologies, p. 49, 2013, <http://cp.literature.agilent.com/litweb/pdf/5988-6966EN.pdf> Roberto Nonis, et al., “Modeling, design and characterization of a new low-jitter analog dual tuning LC-VCO PLL architecture”, IEEE Journal of Solid-State Circuits, Vol. 40, No. 6, 2005

  The present invention has been made to solve the above problems, and has as its object to provide a dielectric constant measurement system, apparatus, and method capable of reducing the measurement time as compared with the related art.

  A dielectric constant measurement system according to the present invention includes a transmitter for transmitting a radio frequency signal in which signals of two frequencies are mixed, a state where an object to be measured does not exist between the transmitter and a state where the object exists. A receiver for receiving the radio frequency signal and calculating a relative permittivity of the object for each of the radio frequency signals, the receiver comprising: a first antenna for receiving the radio frequency signal; A detector that detects the detected radio frequency signal and outputs a difference frequency signal between the two frequency signals, a state where the object does not exist between the transmitter and the receiver, and a state where the object exists. For each of the phase measurement unit for measuring the phase of the difference frequency signal, the phase of the difference frequency signal measured in the absence of the object, and the difference frequency signal measured in the presence of the object Rank If, from the thickness of the object, it is characterized in that and a dielectric constant calculator for calculating a relative dielectric constant of the object.

In one configuration example of the dielectric constant measurement system according to the present invention, the receiver further includes an amplifier provided between the detector and the phase measurement unit and amplifying an output signal of the detector.
In one configuration example of the dielectric constant measurement system of the present invention, the receiver is provided between a first oscillator that outputs a first local signal and the amplifier and the phase measurement unit, The difference frequency signal output from the first oscillator is mixed with the first local signal output from the first oscillator, thereby changing the frequency of the difference frequency signal to the radio frequency signal and the first local signal. A first mixer that converts the frequency to a lower frequency.

Further, in one configuration example of the dielectric constant measurement system of the present invention, the transmitter includes a second oscillator that outputs an intermediate frequency signal, a third oscillator that outputs a second local signal, A second mixer for mixing the intermediate frequency signal output from the oscillator with the second local signal output from the third oscillator, and a second mixer for transmitting the radio frequency signal output from the second mixer Antenna.
In one configuration example of the dielectric constant measurement system of the present invention, the second mixer passes the second local signal and a signal having a sum frequency of the second local signal and the intermediate frequency signal. A single sideband mixer having a pass band characteristic of blocking a signal having a frequency difference between the second local signal and the intermediate frequency signal.
Further, one configuration example of the dielectric constant measurement system of the present invention further includes a band-pass filter provided between the second mixer and the second antenna, wherein the second mixer includes the second mixer. Has a pass band characteristic of passing a signal having a frequency of a sum of the second local signal and the intermediate frequency signal, and a signal having a frequency of a difference between the second local signal and the intermediate frequency signal. A double-sideband mixer, wherein the band-pass filter has a frequency of a sum of the second local signal and a sum of the second local signal and the intermediate frequency signal among signals output from the second mixer. Of the second local signal and the intermediate frequency signal.
In one configuration example of the dielectric constant measurement system according to the present invention, the transmitter includes a second oscillator that outputs a signal having a frequency equal to the sum of an intermediate frequency signal and a second local signal, and the second local oscillator. A third oscillator for outputting a signal, a multiplexer for multiplexing the signal output from the second oscillator and the second local signal output from the third oscillator, A second antenna for transmitting the output radio frequency signal.

  Further, the dielectric constant measuring apparatus of the present invention detects an antenna for receiving a radio frequency signal, detects a radio frequency signal received by the antenna, and detects a difference frequency signal between two signals included in the radio frequency signal. An output detector, a phase measurement unit that measures the phase of the difference frequency signal in each of a state where the object to be measured does not exist in the arrival direction of the radio frequency signal and a state where the object exists, and Phase of the difference frequency signal measured in the absence of the object, the phase of the difference frequency signal measured in the presence of the object, and the thickness of the object, the relative dielectric constant of the object to calculate the relative permittivity And a rate calculation unit.

  Further, according to the dielectric constant measuring method of the present invention, a transmitter transmits a radio frequency signal in which signals of two frequencies are mixed in a state where an object to be measured does not exist between the transmitter and the receiver. And the second step, wherein the receiver receives the radio frequency signal in a state where the object is not present, and the receiver detects the radio frequency signal in a state where the object is not present, A third step of outputting a difference frequency signal between the two frequency signals, a fourth step of the receiver measuring a phase of the difference frequency signal in a state where the object is not present, and the transmitter A fifth step of transmitting a radio frequency signal in which the signals of the two frequencies are mixed in the presence of the object, and a sixth step of receiving the radio frequency signal in the presence of the object by the receiver. Steps and the receiving A seventh step of detecting the radio frequency signal in a state where the object is present and outputting the difference frequency signal, and the receiver is configured to detect a phase of the difference frequency signal in a state where the object is present. Eighth step of measuring, the receiver, the phase of the difference frequency signal measured in the absence of the object, the phase of the difference frequency signal measured in the presence of the object, A ninth step of calculating a relative dielectric constant of the object from the thickness.

  According to the present invention, a radio frequency signal in which signals of two different frequencies are mixed is transmitted from a transmitter, and a state where an object to be measured does not exist between a transmitter and a receiver and a state where an object exists are present. Since the radio frequency signal is received for each and the relative permittivity of the object is calculated based on the information on the phase of the radio frequency signal, the time sweep of the frequency of the radio frequency signal is unnecessary, and the conventional VCO requires it. Since the settling time is not required, the measuring time can be shortened.

FIG. 1 is a block diagram illustrating a configuration of a dielectric constant measurement system according to a first example of the present invention. 4 is a flowchart illustrating an operation of the dielectric constant measurement system according to the first example of the present invention. FIG. 3 is a diagram illustrating frequencies of a radio frequency signal and a difference frequency signal in the dielectric constant measurement system according to the first example of the present invention. FIG. 3 is a diagram illustrating a principle of calculating a relative dielectric constant of an object. FIG. 6 is a block diagram illustrating a configuration of a dielectric constant measurement system according to a second example of the present invention. 6 is a flowchart illustrating an operation of a dielectric constant measurement system according to a second example of the present invention. FIG. 7 is a diagram illustrating frequencies of a radio frequency signal and a difference frequency signal in a dielectric constant measurement system according to a second example of the present invention. It is a figure which shows the cross section of the object used for the test measurement in 2nd Example of this invention, and the thickness of an object. It is a figure showing the measurement result of the relative permittivity in the 2nd example of the present invention. FIG. 11 is a block diagram illustrating a configuration of a transmitter of a dielectric constant measurement system according to a third example of the present invention. FIG. 14 is a block diagram illustrating a configuration of a transmitter of a dielectric constant measurement system according to a fourth embodiment of the present invention. FIG. 14 is a block diagram illustrating a configuration of a receiver of a dielectric constant measurement system according to a fifth example of the present invention. FIG. 10 is a block diagram illustrating a configuration of a conventional dielectric constant measurement system. It is a figure explaining the frequency of the radio frequency signal and the intermediate frequency signal in the conventional dielectric constant measurement system.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a dielectric constant measuring system according to a first embodiment of the present invention. The dielectric constant measuring system includes a transmitter 1 and a receiver 2 (dielectric constant measuring device).

  The transmitter 1 includes oscillators 10 and 11, a mixer 12, and an antenna 13. The receiver 2 includes an antenna 20, a detection diode 21 (detector), an ADC 22, a phase measurement unit 23, a relative permittivity calculation unit 24, and a calculation result output unit 25.

FIG. 2 is a flowchart illustrating the operation of the dielectric constant measurement system according to the present embodiment. First, in a state where there is no object 3 to be measured between the transmitter 1 and the receiver 2, the transmitter 1 transmits radio frequency signals of _two frequencies f ₁ and f ₂ (f ₂ > f ₁ ) (hereinafter, referred to as “f _1” ). An RF signal) is emitted toward the receiver 2 (step S100 in FIG. 2). Specifically, the oscillator 10 of the transmitter 1 outputs an intermediate frequency signal (hereinafter referred to as an IF signal) having a frequency f _if = f ₂ −f ₁ , and the oscillator 11 outputs a local signal having a frequency f _lo = f ₁ . A signal (hereinafter, LO signal) is output.

The mixer 12 of the transmitter 1 mixes the IF signal from the oscillator 10 and the LO signal from the oscillator 11. The mixer 12 passes a signal having a frequency of f ₁ = f _lo , f ₂ = f _lo + f _if and blocks a signal having a frequency of f _lo −f _if , and has a single sideband (SSB: Single) having a pass band characteristic. Sideband) mixer. For this reason, the mixer 12 outputs an RF signal in which the frequencies f ₁ and f ₂ are mixed as shown in FIG. The antenna 13 transmits the RF signal output from the mixer 12 to the receiver 2.

The detection diode 21 of the receiver 2 square-detects the RF signal received by the antenna 20, and outputs a difference frequency signal between the RF signals of the two frequencies (Step S101 in FIG. 2). As described above, assuming that the frequencies of the RF signals are f ₁ and f ₂ , the frequency of the difference frequency signal is f ₂ −f _{1 as shown} in FIG.

Here, if the input _Sano of the detection diode 21 is described as in Expression (1), the output _Scath of the detection diode 21 is expressed by Expression (2) due to the square detection operation of the detection diode 21.

Θ ₁ and θ ₂ in the equations (1) and (2) are the phases of the RF signals of the frequencies f ₁ and f ₂ received by the antenna 20, respectively. As is apparent from the fifth term on the right side of the equation (2), it is found that a difference frequency signal having a phase component of θ ₂ −θ ₁ and a frequency f ₂ −f ₁ is generated.

Next, the ADC 22 of the receiver 2 converts the difference frequency signal output from the detection diode 21 into a digital signal (Step S102 in FIG. 2). Although not explicitly described in the present embodiment, as will be described in the embodiments described later, the DC component of the first term on the right side and the harmonic components of the second to fourth terms on the right side (frequency f ₁ , f ₂ , and f ₁ + f ₂ ) are desirably removed so that only the difference frequency component is input to the ADC 22.

The phase measuring unit 23 of the receiver 2 measures the phase of the difference frequency signal (more precisely, the amount of change in the phase of the difference frequency signal with respect to the reference IF signal on the transmission side) (step S103 in FIG. 2). In this embodiment, the phase of the difference frequency signal measured when there is no object 3 between the transmitter 1 and the receiver 2 (when only air is present) is defined as θ _air . The phase measurement unit 23 can be configured by, for example, a DSP (Digital Signal Processor).

Next, the user using the dielectric constant measurement system places the object 3 having the known thickness L between the transmitter 1 and the receiver 2.
The transmitter 1 irradiates the object 3 with the RF signals of the _two frequencies f ₁ and f ₂ in the state where the object 3 is arranged as described above (Step S104 in FIG. 2). The process of step S104 is the same as step S100.

The detection diode 21 of the receiver 2 square-detects the RF signal transmitted from the antenna 13 of the transmitter 1 and transmitted through the object 3 and received by the antenna 20, and detects the RF signal of two frequencies f ₁ and f ₂ . Is output (step S105 in FIG. 2).

The operations of the ADC 22 and the phase measurement unit 23 of the receiver 2 (steps S106 and S107 in FIG. 2) are the same as those in steps S102 and S103, respectively. In the present embodiment, the phase of the difference frequency signal measured when the object 3 exists between the transmitter 1 and the receiver 2 is assumed to be θ _sample .

Next, the relative permittivity calculation unit 24 of the receiver 2 determines that the phase θ _air of the difference frequency signal measured when the object 3 does not exist between the transmitter 1 and the receiver 2, and the object 3 exists. From the measured phase θ _sample of the difference frequency signal and the known thickness L of the object 3 in the transmission direction of the RF signal (the direction from left to right in FIG. 1), the relative permittivity ε _{r of the} object 3 Is calculated (step S108 in FIG. 2).

If the user inputs a state signal indicating whether the object 3 exists between the transmitter 1 and the receiver 2 or not to the relative permittivity calculating unit 24, the relative permittivity calculating unit 24 It is possible to identify two states.
Here, the principle of calculating the dielectric constant epsilon _r of this embodiment will be described with reference to FIG. 4 (A) ~ FIG 4 (D). FIG. 4 (A) the ratio of the RF signal of frequency f _1, f ₂ is irradiated in sequence on small objects 3 dielectric constant epsilon _r, the frequency f _1, f ₂ of the RF signal transmitted through the object 3 phase The process of sequentially measuring θ ₁ and θ ₂ is schematically illustrated. In this case, it is assumed that the phase difference Δθ = θ ₂ −θ ₁ is obtained as shown in FIG.

On the other hand, FIG. 4C shows an RF signal of frequencies f ₁ and f ₂ transmitted through the object 3 by sequentially irradiating an RF signal of frequencies f ₁ and f _{2 to} the object 3 having a large relative permittivity ε _r. Schematically illustrates the process of measuring the phases θ ₁ and θ ₂ in order. In this case, the phase difference Δθ = θ ₂ −θ ₁ is as shown in FIG. The phase difference [Delta] [theta] (phase slope) as takes a different value depending on the relative dielectric constant epsilon _r of the object 3. The relative permittivity ε _r of the object 3 can be obtained by Expression (3).

C in equation (3) is the speed of light. The principle of calculating the relative permittivity ε _r is disclosed in Non-Patent Document 1.
In the present embodiment, the transmitter 1 transmits an RF signal in which the frequencies f ₁ and f ₂ are mixed, but the phase information measured by the phase measuring unit 23 includes the information of the phase difference Δθ = θ ₂ −θ _1. It is. Therefore, the dielectric constant calculator 24 of this embodiment, it is possible to determine the dielectric constant epsilon _r of the object 3 by the equation (3) to based the following equation (4).

Note that the fixed phase offset generated in each element of the dielectric constant measurement system is canceled by taking the difference between the phases θ _sample and θ _air . Therefore, there is no possibility that the phase offset affects the calculation of the dielectric constant epsilon _r.

The calculation result output unit 25 of the receiver 2 outputs the calculation result of the relative permittivity calculation unit 24 (Step S109 in FIG. 2). Specifically, the calculation result output unit 25, and transmits for example, to display the value of the relative dielectric constant epsilon _r of the object 3 relative dielectric constant calculator 24 has calculated, the information of the relative permittivity epsilon _r to the outside I do. Thus, the processing of the dielectric constant measurement system according to the present embodiment ends.

  The relative permittivity calculation unit 24 and the calculation result output unit 25 can be realized by a computer having a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. The CPU of the computer executes the processing described in this embodiment or the following embodiment according to a program stored in the storage device.

In this embodiment, the transmitter 1 transmits a two-tone RF signal in which signals of two different frequencies are mixed, and determines the relative permittivity ε _r of the object 3 based on information on the phase of the RF signal transmitted through the object 3. Since the calculation is performed, the time sweep of the frequency of the RF signal is not required, and the settling time required in the conventional VCO is not required, so that the measurement time can be reduced.

[Second embodiment]
Next, a second embodiment of the present invention will be described. FIG. 5 is a block diagram showing a configuration of a dielectric constant measuring system according to a second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. This embodiment describes a specific example of the first embodiment. The dielectric constant measuring system according to the present embodiment includes a transmitter 1a and a receiver 2a (dielectric constant measuring device).

The transmitter 1a includes oscillators 10 and 11a, a mixer 12, an antenna 13, and a frequency multiplier 14.
The receiver 2a includes an antenna 20, a detection diode 21, an ADC 22, a phase measurement unit 23, a relative permittivity calculation unit 24, a calculation result output unit 25, an IF amplifier 26, an oscillator 27, and an IF mixer. 28.

FIG. 6 is a flowchart illustrating the operation of the dielectric constant measurement system according to the present embodiment. The transmitter 1a irradiates the receiver 2a with RF signals of _two frequencies f ₁ and f _{2 in} a state where there is no object 3 to be measured between the transmitter 1a and the receiver 2a (step in FIG. 6). S200).

The oscillator 10 of the transmitter 1a outputs an IF signal having a frequency f _if = f ₂ −f ₁ as in the first embodiment. On the other hand, the oscillator 11a is frequency output signals _{f a (f a <f lo} ). The frequency multiplier 14 outputs a LO signal having _a frequency f _lo = f ₁ = f _a × N which is N times (N is an integer of 2 or more) times the signal output from the oscillator 11a.

The mixer 12 of the transmitter 1a mixes the IF signal from the oscillator 10 and the LO signal from the frequency multiplier 14. As described in the first embodiment, the mixer 12 allows the signal of the frequency of f ₁ = f _lo , f ₂ = f _lo + f _if to pass the signal, and cuts off the signal of the frequency of f _lo −f _if. Having. Therefore, mixer 12 outputs an RF signal frequency f ₁ and f ₂ are mixed as shown in FIG. 7 (A). Reference numeral 120 in FIG. 7A indicates a pass band of the mixer 12. The antenna 13 transmits the RF signal output from the mixer 12 to the receiver 2a.

As in the first embodiment, the detection diode 21 of the receiver 2a square-detects the RF signal received by the antenna 20 and outputs a difference frequency signal between the _two RF signals f ₁ and f _2. (Step S201 in FIG. 6).

The IF amplifier 26 of the receiver 2a amplifies the output signal of the detection diode 21 (Step S202 in FIG. 6). As described in the first embodiment, the output of the detection diode 21 includes a DC component and a harmonic component in addition to the difference frequency signal. Is removed by the band characteristic of Accordingly, the IF amplifier 26 outputs an amplified difference frequency signal having the frequency f ₂ −f ₁ as shown in FIG. 7B.

Next, the IF mixer 28 of the receiver 2a outputs the difference frequency signal of the frequency f ₂ −f ₁ output from the IF amplifier 26 and the LO signal for the receiver of the frequency f _{lo — rx} output from the oscillator 27. The frequency of the difference frequency signal is converted (down-converted) by mixing (step S203 in FIG. 6). The down-converted by the mixer 28, the frequency of the difference frequency signal f ₂ -f ₁ is converted into f ₂ -f ₁ -f _lo _ _rx as shown in FIG. 7 (C).

The ADC 22 of the receiver 2a converts the difference frequency signal output from the IF mixer 28 into a digital signal (Step S204 in FIG. 6).
The operation of the phase measurement unit 23 of the receiver 2a (Step 205 in FIG. 6) is the same as in the first embodiment. Also in this embodiment, the phase of the difference frequency signal measured when there is no object 3 between the transmitter 1a and the receiver 2a is assumed to be θ _air .

Next, the user places the object 3 having the known thickness L between the transmitter 1a and the receiver 2a. The transmitter 1a irradiates the object 3 with RF signals of _two frequencies f ₁ and f ₂ in a state where the object 3 is arranged (Step S206 in FIG. 6). The processing in step S206 is the same as that in step S200.

The detection diode 21 of the receiver 2a square-detects the RF signal transmitted from the antenna 13 of the transmitter 1a, transmitted through the object 3, and received by the antenna 20, and detects the RF signals of the two frequencies f ₁ and f ₂ . Is output (step S207 in FIG. 6).

The operations of the IF amplifier 26, the IF mixer 28, the ADC 22, and the phase measuring unit 23 (steps S208, S209, S210, S211 in FIG. 6) of the receiver 2a are the same as those in steps S202, S203, S204, and S205, respectively. Also in the present embodiment, the phase of the difference frequency signal measured when the object 3 exists between the transmitter 1a and the receiver 2a is assumed to be θ _sample .

The dielectric constant calculator 24 of the receiver 2a is the as in the first embodiment Equation (4) to calculate the relative dielectric constant epsilon _r of the object 3 (Fig. 6 step S212).
The operation of the calculation result output unit 25 of the receiver 2a (step 213 in FIG. 6) is the same as in the first embodiment.

Next, a result of actually measuring the relative permittivity ε _r of the object 3 using the permittivity measuring system of the present embodiment will be described. Here, as shown in FIG. 8A, the dielectric constant of the object 3 whose thickness L changes stepwise was measured. Indices i1 to i9 in FIG. 8A indicate positions on the object 3. FIG. 8B shows the thickness L of the object 3 at the positions of the indexes i1 to i9. In this example, the thickness L changes stepwise from 0.8 mm to 40 mm.

In this measurement, f _if = 15 GHz, f _a = 14.888... GHz, N = 18, f _lo = 268 GHz, f ₁ = 268 GHz, f ₂ = 283 GHz, and f _{lo — rx} = 15.01 GHz. The material of the object 3 shown in FIG. 8A is a resin, and the relative permittivity of the object 3 in the terahertz band is 2.55. The measurement results of the relative permittivity epsilon _r shown in FIG. Ε ₃ in FIG. 9 is the correct relative permittivity of the object 3.

FIG. 9 shows that the relative permittivity ε _r can be measured with a maximum error of 5.8%. The measurement time required for each point of the indexes i1 to i9 was 0.028 ms. The reason why the measurement time is 0.028 ms is that 285 cycles of a 10 MHz difference frequency signal (one cycle of 0.1 μs) input to the ADC 22 are measured.

  On the other hand, in order to perform the same measurement with a conventional dielectric constant measurement system using a VNA, a measurement time of 6 ms is required (refer to the document “Keysight E8361A / C PNA Network Analyzer”, keysight, p.79, < http://literature.cdn.keysight.com/litweb/pdf/E8361-90007.pdf?id=451064> ”). Therefore, according to the present embodiment, it can be seen that the measurement time can be reduced to 1/200.

  Thus, in this embodiment, the same effects as in the first embodiment can be obtained. Further, in the present embodiment, since the difference frequency signal is down-converted, an ADC having a lower speed than that of the first embodiment can be adopted.

[Third embodiment]
Next, a third embodiment of the present invention will be described. FIG. 10 is a block diagram showing a configuration of a transmitter of a dielectric constant measuring system according to a third embodiment of the present invention. The same components as those in FIGS. 1 and 5 are denoted by the same reference numerals. The transmitter 1b according to the present embodiment includes oscillators 10 and 11, an antenna 13, a double sideband (DSB) mixer 12b, and a bandpass filter 15.

The operations of the oscillators 10 and 11 are as described in the first embodiment. The DSB mixer 12b mixes the IF signal from the oscillator 10 and the LO signal from the oscillator 11. At this time, DSB mixer 12b, unlike the first, mixer 12 of the second embodiment, not only passes signals of a frequency of f _1, f _2, of _{f lo -f if = 2f 1 -f} 2 The signal of the frequency is also passed.

The band-pass filter 15 passes a signal having a frequency of f ₁ and f ₂ among signals output from the DSB mixer 12b and blocks a signal having a frequency of f _lo −f _if = 2f ₁ −f _2. Has characteristics. Therefore, the band-pass filter 15 outputs an RF signal in which the frequencies f ₁ and f ₂ are mixed. The antenna 13 transmits the RF signal output from the band pass filter 15.
Thus, in the present embodiment, it is possible to realize the transmitter 1b having the same function as that of the first embodiment.

As the configuration of the receiver, the receiver 2 of the first embodiment may be used, or the receiver 2a of the second embodiment may be used.
Further, instead of the oscillator 11, an oscillator 11a and a frequency multiplier 14 of the second embodiment may generate the LO signal from the signal of the frequency f _a with.

[Fourth embodiment]
Next, a fourth embodiment of the present invention will be described. FIG. 11 is a block diagram showing a configuration of a transmitter of a dielectric constant measuring system according to a fourth embodiment of the present invention. The same components as those in FIGS. 1 and 5 are denoted by the same reference numerals. The transmitter 1c according to the present embodiment includes oscillators 10c and 11, an antenna 13, and a multiplexer 16.

The oscillator 10c outputs an IF signal of f _lo + f _if = f ₂ . The multiplexer 16 multiplexes (frequency addition) the IF signal of the frequency f _lo + f _if = f ₂ from the oscillator 10c and the LO signal of the frequency f _lo = f ₁ from the oscillator 11. For this reason, the multiplexer 16 outputs an RF signal in which the frequencies f ₁ and f ₂ are mixed. The antenna 13 transmits the RF signal output from the multiplexer 16.
Thus, in the present embodiment, it is possible to realize the transmitter 1c having the same function as that of the first embodiment.

As the configuration of the receiver, the receiver 2 of the first embodiment may be used, or the receiver 2a of the second embodiment may be used.
Further, instead of the oscillator 11, an oscillator 11a and a frequency multiplier 14 of the second embodiment may generate the LO signal from the signal of the frequency f _a with.

[Fifth embodiment]
Next, a fifth embodiment of the present invention will be described. FIG. 12 is a block diagram showing a configuration of a receiver of a dielectric constant measuring system according to a fifth embodiment of the present invention. The same components as those in FIGS. 1 and 5 are denoted by the same reference numerals. The receiver 2d of the present embodiment includes an antenna 20, a detection diode 21, an ADC 22, a phase measurement unit 23, a relative permittivity calculation unit 24, a calculation result output unit 25, and an IF amplifier 26. You.

  In the present embodiment, the IF amplifier 26 described in the second embodiment is inserted between the detection diode 21 and the ADC 22 of the receiver 2 of the first embodiment. Thereby, the output signal of the detection diode 21 can be amplified, and the DC component and the harmonic component included in the output signal of the detection diode 21 can be removed.

As the configuration of the transmitter, any one of the transmitters 1, 1a, 1b, and 1c of the first to fourth embodiments may be used.
In this embodiment, since the down-conversion of the difference frequency signal as in the second embodiment is not performed, it goes without saying that a high-speed ADC similar to that of the first embodiment is required.

[Sixth embodiment]
In the first to fifth embodiments, the thickness L of the object 3 to be measured is set to a known value. However, the thickness L of the object 3 is detected by using a thickness detection unit (not shown). The value of the thickness L may be input to the relative permittivity calculation unit 24. Examples of the thickness detector include, for example, a thickness detector using ultrasonic waves, a thickness detector using infrared light, and a thickness detector that calculates a thickness L from a visible image of the object 3 acquired by a camera. Various existing techniques for thickness detection, such as a part, can be applied. Thus, in the present embodiment, even for the object 3 whose thickness L is unknown, the thickness L can be obtained in real time and the relative permittivity ε _r of the object 3 can be calculated.

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

  1, 1a: Transmitter, 2, 2a: Receiver, 10, 11, 11a, 27: Oscillator, 12: Mixer, 12b: Double-sideband mixer, 13, 20: Antenna, 14: Frequency multiplier, 15: Band Pass filter, 16: multiplexer, 21: detection diode, 22: AD converter, 23: phase measurement unit, 24: relative permittivity calculation unit, 25: calculation result output unit, 26: IF amplifier, 28: IF Mixer.

Claims (9)

A transmitter for transmitting a radio frequency signal in which signals of two frequencies are mixed,
A receiver that receives the radio frequency signal for each of the state where the object to be measured does not exist between the transmitter and the state where the object exists, and calculates the relative permittivity of the object,
The receiver,
A first antenna for receiving the radio frequency signal;
A detector for detecting a radio frequency signal received by the first antenna and outputting a difference frequency signal between the two frequency signals;
A phase measurement unit that measures the phase of the difference frequency signal for each of the state where the object is not present between the transmitter and the receiver and the state where the object is present,
From the phase of the difference frequency signal measured in the absence of the object, the phase of the difference frequency signal measured in the presence of the object, and the thickness of the object, the relative permittivity of the object A dielectric constant measurement system, comprising: a relative dielectric constant calculation unit that calculates the relative dielectric constant. The dielectric constant measurement system according to claim 1,
The dielectric constant measurement system, further comprising an amplifier provided between the detector and the phase measurement unit, for amplifying an output signal of the detector. The dielectric constant measurement system according to claim 2,
The receiver,
A first oscillator for outputting a first local signal;
The difference frequency signal, which is provided between the amplifier and the phase measurement unit, is mixed by mixing the difference frequency signal output from the amplifier and the first local signal output from the first oscillator. A dielectric constant measurement system, further comprising: a first mixer that converts a frequency of a signal to a lower frequency than the radio frequency signal and the first local signal. The dielectric constant measurement system according to any one of claims 1 to 3,
The transmitter is
A second oscillator for outputting an intermediate frequency signal,
A third oscillator that outputs a second local signal;
A second mixer that mixes the intermediate frequency signal output from the second oscillator with a second local signal output from the third oscillator;
A second antenna for transmitting a radio frequency signal output from the second mixer. The dielectric constant measurement system according to claim 4,
The second mixer passes the second local signal and a signal having a sum frequency of the second local signal and the intermediate frequency signal, and outputs the second local signal and the intermediate frequency signal. A dielectric constant measuring system, which is a single sideband mixer having a passband characteristic of blocking a signal of a difference frequency. The dielectric constant measurement system according to claim 4,
A bandpass filter provided between the second mixer and the second antenna;
The second mixer includes a second local signal, a signal having a sum frequency of the second local signal and the intermediate frequency signal, and a frequency having a difference between the second local signal and the intermediate frequency signal. A double-sideband mixer having a passband characteristic for passing the signal of
The band-pass filter, among the signals output from the second mixer, the second local signal, and a signal having a frequency of the sum of the second local signal and the intermediate frequency signal, A dielectric constant measurement system having a pass band characteristic of blocking a signal having a frequency of a difference between a second local signal and the intermediate frequency signal. The dielectric constant measurement system according to any one of claims 1 to 3,
The transmitter is
A second oscillator that outputs a signal having a frequency equal to the sum of the intermediate frequency signal and the second local signal;
A third oscillator that outputs the second local signal;
A multiplexer for multiplexing a signal output from the second oscillator and a second local signal output from the third oscillator;
A second antenna for transmitting a radio frequency signal output from the multiplexer. An antenna for receiving a radio frequency signal;
A detector that detects a radio frequency signal received by the antenna and outputs a difference frequency signal between two signals included in the radio frequency signal;
A phase measurement unit that measures the phase of the difference frequency signal for each of a state where the object to be measured does not exist in the arrival direction of the radio frequency signal and a state where the object exists.
From the phase of the difference frequency signal measured in the absence of the object, the phase of the difference frequency signal measured in the presence of the object, and the thickness of the object, the relative permittivity of the object A dielectric constant measurement device, comprising: a relative dielectric constant calculation unit for calculating. A first step in which a transmitter transmits a radio frequency signal in which signals of two frequencies are mixed in a state where no object to be measured exists between the transmitter and the receiver;
A second step in which the receiver receives the radio frequency signal in a state where the object is not present;
A third step in which the receiver detects the radio frequency signal in a state where the object is not present, and outputs a difference frequency signal between the two frequency signals;
A fourth step in which the receiver measures the phase of the difference frequency signal in the absence of the object;
A fifth step in which the transmitter transmits a radio frequency signal in which the signals of the two frequencies are mixed in a state where the object is present;
A sixth step in which the receiver receives the radio frequency signal in a state where the object is present;
A seventh step in which the receiver detects the radio frequency signal in a state where the object is present, and outputs the difference frequency signal;
An eighth step in which the receiver measures the phase of the difference frequency signal in the presence of the object;
The receiver, the phase of the difference frequency signal measured in the absence of the object, the phase of the difference frequency signal measured in the presence of the object, from the thickness of the object, the ratio of the object A ninth step of calculating a dielectric constant.