KR100925016B1 - Apparatus for Measuring the Dielectric Constant and Method therefor - Google Patents

Abstract

The present invention relates to an apparatus and method for measuring permittivity using a 6-port network, including a directional coupler for transmitting and receiving signals separately, a 6-port network circuit capable of knowing the magnitude and phase of a transmitted and received signal through a DC voltage, and having a small size. A low noise amplifier for amplifying a DC voltage and removing high frequency noise, and a central processing unit for calculating the dielectric constant using the DC voltage. Through this, a high frequency signal can be transmitted through an antenna to determine a reflection coefficient by checking a received signal that changes according to a change in dielectric constant, and a dielectric constant of a remotely measured object can be calculated through a relationship with a relative dielectric constant already stored.

According to the present invention, since the dielectric constant can be measured remotely using the radar sensor, the dielectric constant can be recognized using a simple calculation through the DC voltage of the received signal without complicated signal processing.

Permittivity measurement, radar sensor, 6-port network, permittivity image, reflection coefficient measurement, relative permittivity

Description

Apparatus for Measuring the Dielectric Constant and Method therefor}

The present invention relates to a dielectric constant measuring apparatus and method, and more particularly, it is possible to measure a reflection coefficient of a measurement target by transmitting a high frequency signal through an antenna and confirming a received signal that changes according to the change in dielectric constant, and the measured reflection coefficient The present invention relates to a dielectric constant measuring apparatus and method that can accurately measure dielectric constant remotely and can be realized by a compact radar sensor.

Among the various properties of an object, the dielectric constant is a property that determines the reflection characteristic of a high frequency signal, which is a value that informs the state of the object. In particular, metals and nonmetals with good surface reflection have a large difference in permittivity, and thus, a permittivity sensor for recognizing the difference has been widely used.

In particular, it is possible to recognize terrain or discover mines by using a dielectric constant sensor when direct contact is not possible, such as underwater mines, terrain exploration, marine deep sea terrain or mineral exploration. In addition, recently, it is applied to the cancer diagnostic sensor by applying it to the cancer diagnostic sensor, and its use as a security sensor for detecting weapons mainly made of metal is gradually expanded.

However, the application of such a dielectric constant sensor has a problem that a large size and a large amount of data processing is required, so that it is very difficult for an individual to carry and the price required for manufacturing is quite expensive, but it has not been widely used despite its various applications.

In general, remote permittivity sensors using the radar principle have used pulse radar. This is because the pulse transmits and receives a large signal for a relatively short time, and thus has good permeability. Therefore, it is advantageous for underwater feature recognition or land mine exploration requiring some permeability, and marine deep sea terrain or mineral exploration.

The dielectric constant recognition sensor using the pulse radar changes the width of the pulse of the received signal when an object having a different dielectric constant appears. By detecting this, an object having a different dielectric constant exists. To recognize this, it is necessary to find out the pulse width of the received signal through a complicated calculation process and extract information through the execution of various complex algorithms such as whether it changes beyond the threshold value to prevent errors. It can only be done. In addition, since the relative dielectric constant is found to find an object having a different dielectric constant compared to the surrounding environment, it is only possible to confirm the existence of an object having a different relative dielectric constant, but to determine what the object is, an additional signal processing algorithm must be performed for a long time.

Therefore, it is very difficult to recognize the relative permittivity in real time using the conventional pulse radar measurement method, and also to recognize the difference in permittivity from the surrounding environment, and there is a lot of complexity and difficulty in determining the relative permittivity value.

The dielectric constant is closely related to the reflection coefficient. Thus, a vector network analyzer capable of measuring the reflection coefficient gives the relative permittivity. For samples designed for vector network analyzers, the relative permittivity values can be obtained from S-parameters by measurement after accurate calibration.

The vector network analyzer operates by transmitting and receiving signals connected to the port and recognizing the magnitude and phase difference of the signals. For this purpose, the vector network analyzer uses high performance expensive circuits such as a precision frequency signal generator and a high performance mixer. It is designed and manufactured by using.

Conventional vector network analyzers are connected by coaxial cables, making it almost impossible to measure distant permittivity. The characteristics up to the coaxial cable can be eliminated by performing standard calibration such as open, short, load, and thru.However, if the antenna is connected to a vector network analyzer and the dielectric constant is to be measured remotely Calibration, including antenna characteristics, is nearly impossible. Therefore, when scanning the surrounding environment through the antenna, it is possible to obtain a result of comparing the dielectric constants in the measurement environment as in the case of using the pulse radar, but there is a problem in that the relative dielectric constant values cannot be obtained.

The problem to be solved by the present invention is to solve the above problems, it is to measure the relative permittivity only by simple signal processing remotely using a 6-port network.

Another object of the present invention is to solve the above problems, and to provide a dielectric constant measuring apparatus that can be implemented as a radar sensor that can be manufactured in a very small size.

Another problem to be solved by the present invention is to solve the above problems, and to recognize the difference between the dielectric constant and the relative dielectric constant with the surrounding objects and to recognize the classification of the object and the type of the object through a portable remote radar sensor using the same To make it possible.

The present invention relates to a dielectric constant measuring apparatus, comprising: a frequency signal generator for generating a reference signal and a transmission signal transmitted to a dielectric constant measuring object; An antenna for transmitting and receiving the transmission signal and the reception signal reflected from the measurement object; A low noise amplifier for amplifying the received signal; A six-port network that receives the reference signal and the received signal and generates distance information represented by power of a high frequency signal using a phase difference between the two signals; A power detector for converting power of the high frequency signal output from the 6-port network into a DC voltage; An analog-digital converter for converting the DC voltage converted by the power detector into data capable of processing; And a central processing unit that controls a frequency of a reference signal or a transmission signal generated by the frequency signal generator and calculates a reflection coefficient and a dielectric constant of the object to be measured using data converted by the analog-to-digital converter. .

Advantageously, said six-port network comprises a first directional coupler and a 90 degree delay transmission line.

Also preferably, the dielectric constant measuring device further comprises; a second directional coupler for separating the frequency signal generated from the frequency signal generator into a reference signal and a transmission signal.

Also preferably, a power amplifier for amplifying the transmission signal; characterized in that it further comprises.

Also preferably, the central processing unit stores the reflection coefficient data measured in advance for at least three or more standard measurement objects for the calculation of the dielectric constant.

And preferably, the central processing unit is characterized in that it comprises a function of generating a dielectric constant image by controlling the beam direction of the antenna.

Meanwhile, the present invention relates to a method for measuring dielectric constant using a 6-port network that receives a reference signal and a received signal and generates distance information represented by power of a high frequency signal using a phase difference between two signals. Measuring a reflection object for the measurement object and the measurement object; (b) calculating and storing the dielectric constant for the measurement object using the reflection coefficient data for the measured standard measurement object; And (c) outputting a dielectric constant calculation result for the measurement object when the change in the stored dielectric constant is less than a preset threshold.

Preferably, before the step (a), (a-1) removing the DC offset voltage (off); characterized in that it further comprises.

And preferably, before the step (a), (a-2) removing the characteristic error of the six-port network; characterized in that it further comprises.

According to the present invention, by measuring the dielectric constant remotely for the measurement target located at a certain distance, there is an effect that can be recognized by using a simple calculation through the DC voltage of the received signal without complicated signal processing.

According to the present invention, a high-sensitivity permittivity measurement is possible by a six-port network composed of passive elements without using a large and expensive hardware filter and mixer required in the conventional system, thereby reducing costs.

According to the present invention, it is possible to increase the sensitivity while miniaturizing the conventional dielectric constant sensor, it can be utilized in a variety of applications such as personal breast cancer diagnostic, fruit sugar meter as well as marine exploration or land mine detection equipment which is a conventional application field It has an effect.

According to the present invention, since the dielectric constant image can be easily obtained by using the antenna beam direction control and image processing technique, there is an effect that can be applied to various applications.

Before describing the details for carrying out the present invention, it should be noted that configurations that are not directly related to the technical gist of the present invention are omitted within the scope of not distracting the technical gist of the present invention.

In addition, the terms or words used in the present specification and claims are consistent with the technical spirit of the present invention on the basis of the principle that the inventor can appropriately define the concept of the term in order to explain the invention in the best way. It should be interpreted as meaning and concept.

In the present invention, by measuring the reflection coefficient precisely through a radar sensor that transmits and receives a high frequency signal, it is possible to measure the dielectric constant of a measurement target object located at a far distance. The radar sensor may comprise a six-port network consisting of two input ports and four output ports.

Hereinafter, a six-port network used in a dielectric constant measuring apparatus according to a preferred embodiment of the present invention will be described with reference to FIG.

1 is a block diagram of a six-port network according to a preferred embodiment of the present invention.

The six-port network, as shown in FIG. 1, represents the frequency signals appearing at the four output ports in a linear relationship to the frequency signals coming into the two input ports, the first directional coupler 101, 90. It also includes a combination of passive elements such as delayed transmission line 102. It also includes a 50 ohm termination port 103 for matching high frequency signals.

The six-port can be configured in various ways using other types of passive devices or devices such as inductors or capacitors, and these configurations can operate with four outputs in a linear relationship to two input signals. Is the same.

When four DC voltages corresponding to the respective output powers are obtained from the output ports of the six-port network as described above, the ratio of the magnitude and phase of the frequency signal coming into the two input ports is obtained using the power detector. Can be.

Hereinafter, a dielectric constant measuring apparatus according to a preferred embodiment of the present invention will be described with reference to FIG. 2.

2 is a block diagram of a dielectric constant measuring apparatus according to a preferred embodiment of the present invention.

As shown in FIG. 2, the dielectric constant measuring apparatus according to the preferred embodiment of the present invention includes a frequency signal generator 211, a second directional coupler 205, an antenna 206, a signal attenuator 203, and a low noise amplifier ( 204, power detector 202, signal processing block 207, analog-to-digital converter 208, central processing unit 209, and six-port network 201.

The frequency signal generator 211 generates a high frequency signal.

Next, the second directional coupler 205 performs a circulator function to separate the high frequency signal generated from the frequency signal generator 211. In addition, the high frequency signal received by the antenna 206 is separated.

Next, the antenna 206 transmits a part of the high frequency signals separated by the second directional coupler 205 to the outside so that the antenna 206 is reflected from the dielectric constant measuring object 210 located at a long distance, and reflects the reflected high frequency signals. Receive. The reflected high frequency signal changes in magnitude and phase of the high frequency signal according to the dielectric properties of the object to be measured 210.

Next, the signal attenuator 203 attenuates some other high frequency signals separated by the second directional coupler 205 to serve as a reference signal LO of the 6-port network 201.

In addition, when the distance to the dielectric constant measuring object 210 is long or there is a medium such as land or sea between the measuring object 210, the frequency signal generator 211 and the second directional coupler 205 are present. It is preferable to amplify the transmission signal by providing a power amplifier (not shown in the figure).

Next, the low noise amplifier 204 amplifies a part of the frequency signal received by the antenna 206 and separated by the second directional coupler 205 to receive the received signal (RF) of the 6-port network 201. ).

The remaining signal received by the antenna 206 and separated from the second directional coupler 205 proceeds to the frequency signal generator 211, which typically has a low frequency power of -40 to -50 dBm or less in magnitude. It does not affect the operation of the frequency signal generator 211 or the power amplifier that can be additionally connected.

Next, the power detector 202 converts a high frequency signal output from the output port of the six-port network 201 in the form of a passive element into a DC voltage.

Next, the signal processing block 207 amplifies the converted DC voltage signal and performs a low pass filter (LPF) process.

Next, the analog-to-digital converter 208 restores the amplified and low pass filtered DC voltage signal to a digital signal.

Next, the central processing unit 209 calculates the reflection coefficient value from the restored digital signal and ultimately measures the relative dielectric constant. The central processing unit 209 may be configured as a digital signal processor (DSP) or a PC.

Finally, since the six-port network 201 has been described above, a detailed description thereof will be omitted.

Hereinafter, a process of calculating the dielectric constant of a measurement target using the dielectric constant measuring device as described above will be described.

When the phase change by the 6-port network 201 is configured as shown in [Table 1], the DC voltage converted at each output port is shown in Equations 1 to 4 below.

a ₁ (LO) a ₂ (RF) b ₃ (Port 3) 360 ° 180 ° b ₄ (Port 4) 270 ° 270 ° b ₅ (Port 5) 270 ° 360 ° b ₆ (Port 6) 360 ° 270 °

In Equations 1 to 4, K _i represents a conversion constant of each power detector 202, and α represents a ratio of magnitudes of two input signals coming into the six-port network 201. Represents the difference in phase.

The reflection coefficients generated between the transmission signal and the reception signal coming into the six-port network 201 are represented by the following equation and the following equation.

In addition, when [Equations 1] to [Equation 4] are expressed with respect to cos (Δθ) and sin (Δθ), Equation 6 and Equation 7 are as follows.

Equation 6 and Equation 7 show the reflection coefficients generated between the transmission signal and the reception signal as shown in Equation 8 below.

According to Equation 8, when the conversion characteristic value of the power detector 202 is known, the reflection coefficient can be calculated immediately by measuring the output voltage. Fast Fourier transform (FFT) and the like method is effective only when the amount of data is more than a certain amount, it is possible to real-time operation because the reflection coefficient can be calculated by directly measuring the DC voltage obtained at the same time as the frequency transmission and reception.

In converting the calculated reflection coefficient into the dielectric constant as described above, it is not preferable to use a direct relationship between the dielectric constant and the reflection coefficient known in the art. This is because the reflection coefficient of [Equation 8] obtained as the received signal always includes the phase change and the magnitude change by the transmission / reception line, and also includes the distance information to the measurement target.

Since the dielectric information of the object is in the DC voltage, the DC offset voltage inevitably generated by the surrounding environment or the circuit configuration may cause distortion of the information. In addition, in order to overcome the inaccuracies in measurement that may occur due to the phase error of the passive components constituting the 6-port network 201, the phase errors of the passive components must be corrected.

Among the above problems, the DC offset voltage is eliminated and the correction for the characteristic change due to the phase error of the passive element constituting the 6-port network 201 may be applied by applying an error correction method used for distance measurement. Considering the phase error using the 6-port network 201, the phase change of the high frequency signal generated by the 6-port network 201 to each output port can be summarized as shown in Table 2 below.

a ₁ (LO) a ₂ (RF) b ₃ (Port 3) 360 ° + Φ ₁ + Φ ₂ 180 ° b ₄ (Port 4) 270 ° + Φ ₂ 270 ° + Φ ₁ b ₅ (Port 5) 270 ° + Φ ₁ 360 ° + 2Φ ₁ b ₆ (Port 6) 360 ° + 2Φ ₁ 270 ° + Φ ₁

In Table 2, the phase error Φ ₁ is an error occurring at the output of the first directional coupler 101, and the phase error Φ ₂ is an error occurring at the 90 degree signal delay line 102. When [Equation 1] to [Equation 4] is corrected based on [Table 2], [Equation 8] regarding the reflection coefficient that can be obtained from the DC output signal is represented by the following [Equation 9]. It can be improved as well.

The error correction using Equation 9 will be described in detail as follows.

When a high frequency signal having a constant frequency is always transmitted to an object located at a certain distance, the phase generated between the transmitted signal and the received signal may be defined as a function of the distance to the object. For this reason, when the distance is constant, the phase of the reflection coefficient obtained in Equation 9 should always be constant. In addition, when the phase of the transmission signal is changed, the phase of the corresponding reflection coefficient should also be changed to the same magnitude. By using such a principle, if the object having a large reflection coefficient, such as a metal, having a large size of a received signal is changed at a specific distance and the phase of the transmitted signal is changed, and the dielectric constant measuring apparatus according to the preferred embodiment of the present invention operates, [ The equation for the correction constant defined in Equation 9 can be obtained, and the correction constant can be obtained simply. This can result in reflection coefficients with errors that can occur in the six-port network 201 being corrected.

The removal of the DC offset voltage is possible by controlling the frequency signal generator 211. If you change the phase of the transmitting frequency from 0 degrees to 360 degrees or sweep the frequency in a certain range of about several hundred MHz to achieve the same effect, the DC output obtained at this time forms a sine wave. Since the voltage corresponding to the voltage value is the offset voltage, the DC offset voltage can be obtained by obtaining the voltage average during this time. The DC offset voltage thus obtained can be corrected by subtracting the DC offset voltage from each port in subsequent measurements. The measured DC offset voltage is valid for a certain time, so after a certain time, repeat the above procedure and measure the offset voltage again to use the new value.

Distance information to the measurement target can be removed through the following [Equation 10]. In the method of obtaining the relative permittivity through the reflection coefficient, the error that is changed by the measurement of the measuring device can be considered using the following Equation 10 based on the relationship between the reflection coefficient and the dielectric constant.

In Equation 10, ε _si and Γ _si represent dielectric constants and reflection coefficients for any object having a known dielectric constant, and may be obtained from three or more materials having different compositions. For most PCB substrates, the permittivity data over frequency can be obtained from the data given without any measurement, which can be used to make more accurate measurements.

The dielectric constant at high frequencies is mostly constant when the frequency change is small. In addition, since the value determined by the ratio of permittivity as shown in [Equation 10] can almost ignore the characteristic change according to frequency, it can be assumed that the left side term of [Equation 10] is almost constant.

The reflection coefficient can vary considerably depending on the distance to the measurement object. The length of the wavelength is determined by the frequency used, but the phase change occurs by 360 degrees according to the length of the wavelength.The higher the frequency used, the shorter the distance to the phase change is. The phase value of will change sensitively. However, if the measured reflection coefficient values for the three materials are all located at the same distance, the reflection coefficient phase change by distance will all affect the same degree, which is determined by a relational expression such as the right side term of Equation 10 above. Will be offset from each other. Therefore, through the above Equation 10, if the three or more different materials that know the dielectric constant at a certain frequency are measured at the same distance, and the dielectric properties are corrected, a very accurate measurement is possible.

In addition, since the phase errors Φ ₁ shown in Equation 9 through Equation 10 cancel each other in the right side term, a constant to be corrected may be further reduced. Here if the one specifying a specific port to another port, this characteristic and normalized (Normalize), K _i One of the parameters may be canceled with each other through Equation 10 above. Therefore, through [Equation 10], it is possible to reduce the constants required for the characteristic correction of the entire dielectric constant measuring apparatus according to the preferred embodiment of the present invention to four.

An additional problem that may occur is that a dielectric constant measuring device may malfunction if other communication or radar systems exist in the frequency band used for the measurement. This problem can be solved by sweeping the transmission / reception frequency generated by the frequency signal generator 211. If the transmit / receive frequency is swept within a range where the dielectric constant can be assumed to be nearly constant, each reflection coefficient exhibiting a characteristic sensitive to the wavelength will change constantly but the resulting dielectric constant will remain about the same. Therefore, even if there are other frequency components affecting the dielectric constant measurement in the swept band, it is possible to recognize the dielectric constant value measured at almost the same value if the noise generating frequency does not match the sweep range of the transmission / reception frequency.

Hereinafter, a dielectric constant measuring method according to a preferred embodiment of the present invention will be described with reference to FIG. 3.

3 is an overall flowchart of a dielectric constant measuring method according to a preferred embodiment of the present invention.

As shown in FIG. 3, first, the DC offset voltage is removed (S10).

Next, the correction constant of the dielectric constant measuring apparatus according to the preferred embodiment of the present invention is found to remove characteristic errors of the 6-port network 201 (S20).

Next, the reflection coefficient for the standard measurement object is measured (S30). It is preferable that three or more standard measurement targets are used.

Next, the reflection coefficient for the measurement target is measured (S40).

Next, the dielectric constant for the measurement object is calculated and stored using the reflection coefficient data for the measured standard measurement object (S50).

Next, it is determined whether the change in the stored dielectric constant is less than the threshold (S60).

Finally, when the determination result of step S60 is less than the threshold value, the dielectric constant information measured for the measurement target is output (S70).

As a result of the determination of step S60, when the change in the stored dielectric constant is greater than or equal to a threshold value, all data are initialized (S80) and fed back to the step S30.

In addition, the dielectric constant image using the present invention can be simply controlled through the antenna. Since the dielectric constant information can be recognized by controlling the beam direction of the antenna using a mechanical or electrical method, an image can be made by connecting blocks that can control the antenna beam. The dielectric constant image can be obtained by considering the maximum possible beam in the antenna as the whole image area, dividing it into pixels, and then repeating the process of obtaining the information by focusing the antenna beam on the pixel. Since it takes only a long time to control the antenna beam by the number of pixels to obtain an image, it is possible to obtain a permittivity image in a very fast time by controlling the antenna beam through an electrical method.

As described above and described with reference to a preferred embodiment for illustrating the technical idea of the present invention, the present invention is not limited to the configuration and operation as shown and described as such, it departs from the scope of the technical idea It will be apparent to those skilled in the art that many modifications and variations can be made to the present invention without this. Accordingly, all such suitable changes and modifications and equivalents should be considered to be within the scope of the present invention.

1 is a block diagram of a six-port network according to a preferred embodiment of the present invention.

2 is a block diagram of a dielectric constant measuring apparatus according to a preferred embodiment of the present invention.

3 is an overall flow chart of a dielectric constant measuring method according to a preferred embodiment of the present invention.

<Description of main parts of drawing>

101: first directional coupler 102: 90 degree delay transmission line

103: Termination port 201: 6-port network

202: power detector 203: signal attenuator

204: low noise amplifier 205: second directional coupler

206: antenna 207: signal processing block

208: analog-to-digital converter 209: central computing unit

210: measurement object 211: frequency signal generator

Claims (9)

A frequency signal generator 211 for generating a transmission signal transmitted to the reference signal and the dielectric constant measurement object; An antenna 206 for transmitting and receiving the transmission signal and the reception signal reflected from the measurement object; A low noise amplifier 204 for amplifying the received signal; A six-port network 201 receiving the reference signal and the received signal and outputting power of a high frequency signal corresponding to the reflected received signal; A power detector (202) for converting power of the high frequency signal output from the six-port network (201) into a DC voltage; An analog-digital converter (208) for converting the DC voltage converted by the power detector (202) into arithmetic data; And Controlling the frequency of the reference signal or the transmission signal generated by the frequency signal generator 211 and using the data converted by the analog-to-digital converter 208 to calculate the reflection coefficient for the object to be measured by the following equation And a central processing unit (209) for calculating the dielectric constant of the object to be measured from the calculated reflection coefficients.

(Wherein Γ is a reflection coefficient for the object to be measured, V ₃ to V ₆ are direct current voltages at each output port of the 6-port network 201 converted at the power detector 202, and K ₃ K ₆ are the conversion constants of each power detector 202.) The method of claim 1, The six-port network (201) comprises a first directional coupler (101) and a 90 degree delay transmission line (102). The method of claim 1, And a second directional coupler (205) for separating the frequency signal generated from the frequency signal generator (211) into a reference signal and a transmission signal. The method of claim 1, And a power amplifier for amplifying the transmission signal. The method of claim 1, The central processing unit (209) stores the coefficient of reflection data measured in advance for at least three or more standard measurement objects for the calculation of the dielectric constant. The method of claim 1, The central processing unit (209) includes a function of generating a dielectric constant image by controlling the beam direction of the antenna (206). In the dielectric constant measurement method using a 6-port network 201 to receive a reference signal and a received signal and generate distance information represented by the power of a high frequency signal using the phase difference between the two signals, (a) measuring a reflection coefficient for the standard measurement object and the measurement object; (b) calculating and storing the dielectric constant for the measurement object using the reflection coefficient data for the measured standard measurement object; And and (c) outputting a dielectric constant calculation result for the measurement object when the change in the stored dielectric constant is less than a preset threshold. The method of claim 7, wherein Before step (a) above, (a-1) removing the DC offset voltage. The method of claim 7, wherein Before step (a) above, (a-2) removing the characteristic error of the six-port network (201).

Images