KR100732935B1 - Measurement probe and system of material's dielectric constant using a transmitted reference impulse, and measurement method thereof - Google Patents

Abstract

The present invention relates to a dielectric constant probe, a measuring device, and a measuring method thereof, comprising: a reference line formed of a dielectric substrate and a microstrip line through which an impulse passes through one surface of the dielectric substrate, separated from the reference line to measure the delay time of the impulse. Delay line formed of a microstrip line for; And a measurement probe formed of a flat waveguide including a patterned surface and a ground layer (GND) formed on an opposite surface of the dielectric substrate, and an impulse generator and a detector using the measurement probe to measure dielectric constant. Dielectric constant measuring device and its measuring method.

According to the present invention, there is provided a dielectric constant measuring probe, a measuring device, and a dielectric constant measuring method, by measuring a delay time of a pulse passing through a measuring probe in the form of a flat waveguide input to a measuring medium, thereby measuring the measuring medium in real time without synchronizing a signal. The permittivity can be measured, probes can be manufactured at low cost, and system calibration is not necessary, making measurement simple.

Permittivity, CMOS, TDR, waveguide, probe, microstrip, impulse generator

Description

Measurement probe and system of material's dielectric constant using a transmitted reference impulse, and measurement method

1 illustrates a time domain reflectometry (TDR) method for measuring a dielectric constant in general;

Figure 2a shows a side view of a measuring probe formed of a flat waveguide introduced into a medium according to the present invention,

2b is a plan view of a measuring probe formed of a flat waveguide introduced into a medium according to the present invention;

3 is a block diagram of a structure of a dielectric constant measuring apparatus according to the present invention;

4 is a block diagram of an internal circuit of an impulse generator which is one of the components of the dielectric constant measuring apparatus according to the present invention;

5 is a diagram illustrating an example in which the dielectric constant measuring apparatus according to the present invention measures, calculates, and displays a dielectric constant of a medium;

6 is a flowchart illustrating a dielectric constant measuring method according to the present invention.

The present invention relates to a dielectric constant measuring device and a method of measuring the same, and more particularly, to form two paths through which an impulse passes, and to measure the propagation delay rate of pulses passing through each path, thereby permitting the dielectric constant in a uniform medium more easily and accurately. And further relates to a dielectric constant measuring apparatus and a measuring method thereof capable of measuring the water content of the uniform medium.

Permittivity (ε) is an important characteristic value that represents the electrical properties of dielectric materials, that is, insulators. The dielectric constant does not represent the electrical characteristics of the DC current, but is directly related to the characteristics of the AC current, in particular alternating electromagnetic waves.

Looking at the meaning of permittivity in dielectrics (insulators), one can understand the permittivity more conceptually. The +-moment components, which are usually scattered within the dielectric, are aligned with the alternating alternating current in the electromagnetic field. That is, the moment components change in accordance with the change direction of the electromagnetic field, thereby enabling the progress of electromagnetic waves in the insulator. In response to such changes in the external electromagnetic field, how sensitively the moment inside the material reacts is called the permittivity.

As such, all materials have electrical properties that are dependent on the dielectric constant. Accurate measurement of the dielectric constant provides scientists and engineers with important information about materials used in various fields.

In other words, permittivity measurement can be important information that provides accurate design parameters for many electronic devices. For example, the dielectric loss, which is closely related to the power loss of the insulated cable, the resistance of the material, and the dielectric constant, can be obtained from the measurement of the dielectric constant.

In addition, by measuring the dielectric constant in a specific medium, it is possible to measure the moisture water content of the medium, this technique has been applied in various fields. For example, it is also used to measure the moisture content of the powder or to check the dryness of the grain. It is very important to measure the moisture content of building sand because the moisture content in building materials such as sand is an important factor in determining the hardness of the building. .

Because of this industrial demand, techniques for measuring dielectric constant in medium using microwaves, which are simple and relatively easy to manufacture, have been studied for a long time, but to date, the method of measuring dielectric constant mainly measures electric resistance and capacitance of a medium. Most of the methods to measure the dielectric constant of the medium.

Recently, a method for measuring the relative dielectric constant of a homogeneous medium using ultrashort impulses in the time domain has been developed. Ultra-short impulse method is faster than the method of measuring the electrical resistance and capacitance, and the use of the method is rapidly expanding. A representative related patent is 'Measurement of moisture content an electrical conductivity' (Patent No. AU628356).

Most of these techniques measure the dielectric constant using time domain reflectometry (TDR), which measures the step response or impulse response characteristics in the time domain of the device under measurement.

Time-domain reflectometry (TDR) is a direct measurement method and broadband vector network that directly measures time-domain response characteristics using a directional coupler, sampler, oscilloscope, etc. by applying a step signal or an impulse signal directly to the device under measurement in the time domain. It can be classified into an indirect measurement method that obtains the response characteristics in the time domain by inverse Fourier transform of the characteristics in the frequency domain obtained by using the analyzer.

Specifically, FIG. 1 illustrates a general time domain reflection measuring technique (TDR), which is a configuration diagram of a TDR measuring apparatus of a direct measurement method. The signal generated by the step signal (or pulse signal) generator is applied to the device under measurement through the coaxial line having the resistance R. In the sampling head connected to the step signal generator, the incident and reflected waves of the step signal are summed and applied to the high speed sampling oscilloscope.

That is, the pulse delay time is measured by the incident wave and the reflected wave, and the dielectric constant and the moisture water content are measured using the measured pulse delay time.

The main applications of time-domain reflectometry include diagnosing defects on transmission lines, measuring transmission rates in media, and their applications (e.g., measuring moisture moisture in feed and sample mixing and drying, soil moisture content, permittivity, groundwater) Level measurement, ground deformation measurement), and measurement of distortion and mutual interference of high-speed digital signals.

 However, such a TDR method requires a special measurement probe, and in particular, a signal synchronization process is required to measure a delay time between a transmission pulse and a reflected pulse, which makes the system complicated and expensive. In addition, it is difficult to measure the dielectric constant in real time, and there is a problem that a system calibration is required for accurate measurement.

In order to solve the above-mentioned problems, the present invention uses ultra-short pulses, and by placing a measurement probe in the form of a flat waveguide in which two paths are formed on a measurement medium, measuring a delay time of a pulse passing through the probe, thereby synchronizing a signal Disclosure of Invention It is an object of the present invention to provide a dielectric constant probe and a method for measuring the dielectric constant so that the dielectric constant can be easily and accurately measured without using the same.

Measurement probe formed of a flat waveguide according to the present invention for achieving the above object is a dielectric substrate, a reference line formed of a straight microstrip line so that the impulse input and output on one surface of the dielectric substrate, and between the input and output terminals of the reference line Partially separated, a delay line formed of a microstrip line so that an impulse input from the input end of the reference line is bypassed and output to the output end of the reference line, and a ground layer formed on the surface on which the reference line is formed and on the opposite surface of the dielectric substrate ( GND) .

Here, the delay line is preferably formed by a U-shaped waveguide connected to both ends of the reference line so that the impulse input to the reference line is bypassed and output .

And the dielectric constant measuring system according to the present invention is an impulse generator for generating an ultra-short impulse; A substrate formed of a dielectric material, a reference line formed by a straight microstrip line on one surface of the substrate, and the generated impulse is input and output, and formed by a microstrip line separated from a portion of the reference line, and an impulse input to the reference line is bypassed. A measurement probe inputted into a medium to be measured by being formed as a flat waveguide including a delay line outputted through the substrate and a ground layer formed on a surface opposite to the substrate; And a detector configured to measure a pulse delay time of the signal passing through the reference line and the delay line, and to calculate and display a permittivity of a medium around the measurement probe using the pulse delay time.

The impulse generator is preferably manufactured in a CMOS process, preferably a clock for generating an initial signal, a buffer for maintaining the clocked signal waveform, and an impulse signal processing of digital data information from a base band. D latch, an AND gate for finally processing the generated signal, and an output drive for stable output of the signal passing through the AND gate.

Preferably, the output drive is implemented by an inverter chain, and the detection unit preferably includes a water content indicator.

The detector may include a high speed correlator.

In addition, the method for measuring the dielectric constant according to the present invention comprises the steps of generating an ultra-short impulse; A measurement probe input to a medium to be measured, a substrate formed of a dielectric material, a reference line formed of a straight microstrip line to input and output the generated impulses on one surface of the substrate, and a pulse input separated from a portion of the reference line to bypass. A delay line formed of a microstrip line and a ground layer formed on a surface on which the reference line is patterned and the substrate, and outputting an impulse passing through the reference line and the delay line; Measuring a delay time of a pulse passing through the delay line based on the pulse passing through the reference line; And calculating and displaying permittivity using the measured pulse delay time.

Furthermore, the pulses output from the reference line and the delay line are preferably generated in a single pulse, and the step of calculating and displaying the permittivity preferably includes displaying the moisture content.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to a preferred embodiment of the dielectric constant probe and measurement system according to the present invention and its measuring method.

2A is a diagram showing a side view of an example of a dielectric constant probe in a measurement medium 10 according to the present invention. The dielectric constant measuring probe is a waveguide through which an impulse passes on one surface of the base substrate 20, and has a line 30 formed of a microstrip line, and a layer of ground (GND) 60 on the opposite surface of the substrate 20. Formed.

Here, the microstrip line is a circuit type for implementing a high frequency distributed circuit, and is widely used in RF & Microwave. Microstrip is a circuit structure in which the GND 60 is completely laid on the bottom, and only the signal line 30 is disposed on the top surface so that the signal is transmitted between the signal line and the GND. In other words, it does not refer to the type of substrate, but to a method of implementing a circuit pattern.

The structure of this microstrip is completely coated with GND metal at the bottom and the height and permittivity of the intermediate dielectric are clearly defined.

In other words, the type of substrate that makes up the circuit by arranging signal lines on the top surface according to the height / dielectric constant conditions is called a microstrip.

In actual circuits, the GND pattern is often present on the signal line side of component connections, but in such a case, the pattern is designed so that the gap between the GND and the signal line is maintained to some extent so as not to affect the characteristic impedance of the microstrip.

2b shows a plan view of a waveguide-type measuring probe as an example of the measuring probe according to the present invention. The line 30 formed of such a microstrip line has a reference line 33 through which an impulse passes and the reference line 33. Separated from the delay line 32 for measuring the delay time of the impulse is formed.

The separate delay line 32 is provided to measure the delay time of the pulse by placing the delay line 32 with respect to the reference line 33, and also by using a single input pulse, a transmission reference impulse (Transmitted reference) By measuring the delay time for the impulse, there is an advantage that the synchronization process of the transmission and reception signal is not necessary.

In addition, for this measurement, since the measurement is made based on the measurement in the absence of the measurement medium, the calibration of the system is not particularly necessary and thus the measurement is easy.

Looking specifically at the principle of measuring the delay time of the pulse, the propagation speed of the impulse passing through the dielectric substrate 20 is determined by the effective dielectric constant (ε _eff ) of the flat waveguide measurement probe located in the measurement medium. In other words,

The impulse produced by the impulse generator enters the input 11 of the measurement probe, and the input impulse is output as the sum of the signal passing through the paths 1) and 33 and the signal passing through the paths 2) 32.

The output signal has two impulses. First, the first impulse is a signal passed through path 1) 33, and is used as a transmitted reference impulse, and the second impulse is path 2) 32. It is an impulse that passed.

In practice, paths 2) 32 and 1) 33 differ by the length L of the sum of the lengths (a) and (b). Therefore, by measuring the transmission time impulse and the delay time (D) of the second impulse, the propagation speed of the impulse is determined. In other words,

----------------(2)

----------------(2)

From equations (1) and (2), the effective dielectric constant is calculated as follows.

The effective dielectric constant of equation (3) is determined by the dielectric constant ε _r of the dielectric substrate and the dielectric constant ε _s of the measurement medium. Since the dielectric constant of the dielectric substrate is given, the dielectric constant of the measurement medium is determined by the effective dielectric constant measured by the measurement probe in the measurement medium.

For example, in the case of measuring the water content of building sand, the higher the water content, the higher the effective permittivity and the higher the relative permittivity of the measurement medium.

In particular, if the thickness h 50 of the dielectric substrate in FIG. 2A is much less than the thickness w 40 of the microstrip line (w / h >> 1), the effective dielectric constant of equation (3) is measured. It is given by the median of the dielectric constant ε _s of the medium and the dielectric constant ε _r of the dielectric substrate.

In other words,

이다.

to be.

In this case, the delay lines 32, a, and b) for signal delay have added waveguides having a U-shape. In this basic concept, delay lines having various structures are possible.

In addition, by using the substrate 20 as a dielectric substrate, the cost is low, manufacturing is easy, precision processing is possible, and measurement errors can be minimized.

3 is a block diagram showing an example of the structure of the dielectric constant measuring apparatus according to the present invention. An impulse generator 110 for generating an impulse, a measurement probe 121 for inputting the generated impulse and probing the measurement medium 122, and a detector 130 for measuring a delay time using a signal output from the measurement probe 121. It is composed of

The impulse generated by the impulse generator 110 is input to the measurement probe 121, and the impulse signal is passed through the reference line and the delay line of the microstrip line formed in the measurement probe 121 to be output, thereby immediately without signal synchronization. The delay time D of the pulse is measured by the detector 130 to calculate and display the dielectric constant 140.

4 is a block diagram of an impulse generator as one component of the dielectric constant measuring apparatus according to the present invention. Impulse generator 110 is implemented using CMOS technology. CMOS (Complementary Metal Oxide Semiconductor) is a kind of semiconductor device, a device composed of a combination of N type and P type having a switching logic. It has a high degree of integration and is easy to mass production, and has an advantage of excellent price competitiveness.

In addition, the above impulse generator 110 uses a clock to generate an impulse to generate a signal 111, to form a reference signal 112, and to generate a transmission reference impulse signal from the baseband. The latch 114 is used.

In addition, the buffer 113 is used to allow a constant square wave to be generated even with a change in the input. The signal passing through the D latch 114 passes through the delay path 115 and the logic signal AND gate 116 in order to delay the original rectangular pulse for an appropriate time.

The output drive 117 is finally configured for proper output performance of the signal passing through the AND gate.

Here, the logic circuit is implemented with a D-Latch 114 to maintain the spherical pulse without changing the input signal. Latch refers to a register and counter that change in time, an operation of reading and registering digital information on a data signal bus at a desired time, or a circuit thereof.

Usually a register consisting of a D flip-flop, the input information is sampled at the clock pulse's rise time and the output is preserved regardless of subsequent inputs until the next clock pulse.

In addition, the output drive 117 is implemented as an inverter chain, so that when the signal passed through the AND gate is directly connected to the band pass filter, the rise time of the pulse is lowered, thereby degrading the performance of the pulse. An output drive implemented in an inverter chain is used to supply the proper current.

Output drives implemented as an inverter chain have the advantage of being able to be implemented with fewer transistors, a wide frequency range and a single output.

5 is a schematic view of the water content measurement of the building sand containing moisture as a use of the dielectric constant measuring apparatus according to the present invention.

Building sand 220 containing moisture is stored in the sand storage container 210 and the measurement probe 230 is input into the sand, that is, the measurement medium 220 in the measurement medium, so that a signal is input and output. The dielectric constant is measured through 240. In addition, the signal delay detector 240 may include a dielectric constant calculation and display unit, and may further include a display unit that calculates and displays the moisture water content according to the dielectric constant.

Wherein the detector 240 preferably comprises a high speed correlator,

The correlator refers to a device for detecting and restoring a signal containing noise and showing similarity and time difference between two signals, and by using a high speed correlator, a dielectric constant can be measured quickly and accurately in real time.

Here, the water content is to use the method of measuring the water content by the dielectric constant.

6 is a flowchart illustrating a dielectric constant measuring method according to the present invention. That is, when compared with the block diagram of the dielectric constant measuring apparatus in FIG. 3, the step of generating an impulse by the impulse generator 110 (S310), the step of probing by the measuring probe 121 in the measurement medium (S320) In operation S330, the signal output from the measurement probe is calculated and displayed by the detector 130.

In addition, the pulses output from the reference line and the delay line are preferably generated from a single pulse. And it may include the step (S331) of calculating and displaying the moisture function 140 using the measured dielectric constant.

That is, the impulse 115 generated in the impulse generator 110 (S310) is input to the measurement probe 121, and the impulse signal passes through the reference line and the delay line of the microstrip line formed in the measurement probe 121. By outputting (S320), it is possible to measure the dielectric constant in real time by measuring the delay time 116 of the pulse (S330), there is an advantage that the synchronization process of the transmission and reception signals using a single pulse is not necessary.

While the invention has been shown and described in connection with specific embodiments thereof, it is well known in the art that various modifications and changes can be made without departing from the spirit and scope of the invention as indicated by the claims. Anyone who owns it can easily find out.

As described above, when the dielectric constant probe and the measuring device and the measuring method according to the present invention are provided, a measurement probe in the form of a flat waveguide is introduced into a medium to be measured, and a delay time of a pulse passing through the probe is measured. By measuring, not only can the dielectric constant be measured in real time easily and accurately without signal synchronization process and system correction, but also the dielectric substrate can be manufactured at low cost.

Claims (10)

Dielectric substrates; A reference line formed of a straight microstrip line to input and output an impulse to one surface of the dielectric substrate; A delay line partially separated between input and output ends of the reference line, the delay line being formed of a micro strip line so that an impulse input from the input end of the reference line is bypassed and output to the output end of the reference line; And A ground layer GND formed on a surface on which the reference line is formed and an opposite surface of the dielectric substrate Measurement probe formed of a flat waveguide comprising a. An impulse generator for generating an ultra-short impulse; A substrate formed of a dielectric, a reference line formed by a straight microstrip line on one surface of the substrate, and the generated impulse is input and output, a microstrip line separated from a portion of the reference line, and an impulse input to the reference line is bypassed. A measurement probe inputted into a medium to be measured by being formed as a flat waveguide including a delay line outputted through the substrate and a ground layer formed on a surface opposite to the substrate; And And a detector configured to measure a pulse delay time of the signal passing through the reference line and the delay line, and to calculate and display a dielectric constant of the medium around the measurement probe using the pulse delay time. The method of claim 2, The delay line is formed by a U-shaped waveguide connected to both ends of the reference line is a dielectric constant measuring apparatus characterized in that the impulse input to the reference line is bypassed and output . The method of claim 2, The impulse generator includes a clock for generating an initial signal; A buffer for maintaining the clocked signal waveform; For Impulse Signal Processing of Digital Data Information from Baseband  D latch; An AND gate for final processing the generated signal; And Output drive for stable output of the signal passing through the AND Gate Dielectric constant measurement apparatus characterized in that it is manufactured by a CMOS process including. The method of claim 4, wherein The output drive is a dielectric constant measuring apparatus, characterized in that implemented by an inverter chain (Inverter chain). The method of claim 2, The detector comprises a high speed correlator. The method of claim 2, The detection unit is a dielectric constant measuring apparatus characterized in that it comprises a water content indicator. Generating an ultrashort impulse; A measurement probe input to a measurement medium, comprising: a substrate formed of a dielectric material; a reference line formed of a straight microstrip line to input and output the generated impulse to one surface of the substrate; A delay line formed of a strip line and a ground layer formed on a surface on which the reference line is patterned and an opposite surface of the substrate, and outputting an impulse passing through the reference line and the delay line; Measuring a delay time of a pulse passing through the delay line based on the pulse passing through the reference line; And Comprising a step of calculating the dielectric constant using the measured pulse delay time. The method of claim 8, And a pulse output from the reference line and the delay line is generated from a single pulse. The method of claim 8, The calculating and displaying the dielectric constant includes displaying a moisture content.

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