KR20140082376A - Microwave tranceiver for measurement of moisture contents of grain - Google Patents
Microwave tranceiver for measurement of moisture contents of grain Download PDFInfo
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Abstract
Description
The present invention relates to a microwave transmitter and receiver for measuring moisture content of grains using microwave attenuation at two frequencies, and more particularly, to a microwave transmitter and receiver for measuring the moisture content of a grain by using two frequencies of 2.38 GHz of S-band and 10.5 GHz of X- To a microwave transmitting and receiving apparatus using microwave attenuation at two frequencies for measuring moisture content of grains using attenuation of microwaves transmitted through a holder.
Moisture measurement is an important area in a very wide area. Precise measurement of moisture is an absolutely critical part of the storage and production process in a wide range of applications, from the food industry to the semiconductor industry. The moisture content of various agricultural products has a great influence on the physical, chemical properties and physiological functions of agricultural products, and is a very important factor in determining the processability, storage and quality of agricultural products. Especially, as a research on the automation of processing and handling of agricultural products and food, measurement of the water content of raw materials in the state of storing, drying and food processing of various cereals has been a very important problem. Therefore, it is urgent to investigate the method of measuring moisture content of frozen cereals, as well as measuring the moisture content of cereals in a flowing state more quickly and accurately. Among them, it is more important in cereal-related fields that are directly related to diet. Although grains need to be stored and stored for a considerable period of time, the greatest factor that can shorten the shelf life of such grains and deteriorate storage conditions is the moisture content and temperature of the grains. Temperature can be measured simply using a thermometer, but the measurement of moisture content is somewhat complex. A high water content not only lowers the utility value but also facilitates the propagation of fungi, bacteria and microorganisms, which causes deterioration. However, well-dried grains reduce the incidence of insect pests and can reduce costs for transport, storage and disposal. Therefore, proper and accurate measurement of moisture is essential, and if we can find the optimal conditions for improvement of storage and productivity, it will be able to improve the quality of dietary life and improve the technical productivity.
Many methods are used to accurately measure such moisture, and there are two major ways to measure moisture accurately: indirect method and direct method. The direct measurement is a method of removing the moisture from the sample by physico-chemical method and comparing the mass before and after the water to determine the relative moisture content and the absolute moisture content. Among these methods, there are the method of vacuum oven and Karl-Fisher method, which have higher measurement accuracy than other methods and are widely used as a method for determining the moisture standard in the laboratory. The direct measurement method is characterized by the fact that accurate and absolute values can be obtained, but it takes a long time to measure. The indirect measurement method uses the various physical phenomena represented by the water contained in the material to convert the degree of the reaction depending on the moisture content of the sample into the moisture percentage. The characteristics of the indirect measurement method are that the accuracy is lower than the direct measurement method, but the measurement is quick, and there are advantages such as continuous measurement and automatic measurement. These methods include many methods such as a method of measuring electrical resistance, a method of measuring dielectric constant, a method of measuring reflection and transmission of near-infrared rays, a method of measuring attenuation of microwave, a method of using neutron scattering, Electric resistance type and permittivity method which are easy to use and low in price of measuring equipment are widely used. The electrical resistance measurement method uses a method of measuring the electrical resistance of a sample and converting it into a moisture percentage. The measurement range of the moisture content is limited to 10% and 20%. In the moisture content outside this range, the change in electrical resistance is very small and causes a large error in measurement. On the other hand, the permittivity method measures the water content by measuring the capacitance of the sample. The dielectric constant of water is about 80 in the RF (Radio Frequency) region, which is relatively large compared to other materials. Therefore, the capacitance of a substance containing moisture changes sensitively according to the moisture content, and the moisture content contained in the substance can be measured by observing the change. It is widely used. The electrical resistance measurement method uses a method of measuring the electrical resistance of a sample and converting it into a moisture percentage. The measurement range of the moisture content is limited to 10% to 20%. In the moisture content outside this range, the change in electrical resistance is very small and causes a large error in measurement. On the other hand, the permittivity method measures the water content by measuring the capacitance of the sample. The dielectric constant of water is about 80 in the RF (Radio Frequency) region, which is relatively large compared to other materials. Therefore, the capacitance of a substance containing water changes sensitively according to the moisture content, and by observing this change, the moisture content contained in the substance can be measured. The measurement range is theoretically measurable in all moisture content areas. In addition, it can be divided into indirect non-destructive measurement, which measures without alteration of the object, and destructive measurement, which involves alteration.
Microwave-based moisture content studies have mainly been performed using waveguide or cavity resonator methods. For this purpose, a sophisticated sample holder should be fabricated and high water content can be measured. However, in order to measure the moisture content of the sample on the basis of the structure and measurement principle of the sample holder It has some disadvantages. Recently, there has been an increasing demand for automation of equipment and facilities related to the processing and distribution of various agricultural products. Especially, it is required to develop a technology to measure water content of raw materials in non-destructive contactless manner in the drying, storage and processing process of grain In this method, a water content measurement method using a transmitting / receiving antenna is proposed, which can rapidly measure a wide range of water content non-contact and non-destructively on the basis of the loss caused by the energy absorption of the transmitted microwave depending on the water content of the sample .
So far, the basic researches on the dielectric properties using the relationship between the water content of grains and the transmission or reflection characteristics of microwaves have been mainly performed and it has been reported that the water content can be measured with high accuracy. However, since the related researches are mostly performed by using precise measuring instruments such as a network analyzer rather than designing actual water content measuring devices, development of water content measuring sensors and signal processing circuits using microwaves is required.
It is an object of the present invention to solve the problems of the prior art, and it is an object of the present invention to provide a microwave transmitting / receiving apparatus using S-band 2.38 GHz and X-band 10.5 GHz frequency, And developed a water content measurement model based on the measured output voltage for grain water content and provided a microwave transmitter and receiver for measurement of moisture content of grain using microwave attenuation at two frequencies, .
In order to achieve the object of the present invention, a microwave transmitting / receiving apparatus for measuring water content of grains using microwave attenuation using two frequencies is a microwave transmitting / receiving apparatus using oscillation frequencies of 2.38 GHz of S-band and 10.5 GHz of X- , A transmitter for transmitting an RF signal through an oscillation, a grain holder filled sample holder through a transmission patch array antenna; A sample holder in which the grain sample is filled between microwave transmitting and receiving patch array antennas; And a receiver for detecting the RF signal input through the receive patch array antenna as a DC signal and for detecting a signal to be attenuated to measure a digital voltage, wherein the same grain sample in the sample holder has the same water content as the microwave The moisture content is determined by determining the moisture content of the grain based on the relationship between the output voltage of the receiving section and the water content in the moisture content measuring apparatus using microwave transmission characteristics.
The microwave transmitter and receiver for measuring moisture content of grains using microwave attenuation using two frequencies of 2.38 GHz and 10.5 GHz according to the present invention uses two frequencies of 10.5 GHz of X-band and 2.38 GHz of S-band Microwave transmitters and receivers were designed and fabricated to measure moisture content of grains. Oscillators, transmit and receive patch antennas and detectors are designed using HP EEsof ADS and manufactured as hybrid MIC. A new calibration model, which is not sensitive to density, is presented by regression analysis of the measured data with the statistical analysis program using this transceiver. As a result of comparing the predicted value of the water content with the measured value, the coefficient of correlation was 0.9276 and the standard error was 0.975%. It is possible to measure the water content of rice with high precision while correcting the product density. Respectively.
Measuring the moisture content of grains at two frequencies is easy to reduce the effects of stationary conditions or product density and improve accuracy. In order to measure the water content in the flow state, a study on the attenuation characteristics according to the microwave frequency using two frequencies shows that the degree of attenuation differs at two frequencies even if the same water content is used. Therefore, It is possible to suggest a moisture content measurement method which is less influenced by the state of the sample.
The water content measuring device is divided into a transmitter and a receiver. The transmitter consists of an oscillator, a transmitting antenna, and an isolator. The receiver is composed of an receiving antenna, a detector, and a digital voltage meter. The water content can be determined.
By the attenuation at two frequencies according to the water content, the DC voltage output from the detector can be correlated with the water content and the influence on the temperature is fixed.
In the microwave penetration experiment, the sample holder filled with the sample was positioned between the microwave transmitting and receiving antennas and then the attenuated signal was detected at the receiving antenna. In order to clarify the influence of the product density on the microwave signal in the development of the water content measurement device using the microwave transmission characteristics, the product density at the same water content The experiment was carried out while varying the range.
A new calibration model, which is not sensitive to temperature and density, is presented by regression analysis of the measured data with a statistical analysis program. The results were compared by comparing the predicted value with the measured value of the water content through the calibration model. A water content measurement model was developed with the sample temperature and the output voltage as independent variables, and the water content of the rice with high accuracy was measured while correcting the effects of the product density and the sample temperature.
1 is a view showing a structure of a water molecule.
2 is a block diagram of a transceiver circuit.
FIG. 3 is a configuration diagram of a microwave tranceiver used for measuring water content of cereals according to the present invention.
4 is a diagram illustrating a two-port oscillator model.
5 is a graph showing the output power at 2.38 GHz of the S-band.
6 is a graph showing a harmonic characteristic of 2.38 GHz at S-band at 2.38 GHz of the S-band.
7 is a graph showing the output power at 10.5 GHz of the X-band.
8 is a graph showing a harmonic characteristic of 10.5 GHz at X-band at 10.5 GHz of the X-band.
9 is a graph showing a phase noise charac- teristic of S-band at 2.38 GHz (phase noise char- acteristic of S-band at 2.38 GHz).
10 is a graph showing a phase noise char- acteristic of X-band at 10.5 GHz at 10.5 GHz.
11 is a diagram showing a circuit configuration of a detector.
12 is a diagram showing an input return loss of the detector.
13 is a graph showing voltage sensitivity showing characteristics of a detector.
14 is a photograph showing the physical diagram (10.5 GHz of X-band) of the microwave transmitting and receiving apparatus.
15 is a view showing a rectangular microstrip patch antenna.
16 is a configuration diagram of a microstrip patch antenna.
17 is a graph showing a result of designing the input return loss and gain of a single microstrip patch antenna.
18 is a graph showing input return loss.
FIG. 19 is a diagram showing a Far-field pattern of H-plane of the H-plane.
FIG. 20 is a diagram showing the relationship between the moisture content and the output voltage of the grain (Relationship between the output voltage and the moisture content of grain).
21 is a diagram showing a relationship curve between an actual value of water content and a predicted value.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
In the present invention, a microwave transmitting / receiving device for measuring moisture content of grains was designed and fabricated using S-band 2.38 GHz and X-band 10.5 GHz frequency. The transmitter of the transceiver is composed of a single bias oscillator using a dielectric resonator with excellent temperature characteristics and a high Q value, an isolator and a transmission patch antenna. The receiver is composed of a receiving patch antenna and a Schottky diode with high frequency characteristics Detector and digital voltage meter. The core components of the measuring device were designed using HP EEsof ADS and manufactured as a hybrid MIC. Using this transceiver, the relationship between the water content and the output voltage of the rice with water content of 12 ~ 20% was measured and the result was statistically regression analyzed to propose a water content measurement model.
The structure of the present invention is described in
2.1 Structure of Water and Characteristics in Electromagnetic Field
1 is a view showing a structure of a water molecule.
As shown in FIG. 1, the structure of the water molecule has an asymmetric structure in which two atoms of oxygen (O) are combined with two atoms of hydrogen (H) to form an angle of about 104.5, - It has the same structure as a pole exists. Such a structure is called a dipole. When a dielectric containing water is placed in an electric field, these dipoles are arranged in the direction of the electric field, where a dipole moment occurs and electrical polarization occurs within the dielectric due to the dipole moment.
When the electric field on which the dielectric is placed is changed, molecules having dipole moments such as water molecules rotate and vibrate due to the force of the dipole moments arranged in the direction of the electric field, and heat is generated by the internal friction. In a dielectric with such a dipole moment, the influence of the polarization is large due to the dipole moment in a high frequency electric field such as a high frequency, and the influence of such a polarization becomes a relative permittivity. In the microwave region (1 to 30 GHz), the dipole orientation does not follow the change of the electric field and absorbs microwave energy. Since water molecules are relatively large in dielectric constant compared to other materials, energy absorption by water is utilized in this region The water content can be measured.
2. Theory
2.2 Measurement method of water content
2.2.1 Heat drying method
In the heating and drying method, the weight of grains containing moisture is measured by a meter, and when the weight of the grain is denoted by M 1 , the weight M 1 of the grain before drying is expressed as (2-1) Can be defined as the sum of the weight M d of the grain and the weight M w of the water.
Weight of grain before drying: M 1 = M d + M w (2-1)
It is now heated in an electric constant temperature drier of grain. Where the heat drying temperature is maintained at 135 and heated for 24 to 72 hours.
After the heating and drying process, the grains are taken out of the dryer and transferred to a dryer to cool the grain so that it does not absorb the atmospheric moisture due to sudden temperature changes. When the sample becomes stable, remove it from the dryer and measure its weight.
Weight of grain after drying: M 2 = M d (2-2)
By measuring the weight M d after drying, the difference between the weight of the sample before drying and the weight of the sample after drying becomes the weight of moisture contained in the grain.
Weight of water: M w = M 1 - M 2 (2-3)
From this, we calculate the water content of the sample as shown in Equation (2-4).
Although the heating and drying method has the advantage of measuring the water content of the grain most accurately, it requires a lot of equipment in the measuring process and takes a long time, which can not be used to actually measure the water content of the grain in the field It is mainly used for comparison with the results of measurement devices developed in laboratories or laboratories.
2.2.2 Electric resistance method
The electrical resistive method places a sample to be measured between two parallel plates and applies a DC voltage between both parallel plates. At this time, the resistance value of each sample is measured using an impedance meter. The resistance value measured here changes according to the water content contained in the sample, so that the moisture of the sample can be measured from the relationship between the resistivity and the water content.
The electrical resistivity method is generally used in a low cost and easy to manufacture, and since it needs to be very thin in the method used for moisture measurement, most of it is used as a sample for crushing raw materials. Especially grain Due to its sensitivity to density changes, accuracy in moisture measurement can be lacking.
2.2.3 Method using radio waves
There are five methods of using radio waves: a capacitor method, a coaxial probe method, a transmission line method, a resonant cavity method and a free space method.
First, the capacitor method, which is used at less than 100 MHz, fills the sample to be measured between two parallel plates and measures capacitance and dissipation between parallel plates using a high frequency oscillator. At this time, the permittivity of the sample is calculated from the relationship between the measured capacitance value, dissociation value, and water content.
In the coaxial probe method, the coaxial probe is brought into contact with the surface of the sample to measure the reflection coefficient when the high frequency signal irradiated from the probe is reflected on the sample surface, and the permittivity of the sample is calculated from the measured reflection coefficient. This method is mainly used to obtain the dielectric constant in liquid or solid materials and can be measured in the frequency band between 200 MHz and 20 GHz.
The transmission line method is a method to calculate the permittivity of a sample by measuring the reflection coefficient and transmission coefficient generated in the transmission line such as a circular waveguide or a spherical waveguide after a part of the sample to be measured is filled or filled with a high frequency signal . At this time, the usable frequency range is the widest between 500 MHz and 110 GHz.
The resonant cavity method measures the resonance frequency and the Q-factor value when the sample is placed in the microwave resonant cavity and when the cavity is empty, and then the difference is calculated. At this time, the resonance frequency and the Q-factor value are different from each other according to the dielectric constant of the sample, and the dielectric constant is calculated from the resonance frequency and the Q-factor value. This method is generally suitable for measuring the permittivity of a single sample, ie, rice grain or soybean grain, and is available in the frequency range of 500 MHz to 10 GHz.
Finally, the free space method used in the present invention is a method using a transmitting / receiving antenna. A sample is placed between the antennas and the attenuation of the signal is measured when the microwave signal radiated from the transmitting antenna is detected by the receiving antenna. At this time, since the attenuation value of the signal differs according to the water content of the sample, the permittivity of the sample can be calculated from this attenuation value. The free space method is mainly used in microwaves and is used in the range of 2 GHz to 18 GHz. The measurement principle is relatively simple and is advantageous for development of an online water content measurement development system. The frequency of the X-band is 8 to 12 GHz because the frequency of this band is included in the frequency of the rotation energy of the dipole moment of the water molecule. Because.
The advantage of microwave for water content measurement is that first, unlike the infrared measurement method for measuring moisture on the surface of a sample, it can accurately measure moisture in the sample. The second is low risk because it uses very low energy (several mW). The third is a non-destructive method. The fourth is less affected by factors such as dust and water vapor. Fifth, accuracy is very high compared with other moisture content measurement methods. Sixth, the stability of the water content measuring device according to online is high.
2.3 Measurement method at two frequencies
In the present invention, the relation between the output voltage and the moisture content was estimated at 2.38 GHz of the S-band and 10.5 GHz of the X-band. It is the same as the measurement method in the previously announced one frequency, but one frequency band is added to measure the water content more precisely. Measuring the moisture content of grains at two frequencies is easy to reduce the effects of stationary conditions or product density and improve accuracy. Also, in order to measure the water content in the flow state, studies on the attenuation characteristics according to the microwave frequency using two frequencies have different degrees of attenuation at the two frequencies even if they have the same water. Therefore, A method of measuring the moisture content which is less affected by the state of the water.
It is easy to see from the graph of the relationship between the output voltage and the water content in Chapter 4 that the output voltage of the X-band is larger than that of the conventional one measurement method. In the S-band, It can be seen that it does not occur as much as the X-band. The reason why we chose S-band is that similar frequency changes are similar to each other. So we can compare S-band by selecting the S-band, It is possible to measure the moisture content more precisely than the moisture content measurement method in one frequency band. In the two frequency bands, first set up the device, measure the output voltage between the antennas, set up the same voltage (0.6 V), measure the output voltage while changing the density to 3 ~ 4 levels and increase the moisture density The output voltage decreases in a polynomial function, and the reason why the X-band output voltage is lower than the S-band voltage is because the microwave absorption is larger at the X-band.
Table 1 shows the measurement results analysis of one and two frequencies at one frequency band and two frequencies.
Add-on device configuration is the same
2.4 How to measure moisture
In this study, the free space transmission method is used to measure the moisture of grains in the fluidized bed in a noncontact and non-destructive manner. In the free space transmission method, a transmission / reception antenna is used. A sample is placed between the antennas and the attenuation and phase of the signal are measured when the microwave signal emitted from the transmission antenna is transmitted through the sample and detected at the receiving antenna.
The permittivity of the sample is
ε = ε - jε (2-5)
, And the propagation number of the microwave passing through the sample is
? =? + j? (2-6)
to be.
Relation between permittivity and wave number
The dielectric constant and the loss factor can be calculated as follows.
At this time, the complex permittivity of the sample can be obtained by using the attenuation value and the phase difference of the measurement signal. Since the complex permittivity of the sample changes with the water content of the sample, the calibration curve for moisture measurement is obtained from the change of the urea and the change of the complex dielectric constant.
1) Transceiver circuit diagram
The design of the transceiver circuit is based on Hewlett Packard's MDS (Microwave Design System), a simulator for microwave integrated circuit design, or LINMIC from Janse Microwave, Germany.
The transmitter consists of an oscillator, a frequency stabilizer, and a transmit antenna. The frequency used is the X-band region where microwave energy absorption of water molecules is large in free water, and an oscillator having an oscillation frequency of 10.5 GHz is used as the CW-source of the transmitter. A HEMT or a GaAs FET having excellent noise characteristics is used as an active element, and a dielectric resonator having an excellent temperature characteristic and a high degree of goodness is used as a frequency stabilizing element. The circuit configuration is used in the form of series feedback with excellent phase noise and output characteristics, and the oscillator design follows a common oscillator design technique that combines the negative resistance and the resonant circuit. The fabricated oscillator and stabilization circuit are connected to the transmitting horn antenna of the WR90 flange through a microsrtip-to-waveguide transition.
The RF output transmitted from the transmitter is attenuated by 20-30 dB after passing through the sample and transmitted to the receiving horn antenna. For non-contact and non-destructive measurements, two standard horn antennas for transmission and reception are used. In the initial experiment, an experimental horn antenna with about 20dB gain is used.
The receiver consists of a receive antenna, a detector, a mixer, a low-pass filter, and an amplifier. A back diode, a point contact diode and a Schottky diode are generally used for RF signal detection. In this study, Schottky diode which is most stable against electrical and mechanical shock and has excellent voltage sensitivity is used. And a DC voltage proportional to the RF power level is generated using a low pass filter. This weak voltage is amplified through an amplifier and then displayed by an oscilloscope or power monitor.
The circuit diagram of the transceiver to be designed in the present invention is shown in FIG. The system for measuring the attenuation and phase change of the microwave is composed of an oscillator, an isolator, a power divider, and a mixer. In order to measure attenuation and phase change of a microwave, a microwave having a constant frequency is first oscillated by using an oscillator. In order to select only a desired frequency within a certain frequency range, a tuner is connected in series to the oscillator.
2 is a block diagram of a circuit construction of a transmitter and receiver.
The microwave irradiated from the oscillator is expressed mathematically as a sinusoidal wave as follows.
e (t) = E 0 and cos (ωt) (2-10)
Here, E 0 can be expressed as
E 0 is the microwave amplitude, and ω = 2πf.
In order to prevent a microwave having a certain frequency from being transmitted to the system, it is necessary to connect an isolator after the tuner to prevent the microwave power from being reflected by the microwave power to damage the oscillator. give. Some of the microwaves passing through the power divider are used to pass through grains and some are used as reference signals, and their amplitudes are reduced to half.
The transmitted microwave e 1 (t) of grains can be expressed by the following equation because the attenuation and the phase change occur when the grains are permeated.
Where A represents the microwave attenuation by the grain and? Represents the phase change.
The microwave and the reference microwave passing through the grain are each frequency-doubled by a post-mixer through another power distributor. Therefore, the microwave obtained through the first mixer and the second mixer
here,
As a result, it is possible to calculate the attenuation and the phase change of the microwave to be measured from the two waveforms obtained from the low-pass filter.
By using the measured attenuation and phase change, it is possible to calculate the complex permittivity value of the grain according to the moisture content of the grain. The calibration curve is set by using the data obtained from this, and the microwave is transmitted through the grains having arbitrary water content The meter reads the moisture content from the calibration curve by the dielectric constant calculated from the attenuation and the phase shift of the microwave.
3. Moisture content measurement system
In the present invention, a device for measuring moisture content of grains using a free space transmission method is designed by selecting a 10.5 GHz band of X-band and a 2.38 GHz band of S-band, which can easily produce a hybrid microwave integrated circuit (MIC) Respectively.
3 is a block diagram of a microwave transmission and reception measuring apparatus used for measuring water content of cereals according to the present invention.
In the present invention, a microwave transmission and reception measuring device for measuring the water content of grains is measured more easily by using 10.5 GHz of X-band and 2.38 GHz of S-band.
The microwave transmission and reception measuring apparatus (moisture measuring apparatus) used for measuring the moisture content of grain includes an
The microwave transmitter and receiver for measuring the moisture content of grain using microwave attenuation using oscillation, oscillation and transmission patch array antennas using two frequencies of S-band 2.38 GHz and X-band 10.5 GHz A transmitter for transmitting the RF signal through the sample holder filled with the grains; A sample holder in which the grain sample is filled between microwave transmitting and receiving patch array antennas; And a receiver for detecting the RF signal input through the reception patch array antenna as a DC signal and detecting a signal to be attenuated to measure a digital voltage, wherein the same grain sample in the sample holder has the same water content as the microwave The moisture content is determined by determining the moisture content of the grain based on the relationship between the output voltage of the receiving section and the water content in the moisture content measuring apparatus using microwave transmission characteristics.
The moisture measuring device is divided into a transmitter and a receiver. The transmitting unit is composed of an
The transmitter includes an
The
First, the
A dielectric resonance oscillator was designed using HP EEsof 's ADS. Particularly, the oscillator is designed as a serial feedback type which has a simple circuit configuration and little variation in oscillation frequency and output in response to load variation. In order to facilitate the application of the bias voltage, a bias was applied in the form of a single source bias. Simulation results obtained from the design show 13 dBm output power and -28 dBc harmonic characteristics at 10.5 GHz of X-band, and 19 dBm output power and -27 dBc harmonic characteristics at 2.38 GHz of S-band . The designed oscillator was fabricated directly on a Teflon substrate with a dielectric constant of 2.6, a thickness of 0.54 mm and a thickness of 0.018 mm.
The
The
The material of the
The
The receiver comprises a receiving
The
The
Experiments were carried out on the propagation characteristics of monolithic rice and Dong - Jin rice in the range of water content of 12 - 20% by using the transceiver. As the water content and the product density increased, the output voltage of the microwave signal decreased almost polynomially through the measurement data and the output voltage tended to decrease within the same water content.
3.1 Oscillator Theory
Microwave oscillators are devices that convert DC power to RF power and are the most basic and essential part of a very high frequency system. Solid-state oscillators use active devices with passive circuits to produce a normal sinusoidal RF output. The initial oscillation starts the oscillation by the noise level or the transient phenomenon by changing the DC power supplied to the active element. The oscillation output gradually grows to a steady state and produces a stable sine wave. That is, the oscillation requires nonlinear characteristics of the active device. At this time, the nonlinear element must have a negative resistance by generating RF power at the output stage.
Oscillators using transistors or field effect transistors are very similar to amplifiers in their analysis. In transistor oscillators, the negative resistance can be effectively obtained by adding an impedance designed to conditionally operate the transistor in unstable regions. Transistors have three terminals, but one terminal is commonly used for input and output, so it is convenient to interpret it as a two-terminal network, where one terminal serves as an input terminal and the other as an output terminal.
4 shows a two-port oscillator model, which is divided into an input matching circuit and an output matching circuit. The input matching circuit is used to start oscillation
In the case of oscillators using MESFETs, the following two conditions are necessary for oscillation to occur in circuit design using small-signal S-parameters.
here,
On the other hand, the oscillation conditions using the reflection coefficient and the stabilization coefficient in the analysis of the two-terminal network including active elements are as follows.
Oscillation condition 1: K < 1 (3-4)
Rash Condition 2:
Rash Condition 3:
Where K = stability factor of the active device
? = S 11 S 22 -S 12 S 21
Γ in = input reflection coefficient of the active device
Γ g = reflection coefficient of the resonant circuit
Γ out = output reflection coefficient of active device
Γ L = float reflection coefficient of load matching circuit
to be.
to be. Using the above equations, it can be proved that oscillation occurs simultaneously at the input and output terminals when oscillation occurs. Substituting equation (3-11) into equation (3-1)
to be. If we rearrange equation (3-12) for Γ G
. In addition, the equation (3-10) is substituted into the equation (3-11) in the same manner as described above, and is summarized for Γ in
. Therefore, by equations (3-12) and (3-13)
. Therefore, the input terminal also oscillates. That is, it means that the oscillator is oscillating at each terminal at the same time. The two conditions are complementary to each other, so if one of the two is satisfied, the other is satisfied at the same time. In Equation (3-7), K is a stabilization factor, and oscillation frequency should be less than 1, since oscillation frequency should be in the unstable region of the device. Therefore, when designing an oscillator circuit, it is necessary to initially select and use a device with unstable characteristics at the set frequency. Otherwise, it is necessary to add components to the common terminal to change the characteristics to make them unstable or to feed some of the output.
3.2 Transmitter
The transmitter of the measuring apparatus is composed of the
First, the oscillator, which is the core part of the transmitter, uses HPF's ATF-13786 MESFET, which is an active device with excellent output and low noise figure, and a resonator that can be tuned easily after fabrication.
In the present invention, a resonator KFR-0531-C-212-A-30C manufactured by Hanwon Co., Ltd. was used. In this case, the diameter of the resonator is 5.31 mm, the thickness is 3.62 mm (including support), the temperature constant is 0 ppm /, the Q value is 6000, and the relative dielectric constant is 38.
A dielectric resonance oscillator was designed using ADS, which is a circuit design software of HP EEsof company, using characteristic data of selected active elements and resonators. Particularly, the oscillator is designed as a serial feedback type which has a simple circuit configuration and little variation in oscillation frequency and output in response to load variation. In addition, the bias is made of a single source type to facilitate voltage application and a regulator is inserted to apply a constant voltage.
5 is a graph showing the output power at 2.38 GHz of the S-band.
6 is a graph showing a harmonic characteristic of 2.38 GHz at S-band at 2.38 GHz of the S-band.
7 is a graph showing the output power at 10.5 GHz of the X-band.
8 is a graph showing a harmonic characteristic of 10.5 GHz at X-band at 10.5 GHz of the X-band.
9 is a graph showing a phase noise charac- teristic of S-band at 2.38 GHz (phase noise char- acteristic of S-band at 2.38 GHz).
10 is a graph showing a phase noise char- acteristic of X-band at 10.5 GHz at 10.5 GHz.
3.3 Receiver
The
In the present invention, a MA40070 zero bias schottky detector diode of MA-com was used for simple circuit implementation without bias.
The circuit diagram of the detector is shown in Fig. The detector is largely divided into a matching circuit of the input part having lengths l 1 and 2 and a rectifying circuit of the output part composed of a capacitor and a resistor. In this case, the length ℓ 2 having the inductance component of the input part is opened to the RF signal to make the signal flow in the diode input direction, and impedance matching is performed by tuning with the length l 1 to reduce the reflection coefficient. In addition, the bypass capacitors shorted the RF signal to measure the DC voltage across the resistor.
12 shows the input reflection loss measured by a hybrid 8520C network analyzer of the hybrid MIC, which was -20.424 dB at 10.5 GHz and a VSWR of 1.2096.
13 is a graph showing a voltage sensitivity characteristic, which is a main parameter showing characteristics of a detector. The DC voltage outputted by varying the power of the
3.4 Microwave Moisture Measurement System
In the present invention, a moisture measuring system using two frequency bands of S-band 2.38 GHz and X-band 10.5 GHz was designed and manufactured to measure moisture content of grain. The moisture content was measured at 2.38 GHz of S-band and 10.5 GHz of X-band, and the system configuration was the same in two frequency bands. The difference was that at 2.38 GHz of S-band, the output power was increased by adding an amplifier to the VCO The X-band 10.5 GHz is used as a dielectric resonant oscillator (10), while the S-band 2.38 GHz antenna is used as a single antenna while the X-band 10.5 GHz
Experiments were carried out by fixing the distance between the antennas in the X-band to 6.2 cm and the distance between the antennas in the S-band to 7 cm. The size of the
Fig. 14 is a physical diagram (10.5 GHz of X-band) of a moisture content measurement microwave transmitter / receiver constructed in accordance with the present invention
3.5 Microstrip patch antenna
15 is a view showing a rectangular microstrip patch antenna.
The microstrip patch antenna shown in Fig. 15 is a dielectric strip having a thickness h and a relative dielectric constant ∈ r on a thin grounding conductor plate, and a conductor strip having a thickness t and a width W printed thereon.
The basic structure of the microstrip antenna is composed of a patch (radiating element), a dielectric substrate, a ground plate, and a power feeding part. It has advantages such as easy fabrication, light weight, small size, thin film type, And a narrow bandwidth.
The structure of the radiating patch can be implemented in various forms such as square, circle, and triangle. A typical microstrip antenna has a radiating element on a single dielectric and uses a microstrip feeder or coaxial line to feed the radiating element.
The easiest way to feed a microstrip patch is to connect the microstrip feedline directly to the edge of the patch. However, this method is difficult to create accurate input impedance matching and can not satisfy efficient radiation and lossless energy transfer conditions simultaneously because the radiating element and the feed line are constructed on the same dielectric. The parasitic radiation by the feed line lowers the radiation characteristics of the antenna, and a high Q value makes the bandwidth characteristic of the antenna worse. Also, a large input impedance change required for high dielectric constant substrates requires deep inset, which affects cross polarization and radiation pattern shapes.
A method of supplying power using a coaxial probe is a method in which the inner conductor of the coaxial line is directly connected to the radiating element and the outer conductor is connected to the ground plane to supply power. And while feeding the coaxial line is difficult, it can achieve exactly 50 Ω and reduce the radiation loss on the coaxial line. This method can adjust the input impedance according to the feeding position, but it is difficult to construct a microstrip circuit such as an impedance matching circuit. It also creates an inductance that prevents resonance of the patch when h is greater than 0.1λ. Also, probe radiation may cause cross-polarization.
3.5.1 Antenna Design and Fabrication
One of the most important priorities for antenna design is substrate selection. In the present invention, a Teflon substrate having a substrate height of 0.8 mm, a copper plate thickness of 0.032 mm, and a dielectric constant of 2.5 was used in order to reduce the circuit and eliminate unnecessary parasitic radiation components.
Antenna analysis simulator using Momentmethod was used to design the microstrip patch antenna.
16 is a configuration diagram of a single microstrip patch antenna.
A single microstrip patch antenna uses a 50 Ω microstrip feed method and a λ / 4 converter is used to match the high input impedance of the patch antenna. The size of a single patch is 8.42 x 14.6 mm.
17 shows the result of designing the antenna, (a) shows the input return loss, and -23 dB was obtained at 10.5 GHz. (b) shows 6.22 dBi at 10.5 GHz as a pattern of gain shown in the polar coordinate system.
18 is a graph showing a design result of input return loss and gain of a single microstrip patch antenna. FIG. 18 shows the return loss of the antenna measured by the HP 8510C network analyzer, and the return loss was -31 dB at 10.5 GHz.
19 shows the result of measuring the H-plane distance pattern using the FR959 automatic antenna measurement system. We obtained a gain of 6.1 dBi at 10.5 GHz and a value similar to the design value of 6.22 dBi.
4. Water content measurement experiment
4.1 Experimental Method
In order to investigate the propagation characteristics of grain, rice was selected as a publicly available material. Rice were harvested from farms attached to the College of Agriculture and Life Sciences, Seoul National University. The water content of rice used in the experiment was 3 ~ 4 between 13 ~ 20%. For the preparation of the samples, the samples were placed in an electric constant temperature dryer of rice using the standard drying method, heat drying method, and the temperature was maintained at 135 and heated for 24 hours.
In the microwave penetration experiment, the sample holder filled with the sample was positioned between the microwave transmitting and receiving antennas and then the attenuated signal was detected at the receiving antenna. In this case, since the samples filled in the sample holders exhibit different attenuation of microwaves depending on the product density at the same water content, in order to clarify the influence of the water content on the microwave signal in the development of the water content measuring device using the microwave transmitting characteristics, Experiments were carried out with samples with different water contents of 3 to 4 levels with fixed densities. Measuring the moisture content of grains at two frequencies is easy to reduce the effects of stationary conditions or product density and improve accuracy. In addition, in order to measure the water content in the flow state, studies on the attenuation characteristics according to the microwave frequency using two frequencies have different degrees of attenuation at the two frequencies even if they have the same water. Therefore, A method of measuring the moisture content which is less affected by the state of the water.
By the attenuation at two frequencies according to the water content, the DC voltage output from the
In the microwave transmission experiment, a
4.2 Water content measurement model
Regression analysis is a statistical technique that analyzes the relationship between two or more variables to determine or predict the degree of impact of one or more variables on certain other variables.
The variable to be analyzed or the variable of interest to be predicted is called a dependent variable and the variable describing the result of the dependent variable is called an independent variable. It is the main content of the regression analysis that reveal the functional relation between the independent variable and the dependent variable, and the influence of the independent variables on the dependent variable using this function relation or predict the value of the dependent variable corresponding to the independent variable value .
In the function relation, the case where the number of independent variables is one is referred to as a simple regression, and the case where two or more independent variables are referred to as a multiple regression. In particular, the linear linear regression analysis is applied to the case where the number of independent variables is one and the function relation is linear. Multiple linear regression analysis is performed when the number of independent variables is two or more, .
In the present invention, a simple linear regression analysis is used in the linear regression analysis.
The water density represents the weight of water per unit volume, and since the volume of the sample holder used in the experiment is constant, it represents the absolute amount of water per unit volume. Therefore, if the amount of the grain sample injected in the given
As shown in the figure, it can be seen that the output voltage decreases almost polynomially with increasing the density of water. This result is almost the same as the previous study. On the other hand, the decreasing rate in each measurement band is different from that in the decreasing S-band in the X-band. This result shows that the absorption of the microwave energy due to the rotation of the water molecule is generally X This is in agreement with the results which are largely seen in -band.
FIG. 20 is a diagram showing the relationship between the moisture content and the output voltage of the grain (Relationship between the output voltage and the moisture content of grain).
In this study, we developed a model that can measure the water content by using 2 frequencies of microwaves used in the experiment because it compensates the fluctuation of measurement factors occurring in the water content by using two frequencies of microwave and improves the accuracy of measurement . In the above analysis, the relationship between the microwave output voltage and the moisture density is considered to be a polynomial function, and this analysis has already been confirmed by various researchers. Therefore, we assumed the following predictive model to measure the water content and then analyzed it using statistical analysis program software version 6.11.
Here, X = microwave output voltage (mV) in the X-
S = microwave output voltage (mV) in the S-band
a ~ c = regression coefficient
To compare and analyze the model, we compared the third - order polynomial relationship between the previously announced microwave output voltage and the water density. The third order polynomial in each measurement frequency band is described as follows.
As shown in Table 4.1, the correlation coefficient of the predictive model expressed by Equation (4-2) proposed in this study is increased and the error is decreased as compared with the case of developing an individual water density prediction model in each measurement band . However, the analysis results in Table 1 show that the accuracy of the model is slightly lower than that of the existing X-band frequency. First, the range of water content of the sample used in the experiment is relatively narrow, , The storage condition of the sample was not good. Therefore, the non - uniformity of the water content due to the water gradient in each sample was found to have a great influence on the microwave propagation characteristics.
Table 2 shows the statistical results of the calibration models for the moisture density. The predictive model of equation (4-2) increases the correlation coefficient and decreases the error than the predictive models of equation (4-3) and equation (4-4).
The regression analysis for equation (4-2) in Table 2 and the definition of water density (4-1) were used to develop the following water content prediction equation.
FIG. 21 is a result of comparing measured values of water content and predicted values using the developed water content prediction equation. Correlation coefficient is 0.9276 and standard error is 0.975%. It is possible to measure water content with relatively high accuracy while correcting product density. A new calibration model which is not sensitive to density is presented by regression analysis of the measured data with a statistical analysis program. The results were compared by comparing the predicted value with the measured value of the water content through the calibration model. Using the output voltage of the sample as an independent variable, a water content measurement model was developed to measure the water content of rice with high precision while correcting the effect of the product density. Therefore, when the propagation characteristics of two microwaves are used, the accuracy of the water content measurement can be improved rather than using a microwave of a single frequency. In the future, in a storage state in which a wide range of sample water content and a moisture content in the sample can be maintained uniformly, Accuracy is expected to be further improved if measurement experiments are performed.
As a result, in the present invention, the water content of grain is more easily measured using 10.5 GHz of X-band and 2.38 GHz of S-band, and a predictive water content measurement transceiver is designed and manufactured.
The moisture measuring device is divided into a transmitter and a receiver. First, the transmitter is composed of an oscillator, an isolator and a transmitting patch antenna. The receiver is composed of a receiving patch antenna, a detector and a digital voltage measuring device. The X-band and S-band device configurations are the same.
The oscillator has an output power of 19.67 dBm at 2.38 GHz of the S-band, a harmonic characteristic of -23 dBc, a phase noise characteristic of -97.83 dBc / Hz, an output power of 11 dBm at 10.5 GHz of the X- dBc and the phase noise characteristic is -107.8 dBc / Hz. The isolator keeps the signal flowing in one direction constantly to protect the oscillator from damage to the reflected signal.
The antenna was able to measure the moisture content of the grain using a patch antenna which reduced the size and volume of the existing horn antenna.
The detector is a circuit that detects the RF signal inputted through the antenna using a nonlinear characteristic of the diode as a DC signal, and is largely composed of a diode and a matching circuit.
Experiments were carried out on the propagation characteristics of monolithic rice and Dong - Jin rice in the range of water content of 12 - 20% by using the transceiver. As the water content and the product density increased, the output voltage of the microwave signal decreased almost polynomially through the measurement data and the output voltage tended to decrease within the same water content. As a factor to correct the product density, it was analyzed that it is possible to measure the water content with high accuracy by using the water density expressed as the product of the water content and the product density. As a result of comparing the measured and predicted values of the water content, the correlation coefficient was 0.9276 and the standard error was 0.975%. As a result, the water content of rice was measured . Therefore, it is expected that the water content measurement device using microwave can be constructed by using the moisture content measurement model developed in this study.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken in conjunction with the present invention. The present invention can be variously modified or modified.
10: oscillator
20: Isolator
30a, 30b: patch array antenna;
40: Sample holder
50: detector
54: Digital voltmeter
Claims (11)
A transmitter for transmitting an RF signal through a grain-filled sample holder through an oscillation, oscillation, and transmission patch array antenna using two frequencies of S-band 2.38 GHz and X-band 10.5 GHz;
A sample holder in which the grain sample is filled between microwave transmitting and receiving patch array antennas;
And a receiver for detecting the RF signal inputted through the reception patch array antenna as a DC signal and detecting a signal to be attenuated to measure the digital voltage,
Since the same grains in the sample holder exhibit different attenuation of microwaves at the same moisture content, the water content of the grain is determined by analogy with the output voltage of the receiving section and the water content in the water content measuring apparatus using microwave transmission characteristics And measuring the moisture content of the grains using microwave attenuation at two frequencies.
The transmitter may further comprise:
A series feedback oscillator which oscillates a stable output by using a dielectric resonator having a low noise figure, a good temperature characteristic and a high Q value, and a small oscillation frequency and a variation of output according to a load variation;
An isolator for allowing the signal of the oscillator to flow in one direction constantly and protecting the oscillator from damage to the reflected signal;
A transmit patch array antenna using a patch antenna with reduced size and volume of a conventional horn antenna;
A microwave transceiver for measuring the moisture content of a grain using microwave attenuation at two frequencies,
The oscillator
In the S-band 2.38 GHz, the output power is 19.67 dBm, the harmonic characteristic is -23 dBc, the phase noise characteristic is -97.83 dBc / Hz, the output power is 11 dBm and the harmonic characteristic is -24 dBc And the phase noise characteristic is -107.8 dBc / Hz. The microwave transmitting / receiving device for measuring moisture content of grains using microwave attenuation at two frequencies.
The isolator uses a RADITEK isolator module with 20 dB of isolation and a maximum VSWR of 1.25 and a patch array antenna with a gain of 10 to 11 dB to minimize the influence of peripheral signals. Microwave transceiver for measurement.
The sample holder is made of acrylic having a thickness of 0.4 cm, and the width of the sample holder is measured to be at least twice as large as the width of the patch antenna in order to minimize leakage of the patch antenna generated when the radio waves are transmitted. A Microwave Transmitter and Receiver for Measuring Moisture Content of Grain Using Microwave Attenuation at Two Frequencies.
The receiving unit
Receiving patch array antenna;
It is composed of a diode and a matching circuit largely consisting of a diode and a matching circuit. It detects the RF signal inputted through the antenna using the nonlinear characteristic of the diode. It is composed of a diode and a matching circuit. A detector formed using a Schottky diode which does not apply a voltage to the gate electrode; And
And a digital voltage meter for measuring an output voltage of the detector because the attenuation of the microwave differs according to the density of the same grain of the same grain sample in the sample holder,
As the water content and the product density were increased through the measurement data, the output voltage of the microwave signal was almost the same as that of the polyphase And the output voltage is reduced within the same moisture content. A microwave transceiver for measuring moisture content of a grain using microwave attenuation at two frequencies.
The detector (detector) is larger length ℓ 1 and divided by the matching circuit and the capacitor and the output of the rectifier circuit consisting of a resistance of an input unit having a ℓ 2, the length ℓ 2 having an inductance component of the time input unit is open for RF signal The impedance is matched with the length l 1 to make the signal flow in the direction of the diode input and to reduce the reflection coefficient, and the bypass capacitor short-circuits the RF signal to measure the DC voltage applied to the resistor. Microwave transmit / receive unit for measuring water content of.
The microwave transceiver (microwave moisture measurement device)
Moisture measurement system using two frequency bands of S-band 2.38 GHz and X-band 10.5 GHz was designed and fabricated. The moisture content of the grain was measured and the moisture content at S-band 2.38 GHz and X-band 10.5 GHz And the system configuration was the same in the two frequency bands. The difference was that the output power was increased by adding an amplification element to the VCO at 2.38 GHz of the S-band, while the dielectric resonance oscillator was used at 10.5 GHz of the X-band , A S-band 2.38 GHz antenna, while a patch array antenna was fabricated at 10.5 GHz of X-band. The microwave attenuation was measured at two frequencies using a microwave Transceiver.
The transmission /
A Teflon substrate having a substrate height of 0.8 mm, a copper plate thickness of 0.032 mm and a dielectric constant of 2.5 was used. In order to design a microstrip patch antenna, an antenna analysis simulator using a Momentmethod was used. And a single patch is 8.42 x 14.6 mm. The microwave transmit / receive device for measuring the moisture content of a grain is characterized by using a micro-strip feeding method and using a? / 4 converter for matching with a high input impedance of a patch antenna.
The water content measurement
In the microwave penetration experiment, a sample holder filled with a sample was positioned between microwave transmitting and receiving antennas (transmitting and receiving patch array antennas), and then a signal attenuated by the receiving antenna was detected. The sample filled in the sample holder In order to clarify the effect of the water content on the microwave signal in the development of the water content measuring device using the microwave permeation characteristics, the product density was fixed and samples with different water contents of 3 to 4 levels The measurement of the moisture content of the grain at two frequencies is easy to reduce the effect of stationary state or product density and improve the accuracy and the DC voltage output from the detector by the attenuation at two frequencies depending on the water content Each The microwave transceiver for measuring the moisture content of grains using microwave attenuation at two frequencies, characterized in that the relationship with yield can be obtained and the effect on temperature is fixed.
Since the volume of the sample holder used in the experiment is constant, the moisture density at the time of measuring the water content represents the absolute amount of water per unit volume. If the amount of the grain sample injected in the sample holder increases, And thus the dielectric constant is increased, which affects the attenuation of the transmitted microwave signal. Therefore, the microwave output voltage according to the type of the grain sample is detected in each measurement band, and the output voltage And the reduction rate in each measurement band is different from that in the decreasing S-band in the X-band, which is generally known as the microwave energy , And the moisture content of the grains (SAS version 6.11), assuming a predictive model to measure the water content using the relationship between the output voltage and the moisture content of the grain. Microwave Transmitter and Receiver for Measuring Moisture Content of Grain Using Microwave Attenuation at.
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