Dual-band microwave radiation detection method and system for characterizing public building fire

Abstract

The invention discloses a dual-band microwave radiation detection method and system for characterizing a public building fire, and the system comprises a signal receiving module, a signal conversion module, a signal collection module and a control module, and the signal receiving module comprises an X-band and Ka-band receiving antenna, a band-pass filter, and a low-noise amplifier; the signal conversion module comprises a frequency mixer, a local oscillator module, a filter and an isolator; the signal receiving module comprises a controllable attenuator, an amplifier and a power meter; the control module comprises a controller, a control circuit and a radio frequency switch. According to the invention, the microwave radiation power of the public building fire is detected in two wavebands, the detection data is integrated and analyzed, and the early fire of the public building is represented by the comprehensive result. According to the invention, the false alarm phenomenon caused by interference sources such as smoke can be eliminated; the device has the capability of identifying fire after obstacles, and the detection range is large; the problem that an existing fire detector is insufficient in timeliness and obstacle crossing performance in early-stage fire detection of public buildings is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of fire detection, and in particular to a dual-band microwave radiation detection method and system for characterizing fires in public buildings. Background Art

[0002] There are usually a lot of combustibles in public buildings, and the rooms are isolated from each other. When a fire occurs, it is difficult to detect and extinguish it in the first time. Common combustibles are mainly wood, cotton products, and plastic products. Once they come into contact with a fire source, they will flash over within 3-5 minutes, causing the fire to spread. Therefore, it is necessary to detect and warn in the early stages of the fire. Existing fire detectors are mainly divided into two categories. One type detects changes in temperature and smoke, such as smoke alarms. When an early warning is issued, the fire has usually spread. The detection ability for early fires is insufficient and it is easily interfered with and produces false alarms. The other type detects images of flames, such as image and infrared detectors. They have higher sensitivity, but are only suitable for open places such as railway stations and airports. They cannot detect situations where obstacles block the flame. In summary, existing fire detectors cannot solve the problem of characterizing and detecting early fires in public buildings. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one purpose of the present invention is to provide a dual-band microwave radiation detection method and system for characterizing public building fires, using a multi-band microwave radiation detection device to resist interference factors and interference radiation sources such as smoke and water vapor, and accurately and timely characterize the early fire of public buildings.

[0004] A dual-band microwave radiation detection method and system for characterizing public building fires according to the present invention includes an X-band receiving module, a Ka-band receiving module, a signal conversion module, a signal acquisition module and a control system. The modules are connected by flexible cables.

[0005] Preferably, the control system comprises a controller and a radio frequency switch, wherein the controller processes and displays data and sends a control signal to select a band; and the radio frequency switch is used for band selection.

[0006] Preferably, the X-band receiving module and the Ka-band receiving module both include a signal receiving antenna, a radio frequency filter, and a radio frequency low-noise amplifier, which are used to collect fire scene microwave signals and perform filtering and amplification.

[0007] Preferably, the signal conversion module includes a mixer, a local oscillator module, an intermediate frequency filter, a frequency multiplier, and an isolator, and is used to convert the radio frequency signal to an intermediate frequency and filter out harmonic signals.

[0008] Preferably, the local oscillator module includes a signal generator and a control circuit. The signal generator is connected to a mixer and is a broadband frequency generator that generates a sinusoidal signal of corresponding frequency and power. The control circuit sends a control signal according to a control instruction to adjust the output frequency of the local oscillator module and returns the frequency and power parameters of the local oscillator module.

[0009] Preferably, the signal acquisition module expands the measurement range through a controllable attenuator so that the detection system works within a linear range; a power meter is used to measure the power of the signal at multiple frequency points within the bandwidth, and the fire radiation power is obtained by weighted averaging.

[0010] Preferably, the dual-band fire microwave radiation detection system can send a control signal through a control system, adjust the radio frequency switch and the local oscillator, detect fire microwave radiation in the X-band or Ka-band, analyze the detection results of the two bands, and accurately detect fires in public buildings.

[0011] A method for characterizing a dual-band microwave radiation detection system for public building fires:

[0012] The power meter includes a power divider, an integration circuit, and an A / D conversion circuit. It divides the detection bandwidth into 10 paths, measures the power separately, and calculates the final value. Fire can be detected based on the power change and a fire alarm signal can be issued. Planck proposed the blackbody radiation law, and its formula is as follows:

[0013]

[0014] Where S is the effective radiation area (m 2 ), h is Planck's constant, which is 6.626×10 -34 J·s; c is the speed of light, 3×10 8 m / s; k is the Boltzmann constant, which is 1.38×10 -23 J / K.

[0015] The general microwave frequency range is 300MHz~3000GHz. The commonly used microwave frequency range in life is 1GHz~100GHz. In this range, the Rayleigh-Jeans law hf<<kT is satisfied. From the equivalent infinitesimal relationship, we can get e hf / kT -1≈hf / kT, substituting it into the above formula, we get:

[0016]

[0017] Let the radiation center frequency be f c , the bandwidth is Δf, integrate the above formula with respect to frequency f, and we get:

[0018]

[0019] The emissivity of the combustible material is e F When , the radiation power formula is as follows:

[0020]

[0021] After a preliminary calculation of the blackbody radiation power, further calculation and analysis are performed for the dual-band fire detection scene. Since the fire source is placed on the ground, its radiation area is assumed to be a hemisphere with a radius of r, and its surface area is 2πr 2 , assuming that the effective receiving area of ​​the antenna is Ae, the formula for the radiated power received by the antenna is as follows:

[0022]

[0023] The definition of microwave band antenna gain is:

[0024]

[0025] Power received by the radiometer:

[0026]

[0027] Where A is the area of ​​the fire source, T is the temperature of the burning material, r is the horizontal distance between the antenna and the fire source, e F is the emissivity, f c is the detection center frequency, and Δf is the detector bandwidth.

[0028] The beneficial effects of the present invention are:

[0029] (1) The signal collected by the signal receiving module is converted to intermediate frequency acquisition through superheterodyne detection, and the signal is amplified in two stages at the RF and intermediate frequencies. The high-frequency amplifier has a small gain requirement and has the characteristics of low noise, high sensitivity and high stability. The overall gain exceeds 80dB and the gain fluctuation is less than 2dB.

[0030] (2) An adjustable attenuator is used in the signal acquisition module to control the gain. For different measurement environments, the control module can send control signals for calibration and adjustment, so that fire can be characterized in different environments. When the fire source is close and the radiation power exceeds the power limit of the device, pre-attenuation is performed to increase the dynamic range of the measurement.

[0031] (3) Using a power meter to perform weighted averaging of power at multiple frequency points can eliminate false alarms caused by signal interference sources such as electrical equipment.

[0032] (4) The control module can be integrated to realize the switching of detection bands and the adjustment of device performance. The operation is convenient, and the detection data can be processed and displayed using an external controller to realize medium and long-distance control and cluster deployment.

[0033] (5) Fire radiation is detected in the microwave band. Due to the high penetration of microwaves, fires behind obstacles can be detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In the attached picture:

[0035] Figure 1 A block diagram of a dual-band microwave radiation detection system for characterizing public building fires proposed by the present invention;

[0036] Figure 2 It is a flowchart of the system proposed by the present invention when it works in the X-band;

[0037] Figure 3 This is a system control signal block diagram proposed by the present invention;

[0038] Figure 4 This is a system control flow chart proposed by the present invention. DETAILED DESCRIPTION

[0039] Reference Figure 1 , a dual-band microwave radiation detection system for characterizing public building fires, comprising:

[0040] Signal receiving module: Receives X-band and Ka-band microwave radiation signals from the fire scene, filters out noise in the corresponding bands and performs low-noise amplification;

[0041] Signal conversion module: converts the signal to intermediate frequency, compensates for conversion loss and filters conversion harmonics;

[0042] Signal acquisition module: controls the gain of the detection device, calculates the signal power, performs weighted averaging and outputs it;

[0043] Control module: processes and displays the power signal output by the signal acquisition module and the configuration information of the device; sends control instructions through the serial port to adjust the RF switch, the output of the local oscillator, and the controllable attenuator.

[0044] Figure 2 In the first embodiment provided by the present invention, a fire microwave radiation detection device is selected when the X-band is used.

[0045] The signal receiving module uses a wideband horn antenna, and the antenna port is located at the front end of the radiation detection system to detect signals, provide basic gain and transmit signals to the link.

[0046] Use a passive filter to filter the signal received by the antenna to remove noise interference. Exemplarily, the RF filter uses a bandpass filter with a frequency range slightly larger than the preset bandwidth of the radiation detection system to reduce the attenuation of the signal within the preset bandwidth. The filter must have good cutoff performance to filter out noise and signals outside the passband received by the antenna, and filter out the image frequency signal before mixing.

[0047] In this embodiment, the signal receiving module uses a low noise amplifier to amplify the received small signal, the noise is lower than 3dB, and the total system gain is greater than 80dB.

[0048] The signal conversion module mixes the signal through a passive double-balanced mixer, filters out harmonic signals through an intermediate frequency filter, and uses an isolator to isolate the ports of the mixer to avoid frequency leakage. Since the intermediate frequency is much lower than the radio frequency and the local oscillator frequency, the spurious suppression effect is better.

[0049] The local oscillator module is used to drive the mixer for down-conversion, and the local oscillator module generates a specific frequency signal through a signal generator. Exemplarily, the local oscillator module uses a wideband voltage-controlled oscillator as a signal generator, and adjusts the frequency and power of the output signal through a control signal of a control circuit.

[0050] The bandwidth of the intermediate frequency filter is the overall bandwidth of the radiation detection device.

[0051] In this embodiment, the external controller is an embedded single chip microcomputer, which communicates with the control terminal through the WIFI module, sends control signals through buttons, and connects to a display to view execution results and measured power values. The control terminal is connected to the local oscillator module and power meter of the detection device through a serial port.

[0052] The signal control module of the present invention is as follows Figure 3 As shown. The control terminal is an embedded processor, which controls the timing of detection and performs frequency adjustment and other operations according to the control instructions generated by the external controller. The external controller can establish communication with the control terminal through Bluetooth, WIFI, serial port, etc., integrate and package the configuration information such as detection frequency, attenuation value, acquisition rate, etc. through the SPI protocol, and send it to the control terminal to adjust the performance of the detection device; the control terminal can return the current configuration information and power measurement results to the external controller for processing and display. After receiving the control signal, the control terminal performs the corresponding operations: control the RF switch, adjust the path, and detect the radiation signal of the corresponding frequency; control the local oscillator module to output the local oscillator signal of the corresponding frequency and power; control the controllable attenuator to adjust the overall gain of the detection device.

[0053] In this embodiment, the power meter includes a power divider, an integration circuit and an A / D conversion circuit, which divides the detection bandwidth into 10 paths, performs power measurement respectively, and calculates the final value. According to the power change, a fire can be detected and a fire alarm signal can be issued. Planck proposed the black body radiation law, and its formula is as follows:

[0054]

[0055] Where S is the effective radiation area (m 2), h is Planck's constant, which is 6.626×10 -34 J·s; c is the speed of light, 3×10 8 m / s; k is the Boltzmann constant, which is 1.38×10 -23 J / K.

[0056] The general microwave frequency range is 300MHz~3000GHz. The commonly used microwave frequency range in life is 1GHz~100GHz. In this range, the Rayleigh-Jeans law hf<<kT is satisfied. From the equivalent infinitesimal relationship, we can get e hf / kT -1≈hf / kT, substituting it into the above formula, we get:

[0057]

[0058] Let the radiation center frequency be f c , the bandwidth is Δf, integrate the above formula with respect to frequency f, and we get:

[0059]

[0060] The emissivity of the combustible material is e F When , the radiation power formula is as follows:

[0061]

[0062] After a preliminary calculation of the blackbody radiation power, further calculation and analysis are performed for the dual-band fire detection scene. Since the fire source is placed on the ground, its radiation area is assumed to be a hemisphere with a radius of r, and its surface area is 2πr 2 , assuming that the effective receiving area of ​​the antenna is Ae, the formula for the radiated power received by the antenna is as follows:

[0063]

[0064] The definition of microwave band antenna gain is:

[0065]

[0066] Power received by the radiometer:

[0067]

[0068] Where A is the area of ​​the fire source, T is the temperature of the burning material, r is the horizontal distance between the antenna and the fire source, e F is the emissivity, f c is the detection center frequency, and Δf is the detector bandwidth.

[0069] The following is a second embodiment of the present invention, which is based on the previous embodiment, with the following differences: Ka-band signals are detected; an embedded single-chip microcomputer is used as an external controller; and control software and a host computer are also included.

[0070] In this embodiment, the external controller is a computer, which communicates with the control terminal through a serial port; displays the radiation power, checks the configuration parameters, and adjusts the device performance; the control terminal receives the signal of the external controller, adjusts the path of the RF switch, the output of the local oscillator, and the attenuation of the controllable attenuator. The control software of the external controller is used for unified control.

[0071] Software control flow chart as follows Figure 4 As shown. After the external controller is turned on, it establishes a connection with the device, and then configures parameters and calibrates data according to the environment, and starts measuring. The default is X-band measurement. Data is received and processed at a certain interval. If the processing result is normal, it waits for the next data reception; if the result is abnormal, it switches to the Ka band for another measurement. If the result is still abnormal, the alarm continues to sound before it is manually released. After the alarm is released, it switches to the X-band to continue measuring. The measurement can be manually ended during the measurement process. The alarm signal is only issued when both detection results are abnormal.

[0072] Since the amplifier and other modules of the fire microwave radiation detector use active devices, they will generate heat when they start running, and the temperature will rise, causing gain drift. Before starting detection, they need to be preheated to allow the device to reach a thermally stable state before starting measurement. According to the change in microwave radiation power, the power meter can detect multiple data per second, and an algorithm is written to determine whether the microwave radiation device has reached stability. Calculate the number of power values ​​that appear per minute, extract the mode and compare it with the mode of the previous few minutes. If the range is less than the threshold, it is determined that the device has reached a stable state, obtain the stable value, and start measuring.

[0073] During the measurement, the difference between the stable value and the measured value is processed. Since fire detection is a continuous process, data changes will not produce sudden changes, but pulse interference will affect fire judgment. First, the data is compared with the data before and after. If it is a sudden change, it is determined to be an abnormal point and the power value of the point is eliminated. After eliminating the abnormal point, the data trend is judged. If the detection is an upward trend and the rising power value is greater than a certain threshold, it is determined that the fire source is detected and an alarm signal is issued.

[0074] In this embodiment, the frequency multiplier is an active device, which maintains the power of the output signal through DC power supply. After mixing, the power is relatively large. The attenuation value of the controllable attenuator is adjusted to attenuate the signal after intermediate frequency filtering to avoid exceeding the linear working range.

[0075] In summary, the present invention discloses a dual-band microwave radiation detection method and device for characterizing fires in public buildings, which can overcome the interference of water vapor, smoke and other signal sources in the fire scene and accurately characterize the occurrence of fire; the controllable attenuator can be adjusted according to actual conditions to control the overall gain of the detection device, and has high stability and adaptability; control instructions can be sent remotely through an external controller to switch the detection band and query the parameters of the detection device.

Claims

1. A dual-band microwave radiation detection system for characterizing public building fires, characterized by: It comprises an X-band receiving module, a Ka-band receiving module, a signal conversion module, a signal acquisition module and a control system, and the modules are connected by flexible cables.

2. A dual-band microwave radiation detection system for characterizing public building fires according to claim 1, characterized in that: The control system includes a controller and a radio frequency switch, wherein the controller processes and displays data and sends a control signal to select a band; and the radio frequency switch is used for band selection.

3. A dual-band microwave radiation detection system for characterizing public building fires according to claim 1, characterized in that: The X-band receiving module and the Ka-band receiving module both include a signal receiving antenna, a radio frequency filter, and a radio frequency low-noise amplifier, and are used to collect fire scene microwave signals and perform filtering and amplification.

4. A dual-band microwave radiation detection system for characterizing public building fires according to claim 1, characterized in that: The signal conversion module includes a mixer, a local oscillator module, an intermediate frequency filter, a frequency multiplier, and an isolator, and is used to convert the radio frequency signal to an intermediate frequency and filter out the harmonic signal.

5. A dual-band microwave radiation detection system for characterizing public building fires according to claim 4, characterized in that: The local oscillator module includes a signal generator and a control circuit, wherein the signal generator is connected to a mixer and is a broadband frequency generator that generates a sinusoidal signal of corresponding frequency and power. The control circuit sends a control signal according to a control instruction, adjusts the output frequency of the local oscillator module, and returns the frequency and power parameters of the local oscillator module.

6. A dual-band microwave radiation detection system for characterizing public building fires according to claim 1, characterized in that: The signal acquisition module expands the measurement range through a controllable attenuator, so that the detection system works within a linear range; a power meter is used to measure the power of multiple frequency points of the signal within the bandwidth, and the fire radiation power is obtained through weighted average.

7. A dual-band microwave radiation detection system for characterizing public building fires according to claim 1, characterized in that: The dual-band fire microwave radiation detection system can send a control signal through a control system, adjust a radio frequency switch and a local oscillator, detect fire microwave radiation in the X-band or Ka-band, analyze the detection results of the two bands, and accurately detect fires in public buildings.

8. A method for a dual-band microwave radiation detection system for characterizing a public building fire according to any one of claims 1 to 7, characterized in that: The power meter includes a power divider, an integration circuit, and an A / D conversion circuit. It divides the detection bandwidth into 10 paths, measures the power separately, and calculates the final value. Fire can be detected based on the power change and a fire alarm signal is issued. Planck proposed the blackbody radiation law, and its formula is as follows: Where S is the effective radiation area (m 2 ), h is Planck's constant, which is 6.626×10 -34 J·s; c is the speed of light, 3×10 8 m / s; k is the Boltzmann constant, which is 1.38×10 -23 J / K; The general microwave frequency range is 300MHz~3000GHz. The commonly used microwave frequency range in life is 1GHz~100GHz. In this range, the Rayleigh-Jeans law hf<<kT is satisfied. From the equivalent infinitesimal relationship, we can get e hf / kT -1≈hf / kT, substituting it into the above formula, we get: Let the radiation center frequency be f c , the bandwidth is Δf, integrate the above formula with respect to frequency f, and we get: The emissivity of the combustible material is e F When , the radiation power formula is as follows: The blackbody radiation power is preliminarily calculated. The following is a further calculation and analysis of the dual-band fire detection scene. Since the fire source is placed on the ground, its radiation area is assumed to be a hemisphere with a radius of r and a surface area of ​​2πr 2 , assuming that the effective receiving area of ​​the antenna is Ae, the formula for the radiated power received by the antenna is as follows: The definition of microwave band antenna gain is: Power received by the radiometer: Where A is the area of ​​the fire source, T is the temperature of the burning material, r is the horizontal distance between the antenna and the fire source, e F is the emissivity, f c is the detection center frequency, and Δf is the detector bandwidth.

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