CN102507361A - Micro solid mode resonance explosive detector - Google Patents

Abstract

The invention discloses a micro solid mode resonance explosive detector, which comprises a base, drive electrodes, reference electrodes, heating resistors, and explosive selective adsorption membranes. The base adopts a micro elastic solid structure, on the upper two sides and lower two sides of the base are symmetrically arranged the drive electrodes, the reference electrodes, the heating resistors, and the explosive selective adsorption membranes, a layer of heating electrodes are laid under each explosive selective adsorption membrane, and two drive electrodes and one reference electrode are arranged on each of the two sides of each explosive selective adsorption membrane. The detector employs piezoelectric effects to drive and excite a micro solid to move under a special vibration mode, and carries out tracking measurement of the resonant frequency on the reference electrodes. The resonant frequency of the micro elastic solid can reach up to tens of or even hundreds of megahertz, so that the inventive detector has high rigidity, good impact resistance and vibration resistance, and good high quality factor under normal pressure by use of special bulk acoustic resonance mode, requires no vacuum packaging, and can obtain high sensitivity.

Description

Micro Solid Mode Resonant Explosives Detector

technical field

The invention relates to an explosive detector, in particular to a micro solid mode resonant explosive detector processed by MEMS technology.

Background technique

In recent years, terrorist bombing attacks have occurred frequently all over the world, and most of them occurred in densely populated places such as subway stations and airports, seriously endangering the lives and property safety of the people. This makes the development of explosive detection devices an urgent task for scientific researchers in various countries. However, due to the wide variety of explosives, the packaging is becoming more and more sophisticated, concealed, and the diversity of attack targets, the accurate and timely detection of explosives has changed. very difficult. Traditional detection devices are bulky, expensive, poor in portability, and their sensitivity needs to be further improved. Some devices use radiation or interventional mechanisms for detection, which will cause damage or damage to the detected object to a certain extent. At this stage, there is an urgent need for cheap, highly selective, non-intrusive, and highly sensitive explosive detectors. If such sensors can be miniaturized, they can be used to realize portable detection at different locations.

After entering the 1990s, microelectromechanical systems (MEMS) began to achieve comprehensive development. Because MEMS devices have the characteristics of small size, light weight, low power consumption, low cost, high reliability, excellent performance, multi-functional integration, and mass production, with the maturity of MEMS technology, people also apply MEMS technology to In the research work of explosive detection devices, various samples based on MEMS technology have been developed. Its simple and practical structure makes it possible for explosive detectors to achieve miniaturization, low cost, and high precision. MEMS technology for detecting explosives usually uses silicon beams as sensitive structures. The silicon beams are in direct contact with explosive samples, and the explosives react through thermal or optical excitation, causing physical quantities such as temperature, displacement, stress, and resonance frequency of the silicon beams to occur. changes and are detected optically or electrically. According to the different physical quantities of the measured silicon beam, it is divided into four types: temperature measurement method, displacement method, piezoresistive method and resonance method. Existing MEMS explosives detectors all adopt micro-cantilever beam structure, which has some obvious deficiencies. For example: the stiffness of the cantilever beam is low, the resonance frequency is difficult to further increase, and it is easily disturbed by the impact or vibration of the external environment; the vibration quality factor of the cantilever beam structure is not high under normal pressure conditions, and it generally works under vacuum conditions. Explosive detectors must be connected to the external gas environment, and it is impossible to carry out vacuum packaging, which limits the improvement of the measurement sensitivity of resonant cantilever beam MEMS explosive detectors.

Contents of the invention

Aiming at the deficiencies in the existing explosives detection technology, the invention proposes a micro-solid mode resonance explosives detector with simple structure, convenient processing, sensitive response and strong anti-interference ability. The detector makes full use of the change of the resonance frequency of the microelastic solid to detect the types of explosives, and does not need to introduce a complex optical system from the outside, and can realize the miniaturization of the detection system. This kind of micro-elastic solid works in a special vibration mode, and its resonance frequency can reach tens of megahertz or even hundreds of megahertz. It has high stiffness, good shock resistance and vibration resistance. The microelastic solid utilizes its special bulk acoustic resonance mode to work, and has a high quality factor under normal pressure, so it does not need vacuum packaging and can obtain high sensitivity.

In order to achieve the above object, the technical solution of the present invention is as follows:

The micro-solid mode resonant explosive detector of the present invention comprises a substrate, a driving electrode, a reference electrode, a heating resistor and an explosive selective adsorption film. The substrate adopts a micro-elastic solid structure, and the drive electrodes and reference electrodes, heating resistors and adsorption films are distributed on both sides of the substrate, and these parts are completely symmetrical on the upper and lower sides of the substrate. Two driving electrodes and one reference electrode are arranged on the left and right sides of the adsorption film. The driving electrode is used to guide the detector to start vibrating, and the reference electrode is mainly used to obtain the vibration state of the detector and observe the change of the resonance frequency of the microelastic solid. The function of the explosive selective adsorption membrane is mainly to adsorb explosive molecules in the surrounding air, such as nitroaromatics, peroxides, nitroesters and other explosive components, and can also inhibit water molecules or oil molecules in the surrounding air. and other non-specific adsorption. A layer of heating resistor is laid under the selective adsorption film of explosives, which is used to heat the explosives to melt and vaporize the explosives after the explosives detection is completed, so as to prepare for the next detection.

The base body is in the shape of a cuboid, and the material is generally silicon, glass or metal.

The driving electrode and the reference electrode are made of piezoelectric material, mainly for the purpose of utilizing the piezoelectric effect of the piezoelectric material to realize the conversion between mechanical signals and electrical signals.

When two sinusoidal voltages with equal frequency and amplitude and a phase difference of 180° are applied to the driving electrodes on both sides of the adsorption film, the driving electrodes will be stretched and compressed in their polarization directions respectively. Correspondingly, the adsorption film will The micro-solids on both sides also produce stretching and compressing movements, so that the reference electrode is subjected to stretching and compressing stress, thereby generating charges to reflect the movement of the micro-solids. Sweep the frequency of the micro-solid, and according to the change of voltage generated on the reference electrode, the resonant frequency of the micro-solid can be obtained, which is related to the characteristics of the material itself and the external size and quality of the material. Therefore, when the explosive falls on the adsorption When the detector is on the membrane, the quality of the detector changes, and its resonant frequency also changes, which can be detected by the output of the reference electrode.

Existing MEMS explosives detectors all use micro-cantilever beam structure, but the cantilever beam structure has low rigidity, poor anti-shock or vibration and other interference capabilities, low vibration quality factor under normal pressure conditions, and measurement sensitivity needs to be further improved. The explosive detector of the present invention is simple in structure, easy to process, and makes full use of the change of the resonance frequency of the elastic solid to detect the types of explosives. Since the resonance frequency of the elastic solid can generally reach hundreds of megahertz, it is much higher than that of the cantilever beam type. The resonant frequency of the structure is equal, so compared with other explosive detectors, such as cantilever beam detectors, the detector of the present invention has strong shock resistance and vibration resistance, and improves the reliability of the detector system. In addition, the quality factor of elastic solids is generally high, so this kind of detector has fast response and high sensitivity.

Description of drawings

Fig. 1 is a schematic structural view of an embodiment of the present invention;

Fig. 2 is a schematic diagram of the selective adsorption mechanism of the detector to explosive molecules according to an embodiment of the present invention; wherein: (a) is before the adsorption film adsorbs explosives, and (b) is after the adsorption film adsorbs explosives;

Fig. 3 is a working principle diagram of an embodiment of the present invention.

Detailed ways

The embodiments of the present invention are described in detail below. Based on the premise of the technical solution of the present invention, the present embodiment provides detailed implementation and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

As shown in Figure 1, the structure of the explosive detector of the present invention is relatively simple. The material of the substrate 13 is silicon, and high-quality glass or metal can also be selected. The electrode material on both sides of the surface is PZT piezoelectric ceramics, and the piezoelectric effect of this material is used in the process of detecting explosives. There are 12 electrodes on both sides of the surface, including driving electrodes and reference electrodes, of which 2, 4, 6, 8, 10, 12, 14, and 16 are driving electrodes, and 3, 7, 11, and 15 are reference electrodes. The driving and reference electrodes on the upper and lower surfaces are completely symmetrical. The driving electrodes are used to guide the detector to start vibrating. When the driving electrodes 2, 4, 6, 8 and 10, 12, 14, and 16 on both sides of the substrate are simultaneously connected with two circuits with equal frequency and amplitude and a phase difference of 180° When a sinusoidal voltage is applied, according to the inverse piezoelectric effect of piezoelectric ceramics, the left and right sides of the substrate 13 (as seen from Figure 1) are stretched and compressed respectively; the function of the reference electrode is to obtain the vibration state of the explosives detector, so as to extract the resonance frequency . When the left and right sides of the matrix 13 (as seen in Figure 1) are stretched and compressed respectively, due to the piezoelectric effect, a corresponding voltage will be generated on the reference electrode, and the driving voltage frequency with the largest voltage value is the resonance frequency of the detector .

As shown in Figure 2, in this embodiment, the central parts 9 and 17 of the surface of the explosive detector are selective adsorption films for explosives, and a piezoresistive silicon dioxide layer of double self-assembled membrane (SAM): 6-mercapto Nicotinic acid (6-MNA) self-assembled film and heptadecafluorodecyltrimethoxysilane (FAS-17) self-assembled film. As a specific sensing layer, 6-MNA self-assembled membrane (SAM) is mainly used to adsorb explosive molecules, as shown in Figure 2 by 18. The 6-MNA self-assembled film has a high ability to recognize explosives containing -NO2 groups, the main reason is that 6-MNA contains -COOH groups, which have strong hydrogen bonds with the -NO2 groups in explosives However, unfortunately, the silica surface is also hydrophilic and has a non-specific adsorption capacity for molecules such as water or oil in the surrounding humid environment, which will make the explosive detection results unreliable. In order to solve this problem, a layer of low surface energy and hydrophobic FAS-17 self-assembled membrane (SAM) is added to the surface of silica, which solves the problem of non-specific adsorption of molecules such as water or oil on the silica surface. . The selective adsorption mechanism of the detector to explosive molecules is shown in Figure 2. In addition, there are other options for explosive selective adsorption membrane materials, such as polymers (such as polysiloxanes, organic polymers, polycarbosilanes), salts, and silica gel.

A layer of heating resistors 1 and 5 are respectively laid under the explosive selective adsorption film for heating the explosive. The function of the heating resistor is to heat the explosive to a certain temperature after detecting the type of explosive, so that the explosive adsorbed on the surface of the detector can be melted or oxidized and decomposed for the next detection.

As shown in Figure 3, the working principle of the above-mentioned explosives detector in the present embodiment is as follows: between the drive electrodes 2, 4, 6, 8 and 10, 12, 14, 16 of the detector, the frequency and amplitude are equal, Two sinusoidal voltages with a phase difference of 180°, the left and right ends of the detector (viewed from the front view) will simultaneously generate tension and compression due to the piezoelectric effect of the electrodes, as shown in Figure 3, the direction of the arrow indicates the movement of the piezoelectric body direction. This will force the reference electrode to also produce stretching or compression movement, and the reference electrodes at the left and right ends generate charges due to the piezoelectric effect, so the output voltage can be observed on the reference electrodes 3, 7, 11, and 15. Sweep the detector with such two sinusoidal voltages, and you can observe the voltage changes of the reference electrodes 3, 7, 11, 15, and the corresponding driving voltage frequency when the voltage is maximum is the resonant frequency of the detector. When the explosives are adsorbed on the selective adsorption films 1 and 9, the resonant frequency will drop due to the increase of the mass of the detector, and the voltages on the reference electrodes 3, 7, 11, 15 will drop. According to the drift of the resonance frequency and the change of the voltage on the reference electrode, the type and concentration of the explosive can be deduced. Finally, the explosives are heated to a temperature slightly higher than the melting point through the heating resistors 1 and 5, and the explosives will melt and evaporate, preparing for the next detection of explosives.

To sum up, the present invention proposes a new type of explosive detector structure - a micro-solid structure. Using the unique high resonance frequency of this structure, the explosive detector has a strong anti-interference ability to external vibrations. At the same time, The micro-elastic solid uses its special bulk acoustic resonance mode to work, and has a high quality factor under normal pressure. Even if a small amount of explosives are adsorbed on the detector, it will cause a significant change in the resonance frequency, which greatly increases the detection efficiency. device sensitivity. In addition, the detector has a simple structure and is relatively convenient to process, which greatly reduces the manufacturing cost.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (7)

1. A micro-solid mode resonance explosive detector is characterized in that it comprises a substrate, a driving electrode, a reference electrode, a heating resistor and an explosive selective adsorption film, and the substrate adopts a micro-elastic solid structure, and both sides of the substrate are arranged symmetrically There are driving electrodes, reference electrodes, heating resistors and selective adsorption membranes, and these parts are arranged symmetrically on the upper and lower sides of the substrate; a layer of heating electrodes is laid under the selective adsorption membrane of explosives, and two driving electrodes are arranged on both sides. electrode and a reference electrode. 2. micro solid mode resonance explosives detector according to claim 1, is characterized in that, described driving electrode and reference electrode all adopt piezoelectric material, add frequency and For two sinusoidal voltages with equal amplitude and 180° phase difference, the left and right ends of the detector will simultaneously stretch and compress due to the piezoelectric effect of the driving electrode, forcing the reference electrode to also produce stretching or compressing movement. The electrodes generate charges due to the piezoelectric effect, and a change in the resonant frequency is observed on the reference electrodes on both sides of the substrate. 3. The micro-solid mode resonance explosives detector according to claim 1, wherein the explosives selective adsorption film adopts the piezoresistive silicon dioxide layer of double SAM: 6-MNA self-assembled film and FAS -17 self-assembled membranes. 4. The micro-solid mode resonance explosives detector according to claim 1, characterized in that, the selective adsorption membrane material for explosives is polymer, salt or silica gel. 5. The micro solid mode resonance explosives detector according to claim 4, characterized in that the polymer is polysiloxane, organic polymer, or polycarbosilane. 6. The micro-solid mode resonant explosives detector according to claim 1 or 2, wherein the base material is silicon, glass or metal. 7. The micro-solid mode resonant explosives detector according to claim 1, wherein the base body is in the shape of a cuboid.

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