In order to be able to keep in line with the information age information surge, the demand for the ability to capture and process information is increasing the development trend of technology, for the sensor performance indicators (including accuracy, reliability, sensitivity, etc.) more and more stringent requirements; at the same time, the operation of the sensor system friendliness is also on the agenda, so it also requires Sensors must be equipped with standard output modes; and the traditional large volume of weak function sensors is often difficult to meet the above requirements, so they have been gradually replaced by a variety of different types of high-performance miniature sensors; the latter are mainly composed of silicon materials, with small size, light weight, fast response, high sensitivity and low cost advantages.
1.1 Sensor miniaturization triggered by computer-aided design (CAD) technology and microelectromechanical systems (MEMS) technology
At present, almost all sensors are in the process of transforming from the traditional structured production design to the simulation-based engineering design based on computer-aided design (CAD), which enables the designers to design low-cost in a relatively short period of time, High-performance new system, this design means a huge shift in a large extent to promote the sensor system to a faster speed to meet the needs of scientific and technological development in the direction of miniaturization.
Research on microelectromechanical systems (MEMS) began in the 1960s, and the scope of its research involves materials science, mechanical control, processing and packaging technology, electronics, and sensors and actuators and other disciplines, and is a very promising emerging research field. The core technology of MEMS is to study the skillful combination of microelectronics, micromachining and packaging technology, which is expected to produce a new type of system with compact size but powerful function. After decades of development, especially the last decade of research and development, MEMS technology has shown great vitality, the effective use of this technology will be miniaturization of information systems, intelligence, multifunctionality and reliability level to a new height. At the current level of technology, micro-cutting processing technology has been able to produce 3D micro-structures with different levels, which can produce very small micro-sensor sensitive components, such as gas sensors, ion sensors, photodetectors, such as silicon as the main constituent material of the sensing/detectors are equipped with excellent sensitive components [1], [2]. Currently, this class of components has been widely used as the main sensitive elements of microsensors in different research fields.
1.2 Current status of microsensor applications
In terms of the current state of technological development, microsensors have already had a profound impact on the signal detection systems in a large number of different applications, such as aeronautics, remote sensing, medical and industrial automation, etc.; microsensors that are currently developed and in the practical stage can be used to measure a wide range of physical, chemical and biological quantities, such as Displacement, speed/acceleration, pressure, stress, strain, sound, light, electricity, magnetism, heat, PH, ion concentration and biomolecule concentration, etc.
2 Intelligent (Smart)
Intelligent sensors (Smart Sensor) is another new type of sensor system that involves a variety of disciplines that appeared at the end of the 1980s. This kind of sensor system was immediately introduced by the scientific research community, especially in the detector application areas, such as distributed real-time detection, network detection and multi-signal detection has been quite popular, and has a greater impact.
2.1 Characteristics of Intelligent Sensors
Intelligent sensors are microprocessor-equipped sensor systems that are not only capable of performing information processing and storing information, but also capable of logical thinking and making conclusions. This category of sensors is equivalent to a microcomputer and sensor complex, its main components include the main sensor, auxiliary sensors and microcomputer hardware devices. Such as intelligent pressure sensors, the main sensor is a pressure sensor, used to detect pressure parameters, auxiliary sensors are usually temperature sensors and environmental pressure sensors. When using this technology can be easily adjusted and corrected due to temperature changes in the measurement error, while the environmental pressure sensor to measure the pressure changes in the working environment and correct the results; and hardware system in addition to being able to amplify the sensor's weak output signals, processing and storage, but also the implementation of the communication links with the computer.
Typically, a general-purpose detection instrument can only be used to detect a physical quantity, the signal conditioning is done by those connected to the main detection components connected to the analog circuitry; but intelligent sensors are able to achieve all the functions, and its accuracy is higher, cheaper, and better processing quality. Compared with traditional sensors, intelligent sensors have the following advantages:
1. Intelligent sensors are not only able to process, analyze and regulate the information, to compensate for the measured value and its error, but also able to carry out logical thinking and conclusions, with the aid of a list of non-linear signals to linearize the processing of digital signals with the aid of software filter filter. In addition, also be able to use software to achieve non-linear compensation or other more complex environmental compensation to improve the measurement accuracy.
2. Intelligent sensors with self-diagnostic and self-calibration functions can be used to detect the working environment. When the working environment is close to its limit conditions, it will issue an alarm signal, and according to its analyzer input signal to give relevant diagnostic information. When intelligent sensors do not work properly due to some internal faults, it is able to find out the anomalies or faulty components with the help of its internal detection link.
3. Intelligent sensors can complete the multi-sensor multi-parameter hybrid measurement, thus further broadening its detection and application areas, and the intervention of the microprocessor makes it easier for intelligent sensors to more convenient to a variety of signals for real-time processing. In addition, its flexible configuration can make the same type of sensor to achieve the best performance, but also to make them suitable for different working environments.
4. Intelligent sensors can be easily processed in real time by a large number of detected data, but also according to the need to store them. The purpose of storing a large amount of information is mainly in order to query after the fact, this kind of information includes the history of the equipment and the detection of analysis results of the index and so on;
5. Intelligent sensors are equipped with a digital communication interface, through which the interface can be directly with its affiliated computers for communication and exchange of information. In addition, the intelligent sensor information management program is also very simple and convenient, for example, the detection system can be controlled remotely or in a locked mode of operation, you can also send the measured data to remote users.
2.2 Intelligent sensor development and application of the status quo
At present, the intelligent sensor technology is in a period of vigorous development, representative of the typical products are the United States Honeywell's ST-3000 series of intelligent transmitters and Germany's Stedman two-dimensional acceleration sensors, as well as a number of other containing microprocessor (MCU) monolithic integration of pressure sensors, multi-dimensional detection capabilities of the pressure sensor, the ability to detect a multi-dimensional sensor, and the ability to detect the pressure sensor. Sensors, intelligent sensors with multi-dimensional detection capabilities and solid-state image sensors (SSIS) and so on. At the same time, the important role of new intelligent sensors based on fuzzy theory and neural network technology in the research and development of intelligent sensor systems is also increasingly being paid great attention by related researchers.
One point to note is that the current intelligent sensor system itself is all digital, but its communication protocol still needs to rely on the standard analog signal of 4 ~ 20 mA to achieve. A number of international standardization research institutions are currently actively studying the introduction of the relevant general fieldbus digital signal transmission standards; however, in the current transition phase is still mostly used in the long-distance range bus addressable sensor (HART) protocol, that is, Highway Addressable Remote Transducer. this is a kind of communication protocol for intelligent sensors, with the This is a communication protocol for intelligent sensors, and the current use of 4 ~ 20mA analog signal system is fully compatible with analog and digital signals can be communicated at the same time, so that the products of different manufacturers have a common.
Energy sensors are mostly used for pressure, force, vibration impact acceleration, flow, temperature and humidity measurement, such as the U.S. Honeywell's ST3000 series of fully intelligent transmitters and Germany's Stroman company's two-dimensional acceleration sensor belongs to this category of sensors. In addition, intelligent sensors in the field of space technology research also have more successful application examples [6].
The development of intelligent sensors will undoubtedly be further expanded to chemical, electromagnetic, optical and nuclear physics and other research areas. It is foreseeable that the emerging intelligent sensors will play a greater and greater role in various fields related to the national life of all mankind.
3 Multifunction sensor (Multifunction)
As mentioned earlier, usually a sensor can only be used to detect a physical quantity, but in many applications, in order to be able to perfectly and accurately reflect the objective and the environment, often need to measure a large number of physical quantities. Multi-function sensor composed of a number of sensitive components is a compact size and a variety of functions with a new generation of detection systems, it can rely on the sensitive components of different physical structures or chemical substances and their different ways of characterization, with a single sensor system to achieve a variety of sensors at the same time. With the rapid development of sensor technology and microcomputer technology, it is now possible to produce a number of sensitive components synthesized in the same material or a single chip on the integrated multifunction sensor.
3.1 Multi-functional sensor implementation rules and structure mode
In summary, the main implementation rules and structure mode of multi-functional sensor system include:
(1) Multi-functional sensor system consists of a number of different kinds of sensitive elements, can be used to measure a variety of parameters at the same time. For example, a temperature detector and a humidity detector can be configured together (i.e., heat-sensitive elements and humidity-sensitive elements are configured on the same sensor carrier) to create a new sensor, so that this new sensor can simultaneously measure temperature and humidity.
(2) A number of different sensitive components are delicately produced in a single piece of silicon, thus constituting a highly integrated and miniaturized multifunctional sensor. Because these sensitive components are synthesized in the same piece of silicon, they work under the same conditions at any time, so it is easy to compensate for system errors and corrections.
(3) With the help of different effects of the same sensor can obtain different information. Take the coil as an example, it shows the capacitance and inductance are different.
(4) In different excitation conditions, the same sensitive element will show different characteristics. In the case of voltage, current or temperature and other excitation conditions are not the same, by a number of sensitive components composed of a multi-function sensor characteristics can be imagined will be how different! Sometimes it is equivalent to a number of different sensors, its multifunctional characteristics can be said to live up to its name.
3.2 Multi-function sensor development and application of the status quo
Multi-function sensor is undoubtedly the current development of sensor technology in a new research direction, a few days ago, many scholars are actively engaged in the field of research work. Such as certain types of sensors to make the appropriate combination of new sensors, such as used to measure fluid pressure and reciprocal pressure of the combination of sensors. Another example, in order to be able to detect a variety of signals at the same time with high sensitivity and small particle size, miniature digital three-port sensor can be used at the same time thermal components, photosensitive components and magnetic components; this combination of sensors are not only capable of outputting analog signals, but also capable of outputting frequency signals and digital signals.
From the current state of development, the hottest area of research is perhaps the various types of biomimetic sensors, and in the sense of touch, stimulation, and audio-visual discrimination and other aspects of the latest research results. From a practical point of view, multifunctional sensors in the application of a variety of types of multifunctional tactile sensors, such as artificial skin tactile sensors is one of them, this sensor system consists of PVDF materials, non-contact skin-sensitive systems, as well as pressure-sensitive conduction function of the rubber tactile sensors and other components. It is reported that the U.S. MERRITT company developed a non-contact skin-sensitive system has achieved greater success, its non-contact ultrasonic sensors, infrared radiation guided sensors, thin-film capacitance sensors, as well as temperature, gas sensors, etc. in the U.S. mainland is widely used.
Compared with other research results, the current research in artificial olfaction seems to be far from satisfactory. The discriminatory signals received by the olfactory elements are very complex, always mixed with thousands of chemicals, which makes the olfactory system to deal with these signals is very intricate.
The typical product of artificial olfactory sensing system is Electronic nose (electronic nose) with different functions. In the past 10 years, the development of this technology has been very fast, and now there are several kinds of commercialized products circulating in the international market, and the United States, France, Germany, and Britain all have more advanced electronic nose products.
"Electronic nose" system usually consists of a cross-selective array of gas sensors and related data processing technology, and with the appropriate pattern recognition system, with the ability to identify simple and complex odors, mainly used to solve the general situation of odor detection. According to the different application objects, "electronic nose" system sensor array sensor materials and the number of configurations are also different, of which the constituent materials include metal oxide semiconductors, conductive polymers, quartz crystal oscillators, etc., and the number of configurations ranges from a few to dozens of different. In short, the "electronic nose" system is a gas sensor technology and information processing technology for the effective combination of high-tech products, its gas sensor size is very small, power consumption is also very low, can easily capture and process the odor signal. Gas flow through the gas sensor array into the "electronic nose" system signal pre-processing elements, and finally by the array response mode to determine the characteristics of the measured gas. The array response pattern uses correlation, least squares, clustering and major element analysis to qualitatively and quantitatively identify the gas being measured. The Cyranose 320 electronic nose manufactured by Cyranosciences, Inc. is one of the more technologically advanced and widely applicable olfactory sensing systems available today. The system consists of two parts, the sensor array and the data analysis algorithm, and the basic technique is to configure several unique thin-film carbon-black polymer composite chemoresistors to form a sensor array, and then use standard data analysis techniques to characterize the gas measured. Standard data analysis techniques are then employed to identify unknown analytes by analyzing the output values collected from this sensor array. The Cyranose 320 electronic nose is said to have applications in food and beverage production and preservation, environmental protection, chemical analysis and identification, disease diagnosis and pharmaceutical analysis, as well as industrial process control and consumer product monitoring and management.
4 wireless networked (wireless networked)
Wireless networks are not new to us, such as cell phones, wireless Internet access, and televisions. Sensors are also not new to us, such as temperature sensors, pressure sensors, and the relatively new odor sensors. However, combining the two together, the concept of wireless sensor networks (Wireless Sensor Networks) is something that has only happened in recent years.
The main component of this network is a cute sensor node. They are cute because they are very small. These nodes can feel the height of the temperature, changes in humidity, pressure increases or decreases, and the rise and fall of noise. What is more interesting is that each node is a microcomputer that can carry out rapid calculations, they will convert the information collected by the sensor into digital signals, encoding, and then through the wireless network established between the node and the node itself to send to a server with a greater processing capacity
4.1 Sensor Networks
Sensor Networks are the current international attention, the highly interdisciplinary and highly interconnected by multiple disciplines, and the most important thing is that sensor networks are not only a network, but also a network. Sensor networks are an emerging frontier research hotspot of international concern and highly interdisciplinary. Sensor network integrates sensor technology, embedded computing technology, modern network and wireless communication technology, distributed information processing technology, etc. It can collaboratively monitor, sense and collect information of various environments or monitoring objects in real time through various types of integrated micro-sensors, process the information through embedded systems, and transmit the sensed information to user terminals through random self-organized wireless communication networks in a multi-hop relay mode. The information is processed by the embedded system, and the sensed information is transmitted to the user terminal by multi-hop relay through random self-organized wireless communication network. Thus, the concept of "ubiquitous computing" can be truly realized. Sensor network research adopts the system development mode, so it is necessary to integrate modern advanced microelectronics technology, microfabrication technology, system-on-chip (system-on-chip) chip design technology, nano-materials and technology, modern information and communication technology, computer network technology, etc., in order to realize its miniaturization, integration, multifunctionality, systemization and networking, especially to realize the unique ultra-low-power system of the sensor network. Network unique ultra-low-power system design. Sensor networks have a very broad application prospects, in the military and defense, industry and agriculture, urban management, biomedical, environmental monitoring, rescue and disaster relief, anti-terrorism, terrorism, remote control of hazardous areas, and many other areas have important scientific research value and great practical value, has attracted the world's military, academia and industry in many countries attaches great importance to, and has become a recognized emerging frontier hot spot into the year 2000 since! It is recognized as one of the emerging hot frontier research areas since 2000, and is considered to be one of the technologies that will have a great impact on the twenty-first century.
4.2 Hot issues and key technologies in sensor network research
Sensor networks are aimed at applications, and their construction is a huge systematic engineering, involving a lot of research work and problems to be solved at every level. The research on wireless sensor network system structure and interface interface technology is of great significance. If we abstract the sensor network into five levels according to its function, it will include the foundation layer (sensor collection), network layer (communication network), middleware layer, data processing and management layer and application development layer.
Among them, the foundation layer is centered on the research of new sensors and sensing systems, including the application of new sensing principles, the use of new materials, and the use of new structural designs, in order to reduce energy consumption, improve the sensitivity, selectivity, speed of response, dynamic range, accuracy, stability, and the ability to work in harsh environmental conditions.
4.3 Applied Research on Sensor Networks
Sensor networks have great application prospects and are considered to be one of the technologies that will have a great impact on the 21st century. Existing and potential sensor applications include: military reconnaissance, environmental monitoring, medical care, building monitoring and so on. With the sensor technology, wireless communication technology, computing technology continues to develop and improve, a variety of sensor networks will be all over our living environment, so as to truly realize the "ubiquitous computing". The following is a brief introduction to some of the applications of sensor networks.
(1) military applications
Sensor network research first originated in the military field, the experimental system has a large-scale sensor network of ocean sonar monitoring, but also to monitor the ground objects of small sensor networks. Modern sensor network applications, by means of aircraft dispersal, special artillery shells, etc., can be a large number of inexpensive sensors densely dispersed in the personnel is not easy to reach the observation area such as enemy positions, to collect useful microscopic data; in a part of the sensors because of destruction and other reasons fail, the sensor network as a whole sensor network body can still complete the task of observation. The above characteristics of the sensor network makes it has significant military value, can be applied to the following scenarios:
▉ ▉ monitoring personnel, equipment, etc., as well as manned systems: through the personnel, equipment attached to a variety of sensors, allows commanders at all levels of accuracy, timely grasp of their own side of the preservation of the state. Through the deployment of a variety of sensors in enemy positions, you can understand the enemy's weapons deployment, for their own side to determine the attack objectives and attack routes to provide a basis.
▉ Monitoring of enemy attacks: Deploying a large number of sensors in enemy sites and possible attack routes, so as to discover enemy attack actions in a timely manner, and strive for valuable response time. And can quickly adjust and deploy new sensor networks according to the battle situation.
▉ Evaluate the results of the battle: Before and after the attack, deploy a sensor network near the attack target, so as to collect data on the degree of destruction of the target.
▉ Reconnaissance of nuclear, biological, and chemical attacks: Sensor networks allow for early detection of biological and chemical contamination on your own position, providing rapid response time to minimize losses. Without sending personnel can obtain some of the nuclear, biological, chemical explosion site detailed data.
(2) environmental applications
Sensor networks applied to environmental monitoring, generally have the advantages of simple deployment, cheap, long-term without replacing batteries, no need to send people on-site maintenance. Through the dense node arrangement, microscopic environmental factors can be observed, providing a brand new way for environmental research and environmental monitoring Sensor network research in the field of environmental monitoring has been a lot of examples. These application examples include: the observation of the life pattern of the island birds; observation of meteorological phenomena and weather forecasting; forest fire alarm; micro observation of biological communities, etc.
▉ Early Warning of Floods: By reasonably arranging a number of sensors such as water pressure, soil moisture, etc. in key locations in the dams and mountainous areas, early warning information can be issued before the arrival of the flood, so as to eliminate the danger in a timely manner or to reduce the loss.
▉ Farmland Management: Through the deployment of a certain density of air temperature, soil moisture, soil fertilizer content, light intensity, wind speed and other sensors in the farmland, you can better manage the management of the farmland micro-control, to promote crop growth.
(3) family applications
Construction and urban management of various wireless sensors can be flexibly and conveniently arranged in the building, access to indoor environmental parameters, so as to provide the basis for the living room environment control and danger alarm.
▉ Smart home: through the wireless sensors arranged in the room temperature, humidity, light, air composition and other wireless sensors, to sense the microcosmic conditions of different parts of the living room, so as to air conditioning, doors and windows, as well as other home appliances for automatic control, to provide people with intelligent, comfortable living environment [16].
▉ Building safety: through the image, sound, gas detection, temperature, pressure, radiation, and other sensors arranged in the building, abnormal events are detected in a timely manner to alert the police and automatically start emergency measures.
▉ Intelligent transportation: through the arrangement of speed, identification sensors on the road, monitoring traffic flow and other information, to provide information services for travelers, found violations can be timely alarm and record [17]. Counter-terrorism and public **** security through special-purpose sensors, especially biochemical sensors to monitor the information of harmful and dangerous substances, to minimize the harm it causes to the lives of the people.
(4) Conclusion
Wireless sensor networks have a very wide range of application prospects, it is not only in the industrial, agricultural, military, environmental, medical and other traditional areas have a huge value, in the future will also be in many emerging areas to reflect its superiority, such as home, health care, transportation and other fields. We can boldly foresee that the future of wireless sensor networks will be ubiquitous, will be fully integrated into our lives. For example, the miniature sensor network may eventually connect home appliances, personal computers and other daily necessities with the Internet to achieve long-distance tracking, the family is responsible for the use of wireless sensor networks for security control, power saving and so on. Wireless sensor networks will be the future of a pervasive and very large network, its application can be involved in all areas of human daily life and social production activities. However, we should also clearly recognize that the wireless sensor network has just begun to develop, its technology, applications are still far from mature, domestic enterprises should seize the business opportunity to increase investment to promote the development of the industry.
Wireless sensor networks are emerging communication application networks, their applications can be involved in all areas of human life and social activities. Therefore, wireless sensor networks will be the future of a pervasive and very large network, requiring a variety of technical support. At present, mature communication technologies are likely to be appropriate improvements and further development, applied to wireless sensor networks, forming a new market growth point, creating a new world of wireless communications.
5 Conclusion
Sensor systems at the current state of the art are developing in the direction of micro-miniaturization, intelligence, multifunctionality and networking. In the future, as CAD technology, MEMS technology, information theory and data analysis algorithms continue to move forward, the future of the sensor system is bound to become more miniaturized, integrated, multifunctional, intelligent and systematic. In a variety of emerging science and technology in the radiation of a wide range of penetration of today's society, as the modern scientific "eyes and ears" of the sensor system, as people quickly access, analyze and utilize the basis of effective information, will be further general concern of all sectors of society.
Microwave sensors rely on the many advantages of microwave, will be widely used in microwave communications, satellite transmission and other wireless communications, and radar, missile guidance, remote sensing, radio telescope. And in some non-contact monitoring and control also has a good application.
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