Abstract: In the current information age, the demand for sensors is increasing daily, and their performance requirements are also becoming more stringent. With the continuous advancements in computer-aided design (CAD), microelectromechanical systems (MEMS), fiber optic technology, information theory, and data analysis algorithms, sensor systems are developing towards miniaturization, intelligence, and multifunctionality. This paper focuses on the current technological status, functions, and development prospects of these three types of sensors, and intersperses some successful application examples in signal detection. Keywords: Miniature sensor, intelligent sensor, multifunctional sensor, signal detection, review I. Introduction In today's society, almost no scientific or technological development and application can be separated from the support of sensor and signal detection technologies. People living in the information age are largely involved in the development, acquisition, transmission, and processing of information resources. Different detectors with varying operating principles and functions serve as windows for information perception, capture, and detection, playing a crucial role in signal detection and information processing systems. At the same time, with the current surge in information volume and the continuous emergence of new information types, sensors used for signal detection are facing many new problems and new demands. In this context, many new types of sensors have emerged, such as fiber optic sensors, CCD sensors, infrared sensors, biosensors, remote control sensors, microwave sensors, superconductor sensors, and liquid crystal sensors. These new sensors, in turn, have greatly propelled the rapid development of information technology. Analyzing the current state of information and technology development, the author believes that advanced sensors in the 21st century must possess excellent characteristics such as miniaturization, intelligence, and multifunctionality. This paper, guided by this principle, systematically discusses the current technological status, functions, and development prospects of miniature sensors, intelligent sensors, and multifunctional sensors, and intersperses successful application examples of these three types of sensors in signal detection. II. Micro Sensors To keep pace with the information age's surge in information volume and the ever-increasing demands for information capture and processing capabilities, the requirements for sensor performance indicators (including accuracy, reliability, and sensitivity) are becoming increasingly stringent. Simultaneously, the ease of operation of sensor systems has become a priority, necessitating standard output modes. Traditional large-volume, low-functionality sensors often struggle to meet these requirements, and are therefore gradually being replaced by various types of high-performance micro sensors. These latter sensors, primarily composed of silicon, offer advantages such as small size, light weight, fast response, high sensitivity, and low cost. 1. Sensor Miniaturization Driven by Computer-Aided Design (CAD) and Microelectromechanical Systems (MEMS) Technologies Currently, almost all sensors are shifting from traditional structured production design to analog engineering design based on Computer-Aided Design (CAD). This allows designers to create low-cost, high-performance new systems in a shorter time. This significant shift in design methods is driving sensor systems towards miniaturization that meets the demands of technological development at an even faster pace. Research on microelectromechanical systems (MEMS) began in the 1960s. Its research scope covers multiple disciplines such as materials science, mechanical control, processing and packaging technology, electronic technology, and sensors and actuators. It is a promising emerging research field. The core technology of MEMS is to study the ingenious combination of microelectronics and micromechanical processing and packaging technology, hoping to create a new type of system that is small in size but powerful in function. After decades of development, especially in the last ten years, MEMS technology has shown great vitality. The effective adoption of this technology has raised the miniaturization, intelligence, multifunctionality and reliability of information systems to a new level. At the current level of technology, micro-machining technology can produce 3D microstructures with different levels, thereby producing micro-sensor sensitive elements with very small volume. Sensors/detectors with silicon as the main component material, such as poison gas sensors, ion sensors and photodetectors, are equipped with excellent sensitive elements[1],[2]. At present, this type of device has been widely used as the main sensitive element of micro sensors in different research fields. 2. Sensor Miniaturization Driven by Sensitive Fiber Optic Technology Currently, sensitive fiber optic technology is increasingly becoming another new development direction for miniature sensor technology. It is expected that with the increasing maturity of insertion technology, the development of sensitive fiber optic technology will further accelerate. The working principle of fiber optic sensors is to use light as a signal carrier and transmit signals through optical fibers. Due to the excellent light transmission performance of optical fibers, extremely low light loss, and the very wide bandwidth for transmitting optical signals, coupled with the fact that the optical fiber itself is a sensitive element, fiber optic sensors possess many superior characteristics unmatched by any other traditional sensors. In summary, the superior characteristics of fiber optic sensors mainly include light weight, small size, high sensitivity, large dynamic measurement range, wide transmission bandwidth, ease of maneuverability, and waveform characteristics that adapt to objective conditions, thus enabling better real-time operation, online detection, and automatic control. For example, a primary displacement fiber optic sensing system includes a light radiator (light source, fiber optic head, and light receiver) and a photoelectric conversion element. Its working principle is as follows: light emitted by the light emitter is transmitted to the reflector via the input optical fiber—the output optical fiber receives the optical signal—the photoelectric conversion element converts the optical signal into an electronic signal; given this working principle, we can completely infer the measurable displacement based on the density of the received light. If the structure of such a primary detection system can be improved and its dead zone eliminated, its resolution can often reach over 0.01 mm. In flexible mechanical manufacturing systems, the fiber optic displacement detector online detection system includes four sets of optical fibers in its optical fiber aperture, two of which are used for address allocation, and the other two perform measurement tasks. Optical fibers can also be applied to contactless measurement of 3D surfaces. In recent years, with the advent of new-generation detection equipment such as semiconductor laser LD, CCD, CMOS image sensors, and orientation detection devices PSD, fiber optic contactless measurement technology has developed rapidly. Among contactless measurement technologies, there are mainly fiber optic methods and out-focus methods. The main feature of the fiber optic method is that it can adjust the light wave of the waveguide by means of the measured variable and add value to the measurement signal by setting the light wave parameters. In the focal point shift method, the offset is converted into the deviation of the objective plane relative to the measurement plane; then, this deviation is converted into the brightness difference of the objective reflected spot or the photosensitive detection value; finally, it is converted into the electronic quantity output value. This method has extremely high resolution, and the volume of its related detector can be manufactured to be quite small. In the case of using holographic optical elements, the conventional structure of the focal point shift method can generally be from T structure to Y structure, so it is possible to design an extremely lightweight emitter and receiver on a semiconductor chip [3]. 3. Current Status of Micro Sensor Applications In terms of the current status of technological development, micro sensors have had a profound impact on signal detection systems in a large number of different application fields, such as aviation, long-distance detection, medical and industrial automation; currently, micro sensors developed and put into practical use can be used to measure various physical quantities, chemical quantities and biological quantities, such as displacement, velocity/acceleration, pressure, stress, strain, sound, light, electricity, magnetism, heat, pH value, ion concentration and biomolecule concentration, etc. III. Smart Sensor Smart sensor is another new type of sensor system involving multiple disciplines that emerged in the late 1980s. Such sensor systems have received widespread attention from the scientific community as soon as they were introduced. They are especially popular in the field of detector applications, such as distributed real-time detection, network detection and multi-signal detection, and have a great impact. 1. Characteristics of intelligent sensors Intelligent sensors refer to those sensor systems equipped with microprocessors that can not only perform information processing and information storage, but also perform logical thinking and conclusion judgment. This type of sensor is like a combination of microcomputer and sensor. Its main components include main sensor, auxiliary sensor and microcomputer hardware. For example, intelligent pressure sensor, the main sensor is pressure sensor, which is used to detect pressure parameters, and the auxiliary sensors are usually temperature sensor and environmental pressure sensor. When using this technology, it is convenient to adjust and correct the measurement error caused by temperature change, while the environmental pressure sensor measures the pressure change of the working environment and corrects the measurement results; while the hardware system can amplify, process and store the weak output signal of the sensor, and also perform communication with the computer [3]. Normally, a general-purpose detection instrument can only be used to detect one physical quantity, and its signal conditioning is done by analog circuits connected to the main detection component; however, intelligent sensors can realize all functions, and they are more accurate, cheaper, and have better processing quality. Compared with traditional sensors, intelligent sensors have the following advantages: (1) Intelligent sensors can not only process, analyze and regulate information, and compensate for the measured values ​​and their errors, but also perform logical thinking and conclusion judgment. They can linearize nonlinear signals with the help of a list and filter digital signals with the help of software filters. In addition, they can also use software to realize nonlinear compensation or other more complex environmental compensation to improve measurement accuracy. (2) Intelligent sensors have self-diagnosis and self-calibration functions and 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 give relevant diagnostic information based on the input signal of its analyzer. When an intelligent sensor cannot work properly due to some internal faults, it can find abnormal phenomena or faulty components with the help of its internal detection link. (3) Intelligent sensors can perform multi-sensor, multi-parameter mixed measurements, thereby further expanding their detection and application fields. The intervention of microprocessors makes it easier for intelligent sensors to process various signals in real time. In addition, their flexible configuration function can enable sensors of the same type to achieve optimal working performance and make them suitable for different working environments. (4) Intelligent sensors can easily process large amounts of detected data in real time and can also store them as needed. The purpose of storing large amounts of information is mainly for later retrieval. This type of information includes historical information of the equipment and indexes of relevant detection and analysis results. (5) Intelligent sensors are equipped with a digital communication interface, through which they can directly communicate and exchange information with their computer. In addition, the information management program of intelligent sensors is also very simple and convenient. For example, the detection system can be remotely controlled or operated in a locked mode, and the measured data can be sent to remote users. 2. Current Status of Intelligent Sensor Development and Application Currently, intelligent sensor technology is experiencing rapid development. Representative products include Honeywell's ST-3000 series intelligent transmitters (USA) and Stellmann's two-dimensional accelerometers (Germany), as well as monolithic integrated pressure sensors with microprocessors (MCUs), intelligent sensors with multi-dimensional detection capabilities, and solid-state image sensors (SSIS). Meanwhile, the important role of novel intelligent sensors based on fuzzy theory and neural network technology in the research and development of intelligent sensor systems is increasingly attracting the attention of researchers. It is important to note that although current intelligent sensor systems are entirely digital, their communication protocols still rely on standard analog signals of 4–20 mA. Some international standardization research organizations are actively researching and developing relevant universal fieldbus digital signal transmission standards; however, in the current transitional phase, the Highway Addressable Remote Transducer (HART) protocol is still widely used. This is a communication protocol suitable for intelligent sensors, fully compatible with systems currently using 4-20mA analog signals. Analog and digital signals can communicate simultaneously, making products from different manufacturers universally compatible. Currently, intelligent sensors are mostly used for measuring pressure, force, vibration and shock acceleration, flow rate, temperature, and humidity. Examples include Honeywell's ST3000 series fully intelligent transmitters and Stellmann's two-dimensional accelerometer. In addition, intelligent sensors have also seen successful applications in space technology research. In future development, intelligent sensors will undoubtedly expand further into research fields such as chemistry, electromagnetics, optics, and nuclear physics. It is foreseeable that emerging intelligent sensors will play an increasingly important role in all areas related to the well-being of humankind. IV. Multifunction Sensors As mentioned earlier, a sensor typically can only detect one physical quantity. However, in many applications, to perfectly and accurately reflect objective phenomena and the environment, it is often necessary to measure a large number of physical quantities simultaneously. Multifunctional sensors composed of several sensitive elements are a new generation of detection systems that are small in size and have multiple functions. They can achieve the functions of multiple sensors simultaneously with a single sensor system by means of different physical structures or chemical substances in the sensitive elements and their different characterization methods. With the rapid development of sensor technology and microcomputer technology, it is now possible to produce integrated multifunctional sensors that integrate several sensitive elements on the same material or a single chip. 1. Execution rules and structural modes of multifunctional sensors In general, the main execution rules and structural modes of multifunctional sensor systems include: (1) Multifunctional sensor systems are composed of several different sensitive elements and can be used to measure multiple parameters simultaneously. For example, a temperature detector and a humidity detector can be configured together (that is, the thermal element and the humidity element are respectively configured on the same sensor carrier) to create a new sensor. In this way, this new sensor can measure temperature and humidity simultaneously. (2) Several different sensitive elements are ingeniously fabricated on a single silicon chip to form a highly integrated and miniaturized multifunctional sensor. Since these sensitive elements are integrated into the same silicon wafer, they always work under the same conditions, so it is easy to compensate and correct system errors. (3) Different information can be obtained by using different effects of the same sensor. For example, the capacitance and inductance of a coil are different. (4) Under different excitation conditions, the same sensitive element will exhibit different characteristics. When the excitation conditions such as voltage, current or temperature are different, the characteristics of a multifunctional sensor composed of several sensitive elements can be imagined to be very different! Sometimes it is just like several different sensors, and its multifunctional characteristics are truly well-deserved. 2. Current status of the development and application of multifunctional sensors Multifunctional sensors are undoubtedly a brand-new research direction in the current development of sensor technology. Many scholars are currently actively engaged in research in this field. For example, some types of sensors are appropriately combined to make them into new sensors, such as combined sensors used to measure fluid pressure and different pressures. For example, in order to detect multiple signals simultaneously with high sensitivity and small particle size, miniature digital three-port sensors can simultaneously use thermal elements, photosensitive elements and magnetic sensitive elements; such sensors can not only output analog signals, but also frequency signals and digital signals [7]. From the current development status, the most popular research area is probably various types of bionic sensors, and the latest research results have been published in the fields of touch, stimulation and audiovisual discrimination. From a practical point of view, the most widely used multifunctional sensors are various types of multifunctional tactile sensors, such as artificial skin tactile sensors. This sensor system is composed of PVDF material, non-contact skin sensitive system and rubber tactile sensor with pressure sensitive conduction function. It is reported that the non-contact skin sensitive system developed by MERRITT in the United States has achieved great success. Its non-contact ultrasonic sensor, infrared radiation guided sensor, thin film capacitive sensor, and temperature and gas sensors are widely used in the United States. Compared with other research results, the current research on artificial olfaction seems to be far from satisfactory. Since the discrimination signal received by the olfactory element is very complex, it is always mixed with thousands of chemical substances, which makes the olfactory system to process these signals extremely complicated. The typical product of artificial olfactory sensing system is the Electronic nose with different functions. In the past 10 years, the technology has developed rapidly, and several commercial products are now circulating in the international market. The United States, France, Germany, the United Kingdom and other countries have launched relatively advanced electronic nose products[8]. The "electronic nose" system usually consists of a cross-selection gas sensor array and related data processing technology, and is equipped with an appropriate pattern recognition system. It has the ability to identify simple and complex odors and is mainly used to solve the problem of odor detection in general situations. Depending on the application, the constituent materials and configuration number of sensors in the sensor array of the "electronic nose" system are also different. Among them, the constituent materials include metal oxide semiconductors, conductive polymers, quartz crystals, etc., and the configuration number ranges from a few to dozens. In summary, the "electronic nose" system is a high-tech product that effectively combines gas sensor technology and information processing technology. Its gas sensor is small in size and has low power consumption, and can easily capture and process odor signals. The airflow passes through the gas sensor array and enters the signal preprocessing element of the "electronic nose" system. Finally, the array response mode determines the characteristics of the gas being measured. The array response mode uses correlation method, least squares method, clustering method and main element analysis method to qualitatively and quantitatively identify the gas being measured. The Cyranose 320 electronic nose produced by Cyranosciences in the United States is one of the most advanced olfactory sensing systems with a wide range of applications. The system is mainly composed of two parts: sensor array and data analysis algorithm. Its basic technology is to configure several unique thin-film carbon-black polymer composite chemical resistors into a sensor array, and then use standard data analysis technology to identify unknown analytes by analyzing the output values ​​collected by the sensor array. It is said that the Cyranose 320 electronic nose is applicable to food and beverage production and preservation, environmental protection, chemical analysis and identification, disease diagnosis and pharmaceutical analysis, as well as industrial production process control and monitoring and management of consumer products [9]. V. Conclusion In summary, sensor systems at the current technological level are developing towards miniaturization, intelligence and multifunctionality. 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