If we compare an intelligent system to a “human,” then sensors are its “sensory organs.” Different types of sensors perceive the surrounding environment and transmit data to the system for calculation, enabling real-time analysis, judgment, and response to the situation. As digitalization and intelligence continue to advance, the applications of various sensors have greatly expanded, playing a huge role in creating a better life for humanity.

A single smartphone contains hundreds of sensors: CMOS image sensors for cameras, ambient light sensors to check lighting conditions, geomagnetic sensors and gyroscopes for navigation, and many more. It is precisely based on these sensors that various applications on the phone can function smoothly, allowing the smartphone to become a portable intelligent device integrating work, life, and entertainment, thus bringing about tremendous changes in people's lifestyles. The visible and infrared photoelectric sensors on Fengyun meteorological satellites can obtain atmospheric information around the clock, accurately predicting the weather. Sensors even work on the moon and Mars, helping humanity explore the mysteries of the universe.

Sharper and More Powerful Than Human Senses>

Sensors are the “sharp eyes” of information systems. Like human eyes, ears, and skin, they perceive the surrounding environment and help us understand the colorful world. The difference is that sensors are sharper and more powerful than human senses. The diversity of information contained in the objective world far exceeds the capabilities of our senses. Human eyes cannot observe infrared or ultraviolet radiation, ears cannot hear infrasound or ultrasound, and we cannot perceive magnetic fields that, while invisible, constantly affect us. Sensors can “feel” all this information that lies beyond the range of our senses.

With the development of productive forces, humanity has increasingly needed to perceive the world in all its aspects. In 1821, scientists developed the world’s first sensor—the temperature sensor—based on the principle that materials generate voltage due to temperature differences. Initially, people directly utilized various physical effects such as light, heat, electricity, force, and magnetism to create various sensors. These sensors were bulky, had low sensitivity, and were inconvenient to use. In the 1970s, integrated sensors emerged, which integrated sensing elements with signal circuits, such as thermocouple sensors, Hall sensors, and photosensitive sensors. These types of sensors are made of solid components like semiconductors, dielectrics, and magnetic materials and output analog signals. Since the end of the last century, digital sensors have developed rapidly, incorporating analog-to-digital conversion modules to achieve digital signal output. Digital sensors integrate intelligent processing units that can automatically collect and process data and adjust working parameters autonomously based on the environment; the photosensitive element in a digital camera is a representative product of this type.

Generally speaking, the working principle of sensors is that the electrical properties of certain materials change with environmental factors. For example, the resistivity of platinum varies with temperature, the resistance of silicon decreases when exposed to visible light, and the surface of quartz generates an electric charge when subjected to pressure. By utilizing the relationship between resistance and temperature, a temperature sensor can be made. Furthermore, by adding a thermal insulation structure to the sensing element, an infrared sensor can be made based on the relationship between the temperature change of the sensing element and the infrared radiation energy. Building on this, non-contact temperature measurement sensors can be created based on the relationship between target temperature and infrared radiation energy. The forehead thermometers people commonly use to measure body temperature utilize this principle. Leveraging rich physical and chemical effects, people have developed a wide variety of powerful sensors, such as an “electronic nose” that is 1,000 times more sensitive than a dog’s nose and can “smell” gas molecules, and infrared cameras that can observe objects in the dark.

No Sensors, No Digitalization or Intelligence

Digitalization is the quantification of attributes of things, expressed as abstract results using numbers. With modern information technology, people can store, process, and disseminate various types of digital information. Sensors can convert various kinds of information contained in things into electrical signals and use analog-to-digital conversion circuits to express these electrical signals as numbers, making them effective tools for digitalization. When you take a photo or video with your phone, the photosensitive sensor converts the received light intensity signal into an electrical signal, which is then expressed and stored as numbers according to specific rules, ultimately forming the image on the phone screen.

Digitalization relies on sensors to acquire information. The amount of information that digital systems need to process is immense, which cannot be obtained by manual means or traditional equipment alone. Sensors enable real-time, efficient, accurate, and rapid acquisition of this information, leading to the emergence of urban big data, weather big data, medical big data, agricultural big data, and more. Using various sensors, people can hold remote meetings, take online courses, make scan-to-pay payments, and even engage in live-streaming e-commerce, thus developing the digital economy. Various technologies involved in the digital economy, including cloud computing, the Internet of Things, artificial intelligence, and 5G communication, are closely related to sensors.

Without sensors, there would be no digitalization or intelligence. Sensors are the first step in an intelligent system; their level determines the capability of the intelligent system and its instruments and equipment. Sensor technology has become a research frontier in the field of high-end information devices internationally, playing an irreplaceable role in areas such as artificial intelligence, smart cities, 5G communication, aerospace, and life sciences. For example, a car may be equipped with over 100 sensors—including pressure, temperature, position, sound, light, and electricity sensors—whose data is processed by the onboard computer to assist the driver in making judgments. Intelligent analysis of data reduces the difficulty of driving, making cars safer and easier to handle. Going further, autonomous vehicles use sensors to acquire real-time road information; once an obstacle is detected, the vehicle intelligently analyzes the situation and avoids it in a timely manner. Buildings in cities, such as skyscrapers, bridges, and tunnels, also need their safety status monitored in real time through video, temperature, pressure, and smoke sensors. When the data is aggregated, the intelligent system analyzes it promptly and distills a small amount of key information for users to make decisions. Even in the future, human senses could become more powerful with the help of sensors, building intelligent systems.

Intelligent Sensors Opening Up New Application Scenarios

Currently, various types of sensors are moving in directions such as further performance improvement, cost reduction, and evolution towards digitalization, intelligence, miniaturization/micro-sizing, green and low-carbon operation, and wearability, showing vigorous development momentum. Among these, the development of intelligent sensors, flexible sensors, and sensors based on new principles is particularly representative and is expected to shape new ways of working and living.

Developing intelligent sensors is an important trend. Using intelligent sensing technology, people design and manufacture various sensing units and microsystems capable of acquiring, storing, and analyzing information, achieving low-cost, high-precision data acquisition. Intelligent sensors are widely used in robotics, autonomous driving, smart manufacturing, motion quantification monitoring, and also in developing non-invasive or minimally invasive health monitoring devices. The popular continuous glucose monitor is a good example. Diabetic patients painlessly insert a flexible sensor into their body. The sensor measures blood glucose levels every five minutes and transmits the data to a mobile application. Patients can observe the glucose curve and adjust their blood sugar promptly through diet and exercise; some patients have even been able to discontinue medication and insulin therapy as a result. Furthermore, researchers are developing degradable electronic devices, allowing intelligent sensors to better contribute to a low-carbon and environmentally friendly life.

Developing flexible sensors is another trend. Many application scenarios require sensors to be fabricated on flexible substrate materials, possessing characteristics such as transparency, flexibility, stretchability, the ability to be freely bent or even folded, portability, and wearability. Common sensing materials for fabricating flexible sensors currently include carbon-based materials (carbon black, carbon nanotubes, graphene, etc.), metal nanomaterials (metal nanowires, metal nanoparticles, etc.), polymer polymers, and protein fibers. For example, a cross-linked supramolecular polymer film electrode material that is stretchable, tear-resistant, and self-healing can be used to manufacture next-generation wearable and implantable flexible electronic devices. Integrating multifunctional flexible sensors with flexible printed circuits can create “smart bands.” When worn on different parts of the body, these bands can monitor and analyze physiological information in real time, helping people, especially those with diminished senses, understand their own health status.

Sensors based on new principles are also continuously emerging. In the field of basic research, new laws are being discovered, and people are using these new scientific insights to create sensors. At the same time, technological progress also places new demands on basic research. In daily life, people want to improve performance parameters of cameras such as pixel count, sensitivity, and speed. In high-speed experiments, streak cameras capable of recording information on the femtosecond scale are needed. In quantum communication, photodetectors with sensitivity down to the single-photon level are required. In aerospace technology, the detection of high-speed moving objects and cold targets is necessary. These demands require scientists to further explore the physical world, discover new phenomena and laws, and enhance sensor performance.

With the rapid development of technology, new materials and new processes are continuously being applied. Sensors with stronger performance, richer varieties, and higher levels of intelligence will create more new scenarios for work and life, helping people “sense” a better life./