In the era of the Internet of Things, sensors are one of the most critical components.
Generally, the Internet of Things (IoT) is structurally divided into three layers: the perception layer, the network layer, and the application layer. Among these, the perception layer plays a crucial role, serving as the data source for network layer transmission and the data foundation for application layer computation. A key component of the perception layer is various types of sensors.
Sensors can be categorized in various ways. For example, based on the non-electrical physical quantity being measured, they can be classified as pressure sensors and temperature sensors. Based on their operating method when converting non-electrical physical quantities into electrical physical quantities, they can be classified as energy conversion type (no additional energy input required during operation) and energy control type (requiring additional energy input during operation). Furthermore, they can be classified according to their manufacturing process, such as ceramic sensors and integrated sensors.
We start by examining various non-electrical physical quantities being measured, and then review the sensors commonly used in the Internet of Things (IoT) field.
Distance sensor
Distance sensors can be divided into two types based on the pulse signals they emit during distance measurement: optical and ultrasonic. Both operate on similar principles: they send pulse signals to the object being measured, receive the reflected signals, and then calculate the distance to the object based on the time difference, angle difference, and pulse velocity.
Distance sensors are widely used in mobile phones and various smart lighting products, and the products can react differently according to the different distances the user is at during use.
Light sensor
The working principle of a light sensor is based on the photoelectric effect, using a photosensitive material to convert the intensity of ambient light into an electrical signal. Depending on the type of photosensitive material, light sensors can be classified in various ways and have different sensitivities.
Light sensors are primarily used for monitoring ambient light intensity in electronic products. Data shows that in typical electronic products, the display consumes over 30% of the total power. Therefore, adjusting the screen brightness according to changes in ambient light intensity becomes a crucial energy-saving measure. Additionally, it can intelligently make the display effect softer and more comfortable.
Temperature sensor
Temperature sensors can be broadly classified into two categories based on their usage: contact and non-contact. The former involves the temperature sensor directly contacting the object being measured to sense changes in the object's temperature through a temperature-sensitive element, while the latter involves maintaining a certain distance between the temperature sensor and the object being measured to detect the intensity of infrared radiation emitted from the object and thus calculate the temperature.
Temperature sensors are mainly used in fields closely related to temperature, such as intelligent insulation and ambient temperature detection.
Smoke sensor
Smoke sensors are commonly classified into two types based on their detection principles: chemical detection and optical detection.
The former utilizes radioactive americium-241, which generates positive and negative ions in an ionized state. These ions move in a directed manner under the influence of an electric field, producing stable voltage and current. Once smoke enters the sensor, it affects the normal movement of the positive and negative ions, causing corresponding changes in voltage and current. The intensity of the smoke can then be determined through calculation.
The latter utilizes photosensitive materials. Under normal circumstances, light can fully illuminate the photosensitive material, generating stable voltage and current. However, if smoke enters the sensor, it will affect the normal illumination of light, resulting in fluctuating voltage and current. The intensity of the smoke can be determined through calculation.
Smoke sensors are mainly used in fire alarms and security detection.
Heart rhythm sensor
Commonly used heart rate sensors primarily utilize the principle of sensitivity to changes in blood flow using infrared light of specific wavelengths. The periodic beating of the heart causes regular changes in the flow rate and volume of blood in the measured blood vessel. After signal noise reduction and amplification, the current heart rate is calculated.
It's worth noting that, due to differences in skin tone, the intensity of infrared light emitted by the same heart rate sensor penetrating and reflecting off the skin varies, leading to some error in the measurement results. Generally, the darker a person's skin tone, the more difficult it is for infrared light to reflect back from blood vessels, thus having a greater impact on measurement error.
Currently, heart rhythm sensors are mainly used in various wearable devices and smart medical devices.
angular velocity sensor
An angular velocity sensor, sometimes called a gyroscope, is designed based on the principle of conservation of angular momentum. A typical angular velocity sensor consists of a rotatable rotor located at a central axis. The rotation of the rotor and the change in angular momentum indicate the direction of motion and relative position of an object. A single-axis angular velocity sensor can only measure changes in a single direction; therefore, a typical system requiring the measurement of changes in the X, Y, and Z axes needs three single-axis angular velocity sensors. Currently, a single commonly used 3-axis angular velocity sensor can replace three single-axis sensors, offering advantages such as smaller size, lighter weight, simpler structure, and higher reliability. Therefore, various forms of 3-axis angular velocity sensors represent the current major development trend.
The most common application of angular velocity sensors is in mobile phones. Popular mobile games like Need for Speed primarily use angular velocity sensors to generate the car's left-right swaying interaction mode. Besides mobile phones, angular velocity sensors are also widely used in navigation and positioning, as well as AR/VR fields.
Besides the sensors mentioned above, common sensors used in the Internet of Things (IoT) include barometric pressure sensors, accelerometers, humidity sensors, and fingerprint sensors. Although their working principles differ, the most basic principle is the same as mentioned above: converting the measured quantity into an electrical quantity through light waves, sound waves, special materials, and chemical principles. However, most of them are upgrades and extensions based on general principles for specific fields.
Since their invention in the Industrial Revolution, sensors have played a vital role in fields such as production control and measurement. Just like the human eye and ear, sensors, as a crucial front-end of the sensing layer in the Internet of Things (IoT), will experience a period of rapid development as the IoT becomes more widespread.
