With the rapid development of science and technology, various advanced technologies and equipment are constantly emerging, bringing great convenience to our lives and work. Among the many scientific and technological concepts, IMU (Inertial Measurement Unit) and MEMS (Micro Electro Mechanical System) often appear in people’s vision. They play a key role in many fields such as aerospace, autonomous driving, and smart wearables. But for many people, the difference between the two is not very clear. Next, let us delve into the mysteries of IMU and MEMS and unveil their mysterious veil.
What is IMU?
IMU, or Inertial Measurement Unit, is an important device that can accurately measure the three-axis attitude angle (or angular rate) and acceleration of an object. It is like a keen perceiver, capturing the motion state information of an object in three-dimensional space in real time. Its working principle is based on Newton’s laws of motion and the law of conservation of angular momentum, and the measurement of the object’s motion parameters is achieved through the internally integrated accelerometer and gyroscope. The accelerometer is like a sensitive balance, which can detect the acceleration signals of the object in the three independent axes of the carrier coordinate system, so that we can know how fast the speed of the object changes in all directions; while the gyroscope is like a precise compass, which is used to measure the angular velocity signal of the carrier relative to the navigation coordinate system, helping us determine the speed and direction of the object’s rotation. With these measurement data, the IMU can accurately calculate the posture of the object in space, providing vital basic information for subsequent motion control and navigation.
In practical applications, most IMUs contain three accelerometers and three single-degree-of-freedom gyroscopes, which are carefully installed on three orthogonal sensitive axes. This ingenious layout enables the IMU to perceive the motion state of the object in an all-around and high-precision manner. For example, in the field of aerospace, IMU is the core component of the aircraft navigation and control system. It is like the “brain” of the aircraft, sensing the attitude and acceleration changes of the aircraft at all times, providing accurate flight information to the pilot, and ensuring that the aircraft flies safely and stably in the vast sky. For example, in self-driving cars, IMU works closely with other sensors, like the “eyes” and “ears” of the car, monitoring the driving status of the vehicle in real time, assisting the vehicle to achieve accurate navigation and stable driving control, and escorting people’s travel.
What is MEMS?
MEMS, or Micro-Electro-Mechanical System, is a micro device or system that integrates a variety of advanced technologies and can be called a masterpiece of modern science and technology. Its size is usually a few millimeters or even smaller, and its internal structure is as fine as microns or even nanometers, like a precision instrument in a microscopic world. MEMS integrates multiple functions such as micro sensors, micro actuators, micro mechanical structures, micro power sources, micro energy, signal processing and control circuits, high-performance electronic integrated devices, interfaces, communications, etc. It is a highly integrated, independent intelligent system.
The birth of MEMS is inseparable from the cross-integration and collaborative innovation of many disciplines such as physics, semiconductors, optics, electronic engineering, chemistry, materials engineering, mechanical engineering, medicine, information engineering, and bioengineering. It uses silicon as the main structural material, and also cleverly uses silicide, metal, alloy, and some polymer materials. Through a series of complex and sophisticated technologies such as lithography, corrosion, thin film, LIGA, silicon micromachining, non-silicon micromachining, and precision machining, it perfectly integrates tiny mechanical structures and electronic components on a tiny chip, creating micro devices with various unique functions.
MEMS sensors are of various types, which can be roughly divided into three categories according to their working principles: physical, chemical, and biological. According to their technical principles, they can be further divided into four categories: sensing MEMS, biological MEMS, optical MEMS, and radio frequency MEMS. Common MEMS products are dazzling, including MEMS accelerometers, MEMS microphones, micromotors, micropumps, microvibrators, MEMS optical sensors, MEMS pressure sensors, MEMS humidity sensors, MEMS gas sensors, etc., and their integrated products. These small and exquisite MEMS devices play an indispensable and important role in many fields such as consumer electronics, medical, automotive, industrial automation, and environmental monitoring, with their many advantages such as small size, light weight, low power consumption, high reliability, low cost, and mass production. For example, in smartphones, MEMS accelerometers and gyroscopes allow us to experience a variety of somatosensory games, adding endless fun to our lives; in the medical field, MEMS sensors can be used for medical monitoring and diagnosis, such as blood sugar monitoring, heart rate monitoring, etc., to provide doctors with accurate disease data and help patients better manage their health.
Technical Principle Analysis
- MEMS Technical Principle
The core technology of MEMS is to use microelectronics and micromachining technology to integrate microsensors, microactuators, micromechanical structures, and signal processing and control circuits on a tiny chip. Take a MEMS accelerometer as an example. It usually contains a movable mass block and an elastic support structure. When there is acceleration, the mass block will produce displacement under the action of inertia. By detecting the change of capacitance, resistance, or piezoelectric effect between the mass block and the fixed electrode, the acceleration can be converted into an electrical signal output. Another example is a MEMS microphone, which uses film vibration to convert sound signals into electrical signals. The film and the back plate form a capacitor structure. The sound causes the film to vibrate, which in turn changes the capacitance value and realizes sound-to-electric conversion. - IMU technical principle
IMU mainly uses accelerometers and gyroscopes to measure the acceleration and angular velocity of an object, and then calculates the object’s posture, velocity, displacement, and other information. Based on Newton’s second law, the accelerometer measures acceleration by detecting the force generated by the mass block under the action of acceleration; the gyroscope uses the principle of conservation of angular momentum to measure angular velocity by detecting the change of angular momentum of the rotating part. In practical applications, IMU usually fuse the data of accelerometers and gyroscopes. For example, when calculating the attitude of an object, the gyroscope can respond quickly to angle changes, but there is a drift error; the accelerometer can provide relatively accurate information on the direction of gravity, but it is easily disturbed by external vibration. Through complementary filtering, Kalman filtering, and other algorithms, the advantages of both can be combined to obtain more accurate attitude estimation. - Comparative differences
From the basic principle level, MEMS focuses on the construction of micro-electromechanical systems, and senses physical quantities through various sensitive components and converts them into electrical signals. It covers a wide range, including various types of sensors and actuators, while IMU focuses on the measurement of inertial physical quantities. The core is to use accelerometers and gyroscopes to obtain the motion information of objects, which is mainly used to determine the attitude and motion state of objects. MEMS technology is an important means to achieve the miniaturization and integration of IMU. Many IMUs are manufactured based on MEMS technology, but MEMS is not limited to the IMU field; but also has a wide range of applications in many other fields.
The structural composition is very different
- Structural characteristics of MEMS
MEMS is usually composed of multiple parts, such as micro-electromechanical sensors, micro-electromechanical actuators, micro-mechanical structures, signal processing, and control circuits. Taking the common MEMS accelerometer as an example, it generally contains a movable mass block, an elastic support structure, and a capacitor plate or piezoresistive element for detecting the displacement of the mass block. The mass block is suspended inside the chip through an elastic support structure. When there is acceleration, the mass block will be displaced due to inertia, thereby changing the distance between the capacitor plates or the resistance value of the piezoresistive element to detect acceleration. Another example is a MEMS microphone, which is mainly composed of a vibration membrane, a back plate, and a support structure. The vibration membrane and the back plate form a capacitor structure. The sound causes the vibration membrane to vibrate, causing the capacitance value to change, thereby converting the sound signal into an electrical signal. In addition, MEMS may also integrate microprocessors, communication interfaces, etc. to achieve more complex functions and data transmission. - Structural components of IMU
IMU generally includes a three-axis accelerometer and a three-axis gyroscope. Some high-end IMUs also integrate components such as a three-axis magnetometer. The three-axis accelerometer is used to measure the acceleration of an object in three orthogonal directions. It is based on Newton’s second law and measures the force generated by the mass block under the action of acceleration. The three-axis gyroscope is used to measure the angular velocity of an object around three orthogonal axes. It uses the principle of conservation of angular momentum to obtain angular velocity information by detecting the change in angular momentum of the rotating parts. The three-axis magnetometer is used to measure the strength of the geomagnetic field to help determine the heading angle of the object. These sensors work closely together to transmit the measured acceleration, angular velocity, magnetic field strength, and other data to the microprocessor. After data fusion and processing, the object’s attitude, velocity, displacement, and other information are calculated. - Comparison of structural differences
From a structural point of view, MEMS has diverse structures because it covers many different types of sensors and actuators. Each MEMS device has its unique structural design to meet specific functional requirements. Its structural design and manufacturing process vary depending on the application scenario and are very flexible. The structure of IMU is relatively fixed, mainly focusing on the core needs of inertial measurement, with three-axis accelerometers and three-axis gyroscopes as basic components, and some adding three-axis magnetometers. This relatively fixed structure enables it to focus on inertial measurement and provide stable and reliable data support for the object’s motion state monitoring.
A review of application fields
Wide application of MEMS
- MEMS has shown strong application potential in many fields with its unique advantages. In the medical field, MEMS accelerometers are innovatively used for non-invasive fetal heart rate detection. Traditional fetal heart rate detection methods have many limitations, such as inaccurate stethoscope counting and expensive and potentially risky ultrasonic Doppler fetal heart rate monitors. The non-invasive fetal heart rate detection method based on MEMS accelerometers has brought breakthroughs. It can convert the fetal heart rate into an analog voltage signal, and after a series of precise signal processing, it finally outputs accurate measurement results, providing pregnant women with a simple, intuitive, and safe self-examination method.
- In the automotive field, MEMS sensors are ubiquitous and play a vital role. MEMS pressure sensors are widely used in many key parts, such as TPMS pressure sensors that monitor tire pressure in real time to ensure driving safety; intake manifold pressure sensors accurately measure the absolute pressure changes in the intake manifold according to the engine load state, and convert them into voltage signals, which together with the speed signal provide the engine electronic control unit with the key basis for determining the basic injection amount of the injector, effectively improving the engine power performance, reducing fuel consumption and reducing exhaust emissions; engine oil pressure sensors can accurately measure oil pressure to ensure the normal operation of engine lubrication, cooling and other functions, and their reliability is directly related to the safety of the car and the driver. In addition, MEMS accelerometers and gyroscopes also play an important role in the anti-lock braking system (ABS), electronic stability program (ESP), and other safety systems of automobiles, helping vehicles to maintain stability during driving and prevent accidents.
- In the field of communications, MEMS optical switches and modulators are key components for the efficient processing and transmission of optical signals. MEMS optical switches can achieve functions such as fast switching, modulation, and filtering of optical paths through the clever movement of micromechanical structures. They have significant advantages such as small size, low power consumption, and fast response speed. They are widely used in optical communication networks to achieve core functions such as switching, routing and cross-connection of optical signals, greatly improving the flexibility and reliability of communication systems; MEMS modulators precisely modulate the phase, amplitude, polarization and other characteristics of optical signals by changing the length or refractive index of the optical path. They are an indispensable and important part of optical communication, optical signal processing, and other fields.
Key application scenarios of IMU
- IMU plays a core role in fields with extremely high requirements for motion and attitude perception. In the field of aerospace, it is the absolute core of aircraft navigation and control systems, providing aircraft with accurate attitude, speed, and position information to ensure that aircraft can fly safely and stably in complex flight environments. Whether it is an aircraft cruising in the atmosphere or a satellite orbiting in the vast universe, IMU monitors and corrects the impact of various factors on the flight status in real time, allowing the aircraft to accurately fly according to the predetermined route and complete various complex tasks.
- In the field of drones, IMU also plays an irreplaceable role. It can realize key functions such as automatic hovering, route planning, and precise attitude control of drones. When a drone performs tasks in the air, IMU is like its “brain”, sensing its own motion state and attitude changes at all times, and adjusting flight parameters in time according to this information to ensure that the drone can fly stably and complete various tasks such as aerial photography, logistics distribution, and mapping.
- In the field of autonomous vehicles, IMU works closely with other sensors such as lidar and cameras to provide vehicles with accurate positioning and attitude information. In complex and changing traffic environments, IMU can help autonomous vehicles maintain a stable driving state and respond to various emergencies in a timely and accurate manner, such as avoiding obstacles and emergency braking, providing solid protection for passengers’ travel safety.
- In the field of robots, especially industrial robots, IMU provides key data support for their motion control and navigation. With the help of IMU, robots can accurately sense their own motion state and position, thereby realizing complex functions such as autonomous walking and flexible obstacle avoidance. On industrial production lines, high-precision IMUs can ensure that robots can accurately complete various operational tasks, improving production efficiency and product quality.
In-depth discussion of advantages and disadvantages
Advantages and limitations of MEMS
MEMS technology has shown significant advantages in many fields due to its unique characteristics. First, MEMS devices are ultra-small and extremely light, making them easy to integrate into various miniaturized devices, providing strong support for the lightweight and portable development of modern electronic products. For example, in smartphones, the tiny size of MEMS accelerometers and gyroscopes enables them to be cleverly integrated into the small space of the mobile phone, bringing users a rich somatosensory interactive experience, such as automatic screen rotation, step counting, and other functions. Secondly, MEMS devices have extremely low power consumption, which greatly extends the battery life of battery-powered devices. Taking smart watches as an example, the low power consumption characteristics of MEMS sensors enable watches to continuously monitor users’ exercise, heart rate, and other data for a long time without frequent charging, providing great convenience for users. In addition, MEMS devices also have the advantage of fast response speed and can quickly sense and respond to changes in external physical quantities. In the airbag triggering system of a car, the MEMS accelerometer can detect the collision signal of the vehicle in a very short time, trigger the airbag in time, and effectively protect the life safety of the driver and passengers.
However, MEMS also has some limitations. Due to its tiny structure, the anti-interference ability of MEMS devices is relatively weak when facing a complex working environment. In a strong electromagnetic interference environment, the measurement accuracy of MEMS sensors may be seriously affected, resulting in deviations in the output data. In addition, the accuracy of MEMS sensors is still somewhat different from that of traditional sensors. In fields such as industrial measurement and scientific research that require extremely high measurement accuracy, MEMS sensors may not be able to meet the needs. At the same time, the manufacturing process of MEMS devices is complex and has strict requirements on the production environment and equipment, which also increases the production cost to a certain extent, limiting its wide application in some cost-sensitive application scenarios.
Strengths and weaknesses of IMU
IMU plays an irreplaceable and important role in the field of inertial measurement, and its strengths are very prominent. IMU can provide high-frequency measurement data, which makes it perform well in applications with extremely high requirements for detecting changes in motion state. During the flight of the drone, the IMU can sense the attitude changes of the drone in real time and quickly provide accurate attitude information for the flight control system, ensuring that the drone can fly stably and flexibly. IMU has strong autonomy. It can independently measure the motion state of an object without relying on external reference signals. In the case where the satellite navigation signal is blocked or interfered with, such as in urban canyons and indoor environments, the IMU can rely on its inertial measurement function to continuously provide reliable position and attitude information for the device to ensure the continuity of navigation and positioning. However, IMU is not perfect. Over time, the measurement error of the IMU will gradually accumulate, which is its most obvious shortcoming. In long-term navigation applications, such as submarine long-distance missions, the error of the IMU will continue to increase with the increase of navigation time, resulting in large deviations in the final positioning and attitude information, which requires regular calibration and correction. In addition, high-precision IMUs are often expensive, which makes their application costly and limits their popularity in some cost-sensitive markets. In consumer electronic products, due to cost constraints, relatively low-precision IMUs are usually selected to balance the relationship between performance and cost.
Comparative summary
Through an in-depth analysis of the advantages and disadvantages of MEMS and IMU, it can be seen that both have their advantages and disadvantages in different application scenarios. In consumer electronics, the Internet of Things and other fields with strict requirements on cost, volume, and power consumption, and relatively low requirements on measurement accuracy, MEMS has become the preferred technology with its advantages of miniaturization, low power consumption, and low cost. For example, in products such as smart bracelets and smart home devices, MEMS sensors can achieve basic motion monitoring, environmental perception, and other functions at a low cost, meeting consumers’ demand for product cost-effectiveness. In aerospace, autonomous driving, industrial robots, and other fields with extremely high requirements on measurement accuracy, real-time, and autonomy, IMU plays an irreplaceable and key role with its high-precision measurement capabilities, fast response speed, and strong autonomy. In the field of aerospace, the safe flight and mission execution of aircraft rely on the high-precision attitude and position information provided by IMU; in the field of autonomous driving, the collaborative work of IMU and other sensors provides a reliable guarantee for the safe driving of vehicles. Therefore, in practical applications, the advantages and disadvantages of MEMS and IMU should be comprehensively considered according to specific needs and scenarios, and the most suitable technology or equipment should be selected to achieve the best performance and benefits.
In summary, there are obvious differences between IMU and MEMS in many aspects. In terms of technical principles, MEMS covers the sensing and conversion of various physical quantities, and IMU focuses on the measurement of inertial physical quantities; in terms of structural composition, MEMS is diverse and flexible, and IMU is relatively fixed; in terms of application fields, MEMS is widely distributed, and IMU focuses on fields with high requirements for motion and attitude perception accuracy; in terms of advantages and disadvantages, MEMS has the advantages of miniaturization, low power consumption, and low cost, but its accuracy and anti-interference ability are weak, and IMU has high measurement accuracy and strong autonomy, but there are problems of error accumulation and high cost. Understanding these differences will help various industries make more appropriate decisions when choosing technologies and equipment, promote the optimized application and innovative development of related technologies in different scenarios, and provide strong support for scientific and technological progress and industrial upgrading.
