MEMS sensors are a cutting-edge, interdisciplinary research field developed based on microelectronics technology. After more than forty years of development, it has become one of the world's most prominent scientific and technological fields. It involves multiple disciplines and technologies such as electronics, mechanics, materials science, physics, chemistry, biology, and medicine, and has broad application prospects.
Medical
MEMS sensors are used in non-invasive fetal heart rate detection. Detecting fetal heart rate is a highly technical task. Because the fetal heart rate is very fast, between 120 and 160 beats per minute, it is difficult to measure accurately using traditional stethoscopes or even ultrasound Doppler instruments that only have amplification function, and manual counting.
While digital display ultrasound Doppler fetal heart monitors are expensive and used only in a few large hospitals, they are not widely available in small and medium-sized hospitals or rural areas. Furthermore, the ultrasound vibrations can have significant adverse effects on the fetus. Although the detection dose is very low, it still falls under the category of invasive detection and is unsuitable for frequent, repetitive examinations or home use.
Based on VTI's MEMS accelerometer, a non-invasive fetal heart rate detection method is proposed, and a simple, easy-to-learn, intuitive, and accurate medical auxiliary instrument for clinical diagnosis and pregnant women's self-examination is developed, falling between a fetal heart stethoscope and a Doppler fetal monitor. The accelerometer converts the fetal heart rate into an analog voltage signal, which is then amplified differentially by an instrumentation amplifier. A series of intermediate signal processing steps, including filtering, are then performed, and an A/D converter converts the analog voltage signal into a digital signal. This digital signal is then input to a microcontroller through an optical isolator for analysis and processing, and finally, the processing result is output.
With appropriate modifications, a fetal heart rate monitor based on a MEMS accelerometer can be used as a terminal to create a remote fetal heart rate monitoring system. The central signal acquisition, analysis, and monitoring host at the hospital provides automatic analysis results, which doctors then diagnose. If any problems are found, the pregnant woman is promptly notified to come to the hospital. This technology allows pregnant women to monitor the fetus's condition at any time, benefiting both the fetus and the mother's health.
Automotive electronics
MEMS pressure sensors are mainly used to measure airbag pressure, fuel pressure, engine oil pressure, intake manifold pressure, and tire pressure. These sensors use single-crystal silicon as the material, employing MEMS technology to fabricate a force-sensitive diaphragm within the material. Impurities are then diffused onto the diaphragm to form four strain gauges, which are then connected in a Wheatstone bridge configuration to achieve high sensitivity.
Automotive MEMS pressure sensors come in several common forms, including capacitive, piezoresistive, differential transformer, and surface acoustic wave types.
"MEMS accelerometers are based on Newton's classical laws of mechanics and typically consist of a suspension system and a sensing mass. Acceleration is detected by the displacement of a micro-silicon mass. They are mainly used in automotive airbag systems, anti-skid systems, car navigation systems, and anti-theft systems. Besides capacitive and piezoresistive types, MEMS accelerometers also come in piezoelectric, tunneling current, resonant, and thermocouple forms. Among these, capacitive MEMS accelerometers are the mainstream product due to their high sensitivity and minimal temperature sensitivity."
A micro gyroscope is an angular rate sensor primarily used for GPS signal compensation in automotive navigation and in automotive chassis control systems. It comes in several types, including vibrating and rotor types. The most widely used is the vibrating gyroscope, which utilizes the Coriolis effect generated when a vibrating mass of single-crystal or polycrystalline silicon is rotated by a base to sense angular velocity.
For example, when a car is turning, the system uses a gyroscope to measure the angular velocity to indicate whether the steering wheel has turned to the correct position, and actively applies appropriate braking to the inner or outer wheels to prevent the car from leaving the lane. Usually, it together with a low-accelerometer constitutes an active control system.
Motion tracking system
In athletes' daily training, MEMS sensors can be used for 3D human motion measurement, recording every movement. Coaches analyze and compare the results repeatedly to improve athletes' performance. As MEMS technology further develops, the price of MEMS sensors will decrease, making them widely applicable in gyms.
"In skiing, pressure sensors, accelerometers, gyroscopes, and GPS in 3D motion tracking can give users extremely accurate observation capabilities. In addition to providing data on the movement of the skis, it can also record the user's position and distance."
The same applies to surfing. 3D motion tracking installed on surfboards can record information such as wave height, speed, surfing time, paddleboard distance, water temperature, and calories burned.
Mobile phone photography field
Before the advent of MEMSDrive, mobile phone cameras mainly achieved image stabilization by moving the lens assembly with a voice coil motor (referred to as lens stabilization technology), which was very limited. Another higher-end image stabilization technology on the market, multi-axis image stabilization, uses a moving image sensor to compensate for shake, but because this technology is bulky and consumes more power than the phone's capacity, it has not been able to be applied to mobile phones.
"Thanks to breakthroughs in size and power consumption of microelectromechanical systems (MEMS), the latest MEMSDrive technology resembles a planar motor attached to the back of the image sensor, driving the image sensor to move along three rotational axes. MEMSDrive's image stabilization technology uses a gyroscope to sense instantaneous shaking during the shooting process, and relies on precise algorithms to calculate the magnitude of the motor's movement and make rapid compensation. This series of actions must be completed within one-hundredth of a second so that the image you get will not be blurred due to shaking."
Currently, there are approximately 600 companies worldwide engaged in the research and development and production of MEMS, and they have developed hundreds of products, including miniature pressure sensors, accelerometers, micro-inkjet printheads, and digital micromirror displays, among which MEMS sensors account for a considerable proportion.
MEMS sensors are a new type of sensor manufactured using microelectronics and micromachining technologies. Compared with traditional sensors, they are characterized by small size, light weight, low cost, low power consumption, high reliability, suitability for mass production, ease of integration, and the ability to achieve intelligent operation. Furthermore, their micrometer-scale feature size allows them to perform functions that are impossible with traditional mechanical sensors.
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