27 Oct, 2022 / BY Neil Sharp

MEMS sensors are (literally) driving the electric vehicles industry

MEMS sensors are essential components in the majority of vehicles we drive today. They reduce fuel consumption, improve vehicle safety, and provide the driver with greater comfort. 

However, electric vehicles are far more high-tech than petrol and diesel vehicles. This is because they are run by computing and electronics; the central processor operates the battery, the electric motors, brakes, and lights, in addition to vehicle infotainment systems and driver comfort systems. Although there are currently no completely autonomous vehicles on our roads, more EVs are being designed with autonomous driving systems. And as human drivers cede control to electronic systems, MEMS sensors are becoming even more essential. 

The benefits of tiny MEMS sensors over standard sensors

  • Shorter electrical distances translate into faster response times
  • Significantly lower cost of manufacture through using integrated circuits
  • Lower power consumption
  • More reliable, better performance, more precise

What types of MEMS sensors are in EVs?

When MEMS sensors detect and measure changes in environmental conditions such as pressure and acceleration, they respond by sending electrical signals that controllers use as input.

The most common types of MEMS sensors in electric vehicles include:

Inertial sensors are the most frequently used sensors in the EV industry. They are used in many critical applications, including accelerometers and gyroscopes. MEMS accelerometers generally function based on one of two principles: movement of a mass or the piezoelectric effect. They can measure either static (gravity) or dynamic (motion or vibration) acceleration. MEMS gyroscopes use vibrating objects and identify the change of angles. 

  • Use in EVs: Inertial sensors are used in today’s advanced driver assistance systems: for example, in vehicles’ rollover safety features. A MEMS gyroscope detects the rotation of a rolling vehicle around the x-axis, which is the main variable used in the crash detection algorithm.
  • Use in autonomous vehicles: In autonomous driving, the vehicle must answer the questions: “Where am I?”, “Where do I want to go?”, and “How will I achieve that?” Navigation systems that use inertial sensors establish a car’s change in position by measuring accelerations and rotations. The system uses global navigation satellite system readings, landmark navigation, or simultaneous localisation and mapping to determine the absolute position and then calculates new positions based on data gathered by the inertial sensor.

Optical MEMS (also known as MOEMS) integrates sensors and actuators on circuitry, which allows them to be aware of their surroundings and perform physical tasks. Lens arrays and microscopic mirrors in MOEMS gather and direct light. However, light intensity is either detected with photodiodes (that create an electrical current or photoresistors (the electrical resistance of which changes when exposed to light).

  • Use in EVs: Optical MEMS, especially micro-mirrors, play a key role in steering laser beams and gathering reflected light to trigger driverless solutions.  
  • Use in EVs: MOEMS devices are used for head-up displays, providing drivers with information and directions without having to take their eyes off the road. The sensors are also used in smart adaptive headlights, which direct their beam where it is needed (around a corner, for example, rather than straight ahead). 

MEMS pressure sensors convert pressure signals into electrical signals via small strain gauges, called piezoresistors, in a thin silicon diaphragm. One side of the diaphragm captures a fixed reference pressure, while the other side is measured as it is exposed to the environment. The change in electrical resistance in the diaphragm measures the effect on the diaphragm due to mechanical strain.

  • Use in EVs: Today’s electric cars are equipped with airbags in the sides of the car as well as in the dashboard to protect passengers from an impact on every side. If the car receives a side impact, the sudden change in pressure in the door cavity is detected using a relative pressure sensor, which deploys the airbag in just over a millisecond. 
  • Use in EVs and autonomous vehicles: Pressure sensors are used to measure the pressure inside Li-ion batteries. If there is a rise in temperature inside the battery pack, the pressure will increase, generating a pressure pulse. This can then trigger the vehicle safety system to warn occupants of a fire and, potentially, activate a fire extinguisher inside the EV.

A magnetometer measures the strength and direction of magnetic fields, including those on or near the Earth and in space. A MEMS sensor generally relies on Lorentz force, which is the combination of electric and magnetic force on a point charge due to electromagnetic fields. It is possible to determine the electrical structure's mechanical deflection proportional to the field's strength, either electronically or optically.

  • Use in traffic management: Wireless vehicle detection systems use magnetometers placed inside the road to detect vehicles. The sensors transmit real-time messages to a traffic management centre.

Thermal sensors measure temperatures. MEMS generally do this by using a resistance temperature detector. These detect any changes in the electrical resistance of a thin layer of material when there has been a change in temperature.

  • Use in an EV: The temperature of each subsystem in EVs must be monitored. For example, battery management systems need accurate temperature monitoring measurements on a cell level, particularly when used in extreme heat conditions. Thermal sensors measure temperature, and this data helps to run the cooling system in a controlled manner when necessary. 

MEMS sensors are driving the market, not just the cars

There is a clear push toward electric vehicles from an environmental perspective; however, governments and consumers are also championing EVs because of their increased use of MEMS sensors and their advanced safety features. 

Tesla has set a high bar with its electric vehicles in terms of comfort, performance, and use of technology. Consumers are now demanding vehicles with advanced technological features requiring more than 100 MEMS sensors in every car. 

Moreover, original equipment manufacturing companies (OEMs) are incorporating a variety of sensors into their cars to meet client performance expectations for better productivity and reduced vehicle downtime. The demand for enhanced sensing techniques is rising in response to the growing desire for driver-assistance technologies that improve comfort and safety.

Additionally, adding more electronic components to cars helps sensors to be integrated since these components are crucial to EV electronic systems, battery management systems, and EV transmission systems.

The market anticipates the rise in EV production, technological advancements, regulations, and shifting consumer tastes will increase demand for automotive sensors.

Conclusion

MEMS and MOEM sensors have been used in vehicles for a while, but the more high-tech electric vehicles become, the more sensors they need. MEMS are small, low-cost, reliable, and quick. They improve the driver experience and make the vehicle safer. Also, vehicles fitted with more advanced autonomous driver technology will further increase the demand for MEMS. These tiny sensors are revolutionising transport—driving the cars and the market. 

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