What Is a MEMS Contactless Thermal Sensor?
MEMS (Micro Electro Mechanical System) is an ultra-compact system that incorporates mechanical components, sensors, actuators, and electronic circuits on a single substrate and is manufactured by applying semiconductor microfabrication technology.
While LSI integrates electronic circuits on a flat surface, MEMS integrates mechanical mechanisms in addition to electronic circuits on a wafer to form a three-dimensional shape or movable structure of a wafer.
The MEMS contactless thermal sensor is a temperature sensor based on this MEMS technology. The thermopile element receives radiant heat energy from the object to be measured, and the surface temperature of the object can be measured in a non-contact manner.
Uses of MEMS Contactless Thermal Sensors
Since MEMS contactless thermal sensors can measure surface temperatures without touching the object, they are used for monitoring abnormal temperatures in transformers and distribution boards, detecting temperatures in energy-saving home appliances, security equipment such as motion sensors, and screening for persons generating heat during room entry control.
In addition, the MEMS contactless thermal sensors take advantage of the features of MEMS to achieve miniaturization and low power consumption and can be used in various fields such as HEMS (Home Energy Management System), BEMS (Building Energy Management System), and FEMS (Factory Energy Management System) for energy reduction and optimal control of facilities.
Principle of MEMS Contactless Thermal Sensors
Typical MEMS contactless thermal sensors consist of a silicon lens, thermopile element, and IC for signal conversion mounted on a small substrate.
Far-infrared rays emitted from the object are focused onto the thermopile element by the silicon lens, and the thermopile element generates a thermoelectromotive force proportional to the incident energy of the far-infrared rays using the Seebeck effect.
The Seebeck effect is an effect in which an electromotive force is generated between two ends of a material when a temperature difference is applied to both ends.
Heating one side of the substance produces carriers (electrons or holes), while the cooler side produces few carriers. This causes an imbalance in carrier density and carriers flow from the hot junction side to the cold junction side, but the carrier migration eventually converges.
After the carriers flow on the hot junction side, they have an opposite charge on the cold junction side, resulting in a potential difference between the hot and cold junction. This potential difference is proportional to the temperature difference between the hot and cold junction, which is proportional to the incident energy of far-infrared radiation.
Some MEMS contactless thermal sensors output the potential difference generated by the thermopile element as a bit value by A/D conversion, while others output the bit value as temperature data by further complementary calculation.