What is the “Doppler” effect? The “Doppler” effect can be understood similarly to when a motor vehicle approaches head-on, the sound heard becomes higher and higher in pitch; when the vehicle leaves, the sound heard is lower than before, and the pitch becomes weaker and lower. From a scientific perspective, this means that the received frequency of sound waves becomes higher as the wave source gradually approaches a person, and lower when it moves away from the source. This phenomenon is known as the “Doppler” effect.

Motor vehicle radar speed detectors utilize the Doppler effect. The speed detector emits laser lines, which are reflected back by the vehicle. During this time, a micro-information processor in the detector detects the difference between the two wavelengths. The denser the wavelengths, the faster the speed.

In a Doppler testing system, when a focusing lens converges two incident beams at a certain angle, as particles in a fluid pass through the fringe area, they sequentially scatter a series of light waves whose intensity varies with time, called a Doppler signal. The frequency of this variation in light wave intensity is called the Doppler shift. The higher the velocity of the particles passing through the fringe area, the higher the Doppler shift. By dividing the particle velocity perpendicular to the fringe direction by the fringe spacing and considering the refractive index of the fluid, a linear relationship between the Doppler shift and fluid velocity can be obtained. The Doppler velocity measurement system uses this linear relationship to determine velocity.

The main part of a Doppler testing system is the Laser Doppler Velocimeter (LDV). The LDV measures the Doppler signals of tracer particles passing through the laser probe and then derives the rate based on the relationship between velocity and Doppler frequency. Since it is a laser measurement, there is no interference with the flow field. With a wide speed range, it is currently the laser sensor instrument with the highest speed measurement accuracy on the market.

Laser sensor application areas: air purifiers, air conditioners with purification functions, PM2.5 detectors, range hoods, smoke alarms, fresh air systems, dedicated PM2.5 sensors, air detectors, wearable devices, etc.