Lior Weiss





Suppose that there’s a police car in the middle of the street with its siren blaring for all to hear. Its sound waves will travel from that particular point in every direction at the same speed so that observer A, who’s standing at the left corner of the street, will hear the siren at a higher pitch than observer B who’s situated at the opposite end of the street.

If the police car moves towards the right end of the street (relative to the diagram), the sound waves produced by the moving vehicle become bunched up to observer B and become more spread out for observer A.


As the police car moves to the right end of the street, its sound waves take a shorter time to reach observer B, while it takes longer to reach observer A. Waves produced by the moving police car bunch up as they approach observer B, enabling the observer to perceive the siren at a higher frequency. These waves get stretched out as the police car moves away from observer A, even though it’s still producing at a consistent source frequency. This observer perceives a shift in frequency.

The phenomenon is called the Doppler Effect. But what exactly is the Doppler Effect? More importantly, what role does it play in Wi-Fi Doppler Imaging

What Is the Doppler Effect?

Every disturbance spreads out spherically from the source of a sound. With a stationary source, all of the waves are emitted from the same point with stationary observers on both ends of the object receiving them at the same wavelength and frequency. As the object moves, it continues to produce disturbances in a sphere. But the point of emission is constantly changing. The wavelength becomes shorter in the direction where the source is moving and longer in the other end.

Also called the Doppler Shift, the phenomenon pertains to an apparent change in frequency of any sound, water, or electro-magnetic wave due to the movement of a source or observer. The effect is not a result of the source’s change in frequency. It can be observed because there is a change in the relative velocity between the source and observer.

The phenomenon is still apparent when an observer moves instead of the source. The frequency at which they perceive the waves changes as they move closer or farther away from the object emitting them.

The Doppler Effect is used in a myriad of applications from medicine to astronomy. In an ultrasound, it helps determine the flow of blood. It’s also used in determining the relative velocities of galaxies and stars. The same phenomenon behind a moving police car's change in pitch aids in Wi-Fi Imaging Technology, helping service providers gain insights on moving people or objects around the home and office.

doppler shift

Doppler frequency | image courtesy of Today's Veterinary Practice


The Doppler Effect and Wi-Fi Doppler Imaging

A breakthrough innovation that’s pushing the capabilities of Wi-Fi, Celeno’s Wi-Fi Doppler Imaging identifies, monitors, locates, and classifies the movement of homeowners, pets, and other objects within the home, office spaces, or public areas. The Wi-Fi silicon chip features cutting-edge Wi-Fi 6 connectivity, as well as Doppler Imaging capabilities.

Celeno’s Wi-Fi-based Doppler Imaging Technology eliminates the need for multiple cameras and radar sensors for imaging as it is capable of discerning what happens around a given space even without line-of-sight. It also addresses consumers’ concerns about having to invest in next-generation infrastructure and gadgets such as radars for home applications every time new technologies are rolled out. So, how can it perceive movement around it without actually seeing it?

That’s where the Doppler Effect comes in.

The Wi-Fi-based imaging technology collects the Doppler and Micro-Doppler signatures of moving objects. Machine learning capabilities coupled with an advanced signal processing quantify the number of objects in the room, assess their movement, classify their actions, and determine their position within the given space. Not only that, the technology can distinguish between people, pets, and objects. It can also tell the difference between adults and kids.

Using only a single device for triangulation, it has the power to detect an object’s range and direction. Its capabilities can be used for safety and security purposes, energy management, elderly care, and so on

Much like Wi-Fi-based Imaging Technology, innovators are coming up with new ways to utilize Doppler shifts to improve people’s quality of life in several applications and environments. Wi-Fi Imaging Technology and the Doppler Effect is a combination we’ll certainly see more of in the coming years.

Do you want to know more about Wi-Fi Doppler Imaging? Click here for a demo that shows Celeno’s Wifi Doppler Imaging technology in action.

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