How Does A Microwave Sensor Work: The Science Behind It

We are familiar with microwave oven to cook the food. It is fitted with a sensor which helps in the cooking process. Let us learn working of such microwave sensor.

Microwave sensor uses high frequency radio waves operating at 360°. The working principle of microwave sensor is same like radar that emits the wave that reflect back forth between the receiver and source as a result monitors the required action by observing the time taken by the emitted wave to reflect back.

The microwave sensor not only used in oven for cooking but also used widely in security system, in vehicles as a speed sensor and reverse car alarm as to detect the object’s motion and also used in weather reporting as it can detect minute changes. In this post, we shall discuss more about microwave sensing and sensor.

What is microwave sensing?

The word sensing means to detect scientifically defined as to detect physical change and observe data and convert into signals.  Let us know what microwave sensing means.

Microwave sensing is the process of detecting the object by emitting microwave radiation. The device detects using microwave radiation of wavelength from 1mm to 1m and frequency ranges from 400000 to 300Hz. Microwave sensing detect the motion of the target using Doppler effects through microwave signals.

There are two types in microwave sensing: active microwave sensing and passive microwave sensing.

Active microwave sensing

The sensor of active microwave sensing uses its own microwave radiation source to illuminate the target. It works independently even in the absence of sun and can be operated day and night. The transmission of radio signal to target and back reflection of signal from the target take place by itself in active sensing.

Passive microwave sensing

The passive microwave sensing uses naturally emitted radiation energy.  Passive microwave sensing is characterized by low spatial resolution. The emitted energy may be radiation from the sun or moisture observed on the surface.

What triggers a microwave sensor?

Microwave sensors are the most effective sensor as the emitted signal from them can transmit through wall and glass. Let us concentrate on reason for microwave sensor to trigger.

The motion of the object within the radiation zone triggers the microwave sensor. When the object moves in front of the sensor, the emission of radiation is interrupted, thus time taken by the signal reflecting back to sensor shortened. The sensor recognizes this time variation result in activation of the device.

The sensor in microwave oven also works in similar way. It triggered by the amount of moisture present in the food. The vapor interrupt the signal from the sensor such that sensor action begins depends on the amount of moisture vapor.

How does a microwave sensor light work?

Microwave sensor is capable of constant emitting of microwave radiation within the detection zone. Let us focus on working of light fitted with the microwave sensor. 

The light of the microwave sensor is associated with the echo pattern of the emitted signal. Microwave sensor send the microwave signal and analyze the echo produce by them after hitting the target and records the time of reflecting back. If motion of the echo pattern changes, the light turn on accordingly.

Image: Microwave motion sensitive light by Santeri Viinamäki, (CC BY-SA 4.0)

How does microwave sensor reheat work?

Microwave reheat sensor is commonly seen in the oven to heat the some food product and beverages. Let us look into the working of microwave reheat sensor.

The sensor reheat detects the amount of moisture and water content in the food and it automatically emit the temperature required them to heat. It also sets time required to reheat the product. Once it is done it start beeping and shut down by itself.

Can microwave sensor be adjusted?

Microwave sensors are sensitive towards the fine movement of the object. Let us check whether microwave sensor can be adjusted according to object orientation.

Microwave sensor can be adjusted that suits one’s personal need. The detection distance can be adjusted by varying the potentiometer. In oven, the temperature required to cook the food can be adjusted according to our need.

The sensor can be adjusted such that they can pickup minute movement from human sized object. In some microwave sensors, adjustment can be made before fitting the light to the sensor.


Microwave sensor is effective and most sensitive motion detect sensors. Unlike other sensors, microwave sensor is used to detect acoustic signals also. The time interval between back and forth reflection of emitted microwave from the sensor is the key point behind the working principle of microwave sensor.

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