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    6. Basics - What is a pyroelectric infrared sensor? -
    Infrared Sensors

    Infrared SensorsBasics - What is a pyroelectric infrared sensor? -

    What is a pyroelectric infrared sensor?

    • A pyroelectric infrared sensor detects infrared by applying the pyroelectric effect of pyroelectric ceramics, which are a type of piezoelectric material.

    What are infrared rays?

    1. Energy which has a thermic effect
    2. Infrared rays are a type of electromagnetic wave similar to radio waves, visible light waves, and ultraviolet rays.

    Features of infrared rays

    Infrared rays are a type of electromagnetic wave which has a wavelength that is longer than visible light but shorter than radio waves. Moreover, they cannot be seen with the human eye, but they do have a thermal energy which can be felt as heat.

    • When it comes to infrared rays, people tend to think that they are only emitted by hot objects, but that is not necessarily the case. All objects which exist in the natural world, whether they are human beings, fire, or ice, emit infrared rays according to their temperature and surface conditions.
      However, only the wavelengths differ according to the temperature of the object. The wavelength distribution of infrared rays emitted by the temperature of a black body is represented according to Planck's law.
    • The amount of radiation energy of the infrared rays emitted from the object with a temperature T[K] is proportional to the fourth power of the absolute temperature (Celsius -273°C). (Stefan-Boltzmann law)
    • According to Wien's displacement law, a human body (310[K]) emits infrared energy with a peak wavelength of 9 to 10 [µm]. Furthermore, the peak wavelength of the infrared rays emitted from the heat object becomes shorter as the temperature increases.

    What is the pyroelectric effect?

    The pyroelectric effect refers to a phenomenon in which a temperature change occurs in a pyroelectric ceramic and causes the spontaneous polarization of the pyroelectric ceramic to change and generate a charge according to the temperature change.
    A pyroelectric infrared sensor uses this pyroelectric effect to detect the temperature change of the ceramic and produce an output.
    At the same time, there is no output when the temperature is in a steady state regardless of the absolute value of the temperature.

    Operational principles of a pyroelectric infrared sensor

    A temperature change occurs when the infrared rays enter the sensor, so the surface temperature of the pyroelectric element (ceramic) rises, and a surface charge is generated by the pyroelectric effect.
    Therefore, the neutral state of the charge collapses during stability, the sensing element surface charge and the adsorption floating ion charge become unbalanced due to different relaxation times, and an unpaired charge is generated.
    This generated surface charge is extracted as an electrical signal by the components inside the sensor and used as an output signal.

    Detection is only possible at the moment when there is a temperature change.
    Detection cannot be performed when there is no temperature change = no movement.

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    1. Electronic Components
    2. Sensors
    3. Infrared Sensors
    4. Basics
    1. HOME
    2. Electronic Components
    3. Sensors
    4. Infrared Sensors
    5. Basics
    6. Basics - What is a pyroelectric infrared sensor? -
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