 Infrared sensor
 As the infrared sensor device, PZT(Lead[Pb:Plumbum] Zirconate Titanate) is used. This material has the nature that the electric charge in the surface is divided into the positive electric charge and the negative electric charge in the usual condition.(Spontaneous polarization)
The distribution of the electric charge is disordered when the infrared rays lash this material and the voltage occurs. The infrared sensor outputs the change of this voltage.
The infrared sensor has the kinds such as the single type, the dual type, the quad type. The dual type is often used to detect the move of the person or the animal.
 The two identical shape elements are used for the dual-type sensor. And, it is put for the pole of the element to become opposite. When the change of the infrared quantity occurs, being simultaneous with the element which was put in this way, because the occurring voltage is opposite, it denies each other and the voltage doesn't appear in the output. The output voltage changes only when there is a difference in the quantity of the infrared rays which enter both elements.
Because the same change occurs to both elements even if the infrared quantity of the background in the place to detect with the sensor changes, little change of the output occurs even if it occurs.
When the person or the animal crosses the sensor, the quantity of the infrared rays which enter both elements becomes not equal and the change of the voltage appears in the output.
Fresnel lens
The Fresnel lens was invented as the lens for the lighthouse. It is called the Fresnel lens from the name of Augustine Fresnel of the French who are the inventor.
This lens made the aspect of the curve of usual lens the plane. The lens with the equal magnification can be thin made. The magnifying glass having to do with the board is this Fresnel lens.
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