Volume changeable polymer humidity sensor

A sensor, comprising

• a first metal layer and a second metal layer, the first metal layer and the second metal layer facing each other, and
• a volume changeable layer disposed between the first metal layer and the second metal layer, the volume changeable layer being configured to absorb a material to change the thickness thereof,
• wherein the first metal layer and the second metal layer are a first semi-transmissive metal layer and a second semi-transmissive metal layer, respectively, the first semi-transmissive metal layer and the second semi-transmissive metal layer each having a thickness of about 2 nm to about 50 nm,
• the first semi-transmissive metal layer is a light incident layer into which external light including a visible wavelength spectrum is incident,
• the second semi-transmissive metal layer configured to transmit light of a resonance wavelength enhanced by repetitive reflection between the first semi-transmissive metal layer and the second semi-transmissive metal layer, and
• the sensor indicates a color change by changing a resonance wavelength of light transmitted through the second semi-transmissive metal layer according to a change in thickness of the volume changeable layer.