Optical humidity sensor based on photonic crystal opal film

A new type of colorimetric sensor for humidity measurements has been proposed on the basis of photonic crystal (PhC) opal films. Sensor does not require electricity and represent a PhC plate saturated by salt solutions on different areas, which becomes transparent with increasing of humidity more than a defined value.

The discovered effect is caused by vanishing of the band gap in transmission spectrum of the PhC film (Fig. 1). Upon reduction of humidity, the film regain its initial spectral properties in tens seconds.

The revealed effect gives an opportunity to detect more than 50 levels of humidity, which is determined by selection of slats. The sensor has high temporal stability and allows registering a relative humidity change with precision of 2%.

(a)	(b)
Fig. 1. a) Change of the transmission of PhC opal film with NaCl salt applied upon an increase of relative humidity from 20 to 80%.; b) Photographs of PhC opal film under various values of relative air humidity (RH). LiCl (in the form of Cyrillic letter Н), NaCl (Г), KCl (У) salts are applied to various regions of film.

Publications:

1. Chubakov V.P., Chubakov P.A., Plekhanov A.I., Humidity sensor based on photonic crystal opal film // Nanotechnologies in Russia, 2012, V.7, № 9-10. pp. 449-501.
2. Chubakov V.P., Chubakov P.A., Plekhanov A.I., Humidity sensor based on photonic crystal opal films // Conference proceedings, Photonics of organic and hybrid nanostructures (Chernogolovka, Russia, 5-9 September 2011). P. 165.