Holographic Humidity Sensors
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1.3 PHYSICAL SCIENCES, Optics
This chapter presents holographic devices for sensing the relative humidity in the environment. The principle of operation of two main types of holographic sensors based on transmission and refection holograms is described and their properties are theoretically modelled. The effect of different factors such as change of the overall refractive index, change of the hologram’s thickness due to swelling/shrinkage of the layer and change in the refractive index modulation due to absorption/desorption of moisture are considered. In the experimental studies an emphasis is given to the reflection holographic humidity sensors which can provide a visual indication of the relative humidity observed as a change of the colour of the reflected light. The work presented focuses on holograms recorded in acrylamide based photopolymers. The results from studies of their sensitivity, reversibility, relative humidity range of operation and response time are summarised. The operational temperature range is also studied.
The potential use of the humidity sensors as user-verifiable security holograms is described as well as applications in packaging and environmental sensing.
Naydenova, I., Jallaparam, R. & Martin, S. (2011). Holographic humidity sensors. In C.T. Okada (ed.) Humidity Sensors,pp. 117-142, Nova Science Publishers. doi:10.21427/rv2k-vq42