Absorption of photonic crystal textile in the mid infrared for thermoregulation
Abstract
A large part of the building energy consumption is attributed to temperature control using Heating, Ventilation
and Air Conditioning (HVAC) systems. A decrease in this consumption, even slightly, will contribute to both
environmental protection and costs saving. Toward this end, personal thermoregulation properties have been
recently developed for the majority of people who spend their time in a sedentary state [1, 2]. Therefore, a
tremendous effort is necessary to develop smart wearable thermoregulating textiles which can respond to the
immediate temperature feeling of the wearer.
We theoretically investigate the effect of absorbance of a photonic membrane of low refractive index on the
human body emission at 34°C in the MIR range. The photonic membrane, embedded in air, is made of
Benzocyclobutene (BCB) and drilled following a triangular array of holes. We took into consideration the
absorption of the BCB by using its complex refractive index. All numerical results have been performed with the
help of the Finite Element Method (FEM).
We showed that the reflection and the transmission coefficients depend on the geometrical parameters of the
membrane and found the occurrence of three peaks of reflection whose origin is due to the structuring of the
membrane. One origin is due to the photonic guided modes inside the membrane, the second one comes from the
local excitation of the electromagnetic field inside the air holes. The dependence of the geometrical parameters
has been quantitatively highlighted through the definition of an efficiency coefficient. We found that, depending
on the geometrical parameters, the BCB membrane can absorb up to 80% of the emission of the human body
emissivity in the wavelength range [7.5, 11.5] μm. We are currently studying the effect of the physical
parameters considering the behavior of the refractive index of both the membrane and the environment on the
absorption rate. The estimation of the temperature of the membrane under the absorption modulation of the
membrane is also under consideration, following the thermal balance calculation. This work paves the way for
the design of a smart responsive photonic membrane. Integrated to a textile, such a membrane can greatly
mitigate the energy demand for indoor heating and ultimately contributes to the relief of the climate issues.