Broadband metasurface absorber for solar thermal applications

Abstract

In this paper we propose a broadband polarization independent selective absorber for solar thermal applications. It is based on a metal-dielectric-metal metasurface structure, but with an inter-layer of absorbing amorphous carbon rather than a low loss dielectric. Optical absorbance results derived from Finite Difference Time Domain modelling are shown for ultra-thin carbon layers in air and on 200nm of gold for a range of carbon thicknesses. A gold-amorphous carbon-gold trilayer with a top layer consisting of a 1D grating is then optimised in 2D to give a sharp transition from strong absorption up to 2m to strong reflection above 2m resulting in good solar selective performance. The gold was replaced by the high melting point metal tungsten and is shown to have very similar performance to the gold case. 3D simulations then show that the gold based structure performs well as a square periodic array of squares, however there is low absorption around 400nm. A cross based structure is found to increase this absorption without significantly reducing the performance at longer wavelengths.

A selective metasurface absorber with an amorphous carbon interlayer for solar thermal applications

“…The strong absorption in the carbon layer combined with the Absorptance very high field strengths generated in between the two gold layers results in very strong absorptance at short wavelengths. However at longer wavelengths where these resonances do no occur, the structure is strongly reflective [11]. Figure 8 shows the FM absorptance measurements for both structure A (4pA, 480µs) and structure B (11pA, 480µs) and are compared with the simulated results.…”

“…Thus in this paper we fabricate and characterise a low temperature MDM selective surface based on a gold-carbon-gold tri-layer structure and analyse its angular optical response, which is very important in solar energy applications. Figure 1 shows a schematic of the optimised structure with dimensions obtained from our previous paper [11]. The tri-layer structure is relatively straightforward to obtain using standard deposition techniques.…”

“…When the cermet is deposited on a highly reflective mirror, the tandem forms a selective surface with high solar absorptance and low thermal emittance [9]. Metaldielectric-metal (MDM) structures are an example of a metamaterial which have a patterened metal layer on a dielectric interlayer on a lower metal [10], [11]. The patterned metal-dielectric-metal structure enables a balance between electric and magnetic resonances to be formed within the structure which results in broadband impedance matching to free space, while the periodicity is small enough such that the structure is strongly reflecting in the IR [10].…”

“…3D schematic view for MDM tri-layer with upper gold patterning : a=b=105nm, c=100nm, p=175nm, amorphous carbon, h 1 = 35nm, lower Au, h 2 = 300nm as shown in[11], on 1mm glassThe paper is organised as follows: The fabrication steps for the tri-layer are discussed in detail along with a FIB image of a cross-section showing resulting layer thicknesses. Then FIB etching of the upper 2D patterned layer is described.…”

Solar thermal characterization of micropatterned high temperature selective surfaces

“…This has enabled an number of new types of selective surface to be developed in order to improve solar absorption and reduce thermal emission of radiation in order to increase the conversion efficiency [11][12][13][14][15][16]. This paper studies the use of laser etching, which may not achieve optimum selectivity, but has the potential to be a low cost, large area technique.…”