  A metamaterial absorber converts solar radiation into heat for applications
in thermoelectric generators and solar thermophotovoltaics. A metamaterial
absorber typically consists of metallic parts separated by an insulator layer
which does not allow the total heat extraction via direct heat conduction.
Here, we propose wide-angle and broadband metamaterial absorber comprising an
insulator layer, metal grating, and metal back plane (IMM) that allows the
total heat extraction via direct heat conduction. We have formulated the
quasi-analytical solution (QANS) of the IMM-absorber by applying the
coupled-mode analysis with new technique for taking finite dielectric constant
of a metal into account. The QANS are consistent with finite difference time
domain (FDTD) simulation. We fine that the IMM-absorbers made by tungsten and
silver metals give the best and worse average absorbance over the wavelength
range 400-1,200 nm, respectively. The best IMM-absorber shows the optimized
average absorbance 96.2%. The broadband absorption results from the excitations
of insulator-metal waveguide resonance and slit waveguide resonance that are
insensitive to incident angles. The averaged absorbance is above 90.0% for the
incident angles 0-66 degree. The IMM-absorber performance may be enhanced by
using metal rod array with engineered supperlattice.
