We are reporting on the analysis of a new design for a thermal source exploiting Si-based suspended micro-bridge structures. A device consists of a metal film perforated by a periodic array of apertures extending into the Si substrate and each of size on order of the wavelength of the light. This perforated film permits resonant coupling of the incident radiation from the underlying silicon photonic crystal with surface plasmons at the metal surface. The coupling provides for unusually high optical emission efficiencies when the structure is thermally excited. The radiation emitted exhibits an enhancement over a narrow wavelength range in the infrared and its spectral response is highly dependent on the direction of observation. The positions of the main resonances, for both reflection and emission from our structures, scale linearly with the periodicity of the metallo-dielectric structure. As one moves off normal incidence, a single main resonance splits into several smaller resonances whose locations scale roughly linearly with observation angle. These structures have been used as emitter/detector sensor chips to selectively detect industrial pollutants like carbon dioxide. Control of the wavelength of resonance, bandwidth and direction of emission play an important role in improving the sensitivity and selectivity of these gas sensors.