Generally speaking, photonic band gap materials have {TAIL ~ the property} of preventing electromagnetic radiation having some discrete wavelength or range of wavelengths from propagating along a given direction in {HEAD ~ a material} 
Generally speaking , photonic band gap materials have { TAIL ~ the property } of preventing electromagnetic radiation having some discrete wavelength or range of wavelengths from propagating along a given direction in { HEAD ~ a material }
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD