Using metal, such as a refractory metal, with an acoustic impedance greater than about 50 Mrayl as the material of first metal Bragg layer 192 and second metal Bragg layer 196, and plastic material having an acoustic impedance of less than about 5 Mrayl as the material of first plastic Bragg layer 194 and second plastic Bragg layer 198 result in an embodiment of acoustic Bragg reflector 190 that p