| CPC H03H 9/02685 (2013.01) [H03H 3/02 (2013.01); H03H 3/08 (2013.01); H03H 9/0211 (2013.01); H03H 9/17 (2013.01); H03H 2003/025 (2013.01)] | 21 Claims |

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1. An apparatus comprising:
an acoustic resonator;
multiple layers of different impedances that overlap at least partially with the acoustic resonator along an axis; and
a grating layer overlapping at least part of the multiple layers along the axis.
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