Frequency selective amplifier

Claim 1

AN ELECTRIC CIRCUIT COMPRISING, IN COMBINATION, AN ALTERNATING CURRENT SOURCE DEVELOPING A SIGNAL AT A GIVEN FREQUENCY, A LOAD, A COUPLING ELEMENT COMPRISING FIRST AND SECOND THIN, AXIALLY POLARIZED CERAMIC DISKS, EACH OF SAID DISKS HAVING FIRST AND SECOND FACES, BONDING MEANS SECURING SAID FIRST FACES TOGETHER IN A CLOSELY SPACED FACETO-FACE RELATION, SAID BONDING MEANS INCLUDING A CONDUCTING MEDIUM EXTENDING BETWEEN SAID FIRST FACES, SAID BONDING MEANS HAVING A THICKNESS LESS THAN THE ACOUSTICAL WAVELENGTH AT THE OPERATING FREQUENCY OF SAID COUPLING ELEMENT, AND SAID BONDING MEANS COVERING SUBSTANTIALLY THE ENTIRE OPPOSING FACES OF SAID DISKS SO AS TO MECHANICALLY COUPLE TOGETHER THE ENTIRELY OF SAID DISKS THEREBY OBTAINING CLOSE ACOUSTICAL COUPLING BETWEEN THEM, AN INPUT ELECTRODE ON ONE OF SAID SECOND FACES, AN OUTPUT ELECTRODE ON THE OTHER OF SAID SECOND FACES, THE IMPEDANCE OF SAID COUPLING ELEMENT BETWEEN SAID CONDUCTING MEDIUM AND SAID INPUT ELECTRODE BEING SUBSTANTIALLY MATCHED TO THE IMPEDANCE OF SAID SOURCE, THE IMPEDANCE OF SAID COUPLING ELEMENT BETWEEN SAID CONDUCTING MEDIUM AND SAID OUTPUT ELECTRODE BEING SUBSTANTIALLY GREATER THAN THE IMPEDANCE OF SAID LOAD, SAID COUPLING ELEMENT BEING DIMENSIONED TO HAVE AN INTERNAL RADIAL RESONANCE AT SAID FREQUENCY, MEANS CONNECTING SAID CONDUCTING MEDIUM AND SAID INPUT ELECTRODE TO SAID SOURCE, AND MEANS CONNECTING SAID CONDUCTING MEDIUM AND SAID OUTPUT ELECTRODE TO SAID LOAD.