Piezoelectric resonator and piezoelectric filter

A piezoelectric resonator for resonating in the length expander mode, comprising:

• (a) a piezoelectric bar, having a length L, a width W, and a thickness T, wherein L>W>T;
• and, having first and second rectangular surfaces confronting each other in parallel and a third rectangular surface extending along the length L of said first and second rectangular surfaces, said third rectangular surface being beveled against said said first and second rectangular surfaces;
• and
• (b) electrodes formed on said first and second surfaces.

A ladder filter comprising:

• at least a filter circuit, each filter circuit having series and parallel resonators for resonating in length expander mode, said series resonator having:
• (a) a first piezoelectric bar formed in a first rectangular parallelopiped having first and second pairs of confronting surfaces with first and second distances respectively, extending in the longitudinal direction of said first piezoelectric bar;
• and
• (b) first electrodes formed on said first pair of confronting surfaces, said parallel resonator having:
• (c) a second piezoelectric bar formed in a second rectangular parallelopiped having third and fourth pairs of confronting surfaces with third and fourth distances respectively, extending in the longitudinal direction of said piezoelectric bar;
• and
• (d) second electrodes formed on said fourth pair of confronting surfaces, a ratio of capacitances between said first and second electrodes being made relatively small in that said first distance is larger than said second distance and said fourth distance is smaller than said third distance.

A ladder filter comprising:

• series and parallel resonators for resonating in length expander mode, said series resonator including:
• (a) a first piezoelectric bar formed in a first rectangular parallelopiped having a length L1, a width W1, a thickness T1 wherein L1>W1>T1;
• and
• (b) first electrodes formed on a first pair of confronting surfaces defined by said length L1 and said thickness T1, said first piezoelectric bar being polarized in a direction perpendicular to said first electrodes, said parallel resonator including:
• (c) a second piezoelectric bar formed in a second rectangular parallelopiped having a length L2, a width W2, a thickness T2 wherein L2>W2>T2;
• and
• (d) second electrodes formed on a second pair of confronting surfaces defined by said length L2 and said width W2.

A ladder filter comprising:

• series and parallel resonators for resonating in length expander mode, wherein said series resonator includes a first piezoelectric bar formed in a first rectangular parallelopiped having a length L1, a width W1, a thickness T1 wherein L1>W1>T1, and first electrodes formed on a first pair of confronting surfaces defined by said length L1 and said thickness T1, said first piezoelectric bar being polarized in a direction perpendicular to said first electrodes, and wherein said parallel resonator includes a second piezoelectric bar formed in a second rectangular parallelopiped having a length L2, a width W2, a thickness T2 wherein L2>W2>T2, and second electrodes formed on a second pair of confronting surfaces defined by said length L2 and said width W2;
• a first pair of supporting and conducting blocks formed on said first electrodes at intermediate portions of said first electrodes in said longitudinal direction of said first piezoelectric bar respectively;
• a second pair of supporting and conducting blocks formed on said second electrodes at intermediate portions of said first electrodes in said longitudinal direction of said second piezoelectric bar respectively, said first supporting and conducting block supporting said first piezoelectric bar, said second supporting and conducting block supporting said second piezoelectric bar;
• and
• a metal plate for making an electrical conduction between one of said first and one of second piezoelectric bars through one of said first and one of second supporting and conducting blocks.