Piezoelectric resonators for overtone oscillations

An overtone oscillation piezoelectric resonator comprising:

• a block made of a vibration medium, and having a cutoff frequency f.sub.3 ;
• a thin layer portion made of the same material as said vibration medium, and provided at a predetermined portion of said block;
• a piezoelectric material portion including an excitation electrode attached to substantially the center of the thin layer portion, for providing a vibration energy entrapping portion having a cutoff frequency f.sub.1 (where f.sub.1 .gtoreq.f.sub.3), a part of said thin layer portion extending between said vibration energy entrapping portion and said part serving as a vibration energy propagating portion having a cutoff frequency f.sub.2 (where f.sub.2 >f.sub.1), said block serving as a vibration energy absorbing area having a cutoff frequency f.sub.3 and adapted to absorb vibration energy propagated through said vibration energy propagating portion,
• wherein configuration of said excitation electrode is determined so as to strongly excite every order of overtone vibrations on a harmonic mode or on a specific anharmonic mode, and an entrapping coefficient n a.sqroot..DELTA./H in said strongly excited mode (where "n" represents a desired harmonic overtone order, "a" the size of said energy entrapping portion, ".DELTA." the amount of plate back defined by (f.sub.2 -f.sub.1)/f.sub.2 and "H" the thickness of the vibration energy propagating portion) is determined such that substantially all of the vibration energy of overtone vibrations whose orders are equal to or higher than n-th order is entrapped within said vibration energy entrapping portion and its periphery while leaking the vibration energy of overtone vibrations whose orders are lower than said n-th order via said vibration energy propagating portion so as to consume the vibration energy through said vibration energy absorbing area, thereby enhancing oscillation caused by the n-th overtone vibration more than oscillation caused by overtone vibrations lower than the n-th order including the fundamental vibration.