Abstract: Provided is an ultrasonic sensor which includes a piezoelectric vibrator made of a lithium niobate (LN) single crystal and may be used in a high temperature region by generating a high ultrasonic wave output, and prevents cracks from being generated in the crystal. A piezoelectric vibrator 1 of the present invention has a surface (Y-axis 36° cut surface) obtained by rotating a surface orthogonal to a Y-axis of the LN crystal about an X-axis by 36°±2° as an output surface. The ultrasonic sensor further includes a retarder 3 made of titanium and a bonding layer 2 for bonding one surface of the retarder 3 to the output surface. The bonding layer 2 is made of silver and frit glass, and the frit glass has a coefficient of linear expansion ranging from 5×10?6 K?1 to 15×10?6 K?1.

Abstract: Provided is an ultrasonic sensor which includes a piezoelectric vibrator made of a lithium niobate (LN) single crystal and may be used in a high temperature region by generating a high ultrasonic wave output, and prevents cracks from being generated in the crystal. A piezoelectric vibrator 1 of the present invention has a surface (Y-axis 36° cut surface) obtained by rotating a surface orthogonal to a Y-axis of the LN crystal about an X-axis by 36°±2° as an output surface. The ultrasonic sensor further includes a retarder 3 made of titanium and a bonding layer 2 for bonding one surface of the retarder 3 to the output surface. The bonding layer 2 is made of silver and frit glass, and the frit glass has a coefficient of linear expansion ranging from 5×10?6 K?1 to 15×10?6 K?1.