Piezoelectric transformer, piezoelectric transformer module, and wireless power transmission system

A piezoelectric transformer using a (2n+1)-order longitudinal vibration mode where n is an integer greater than 2, the piezoelectric transformer comprising:

• a piezoelectric board having:
• a length of (2n+1)×λ/2, a width less than λ/2, and a thickness less than λ/2, wherein λ is the wave length of the vibration mode, and (2n+1)th regions dividing the piezoelectric board along a length direction,
• wherein the first region to the (n−k)th region and the (n+k+2)th region to the (2n+1)th region are each polarized in a direction of the thickness of the piezoelectric board, where k is a positive integer smaller than n,
• wherein the (n−k+1)th region to nth region and the (n+2)th region to the (n+k+1)th region are polarized in a direction of the length of the piezoelectric board,
• wherein the (n+1)th region is non-polarized;
• first pairs of opposing electrodes and second pairs of opposing electrodes disposed in the first region to the (n−k)th region and the (n+k+2)th region to the (2n+1)th region, respectively, and arranged in the direction of polarization of the respective regions;
• and
• at least one third electrode disposed between the (n−k+1)th region to the nth region and the (n+2)th region to the (n+k+1)th region.

A wireless power transmission system comprising:

• a power transmitting apparatus including a transmission-side active electrode, a transmission-side passive electrode, and a voltage generation circuit configured to apply a voltage between the transmission-side active electrode and the transmission-side passive electrode;
• and
• a power receiving apparatus including a reception-side active electrode adjacent to the transmission-side active electrode and a reception-side passive electrode adjacent to the transmission-side passive electrode when the power receiving apparatus is positioned on the power transmitting apparatus, a step-down circuit configured to step down a voltage generated between the reception-side active electrode and the reception-side passive electrode, and a load circuit configured to receive an output voltage of the step-down circuit,
• wherein the transmission-side active electrode and the reception-side active electrode are capacitively coupled to each other to transmit power from the power transmitting apparatus to the power receiving apparatus, and
• wherein the wireless power transmission system comprises a piezoelectric transformer using a fifth-order longitudinal vibration mode, the piezoelectric transforming including:
• a piezoelectric board having:
• a length of 5λ/2, a width less than λ/2, and a thickness less than λ/2, wherein λ is the wave length of the vibration mode, and
• five regions dividing the piezoelectric board along the length of the piezoelectric board,
• wherein the first region and the fifth region are disposed adjacent to respective outer edges of the piezoelectric board and are polarized in a direction of either the thickness or the length of the piezoelectric board,
• wherein the third region is disposed between the first region and the fifth region and is non-polarized, and
• wherein the second region is disposed between the first region and the third region and the fourth region is disposed between the third region and the fifth region;
• a first pair of opposing electrodes and a second pair of opposing electrodes disposed in the first and fifth regions, respectively, and arranged in the direction of polarization of the respective regions;
• and
• a third electrode disposed in the third region.