Piezoelectric structure

A piezoelectric structure receives input from a voltage source to generate polarization and output voltage. Two surfaces are formed on the direction normal to the polarized direction. One surface has an input electrode electrically connecting to the voltage source and an output electrode to output voltage. Another surface has a ground electrode. The distance between the input electrode and the ground electrode is different from the distance between the output electrode and the ground electrode. Through the height difference of the two electrodes, the step-up and step-down ratio can be altered.

FIELD OF THE INVENTION

The present invention relates to a piezoelectric structure and particularly to a piezoelectric structure that is capable of altering the step-up ratio and step-down ratio.

BACKGROUND OF THE INVENTION

Piezoelectricity basically is an energy transformation phenomenon between mechanical energy and electrical energy. As there is a cause and effect relationship between electric charge and strain, for an object which can generate piezoelectricity, as long as its crystal structure can generate electron dipole moment (EDM) when subject to an external force, transformation between the mechanical energy and electrical energy occurs. Then piezoelectricity can take place.

Generation of EDM is caused by a special arrangement of the positive ions and negative ions inside the crystal. Different crystal lattice systems in the material can generate different EDM. The basic condition is the asymmetrical center of the crystal lattice. If there is a symmetrical center in the crystal lattice, the positive ions and the negative ions will be neutralized. Then EDM cannot be generated. And transformation between the mechanical energy and electrical energy does not take place. Transformation between the mechanical energy and electrical energy generally has three forms: (1) transforming mechanical energy to kinetic energy, (2) transforming electrical energy to mechanical energy, and (3) transforming electrical energy to mechanical energy, then to electrical energy again to be output. Piezoelectric ceramics can transform mechanical energy to electrical energy and vice versus, thus is widely used. It may be used to fabricate pressure detection elements, accelerators, micro-motors and the like. The piezoelectric film can meet the requirements of thin and light that are demanded by many modern electronic products, hence it may be used in electronic elements for bio-detection and communication and the like. Its application potentials are highly appreciated in academics and industries.

Refer toFIGS. 1A and 1Bfor a conventional piezoelectric structure. Its structure is based on a principle announced by Berlincourt in 1973 named “unipoled PZT”. The relationship of thickness of the polarized areas of the piezoelectric structure that are corresponding to the input/output areas is changeable. The generated polarization process can alter the step-up ratio and step-down ratio of the piezoelectric structure. This is the principle of the structure. However, in the conventional techniques, changing the polarized areas of the input electrode and the output electrode by fixing the distance between the input electrode/output electrode and the ground electrode of the piezoelectric structure (namely di=do) to alter the step-up ratio and step-down ratio. This causes a problem which is if there is a desire to alter the step-up or step-down ratio, the polarized areas of the electrode and output electrode must be changed. Hence the size of the piezoelectric structure has to be increased or reduced. Its industrial applicability is greatly affected by the fabrication techniques and installation space of the piezoelectric structure.

U.S. Pat. No. 6,707,235 discloses an annular piezoelectric structure which has a first portion and a second portion. These two portions connect to an AC power supply. And other portions can produce and transform vibration generated by piezoelectric structure. The polarized direction of the annular piezoelectric structure is normal to the perimeter surface of the annular body. It generates different step-up and step-down ratios through different shapes of the piezoelectric structure. The different shapes of the piezoelectric structure create difficulty in manufacturing.

SUMMARY OF THE INVENTION

Therefore the primary object of the present invention is to solve the aforesaid disadvantages. The invention aims to alter the step-up ratio and step-down ratio of the piezoelectric structure through the polarized areas of the piezoelectric material and the relative height difference between two electrodes of the input and output voltages. Compared with the conventional piezoelectric structure of the same input voltage and similar size, the invention can provide a higher or lower output voltage and save installation space.

Another object of the invention is to provide a piezoelectric structure with a profile which is changeable easily. Compared with the conventional techniques of the same input voltage, the invention can generate a higher or lower output voltage. Fabrication process and time also can be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer toFIGS. 2A,2B,3A and3B. The piezoelectric structure20according to the invention is connected to a voltage source10. The piezoelectric structure20has a polarized direction, an input electrode21electrically connected to the voltage source10that is normal to one of two surfaces of the polarization, and an output electric electrode22to output a higher or lower voltage after the piezoelectric structure20is activated. There is another surface other than the surface where the input and output electrodes are located that has a ground electrode23which is grounded. The main feature of the invention is that the distance between the input electrode21or the output electrode22and the ground electrode23is not equal because of the thickness of the piezoelectric plate.

According to the equation announced by Berlincourt, assumed the conventional step-up or step-down ratio is a α1, the step-up or step-down ratio of the invention is a α2, the conventional input/output electrode polarized areas are respectively A1and Ao, the input/output electrode polarized areas of the invention are respectively a1and ao, the distances between the conventional input/output electrodes and the ground electrode23are respectively D1and Do, and the distances between the input/output electrodes and the ground electrode23of the invention are respectively d1and do, when Ai=ai, Ao=ao,

According to the principle set forth above,

Hence according to the invention, the distance between the output electrode22and the ground electrode23is not equal to the distance between the input electrode21and the ground electrode23. Referring to the drawings, with do<d1, the ratio of α1and α2is the conventional step-up or step-down ratio against the step-up or step-down ratio of the invention. Through that ratio, by altering the distance between the input electrode21or output electrode22and the ground electrode23, the step-up or step-down ratio of the piezoelectric structure20can be adjusted. Thereby a desired output voltage may be selected according to the duty voltage required for a load30.

Refer toFIG. 4for an embodiment of the invention. The input electrode21and output electrode22may be changed, and the input electrode21is located in the range covered by the output electrode22, or the output electrode22may be located in the range covered by the input electrode21to generate a different step-up or step-down ratio. Through the combination of different polarized area of the electrodes21and22, and altering distance between the input and output electrodes21,22and the ground electrode23, different output voltages can be achieved and supplied corresponding to the duty voltage required by the load30.

Refer toFIGS. 5A and 5Bfor another embodiment of the invention, and also refer to the principle of the piezoelectric structure20previously discussed. The ratio of polarized area between the output electrode22and the input electrode21may be same or different to get different output voltage. Adopted the method shown inFIG. 3, by altering the location of the input end of the load30to the output electrode22of the piezoelectric structure20that are connected electrically (altering the output electrode22to be surrounded by the input electrode21), many different combinations of step-up and step-down ratios can be generated to provide a desired duty voltage for the load30.