1. Field
The embodiments discussed herein are related to an electric power generation device using thermoelectric conversion and piezoelectric conversion, to a pertinent electric power generation method, and to a pertinent electric power generation device manufacturing method.
2. Related Art
Efforts have been made to promote the development of a sensor network containing sensor modules that integrate sensors, a data processing function, and a radio communication function provided on a network. It is desired that such sensor modules perform self-generation without using a battery. For self-generation, studies are being made of electric power generation methods which use on-site environments and serve to provide miniaturized devices, such as methods using solar cell power generation, thermoelectric power generation, and piezoelectric power generation. Miniaturization of electric power generation devices are desired also for securing wide application ranges.
A unimorph type piezoelectric element is known which contains a piezoelectric capacitor including a lower electrode made of Pt or the like, a piezoelectric layer made of PZT or the like, and an upper electrode made of Al or the like and formed on the upper surface of a cantilever structure comprising a silicon layer or the like. A weight is connected to the movable end of the cantilever.
The electric power generated by a piezoelectric element is too small in quantity to be used as a power supply. Therefore, in many cases, a plurality of piezoelectric elements are connected in parallel to obtain practicable electric power. It is not easy for a large number of cantilever-structured unimorph type piezoelectric elements to be combined in a compact device.
A configuration is disclosed in which a plurality of piezoelectric elements consisting of piezoelectric plates formed on metal plates are laminated on a common support structure and supported in the peripheral portion, with weights applied to the central portions of the piezoelectric elements from a common weight applying means (e.g., Patent Document 1). This configuration is intended to use weights repeatedly applied by traffic of automobiles and railroad trains and accordingly has a structure with high mechanical strength.
The output voltage of a thermoelectric element containing a pair of thermoelectric material articles connected together depends on the temperature difference, but in many cases, the voltage is low, making it necessary to connect a large number of pairs of thermoelectric elements in series in order to obtain a practicable voltage. For example, an output voltage is increased by using a large number of n-type configurations, each consisting of a pair of a p-type semiconductor and an n-type semiconductor arranged adjacently to each other and electrically connected together at one end, that are disposed between a high temperature side and a low temperature side and connected in series. Thermoelectric elements require no movable portion and can be integrated easily. However, it is necessary to insulate adjacent thermoelectric members from one another.
A configuration is proposed wherein, in a structure in which p-type semiconductors and n-type semiconductors are laminated, insulating layers are interposed on lamination interfaces that are other than p-n connections (e.g., Patent Document 2). All layers are laminated in a green state, and are integrally calcined.
There is a proposal for a thermoelectric conversion module composed of a plurality of thermoelectric elements connected in series, with the spaces between thermoelectric elements filled with insulating resin to fix the thermoelectric elements to each other (e.g., Patent Document 3).
There is another proposal for a thermal displacement conversion device that combines a thermoelectric power generation device and a piezoelectric actuator (e.g., Patent Document 4). A thermoelectric element formed of a thermoelectric conversion material generates a voltage which is proportional to an applied temperature, and this voltage causes displacement of the piezoelectric actuator.