Abstract:
An energy converter for converting a sound energy into a kinetic energy is comprised of a source device for radiating the sound energy, and a body having a cover member for absorbing the sound energy and a reflecting member mounted thereon with the cover member in such a manner that the sound energy after passing through the cover member reaches the reflecting member so as to be tangential thereto.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an energy converter, and in particular to a sound wave operated energy converter which can establish a rotational movement, a linear movement or other movement. 
     A conventional energy converter, which is pending in the United States Patent and Trademark Office under the Ser. No. of 07/917,964 (filing date: Jul. 24, 1992), is shown in FIGS. 13 and 14. The conventional energy converter includes a rotor 23 from which a plurality of equally pitched blades 23a are extended outwardly in the radial direction, and a cylindrical housing 21 in which the rotor 23 and blades 23a are arranged. At an inner surface of the housing 21, there are secured a plurality of equally pitched resonators 22 so as to surround the blades 23a. When each resonator 22 generates a sound wave, the resulting radiation or sound pressure affects the blades 23a, which brings a rotation of the rotor 23. 
     In the foregoing structure, whenever the blade 23a is substantially perpendicular to the direction along which radiation pressure is transmitted the former can receive the energy of the latter efficiently. Is the blade 23a makes an acute angle with respect to the foregoing direction after the foregoing rotation of the rotor 23a, the energy receipt at the blade 23a becomes less efficient. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide an energy converter without the foregoing drawback. 
     In order to attain the foregoing object, an energy converter for converting a sound energy into a kinetic energy is comprised of a source device for radiating the sound energy, and a body having a cover member for absorbing the sound energy and a reflecting member mounted thereon with the cover member in such a manner that the sound energy after passing through the cover member reaches the reflecting member so as to be tangential thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be more apparent and more readily appreciated from the following detailed description of a preferred exemplarily embodiment of the present invention, taken in connection with the accompanying drawings, in which; 
     FIG. 1 is a plane cross-sectional view of an energy converter according to a first embodiment according to the present invention; 
     FIG. 2 is a vertical cross-sectional view of the device in FIG. 1; 
     FIG. 3 is a perspective view of a rotor of the device in FIG. 1 
     FIG. 4 is a view showing a neighbourhood of a resonator of the device in FIG. 1 
     FIG. 5(A) is a side view of the resonator; 
     FIG. 5(B) is a plane view of the resonator; 
     FIG. 6 is an exploded perspective view of the resonator including positive and negative electrodes; 
     FIGS. 7 and 8 show a brief operation principle of the device in FIG. 1; 
     FIG. 9(A) shows a schematic operation principle of the device in FIG. 1; 
     FIG. 9(B) shows a graphic operation principle of the device in FIG. 1; 
     FIG. 10 shows another graphic operation principle of the device in FIG. 1; 
     FIG. 11 is view explaining the operation of the device in FIG. 1; 
     FIG. 12 is a perspective view of a rotor of a device according to a second embodiment of the present invention; 
     FIG. 13 is a plane view of a conventional energy converter; and 
     FIG. 14 is a vertical cross-sectional view of the device in FIG. 13. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described hereinunder in detail with reference to the accompanying drawings. 
     Referring first to FIGS. 1 and 3, an energy converter which is in the form of a sound wave operated actuator includes a housing 1 which has a main body 1a having an inner space, an upper lid 1b closing an upper opened end of the inner space, and a lower lid 1c closing a lower end of the inner space. A plurality of windows 1d are formed in the main body 1a. Within the inner space of the housing 1, an amount of fluid 6 as a medium is filled. 
     A rotor 5 is accommodated within the inner space of the housing 1 and is rotatably supported at each of the lids 1b and 1c. The rotor 5 includes a cylindrical body 5a, a shaft 5c on which the cylindrical body 5a is fixedly mounted, and a cover member 5b which covers or surrounds the entirety of the outer surface of the cylindrical body 5a. The outer surface of the cylindrical body 5a serves for reflecting sound waves and the cover member 5b is set to absorb sound waves for the transmission thereof to the cylindrical body 5a. 
     A pair of diagonally spaced resonators 2 and another pair of diagonally spaced resonators 3, each of which is supported at the corresponding window 1d in a fluid-tight fashion by a rubber bush 4, are arranged in such a manner that two different resonators 2 and 3 are adjacent each other. A plate 7 with an aperture 7a is secured to the main body 1a of the housing 1 so as to close the respective window 1d, which results in that an air chamber 8 is defined which is in opposition to the fluid 6 via the resonators 2 (3). The air chamber 8 serves to effectively propagate the sound wave when the resonators 2 and 3 are turned on. If the actuator is desired to be used within air, the rubber bush 4 as a sealing means is not required. On the other hand, when the actuator is desired to be used within a liquid, the rubber bush 4 is an essential element as a sealing means. The illustrated embodiment shows the former case, and the air chamber 8 is, via the aperture 7b, in fluid communication with atmosphere. 
     If the actuator is set to used in liquid, by coinciding the same with the liquid 6, no effective seal between the housing 1 and the shaft 5a is required. 
     Each of the resonators 2 and 3 is adapted to emit or radiate, along its axial direction, the sound wave or sound beam so that the outermost portion thereof forms a tangent to the outer surface of the rotor 5. Each of the resonators 2 and each of the resonators 3 serve for rotating the shaft 5 in the positive direction and the negative direction, respectively. 
     In the present embodiment, a disk-shaped piezoelectric element is used for constituting each of the resonators 2 and 3. The piezoelectric element is made of PZT (lead zirconate titanate), is of 1.2 mm in thickness, and is so rated with a longitudinal resonance frequency of 1.7 MHz as to be used at an ultrasonic area. 
     Referring to FIG. 4, there is illustrated a detailed structure of a portion in the neighbourhood of the resonator 2. It is to be noted that similar structure can be seen in the resonator 3. The disk-shaped resonator 2 is surrounded by a positive electrode 9, a negative electrode 10, and the rubber bush 4. As shown in FIGS. 5(A) and 5(B), the resonator 2 has at its central portion and outer peripheral portion, respectively, a positive electrode 2a and a negative electrode 2b. The negative electrode 10 has, as shown in FIG. 6, an annular portion 10a and an inwardly extending terminal 10b. The annular portion 10a is in contact with the negative electrode 2b of the resonator 2 (the resonator 3). The terminal 10b of the negative electrode 10 is soldered with one end of a wire 11b. The positive electrode 9 has an annular portion 9a and a pair of opposed inward extending terminals 9b and 9c. The annular portion 9a is located in parallel with the resonator 2 (3) so as not to be in contact therewith. The terminal 9b of the positive electrode 9 is soldered with one end of the wire 11a. The terminal 9c formed in a spring mode is in contact with the positive electrode 2a of the resonator 2. The frequency of the sound wave at the resonator 2 is adjustable by controlling the voltage and/or current in the wires 11a and 11b. In light of the fact that the resonator 2(3) is within the liquid 6, for the prevention of deterioration of the resonator 2 (3), each of electrodes 2a, 2b, 3a, 3b is in the form of a thin film which is obtained by the sputtering manner or CVD method. 
     A sound field as shown in FIG. 9(A) is established at a side of the liquid 6 by the vibration of the resonator 2. The sound energy flux density of the sound field extends along the axial direction of the resonator 2. Though the actual acoustic radiation pressure is as complicated as the sound wave distribution, in the case of the disk-shaped resonator having a diameter of 20 mm within the liquid medium, the sound wave caused by the vibrations of the disk-shaped resonator generates the sound field as illustrated in FIG. 9(B). When the frequency of the vibration of the disk-shaped resonator is approximately 1 MHz or more, the sound field exhibits a half value angle of about 2 through 3 degrees or less, and is formed like a beam. Thus, the sound field can be approximated to a plane progressive wave in practical use. On the other hand, when the frequency of the vibration of the resonator is high, there arises the damping or less. Thus, when the frequency of the vibration of the resonator is not less than 10 MHz, the damping distance is several tens of centimeters or less in liquid as shown in FIG. 10, which results in that it is preferable to operate or vibrate the resonator at a frequency ranging from 1 through 10 MHz in order to constitute an energy converter of a few centimeters through several tens of centimeters in size or scale. 
     Moreover, when a liquid is the radiation medium for the sound wave, it is possible to input a sound power which is larger by three digits than the case where a gas is the radiation medium for the sound wave. For instance, in the case where the PZT is used as the resonator, it is possible to input a sound power of 800 W/cm 2  into water, however, it is only possible to input a sound power of less than about 0.2 W/cm 2  into atmosphere. Hence, liquids are suitable for the medium. However, it is not appropriate to employ a liquid, which absorbs or damps the sound wave considerably, for the radiation medium. In addition, when a liquid is disposed at one side of the resonator and a gas is disposed at the other side of the resonator as is in the present embodiment, almost all of the energy generated by the resonator can be inputted into the liquid. In such a case, the electro-acoustic efficiency reaches 90% or more. 
     The force F, which a substance receives from a radiation pressure when the substance is in limitless plane progressive sound field whose sound energy density is E, depends on the characteristics of the substance as shown in FIG. 11. If the area of the outer surface of a resonator is defined to be S, in the case where the substance possesses full absorption characteristics, the formula of F=SE is established. In the case where the substance possesses full reflection characteristics, the formula of F=2SE is established. If the substance possesses partial absorption characteristics, the formula of F=SE(1+R), where R is the reflective rate of the sound intensity, is established. A rubber is the most popular as the absorption substance. Most substances possess partial absorption characteristics. The reflective rate R is related to the impedance of Z1 and Z2 of the medium and substance, respectively which establishes the formula of ((Z2-Z1)/(Z2+Z1)) 2 . This rate becomes about 90% (about 70%) with the combination of water and SUS or stainless steel (water and Al or alminum). 
     In the present embodiment, the sound wave is set to be emitted or radiated obliquely to the cover member 5b as the absorption element and the resulting wave is reflected by the outer surface of the cylinder 5a. By adjusting the raw material and thickness of the cover member 5b in such a manner that the sound wave may be substantially damped during its travel in the cover member 5b, a minimum reflected sound field can be established, which brings in that, as seen from FIG. 7, the cover member 5b receives only the radiation force f1 due to the incidence sound field near the outer surface of the cylinder body 5a. Thus, the foregoing structure enables the rotor 5 to receive at its outermost periphery the tangential component F&#39; of the radiation force f1 due to the incidence sound field, resulting in that the maximum torque can be obtained. Without absorption element 5b, due to cancellation of both radiation forces in opposite directions, the rotor 5 remains fixed. 
     The cover member 5b is set to receive a force for rotating the rotor in the counter-clockwise direction by absorbing an energy from the resonator. The cover member 5b receives the force f1 upon incidence of the sound wave and the force f2 upon reflection thereof. The component of the forces f1 and f2 is applied to the rotor 5 in the tangential direction thereof, and results in a large rotating force or torque. It is to be noted that as seen in FIG. 8 the cylinder body 5a receives the force f3 upon incidence of the sound wave and the force f4 upon reflection thereof. 
     The transmission coefficient of the sound intensity in the cover member 5b, which is the reciprocal of the reflection coefficient thereof, is represented in the formula of T=1-R=4Z1Z2/ (Z1+Z2) 2 . 
     The sound impedance in water equals that in rubber, which leads to R=0 and T=100%. In the light of the fact that the sound wave absorption and ability of rubber is high, the rubber is the most suitable for the cover 5b. In addition, the reflection coefficient of sound intensity is about 90% with the combination of water and stainless steel like the combination of water and SUS, which reveals that stainless steel is excellent as a raw material of the cylinder 5a. 
     In order to obtain 100% in reflection coefficient, a gas is available instead of the metal reflecting member. FIG. 12 shows another embodiment in which the sound wave is set to be reflected at the border portion between a rubber layer 14 and an air layer 13. 
     For obtaining the maximum torque, half of the energy of the sound wave is to be absorbed at its first incidence in the cover 5b and the remaining half of the energy is to be absorbed after its reflection. By adjusting any of the frequency of the resonator, the distance between the resonator and the cover, rating of the cover 5b, the sound wave energy can be converted into a rotational movement or other movement in efficiency. 
     As mentioned above, no friction is generated during energy conversion as seen in the conventional manner, which results in the establishment of an efficient energy conversion. The present invention enables the energy converter to be used in a liquid and such usage increases the cooling effect of the converter. Furthermore, pressure can be derived from the sound wave at its incidence and reflection, which enables flexibility in design such as a location of the rotor. 
     It should be apparent to one skilled in the art that the above-described embodiments are merely illustrative of but a few of the many possible specific embodiments of the present invention. Numerous and various other arrangements can be readily devised by those skilled in the art without departing from the spirit and scope of the invention as defined in the following claims.