Title:
MECHANICAL TO ELECTRICAL TRANSDUCER DEVICE
United States Patent 3801839


Abstract:
A transducer element is disclosed herein made of, for example, a vulcanized chloroprene elastomer mixed with channel black to exhibit electrostrictive properties and biased with a DC voltage to convert a mechanical impact or vibration to corresponding electrical energy.



Inventors:
YO K
Application Number:
05/311433
Publication Date:
04/02/1974
Filing Date:
12/01/1972
Assignee:
RION KK,JA
Primary Class:
Other Classes:
252/62.9R, 310/319, 310/326, 310/328, 310/329, 310/800
International Classes:
B06B1/06; G01D5/14; H04R17/00; G01D5/16; G01H11/08; G01L1/00; G01L1/16; H01L41/113; H01L41/18; H01L41/193; H04R17/08; (IPC1-7): H01V7/02
Field of Search:
310/8,9.5 252
View Patent Images:
US Patent References:
2231159Piezoelectric device1941-02-11Gerlach



Primary Examiner:
Goldberg, Gerald
Assistant Examiner:
Budd, Mark O.
Attorney, Agent or Firm:
Wenderoth, Lind & Ponack
Claims:
What is claimed is

1. A mechanical-to-electrical transducer device comprising a transducer element for converting mechanical energy to electrical energy, formed of a vulcanized elastomer having mixed therewith 5 to 40 parts, based on the weight of the elastomer, of an electrically conductive material selected from the group consisting of channel black and furnace black and means for applying a DC biasing voltage across said transducer element.

2. A mechanical-to-electrical transducer device as claimed in claim 1, wherein said elastomer is selected from the group consisting of chloroprene rubbers, nitrile rubbers, isoprene rubbers, chlorosulfonated polyethylene elastomers and fluoro-elastomers including polar substituents in the side chains thereof.

3. A mechanical-to-electrical transducer device as claimed in claim 1, wherein said elastomer is selected from butadiene elastomers not including polar substituents in the side chains thereof.

4. A mechanical-to-electrical transducer device as claimed in claim 1, wherein said DC voltage across said transducer element has a value sufficient to establish an electric field whose strength ranges from 10 to 10 × 103 volts per centimeter of the thickness of the transducer element.

Description:
BACKGROUND OF THE INVENTION

This invention relates to a mechanical-to-electrical transducer device utilizing an electrostrictive material consisting essentially of an elastomer, and more particularly to such a device for converting a mechanical force, for example, a sound or a mechanical vibration to electrical energy and vice versa.

In addition to single crystal Rochelle salt, quartz, lead zirconate-titanate porcelains etc., there have been previously discovered synthetic high molecular compounds specially processed as piezoelectric materials. These synthetic high molecular compounds have been utilized in the form of film, such as polyvinylidene fluorides, polyvinyl chlorides, polycarbonates, 11-nylon etc. It is well known that films of such high molecular compounds can be rendered considerably high in piezoelectric properties by elongating the film maintained at a temperature adjacent to the softening point thereof, applying a DC voltage across the film in the direction of thickness thereof and raising the temperature of the film while the DC voltage continues to be applied thereacross. Then the film is allowed to be cooled to room temperature after which the voltage is removed from the film. It is said that this improvement in the piezoelectric properties of the high molecular films attributes to both spontaneous polarization caused from the rearrangement of dipoles therein due to the effect of polarization and the electrostriction of the films.

On the other hand, the spontaneous polarization has been heretofore difficult to effect in rubber-like materials or elastomers although the electrostriction is a long-established phenomenon occurring in such elastomers. This is because such materials include bridged bonds formed of high molecular components and effect the micro-brownian motion. Therefore it is considered presently difficult to impart piezoelectric properties to such elastomers.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new and improved transducer device utilizing an electrostrictive material consisting essentially of an elastomer for converting mechanical energy to an electrical energy with a high efficiency.

It is another object of the present invention to provide a new mechanical to electrical transducer device having a high flexibility in both shape and size depending upon the desired performance.

The present invention accomplishes these objects by the provision of a mechanical to electrical transducer device including a transducer element for converting mechanical energy to electrical energy, characterized in that the transducer element is formed of a vulcanized elastomer having mixed therewith a predetermined amount of a filler of electrically conductive material and has a DC biasing voltage applied thereacross.

The elastomers may be preferably selected from the group consisting of chloroprene rubbers, nitrile rubbers, isoprene rubbers, chlorosulfonated polyethylene elastomers, and fluoro-elastomers including polar substituents in the side chains thereof. Alternatively, it may be a butadiene elastomer not including no polar substituents in the side chains thereof.

The electrically conductive material of the filler may be advantageously selected from the group consisting of carbon black and graphite.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a sectional view of a mechanical-to-electrical transducer device with an electric circuit embodying the principles of the present invention;

FIG. 2 is a view similar to FIG. 1 but illustrating a modification of the invention; and

FIG. 3 is a block diagram illustrating one application of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is based upon the discovery that certain elastomers mixed with suitable electrically conductive fillers exhibit conspicuous electrostrictive and piezoelectric properties as long as they are biased with DC voltages. Vulcanized elastomers exhibit the electrostriction dependent upon both the types of fillers, such as reinforcing agents and aging resisters involved, and the mixing and kneading process.

It has been found that the filler formed of a suitable electrically conductive material such as carbon black much enhances the electrostrictive properties of the vulcanized elastomers. Particularly, after elastomers including polar substituents in the side chains thereof, for example, chloroprene rubbers, chlorosulfonated polyethylene elastomer, polyisoprene rubbers, and fluoro-elastomers etc. have been suitably mixed with channel black and vulcanized, the elastomers thus processed can have electrostrictive constants amounting to a value to 10-5 c.g.s. in e.s.u. When put in a DC electric field having, for example, a strength of 300 volts per each centimeter of the thickness of the material, the vulcanized elastomers exhibit piezoelectric properties. For example, their piezoelectric constants d11 have been measured to be in the order of 10-5 c.g.s. in e.s.u. This figure is substantially identical to the value of the piezoelectric constant of lead zirconate porcelains. Also a "g" constant (4πd1111) representing a voltage sensitivity is in the order of 0.5 volt per grams-centimeter. That is, a force of one dyne per square centimeter is converted to an electric output of 0.5 × 10-3 volt. This means that microphones formed of the elastomers materials as above described to receive directly a sound pressure has a sensitivity of -66 dB. sufficient for practical purposes.

It has been also found that the present invention is effective for imparting high electrostrictive and piezoelectric properties to some elastomers not including polar substituents in the side chains thereof as will be described hereinafter.

EXAMPLE I

100 parts of a chloroprene rubber of the W type, 4 parts of magnesia(MgO), 1 part of stearic acid and 35 parts of channel black were thoroughly mixed with one another and then vulcanized at a temperature of 150°C for 30 minutes. The vulcanized elastomer had a dielectric constant and an electrostrictive constant measured at 90 and 10-5 c.g.s. in e.s.u. respectively.

For comparison purposes, the same starting materials were used in the same amounts as above described except for channel black being omitted and the process as above described was repeated. The resulting dielectric constant and electrostrictive constant had measured values of 11 and 10-7 c.g.s. in e.s.u. respectively.

EXAMPLE II

100 parts of a nitrile rubber including 30 percent of nitrile and commercially available under Hycar DN 302 (trade mark), 5 parts of zinc oxide(ZnO), 1 part of stearic acid, 1.5 parts of dibenzothiazol disulfide, and 40 parts of furnace black were intimately mixed with one another and vulcanized at 150°C for 20 minutes. The results of various measurements indicated a dielectric constant of 52 and an electrostrictive constant of 10-6 c.g.s. in e.s.u. With furnace black omitted, the process as above described was repeated to yield a dielectric constant of 8 and a electrostrictive constant of 10-8 c.g.s. in e.s.u.

Nitrile rubbers are inherently inferior in electrostriction to chloroprene rubbers but the substitution of furnace black for channel black improves the electrostriction. For example, the same results as above described were given with 20 parts by weight of channel black.

EXAMPLE III

100 parts of an isoprene elastomer, 5 parts of zinc oxide(ZnO), 3 parts of stearic acid, 2.5 parts of sulfur, 1 part of dibenzothiazolyl disulfide, 0.2 part of tetramethylthiuram disulfide and 20 parts of channel black were fully mixed with one another and vulcanized at 160°C for 15 minutes. The product was measured to have a dielectric constant of 80 and an electrostrictive constant of 2.3 × 10-6 c.g.s. in e.s.u.

As in Example I, the same materials were used in the same amount as described above with the channel black omitted and the above process was repeated. The results of measurements indicated that the dielectric constant and electrostrictive constant had respective values of 2.8 and 2.6 × 10-8 c.g.s. in e.s.u.

EXAMPLE IV

100 parts of a copolymer of propylene hexafluoride and vinylidene fluoride elastomer, 15 parts of magnesia(MgO), 3 parts of N, N'-dicinnanylidene -- 1.6 -- hexane diamine and 5 parts of channel black were thoroughly mixed with one another and then vulcanized at 150°C for 30 minutes. The resulting dielectric constant and electrostrictive constant had values of 55 and 4.0 × 10-6 c.g.s. in e.s.u. respectively. Further the products was high in oil, chemical and weather resistances so that it could be used at temperature as high as 250°C.

The process as above described was repeated with the same materials but the channel black omitted to provide a dielectric constant of 9.5 and an electrostrictive modulus of 5 × 10-8 c.g.s. in e.s.u.

EXAMPLE V

100 parts of a chlorosulfonated polyethylene elastomer; 10 parts of magnesia(MgO), 2 parts of dipentamethylenethiuram tetrasulfide, 10 parts of dioctyl phthalate and 15 parts of channel black were formed into an intimate mixture. Then the mixture was vulcanized at 150°C for 30 minutes.

The results of measurements indicated a dielectric constant of 85 and an electrostrictive constant of 10-6 c.g.s. in e.s.u. The product could be continuously used at 150°C and exhibited a chemical resistance.

The process as above described was repeated with the channel black and dioctyl phthalate omitted to provide a dielectric constant of 5.6 and an electrostrictive constant of 6 × 10-8 c.g.s. in e.s.u.

EXAMPLE VI

100 parts of a butadiene rubber of high transtype (which does not include polar substituents in the side chains thereof), 5 parts of zinc oxide(ZnO), 2 parts of stearic acid, 3 parts of tetra-methylthiuram disulfide and 20 parts of channel black was used. The vulcanization was effected at 160°C for 15 minutes. The dielectric constant and electrostrictive constant had measured values of 54 and 5 × 10-6 c.g.s. in e.s.u. respectively.

With the channel black omitted, a dielectric constant and an electrostrictive constant were measured at 14 and 1.2 × 10-8 c.g.s. in e.s.u. respectively.

In the above Examples, the dielectric constant and electrostrictive constant were measured in an electric field having a strength of 300 volts per centimeter.

Examples of elastomers for use in practicing the present invention involve chloroprene rubbers, nitrile rubbers, isoprene rubbers, fluoro-elastomers, chlorosulfonated polyethylene elastomers, butadiene rubbers. Preferable examples of those elastomers may be chloroprene rubbers and nitrile rubbers high in content of nitrile. Among the fluoro-elastomers, a copolymer of propylene hexafluoride and vinylidene fluioride is advantageously used and the butadien rubbers are preferably of high trans-type.

The amount of carbon black added depends upon both the type thereof and the type of the elastomer. It has been found that the maximum amount of the carbon black should not exceed a magnitude above which the associated elastomer after having been vulcanized become conductive, that is, has a resistivity of 106 megohms-centimeter or less. In other words, the carbon black can be added to the associated elastomer in an amount of ranging from 5 to 40 part relative to, 100 parts of the weight of the elastomer. As above described in conjunction with Example II, channel black is superior to furnace black. That is, channel black may be used in amounts less than that of furnace black and still give similar results.

Also it has been found that the DC voltage applied across the electrostrictive element has preferably a value sufficient to establish an electric field whose strength ranges from 10 to 10 × 103 volts per centimeter of the thickness of the element.

Referring now to FIG. 1 of the drawing, there is illustrated a mechanical-to-electrical transducer device constructed in accordance with the principles of the present invention whereby an impulsive motion, for example, an impact or a mechanical strain is converted to corresponding electrical energy. The arrangement illustrated comprises a disc-shaped transducer element 10 formed of an electrostrictive elastomer such as above described in conjunction with the Examples of the present invention, a hot electrode 14 of any suitable metallic material such as brass coextensive with and disposed on one of the opposite faces of the disc, and an electrically insulating block 14 encircling in contact relationship both the lateral surface of the interconnected element and electrode 10 and 12, respectively and the exposed surface of the electrode 12 to leave only the central exposed portion of the electrode surface with an output electrode 16 disposed on that exposed surface portion. Then the assembly thus-produced has the entire surface covered with a metallic shield 18 except for the exposed surface portion and a damper element 20 is formed, for example, of a foamed urethane attached to the other face of the transducer element 10 through the metallic shield 18. Then the output electrode 16 and the metallic shield 18 are connected to a pair of output terminals 22.

In order to bias the transducer element 10 with a DC voltage, a source 24 of DC voltage is connected across the output electrode 16 and the metallic shield 20 through a resistor 26.

Under these circumstances, an impact can be applied to the damper element 20 in the direction of the arrow A shown in FIG. 1. This results in the generation of a corresponding AC output at the output terminals 22.

With the transducer element 10 formed into a thickness of 2 millimeters of the electrostrictive elastomer of Example V and having a bias voltage of 18 volts applied thereacross, the transducer device as shown in FIG. 1 could generate an output of 50 millivolts in response to an iron ball(not shown) with a weight of 12 grams falling upon the damper element 20 thereof. Thus it will be appreciated that the present invention provides a durable impact meter having a high sensitivity. This is because the elastomer involved is soft enough to decrease its mechanical impedance to an extremely small value and still the elastomer itself serving as a sensor element which is very tough to motions of mechanical systems, for example, impacts.

FIG. 2 shows a modification of the present invention applied to a vibration pick-up device. As shown, a two-part housing 30 has a disc-shaped transducer element 32 formed of an electrostrictive material prepared in accordance with the present invention and suitably fixed on one of two opposite faces thereof to the inner surface of the wall of the housing 30 through a thin metallic electrode 34 and a weight 36 coextensive with and disposed on the other face of the element 32 through another thin metallic electrode 38. Then both electrodes 34 and 38 are connected to a pair of output terminals 40 through leads and across a bias source 42 of DC voltage.

In operation, any vibration is applied to the device in direction of the arrow B shown in FIG. 2. This results in the generation of a corresponding AC output across the output terminals 40.

FIG. 3 illustrates a transducer device 44 such as shown in FIG. 1 connected through any suitable auxiliary device 46 to both an display device 48 and a recorder 50. The auxiliary device 46 may be an amplifier for suitably amplifying the output from the transducer device 44 or a translator for changing the output from the transducer device 44 to another electric quantity through electrical computations. Then the output from the device 44 is displayed on the display device 48 and recorded by the recorder device 50.

The present invention is very superior in utility to the prior art type of piezo-electric single crystals and porcelains because the elastomer involved is extremely small in mechanical impedance and formed in any desired shape and size. Further the invention can readily and economically provide mechanical-to-electrical transducer devices having any desired performance by properly combining various types of elastomers with one another.

While the present invention has been described in conjunction with a few preferred embodiments thereof it is to be understood that various changes and modifications may be resorted to without departing from the spirit and scope of the invention. For example, the present invention is equally applicable to electrical-to-mechanical transducer devices.