JPS5922378A - Piezoelectric converter and method of producing same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to piezoelectric transducers, and more particularly to a piezoelectric transducer comprising a polymer formed into a cylindrical shape and a method for manufacturing the same.

The pressure of polymeric materials has been known for a long time.

Piezoelectricity results from a polarized arrangement of repeating molecular units in long molecular chains, each unit forming a molecular dipole. Although this net molecular polarization can occur naturally, the piezoelectricity of the polymer is increased by polarizing the long molecular chains. This can be done by stretching the Nishinomiya 1 polymer to elongate the molecular chains, or by polarization, that is, applying a large electric field to the material and reorienting the molecular dipoles in the direction of the electric field to produce the desired net polarization arrangement. It is done by letting A well-known development and application of polymeric converters is the use of bipolymers in a 7-t form. A significant problem in the polarization of existing transducer materials is the arcing that occurs when a single strong electric field is applied by the electrodes at each end of the polymer note. Arcs that form around the edges of flat sheets are difficult to prevent, and they prevent effective polarization of the material. This is because the electric field is short-circuited.

The present invention provides a transducer with a cylindrical structure that provides two important advantages. The first is to enable polarization of polymeric materials without causing arcing, which was a problem in the past.
Second, by knitting the cylindrical transducer into a desired shape, a fixed form of transducer is possible.

The present invention further provides stretching the polymer coating of the inner conductor;
A method of manufacturing a linear transducer is provided comprising the step of applying a high voltage between the outer surface of the coating and an inner conductor. This provides an effective method of continuously changing the polarization ratio of a polymeric converter as opposed to previously known batch processing. Desirably, the assembly is constructed from polyvinylidene fluoride.

The present invention will be explained in detail below according to examples.

Referring to FIG. 1A, a wire transducer 10 according to the present invention is shown. The transducer has a center conductor 12 and a side 1
．． It consists of a shell of polarized polymeric material 14 surrounding it. Polymer i'#414 is a piezoelectric polymer, in a preferred embodiment polyvinylidene fluoride (hereinafter referred to as PVDF).
Consists of.

PVDF is CF2-CH, a semi-crystalline polymer formed by long molecular chains dividing the molecular units. PVDF generates piezoelectricity when a repeating molecular unit in a long molecular chain produces a net polarization. When the transducer is required to be used in a conductive medium, such as in seawater, the transducer does not require the addition of electrodes to the outer surface of the coating 14 to utilize piezoelectric signals. Figure A shows an example of such an application. Transducer 10 is formed from a length of central conductor 12 and a polymeric jacket 14, one end of which is sealed by an electrically insulating cap 15. Typically, the length of linear transducer 10 is a fraction of the wavelength of the signal selected in the medium in which transducer 10 is used.

The cap 15 has a polymeric coating in the end region to be sealed.
formed by applying heat to and welding the insulating strips together. FIG. 1A also shows a utilization device 17 connected to the center conductor 12 and connected by an electrode 19 to the outer surface m of the polymeric coating 14 via a conductive medium 18 (here seawater). Ru. Utilization equipment +f17 processes the signals generated by converter 10 and includes a known signal processing device and display. For applications in nonconductive media or other applications, a second conductor 16, such as an outer conductive coating, is provided on the outside of the polymeric material 14 and the first B
A transducer 10' as shown is formed. The utilization device 17 in this case includes conductors 12 and 16 for processing the signals generated by the sandwiched piezoelectric layer 14.
directly read.

Polymeric materials, such as P, V D F, when their long molecular chains are stretched and one repeating molecular unit is oriented in a certain direction, generate E-like dipole mo knots and exhibit significant piezoelectricity. These are brought about by stretching and polarizing the polymer, respectively, by applying an electric field along the direction in which the dipoles are to be oriented. Piezoelectric capability is further increased by forcing the semi-crystalline structure of PVDF into crystalline Form I (FORM I, or B). Crystal form ■ has dipole fractions of repeating units oriented in the same direction. It was found that the crystal ratio to crystalline form (III) is brought about by stretching and polarization of the polymer.

Details regarding piezoelectricity of polymers and various geometries for PVDF can be found in 1973, Advances in Poly.
mer5science, Springer-Verl
ag, Vol. 11 R, Hayakawa and Y
, rPiezo electric by Wada
y and Re1ated Properties
f PolyIner Films J.

Referring now to FIG. 2, there is shown an apparatus used for monopolymer polarization and linear transducer fabrication. First, a 7-polymer material 20, for example I) V D F pellets, is placed in hopper 2.
Put it in 2.

I) V D I-The pellets 20 are conveyed to the melting chamber 26 by the feed screw 24 . The P, V D F pellets 20 in the melting chamber 26 are melted in an area defined by a heating coil 28, which surrounds the lower portion of the chamber 26 and provides sufficient heat to melt the polymer pellets. The conductor 60 is withdrawn from a supply reel (not shown) and is connected to the molten polymer 20 at the bottom of the melting chamber 26.
A wire 67 having a pattern 66 of polymeric material is fed through the extrusion die 32 with a center . The thickness of the coating 66 is 120' of molten material (I: 3U of iuT conductor).
is determined by the velocity of the melt and the hydrostatic pressure of its melted interest. Typical temperatures for the extrusion process are on the order of about 250°C. The wire 60 is then passed through the area where an air injector 64 directs a jet of air onto the wire 37 to reduce the temperature of the two coatings 66 and cause them to solidify onto the conductor 60. The conductor 60 with the solidified polymer coating 66 is drawn into the elongated die 40 . The tice shape has beveled or stepped holes to reduce the cross-section of the coating 66. Wire 57 is pulled through the elongated die by rollers 48. Roller 48 rotates in the opposite direction as indicated by the arrow in FIG. 2, gripping wire 67 and pulling it out of die 40. Elongation of the coating 66 occurs as the coating 66 is pulled at a predetermined speed across the die 40, and the tapered hole in the die holds a portion of the coating 66 back. The cross section of the coating 36 is reduced with an elongating die 40 by a factor S (stretching ratio 5:1). Other stretch rates can also be used to achieve a given level of overall molecular orientation. For a stretching rate of 5, the coating 66 exits the extrusion die 62 at a speed of 4 of the conductor 60 and exits the elongation die 4U at the same speed as the conductor 60 at 1 pressure. The extension die is located near the extrusion die 62.

This is due to the stretching operation of the stretching die mold 40.

This is because the coating slides over the wire between the two dies. The temperature of the elongation die is maintained by the heating coil 41 to facilitate elongation of the coating 66 and to prevent it from becoming hot enough to cause the molecules to return to their original position after elongation. The preferred temperature for the elongated die mold is a rotation of 110-130'C. Approximately 130°
The temperature should not exceed C or else the molecular arrangement achieved by elongation will be lost and shattered. As the coating slides over the wire between extrusion die 62 and elongation die 40, the lubricant on the wire facilitates the elongation action. The ventilation between the two dies is adjusted so that the temperature of the membrane rupture exiting the extrusion die 62 is within the temperature range of the elongation die 40.

When the coated conductor 6U emerges from the elongated die 40i, it bleeds through the polarizing electrode 42 to a take-up reel (not shown), where the conductor 30 is connected to a voltage. The polarizing electrode 42 has a cylindrical shape. and is connected to a high voltage source 44, which supplies a voltage to generate an electric field in the coating filter 6. The electric field extends radially from the conductor 60 and causes the molecular dipoles of the polymer to Polarize sufficiently. 5th
The figure shows a cross-section of transducer wire 37, with arrow 69 representing the direction of the electric field applied by voltage source 44. The arrow also represents the direction in which the molecular dipoles are aligned. The applied voltage is selected to generate an electric field of at least 100 volts per micrometer. The length of the polarizing electrode and the speed at which the wire 67 is withdrawn through the electrode 42 are selected such that the electric field of a given magnitude is present for a sufficient period of time to effect polarization. Typically, 80 degrees of possible polarization is achieved in the first 5 minutes. If a transducer of the type shown in FIG. 1B is desired, the ruptured wire 30 may have conductive layer 16 deposited over coating 66; 1'l].

It has been found that by applying a polarizing electric field at the same time as stretching the polymer, the polymer can be stimulated by applying a polarizing electric field. This can be explained by considering that a mouse's energy is required. Conventionally, this energy -#lI is applied mechanically by a stretching step using VC to stretch a long molecular chain, and the required energy is The remainder was given electrically at a later time by the polarization fhystep by directing the dipole claw Mrc force of the molecular chain.However, due to the decrease in efficiency due to separate application, the required polarization [beyond the he energy] The simultaneous use of mechanical and electrical energy makes it possible to efficiently supply the required energy.

This has the advantage of allowing lower fields or faster separation ratio times for a given level of polarization.

Referring to FIG. 6, another embodiment for producing the wire conversion of the present invention by simultaneously carrying out the drawing step and the polarization step is shown. The extrusion device for the coated conductor 3 [a--is the same as that in FIG. 2 and is therefore not shown.

60 conductors exiting the extrusion die 62 are sent to the die 50.

The "th" part 52 of the elongated die mold 50 holds the elongated die 40.
The same shell has a tapered or stepped hole. The temperature is also maintained at the same predetermined temperature by the disconnected coil 54. The wire 67 is then inserted into the second elongated die 50.
It is drawn out into section 56. That part is the constricted area 57
The temperature of the second region 56, which is separated from the first portion by the heating coil 58 and is maintained by the heating coil 58, has a lower thermal conductivity than the elongation temperature. This prevents depolarization of the polymeric coating 66 after stretching. At this time, the high voltage vertical source 6
A zero is read directly between ground and the conductive die. As previously mentioned, the center conductor 60 of the Conversion 2 wire is grounded and placed on a take-up reel (not shown). In this way, elongation and polarization occur simultaneously. The combination of coil 54 and reduced heat transfer to region 56 of die 50 lowers the temperature where the wire exits to about 90° C. or below. The optimum temperature for simultaneous elongation and polarization is about 50°C. A rapid cooling step after exiting the elongated die 50 is provided to fix the polarization.

Now, referring to FIG. 4, the transformation of the present invention? An example of application to Fang Wonna will be shown. Means of transportation, e.g. water vessel 1
00 pulls the transducer play 110 to a predetermined depth. The transducer array 110 is also formed by a plurality of P V D'Ii' wire transducer elements 112 . Each converter element 11
2 is similar to the wire converter 10 shown in FIG. 1A,
It consists of a conductor 12 surrounded by a cylindrical polarized polymer 14, one end of which is camped to insulate the central conductor. The opposite 11111 of conductor 12 is connected to one conductor of multiconductor cable 120. Each converter element 1
21d cable 1200 is connected to one conductor. Then, the sonar system 1i111 device 130 is connected to each converter element 11.
The signals to 2 are individually processed. Of course, all the conductors are conductive so as not to short the signals produced between the inner surface of the layer 14 (which is read in tandem with the conductor 12) and the outer surface of the layer 14 (which is in contact with the water). insulated from sexual seawater.

Each transducer element can also be formed by knitting a length of transducer 10 into pieces of a predetermined shape. For example, a predetermined length of transducer 10 may be loosely zigzag shaped and then stiffened to provide the desired wavelength of molecules 19 in the irrigation water. It can be made into a square of about the same size.

The sonar device of FIG. 4 can operate in active or passive mode. In the active mode, the sonar combating device 160 enriches the beamformer and initially transmits drowsiness signal pulses in the appropriate phase relationship to the transducer elements 112 and transmits the drowsiness signal pulses to the transducer array 1
20 to generate a sound wave beam in a predetermined direction. The sonar controller then operates the transducer elements 112 in a predetermined phase relationship to detect reflected signals from a predetermined direction. In passive mode, only the latter function is performed. In either case, the 5 reflected signals are directly processed by a suitable signal processing device, and the results are transmitted to the utilization device 2, e.g.
sent to the display. Beamforming functions for transmitting and receiving signals are well known in the art.

It will be apparent to those skilled in the art that modifications to the embodiments of the invention are possible within the scope of the invention.

For example, larger diameter wires can be used to create polarized polymer coatings. Alternatively, the cylindrical polymer can be later cut and removed from the wire, or the polymer sheath can be directly extruded to create a narrow continuous sheet of polarized ifi polymer.

[Brief explanation of the drawing]

FIG. 1A shows a first embodiment of the transducer of the invention. FIG. 1B shows a second embodiment of the transducer. FIG. 2 is a sectional view of a linear transducer suppression device, and FIG. 6 is a sectional view of a second embodiment of a portion of the device shown in FIG. FIG. 4 shows an example of underwater use of a converter tube using a plurality of converter elements shown in FIG. 1A. FIG. 5 is a cross-sectional view of the transducer, with arrows indicating the direction of the polarization electric field and the direction of arrangement of molecular dipoles. (Explanation of symbols) 10: Transducer 12: Center conductor 14: Coating 15: Camp 17: Utilization device 28: Heating coil 60: Conductor 62: Extrusion die 40: Elongation die 42: Polarization awakening pole 44: High section pressure source. IG4

Claims (5)

[Claims] (1) A center conductor, a molecularly polarized polymer surrounding the conductor; A converter consisting of. (2) A fifth conductor having a separate length, and a piezoelectric material layer provided around the surface portion of the conductor. A piezoelectric material layer provided on the surface of the piezoelectric layer facing the first conductor A transducer consisting of a second conductor; (3) Supply a wire with a center conductor of 9 turns 'Jt' wrapped by a polymeric insulator. Consisting of 4 steps of applying an electric field between the center conductor and the outer surface of the polymeric insulator? A method for manufacturing a linear transducer. (4) A method for manufacturing a linear transducer comprising the steps of: coating a conductor with a polymer layer, stretching the polymer on the conductor, and applying an electric field between the conductor and an outer surface of the polymer. (5) the step of stretching the polymer and the step of applying the electric field are performed simultaneously h. A method for manufacturing a linear transducer according to claim (4).