EP0732864A2 - Acoustic transducer - Google Patents

Acoustic transducer Download PDF

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Publication number
EP0732864A2
EP0732864A2 EP96103044A EP96103044A EP0732864A2 EP 0732864 A2 EP0732864 A2 EP 0732864A2 EP 96103044 A EP96103044 A EP 96103044A EP 96103044 A EP96103044 A EP 96103044A EP 0732864 A2 EP0732864 A2 EP 0732864A2
Authority
EP
European Patent Office
Prior art keywords
film
receiver
acoustic
acoustic transmitter
polymer film
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP96103044A
Other languages
German (de)
English (en)
French (fr)
Inventor
Richard Hunter Brown
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Whitaker LLC
Original Assignee
Whitaker LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Whitaker LLC filed Critical Whitaker LLC
Publication of EP0732864A2 publication Critical patent/EP0732864A2/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R17/00—Piezoelectric transducers; Electrostrictive transducers
    • H04R17/005—Piezoelectric transducers; Electrostrictive transducers using a piezoelectric polymer

Definitions

  • This invention relates to an acoustic transducer utilising polymer piezoelectric material.
  • piezoelectric polymer film may be used both to send and receive acoustic or ultrasonic signals into and from air as a transmission medium.
  • the piezoelectric polymer film is used in the form of a membrane where a change in applied voltage to the film electrodes (considering first a transmitter that acts similar to a loudspeaker) causes a change in length dimension, thus creating an effective change in radius of curvature and thus a perceptible radiation of acoustic energy into air, or conversely (as a microphone), where a change in sound pressure causes a change in radius of curvature and thus generates a corresponding voltage output.
  • the known devices function reasonably well, it is desirable to improve thereupon and especially provide a device that is usable in a cylindrical cavity or conduit where the performance of known devices is limited.
  • the present invention provides an acoustic device comprising a cylinder of uniaxially-oriented piezoelectric polymer film with its machine axis aligned substantially circumferentially, such that in transmission mode an applied electrical signal creates an acoustic signal radiating from one end of the cylinder, and in reception mode an incident acoustic signal arriving into one end of the cylinder creates a corresponding electrical response across the film electrodes.
  • the device of the present invention is formed by rolling into a compliant cylinder a piezoelectric polymer film with the predominant piezoelectric sensitivity oriented in a substantially circumferential direction.
  • an applied varying electrical signal creates a change in diameter of the cylindrical assembly.
  • this change in diameter tends to launch an acoustic wave radiating outwards from the cylinder.
  • the transducer is mounted within a cylindrical cavity or conduit, in which case the cylindrical radiating wave is suppressed and the predominant radiation direction is along the axis of the cylinder or conduit.
  • the cylindrical assembly is held in place by means of an adhesive tape applied fully over one side of the piezoelectric polymer film prior to assembly.
  • adhesive tape typically comprises a polyester carrier film, coated on each side with a layer of acrylic adhesive. Due to the mechanical properties of the piezoelectric polymer film and such adhesive tape, the compliance of the assembly is high, and so mechanical resonances within the assembled device are not sharply defined in frequency. This permits operation over a band of frequencies, rather than constraining operation to a single very specific frequency.
  • a device of the present invention may preferably employ a piezoelectric polymer film element having dimensions approximately 15mm x 40mm, with film thickness of 28 ⁇ m and one surface bearing a layer of double-coated adhesive tape such that when the film element is wound up around a 4mm mandrel, its final diameter is in the region of 4.7mm with a length of 15mm.
  • the electrode pattern is deposited on the film by means of screen-printing with suitable conductive ink which may preferably allow contacts to be formed thereto by means of crimped connectors. To allow such connectors to be applied without risk of forming an electrical short-circuit through the film thickness, it is necessary to design an electrode pattern which offers displaced top and bottom lead-attach pads.
  • such pads are allowed to project to the rear of the cylinder, parallel to its axis, thereby allowing metal contact pins to be fixed in line with the transducer.
  • the patterned film electrode pads are allowed to project beyond the cylinder, but are allowed to bend through a right angle for subsequent termination direct to a printed-circuit board by means of, for example, metal eyelets or rivets. Other forms of electrical connection are not excluded.
  • a transducer according to the present invention is based on a piece of piezoelectric polymer film 10 which is metallised on either side with electrodes 12 and 14.
  • the electrodes 12 and 14 have connector portions 12a and 14a brought out to one side of the transducer.
  • the film 10 is laminated with an adhesive suitably in the form of a carrier tape 16 coated on each side with adhesive 18 and 20 as seen in Figure 2.
  • contact pins 22 are fixed to the film/tape composite described above and the film/tape composite is then wrapped around a mandrel 24 in a scroll-like manner to form the transducer of the present invention.
  • the piezoelectric polymer film 10 is uniaxial film with the principal or machine axis aligned in the direction of the arrow A such that in the resulting transducer of Figure 4 the machine axis is circumferential.
  • the transducer may be provided with a plug or base 26 which acts as an acoustic reflecting surface.
  • the radiation (or reception) efficiency is enhanced by the plug or base 26, with a corresponding change occurring in the frequency response of the transducer, as with the end closed off, standing waves occur at a lower frequency than when the end is open.
  • the transducer may optionally include a reducing nozzle 30 which further enhances radiation (or reception) efficiency by providing a reduction in diameter through which the acoustic waves are transmitted or received just in front of the transducer.
  • Figure 6 illustrates the transducer of the present invention mounted as part of a cartridge 32 which includes the base 26 and the reducing nozzle 30, along with a cylindrical containment 34.
  • Figure 7 shows the transducer of the present invention for use in propagating or detecting sound (acoustic waves) within a conduit 36.
  • the conduit 36 for the acoustic signal is formed of a material which is electrically conductive or semi-conductive (such as carbon-loaded rubber) and thus may carry electrical signals unrelated to the acoustic signals being generated and detected by the transducer
  • suitable piezoelectric polymer film material such as uniaxially-oriented PVDF (polyvinylidene fluoride) can withstand an applied electric field strength of around 30 volts per micrometer of thickness.
  • the PVDF film has a thickness of 28 ⁇ m, hence the applied electrical drive signal should not exceed 840 volts.
  • sound pressure levels in excess of 112dB may be detected after propagating a distance of one metre down a conduit 5mm in diameter.
  • a similarly constructed transducer may show a sensitivity of -80dB (re 1 V/Pa).
  • the foregoing example has the machine axis of the film circumferential.
  • the machine axis could be slightly out of true circumferential alignment, provided the major directional component is circumferential, for example by winding the film in a shallow helix.
  • a transducer according to the present invention has been found to operate successfully within certain ranges of frequency, particularly in the region of 2kHz to 25kHz when the transducer is tested in free space at close range. Since the attenuation of sound increases with frequency, the received signal after propagating some distance in air will show a corresponding reduction in signal content at high frequencies. For this reason, it is found preferable to operate such devices nearer the lower end of the range referred to above - i.e. in the region of 2kHz to 3kHz.
  • the device thus allows transmission of acoustic waves through a duct or conduit, whereby a transducer according to the present invention could be disposed at each opposite ends of the duct or conduit with one being operated as a transmitter and the other as a receiver such that the signal could be passed therealong.
  • a reflector could also be used at one end and electronics provided to switch one transducer between transmit and receive modes.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Piezo-Electric Transducers For Audible Bands (AREA)
  • Transducers For Ultrasonic Waves (AREA)
EP96103044A 1995-03-11 1996-02-29 Acoustic transducer Withdrawn EP0732864A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB9505003.5A GB9505003D0 (en) 1995-03-11 1995-03-11 "Acoustic transducer"
GB9505003 1995-03-11

Publications (1)

Publication Number Publication Date
EP0732864A2 true EP0732864A2 (en) 1996-09-18

Family

ID=10771102

Family Applications (1)

Application Number Title Priority Date Filing Date
EP96103044A Withdrawn EP0732864A2 (en) 1995-03-11 1996-02-29 Acoustic transducer

Country Status (3)

Country Link
EP (1) EP0732864A2 (2)
JP (1) JP3930580B2 (2)
GB (1) GB9505003D0 (2)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6441540B1 (en) * 1999-11-05 2002-08-27 Toray Techno Co., Ltd. Cylindrical piezoelectric transducer and cylindrical piezoelectric vibrating element
EP1254585A4 (en) * 1999-12-09 2008-10-29 Sonionmicrotronic Nederland MINIATURE MICROPHONE
GB2579672A (en) * 2018-12-12 2020-07-01 Thales Holdings Uk Plc A piezo-resistive hydrophone
CN111373768A (zh) * 2017-11-21 2020-07-03 日东电工株式会社 用于形成压电扬声器的层叠体
US12071761B2 (en) 2017-11-21 2024-08-27 Nitto Denko Corporation Sound reducing system

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013027696A1 (ja) * 2011-08-24 2013-02-28 株式会社村田製作所 アクチュエータ素子及び該アクチュエータ素子の製造方法
US20200314555A1 (en) * 2015-12-04 2020-10-01 Harman Becker Automotive Systems Gmbh Electro-active loudspeaker

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6441540B1 (en) * 1999-11-05 2002-08-27 Toray Techno Co., Ltd. Cylindrical piezoelectric transducer and cylindrical piezoelectric vibrating element
EP1254585A4 (en) * 1999-12-09 2008-10-29 Sonionmicrotronic Nederland MINIATURE MICROPHONE
CN111373768A (zh) * 2017-11-21 2020-07-03 日东电工株式会社 用于形成压电扬声器的层叠体
EP3716647A4 (en) * 2017-11-21 2021-08-18 Nitto Denko Corporation LAMINATE BODY FOR FORMING A PIEZOELECTRIC SPEAKER
US11252510B2 (en) 2017-11-21 2022-02-15 Nitto Denko Corporation Piezoelectric speaker-forming laminate
US12071761B2 (en) 2017-11-21 2024-08-27 Nitto Denko Corporation Sound reducing system
GB2579672A (en) * 2018-12-12 2020-07-01 Thales Holdings Uk Plc A piezo-resistive hydrophone
GB2579672B (en) * 2018-12-12 2021-01-06 Thales Holdings Uk Plc A piezo-resistive hydrophone

Also Published As

Publication number Publication date
GB9505003D0 (en) 1995-04-26
JPH08265897A (ja) 1996-10-11
JP3930580B2 (ja) 2007-06-13

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