Nova Patents
US3663841A

Ultrasonic transducers

Abstract

This record has no abstract on file.

US3663841A, drawing sheet 1
Sheet 1 of 6

Term

Term ended

Expired 16 May 1989, 37.4 years ago.

  1. Priority and filed
  2. Granted
  3. Expired
  4. Today

5 claims: 5 independent, 0 dependent

  1. 1
    What we claim is:1. A transducer for radiating ultrasonic power when energized by an electrical signal of ultrasonic frequency, comprising, in combination: a piezoelectric element having an annular shape;electrodes provided upon the inner and the outer curved surfaces of said piezoelectric element to permit said element to be vibrated in a circumferential mode when said electrical signal is applied to said electrodes;a radiating member having the shape of a truncated cone with a continuous conical portion closed at one end thereof by a flat portion unitary and integral with said conical portion and open at the other end thereof with a free unsupported periphery;ULTRASONIC TRANSDUCERS This invention relates to ultrasonic transducers, and more particularly to such transducers capable of radiating ultrasonic power at a relatively high level (above 10 watts r.m.s) for use, for example, for rodent repelling purposes. It is an essential feature of certain rodent repelling devices that the ultrasonic signal should be radiated at a frequency which does not affect human beings and other animals it is not desired to disturb. Further, the frequency of the radiated signal must fall within the critical range of maximum sensitivity of the animal to be repelled. The transducer should be capable of being designed to operate in explosion hazard areas and have a very low failure rate. In addition it is desirable that the transducer should radiate the ultrasonic signals in as broad a field as possible and with the maximum power. Hom type dynamic loud speakers (Tweeters) have been employed to convert the electrical signals generated for pest control into ultrasonic waves. These devices have a number of limitations and problems associated with their use for this purpose. Primarily a tweeter is designed to operate from about 5 kc/s up to a maximum of 20 kc/s. Because the critical sensitivity of the rodent to be repelled lies between 20 and 50 kc/s the tweeter is operated beyond its upper limit with a consequent 25 large reduction in power. Dynamic speakers of whatever type have a resonant frequency much below that of the desired ultrasonic frequency and therefore considerable power is required to drive the diaphragm and this introduces unacceptable losses. Because of the small diaphragm diameter and 30 associated horn, at high frequencies the angle of radiation is narrow and sharply directional necessitating a number of speakers to cover a given area. Dynamic speakers used for this purpose are inherently unreliable when operated above 20 kc/s and the presence of a current carrying voice coil which dissipates heat can make the speaker unsuitable in certain explosion hazard areas. The present invention consists in an ultrasonic transducer which includes a piezo-electric element of annular form having electrodes provided upon its inner and outer curved surfaces to permit the crystal to be vibrated in the circumferential mode, wherein a radiating member in the form of a cup or tube closed at one end is fitted to the annulus, support means being attached to the bottom of the cup or tube. IN THE ACCOMPANYING DRAWINGS: FIG. 1 is a longitudinal section through an ultrasonic transducer according to the present invention, and FIGS. 2 and 3 show two modifications to FIG. 1. In carrying the invention into effect according to one convenient mode by way of example, FIG. 1 shows an ultrasonic transducer arranged to convert electrical signals into radiated ultrasonic energy in the region of one fixed frequency for the purpose of repelling rodents. The transducer includes a piezo-electric ceramic ring 1 formed from Barium Titanate, Lead Zirconate or other polarized polycrystalline material having silvered surfaces 2 and which can be caused, when energized by a suitable electri- £n · . - ------------—....... cal generator via leads 3, to vibrate in the circumferential °° i sudabl® m®ans being provided for bracing the Within the ring 1 there is fitted a radiating member in the form of a tapered cup or tube 4 closed at one end and dimensioned to resonate at a common frequency with the ring 1, 55 which frequency is made to coincide with the sharply critical threshold of the rodent’s sensitivity. The whole assembly is impedance matched into air and eliminates the need for a conventional diaphragm. To facilitate mounting the device without damping and to 70 increase the acoustic coupling, the cup 4 is mounted on a bracket 5 with the aid of a bolt 6 and resilient washer 7 at or adjacent to the geometrical center of the base of the cup 4, the best position preferably being ascertained by finding the node with the aid of a powder. 3,6ι said annular piezoelectric element being in direct contact with said continuous conical portion of said radiating member between said unitary integral flat portion and said free unsupported periphery in an annular line of contact whereby said radiating member may be caused to 5 resonate at said ultrasonic frequency with said unsupported periphery positioned at an antinode;said annular line of contact being disposed in a plane substantially parallel to a plane containing said unitary integral flat portion of said radiating member;and support means attached to said closed end of said radiating member at a node on said unitary integral flat portion of said radiating member.
  2. 2
    A transducer for radiating ultrasonic power in accordance with claim 1, wherein said radiating member is in an interference fit in said piezoelectric element.
  3. 3
    A transducer for radiating ultrasonic power in ac20 ,841 cordance with claim 1, wherein, said radiating member is fitted in said piezoelectric element, and said piezoelectric element is fitted into a second radiating member having the shape of a truncated cone with a continuous conical portion closed at one end thereof by a flat portion unitary and integral with said conical portion and open at the other end thereof with a free unsupported periphery,
  4. 4
    A transducer for radiating ultrasonic power in accordance with claim 3, wherein a vibration absorber couples 10 the closed ends of both said radiating members with said piezoelectric element disposed between both said radiating members. *
  5. 5
    A transducer for radiating ultrasonic power in accordance with claim 4, wherein said vibration absorber is attached at a node on said closed end of each said radiating member. 6 * ♦ * ♦ ♦
Independent claims5