# US 4,395,913 A · Broadband electromagnetic acoustic transducers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,395,913 A - Document ID: US4395913A - Status: Granted - Kind: A - Application number: 06/288,961 - Filed: 1981-07-31 - Granted: 1983-08-02 - Earliest claimed: 1981-07-31 - Assignees: Rockwell International Corporation - Inventors: William E. Peterson - Web page: https://patentgrep.com/patent/US4395913A ## CPC - B06B 1/04: operating with electromagnetism (dynamo-electric motors with vibrating magnet, armature or coil system H02K33/00) - G01N 29/2412: {using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]; (investigating the presence of flaws using eddy currents G01N27/90, magnetostrictive transducers B06B1/08, measuring magnetostrictive properties G01R33/18)} - G01N 2291/0422: Shear waves, transverse waves, horizontally polarised waves - B06B: METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, {e.g.} FOR PERFORMING MECHANICAL WORK IN GENERAL (for particular applications, see the relevant subclasses, e.g. B07B1/40, B23Q17/12, B24B31/06; measurement of mechanical vibrations G01H; in direction finding, locating, distance or velocity measuring G01S; {generating seismic energy G01V1/02}; control of mechanical vibrations in general G05D; sound-producing devices, e.g. bells, sirens, whistles G10K, {e.g. methods or devices for transmitting, conducting, or directing sound in general G10K11/00}; generation of electrical oscillations H03B; electromechanical resonators in general H03H; electromechanical transducers {for communication techniques, e.g. microphones, speakers} H04R) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract A broadband electromagnetic acoustic transducer is disclosed for use with an electrically conductive object. The transducer includes a source of magnetic flux for establishing a static magnetic field in the object and an electrical conductor for inducing eddy currents in the object when an alternating current is applied to the conductor. The magnetic field and the conductor are oriented so that the vector product of the magnetic field and the eddy currents produces an instantaneous force field in the object which is periodically alternately directed with a logarithmic periodicity. The source of magnetic flux may be provided by a plurality of alternately oriented magnets aligned along a propagation direction. Alternatively, the conductor may be a serpentine conductor with a plurality of parallel elements which are perpendicular to a propagation direction, the ratio of adjacent spacings between the elements being constant. ## Claims ### Claim 1 A broadband electromagnetic acoustic transducer for use with an electrically conductive object, comprising: a source of magnetic flux for establishing a static magnetic field in said object and an electrical conductor for inducing eddy currents in said object when an alternating current is applied to said conductor, said magnetic field and said conductor being so oriented that the vector product of said magnetic field and said eddy currents produces an instantaneous force field in said object, said force field being periodically alternately directed with a logarithmic periodicity such that the ratio of adjacent alternating periods within said force field is constant. ### Claim 2 (depends on 1) The transducer claim 1, wherein the smallest period of said logarithmic periodicity corresponds to the shortest wavelength acoustic wave to which said transducer is to respond and the largest period of said logarithmic periodicity corresponds to the longest wavelength acoustic wave to which said transducer is to respond. ### Claim 3 (depends on 1) The transducer of claim 1, wherein said source of magnetic flux further comprises a first plurality of alternately oriented magnets aligned along a propagation direction and a second plurality of alternately oriented magnets aligned along said propagation direction and adjacent to said first plurality such that adjacent magnets in said first and second pluralities are alternately oriented; and wherein said conductor further comprises a first conducting element extending under said first plurality of magnets parallel to said propagation direction, a second conducting element extending under said second plurality of magnets parallel to said propagation direction, and a connecting conducting element linking said first and second conducting elements at an end of said transducer. ### Claim 4 (depends on 1) The transducer of claim 1, wherein said conductor is periodically alternately oriented such that the ratio of adjacent periods of said conductor is constant. ### Claim 5 (depends on 4) The transducer of claim 4, wherein said conductor further comprises a serpentine conductor with a plurality of parallel elements perpendicular to a propagation direction, the ratio of adjacent spacings between said elements being constant. ### Claim 6 (depends on 1) The transducer of claim 1, wherein said magnetic field is periodically alternately oriented such that the ratio of adjacent periods of said field is constant. ### Claim 7 (depends on 6) The transducer of claim 6, wherein said source of magnetic flux further comprises a plurality of alternately oriented magnets aligned along a propagation direction. ### Claim 8 (depends on 7) The transducer of claim 7, wherein said conductor further comprises a coil encircling said plurality of magnets. ### Claim 9 (depends on 8) The transducer of claim 8, wherein the axis of said coil is parallel to said propagation direction. ### Claim 10 (depends on 8) The transducer of claim 8, wherein the axis of said coil is perpendicular to said propagation direction. ### Claim 11 A broadband electromagnetic acoustic transducer for use with an electrically conductive object, comprising: a plurality of alternately oriented magnets aligned along a propagation direction to establish a static magnetic field which is periodically alternately oriented such that the ratio of adjacent periods of said field is constant; and an electrical conductor for inducing eddy currents in said object when an alternating current is applied to said conductor, said magnets and said conductor being so oriented that the vector product of said magnetic field and said eddy currents produces an instantaneous force field in said object, said force field being periodically alternately directed with a logarithmic periodicity such that the ratio of adjacent alternating periods within said force field is constant. ### Claim 12 A broadband electromagnetic acoustic transducer for use with an electrically conductive object, comprising: a source of magnetic flux for establishing a static magnetic field in said object; and a serpentine electrical conductor for inducing eddy currents in said object when an alternating current is applied to said conductor, the conductor including a plurality of periodically alternately oriented parallel elements perpendicular to a propagation direction such that the ratio of adjacent periods is constant, said magnetic field and said conductor being so oriented that the vector product of said magnetic field and said eddy currents produces an instantaneous force field in said object, said force field being periodically alternately directed with a logarithmic periodicity such that the ratio of adjacent alternating periods within said force field is constant. ### Claim 13 A broadband electromagnetic acoustic transducer for use with an electrically conductive object, comprising: a first plurality of alternately oriented magnets aligned along a propagation direction; a second plurality of alternately oriented magnets aligned along said propagation direction and adjacent to said first plurality such that adjacent magnets in said first and second pluralities are alternately oriented, said magnets establishing a periodic alternately oriented static magnetic field such that the ratio of adjacent periods of said field in said propagation direction is constant; and an electrical conductor for inducing eddy currents in said object when an alternating current is applied to said conductor, said conductor including: a first conducting element extending under said first plurality of magnets, a second conducting element extending under said second plurality of magnets, and a connecting conducting element linking said first and second conducting elements, said magnets and said conductor being so oriented that the vector product of said magnetic field and said eddy currents produces an instantaneous force field in said object, said force field being periodically alternately directed with a logarithmic periodicity such that the ratio of adjacent alternating periods within said force field is constant. ### Claim 14 A method of generating a broadband acoustic wave in an electrically conductive object, comprising the steps of: providing a source of magnetic flux to establish a static magnetic field in the object; providing an electrical conductor to induce eddy currents in the object when an alternating current is applied to the conductor; and orienting the source of magnetic flux and the conductor so that the vector product of the magnetic field and the eddy currents produces an instantaneous force field in the object, the force field being periodically alternately directed with a logarithmic periodicity such that the ratio of adjacent alternating periods within the force field is constant. ### Claim 15 (depends on 14) The method of claim 14, wherein the step of providing a source of magnetic flux further comprises providing a source of magnetic flux to establish a static magnetic field in the object which is periodically alternately oriented such that the ratio of adjacent periods of the field is constant. ### Claim 16 (depends on 14) The method of claim 14, wherein the step of providing an electrical conductor further comprises providing an electrical conductor which is periodically alternately oriented such that the ratio of adjacent periods of the conductor is constant. ### Claim 17 (depends on 15, 16) The method of claim 15 or 16, further comprising the step of applying an alternating current to the conductor which is swept in frequency such that the broadband acoustic wave is generated in the form of an impulse.