CA1207076A - Multi-focus ultrasonic transducer - Google Patents
Multi-focus ultrasonic transducerInfo
- Publication number
- CA1207076A CA1207076A CA000434783A CA434783A CA1207076A CA 1207076 A CA1207076 A CA 1207076A CA 000434783 A CA000434783 A CA 000434783A CA 434783 A CA434783 A CA 434783A CA 1207076 A CA1207076 A CA 1207076A
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- section
- spiral
- piezoelectric element
- transducer
- focal length
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Abstract
A B S T R A C T
An ultrasonic transducer providing a plurality of different focal lengths within a unitary structure and comprising a piezoelectric element having a cylindrical spiral surface with respective sections of the spiral surface providing respective different focal lengths. Each section of the spiral surface can include electrodes in the form of a Fresnel zone pattern to provide focusing in the orthogonal dimension to the spiral axis.
An ultrasonic transducer providing a plurality of different focal lengths within a unitary structure and comprising a piezoelectric element having a cylindrical spiral surface with respective sections of the spiral surface providing respective different focal lengths. Each section of the spiral surface can include electrodes in the form of a Fresnel zone pattern to provide focusing in the orthogonal dimension to the spiral axis.
Description
7~
FIELD OF THE lNV~;N'l'IO~
This invention relates to ultrasonic transducers and more particularly to-a transducer having multiple focal lengths in a single unitary structure~
BACKGROUND OF THE INVENTION
Ultrasonic transducers, employed for example for medical diagnostic purposes, are known in which the transducer is focused for an intended focal length. Such transducers generally include a spherically curved ceramic piezoelectric element suppo~ted on an acoustic backing material, or a flat piezoelectric element supported on an acoustic backing material with an acoustic lens disposed on the front surface of the flat element to provide the intended focusiny. These known transducers are operative for only a single focal length, and a different transducer must be constructed for each focal length of interest.
According to the present invention there is provided an ultrasonic transducer comprising: a piezoelectric element having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a dif-ferent focal length; a rear electrode provided on the rear surface of the piezoelectric element; a front electrode provided on the front surface of each section of the piezoelectric element; and means for supporting the piezoelectric element and electrode layers.
, j~;, :
:~LZ~76 Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:-Fig. 1 is a pictorial view of a multiple focus ultrasonictransducer in accordance with one embodiment of the invention;
Fig. 2 is a side elevation view of the transducer of Fig.
, l;
Fig. 3 is a front view of the transducer of Fig. l;
Fig. 4 is an exploded pictorial view of the piezoelectric film and backing;
Fig. 5 is a cutaway pictorial view illustrating the electrode pattern on one section of the spiral surface, Fig. 6 is a side view of an alternative embodiment of the novel transducer employing two piezoelectric elementS;and Fig. 7 is a diagrammatic side view of the piezoelectric element illustrating the multiple foci.
!
f j ~Z07~76`
Referring to ~igs. 1 and 29 there is shown an ultrasonic transducer
FIELD OF THE lNV~;N'l'IO~
This invention relates to ultrasonic transducers and more particularly to-a transducer having multiple focal lengths in a single unitary structure~
BACKGROUND OF THE INVENTION
Ultrasonic transducers, employed for example for medical diagnostic purposes, are known in which the transducer is focused for an intended focal length. Such transducers generally include a spherically curved ceramic piezoelectric element suppo~ted on an acoustic backing material, or a flat piezoelectric element supported on an acoustic backing material with an acoustic lens disposed on the front surface of the flat element to provide the intended focusiny. These known transducers are operative for only a single focal length, and a different transducer must be constructed for each focal length of interest.
According to the present invention there is provided an ultrasonic transducer comprising: a piezoelectric element having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a dif-ferent focal length; a rear electrode provided on the rear surface of the piezoelectric element; a front electrode provided on the front surface of each section of the piezoelectric element; and means for supporting the piezoelectric element and electrode layers.
, j~;, :
:~LZ~76 Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:-Fig. 1 is a pictorial view of a multiple focus ultrasonictransducer in accordance with one embodiment of the invention;
Fig. 2 is a side elevation view of the transducer of Fig.
, l;
Fig. 3 is a front view of the transducer of Fig. l;
Fig. 4 is an exploded pictorial view of the piezoelectric film and backing;
Fig. 5 is a cutaway pictorial view illustrating the electrode pattern on one section of the spiral surface, Fig. 6 is a side view of an alternative embodiment of the novel transducer employing two piezoelectric elementS;and Fig. 7 is a diagrammatic side view of the piezoelectric element illustrating the multiple foci.
!
f j ~Z07~76`
Referring to ~igs. 1 and 29 there is shown an ultrasonic transducer
2 con~L,.Ic~ed in accordance with one ~ ~n~- and ~ich cornprises a piezoelectric
3 film 10 supported on a support or b~cking 12 of acoustic ~l~mpjn~ materi~l and
4 having a cylindrical spiral-shaped surface 14 of uniform width ~nd length which is of spiral or generally spiral con~iguration. A fiLler material 16 for aco~ tic 6 damping is disposed rearward of support 12, the entire assembly being contained within a housing 18. As seen ~ Pig. 1 ~nd Fig. 3, the piezoelectric film 10 is 8 divided into respective sections nlong the length thereof, each section having a 9 respective different focal length. Referring to Fig. 7, section 10a h~ a focus at 1~ section 10b has a focus at 2~ section 10c has a focus at 03, and section 10d has 11 a focus at i The focal points l through 04 lie along an axis 20 which is the 12 optical a2ds of the tr~n~dllc~r. The sections can be of continuously increasing 13 radius to provide a true spiral, or each section can be of constant or more uniform 14 radius to ayp.o~iluate a spiral path.
Each section of the film 10 has a Fresnel zone pattern thereon across the 16 width of the film surface to prvvide focusing in the width dimension. Focussing in 17 the longitudinal direction of the spir~l is provided by the curved surfaces of the 18 spir~l sections. The ~resnel zone pattern for each section is slightly different than 19 the others to account for the different focal lengths. The Presnel pattern for each section is provided by conductive strips 22 formed on the front surface of the 21 Ij film 10~ the front electrodes being electric~lly interconnected to provide an 22 1 intended capacitance and reactance. A rear electrode 24 is provided on the rear 23 I surface of the film 10 in the form of a continuous conductive layer providing a 24 ~ common electrode for the several spiral sections.
Ihe Fresnel zone pattern for one spiral section is illustrated in Fig. S. The 26 pattern includes a plurality of electrode areas symmetric about a center ~ine, each 27 of the electrode Rreas being of defined width and spaced from adjacent electrode ' - 12~7~6 areas by defined amount. The center line of each electrode area lies at a 2 tlict~nce d from the center line of the Fresnel pattern and can be found by d = + ~ (n ~ )(2a + n ~ )I 1/2 Eq. 1 6 where n is a successive integer 09 1~ 2, 3, etc., for each electrode area;
7 a is the mesn focal length for the psrticular section of the spiral surface;
and 9 A is the wavelength per cycle.
The width of each electrode area ~ d can be obtained by substituting n +
11 : 0.25 for the integer n in equation 1. The center of each area between the 12 electrode areas can be found by substituting (2n + 1) /2 for the integer n in 13 equation 1.
14 If the number of electrode areas is relatively small, equation 1 reduces to 16 d - + (2an ~ )1/2 Eq. 2 18 As an PYAmple, for a frequency f of 1 M~[z, a focal length of 10 centi-19 meters, and a sound velocity v in water of 1.5 x 105 centimeters per second, the wavelength ~ is equal to v~f = 11.5 x 105) /106 = 0.15 centimeters per cycle.
21 Thus, the center of the electrode areas in the section under discussion are 22 expressed as follows:
24 d = + (2a ~ )1/2 (n)l/2 = 1 73~ nl/2 Eg. 3 2~
26 For purposes of the above example, the section is considered as having a 27 eonstant radius, and therefore constant focal length, LhouE;lIouL its extent. Since 28 the surface is actually a portion of a cylindrical spiral which has a slightly varying 7'~117~
focal length throughout its zone length, the location of the electrode areas should 2 be calculated for the mean focal length for the zone. Or, the electrode areas can 3 ~ be calculated separately for the end portions of a zone to accommodate the focal 4 length variations.
I For each section of the spiral, the electrode areas are electrically 6 , connected in series or parPllel, or in a series parallel combination to provide an 7 intended capacitance to achieve a reactance of particular v~lue, typically in the 8 , range of 2S-50 ohms. Each section has a respective electrical terminal 25 (Fig. 5 9 ! for connection to electronic circuitry for energizing the tr~n~d~lcPr for trans-, mission for receiving and processin~ signals produced in response to received 11 ul~asonic energy. The rear electrode is common to all sections and has a common 12 terminal which serves as the second terminal for all sections. Irl the illustrated 13 ~ embodiment, the piezoelectric film is polyvinylidene fluoride (PVF2), and the 14 electrodes are formed of a nickel-chrome alloy. The electrodes are provided on the film in any known manner, such as by vacuum sputtering. The polyvinylidine 16 fluoride has a broadband frequency response, and therefore the thickness c>f the 17 film is not as critical as with typical PZT materials which have a much narrower 18 ; band frequency response. For a fre~u~ y constant of about 20 KHz-inches, the 19 ll film operative at 1 MHz can have a thickness of about 250-500 microns. For a , dielectric constant K of 13, the capacitance C for each square centimeter of the 21 1 electrode are~ of a Fresnel pattern is 23 ,' C=e K/t Eq.4 ' where e is the permittivity of ~ree space (0.088 X 10 12) and where t is the 26 I film thickness in centimeters. For a film thickness of 250 microns, the capaci-27 tance C is equal to 46 picofarads per square centimeter. For a reactance Xc of 28 50 ohms, the capacitance is :~2~7~7~
C = (2~r f X~ ) 1 = 3185 picofarads Eq. 5 3 For each section or zone in which the electrode areas are connected in parallel, the 4 total electrode area is 3185 picofarads/46 picofarads per square centimeter, which equals 69 square centimeters.
6 In the event that focusing in two orthogonal axes is not needed, the Fresnel 7 pattern can be eliminated, and the front electrode provided by a con~ ous 8 electrode film forn~ed on each section of the front surface of the piezoelectric 9 material, each front electrode having a respective electrical terminal. In this version, a line focus would be provided by each sectioll of the spir~l surface, as 11 : distinguished from a point focus provided in the embodiment described above.
12 Another ernhorliment is shown in Fig. 6 in which a pie~o~lectric film 10 is 13 supported on a ceramic piezoelectric materii~130 such as PZT (lead zirconate 14 titanate). Both piezoelectric materials are disposed in a cylindrical spiral path, as in the above embodiment. This dual layer s¢ucture is supported on an acoustic 16 d~mring backing materii~l, as in the above embodiment, and can otherwise be 17 similarly housed. In typical fabrication~ the PZT material 30 is bent into the spiral 18 configuration while in its plastic state prior to firing, and after firing, it will retain 19 its spiral shape. The piezoelectric film 10 can then be bonded to the PZT material.
Front and re~r electrodes are provided for each piezoelectric layer, the elec~ode 21 areas being connected to respective terminals. The Fresnel electrode pattern can 22 be provided for each zone on the front surface of the film, and on the rear surfPce 23 of the PZT layer, with a common electrode layer interposed between the rear 24 surface of thie film and the front surface of the PZT material. Alternatively, each piezoelectric layer can have the Fresnel pattern for each zone on its front surface, 26 and a rear electrode layer on its rear surface, with an electrically insulating spacer 27 provided between the front electrodes of the PZT material and the rear electrode 28 of the film materiPl to maintain electrical isolation between the two transducers.
~207Q~;
The polyvinylidene fluoride film is ma~re effective for ultrasonic reception than for transmission, while the PZT
material is superior for transmission rather than reception.
Thus, in the composite structure illustrated in Fig. 6, the PZT layer is energi~ed with an appropriate driving signal for transmittins ultrasonic energy in a focused manner to an object under study, and the film layer is operative to receive energy preferentially focused onto the respective section or zone of the film to generate output signals representative of received ultrasonic energy~
The novel transducer finds particular application as an immersion transducer for medical diagnostic purposes. The immersion transducer is placed in a vessel containing water or other liquid, the transducer being spaced from the subject by the interposed liquid. Ultrasonic energy is coupled via the liquid from the transducer to the subiect,which is also immersed in the liquid. Alternatively, a thin layer of liquid or gel can be employed to couple the transducer directly to living tissue.
The invention is also useful in other frequency applic-ations. For example, the transducer can be employed for sonar, in which case the transducer dimensions would be appropriately scaled up to accommodate the lower frequencies employed for sonar work. For medical diagnostic purposes, frequencies are typically in the range of 1-10 MHz, while sonar is operative at about 30 KHz.
It will be seen that the described embodiments provide an ultrasonic transducer which, within a single unitary structure, provides a plurality of different focal lengths.
The novel transducer comprises a piezoelectric element having .~.
iL2~7~76 a cylindrical spiral or yenerally cylindrical spiral surface with respective sections or zones of the cylindrical spiral providingrespective different focal lengthsO Preferably, the piezoelectric element is a plastic piezoelectric film, such as polyvinylidene fluoride (PVF2), disposed on a support member providing the cylindrical spiral surface. The sections each have a corresponding focus lying in a common plane disposed transversely to the spiral surface. The curved surface of the spiral provides focusing in one dimension, along the length of the spiral. Focusing in the orthogonal ~;~^nsion is provided by a Fresnel zone pactexn on the front surface of each section of the piezoelectric film. The zone pattern is formed by electrodes on the front surface of the film extending across the width of the film. The front electrodes of the several sections are electrically connected in series or parallel, or in a series-parallel combination, depending upon the capacitance and reactance required for specific applications. The electrode pattern for each section terminates in a respective electrical terminal for coupling to excitation or reception circuitry. A rear electrode is provided on the back surface of the film, typically in the form of a continuous conductive layer with a common terminal for all sections. The Fresnel pattern can be eliminated and replaced by a continuous electrode for each zone on the front surface of the spiral film in applications where ultrasonic focusing is desired in only one dimension in order to provide a line focus.
The invention is not to be limited except as indicated in the appended claims.
_g _
Each section of the film 10 has a Fresnel zone pattern thereon across the 16 width of the film surface to prvvide focusing in the width dimension. Focussing in 17 the longitudinal direction of the spir~l is provided by the curved surfaces of the 18 spir~l sections. The ~resnel zone pattern for each section is slightly different than 19 the others to account for the different focal lengths. The Presnel pattern for each section is provided by conductive strips 22 formed on the front surface of the 21 Ij film 10~ the front electrodes being electric~lly interconnected to provide an 22 1 intended capacitance and reactance. A rear electrode 24 is provided on the rear 23 I surface of the film 10 in the form of a continuous conductive layer providing a 24 ~ common electrode for the several spiral sections.
Ihe Fresnel zone pattern for one spiral section is illustrated in Fig. S. The 26 pattern includes a plurality of electrode areas symmetric about a center ~ine, each 27 of the electrode Rreas being of defined width and spaced from adjacent electrode ' - 12~7~6 areas by defined amount. The center line of each electrode area lies at a 2 tlict~nce d from the center line of the Fresnel pattern and can be found by d = + ~ (n ~ )(2a + n ~ )I 1/2 Eq. 1 6 where n is a successive integer 09 1~ 2, 3, etc., for each electrode area;
7 a is the mesn focal length for the psrticular section of the spiral surface;
and 9 A is the wavelength per cycle.
The width of each electrode area ~ d can be obtained by substituting n +
11 : 0.25 for the integer n in equation 1. The center of each area between the 12 electrode areas can be found by substituting (2n + 1) /2 for the integer n in 13 equation 1.
14 If the number of electrode areas is relatively small, equation 1 reduces to 16 d - + (2an ~ )1/2 Eq. 2 18 As an PYAmple, for a frequency f of 1 M~[z, a focal length of 10 centi-19 meters, and a sound velocity v in water of 1.5 x 105 centimeters per second, the wavelength ~ is equal to v~f = 11.5 x 105) /106 = 0.15 centimeters per cycle.
21 Thus, the center of the electrode areas in the section under discussion are 22 expressed as follows:
24 d = + (2a ~ )1/2 (n)l/2 = 1 73~ nl/2 Eg. 3 2~
26 For purposes of the above example, the section is considered as having a 27 eonstant radius, and therefore constant focal length, LhouE;lIouL its extent. Since 28 the surface is actually a portion of a cylindrical spiral which has a slightly varying 7'~117~
focal length throughout its zone length, the location of the electrode areas should 2 be calculated for the mean focal length for the zone. Or, the electrode areas can 3 ~ be calculated separately for the end portions of a zone to accommodate the focal 4 length variations.
I For each section of the spiral, the electrode areas are electrically 6 , connected in series or parPllel, or in a series parallel combination to provide an 7 intended capacitance to achieve a reactance of particular v~lue, typically in the 8 , range of 2S-50 ohms. Each section has a respective electrical terminal 25 (Fig. 5 9 ! for connection to electronic circuitry for energizing the tr~n~d~lcPr for trans-, mission for receiving and processin~ signals produced in response to received 11 ul~asonic energy. The rear electrode is common to all sections and has a common 12 terminal which serves as the second terminal for all sections. Irl the illustrated 13 ~ embodiment, the piezoelectric film is polyvinylidene fluoride (PVF2), and the 14 electrodes are formed of a nickel-chrome alloy. The electrodes are provided on the film in any known manner, such as by vacuum sputtering. The polyvinylidine 16 fluoride has a broadband frequency response, and therefore the thickness c>f the 17 film is not as critical as with typical PZT materials which have a much narrower 18 ; band frequency response. For a fre~u~ y constant of about 20 KHz-inches, the 19 ll film operative at 1 MHz can have a thickness of about 250-500 microns. For a , dielectric constant K of 13, the capacitance C for each square centimeter of the 21 1 electrode are~ of a Fresnel pattern is 23 ,' C=e K/t Eq.4 ' where e is the permittivity of ~ree space (0.088 X 10 12) and where t is the 26 I film thickness in centimeters. For a film thickness of 250 microns, the capaci-27 tance C is equal to 46 picofarads per square centimeter. For a reactance Xc of 28 50 ohms, the capacitance is :~2~7~7~
C = (2~r f X~ ) 1 = 3185 picofarads Eq. 5 3 For each section or zone in which the electrode areas are connected in parallel, the 4 total electrode area is 3185 picofarads/46 picofarads per square centimeter, which equals 69 square centimeters.
6 In the event that focusing in two orthogonal axes is not needed, the Fresnel 7 pattern can be eliminated, and the front electrode provided by a con~ ous 8 electrode film forn~ed on each section of the front surface of the piezoelectric 9 material, each front electrode having a respective electrical terminal. In this version, a line focus would be provided by each sectioll of the spir~l surface, as 11 : distinguished from a point focus provided in the embodiment described above.
12 Another ernhorliment is shown in Fig. 6 in which a pie~o~lectric film 10 is 13 supported on a ceramic piezoelectric materii~130 such as PZT (lead zirconate 14 titanate). Both piezoelectric materials are disposed in a cylindrical spiral path, as in the above embodiment. This dual layer s¢ucture is supported on an acoustic 16 d~mring backing materii~l, as in the above embodiment, and can otherwise be 17 similarly housed. In typical fabrication~ the PZT material 30 is bent into the spiral 18 configuration while in its plastic state prior to firing, and after firing, it will retain 19 its spiral shape. The piezoelectric film 10 can then be bonded to the PZT material.
Front and re~r electrodes are provided for each piezoelectric layer, the elec~ode 21 areas being connected to respective terminals. The Fresnel electrode pattern can 22 be provided for each zone on the front surface of the film, and on the rear surfPce 23 of the PZT layer, with a common electrode layer interposed between the rear 24 surface of thie film and the front surface of the PZT material. Alternatively, each piezoelectric layer can have the Fresnel pattern for each zone on its front surface, 26 and a rear electrode layer on its rear surface, with an electrically insulating spacer 27 provided between the front electrodes of the PZT material and the rear electrode 28 of the film materiPl to maintain electrical isolation between the two transducers.
~207Q~;
The polyvinylidene fluoride film is ma~re effective for ultrasonic reception than for transmission, while the PZT
material is superior for transmission rather than reception.
Thus, in the composite structure illustrated in Fig. 6, the PZT layer is energi~ed with an appropriate driving signal for transmittins ultrasonic energy in a focused manner to an object under study, and the film layer is operative to receive energy preferentially focused onto the respective section or zone of the film to generate output signals representative of received ultrasonic energy~
The novel transducer finds particular application as an immersion transducer for medical diagnostic purposes. The immersion transducer is placed in a vessel containing water or other liquid, the transducer being spaced from the subject by the interposed liquid. Ultrasonic energy is coupled via the liquid from the transducer to the subiect,which is also immersed in the liquid. Alternatively, a thin layer of liquid or gel can be employed to couple the transducer directly to living tissue.
The invention is also useful in other frequency applic-ations. For example, the transducer can be employed for sonar, in which case the transducer dimensions would be appropriately scaled up to accommodate the lower frequencies employed for sonar work. For medical diagnostic purposes, frequencies are typically in the range of 1-10 MHz, while sonar is operative at about 30 KHz.
It will be seen that the described embodiments provide an ultrasonic transducer which, within a single unitary structure, provides a plurality of different focal lengths.
The novel transducer comprises a piezoelectric element having .~.
iL2~7~76 a cylindrical spiral or yenerally cylindrical spiral surface with respective sections or zones of the cylindrical spiral providingrespective different focal lengthsO Preferably, the piezoelectric element is a plastic piezoelectric film, such as polyvinylidene fluoride (PVF2), disposed on a support member providing the cylindrical spiral surface. The sections each have a corresponding focus lying in a common plane disposed transversely to the spiral surface. The curved surface of the spiral provides focusing in one dimension, along the length of the spiral. Focusing in the orthogonal ~;~^nsion is provided by a Fresnel zone pactexn on the front surface of each section of the piezoelectric film. The zone pattern is formed by electrodes on the front surface of the film extending across the width of the film. The front electrodes of the several sections are electrically connected in series or parallel, or in a series-parallel combination, depending upon the capacitance and reactance required for specific applications. The electrode pattern for each section terminates in a respective electrical terminal for coupling to excitation or reception circuitry. A rear electrode is provided on the back surface of the film, typically in the form of a continuous conductive layer with a common terminal for all sections. The Fresnel pattern can be eliminated and replaced by a continuous electrode for each zone on the front surface of the spiral film in applications where ultrasonic focusing is desired in only one dimension in order to provide a line focus.
The invention is not to be limited except as indicated in the appended claims.
_g _
Claims (14)
1. An ultrasonic transducer comprising:
a piezoelectric element having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a different focal length;
a rear electrode provided on the rear surface of the piezoelectric element;
a front electrode provided on the front surface of each section of the piezoelectric element; and means for supporting the piezoelectric element and electrode layers.
a piezoelectric element having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a different focal length;
a rear electrode provided on the rear surface of the piezoelectric element;
a front electrode provided on the front surface of each section of the piezoelectric element; and means for supporting the piezoelectric element and electrode layers.
2. The transducer of claim 1 wherein the front elec-trode for each section includes:
a one-dimensional Fresnel zone pattern on the front surface of the section of the spiral surface and disposed along an axis transverse to the spiral axis;
each section having a Fresnel zone pattern of different focal length corresponding to the focal length of the associated section of the spiral surface.
a one-dimensional Fresnel zone pattern on the front surface of the section of the spiral surface and disposed along an axis transverse to the spiral axis;
each section having a Fresnel zone pattern of different focal length corresponding to the focal length of the associated section of the spiral surface.
3. The transducer of claim 1 wherein the Fresnel zone pattern for each section of the spiral surface is symmetric about the center line of the spiral surface.
4. The transducer of claim 1 wherein the piezoelectric element is a piezoelectric film disposed in a cylindrical spiral path.
5. The transducer of claim 4 wherein the piezoelectric film is of polyvinylidine fluoride.
6. An ultrasonic transducer comprising:
a piezoelectric element having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a different focal length, the element having a front surface and a rear surface;
a rear electrode provided on the rear surface of the piezoelectric element;
a front electrode provided on the front surface of each section of the piezoelectric element;
the front electrode for each section including a one dimensional Fresnel zone pattern on the front surface of the section of the spiral surface and disposed along an axis trans-verse to the spiral axis; and each section having a Fresnel zone pattern of differ-ent focal length corresponding to the focal length of the associated section of the spiral surface, the Fresnel zone pattern for each section being provided by an array of spaced electrode areas, the array extending along the spiral axis.
a piezoelectric element having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a different focal length, the element having a front surface and a rear surface;
a rear electrode provided on the rear surface of the piezoelectric element;
a front electrode provided on the front surface of each section of the piezoelectric element;
the front electrode for each section including a one dimensional Fresnel zone pattern on the front surface of the section of the spiral surface and disposed along an axis trans-verse to the spiral axis; and each section having a Fresnel zone pattern of differ-ent focal length corresponding to the focal length of the associated section of the spiral surface, the Fresnel zone pattern for each section being provided by an array of spaced electrode areas, the array extending along the spiral axis.
7. The transducer of claim 6 wherein the electrode areas of each section are electrically interconnected to pro-vide a predetermined capacitance and reactance.
8. An ultrasonic transducer comprising:
a piezoelectric element having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a different focal length, the element having. a front surface and a rear surface;
a rear electrode provided on the rear surface of the piezoelectric element;
a front electrode provided on the front surface of each section of the piezoelectric element;
means for supporting the piezoelectric element and electrode layers;
the front electrode for each section including a one-dimensional Fresnel zone pattern on the front surface of the section of the spiral surface and disposed along an axis transverse to the spiral axis, each section having a Fresnel zone pattern of different focal length corresponding to the focal length of the associated section of the spiral surface; wherein the Fresnel zone pattern includes electrode areas, each extending along the longitudinal axis of the spiral surface, the pattern extending across the transverse axis, the electrode area being of defined width and spacing for the respective sections.
a piezoelectric element having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a different focal length, the element having. a front surface and a rear surface;
a rear electrode provided on the rear surface of the piezoelectric element;
a front electrode provided on the front surface of each section of the piezoelectric element;
means for supporting the piezoelectric element and electrode layers;
the front electrode for each section including a one-dimensional Fresnel zone pattern on the front surface of the section of the spiral surface and disposed along an axis transverse to the spiral axis, each section having a Fresnel zone pattern of different focal length corresponding to the focal length of the associated section of the spiral surface; wherein the Fresnel zone pattern includes electrode areas, each extending along the longitudinal axis of the spiral surface, the pattern extending across the transverse axis, the electrode area being of defined width and spacing for the respective sections.
9. The transducer of claim 8 wherein the Fresnel zone pattern for each section of the spiral surface is of different width and spacing to provide a respective focal length.
10. The transducer of claim 9 wherin the supporting means includes acoustic damping material.
11. The transducer of claim 9 wherein the supporting means includes a block of acoustic damping material having a cylindrical spiral surface on which the piezoelectric element is disposed.
12. The transducer of claim 11 wherein the piezoelectric element has a uniform width.
13. An ultrasonic transducer comprising:
a housing;
a piezoelectric element supported in the housing and having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a diff-erent focal length;
a front electrode provided on the front surface of each section of the piezoelectric element; and a rear electrode provided on the rear surface of the piezoelectric element.
a housing;
a piezoelectric element supported in the housing and having a cylindrical spiral surface, the surface having respective sections along the length thereof, each of a diff-erent focal length;
a front electrode provided on the front surface of each section of the piezoelectric element; and a rear electrode provided on the rear surface of the piezoelectric element.
14. The transducer of claim 13 wherein the front electrode for each section includes:
a one-dimensional Fresnel zone pattern on the front surface of the section of the spiral surface and disposed along an axis transverse to the spiral axis;
each section having a Fresnel zone pattern of different focal length corresponding to the focal length of the associated section of the spiral surface.
a one-dimensional Fresnel zone pattern on the front surface of the section of the spiral surface and disposed along an axis transverse to the spiral axis;
each section having a Fresnel zone pattern of different focal length corresponding to the focal length of the associated section of the spiral surface.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000434783A CA1207076A (en) | 1983-08-17 | 1983-08-17 | Multi-focus ultrasonic transducer |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000434783A CA1207076A (en) | 1983-08-17 | 1983-08-17 | Multi-focus ultrasonic transducer |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1207076A true CA1207076A (en) | 1986-07-02 |
Family
ID=4125898
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000434783A Expired CA1207076A (en) | 1983-08-17 | 1983-08-17 | Multi-focus ultrasonic transducer |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1207076A (en) |
-
1983
- 1983-08-17 CA CA000434783A patent/CA1207076A/en not_active Expired
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