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`............ .. 73/187
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`18 Claims, 11 Drawing Sheets
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`
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`Page 1 of 17
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`
`RAY-1008
`
`(12) United States Patent
`US 6,904,798 B2
`(10) Patent N0.:
`Boucher et al.
`(45) Date of Patent:
`Jun. 14, 2005
`
`USOO6904798B2
`
`(54) MULTI-FUNCTIONAL MARINE SENSING
`INSTRUMENT
`
`75
`
`P
`Inventors: Ste hen G. Boucher, Amherst, NH
`(US); Robert M. Cullen, Temple, NH
`(US); Jun Lan, Milford, NH (US)
`
`(73) Assignee: Airmar Technology Corporation,
`Milford, NH (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 10/630,625
`
`(22)
`
`Filed:
`
`Jul. 30, 2003
`
`(65)
`
`Prior Publication Data
`
`US 2004/0074294 A1 Apr. 22, 2004
`
`(60)
`
`Related US. Application Data
`Provisional application No. 60/429,514, filed on Nov. 26,
`2002, and provisional application No. 60/402,493, filed on
`Aug. 8, 2002.
`
`(51)
`Int. Cl.7 .............................................. .. G01P 13/00
`(52) U.S.Cl. .............................. .. 73/170.02
`(58) Field of Search
`73/170.02, 170.03,
`73/170.11, 170.13, 181, 185, 187, 861.78,
`861.79, 861.81
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`6/1984 Nakatani
`4,455,503 A
`6/1989 Boucher
`4,836,020 A
`2/1993 Pyzik
`5,182,952 A
`8/1993 Masreliez
`5,235,557 A
`5,581,025 A * 12/1996 Boucher et al.
`
`5,719,824 A
`5,838,635 A
`FOREIGN PATENT DOCUMENTS
`
`2/1998 Boucher
`11/1998 Masreliez
`
`DE
`DE
`EP
`
`44 12 964 A1
`100 09 644 A1
`0 973 150 A2
`
`10/1994
`9/2001
`1/2000
`
`OTHER PUBLICATIONS
`
`Transom Mount. Airmar Technology Corporation. [online],
`2000 #17—1205, [retrieved on Mar. 31, 2004]. Retrieved
`from the
`Internet,<URL:http://www.airmar.com/pdfs/cat/
`marine/transomimount/transom.pdf>.
`
`* cited by examiner
`
`Primary Examiner—William Oen
`(74) Attorney, Agent, or Firm—Hamilton, Brook, Smith &
`Reynolds, RC.
`
`(57)
`
`ABSTRACT
`
`A marine sensor device mounts in a single opening in a hull
`of a marine vessel. The sensor includes a housing secured in
`the opening. Positioned within the housing is a body con-
`taining at least two sensors. The body is removable from the
`housing. A magnetized paddlewheel can be disposed in a
`first cavity formed on a first half of the body, the paddle-
`wheel has a plurality of paddles extending from a circular
`central hub and rotatably mounted on an axle extending
`transverse a fore and aft direction of travel of the vessel. A
`
`magnetic sensor can be located adjacent the paddles, the
`magnetic sensor senses the rotation of the paddles and
`provides speed indications. The magnetic sensor can be a
`Hall-eifect device. A sonic transducer for depth detection
`can be disposed within a second cavity formed on a second
`half of the body. A thermal sensor for sensing water tem-
`perature can be disposed in a well formed in the body.
`
`

`

`
`
`
`US. Patent
`
`Jun. 14, 2005
`
`Sheet 1 0f 11
`
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`Page 2 of 17
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`Page 3 of 17
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`US 6,904,798 B2
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`US. Patent
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`Jun. 14, 2005
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`Page 4 of 17
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`Jun. 14, 2005
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`Jun. 14, 2005
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`Sheet 4 0f 11
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`US 6,904,798 B2
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`RAY-1008
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`Jun. 14, 2005
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`Jun. 14, 2005
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`Jun. 14, 2005
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`»¼½¾¿ÀÀÁ
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`
`1
`MULTI-FUNCTIONAL MARINE SENSING
`INSTRUMENT
`
`RELATED APPLICATIONS
`
`This application claims the benefit of US. Provisional
`Application No. 60/429,514, filed Nov. 26, 2002 and US.
`Provisional Application No. 60/402,493, filed Aug. 8, 2002
`and includes the disclosures discussed in US. Pat. No.
`4,898,029, issued Feb. 6, 1990, which is a continuation of
`US. Pat. No. 4,836,020, issued Jun. 6, 1989, which reissued
`on Jul. 7, 1992 as Re. 33,982, and which is a continuation
`of US. application Ser. No. 7,527, filed Jan. 28, 1987, now
`abandoned, the entire teachings of which are incorporated
`herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`There are many types of marine sensors available for
`commercial and pleasure craft today. Some of them include
`instruments for measuring water depth, boat speed, water
`temperature, as well as, locating fish. Certain depth mea-
`suring devices employ an ultrasonic transducer that emits an
`acoustic beam downwardly from the boat. When the beam
`strikes something, such as the bottom, the beam reflects an
`echo back to the transducer. This is converted into electrical
`
`energy, amplified and displayed as information on a screen.
`The information can be displayed on a paper graph, flashing
`device, or video display.
`For the most part, speed, depth, and temperature measur-
`ing instruments were three separate devices that required
`drilling three holes in the hull. Today,
`these measuring
`sensors have been combined into a single instrument which
`provides information with respect to all three parameters of
`speed, temperature, and depth. However, these single instru-
`ments do not allow the sensors to be readily removable from
`within the hull. In particular, the depth sensor cannot be
`removed while the vessel is afloat because the size of the
`
`transducer element is greater than the opening in the hull.
`Despite the above efforts, and that of other workers in the
`art, a need exists for a through-hull device with that allows
`the sensing components to be removable from within the
`hull while the vessel is afloat.
`
`SUMMARY OF THE INVENTION
`
`A marine sensor device mounts in a single opening in a
`hull of a marine vessel. The sensor includes a housing
`secured in the opening. Positioned within the housing is a
`body containing at least two sensors. The body is removable
`from the housing. A magnetized paddlewheel can be dis-
`posed in a first cavity formed on a first half of the body, the
`paddlewheel has a plurality of paddles extending from a
`circular central hub and rotatably mounted on an axle
`extending transverse a fore and aft direction of travel of the
`vessel. A magnetic sensor can be located adjacent
`the
`paddles,
`the magnetic sensor senses the rotation of the
`paddles and provides speed indications. The magnetic sen-
`sor can be a Hall-effect device. Asonic transducer for depth
`detection can be disposed within a second cavity formed on
`a second half of the body. Athermal sensor for sensing water
`temperature can be disposed in a well formed in the body.
`In some embodiments,
`the cross-sectional area of the
`paddles in a plane transverse a direction of flow of water
`being traversed by the marine vessel and in a plane parallel
`the direction of flow versus the available cross sectional area
`
`in the respective planes define a Cross-Sectional ratio having
`a range between about 0.25 and 0.5. Moreover, the lowest
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
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`60
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`Page 13 of 17
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`US 6,904,798 B2
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`2
`point on the periphery of the hub can be located tangentially
`adjacent to or vertically above the lowest point in the first
`cavity. It is important to maintain the Cross-Sectional ratio
`is preferably maintained between 0.25 and 0.5 to reduce the
`build—up of negative cavity pressure and thus minimize the
`tendency to cavitate within the cavity at high speeds.
`In some embodiments, the Cross-Sectional ratio in the
`plane parallel to the direction of flow is different than the
`Cross-Sectional ratio in the plane transverse the direction of
`flow. In other embodiments, the Cross-Sectional ratio in the
`plane parallel to the direction of flow is about equal the
`Cross-Sectional ratio in the plane transverse the direction of
`flow. The first cavity can be an asymmetric cavity
`The transducer can be a piezoelectric element having an
`aspect ratio defined in terms of the length, width, and height
`of the piezoelectric element. The aspect ratio being opti-
`mized such that the maximum acoustic energy of the ele-
`ment is produced when the element vibrates with a fre-
`quency of about 150 kHz to about 250 kHz. The maximum
`acoustic energy of the piezoelectric element is produced
`when the element vibrates with a frequency of about 235
`kHz. In some embodiments, the piezoelectric element can be
`made of PZT.
`
`In one embodiment, the length of the piezoelectric ele-
`ment can be about 1.0 to 1.3 inches in length, about 0.1 to
`0.5 inches in height, and about 0.1 to 0.5 inches in width. In
`another embodiment, the length of the piezoelectric element
`can be about 1.25 inches, the height is about 0.23 inch, and
`the width is about 0.22 inch. The transducer can have a
`beamwidth of about 11°><38° at about —3 dB.
`
`The sensor body is disposed in a housing that fits into a
`single circular opening through a hull of the vessel. The
`housing contained at least two removable sensors, a speed
`sensor and a depth scnsor. Optionally, a temperature sensor
`may be disposed in the housing.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The foregoing and other objects, features and advantages
`of the invention will be apparent from the following more
`particular description of preferred embodiments of the
`invention, as illustrated in the accompanying drawings in
`which like reference characters refer to the same parts
`throughout the different views. The drawings are not nec-
`essarily to scale, emphasis instead being placed upon illus-
`trating the principles of the invention.
`FIG. 1 is a perspective view of a high speed through-hull
`speed sensor of one embodiment of the invention.
`FIG. 2 is a front view of the sensor of FIG. 1.
`
`FIG. 2A is a top view of the sensor along the line 2A—2A
`of FIG. 2.
`
`FIG. 2B is a bottom view of the sensor along the line
`2B—2B of FIG. 2
`
`FIG. 2C is a side view of the sensor along the line 2C—2C
`of FIG. 2.
`
`FIG. 3 is an exploded View of the sensor of FIG. 1.
`FIG. 4 is a perspective view of an inner tubular body of
`the sensor of FIG. 1.
`
`FIG. 5 is a front view of the tubular body of FIG. 4.
`FIG. 5A is a top view of the tubular body along the line
`5A—5A of FIG. 5.
`
`FIG. 5B is a bottom view of the tubular body along the
`line 5B—5B of FIG. 5.
`
`FIG. 5Ba is another bottom view of the tubular body
`illustrating the cross sectional area of a cavity of the body as
`occupied by a paddle of a paddlewheel speed sensor.
`
`

`

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`
`US 6,904,798 B2
`
`3
`FIG. 5Bb is a detailed view of the cross sectional area of
`
`the cavity identified in FIG. 5Ba as occupied by the paddle.
`FIG. 5Bc is a detailed view of the cross sectional area of
`
`the cavity identified in FIG. 5Ba when not occupied by the
`paddle.
`FIG. 5C is a side view of the tubular body.
`FIG. 5D is a partial cutaway side view of the tubular body
`shown as shown in FIG. 5C, the partial view being taken
`along the line 5D—5D with the paddlewheel fully shown
`illustrating the cross sectional area of the cavity of the body
`as occupied by a paddle of a paddlewheel speed sensor.
`FIG. 5Da is a detailed view of the cross sectional area of
`
`10
`
`the cavity identified in FIG. 5D as occupied by the paddle.
`FIG. 5Db is a detailed view of the cross sectional area of
`
`15
`
`the cavity identified in FIG. 5D when not occupied by the
`paddle.
`FIG. 6 is an exploded view of the tubular body of FIG. 4.
`FIG. 6A is a detailed view of a support board and a lower
`tube portion of the tubular body of FIG. 4
`FIG. 7 is a perspective view of the sensor with a single
`center skeg in accordance with the invention.
`FIG. 8 is a perspective view of the sensor with no skeg in
`accordance with the invention.
`
`FIG. 9 is a perspective view of the sensor with two outer
`skegs in accordance with the invention.
`FIG. 10 is a perspective view of the sensor with a center
`and two outer skegs in accordance with the invention.
`FIG. 11 is a perspective view of the ultrasonic transducer
`of the sensor of FIG. 1.
`
`FIG. 12 is a plot of the athwartships beam pattern of the
`transducer of FIG. 11.
`
`FIG. 13 is a plot of the fore aft beam pattern of the
`transducer of FIG. 11.
`
`FIG. 14 is a perspective view of the ultrasonic transducer
`of the sensor of FIG. 1 with dimensions.
`
`FIG. 15A is a 3-dimensional displacement map exhibiting
`a “good” coupling mode.
`FIG. 15B is a 3-dimensional displacement map exhibiting
`a “poor” coupling mode.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Referring now to FIGS. 1—3, there is shown a high speed
`through-hull tri-sensor device 10 for marine vessels. The
`device 10 can be mounted through a hull of the marine
`vessel. The device 10 has a housing designated, generally,
`by the numeral 12,
`the housing 12 having a vertically
`extending threaded cylinder 12S, and lower flared portion
`12L, respectively. The illustrated sensor device 10 is shown
`by way of example only. The invention is not limited for use
`in such a device, the present invention can be used in any
`other suitable sensor device, such as, for example, a transom
`mounted sensor.
`
`The threaded cylinder 128 is positioned in an opening
`through the hull. A hull nut 13 with internal threads engage
`a set of external threads 21 on the exterior periphery of the
`threaded cylinder 128. When the device 10 is positioned in
`the hull, the hull is wedged between the hull nut 13 and the
`flared portion 12L.
`Referring also to FIGS. 4—6, a tubular body 52 is shown
`having an upper portion 52a and a lower portion 52b, the
`lower portion 52b forming an asymmetric paddlewheel
`cavity 30. The paddlewheel cavity 30 is positioned on one
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`side of the lower portion 52b of the body and is considered
`to be asymmetric as contrasted to the paddlewheel cavity of
`prior art devices which used the entire lower portion of the
`circular tube. The body 52 is adapted to slide into the
`threaded cylinder 12$. O—rings 32 and 34, respectively, are
`positioned in grooves on the periphery of the body 52 and
`form a fluid-tight seal between the body 52 and threaded
`cylinder 128. The body 52 is of tubular shape and is formed
`of metal or plastic. A cap 14 with internal threads engage
`with the threads 21 so that the cap 14 can be hand tightened
`onto the threaded cylinder 128 to seal the tubular body 52
`within the threaded cylinder 12S.
`Acable 16 containing wires 19 (FIGS. 1 and 6) is coupled
`through a bored hole 27 formed in an enlarged wall of the
`threaded cylinder 128. The wires 19 provide electrical
`connection to components, such as a Hall-effect device 56,
`a transducer 60, and a thermistor 62 (FIG. 5C), each of
`which are positioned within the lower tube portion 52b.
`Referring in particular to FIGS. 3 and 6, a paddlewheel 26
`is mounted on axle 28 within the asymmetric cavity 30
`formed in the lower tube portion 52b. The paddlewheel 26
`is an integral structure having a hub 38 from which four
`symmetric shaped paddles 42 extend about the periphery
`thereof. The axle 28 rotates within bearings 37 disposed in
`a bore 39 which extends through a central opening in the hub
`38, and into opposing recessed holes in the cavity side walls
`formed in the lower tube portion 52b. The paddlewheel 26
`is thereby rotatably suspended within the cavity 30. In some
`embodiments, the paddlewheel 26 is formed of amorphous
`magnetized material, such as barium ferrite. The paddles 42
`can be polarized with respect to the hub 38, or with respect
`to each other. As the paddles 42 rotate about the axle 28
`when the vessel traverses the water, the variation in mag-
`netic field is sensed by the Hall-effect device 56 mounted on
`a support board 57 positioned in the lower tube portion 52b.
`The flared portion 12L is mounted flush against the outer
`surface of the hull to prevent impact with objects as the
`marine vessel moves through the water. A skeg 15 extends
`from the lower tube portion 52b of the body 52 to straighten
`the flow of water past the paddlewheel 26, for example,
`when the vessel, such as sail boat heels over as it moves
`through the water.
`Also, a preferred location for the Hall-effect device 56 is
`within the lower tube portion 52b adjacent the cavity 30,
`where it can be encapsulated and protected from the water.
`Therefore,
`the tubular body 52 in some embodiments is
`constructed of material that is permeable to the magnetic
`field emanating from the paddlewheel.
`The thermal sensing device 62 and Hall-effect device 56,
`can be of the types as described in US. Pat. No. 4,555,938,
`the entire contents of which are incorporated herein by
`reference, and are electrically coupled respectively via wires
`19 to a temperature display 80 and a speed display 70 by way
`of terminals 100a and 100b extending from the board 57
`(see,
`in particular, FIGS. 1, 3, 6, and 6A). The thermal
`sensing device 62 and the Hall-effect device 56 are con-
`tained within the lower tube portion 52b of the tubular body
`52. The thermal sensing device 62 extends from the board 57
`and is positioned within a well 62w (FIG. 6A) of the lower
`tube portion 52b.
`The upper wall 44 (FIGS. 3 and 6) of cavity 30 is an
`arched surface, closely spaced from the tip T of the four
`paddles 42 as they rotate about axle 28. The periphery P of
`the hub 38 is approximately flush with the bottom surface B
`of the cavity. The types of paddlewheels that can be used in
`the present invention are described in detail in US. Pat. Nos.
`
`Page 14 of 17
`
`
`

`

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`RAY-1008
`
`US 6,904,798 B2
`
`5
`4,898,029, 4,836,020, and Re. 33,982, all of the contents of
`which are incorporated herein by reference.
`Note however that to further minimize build-up of nega-
`tive cavity pressure and thus reduce the tendency to cavitate
`within the cavity at higher speeds, the cross-sectional shape
`80 of the paddles 42, in the present embodiment is changed
`from the above-referenced art. The cross-sectional shape
`taken in a plane parallel the direction of flow versus the
`available cross-sectioned space 82 in the cavity 30 in the
`same plane, i.e., Cross-Sectional Ratio, is preferably and
`optionally between about 0.25 to 0.5. This ratio is in the
`order of 0.30. This ratio is achieved by using a relatively thin
`cross-sectional paddle and by symmetrically rounding off
`the side walls Z of the paddles at the tips and symmetrically
`removing material from the sidewalls as they join the hub.
`This reduces the numerator of the ratio, i.e., paddle cross-
`section.
`
`Note also that the cavity 30 has an asymmetric shape,
`which results from positioning the paddlewheel 26 off-
`center relative to a center plane 84 extending along the
`length of the tubular body 52, that is, extending into the
`page. This arrangement as well as the small size of the
`transducer 60 has the particular advantage of placing the
`transducer 60, thermal sensing 62, and Hall-effect device 56,
`as well as the paddlewheel 26, all within a single structure,
`namely,
`the tubular body 52, and more particularly,
`the
`lower portion 52b of the tubular body 52.
`Also note that the Cross-Sectional Ratio may vary within
`the cavity 30, as illustrated in FIGS. 5D, 5Da, and 5Db.
`Although the cross-sectional shape 80 of the paddles 42 is
`the same when taken in a plane transverse the direction of
`flow (FIG. 5Da),
`the available cross-sectioned space 92
`(FIG. 5Db) in the cavity in the same plane can be different
`than the available cross-sectioned space 82 shown in FIG.
`5Bc. As such, the Cross-Sectional Ratio for the plane of FIG.
`5D is about 0.34. However,
`in some embodiments the
`Cross-Sectional Ratio is the same for both planes, even
`though the shape of the cross-sectioned shapes 82 and 92 are
`different.
`FIGS. 8—10 show alternate embodiments of the device
`
`discussed above. Recall that a single skeg 15 was positioned
`at the center of lower portion 12L of the sleeve 12 (shown
`again in FIG. 7 for reference). However, there can be more
`than one skeg located at different positions on the lower
`portion 12L. For example, as shown in FIG. 9, there are a
`pair of parallel skegs 15a and 15b located near respective
`outer regions of the lower portion 12L. These can also be
`combined with the center skeg 15 as shown in FIG. 10.
`Optionally, in some implementations, the device 10 does not
`include a skeg as illustrated in FIG. 8.
`Referring to FIG. 11, the transducer 60 is formed of a
`piezoelectric element 102 coated with an upper and lower
`layer of silver 104, 106 that provides an electrical connec-
`tion with terminals 100a and 100b on board 57 (FIGS. 3, 6)
`to an electronic driver assembly 90 (FIG. 1) associated with
`a depth indicator 90 (FIG. 1). The transducer 60 is made to
`fit within the lower tube portion 52b of the body 52 such that
`the body can be removed from the housing 12 while the
`vessel is afloat. Other than the radiating face (not shown),
`the piezoelectric element 102 is enclosed in a resilient
`backing member 61 (FIGS. 3, 6), preferably consisting of
`cork material or an equivalent material. That is, the backing
`member 61 encloses the piezoelectric element 102 at the top
`and sides of the generally rectangular piezoelectric crystal
`102. The piezoelectric element 102 can be made from
`well-know lead zirconate titanate material, barium titanate
`material or other equivalent material.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`The purpose of the backing member 61 enclosing the top
`and side walls of the piezoelectric element 102 is to provide
`a barrier against unwanted transmission of acoustic waves
`toward the top of the enclosure, rather than in the preferred
`direction, out the bottom. Hence, the backing member 61
`acts as a pressure release material as if the top and sides of
`the piezoelectric element are pushing against air, while the
`bottom, or radiating face effectively vibrates or pushes
`against the water.
`The entire inner portion of the housing is encapsulated in
`potting material 64 (FIGS. 1, 4), such as polyurethane to
`ensure water-tight encapsulation and at
`the same time,
`provide a path for acoustic energy from the piezoelectric
`element 102 to travel unimpeded out the bottom of the
`housing.
`In a typical operation, a drive voltage from the drive
`assembly 90 is applied across the upper and lower layers
`104, 106 of the transducer 60 at a frequency of about 235
`kHz for about 100 to 1000 Msec. After which, the drive
`voltage stops, such that the transducer 60 waits for the echo
`to be reflected from the bottom of the body of water back to
`the transducer 60. By determining the time difference
`between the transmission of the ultrasonic signal and the
`detection of the echo,
`the depth indicator 91 (FIG. 1)
`calculates the depth of the water.
`A particular feature of the sensor 10 is that the speed
`sensor, depth sensor, and temperature sensor all fit within the
`housing or tubular body 52 that fits through a single opening
`in the hull of the vessel. Hence, the relationship between the
`height (h), width (w), and length (l) of the piezoelectric
`element 102, or aspect ratio,
`is optimized such that the
`ultrasonic transducer 60 fits within the lower tube portion
`52b in one orientation while the acoustic energy from the
`transducer 60 is maximized at a particular frequency, in this
`case, 235 kHz. In this way, the transducer 60 provides broad
`beam coverage athwartships, as shown in FIG. 12, so that
`depth reading is substantially immune to the rolling of the
`boat and substantially immune to the dead rise angle where
`the transducer is mounted. The longitudinal beam is opti-
`mized for high acoustic signal by making its length as large
`as possible (within the space available), consistent with
`good piezoelectric coupling to the water as described in the
`next paragraph. The word “coupling” means how effectively
`an electrical signal can be converted to an acoustic signal in
`water (as well as the reverse, how effectively an acoustic
`signal can be converted into an electrical signal). More
`explicitly,
`these interactions are called ‘transmit’ and
`‘receive’ as specific functions. The objective of the FEA
`analysis is to design a transducer so that it is efficient in both
`functions. In other words, the objective is to design trans-
`ducer dimensions to produce strong ‘coupling’ between
`electrical and acoustical signals.
`The dimensions of the piezoelectric element 102 are
`critical to the device’s performance because these dimen-
`sions greatly influence how effective the piezoelectric ele-
`ment is in transmitting and receiving acoustic signals. Selec-
`tion of these dimensions is based on detailed modeling,
`which is used to predict which vibration modes of the
`element (among a multiplicity of vibration modes) can
`optimally transmit and receiver acoustic signals in the water.
`[Some (undesired) vibration modes couple poorly to water
`even though these modes have strong vibrations.] Optimi-
`zation of acoustic coupling is based on modeling by a
`mathematical technique known as finite element analysis
`(FEA). Airmar has refined the FEA technique so that the
`model can predict several important features: the frequency
`of the vibration, the shape of the vibration, the strength of
`
`Page 15 of 17
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`

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`1. A sensor for a marine vessel comprising:
`a housing that fits through a single opening in a hull of the
`vessel;
`a removable body disposed in the housing;
`a magnetized paddlewheel disposed in a first cavity
`formed on a first half of the body, the paddlewheel
`having a plurality of paddles extending from a circular
`central hub and rotatably mounted on an axle extending
`transverse a fore and aft direction of travel of the
`vessel;
`
`RAY-1008
`
`Page 16 of 17
`
`
`US 6,904,798 B2
`
`8
`provided by the manufacturer, mainly because the model
`values are measured at the operating (ultrasonic) frequency
`whereas the manufacturer’s values are typically measured at
`low frequency (below 1 kHz). When comparing theory and
`experiment
`for
`the “best match” of a fully assembled
`transducer, the resonance frequency and the acoustic sensi-
`tivity (in both transmission and reception of ultrasonic
`acoustic waves) are considered. In summary, the ability of
`FEA modeling to predict transducer performance depends of
`the values of the material properties used at the outset of the
`FEA calculation—the more accurate the material values, the
`more accurate are the FEA predictions.
`Referring to TABLE 1, the temperature expansion coef—
`ficient is listed in the second set of numbers, and the charge
`sensitivity [d], listed in the third set of numbers, relates the
`electrical charge produced in PZT4 to the stress applied to
`the material. (The subscript notation is standard to those
`skilled in the art.) The relative dielectric constant [k] is listed
`in the fourth set of numbers, and the elastic compliance [s],
`listed in the fifth set of numbers, primarily determines the
`mechanical resonance frequencies of the transducer 60.
`Finally, the two constitutive equations shown at the end of
`TABLE 1 couple the mechanical and piezoelectric variables.
`With the above discussed FEA model, the aspect ratio of
`the piezoelectric element 102 is optimized for the specific
`material properties listed in TABLE 1. That is, the trans-
`ducer designer chose dimensions and iterated these dimen-
`sions until a “high coupling” mode (FIG. 15A) was
`achieved. (In FIGS. 14 and 15A, only one quadrant
`is
`modeled as shown, since the other quadrants can be deduced
`on the basis of symmetry of element 102.) When “high
`coupling” occurs, most of the vibration is uniform so that a
`well-defined acoustic beam is formed. In comparison, “poor
`coupling” (FIG. 15B) occurs when the vibration is non-
`uniform and portions of the element are expanding while
`other portions are contracting (as in the undulations exhib-
`ited in FIG. 15B). In this “poor” case, only a weak acoustic
`beam is produced. A further requirement for an optimized
`mode is that no (undesired) vibration modes are found at
`nearby frequencies. Otherwise, the undesired modes can be
`inadvertently excited, and thereby weaken the desired mode.
`Optimized dimensions for element 102 were observed when
`a desired vibration mode (FIG. 15A) and desired beam
`patterns, as shown in FIGS. 12 and 13, were found between
`about 150 and 250 kHz. In a particular embodiment, the
`maximum acoustic signal occurred at about 235 kHz, for an
`element 62 having a length of about 1.25 inches, a height of
`about 0.23 inches and width of about 0.22 inches. For other
`
`embodiments, the length, height, and width of the element
`62 can vary between 1.0 to 1.3 inches in length, 0.1 to 0.5
`inches in height, and 0.1 to 0.5 inches in width depending
`upon the desired frequency.
`While this invention has been particularly shown and
`described with references to preferred embodiments thereof,
`it will be understood by those skilled in the art that various
`changes in form and details can be made therein without
`departing from the scope of the invention encompassed by
`the appended claims.
`What is claimed is:
`
`7
`acoustic signals, the acoustic beam pattern, and electrical
`impedance of the element. Each of these features is impor-
`tant in the transducer’s overall performance. Transducer
`designers iterate the dimensions until they have achieved the
`best performance. Examples of Airmar’s modeling process
`are described in detail in “Proceedings of the 1994 IEEE
`Ultrasonics Symposium,” Cannes, France, pp. 999—1003,
`catalog 94CH3468-6; “Proceedings of the 1998 IEEE Ultra-
`sonics Symposium,” Sendai, Japan, pp. 1051—1055, catalog
`98CH36102; and “Proceedings of the 2001 IEEE Ultrason-
`ics Symposium,” Atlanta, Ga., pp. 467—470, catalog
`01CH37263, each of which is incorporated by reference in
`its entirety. Other commercially available FEA software are
`applicable to modeling, such as ANSYS Inc., Canonsburg,
`Pa., which analyzes in the frequency domain, and
`Weidlinger Associates, Inc., Los Altos, Calif., which ana-
`lyzes in the time domain.
`Material properties of the piezoelectric material are pro-
`vided as input parameters to the FEA model. The material
`properties of the piezoelectric element 102 for PZT4 are
`shown in Table 1, listing both “book” values commonly
`found in textbooks and “model” values.
`
`TABLE 1
`
`Material parameters for PZT4, Poled direction is along Z(or “3")
`Dielectric loss
`Maximum
`stress kg/cm7
`tangent
`—
`0.005
`0.002
`300
`
`Density kg/m3 Mechanical Q
`7500
`500
`7650
`750
`
`Book
`Model
`
`Temperature Expansion Coefficients (10’5/degree C)
`
`Non-pole
`direction
`
`3.8
`
`Pole direction
`
`1.7
`
`Piezoelectric Constants (10’12 Coulomb/Newton)
`
`Book
`Model
`
`d13
`—123
`—123
`
`d33
`289
`335
`
`d15
`496
`525
`
`The “(1” matrix is the charge sensitivity, related by Q = d T, where Q is
`the charge vector and T us the mechanical stress vector.
`Dielectric Constants (£0 = 8.854 * 10’12 Farad/meter)
`
`Book
`Model
`
`K11/9)
`1475
`1490
`
`K33/Eu
`1300
`1325
`
`Elastic Constants (10’12 mZ/Newton)
`
`Book
`Model
`
`511
`12.3
`12.2
`
`S12
`—4.05
`—3.66
`
`S13
`—5.31
`—5.25
`
`533
`15.5
`15.0
`
`S44
`39.0
`40.5
`
`566
`33
`32
`
`The “s” matrix is the compliance of the material, related by the following
`coupled equation. By symmetry, Sij = Sji.
`i = SijTj + dimEm
`DD = KnmEm + anTk
`where
`e is vector of mechanical strain
`T is vector of mechanical stress
`E is vector of electric field
`D is vector of dielectric displacement
`
`The model values have been refined for the material prop-
`erties (of PZT, for example) by iteratively adjusting the
`values to obtain the best match between experiment and
`predictions of the FEA over a number of trials. The values,
`deduced in this way, are typically more precise than those
`
`5
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`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`65
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`

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`US 6,904,798 B2
`
`9
`a magnetic sensor located adjacent the paddles; and
`a sonic transducer disposed in a second cavity formed on
`a second half side of the body.
`2. The sensor of claim 1, wherein the cross-sectional area
`of the paddles in a plane transverse a direction of flow of
`water being traversed by the marine vessel and in a plane
`parallel
`the direction of flow versus the available cross
`sectional area in the respect