Low-frequency broadband sound source for underwater navigation and communication

An underwater sound source includes an acoustical driver, a controller of the acoustical driver, and a resonant tube acoustically coupled to the acoustical driver. The resonant tube has a pair of slotted portions, in which each slotted portion is disposed along the length of the resonant tube at a location corresponding to a node of a harmonic of the resonant tube. The sound system is configured to emit an output signal within a bandwidth defined by a dual resonance characteristic of the resonator tube. The sound source may also include a pair of coaxial tubular sleeves disposed around the resonant tube, each sleeve configured to slidably cover one of the slotted portions, and tune the resonance frequency of the tube over a wide range. At a high frequency end, when slots are uncovered, the frequency response of the resonant tube obtains a dual-resonant form.

BACKGROUND

This application is related to the disclosures of U.S. Pat. No. 8,670,293, entitled “BROADBAND SOUND SOURCE FOR LONG DISTANCE UNDERWATER SOUND PROPAGATION”, U.S. Pat. No. 4,855,964, entitled “VENTED-PIPE PROJECTOR”, and non-patent literature document entitled “High-efficient tunable sound sources for ocean and bottom tomography, 15 years of operating history”, by Andrey K. Morozov et al., OCEANS 2016 MTS/IEEE Monterey, September 2016, the disclosures of which are hereby incorporated by reference herein in their entirety and for all purposes.

A first test of one aspect of a tunable underwater organ-pipe sound source had been successfully conducted on Nov. 9, 2001. The tunable sound source had many useful characteristics including its ability to operate at any depth underwater. In addition, its output was essentially free of unwanted high frequency harmonics. The acoustical driver of the sound source was tuned to match the frequency and phase of a reference frequency-modulated signal. Over time, this tunable underwater organ-pipe formed the basis for a variety of related devices. In some examples, related devices were designed to have a bandwidth of about 200-300 Hz. Some alternative devices were designed to sweep the frequency of their outputs in a linear manner. In some examples, the sweep range was from about 140 Hz to about 205 Hz. In some examples, the sweep range was from about 500 Hz to about 1000 Hz. In some other examples, the sweep range was from about 800 Hz to about 1200 Hz. In some examples, the sound source could sweep the range of frequencies in about one second. In one example, a sound source was configured to sweep a range of output frequencies in a few minutes. In one example, a tunable sound source configured to sweep its output range in a linear fashion over 135 seconds was employed to make ocean acoustic tomography measurements. In another example, a tunable sound source was configured to emit 80 second narrow-band chirps.

In another example, a tunable underwater sound source has been bottom-deployed in a swept frequency array to produce high-resolution seismic imaging of deep underwater geological formations. Such imaging may be obtained by the use of beam-formed and beam-steered seismic signals to produce high-resolution imaging of geological structures.

SUMMARY

In one aspect, an underwater sound source may include an acoustical driver, a controller of the acoustical driver, and a resonator tube acoustically coupled to the acoustical driver. The resonator tube may further include a first slotted portion including a first at least two co-radial resonator slots, and a second slotted portion including a second at least two co-radial resonator slots. A total length of the resonator tube may define a plurality of harmonics of the resonator tube. The first slotted portion may be located at a first position along the total length of the resonator tube corresponding to a first node of one of the plurality of harmonics, and the second slotted portion is located at a second position along the total length of the resonator tube corresponding to a second node of one of the plurality of harmonics. The controller of the acoustical driver may be configured an output signal of the underwater sound source to within a bandwidth defined by a frequency response of the resonator tube.

In one aspect of the underwater sound source, the resonator tube has an outer diameter within a range of one tenth of the total length of the resonator tube to one half of the total length of the resonator tube.

In one aspect of the underwater sound source, each of the first at least two co-radial resonator slots of the first slotted portion has a width within a range of one tenth of a radius of the resonator tube and one half of the radius of the resonator tube, and each of the second at least two co-radial resonator slots of the second slotted portion has a width within a range of one tenth of the radius of the resonator tube and one half of the radius of the resonator tube.

In one aspect of the underwater sound source, the first slotted portion and the second slotted portion define a medial section of the resonator tube therebetween, the first slotted portion and a first end of the resonator tube define a first terminal section of the resonator tube therebetween, and the second slotted portion and a second end of the resonator tube define a second terminal section of the resonator tube therebetween.

In one aspect of the underwater sound source, the first terminal section has a first section length, the second terminal section has a second section length, and the medial section has a medial section length. The medial section length may differ from the first section length and the medial section length may differ from the second length.

In one aspect of the underwater sound source, the first of the at least two co-radial resonator slots of the first slotted portion are separated by a first bridge connecting a first end of the medial section and a first end of the first terminal section, and the second of the at least two co-radial resonator slots of the second slotted portion are separated by a second bridge connecting a second end of the medial section and a first end of the second terminal section.

In one aspect of the underwater sound source, the frequency response of the resonator tube includes a dual resonance transfer function defined by a first resonance frequency and a second resonance frequency, and the bandwidth is between 10% and 15% of a medial frequency.

In an aspect, an underwater sound source may include an acoustical driver, a controller of the acoustical driver, a resonator tube acoustically coupled to the acoustical driver, a first coaxial tubular sleeve, and a second coaxial tubular sleeve. The resonator tube may further include a first slotted portion comprising a first at least two co-radial resonator slots; and a second slotted portion comprising a second at least two co-radial resonator slots. A total length of the resonator tube may define a plurality of harmonics of the resonator tube. The first slotted portion may be located at a position along the total length of the resonator tube corresponding to a first node of one of the plurality of harmonics, and the second slotted portion is located at a position along the total length of the resonator tube corresponding to a second node of one of the plurality of harmonics. The resonator tube may be disposed within the first coaxial tubular sleeve thereby forming a first gap between a first portion of an exterior surface of the resonator tube and an interior surface of the first coaxial tubular sleeve, and the resonator tube may be disposed within the second coaxial tubular sleeve thereby forming a second gap between a second portion of the exterior surface of the resonator tube and an interior surface of the second coaxial tubular sleeve. The first coaxial tubular sleeve may be configured to slide upon the first portion of the exterior surface of the resonator tube and the second coaxial tubular sleeve may be configured to slide upon the second portion of the exterior surface of the resonator tube. The underwater sound source may be configured to operate in a first acoustic mode when the first slotted portion is covered by the first coaxial tubular sleeve and the second slotted portion is covered by the second coaxial tubular sleeve, and the underwater sound source may be configured to operate in a second acoustic mode when the first slotted portion is uncovered by the first coaxial tubular sleeve and the second slotted portion is uncovered by the second coaxial tubular sleeve.

In one aspect of the underwater sound source, the first gap has a width in a range between 1 mm and 5 mm, and the second gap has a width in a range between 1 mm and 5 mm.

In one aspect of the underwater sound source, wherein the controller of the acoustical driver is configured to control an output frequency of the acoustical driver to a tube resonance frequency determined at least in part by a location of the first coaxial tubular sleeve and a location of the second coaxial tubular sleeve when the underwater sound source is configured to operate in the first acoustic mode.

In one aspect of the underwater sound source, the controller of the acoustical driver is configured to control an output signal of the underwater sound source to within a bandwidth defined by a frequency response of the resonator tube.

In an aspect, an underwater sound system, may include an underwater sound source, a transmission comprising a lead screw, a motor in mechanical communication with the transmission and configured to impart a rotary motion to the lead screw, and

a water pressure housing, wherein an exterior surface of the water pressure housing is in mechanical communication with the transmission and the motor, and wherein an interior of the water pressure housing is configured to contain one or more electrical components configured to control and power the motor. The underwater sound source may include an acoustical driver, a controller of the acoustical driver, a resonator tube acoustically coupled to the acoustical driver, a first coaxial tubular sleeve, and a second coaxial tubular sleeve. The resonator tube may further include a first slotted portion comprising a first at least two co-radial resonator slots; and a second slotted portion comprising a second at least two co-radial resonator slots. A total length of the resonator tube may define a plurality of harmonics of the resonator tube. The first slotted portion may be located at a position along the total length of the resonator tube corresponding to a first node of one of the plurality of harmonics, and the second slotted portion is located at a position along the total length of the resonator tube corresponding to a second node of one of the plurality of harmonics. The resonator tube may be disposed within the first coaxial tubular sleeve thereby forming a first gap between a first portion of an exterior surface of the resonator tube and an interior surface of the first coaxial tubular sleeve, and the resonator tube may be disposed within the second coaxial tubular sleeve thereby forming a second gap between a second portion of the exterior surface of the resonator tube and an interior surface of the second coaxial tubular sleeve. The first coaxial tubular sleeve may be configured to slide upon the first portion of the exterior surface of the resonator tube and the second coaxial tubular sleeve may be configured to slide upon the second portion of the exterior surface of the resonator tube. The underwater sound source may be configured to operate in a first acoustic mode when the first slotted portion is covered by the first coaxial tubular sleeve and the second slotted portion is covered by the second coaxial tubular sleeve, and the underwater sound source may be configured to operate in a second acoustic mode when the first slotted portion is uncovered by the first coaxial tubular sleeve and the second slotted portion is uncovered by the second coaxial tubular sleeve. The lead screw may be in mechanical communication with the first coaxial tubular sleeve and the second coaxial tubular sleeve. The rotary motion imparted to the lead screw may result in a motion of imparted to the first coaxial tubular sleeve and the second coaxial tubular sleeve.

In one aspect of the underwater sound system, the lead screw is configured to move the first coaxial tubular sleeve and the second coaxial tubular sleeve symmetrically in opposing directions when the lead screw is rotated by the motor.

In one aspect of the underwater sound system, the transmission is covered with one or more oil-filled bellows configured to prevent water from contacting the transmission.

In an aspect, a method of transmitting signals underwater may include providing an underwater sound source, including an acoustical driver, a controller of the acoustical driver, and a resonator tube acoustically coupled to the acoustical driver, and controlling, by the controller, an output signal of the underwater sound source to within a bandwidth defined by a a frequency response of the resonator tube. The resonator tube may include a first slotted portion comprising a first at least two co-radial resonator slots, and a second slotted portion comprising a second at least two co-radial resonator slots. A total length of the resonator tube may define a plurality of harmonics of the resonator tube. The first slotted portion may be located at a first position along the total length of the resonator tube corresponding to a first node of one of the plurality of harmonics, and the second slotted portion may be located at a second position along the total length of the resonator tube corresponding to a second node of one of the plurality of harmonics.

DESCRIPTION

Over 15 years of operating history, tunable underwater transducers have demonstration exceptional performance. However, the tunable transducers have limitations, when used for arbitrary waveforms. They can only transmit frequency-modulated signals. Examples of such frequency-modulated signals may include chirp signals and linearly-swept signals. A doubly-resonant organ pipe provides transmission of arbitrary waveforms over a much wider frequency band. As with the single-resonance pipes, the sources can be used at all depths and are efficient and very light if built from composites. The doubly-resonant organ pipes comprise an inner resonator tube with thin walls tuned to a certain frequency surrounded by a larger-diameter tube (Morozov 2014, U.S. Pat. No. 8,670,293). The doubly-resonant free flooded pipes may have good performance, but their bandwidth may be much smaller than the range of frequencies covered by tunable frequency sweeping projectors. For example one aspect of such a transducer had a bandwidth of only about 34 Hz around a 500 Hz central frequency. Such a narrow bandwidth can be compared to a 500 Hz bandwidth (between about 500 Hz and about 1000 Hz) which had been practically achieved by a tunable organ pipe transducer built from pipes having the same diameter and using the same spherical acoustical driver.

As disclosed above, such tunable frequency sound sources may be configured to emit sound over a range of about 140 Hz to about 205 Hz, about 20 Hz to about 300 Hz, about 500 Hz to about 1000 Hz, and about 800 Hz to about 1200 Hz. Thus, a tunable frequency sound source may be configured to emit sound within a range of about 140 Hz to about 1200 Hz. In some non-limiting examples, a tunable frequency sound source may be configured to emit sound at a frequency of about 140 Hz, about 160 Hz, about 180 Hz, about 200 Hz, about 205 Hz, about 220 Hz, about 240 Hz, about 260 Hz, about 280 Hz, about 300 Hz, about 400 Hz, about 500 Hz, about 600 Hz, about 800 Hz, about 900 Hz, about 1000 Hz, about 1100 Hz, about 1200 Hz, and any value or range of values therebetween, including end points.

It may be recognized that a system composed of a wideband tunable resonator may be useful to provide high precision oceanographic tomographic measurements and navigation. As disclosed above, a local dual-resonance system can be used to produce arbitrary signal transmissions. It may therefore be recognized that such arbitrary acoustic signals may be used as basis for underwater digital communication. It may be understood that for underwater navigation, it may be necessary to have a tunable resonant system for determining local positioning and a broadband dual-resonant system for transmitting parameters necessary to improve precision of the position estimation.

It may therefore be recognized that a hybrid underwater sound source that (1) can cover a large frequency band for determining precise acoustic ocean tomography and (2) have the capability to produce arbitrary signals for communication purposes, would be a desirable multipurpose device. The sum effect of the hybrid system may include a combination of high precision navigation and ocean tomography functions and supporting digital communications. The combination of the two functions may permit a single device to determine navigational and tomographic information and transmit additional data about navigation beacon positions and identities, and predictions related to variability of ocean characteristics. Such a system may have analogous functions to a satellite GPS system which provides both position via time delay calculations and additional information regarding the broadcasting satellite. The combined functionality may dramatically increase the precision of underwater navigation.

In some aspects, the traditional tunable organ-pipe sound source (seeFIG. 1) transmits a frequency sweep signal by mechanical tuning a resonator tube (or organ pipe) to match the frequency and phase of a reference signal.FIG. 2depicts schematically an aspect of the tunable organ-pipe sound source200. The organ-pipe sound source200comprises a resonator tube210which acts as a simple, efficient, narrow-band, medium-output projector that operates at any ocean depth. The resonator tube210has resonator slots215(or vents), that are progressively covered or uncovered by symmetrically sliding coaxial tubular sleeves220. The resonator tube210is disposed within each of the coaxial tubular sleeves220. The output frequency of the tunable organ-pipe sound source200varies with the sleeve position. A computer-controlled electromechanical actuator moves the cylindrical sleeves220along the resonator tube210. In addition, the voltage and/or current driving the acoustic driver225may be adjusted by means of a control device (for example, a phase-locked loop) so that the acoustic driver225may emit sound at the resonance frequency determined by the position of the cylindrical sleeves220. In this manner, the organ-pipe sound source200may be kept in resonance at the instantaneous frequency over the range of swept frequency signals by adjusting the input voltage of the acoustic driver225to maintain the resonance of the output.

The sound of the organ-pipe sound source200may be driven by a volume velocity acoustic driver225. In some examples, the acoustic driver225may be a piezo-ceramic sphere2. In other examples, the acoustic driver225may be a tonpilz piezo driver. A computer may synthesize a frequency-modulated signal to drive the acoustic driver225through one or more components of a drive controller. In some examples, the drive controller may compare a phase between an output signal from a hydrophone in the resonant tube to the signal on the input of the acoustic driver225. In some examples, the drive controller may use a phase-lock loop (PLL) system to keep the resonator tube210frequency the same as that of the drive signal. In some examples, the estimated PLL precision is better than 3 degrees of phase error. The use of a PLL system may maintain a small amount of error during a high rate of frequency change of the organ pipe sound source200output with a constant Q-factor over the working frequency band.

FIGS. 3A,B illustrate engineering drawings of the resonator tube210that may be used in a dual frequency sound system. In some aspects, the resonator tube210may be made of a metal, for example aluminum. The resonator tube210may be defined by an overall length305from a first end to a second end. The resonator tube210may also be defined by an outer diameter310and an inner diameter315. The resonator tube210may also include one or more slotted portions320a,bdisposed along the overall length305of the resonator tube210, each slotted portion320a,bcomprising one or more resonator slots. In some aspects, the resonator slots of a slotted portion may all be co-radial. The resonator slots may be defined by a width322a,b. The slotted portions320a,bmay divide the resonator tube210into multiple sections.FIG. 3Adepicts an example in which two slotted portions320a,bare illustrated. The slotted portions may divide the resonator tube210into a medial portion340, and two terminal portions335a,b. The medial portion340may be defined on either side by one of the slotted portions320a,b. A first terminal portion335amay be defined by a first slotted portion320aon one side and a first end of the resonator tube210. A second terminal portion335bmay be defined by a second slotted portion320aon one side and a second end of the resonator tube210. The medial portion340may be defined by a medial portion length342, and each of the two terminal portions335a,bmay be defined by a terminal portion length337a,b, respectively.

FIG. 3Billustrates a cross sectional view of the resonator tube210ofFIG. 3Athrough second slotted portion320bat line A-A.FIG. 3Bdepicts three slots321a-cthat compose slotted portion320b. Each of the resonator slots321a-chas a slot width322b. In some examples, the resonator slots352a-cmay be co-radial and may be disposed equally about the resonator tube210at the slotted portion320b. Between the resonator slots may be bridges352a-c. With reference toFIG. 3A, bridges352a-cmay connect the second terminal portion335bwith the medial portion340of the resonator tube210. It may be recognized that a similar cross section through slotted portion320amay depict multiple resonator slots separated by multiple bridges as depicted inFIG. 3B. Additionally, a similar cross section through slotted portion320amay depict multiple bridges configured to connect the first terminal portion335awith the medial portion340.

In some examples, the resonator tube210may have an overall length305of about 52.5 in., an outer diameter310of about 8.94 in., and an inner diameter315of about 8.00 in. In such an example, the resonator tube210may have a thickness of about 0.47 in. Additionally, in some examples, each resonator slot of the slotted sections320a,b(for example, resonator slots321a-cof second slotted section320b) may have a width322a,bof about 2.0 in. The first terminal portion335aof the resonator tube210may be defined by an outer edge of the first slotted portion320aand may have a first terminal portion length337a. Similarly, the second terminal portion335bof the resonator tube210may be defined by an outer edge of the second slotted portion320band may have a second terminal portion length337a. The medial portion340may be defined as the portion of the resonator tube210disposed between the first terminal portion335aand the second terminal portion335b. In some examples, the length337aof the first terminal portion335amay be the same as the length337bof the second terminal portion335b. In some alternative examples, the length337aof the first terminal portion335amay differ from the length337bof the second terminal portion335b.

In one example, the lengths337aand337bof the two terminal portions335aand335b, respectively, may be about 15.60 in. In one example, the length342of the medial portion340may be about 21.3 in. In some examples, the widths322a,bof the resonator slots of the slotted portions may be about 2.0 in. It may also be recognized that the number of resonator slots in each slotted portion is not limited to three resonator slots, such as352a-cas illustrated inFIG. 3B. For example, a slotted portion may have one resonator slot, two resonator slots, three resonator slots, four resonator slots, or any number of resonator slots that may result in the functions herein disclosed. Multiple resonator slots may be co-radial and disposed symmetrically about a longitudinal axis of the resonator tube210or they may be disposed asymmetrically about the longitudinal axis of the resonator tube210. The length of each bridge, such as bridges352a-cmay be determined by the number, disposition, and length of the resonator slots (for example resonator slots321a-c). For example, each bridge352a-cmay have the same width of about 1.5 in. It may be recognized that the multiple bridges within one slotted portion may all have the same width or they may have different widths. Additionally, the multiples bridges within a first slotted portion may have a thickness that is the same as or differs from a thickness of the multiple bridges within a second slotted portion.

It may be understood that the values for the dimensions disclosed above are merely examples, and as such are not intended to limit dimensions of alternative aspects of the resonator tube210. For example, the outer diameter310of the resonator tube210may be determined by overall length305of the resonator tube210. For example, the outer diameter310may range between a value of 0.20 times the overall length305of the resonator tube210to about 0.50 times the overall length305of the resonator tube210. Non-limiting examples of the outer diameter310of the resonator tube may include about 0.20 times the overall length305of the resonator tube210, about 0.25 times the overall length305of the resonator tube210, about 0.30 times the overall length305of the resonator tube210, about 0.35 times the overall length305of the resonator tube210, about 0.40 times the overall length305of the resonator tube210, about 0.45 times the overall length305of the resonator tube210, about 0.50 times the overall length305of the resonator tube210, or any value or range of values therebetween including endpoints.

In another example, the widths322a,bof the resonator slots may be determined by a radius of the resonator tube210. For example, the widths322a,bof the resonator slots may range between a value of 0.10 times the radius of the resonator tube210to about 0.50 times the radius of the resonator tube210. Non-limiting examples of the widths322a,bof the resonator slots may include about 0.10 times the radius of the resonator tube210, about 0.15 times the radius of the resonator tube210, about 0.20 times the radius of the resonator tube210, about 0.25 times the radius of the resonator tube210, about 0.30 times the radius of the resonator tube210, about 0.35 times the radius of the resonator tube210, about 0.40 times the radius of the resonator tube210, about 0.45 times the radius of the resonator tube210, about 0.50 times the radius of the resonator tube210, or any value or range of values therebetween including endpoints.

For example, as noted above, the lengths337a,bof the terminal portions335a,bmay be the same or they may differ. In some alternative examples, the thickness of the medial portion340may be the same as the thickness of both of the terminal portions335a,b. In some aspects, the terminal portions335a,bmay have the same thickness which may differ from the thickness of the medial portion340. In yet some other aspects, the first terminal portion335amay have a thickness that differs from the thickness of the second terminal portion335b. In yet some additional aspects, each of the first terminal portion335a, the medial portion340, and the second terminal portion335bmay have a thickness that differs from the thickness of the other portions.

In consideration of the location of the slotted portions320a,b, one may consider the natural harmonics of a tubular organ pipe having both ends open.FIGS. 4A and 4Billustrate a first acoustic mode and a second acoustic mode of an organ-pipe resonator400, respectively. The organ-pipe resonator400may have a length405(denoted I) and a diameter410(denoted d). For a resonator tube500having dimensions 52.5 in. in length, and 8 in. in diameter, the first harmonic, f1, may be about 500 Hz in seawater. Similarly, the second harmonic, f2, may be three times f1or about 1500 Hz.

FIG. 4Adepicts a first resonant waveform415corresponding to the first acoustic harmonic. It may be observed that the first resonant waveform415has two stable nodes417a,bin which each of the stable nodes417a,bis located at an end of the organ-pipe resonator400.FIG. 4Bdepicts a second resonant waveform425corresponding to the second acoustic harmonic. It may be observed that the second resonant waveform425also has two stable nodes427a,bin which each of the stable nodes427a,bis located at an end of the organ-pipe resonator400. Additionally, the second resonant waveform425has a second pair of stable nodes437a,bthat may be described as internal nodes. A first of the second pair of stable nodes437amay be located at a distance of about ⅓ of the length405of the resonator400from a first end of the resonator. A second of the second pair of stable nodes437bmay be located at a distance of about ⅓ of the length405of the resonator tube400from a second end of the resonator.

Dotted lines420adepict the location of the first slotted portion equivalent to320ainFIG. 3A, and dotted lines420bdepict the location of the second slotted portion equivalent to320binFIG. 3A. It may therefore be understood that the slotted portions320a,bmay be positioned to correspond to the internal nodes437a,bof the second harmonic f2of the organ-pipe resonator400. In one example, an inner edge of the first slotted portion320amay correspond to the location of the first internal stable node437a. In another example, an inner edge of the second slotted portion320bmay correspond to the location of the second internal stable node437b. Alternatively, an outer edge of the first slotted portion320amay correspond to the location of the first internal stable node437aand an outer edge of the second slotted portion320bmay correspond to the location of the second internal stable node437b.

As disclosed above with respect toFIG. 2, the tunable organ-pipe sound source200may include the resonator tube210and multiple coaxial tubular sleeves220.FIGS. 3A,B depict aspects of the resonator tube210.FIGS. 5A,B depict aspects of a coaxial tubular sleeve520.FIG. 5Adepicts a radial cross-sectional view of one of a pair of coaxial tubular sleeves520. Each coaxial tubular sleeve520may have an outer diameter510, an inner diameter515, and a length505. The coaxial tubular sleeve520may also include one or more bolt-holes550a-d. The bolt-holes550a-dmay be configured to receive bolts to affix one or more linear actuators to the coaxial tubular sleeves520. Such linear actuators may be associated with one or more transmissions each transmission comprising a lead screw and a motor. In some aspects, the linear actuators may include a metal bar having a wheel at the end thereof. The wheel of each metal bar may be configured to turn on the outer surface of the resonator tube210while the coaxial tubular sleeves520are displaced along a longitudinal axis of the resonator tube210. Without limitation, the coaxial tubular sleeves520may be dimensioned so that the resonator tube210may be located within the interior of the tubular sleeves520.

In operation, the coaxial tubular sleeves520are configured to slide over the exterior surface of the resonator tube210by means of the one or more linear actuators. In some examples, the one or more linear actuators may be moved by a transmission comprising a lead screw. In some examples, the lead screw may be actuated by a motor powered by an electrical power source. Further, the motor may be controlled by one or more electronic controllers. Each coaxial tubular sleeve520is designed to cover or uncover one of the slotted portions320a,b. It may be recognized that there may be as many coaxial tubular sleeves520as there are slotted portions320a,bin a tunable organ-pipe sound source200. In some examples, there may be two slotted portions320a,band coaxial tubular sleeves520. In some other examples, there may be three slotted portions320a,band coaxial tubular sleeves520. In some further examples, there may be four slotted portions320a,band coaxial tubular sleeves520. In some aspects, there may be an even number of slotted portions320a,band coaxial tubular sleeves520. In some examples, there may be an even number of slotted portions320a,band coaxial tubular sleeves520disposed symmetrically about the center of the resonator tube210.

In some aspects, the coaxial tubular sleeves520may be independently actuated by one or more linear actuators. In some aspects, the coaxial tubular sleeves can be actuated by one linear actuator through a lead screw transmission and move in the opposite directions symmetrically from the center of the resonant tube. In some aspects, a first coaxial tubular sleeve520may be actuated to slide in a direction opposite to the direction of a second coaxial tubular sleeve520. In some aspects, a first coaxial tubular sleeve520may be actuated to slide in a same direction as that of a second coaxial tubular sleeve520. In some aspects, multiple coaxial tubular sleeves520may be actuated together by cooperating linear actuators. In some aspects, the coaxial tubular sleeves520may all be moved in a concerted manner so that they all move about the same distance.

In some examples, the coaxial tubular sleeves520may have a length505of about 9.25 in. In some examples, the coaxial tubular sleeves520may have an outer diameter510of about 10.0 in. In some examples, the coaxial tubular sleeves520may have an inner diameter515of about 8.976 in. In some examples, the inner diameter515may be about 9 in. In such examples, the coaxial tubular sleeves520may have a thickness of about 0.5 in. As disclosed above, in some examples of a tunable organ-pipe sound source200, the outer diameter of the resonator tube210may be about 8.94 in. If the inner diameter515of the coaxial tubular sleeve520is about 8.976 in., there may be a gap of about 0.018 in. (about 0.45 mm) between the outer surface of the resonator tube210and the inner surface of the coaxial tubular sleeve520. In some other examples, the gap may be about 1 mm. In still other examples, the gap may be about 1.5 mm. It may be recognized that the gap between the outer surface of the resonator tube210and the inner surface of the coaxial tubular sleeve520may have any value consistent with the function of the tunable organ-pipe sound source200. In some examples, the value of the gap may be between about 0.4 mm and about 3.0 mm including, without limitation, a value of about 0.4 mm, about 0.45 mm, about 0.5 mm, about 0.6 mm, about 0.7 mm, about 0.8 mm. about 0.9 mm, about 1.0 mm, about 1.1, mm, about 1.2 mm, about 1.5 mm, about 1.75 mm, about 2.0 mm, about 2.5 mm, about 3.0 mm, or any value or range of values therebetween including endpoints. In some examples, the gap may have a dimension that ranges between about 1.0 mm and about 5.0 mm, including, without limitation, about 1.0 mm, about 1.5 mm, about 2.0 mm, about 2.5 mm. about 3.0 mm, about 3.5 mm, about 4.0, mm, about 4.5 mm, about 5.0 mm, or any value or range of values therebetween including endpoints.

It may be recognized that when a tunable organ-pipe sound source200is submersed in water, the water may fill at least a portion of the interior of the resonator tube210. The water disposed within the at least portion of the interior of the resonator tube210may be in fluid communication with the free water exterior to the organ-pipe sound source200via the water in the slotted sections320a,band the water filling the gaps between the outer surface of the resonator tube210and the inner surface of the coaxial tubular sleeve520.

FIG. 6depicts a realization of a tunable organ-pipe sound source including the resonator tube and two coaxial tubular sleeves resting on a rolling jack stand.

FIG. 7is a concept drawing of one aspect of an underwater sound system700. The sound system may be composed of an organ-pipe sound source705, a transmission assembly750, and deep water pressure housing760. The organ-pipe sound source705may include a resonator tube710disposed within a pair of coaxial tubular sleeves730a,b. The resonator tube710may be divided by two slotted portions720a,binto a first terminal portion712a(bounded by a first end of the resonator tube710and a first edge of first slotted portion720a), a second terminal portion712b(bounded by a second end of the resonator tube710and a first edge of second slotted portion720a), and a medial portion714(bounded by a second edge of the first slotted portion720aand a second edge of the second slotted portion720b). As an example, first slotted portion720ais composed of one or more slots722aand one or more bridges724a. The one or more bridges724aform end boundaries of the one or more resonator slots722aand are configured to mechanically link the first terminal portion712awith the medial portion714. If the first slotted portion720ais composed of more than one slot722a, the multiple slots722amay be co-radial. It may be recognized that second slotted portion720bis composed of one or more resonator slots722band one or more bridges724b. The one or more bridges724bform end boundaries of the one or more resonator slots722band are configured to mechanically link the second terminal portion712bwith the medial portion714. If the second slotted portion720bis composed of more than one slot722b, the multiple slots722bmay be co-radial. Each of the coaxial tubular sleeves730a,bis configured to slide on the outer surface of the resonator tube710and to slidably occlude one of each of the slotted portions720a,b.

The transmission assembly750may include a motor752configured to rotate a lead screw754. Rotation of the lead screw754may cause a linear motion of the sleeve brackets756a,b. The linear motion of sleeve bracket756amay cause coaxial tubular sleeve730ato slide along the outer surface of the resonator tube710and to cover or uncover slotted portion720a. The linear motion of sleeve bracket756bmay cause coaxial tubular sleeve730bto slide along the outer surface of the resonator tube710and to cover or uncover slotted portion720b. In some aspects, the motions of sleeve brackets756a,bmay be coordinated and to move symmetrically in opposing directions. Although not shown inFIG. 7, the lead screw754or the transmission may be covered by one or more rubber bellows filled with oil to protect the lead screw754from corrosion when submerged under water.

Deep water pressure housing760may serve as a mechanical mounting structure for the transmission assembly750and or the organ-pipe sound source705. The deep water pressure housing760may also house various components including a power supply for the motor752, an electronic control assembly, a general purpose computer system, and a communication system. The electronic control assembly may include those electronic components configured to control the motion of the motor752, including the direction of the motor rotation and the speed and acceleration of motor rotation. The general purpose computer system may include any one or more components which, without limitation, may include one or more processor or microprocessors, one or more memory components (including, without limitation, one or more static or dynamic memory components), and one or more interface components. The memory components may include instructions that, when executed by the processor or microprocessor, cause the processor or microprocessor to calculate parameters related to the operations of the underwater sound system700. The instructions may also result in the processor or microprocessor directing the operations of the components of the underwater sound system700, including, without limitation, directing the motor to adjust the positions of the coaxial tubular sleeves730a,bvia the control system and to adjust the output frequency of the a controllable acoustical driver. The interface components may also permit the one or more processors or microprocessors to transmit and/or receive data via the communication system.

FIG. 8illustrates a realization of the underwater sound system800as depicted inFIG. 7. Components depicted inFIG. 8, are the deep water pressure housing860, actuator motor852, the medial portion814and two terminal portions812a,bof the resonator tube and the coaxial tubular sleeves830a,b.FIG. 8also depicts wheeled stabilizer bars870that are mechanically associated with the coaxial tubular sleeves830a,b. The stabilizer bars870may help stabilize the motion of the coaxial tubular sleeves830a,bas the slide on the exterior surface of the resonator tube. In particular, they may prevent an edge of one of the coaxial tubular sleeves830a,bfrom catching an edge of a resonator slot in the slotted portions.

FIG. 9Adepicts an organ-pipe sound source in a first configuration905ain which the coaxial tubular sleeves920acompletely cover the slotted portions921.FIG. 9Bdepicts an organ-pipe sound source in a second configuration905bin which the coaxial tubular sleeves920bcompletely uncover the slotted portions921. In the first configuration905a, the coaxial tubular sleeves920acompletely cover the slotted portions921. Upon activation, the driving oscillator925imparts an oscillating pressure force to water in the interior932of the resonator tube. The pressure force is primarily transmitted to the exterior of the resonator tube at the tube ends. However, some amount of the pressure force is transmitted to the exterior of the resonator tube via the resonator slots922and through the gap934between the inner surface of the coaxial tubular sleeve920aand the outer surface of the resonator tube910. The gap934may have a length936as measured from the center of the resonator slot922to the closer end of the coaxial sleeve920a,b. It may be recognized that, due to the surface tension of the water against the two surfaces, the water in the gap934presents a high impedance acoustic path to the exterior of the resonator tube910. Because the primary path for the pressure force of the water in the interior932of the resonator tube910is through the low acoustic impedance ends of the resonator tube910, the water oscillation is primarily at the first resonant frequency of the resonator tube910.

As depicted inFIG. 9B, the coaxial tubular sleeve920bis configured to completely uncover the resonator slots922. As a result, the resonator slots922present a direct and low impedance path to the water in the exterior of the resonator tube. Because the resonator slots922are located approximately at the interior nodes of the second resonant frequency of the resonator tube, the resonator tube emits sound waves at the second resonant frequency. It may be recognized that the motion of the coaxial tubular sleeve920a,brelative to the resonator slots922will result in a change in the length936of the gaps934. Without being bound by theory, it may be recognized that the motion of the coaxial tubular sleeve920a,bwill therefore change the acoustic impedance coupling through the gap934due to the change in the length936of the gap934. This impedance coupling will be at a maximum in configuration905a, in which the resonator slots922and slotted portion921are completely covered. This impedance coupling will be at a minimum in configuration905b, in which the resonator slots922and slotted portion921are completely uncovered.

Finite element analysis simulations have been calculated to determine the output of an organ-pipe sound source substantially as disclosed above inFIGS. 2, 3A, 3B, 5A, and 5B. For the purposes of the simulations, Table 1 displays the organ pipe configuration used in the calculations.

TABLE 1Organ Pipe ComponentMetricValueResonator Tube:Overall length52.5″Medial portion length21.3″Terminal portion length15.6″(Both Identical)Inner diameter8.00″(All Portions)Outer diameter8.94″(Terminal Portions)Outer diameter8.7″(Medial Portion)Slot number3(Radially Symmetric)Resonator slot Width2.00″Bridge number3(Radially symmetric)Bridge width1.56″Coaxial SleevesOverall length9.25″Inner diameter9.04′Outer diameter10.00′Tube/SleeveTube/Sleeve gap0.12″(At medial portion)
It should be understood that while the specific results of the simulations may reflect the dimensions used in the calculations (see Table 1), the analysis of the simulation results may be generalized to an organ-pipe sound source having any one or more alternative dimensions as disclosed above.

FIG. 10depicts the finite element analysis (FEA) mesh used to calculate the sound pressure output of an organ-pipe sound source having dimensions disclosed in Table 1 above. Because the organ-pipe sound source is axially symmetric, a two-dimensional axially symmetric simulation was run. As indicated inFIG. 10, the center of the organ-pipe sound source (corresponding to x/y coordinates 0/0) is equally offset from each of the two ends of the resonator tube and located along the central longitudinal axis of the resonator tube. The X and Y axes are labeled in meters from the center of the sound source. The simulations were run in steps corresponding to positions of the coaxial sleeves as the coaxial sleeves were slidably moved from a position completely covering the resonator slots to a position completely uncovering the resonator slots. Initially, each coaxial sleeve was positioned so that the longitudinal center of the coaxial sleeve was positioned directly over the respective center of the slotted portion. Each sleeve was then slidably moved to a respective terminal end of the resonator tube in increments of 2 cm. The sleeves were moved symmetrically during the simulation.

FIGS. 11A and 11Bdepict results of FEA simulations for an organ-pipe sound source having the resonator slots completely covered by the coaxial sleeves (FIG. 11A) and for an organ-pipe sound source having the resonator slots completely uncovered by the coaxial sleeves (FIG. 11B). The sound pressure level (SPL) in dB re I uPa is shown inFIG. 11Aat an initial frequency of about 500 Hz, when the resonator slots were completely closed, and inFIG. 11Bat a final frequency, when the resonator slots were completely opened. Initially, when the resonator slots were covered by the coaxial sleeves, the pipe operated as a half wavelength resonator at about 500 Hz, and radiated sound though through the open terminal ends. As the resonator slots are uncovered, the sound source operates like a four element array and radiates sound from the terminal ends as well as through the opening resonator slots. The transition from fully covered state to the fully uncovered state is smooth without a sudden change in frequency response. The directionality pattern also remains approximately 90 degrees in the horizontal direction in all frequency ranges.FIG. 12depicts another graph of the absolute pressure (Pa) contours generated by the FEA simulation for the resonator tube having the resonator slots completely uncovered (frequency at about 1063 Hz).

The resonator slots are symmetrically located at a distance of about ⅓ from the resonator tube edges, where the second harmonic of the resonator tube has internal nodes. According to the simulation, the motion of the coaxial sleeves with respect to the resonator slots should have a minor effect on the second harmonic frequency. Additionally, the resonance frequency of the first harmonic can be moved toward the resonance frequency of the second harmonic. This behavior is depicted inFIG. 13which is set of frequency responses of the sound system for shifts of the coaxial sleeves. In these simulations, the sleeve length was 9.5″ (24 cm), and was shifted from a first configuration (slotted portions completely covered as depicted inFIG. 9A) to a second configuration (slotted portions completely uncovered as depicted inFIG. 9B). The frequency responses were calculated for a symmetric shift of 1 cm for the two coaxial tubes. It may be observed that the first resonance (first harmonic) changes from about 500 Hz to about 1050 Hz, while the second resonance (second harmonic) changes from about 1250 Hz to about 1400 Hz, which corresponds to only about a 12% change Between the resonance peaks, the pressure level amplitude drops more then 10 times (−20 dB). Without being bound by theory, the change in the first harmonic resonant frequency may be due to a change in the acoustic coupling between the water in the interior of the pipe and the exterior via the water in the gaps. As disclosed above with reference toFIGS. 9A,B, as the length of the gap decreases, the acoustic impedance coupling therethrough decreases.

Thus, the simulation indicates that the tunable organ-pipe sound system can potentially create a broadband frequency domain between two resonances corresponding to the first harmonic and the second harmonic. This approach has been described in U.S. Pat. No. 4,855,964 to B. L. Fanning and G. W. McMahon and entitled “Vented-Pipe Projector.”

Experimental work was initiated to expand the frequency band of an organ-pipe sound source at the high frequency end of the range. Measurements were made of the acoustic output of a test instrument having substantially the same dimensions as those disclosed above in Table 1.FIGS. 14A-Jare amplitude versus frequency measurements of the acoustic output of the test device as the coaxial sleeves are synchronously and symmetrically moved in 2 cm increments from an initial configuration of the resonator slots being completely covered (center of the coaxial sleeve initially located over the center of the resonator slot).

It may be observed that the frequency of the first harmonic resonance increases as the coaxial sleeves are moved, in a manner similar to that depicted inFIG. 13(simulation values). However, a second resonance begins to appear when the first harmonic resonance frequency reaches a value of about 874.37189 Hz (FIG. 14G). The dual resonance depicted inFIG. 14Goccurs after each of the coaxial sleeves is displaced 12 cm. If the center of the coaxial sleeves (total length 9.25 in. or about 23.5 cm) are located initially at the center of the resonator slots (width about 2 in. or about 5 cm), then the second resonance peak is observed when the edge of the coaxial sleeves have uncovered about 2.75 cm of the resonator slot. This result is surprising and unexpected in view of the simulations depicted inFIG. 13, in which no dual-resonant first harmonic peaks are observed. In reference toFIGS. 14G-14J, it is observed that the second peak of the dual-resonant feature does not correspond to a frequency associated with a second harmonic mode as disclosed in B. L. Fanning and G. W. McMahon. The dual-resonance acoustic emission depicted inFIGS. 14G-Jappears related to the width of the resonator slots and the amount of the resonator slots uncovered by the coaxial sleeves. For example, if the resonator slot width is much larger that the width along the tube axis and the resonator slots are opened widely (for example, more than 2″), then the multiple resonances appear. In one aspect, for example, the width of the resonator slot may be fashioned to be about ½ of a radius of the inner diameter of the resonator tube.

An additional difference between the experimental results inFIGS. 14A-Jand the simulation results inFIG. 13is a clear indication of a shift in the second harmonic resonance to higher values. In the initial configuration of the system (FIG. 14A), the peak of the second harmonic is clearly visible at the right side of the graph. However, as the coaxial sleeves are moved relative to the resonator slots, (in the progression ofFIGS. 14A-14F) the peak of the second harmonic moves to higher frequencies until only a small portion of the tail of the peak is observed atFIG. 14F. This behavior is surprising because it is not predicted by the simulations as depicted inFIG. 13. Similarly, this behavior was not anticipated by B. L. Fanning and G. W. McMahon who suggested that the first harmonic frequency peak could be adjusted to being arbitrarily close to the second harmonic frequency peak.

Without being bound by theory, an explanation for the multiple resonance peaks associate with the first harmonic may be considered as follows. When the coaxial sleeves are positioned to cover at least a major portion of the resonator slots having a wide width (that is, around 2 inches or wider), the resonator tube acts as a single resonator in which the two terminal portions and the medial portion of the resonator tube are strongly acoustically coupled. However, once the coaxial sleeves are positioned to uncover more than half of the resonator slots, the coupling among the three tube portions (two terminal portions and the medial portion) weakens considerably, and the portions begin to act as individual resonators. It may be suggested that the present simulation did not predict this effect because the present simulation only considered acoustic coupling through the water, including the water in the resonator tube interior and the gaps, and did not include acoustic coupling among the tube the portions via the metal bridges.

Again, without being bound by theory, it is believed that the two first harmonic resonance peaks depicted inFIGS. 14G-Jare due to independent resonances of the medial portion and the two terminal portions. In an example in which the two terminal portions have equal tube lengths, and the length of the medial portion differs from that of the two terminal portions, the first harmonic resonance may be split into two resonance peaks. The difference in the frequencies may be related to the relative differences of the lengths of the tube portions. It may be suggested that three first harmonic resonance peaks may be produced by an organ-pipe sound source if the tube portions—that is, a first terminal portion, the medial portion, and a second terminal portion—do not have a common tube length.

Additionally, the frequencies at the first harmonic may also be dependent on the relative thickness of the tubes comprising the portions. For example, any one or more of the portions of the resonator tube may have a wall thickness about ⅛th of a radius of the inner diameter of the resonator tube. Additional adjustments to the multiple frequencies at the first harmonic may also be obtained by fabricating the resonator tube portions with different tube thicknesses. It may be recognized that the multiple first harmonic frequencies may be adjusted close to each other with very small amplitude variability over the working frequency band.

The results depicted above with respect toFIGS. 14A-Jsuggest a simple way to manufacture a tunable sound source with a broadband output that may be defined by a frequency response of the resonator tube at the high frequency end of the range. While the organ-pipe sound source disclosed above may produce dual resonances of the first harmonic, the same approach can be used to fabricate a broadband triple or greater resonance sound source.

FIGS. 15A and 15Bdepict the real and imaginary components, respectfully, of the admittance of a tunable organ-pipe sound source as disclosed above in which the resonator slots of the slotted portions are completely uncovered by the coaxial sleeves. A tunable organ-pipe sound source in this configuration may therefore act as a broadband sound source having an output defined by the frequency response of the resonator tube. As depicted finFIG. 15A, the frequency response of the resonator tube may be composed of a dual resonance transfer function defined by a first resonance frequency and a second resonance frequency. It can be observed that the output of the sound source in this configuration has the dual resonance frequencies (1505and1510) both having about the same amplitude. In the example depicted inFIG. 15A, the higher frequency resonance peak1505has a frequency of about 940 Hz and the lower frequency resonance peak1510has a frequency of about 890 Hz. The two resonances may be disposed between the first harmonic (at about 500 Hz) and the second harmonic (at about 1500 Hz) of the resonant tube. The first resonance peak1505and the second resonance peak1510may define a communication bandwidth1530for transmitting one or more information-containing signals underwater. As a non-limiting example, a communication bandwidth1530may be about 100 Hz and include frequencies between a lower limit1525of about 845 Hz and an upper limit1520of about 955 Hz1520and centered at a medial frequency1515of about 915 Hz. In some aspects, the medial frequency1515may be an average of the frequency of the first resonance peak1505and the frequency of the second resonance peak1510. In general, the communication bandwidth1530may be chosen to have a frequency of about 10% to about 15% of the medial frequency1515. In some non-limiting examples, the communication bandwidth may have a frequency of about 10% of the medial frequency1515, of about 11% of the medial frequency1515, of about 12% of the medial frequency1515, of about 13% of the medial frequency1515, of about 14% of the medial frequency1515, of about 15% of the medial frequency1515, or any such percentage or range of percentages therebetween including endpoints. This bandwidth may be sufficient for a long range underwater communication system for a precise underwater positioning support.

FIG. 15Bdepicts the imaginary or phase-related components of the tunable organ-pipe sound source as disclosed above in which the resonator slots of the slotted portions are completely uncovered by the coaxial sleeves. It may be noted that over the range of frequencies measured, little phase variability is observed at the frequencies corresponding to the two resonance peaks (1505and1510) corresponding to the characteristic resonance frequencies of the organ-pipe operating in the broadband mode.

It may be understood that a broadband organ-pipe sound source may be composed solely of the resonant tube, acoustical driver, and acoustical driver controller as disclosed above. Such a device may operate in a single signal transmission mode that sources arbitrary acoustic signals within the broad range of the bandwidth.

A second, tunable organ-pipe sound source may be composed of the broadband organ-pipe sound source disposed within the coaxial tubular sleeves. Such a device may operate in two signal transmission modes. When operated in a first mode, the slotted portions may be covered by the coaxial tubular sleeves which may be slid along the exterior surface of the resonant tube to select a resonant output frequency. The controller of the acoustical driver may control the frequency output of the acoustical driver to match the resonant output frequency determined by the position of the coaxial tubular sleeves. In this first mode, the tunable organ-pipe sound source may be programmed to transmit single frequency pulses, frequency modulated pulses, chirps, or linear swept-frequency signals. Such signals may be useful for underwater tomographic measurements. When operated in the second signal transmission mode, the coaxial tubular sleeves may be fixed at a position to uncover the slots in the slotted portions of the resonant tube. In this configuration, the tunable organ-pipe sound source may function like the broadband organ-pipe sound source disclosed above.

While various details have been set forth in the foregoing description, it will be appreciated that the various aspects of the present disclosure may be practiced without these specific details. For example, for conciseness and clarity selected aspects have been shown in block diagram form rather than in detail. Some portions of the detailed descriptions provided herein may be presented in terms of instructions that operate on data that is stored in a computer memory. Such descriptions and representations are used by those skilled in the art to describe and convey the substance of their work to others skilled in the art.

Although various embodiments have been described herein, many modifications, variations, substitutions, changes, and equivalents to those embodiments may be implemented and will occur to those skilled in the art. Also, where materials are disclosed for certain components, other materials may be used. It is therefore to be understood that the foregoing description and the appended claims are intended to cover all such modifications and variations as falling within the scope of the disclosed embodiments. The following claims are intended to cover all such modification and variations.

All of the above-mentioned U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, non-patent publications referred to in this specification and/or listed in any Application Data Sheet, or any other disclosure material are incorporated herein by reference, to the extent not inconsistent herewith. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.

Although various embodiments have been described herein, many modifications, variations, substitutions, changes, and equivalents to those embodiments may be implemented and will occur to those skilled in the art. Also, where materials are disclosed for certain components, other materials may be used. It is therefore to be understood that the foregoing description and the appended claims are intended to cover all such modifications and variations as falling within the scope of the disclosed embodiments. The following claims are intended to cover all such modification and variations.

In summary, numerous benefits have been described which result from employing the concepts described herein. The foregoing description of the one or more embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or limiting to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The one or more embodiments were chosen and described in order to illustrate principles and practical application to thereby enable one of ordinary skill in the art to utilize the various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the claims submitted herewith define the overall scope.

Various embodiments are described in the following numbered examples:

An underwater sound source comprising:an acoustical driver;a controller of the acoustical driver; anda resonator tube acoustically coupled to the acoustical driver, wherein the resonator tube further comprises:a first slotted portion comprising a first at least two co-radial resonator slots; anda second slotted portion comprising a second at least two co-radial resonator slots,wherein a total length of the resonator tube defines a plurality of harmonics of the resonator tube,wherein the first slotted portion is located at a first position along the total length of the resonator tube corresponding to a first node of one of the plurality of harmonics,wherein the second slotted portion is located at a second position along the total length of the resonator tube corresponding to a second node of one of the plurality of harmonics, andan output signal of the underwater sound source to within a bandwidth defined by a frequency response of the resonator tube.

The underwater sound source of Example 1, wherein the resonator tube has an outer diameter within a range of one tenth of the total length of the resonator tube to one half of the total length of the resonator tube.

The underwater sound source of any one or more of Example 1 through Example 2, wherein each of the first at least two co-radial resonator slots of the first slotted portion has a width within a range of one tenth of a radius of the resonator tube and one half of the radius of the resonator tube, andwherein each of the second at least two co-radial resonator slots of the second slotted portion has a width within a range of one tenth of the radius of the resonator tube and one half of the radius of the resonator tube.

The underwater sound source of any one or more of Example 1 through Example 3, wherein the first slotted portion and the second slotted portion define a medial section of the resonator tube therebetween,wherein the first slotted portion and a first end of the resonator tube define a first terminal section of the resonator tube therebetween, andwherein the second slotted portion and a second end of the resonator tube define a second terminal section of the resonator tube therebetween.

The underwater sound source of Example 4, wherein the first terminal section has a first section length the second terminal section has a second section length, and the medial section has a medial section length, and wherein the medial section length differs from the first section length and the medial section length differs from the second length.

The underwater sound source of any one or more of Example 4 through Example 5, wherein the first of the at least two co-radial resonator slots of the first slotted portion are separated by a first bridge connecting a first end of the medial section and a first end of the first terminal section, andwherein the second of the at least two co-radial resonator slots of the second slotted portion are separated by a second bridge connecting a second end of the medial section and a first end of the second terminal section.

The underwater sound source of any one or more of Example 1 through Example 6, wherein the frequency response of the resonator tube comprises a dual resonance transfer function defined by a first resonance frequency and a second resonance frequency, and the bandwidth is between 10% and 15% of a medial frequency defined as an average of the first resonance frequency and the second resonance frequency.

An underwater sound source comprising:an acoustical driver;a controller of the acoustical driver;a resonator tube acoustically coupled to the acoustical driver, wherein the resonator tube further comprises:a first slotted portion comprising a first at least two co-radial resonator slots; anda second slotted portion comprising a second at least two co-radial resonator slots,wherein a total length of the resonator tube defines a plurality of harmonics of the resonator tube,wherein the first slotted portion is located at a position along the total length of the resonator tube corresponding to a first node of one of the plurality of harmonics,wherein the second slotted portion is located at a position along the total length of the resonator tube corresponding to a second node of one of the plurality of harmonics; anda first coaxial tubular sleeve and a second coaxial tubular sleeve,wherein the resonator tube is disposed within the first coaxial tubular sleeve thereby forming a first gap between a first portion of an exterior surface of the resonator tube and an interior surface of the first coaxial tubular sleeve,wherein the resonator tube is disposed within the second coaxial tubular sleeve thereby forming a second gap between a second portion of the exterior surface of the resonator tube and an interior surface of the second coaxial tubular sleeve, andwherein the first coaxial tubular sleeve is configured to slide upon the first portion of the exterior surface of the resonator tube and the second coaxial tubular sleeve is configured to slide upon the second portion of the exterior surface of the resonator tube,wherein the underwater sound source is configured to operate in a first acoustic mode when the first slotted portion is covered by the first coaxial tubular sleeve and the second slotted portion is covered by the second coaxial tubular sleeve, andwherein the underwater sound source is configured to operate in a second acoustic mode when the first slotted portion is uncovered by the first coaxial tubular sleeve and the second slotted portion is uncovered by the second coaxial tubular sleeve.

The underwater sound source of Example 8, wherein the first gap has a width in a range between 1 mm and 5 mm, and the second gap has a width in a range between 1 mm and 5 mm.

The underwater sound source of any one or more of Example 8 through Example 9, wherein the controller of the acoustical driver is configured to control an output frequency of the acoustical driver to a tube resonance frequency determined at least in part by a location of the first coaxial tubular sleeve and a location of the second coaxial tubular sleeve when the underwater sound source is configured to operate in the first acoustic mode.

The underwater sound source of any one or more of Example 8 through Example 10, wherein the controller of the acoustical driver is configured to control an output signal of the underwater sound source to within a bandwidth defined by a a frequency response of the resonator tube.

An underwater sound system, comprising:an underwater sound source, comprising:an acoustical driver;a controller of the acoustical driver;a resonator tube acoustically coupled to the acoustical driver, wherein the resonator tube further comprises:a first slotted portion comprising a first at least two co-radial resonator slots; anda second slotted portion comprising a second at least two co-radial resonator slots,wherein a total length of the resonator tube defines a plurality of harmonics of the resonator tube,wherein the first slotted portion is located at a position along the total length of the resonator tube corresponding to a first node of one of the plurality of harmonics,wherein the second slotted portion is located at a position along the total length of the resonator tube corresponding to a second node of one of the plurality of harmonics; anda first coaxial tubular sleeve and a second coaxial tubular sleeve,wherein the resonator tube is disposed within the first coaxial tubular sleeve thereby forming a first gap between a first portion of an exterior surface of the resonator tube and an interior surface of the first coaxial tubular sleeve,wherein the resonator tube is disposed within the second coaxial tubular sleeve thereby forming a second gap between a second portion of the exterior surface of the resonator tube and an interior surface of the second coaxial tubular sleeve, andwherein the first coaxial tubular sleeve is configured to slide upon the first portion of the exterior surface of the resonator tube and the second coaxial tubular sleeve is configured to slide upon the second portion of the exterior surface of the resonator tube,wherein the underwater sound source is configured to operate in a first acoustic mode when the first slotted portion is covered by the first coaxial tubular sleeve and the second slotted portion is covered by the second coaxial tubular sleeve, andwherein the underwater sound source is configured to operate in a second acoustic mode when the first slotted portion is uncovered by the first coaxial tubular sleeve and the second slotted portion is uncovered by the second coaxial tubular sleeve;a transmission comprising a lead screw in mechanical communication with the first coaxial tubular sleeve and the second coaxial tubular sleeve;a motor in mechanical communication with the transmission and configured to impart a rotary motion to the lead screw, thereby moving the first coaxial tubular sleeve and the second coaxial tubular sleeve; anda water pressure housing, wherein an exterior surface of the water pressure housing is in mechanical communication with the transmission and the motor, and wherein an interior of the water pressure housing is configured to contain one or more electrical components configured to control and power the motor.

The underwater sound system of Example 12, wherein the lead screw is configured to move the first coaxial tubular sleeve and the second coaxial tubular sleeve symmetrically in opposing directions when the lead screw is rotated by the motor.

The underwater sound system of any one or more of Example 12 through Example 13, wherein the transmission is covered with one or more oil-filled bellows configured to prevent water from contacting the transmission.

A method of transmitting signals underwater, comprising:providing an underwater sound source, comprising:an acoustical driver;a controller of the acoustical driver; anda resonator tube acoustically coupled to the acoustical driver, wherein the resonator tube further comprises:a first slotted portion comprising a first at least two co-radial resonator slots; anda second slotted portion comprising a second at least two co-radial resonator slots,wherein a total length of the resonator tube defines a plurality of harmonics of the resonator tube,wherein the first slotted portion is located at a first position along the total length of the resonator tube corresponding to a first node of one of the plurality of harmonics, andwherein the second slotted portion is located at a second position along the total length of the resonator tube corresponding to a second node of one of the plurality of harmonics; andcontrolling, by the controller, an output signal of the underwater sound source to within a bandwidth defined by a frequency response of the resonator tube.