AU2012241194A1 - Marine mammal warning apparatus - Google Patents

Abstract

There is provided a spindle-shaped two-part housing (10) comprising a battery compartment (11) and a working compartment (12), each formed of polyacetal copolymer of Shore D hardness 80. The respective housing portions (11, 12) are joined with threaded portions (14, 15) and sealed by O-ring (16). Each tapered outer end portion is pierced by a bore (17) intersected by an axial bore (21) passing into an end flat (20) to secure the apparatus to nets. The portion (12) has a floor portion (22) comprising a central end wall portion (23) and an annular land (24) that has adhesively bonded thereto the periphery of a piezoelectric sound generator assembly (27). Adhesively secured to an intermediate land (31) and extending across the bore is a circuit assembly (32) built on circuit board (33) and including programmable driver means for driving the piezoelectric sound generator assembly (27) via leads (33). The circuit assembly is powered via a pair of coaxial spring contacts (34, 35) contacting a battery and in response to immersion by water terminals (36). The circuit board (33) and the inner end of the female threaded portion (15) is filled with an epoxy resin encapsulant plug (37) of Shore D hardness 80, forming a resonant system with the housing (10) and piezoelectric sound generator assembly (27).. C-4

Description

1 MARINE MAMMAL WARNING APPARATUS FIELD OF THE INVENTION This invention relates to marine mammal warning apparatus. This invention has particular application to a warning device attachable to beach protection nets or 5 the like for reducing the incidence of entrapment of humpback whales, and for illustrative purposes the invention will be described with reference to this application. However we envisage that this invention may find use in other applications such as providing marine mammal avoidance for other structures such as drift nets. 10 BACKGROUND OF THE INVENTION The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the referenced prior art forms part of the common general knowledge in Australia. 15 It is known to provide an audible warning for cetaceans where there is a risk of entrapment in structures that are invisible or poorly visualized by echolocation. "Pinger" is a generic term used to describe acoustic marine mammal deterrents. Pingers are used to reduce the incidental entanglement of dolphins, porpoises and 20 whales in commercial fishing gear. Known as "cetacean bycatch", an estimated 300,000 marine mammals are lost annually in nets. Governments around the world acknowledge that cetacean bycatch is a serious environmental problem. The use of pingers is legally enforced in North America and Europe via 25 Government mandates. In other countries pingers are deployed voluntarily by fishers who understand that pinger use improves the profitability of fishing efforts. Pingers are currently the only known effective cetacean bycatch mitigation tool available to the global commercial fishing industry. 30 In the context of the present art it is somewhat immaterial whether a pinger acts as a repellent device, sonically illuminates the protected apparatus or merely indicates the presence of itself to the target species.

2 The art of pingers has been characterized by a waterproof housing containing four main components, being a primary storage battery, and an electronic driver circuit, a sound generating device and an on/off switch. The electronic driver circuit may be adapted to drive a coil driven speaker at a frequency generated by an oscillator 5 associated with the circuit. Alternatively, and most commonly, the electronic driver circuit produces an output to drive a piezo transducer. A disadvantage of prior art portable acoustic harassment devices is an inability to manage power consumption. Units weigh in excess of 1kg because of the 10 necessary battery weight to get the benchmark about 50 day operating life. The energy of the sound wave in water increases proportionally with frequency. The overall propagation efficiency of a theoretical source (ratio of energy input by the power source to the wave energy propagated by the source) increases with frequency. However, lower frequencies are less attenuated with distance from the 15 source. The absorption of sound in seawater forms part of the total transmission loss of sound from a source to a receiver. It depends on the seawater properties, such as temperature, salinity and acidity as well as the frequency of the sound. The details 20 of the underlying physics of absorption are complex. The major contribution to transmission loss is the spreading of the acoustic wave as it propagates away from the source, where the energy flux decreases with the square of the distance. Nonetheless, in so far as frequency dependent attenuation is concerned, Francois and Garrison (1982) and Ainslie and McColm (1998) have developed empirical 25 formulae that derive attenuation figures that can be averaged to 0.783 dB/km at 10kHz and 0.182 dB/km at 3kHz. These estimates assume measurement at 1m depth in 18 0 C seawater of 35ppt salinity and about pH8. Prior art pingers have tended to operate at about 10kHz, with big batteries and 30 high power consumption to achieve at least 132db at 1 metre from the pinger at a depth of 1 metre. While all cetaceans (and humans) hear frequencies at or about 10kHz, it remains that the middle of the humpback whale's audible range is at 3 lower frequencies. To date the prior art has not been able to produce a low frequency pinger that is light weight and energy efficient. SUMMARY OF THE INVENTION 5 In one aspect the present invention resides broadly in marine mammal warning apparatus including: a housing; a piezoelectric sound generator mounted in said housing; a wall portion spaced from said piezoelectric sound generator in said 10 housing, said wall portion, housing and piezoelectric sound generator forming a sealed, resonant system; a circuit sealed in said housing and having a tunable oscillator output tuned to drive said piezoelectric sound generator to cause said resonant system to resonate, and an output timer function driving said output in pulses of a selected 15 duration on a selected cycle time; a water sensing switch activating said circuit when the switch is in contact with water in use; and a voltaic cell sealed in said housing and connected to said circuit. 20 The housing may be of any shape consistent with its use. As the apparatus may be used at depth where hydrostatic pressure may be material, the housing is preferably shaped to resist pressure. For example, the housing may be a solid of rotation such as a sphere, cylinder or the like. The housing shape may be elongate or otherwise streamlined. For example the shape may be chosen to 25 minimize water resistance or the tendency to snag. The body may be spindle shaped, whereby substantially solid tapered end portions bound an enlarged waist portion in which the housing function may be formed and the component parts accordingly mounted. 30 As the housing may be used to propagate the sound to a seawater medium, the housing is preferably shaped to limit off-frequency noise. For example, the housing may be substantially ovoid in shape. The housing may be provided with means for securing the apparatus to the structure to be protected. For example 4 the housing may be provided with one or more apertures and adapted to receive a cable tie or the like. The housing may be a sealed assembly or may comprise an openable two- or 5 three-part housing. For example, the two part housing may comprises a part mounting the sound generator, circuit, water sensing switch and plug and a part housing the voltaic cell. The openable, two part housing may be parted at a plane transverse the long axis. 10 The openable two part housing may comprise two parts interconnectable by any suitable complementary interengagement means operable to form a sealed component space. For example the two parts may include a bayonet fitting acting against an axial gasket. Alternatively, in the case of ovoid and similar shaped housings having an axial disposition, the housing may be a two-part housing 15 parted at a plane transverse the long axis, the parts having complementary threaded portions operable to form a sealed component space, one of said parts mounting the transducer, circuit, water contacts and plug and the other said part housing the voltaic cell. The housing may comprise a two-part, screw-together spindle shaped waterproof housing. 20 The wall portion may be assembled to the housing, such as in the form of a threaded or bonded plug. The wall portion may be formed integrally with a portion of the housing. The wall portion may be cast in situ. A cast in situ wall portion may serve as an encapsulant for some of all of the circuit. The wall portion may 25 be formed as an epoxy plug cast across a housing part mounting the sound generator, circuit and water sensing switch. The piezoelectric sound generator may be selected to generate sound of a frequency particular to the marine mammal species targeted. While prior art 30 pingers are typically operated at about 9kHz, it has been determined that humpback-optimized pingers may operate at about 3kHz. The ability of a housing to disperse 3kHz sound efficiently surprisingly appears to be related to the choice of material for its construction. Moreover, it appears that there is less internal 5 dispersion and broad banding of the 3kHz pure tone if the plug is substantially matched to the housing at least in terms of its hardness, and the housing, plug and piezoelectric sound generator form a resonant system. The hardness of the housing and plug is preferably at least Shore D 80 hardness to operate at from 3 5 to 9kHz. It has also been determined that the use of a cast encapsulant wall portion of hardness substantially similar to the housing hardness and disposed across the housing in spaced relation to the piezoelectric sound generator enables the 10 components to form a resonant system. It is preferable that the housing and wall portion continue to form an acoustic unit across a range of service conditions. The expected duty in deep water and low temperature and in the heat on the deck of deploying vessels will tend to break the 15 acoustic bond between the plug and the housing. Accordingly it is preferred that the materials forming the housing and plug respectively have substantially the same linear coefficient of thermal expansion (CTE). The housing is preferably formed of environmentally stable polymer. The housing 20 may be formed of any suitable moulded, cast or machined polymer material. For example, the housing may be cast from a thermoset, precision moulded in thermoplastic or machined from either class. The housing may be precision moulded in or machined from polyphenylene sulphide (Shore D hardness = 88, linear coefficient of thermal expansion (CTE) 40 pm/m-OC). Alternatively, the 25 housing may be moulded in or machined from polyacetal copolymer (typically Shore D hardness = 85, linear CTE = 90 pm/m-OC). As the housing must necessarily transmit sound, an understanding of the property of the housing material in terms of the ability for vibration to pass through the 30 material is important. The selection criteria may include material flexibility and shock resistance to blows typically experienced on commercial fishing vessels. The general durability of the housing material, such as its ability to withstand cuts and knocks, and UV stability, may influence selection.

6 The curable resin encapsulant may be selected from an epoxy resin. The epoxy resin may be a 100% curable solids epoxy resin, or may include fillers selected to modify the CTE and/or Shore D hardness of the base resin. An understanding of 5 the property of the raw materials in terms of the ability for vibration to pass through the material is important to the selection. The selection criteria may also include properties such as the material flexibility when set, the heat of curing in situ, and the like. Shock resistance is a consideration, from blows often experienced on commercial fishing vessels. 10 The water sensing switch may take any suitable form as would be apparent to a person skilled in the art. For example, the water sensing switch may include a pair of water contacts connected to the circuit. The water contacts are preferably of conductive corrosion-resistant metal. The water contacts may be pressed into 15 apertures provided through the housing wall. Where the housing material has the required elastic recovery, the water contacts may be pressed in to form a seal. Otherwise the water contacts may be mounted with sealant. The water contacts may be provided with an annular barb or barbs to resist removal. Any suitable solid state sensor switch may be used in conjunction with the water contacts to 20 switch the apparatus on contact with sea water. The piezoelectric sound generator is preferably bonded into the housing. The piezoelectric sound generator may be in the form of a disc, wherein an inner wall of the housing includes a peripheral land to which the disc is bonded. Preferably, 25 the piezoelectric sound generator is circular and is bonded by its peripheral edge to a circular land provided within the housing. The piezoelectric sound generator may be selected to cause the resonant system to resonate at a frequency of about 3kHz. The circuit assembly may utilize the RC characteristics of the piezo element itself to make a resonant circuit, or the piezo element may be driven by a self 30 contained resonant circuit. The circuit assembly may be built on a printed circuit board in the form of a disc and wherein an inner wall of the housing may include a peripheral land spaced 7 from the piezoelectric sound generator to which the peripheral edge of the printed circuit board may be bonded. However, it is envisaged that the circuit assembly may comprise a VLSIC component having lead-outs for the water contacts and piezoelectric sound generator connections and lead-ins for the battery. 5 The circuit may be configured to produce any selected output in terms of the pulse duration and pulse cycle time. The competing priorities are limiting power consumption while providing adequate warning. For example, the circuit assembly may be configured to pulse the piezo transducer for about 400 milliseconds on a 10 cycle of about 5 seconds, which has been empirically determined to produce a deterrent response in humpback whales. The circuit assembly may be programmable to control one or more of pulse duration, pulse on/off cycle time and piezoelectric sound generator output power. 15 The programmability may be in the form of "bench programming" to match the parameters to the assembly components whose propagation properties in assembly are known. Alternatively, the circuit assembly may be programmable to fine tune the parameters after assembly. For example, the circuit may be tunable by using water contacts forming the water sensing switch as programming input 20 terminals. The circuit assembly is preferably configured whereby a sound pressure level of the pulse is 135dB +/- 5dB at a distance of 1 meter and a depth of 1 meter in sea water. Again the trade-off is between duration, for which the benchmark is 50 25 hours of operation, and loudness for which the benchmark is 132dB at 1 metre distance and 1 metre depth. In an ideal system the resonant frequency of the system is substantially independent of amplitude for all reasonable amplitudes. However, in real systems 30 the amplitude of the piezoelectric sound generator may drag the assembly to a first or higher order resonance and a consequence of non-ideality in the system. At resonance the sound power transfer to the seawater medium, relative to the power consumed by the piezoelectric sound generator, is at a maximum.

8 Accordingly it is preferred that the circuit assembly be programmed to drive the piezoelectric sound generator at the minimum amplitude achieve both resonance with the housing and wall assembly and a sound pressure level of 135dB +/- 5dB at a distance of 1 meter and a depth of 1 meter in sea water. 5 In order to provide sufficient energy density with light weight, the voltaic cell is preferably a high performance primary cell. For example, the voltaic cell may be selected from lithium primary cells. The high performance lithium voltaic cell may be selected from lithium /thionyl chloride primary cells. 10 The relatively low voltage of Li-SOC 2 (3.5V nominal) cells would ordinarily require is of a solid state RPS and heat sink to drive the piezo. However, the low current demand of the optimized embodiments means that high efficiency, ultra-small, monolithic, CMOS charge-pump voltage doublers can be used in the encapsulated 15 circuit to provide adequate output current. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described with reference to the following non-limiting embodiment of the invention as illustrated in the drawings and wherein: 20 Fig. 1 is a functional diagram of apparatus in accordance with the present invention; Fig. 2 is a longitudinal section through a typical apparatus in accordance with the present invention. 25 In the figures there is provided a generally spindle-shaped marine mammal warning apparatus 10 including a two part housing comprising a battery compartment portion 11 and a working compartment portion 12, each formed of polyacetal copolymer of Shore D hardness 80. The respective housing portions 30 11, 12 are provided with corresponding male 14 and female 15 threaded portions, the interconnection being rendered waterproof under pressure by O-ring 16.

9 The housing portions 11, 12 each have a tapered outer end portion of solid section and pierced by a transverse bore 17 spaced from and end flat 20, and intersected by an axial bore 21 passing into the end flat 20. The transverse 17 and axial 21 bores provide for securing the warning apparatus 10 to nets by lacing, cable/zip 5 ties or toggles (not shown). The working compartment portion 12 comprises a bore having a floor portion 22 comprising a central end wall portion 23 and an annular land 24, radially spaced by an annular channel 25. The annular land 24 has adhesively bonded thereto the 10 peripheral mounting annulus 26 of a piezoelectric sound generator assembly 27. The piezoelectric sound generator assembly 27 has a resonator face 30 in passive contact with the central wall portion 23 at rest. The working compartment portion 12 includes an intermediate annular land 31 15 forming a step in the bore. Adhesively secured to the intermediate land 31 and extending across the bore is a circuit assembly 32 built on circuit board 33. The circuit assembly 32 includes programmable driver means for driving the piezoelectric sound generator assembly 27 via leads 33. The circuit assembly is powered via a pair of coaxial spring contacts 34, 35 adapted to engage in 20 compression with the top contacts of a corresponding battery (not shown) located in the battery compartment portion 11. The circuit assembly 32 is powered up in response to immersion of a pair of water terminals 36. The working compartment portion 12 is filled with an epoxy resin encapsulant plug 25 37 between the circuit board 33 and the inner end of the female threaded portion 15. The plug 37 in this case is formed in E-CAST F-28 (United Resin Corporation). E-CAST F-28 is an unfilled, medium viscosity, high strength resin with good release, excellent adhesion, clarity and room temperature rigid cure. 30 The circuit assembly 32 includes functional components as represented in the functional diagram of Figure 2, wherein a 3.6V Li-ion primary cell 38 is drawn connected (in conventional-current) to an in-series pair of solid state voltage doublers 40, producing a 10.8VDC power supply. An inductive driver circuit 41 is 10 powered by the power supply and controlled by an 8-bit CPU 42 programmable as to pulse duration between 300-400mS, sleep time, driver frequency and driver amplitude. The CPU 42 is powered up in response to immersion of the water terminals 36 and in turn switches the driver 41 according to the preprogrammed 5 regime. The driver 41 in turn powers a piezoelectric sound generator 43 with, in this case a 3kHz AC driver signal. It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and 10 variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is set forth in the claims appended hereto.

Claims (19)

1. Marine mammal warning apparatus including: a housing; a piezoelectric sound generator mounted in said housing; a wall portion spaced from said piezoelectric sound generator in said housing, said wall portion, housing and piezoelectric sound generator forming a sealed, resonant system; a circuit sealed in said housing and having a tunable oscillator output tuned to drive said piezoelectric sound generator to cause said resonant system to resonate, and an output timer function driving said output in pulses of a selected duration on a selected cycle time; a water sensing switch activating said circuit when the switch is in contact with water in use; and a voltaic cell sealed in said housing and connected to said circuit.

2. Marine mammal warning apparatus according to claim 1, wherein said housing is an openable, two part housing.

3. Marine mammal warning apparatus according to claim 2, wherein said openable, two part housing is parted at a plane transverse the long axis, the parts having complementary threaded portions operable to form a sealed component space, one of said parts mounting the sound generator, circuit, water sensing switch and wall and the other of said parts housing the voltaic cell.

4. Marine mammal warning apparatus according to claim 3, wherein said wall is cast in situ.

5. Marine mammal warning apparatus according to claim 4, wherein said wall is formed as an epoxy plug cast across said part mounting the sound generator, circuit and water sensing switch. 12

6. Marine mammal warning apparatus according to claim 5, wherein said epoxy plug functions as an encapsulant for some of all of the circuit.

7. Marine mammal warning apparatus according to claim 1, wherein said piezoelectric sound generator is selected to cause said resonant system to resonate at a frequency of about 3kHz.

8. Marine mammal warning apparatus according to claim 7, wherein said wall portion and said housing have a hardness of at least Shore D 80 hardness to operate at from 3 to 9kHz.

9. Marine mammal warning apparatus according to claim 7, wherein said wall portion is a wall cast in situ.

10. Marine mammal warning apparatus according to claim 1, wherein the materials forming the housing and wall portion respectively have substantially the same linear coefficient of thermal expansion (CTE).

11. Marine mammal warning apparatus according to claim 1, wherein said housing is moulded in or machined from polyacetal copolymer.

12. Marine mammal warning apparatus according to claim 11, wherein said wall portion is formed from a curable epoxy resin encapsulant.

13. Marine mammal warning apparatus according to claim 1, wherein said water sensing switch includes a pair of water contacts connected to the circuit.

14. Marine mammal warning apparatus according to claim 1, wherein said piezoelectric sound generator is in the form of a disc, wherein an inner wall of the housing includes a peripheral land to which the disc is bonded.

15. Marine mammal warning apparatus according to claim 1, wherein said circuit assembly is built on a printed circuit board in the form of a disc and wherein 13 an inner wall of the housing includes a peripheral land spaced from the piezoelectric sound generator to which the peripheral edge of the printed circuit board is bonded.

16. Marine mammal warning apparatus according to claim 1, wherein said circuit assembly is configured to pulse the piezo transducer for about 400 milliseconds on a cycle of about 5 seconds.

17. Marine mammal warning apparatus according to claim 1, wherein said circuit assembly is programmable to control one or more of pulse duration, pulse on/off cycle time and piezoelectric sound generator output power.

18. Marine mammal warning apparatus according to claim 17, wherein said circuit assembly is programmable to fine tune the parameters after assembly using water contacts forming the water sensing switch as programming input terminals.

19. Marine mammal warning apparatus according to claim 1, wherein said circuit assembly is configured to generate a sound pressure level of 135dB +/- 5dB at a distance of 1 meter and a depth of 1 meter in sea water.