Transducer for vibration absorbing, sensing, and transmitting

This application is a 35 U.S.C. 371 U.S. National Stage Application of PCT International Application Serial No. PCT/GB2008/050904 filed Oct. 03, 2008 which claims benefit of U.K. Application Serial No. GB0719246.1 filed Oct. 03, 2007 both are herein incorporated in their entirety by reference.

This invention relates to a transducer for damping vibration energy from a surface. A proportion of this energy may be converted and stored as electrical energy.

The primary purpose of the invention is to reduce sound or vibration transmitted through large structures (for example ships, oil rigs, bridges, buildings and other structures) by converting this movement into electrical energy.

It is already known that energy may be absorbed or harvested by converting the movement or vibration of a surface into electrical energy which can then be used as a power source or dissipated. However, previous applications have been on a smaller scale and traditionally preferred to use piezoelectric transducers. While such actuators can be used for small scale power harvesting, larger forces such as might be found in the scale of structures being considered (for example the hull of a large cruise ship) need to be an order of magnitude more powerful.

The transducer may also function as a sensor. This may replace, or, supplement existing sensing applications. In the example of bridges, the sensor signal may be used to monitor vibration levels from traffic.

Traditionally, to provide audio coverage for a large area would have required many speakers. However, if the structure is driven with an audio signal, wide coverage may be achieved with fewer sound sources and associated wiring and amplification.

According to the invention, there is provided a transducer for absorbing acoustic or vibration energy from a surface radiating audible sound or vibrations, the device comprising a body containing an actuator of the magnetostrictive type, comprising, a reaction mass, linear bearing or some other form of guide or sleeve and an arrangement of magnets, spacers and coil windings surrounding a core of Giant Magnetostrictive Material (GMM) generally to the same formulation as our previous patent application (European Patent Application Number 02708456.5, International Patent Number PCT/GB02/01111). When accelerated by the vibrational energy of the panel, the reaction mass component of the transducer imparts a force into the GMM element of the transducer. This results in a change in the magnetic properties of the GMM, this change manifests itself as a change in the magnetic field surrounding the GMM. This fluctuating magnetic field is used to induce an electric current in the coil surrounding the GMM. This electrical current may be absorbed into a connected power storage system such as a battery, capacitor or other power retaining solution, Preferably, the mass is in series with the actuation portion of the transducer within the enclosure in an axial arrangement, more preferably it runs in a bearing to support the mass. The bearing can be of a linear format or in another embodiment, by two smaller ring bearings. In an embodiment of either design, oil filling may be advantageous to reduce friction within the unit and minimise noise generated within the transducer.

It has been found that by constraining the movement to within the limits of the bearing running axially to the actuation direction is very effective however the design is not restricted to this permutation

The transducer can also be used as a vibration generator or audio transducer whereby an electrical signal is applied to the coil windings which in turn generates a magnetic field causing the GMM element to change shape generating a vibration on the mounted surface. The coils windings for the absorbing or vibration generating function may be the same or separate for each function but wound on the same bobbin.

In a second embodiment of the invention the control of the axis of thrust is important as can be seen in our patent application (International Patent Application Number WO2004/057912 A3) for a transverse axis lever device. In this embodiment the vibration from the mounting surface is amplified by the mechanical lever system, such that the reaction mass works in conjunction with the compressive forces on the GMM amplifying the amount of compression and subsequent electrical energy generated.

Preferably, the transducer is a magnetostrictive actuator comprising a magnetostrictive element and an electromagnetic coil associated therewith, the element being mechanically connected to the foot, and the coil being energised by the vibration from the mounting surface so as to cause the element to deliver an output force to the power system for storage and subsequent reuse.

The transducer as with the first embodiment, can also be used as a vibration generator or audio transducer whereby an electrical signal is applied to the coil windings which in turn generates a magnetic field causing the GMM element to change shape and movement amplified by the lever generating a vibration on the mounted surface. The coils windings for the absorbing or vibration generating function may be the same or separate for each function but wound on the same bobbin.

It can be seen that the design is not limited to the use of magnetostrictive cores as defined and shown in our associated patent applications, and could benefit from multiple wound coils to distinguish between vibration at specific frequencies as per our previously mentioned patent. This could include multiple elements including piezo and other smart material exciters, flexi tensional devices similar to the one protected by patent (U.S. Pat. No. 4,845,688) transverse lever devices as per our own application referred to above and laminated smart materials that use any combination of the above.

Mass, spring type and coil windings may be selected to operate under different frequency regimes. In certain applications it may be desirable to combine two transducer topologies, for example low frequency element for noise reduction and higher frequency element for audio transmission. The optimal range of effectiveness of the devices can vary dependent on application but are in the region of 20 Hz-2000 Hz for vibration damping and 100 Hz-18 kHz for audio transmission.

Another embodiment of the device is to contain within its structure an integrated sensor such as a piezoelectric device or similar that senses vibrations from the mounting surface it is mounted onto so providing a reference that the control electronics can respond and react against. This might be for the purposes of sensing unusual or non-predicted vibrations, such that an alarm might be triggered or for vibration control applications where the sensor is used to detect vibration from the surface and the transducer is activated 180 degrees out of phase to cancel the vibration. Similarly this aspect of the invention could allow the device to be used as an accelerometer where a two way signal can be used to compensate for a specific vibrational circumstance for example on the hull of a ship where ice may be occasionally encountered and surface activation (vibration) may be required to remove it.

Another embodiment of the device is for application as a distributed mode loudspeaker fire alarm system, since the device can have improved fire resistance compared with conventional audio devices. In this implementation the transducer would normally be in the vibration damping mode. However, in response to an alarm signal, a pre-recorded message, announcement and/or warning sound could be transmitted into the structure.

The attachment of the device to the surface may be permanent or temporary, but in either case the foot that will be attached to the surface will be adhered or fastened to remain in intimate contact with the surface. As the environment in which the device operates will be frequently immersed in water, oil, diesel and other noxious elements found in the hull of a boat or structure the device will be designed to withstand this environment for many years operating in a safe and non hazardous manner throughout its lifetime.

The design of the transducer allows it to be operated as a sensor to allow, for example, monitoring of vibration. Further, by applying electrical signals to the transducer, audio signals may be transmitted into the structure on which the transducer is mounted. The design of the transducer is such that it functions in any mounting orientation.

Some embodiments of the invention are described, as examples only, with reference to the drawings, in which:

FIG. 1 is a sectional elevation of the axial device according to the first embodiment of the invention featuring a linear bearing,

FIG. 2 is a sectional elevation of the axial device according to the first embodiment of the invention featuring dual bearing rings,

FIG. 3 is a sectional elevation of the axial device according to the first embodiment of the invention featuring an external mounting flange,

FIG. 4 is a sectional elevation of the axial device according to the first embodiment of the invention showing an alternate mounting position,

FIG. 5 is a sectional elevation of the axial device according to the first embodiment of the invention featuring a double GMM core,

FIG. 6 is a sectional elevation of the axial device according to the first embodiment of the invention featuring an alternate GMM core construction,

FIG. 7 is a sectional elevation of the axial device according to the first embodiment of the invention showing a more compact version of the core build,

FIG. 8 is a sectional elevation of the transverse device according to the second embodiment of the invention featuring a single GMM core,

FIG. 9 is a sectional elevation of the transverse device according to the second embodiment of the invention featuring dual GMM cores,

FIGS. 10-12 are sectional elevations of the transverse device according to the second embodiment of the invention showing alternate mounting axis and methods.

Referring to FIG. 1 , the absorber device comprises a casing 1 containing an core assembly 2 - 6 in intimate contact with a reaction mass 7 pretensioned against the actuator by a spring 8 which keeps the device in tension. The reaction mass is mounted within a linear bearing 9 or alternatively two annular bearing rings, 10 as shown in FIG. 2 . The core assembly consists of various parts including a moulded bobbin 2 , coil 3 , magnets 4 , spacers 5 and GMM element 6 . The core assembly 2 - 6 is of the type described and claimed in our co-pending International Patent Application, European Patent Application Number 02708456.5. The foot 11 is securely fastened to case 1 . O-ring 12 prevents water ingress. A vibration sensor such as an accelerometer 13 is mounted on the foot 11 .

The whole device is connected to an external energy storage device (not shown). In use, the device is permanently or temporarily attached to a surface to which vibrations to be absorbed with the foot 11 by means of either a permanent adhesive, or fixings through a modified foot featuring mounting flanges 15 as shown in FIGS. 3 and 4 .

FIG. 5 shows a double transducer stack, which might be used to increase efficiency. FIG. 6 shows an alternative transducer arrangement whereby the disc magnets 4 shown in FIG. 1 are replaced with a cylindrical magnet 14 , to reduce the diameter of the core.

FIG. 7 shows a more compact arrangement where the actuator core is encompassed by the reaction mass 7 in order to create a lower profile device. Most components are as per FIG. 1 . However, this embodiment also includes the mounting flange 15 and use of oil to fill the cavity 16 .

FIG. 8 shows an alternative embodiment. In this implementation, the actuator assembly identified in description of FIG. 1 , is replaced with a transverse axis lever device as detailed in co-pending patent application number WO2004/057912A3. The case 1 , foot 11 and O-ring 12 remain as shown in FIG. 1 . However, the internal components of the case 1 are replaced by the transverse axis lever device, comprising a core assembly of bobbin 2 , coil 3 , magnet 4 , spacer 5 , GMM 6 & domed spacer 17 . The core is located within the transducer assembly, and comprises a base-plate 18 attached to body 19 with hinge 20 . The transducer assembly is held in tension by spring 8 .

FIG. 9 shows an enhancement of this embodiment which utilises two core assemblies to increase either energy harvesting efficiency, audio quality, or to optimise transducer for applications where it is used as both energy harvesting device and acoustic source.

FIG. 10 shows the transverse axis lever device embodiment mounted vertically with mounting flanges. FIG. 11 shows the same actuator arrangement. However, in this implementation the transducer is adhered with an adhesive or double sided adhesive pad 21 . FIG. 12 illustrates that the device may also be mounted horizontally using either flanges, as illustrated, or adhesive as FIG. 11 .