Magnetic

Magnetic emulation is provided by a linear array of positively buoyant permanent magnets called Dyads. Dyads are mild steel cylinders driven into magnetic saturation by permanent magnet disc stacks to form a large dipolar magnet.

Dyads were developed by the Australian Defence Science and Technology Organisation (DSTO). A number of Dyads configured in a linear array can produce the magnetic field of a selected class of ship, acceptable as a valid target by the most modern mines. The modular nature of the sweep provides the capacity to emulate different ship classes since the sweep signature can be modified by varying the number of Dyads in the array, the polarity (positive or negative pole in the direction of tow) and the distance separating each Dyad.

The ability to manipulate sweep signatures means that the system can be used in either Target Setting Mode (ship emulation) or Mine Setting Mode, and the resultant signature structure can be optimised to reflect the requirements of any geographic location.

The Dyads are manufactured in two sizes: Mini Dyads have the capability to sweep in both Emulation (TSM) and Mine Setting Mode (MSM) for mines targeted against degaussed warships up to destroyer size, and smaller merchant ships. Maxi Dyads have the capability to sweep in both Emulation (TSM) and Mine Setting Mode (MSM) for mines targeted against degaussed warships up to CVA size, and large merchant ships.

Maxi Dyad

Mini Dyads in a storage yard

The Dyads provide magnetic influences in all three axes and are configured to provide a signature which has the same length as the vessel class being emulated, providing a similar spatial and temporal signature.

Seven Dyads with the same polarity and spacing

Seven Dyads with different polarity and spacings

Mini Dyad Description

Each Dyad is a positively buoyant steel cylinder consisting of mild steel tubes and stainless steel sleeves incorporating ferrite permanent magnet discs which provide the magnetising force (the word 'dyad' is a mathematical term and is an oblique reference to the ferrite magnet discs used to magnetise the cylinder).

Mild steel will lose magnetism as a function of time, due to ambient temperature changes, exterior magnetic field induced changes and the effects of vibration or shock. However, since the magnetising force from the disc stacks of ferrite permanent magnets is always present, the mild steel is constantly being magnetised and maintained in a state of magnetic saturation. While the ferrite magnet stacks retain their integrity there will be no reduction in magnetic moment. Mechanical energy such as shock or vibration does not degrade the magnetic characteristics of the high energy density magnets used and the demagnetisation experienced with in-service Dyads after 100,000 hours is essentially zero. Thus, the magnetising force necessary to maintain the magnetic moment of the Dyad will be present during the life of the Dyad, which is estimated to be in excess of 15 years.

Mini Dyad Parameters

Maxi Dyad Description

The maxi Dyad is of similar construction to the mini Dyad but with a greater circumference and much larger magnet discs to provide a substantially higher magnetic moment.

Maxi Dyad Parameters

Shock Testing

The ADI Dyad influence sweep using both mini Dyads and maxi Dyads, has been extensively shock tested and has demonstrated exceptional shock resistance.  As an example, assemblies of four Mk. 8 torpedo warheads were detonated directly beneath a sweep in 18 meters of water.  All Dyads survived in an operational condition and there was no reduction in magnetic moment.  Additionally, the Pipe Noisemakers remained operational.  The sweep has been accepted into the Royal Australian Navy (RAN) as shock proof.

Contact Details

For further information relating to mine countermeasures, please contact the General Manager Mine Countermeasures,
Jack Byrnes
ADI Limited
Building 314, Level 1
Garden Island NSW 2011

Tel: +61 2 9562 2991
Fax: +61 2 9562 2988
Email: jack.byrnes@adi-limited.com