Exploring ship demagnetization technology
2026-09-08
To ensure its own navigation safety, in May of this year, the US Navy spent several weeks clearing the passage of the Strait of Hormuz and discovered more than 10 submerged magnetic mines. These magnetic mines can lurk underwater for a whole year and may pose a significant threat to passing ships.
Magnetic mines do not require direct contact with the ship's hull. As long as a ship passes over it, if the magnetic field of the ship's hull is too strong, it can cause the magnetic sensors inside the mine to deflect, resulting in an explosion and achieving the goal of severely damaging the ship. In the Earth's large magnetic field, ships cruising at sea are also a moving magnetic field. To avoid the threat of magnetic weapons, reduce the probability of magnetic anomaly detection, and improve the concealment of ships, it is necessary to regularly demagnetize the ships.
The trouble of steel giant ships
The Earth is a huge magnetic field, and the metal shell of ships is made of natural magnetic materials. Ships that sail in the ocean for a long time will gradually be magnetized, producing two types of magnetic fields. One is to induce a magnetic field. This is the gradual formation of the metal shell of a ship under the influence of the Earth's magnetic field, which varies with the ship's heading and the magnetic latitude of the sea area it is in. Another type is a fixed magnetic field. This is gradually accumulated and formed during ship construction, machine operation, wave crashing, and exposure to large magnetic field impacts. The magnetic field is relatively stable and does not change with the ship's heading and the sea area it is in. These two types of magnetic fields are combined to form the unique magnetic field characteristics of a ship. Magnetic weapons such as magnetic mines are detonated by sensing the magnetic field disturbance of ships.
The working principle of a magnetic mine is not complicated: the mine is equipped with a magnetic sensor inside. When the ship's magnetic field is strong enough, the magnetic sensor will trigger the detonation circuit, causing the mine to explode. Due to the fact that it does not require direct contact with ships to detonate, magnetic mines are usually dispersed and deployed on the seabed, with extremely strong concealment.
From magnetic mines during World War II to magnetic anomaly detectors in modern anti submarine helicopters, magnetic weapons have always been a significant threat to surface vessels and submarines. A small magnetic mine can severely damage or even sink a modern ship. Therefore, modern ships must undergo regular demagnetization.
Magnetic control: the core principle of demagnetization
The traditional demagnetization technology is to generate a magnetic field that is equal in magnitude and opposite in direction to the ship's magnetic field through an electrified coil surrounding the ship, in order to cancel out the original magnetic field. Ship demagnetization involves two different technologies for two types of magnetic fields.
Ship maintenance "- temporary coil demagnetization method. A fixed magnetic field cannot disappear on its own and requires regular demagnetization treatment. This work is usually carried out at specialized demagnetization stations or by demagnetization ships. At the demagnetization station, the staff tied the ship with cables one by one. These cables, whether thick or thin, are wound around the ship's hull. When powered on, the strong electromagnetic field generated by the coils will "disrupt" the magnetic domain structure inside the ship, thereby removing the accumulated fixed magnetic field.
The demagnetization process of temporary coil demagnetization method is a bit complex, requiring precise measurement and repeated adjustment. Firstly, hundreds of probes laid under the dock are used to measure the magnetic field of the ship in two opposite directions, and the size of the fixed magnetic field is determined through analysis and calculation; Then wrap the cable and set the current parameters based on the measurement results. During the power on process, the magnetic field changes need to be continuously monitored, and finally, after repeated power on and measurement, the remaining magnetic field meets the standards.
The location of demagnetization stations also has great considerations. The demagnetization site needs to meet multiple conditions such as hydrology, meteorology, and magnetic field simultaneously. According to the form of the facility, demagnetization stations are usually divided into dock type (building low magnetic or non-magnetic docks on the shore), tunnel type (building tunnels at the foot of the mountain for ships to enter and exit), and dock type (using non-magnetic materials to build floating docks). In addition, there are demagnetization ships that can move to different sea areas to serve ships.
Dynamic adjustment "- fixed winding demagnetization method. Temporary coil demagnetization can eliminate the accumulated fixed magnetic field, but the induced magnetic field constantly changes with heading and latitude, making it difficult to solve the problem once and for all with a single demagnetization operation. Therefore, modern ships are pre embedded with fixed demagnetization windings inside the hull during construction. Taking the Nimitz class aircraft carrier as an example, its demagnetization system consists of approximately 12 independent coils, and the current is adjusted in real-time by a computer. These windings are connected to the ship's control system and can adjust the current in real-time based on factors such as the ship's magnetic latitude, heading, and sway, generating corresponding compensation magnetic fields. Fixed winding demagnetization is like a ship's built-in "dynamic balance system", which can constantly adjust its own magnetic field state and weaken the magnetic signal of the aircraft carrier by nearly 90%.
The above two demagnetization methods have clear division of labor: fixed winding demagnetization is responsible for daily dynamic compensation, and temporary coil demagnetization is responsible for regular deep cleaning. The two complement each other and jointly provide continuous demagnetization services for ships.
From 'bulky and coarse' to intelligent
Since its inception, ship demagnetization technology has undergone profound changes. Overall, before 2000, Wei was in the passive demagnetization stage, mainly relying on low magnetic steel and structural optimization to weaken the static magnetic field of ships, achieving a magnetic field reduction of 30% to 50%, but unable to dynamically adjust the demagnetization effect according to environmental changes. Since 2000, fixed demagnetization coils have gradually been widely used, and the control accuracy has been continuously improved. However, this active demagnetization technology faces a prominent problem: high power consumption. The demagnetization system requires continuous consumption of a large amount of electrical energy to maintain normal operation.
In recent years, with the emergence of new technologies, ship demagnetization technology has gradually undergone changes. For example, a hybrid energy storage architecture consisting of flywheel energy storage, solid-state batteries, and supercapacitors has been introduced into demagnetization systems. In addition, by optimizing the demagnetization site and operation process, the demagnetization operation time of ships has been significantly reduced, and the process has been highly automated. These technological breakthroughs have continuously improved the magnetic characteristic suppression rate of demagnetization systems.
As the Navy demagnetizer said, demagnetization is to put an "electromagnetic invisibility cloak" on ships to help them resist attacks from magnetic weapons. Although this' electromagnetic invisibility cloak 'has no physical object, it concerns the safety of every ship. As detection technology becomes increasingly sophisticated, demagnetization technology will also become more advanced. In the future battlefield, this electromagnetic game of "hiding oneself and discovering enemies" will become increasingly intense. (Looking into the New Era)
Edit:He ChenXi Responsible editor:Tang WanQi
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