Degaussing is the process of decreasing or eliminating an unwanted magnetic field. It involves exposing the targeted material to an external, reversing magnetic field which cancels out the effects of the unwanted field. Degaussing is commonly used to erase data from magnetic storage like hard drives and magnetic tapes. It can also be used to eliminate the magnetic signature from ships and other metal objects.
Why is degaussing done?
There are a few key reasons degaussing may need to be performed:
- Data destruction – Degaussing is an effective way to completely erase data from magnetic storage like hard drives. It disrupts the magnetic domains to remove any residual data.
- Security – Degaussing can be used to erase sensitive information and prevent data recovery. This is important for maintaining data security.
- Reduce electromagnetic interference (EMI) – Degaussing reduces the unwanted magnetic fields that can cause interference in electronic devices.
- Stealth purposes – Ships and submarines are degaussed to neutralize their magnetic fields. This makes them less detectable by mines and other systems that sense magnetic signatures.
How does the degaussing process work?
The degaussing process involves two key steps:
- Exposure to an alternating magnetic field – The target object is exposed to a reversing, gradually decaying AC magnetic field. This field alternates the magnetization of the material’s domains back and forth repeatedly.
- Remanence – When the alternating field is removed, little or no net magnetization is left. This leaves the material in a degaussed state with weak residual magnetism.
The alternating magnetic field is produced by running current through coils in a degaussing device. As the current and field decrease, the magnetization of the domains is scrambled leaving only small amounts of remanence. This erases any previous magnetic patterns.
What equipment is used?
There are a few common pieces of equipment used for degaussing:
- Degaussing coils – Copper wire coils are used to produce the alternating magnetic field. The coils can be handheld or built into degaussing machines.
- Degaussing wands – Handheld wands contain degaussing coils powered by batteries or AC power. They are passed over storage media to degauss it.
- Bulk degaussers – Large machines into which storage media can be inserted to deguass multiple items at once.
- Magnetic field generator – Used for ship degaussing, these generators create a reversing field that degausses a ship’s hull.
The strength of the field needed depends on the type of material being degaussed. Hard drives may require fields exceeding 10,000 Oe to ensure data erasure.
Degaussing magnetic media
For magnetic storage media like hard disk drives, the degaussing process involves:
- Ramping up the alternating magnetic field produced by the degaussing coils
- Exposing the entire drive to the peak field strength for a few seconds
- Ramping down the magnetic field gradually
- Repeating steps 1-3 in the opposite direction to deguass any remaining areas
This scrambles the magnetic domains and removes any previously stored data. Some guidelines for degaussing magnetic media include:
- Using certified data erasure degaussers
- Passing degaussing wands over both sides of devices multiple times
- Degaussing to a level that meets government and industry standards
- Verifying degaussing effectiveness through read-verify tests
Hard Drive Degaussing
For hard disk drives specifically, degaussing aims to scramble and randomize the magnetic domains on the platters inside to erase any data. Both the drive’s cover and platters need to be fully exposed to the alternating field. Handheld degaussing wands are commonly used for hard drives.
Tape Degaussing
Magnetic tape contains ferromagnetic particles that store data. Passing a powerful degausser field along the tape’s length realigns these particles to erase stored data. Handheld wands can be used but bulk deguassing machines designed for tape are ideal.
Ship Degaussing Systems
On ships, an electrical degaussing system is used to neutralize the magnetic fields generated by their ferromagnetic hulls. This is done to minimize detection by mines, magnetometers and other systems. The main components include:
- Main degaussing coil – Coils wrapped around the ship to induce the reversing magnetic field across the hull.
- Degaussing power supply – Provides AC power to the coil. This can be sized 30KW or larger for warships.
- Fluxgate sensors – Measure the ship’s residual magnetization at various locations.
- Control console – Used to set and monitor the degaussing system.
Ships may have additional stabilization coils to optimize the field at certain locations. The amount of magnetic degaussing needed depends on the ship’s course. Thus the system can be adjusted to continually compensate for the current heading.
Naval Vessel Degaussing
On naval ships, the degaussing process involves:
- Turning on the main degaussing coil power supply to ramp up current
- Reversing the coil current direction periodically to induce alternating field
- Monitoring field strength and ship magnetization with sensors
- Adjusting current to optimize degaussing effectiveness for the given course
- Periodic degaussing compensation for course changes
Minesweepers may also tow specialized degaussing sleds to neutralize magnetic mine threats in naval operating areas.
How effective is degaussing?
When done properly, degaussing is an effective process for accomplishing objectives like data destruction, EMI reduction, and stealth purposes. Some key points regarding effectiveness include:
- It can reliably erase data from magnetic media like hard drives and tape with proper field strengths.
- Ship degaussing can significantly reduce magnetic signature, but not fully eliminate it.
- Effectiveness is highly dependent on using proper field strengths for the media. Weak degaussing may not work.
- Results should be verified through read-verify tests or magnetic sensors.
- Degaussing may become less effective over time as magnetization returns.
Degaussing is not foolproof. But it can reliably render data unrecoverable under many circumstances. It remains an important data destruction technique alongside physical destruction methods.
Degaussing standards and regulations
There are some degaussing standards that help ensure proper effectiveness:
- NSA/CSS 9-12 – Sets degausser magnetic field requirements for sanitizing and destroying media.
- NIST 800-88 – Provides guidelines for media sanitization including use of degaussing.
- ISO/IEC 27001 – Information security standard that references degaussing for secure data destruction.
- DOD 5220.22-M – Defines DoD requirements for degaussing and secure data erasure.
Using degaussing methods compliant with these and other standards can help ensure proper erasure and effectiveness. Certain industries like finance and healthcare may also have regulatory requirements regarding degaussing and data destruction.
Advantages of degaussing
Some of the key advantages of degaussing include:
- Permanent and complete data erasure – Properly degaussing magnetic media destroys data in a way that makes recovery essentially impossible.
- Fast process – Degaussing can quickly erase data and remove magnetic signatures.
- Environmentally friendly – It does not involve chemicals or physical destruction of devices.
- Reusable media – Storage media can potentially be reused after degaussing rather than physically destroying it.
- Low cost – Handheld degaussing wands have low equipment costs compared to many other data destruction methods.
For the right applications, degaussing provides a fast, reliable, cost-effective magnetic media erasure solution.
Limitations of degaussing
Degaussing also has some limitations including:
- Not effective for non-magnetic media like SSDs and optical discs
- Possibility of remnant magnetization remaining after degaussing
- Requirements for proper field strength and usage techniques
- Eventual re-magnetization can occur over time
- Not designed to physically destroy media
- More expensive bulk degausser equipment required for high volumes
For these reasons, degaussing may need to be combined with physical destruction or encryption for a defense-in-depth data security approach.
Conclusion
In summary, degaussing is the process of exposing magnetic media to an alternating magnetic field to erase data and reduce or eliminate unwanted magnetization. It is an effective data sanitization technique for magnetic storage media when done properly using adequate field strengths. Degaussing can provide fast, low cost destruction of data on hard drives, tapes and other media. It also serves important security purposes by eliminating magnetic signatures from ships and submarines. Following established standards helps ensure degaussing effectiveness. While it has some limitations, degaussing remains an important capability for permanent data erasure and magnetically “wiping the slate clean”.