There are several difficulties that come with attempting to shield a room with MuMetal® cladding. Depending on the volume of the room and the shielding factor required, it may be necessary to use more than one layer of material, and so one must consider any structural reinforcement required. A further difficulty of cladding an entire room is ensuring there is a continuous path for the field to travel through. The main issues arise in the corners, where it is difficult to ensure the panels are in contact to avoid any magnetic flux leakage. Each room will more than likely be completely unique, so multiple rooms would require very different designs and pieces. We must also adhere to the ventilation and lighting requirements for the room, both of which can be troublesome both structurally and magnetically.
At Magnetic Shields Ltd we have put time and research into developing a solution to the problems outlined, in the form of a free standing magnetically shielded room, or MuRoom®. The MuRoom® is a free standing magnetically shielded room, which can be developed to cater to many different requirements such as workable volume, desired shielding factor, and different access points. The MuRoom® is made in a similar fashion to the MuMetal® cladding solutions, by using MuMetal® panels. However these are joined together and supported using an aluminium frame. With the MuRoom® we also gain the advantage of portability, something that is clearly unachievable if cladding an existing room. As we can see it is far more cost efficient to use a portable self-standing MuRoom® than to clad on a room by room basis.Contact our Technical Sales Team for assistance.
Sometimes an application may require shielding across a larger frequency range than MuMetal® can effectively shield. Rooms can be created for both magnetic and RF shielding by layering high permeability material with electrically conductive materials in order to meet such requirements. For optimum shielding performance we may recommend using multiple wall layers and will discuss the need for electrical access ports within the room. We can also source field-free lighting for use within the room.
Our on-site one layer magnetically shielded room has been constructed with 1mm thick MuMetal® , supported by an aluminium frame constructed using a profile system. If further layers were required, the aluminium frame acts as a magnetically insulating material due to a low permeability, making it ideal for use with magnetic shielding. This room reaches an average shielding factor of over 150 (43.5 dB) across a central 500mm² volume, and over 100 (40 dB) within the central 1000mm² volume . These results are largely attributed to developments into the panel joining techniques. With this joint system in place we have created a high performance, structurally sound shield. The internal volume of the room is 2m x 2m x 3m, and features rounded corners to maximise the shielding capabilities further.
A map of the magnetic field inside Magnetic Shields’ MuRoom® depicts the working area of the room. Some leakage is observed at the door due to material boundaries; however, this effect is very localised, and the room does not fall below a shielding factor of 30 (29.5 dB) at any point.
Various cutting-edge experiments can be adversely affected by magnetic fields and may require shielding from electromagnetic fields with a magnetically shielded room (MSR). Tiny magnetic impulses of the active nerves of the human body may be the focus of a biological experiment. While these impulses can be detected, their signals can be swamped by background fields. Electron microscopes can also suffer from external magnetic fields. Just as optical microscopes exploit photon wavelengths to illuminate a sample of interest, electron microscopes make use of the shorter wavelength of electrons in an electron beam to more highly resolve the sample. These highly sensitive imaging devices benefit from magnetic shielding.
Shielding Medical Imaging Devices
Magnetoencephalography (MEG) employs the use of incredibly sensitive magnetometers, such as SQUIDs (superconducting quantum interference devices) to pick up on low level fields induced by the synchronized ionic neural currents within the brain. MEG records data temporally so that a vast array of neurological brain processes can be effectively watched in real-time and researched; from mapping the brain’s responses to stimuli to investigating structural abnormalities within the brain. While MEG is valuable for a wide range of non-invasive neurological research, it is also extensively used in conjunction with other forms of imaging techniques such as positron emission tomography (PET) and electroencephalography (EEG). The ambient Earth’s field is approximately 50μT; the field produced by the brain is of the order 10-9μT (or 1fT). It is clear to see that to achieve any sort of useful reading of these small fields, it is necessary to shield from the much greater ambient field.
We wish to remove the field signal which is of no interest; this can be done using an appropriately designed magnetic shield. Small shields are used commonly in numerable applications based upon the principle that a highly permeable material can divert field around the volume of interest, so that this volume is nearly or totally field free. If we were to simply scale the shield to the dimensions of a room, with large planar surface areas we would see a reduction in the efficiency of the shield. However, the increasing demand for magnetically shielded rooms with high field attenuation has led to us to design optimal magnetically shielded rooms involving multiple mumetal® layers and the introduction of copper or aluminium sheet metal to shield RF fields, allowing impressive shielding factors to be achieved.
Shielding Electron Microscopes
An electron moving in a magnetic field experiences a force tending to change its direction of motion unless that motion is parallel to the field. A beam of electrons can be focused using electromagnetic lenses. Optical lenses diffract photons travelling through them and converge the outgoing beam. The principle of an electromagnetic lens is similar; the beam of electrons can be focused by altering the path of the incoming electrons. The basic design of an electromagnetic lens consists of a solenoid through which the beam can pass on its way towards the sample. Applying a current to the solenoid induces a magnetic field according to Lenz’ law which, since electrons are extremely sensitive to magnetic fields, deflects the electrons to a focused point. Both scanning electron microscopes (SEM) and transmission electron microscopes (TEM) rely on this process. The resolving power of a microscope is inherently dependent on the wavelength of the electromagnetic radiation used to create the image. As the wavelength of the radiation is decreased, the resolving power is increased. Since electron wavelengths are approximately 100,000 times shorter than photon wavelengths, electron microscopes offer superior resolving power to optical microscopes. While the precision of electron microscopes is of huge benefit, there are disadvantages of electron microscopy that require addressing. External magnetic fields disturb the electron beam and diminish the overall resolving power of the microscope. Housing the microscope in a magnetically shielded room ensures the microscope can achieve its upper limit of resolution.