Common Magnetically Shielded Room Applications
Various cutting-edge experiments can be adversely affected by magnetic fields and may require shielding from electromagnetic fields with a MuRoom. 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) or OPMs (optically pumped magnetometers) 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 0.5 Gauss [50μT]; the field produced by the brain is of the order 1 nanoGauss [1 picoTesla]. 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 high permeability material can divert field around the volume of interest, so that this volume is nearly or totally free from magnetic fields. 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 shielded rooms involving multiple layers of our final annealed MuMetal® and eddy-current shielding like copper or aluminium sheet metal to shield RF fields, allowing impressive shielding factors to be achieved. For the most demanding applications, degaussing (neutralization) coils are used along with our MuRoom, reducing the internal fields to practically zero.
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.
Paleomagnetism
Paleomagnetism is the study of the record of Earth's magnetic field in rocks or other archaeological materials. The iron-containing minerals in rock samples allow them to become magnetized when exposed to magnetic fields. Paleomagnetists will demagnetize the rock samples, leaving behind only the the natural remanent magnetism (NRM) in the rock sample. NRM is the permanent magnetism of a rock or sediment. In of its forms preserve a record of the Earth's field at the time the mineral was laid down as sediment or crystalized in magma and also the tectonic movement of the rock over millions of years from its original position. The natural remanent magnetism is very small but can be measured with very sensitive instruments. A MuRoom® supports this research by reducing unwanted ambient magnetic fields so the only field being measured is the one produced by the NRM in the rock sample. A multi-layered MuMetal Room provides researchers with a homogeneous, low-field environment that is acceptable for their test environment.
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