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Magnetic shielding for electrical equipment  
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Laboratories

Systron LabShield®, the advanced shielding system to protect ebeam applications such as electron microscopes, ebeam writers etc. from electromagnetic interference.

Magnetically shielded room for electron microscope  
Modern research deals with tiny structures often even with dimensions on the atomic scale. The research instruments are particularly sensitive to any disturbances like climate changes, accoustic, vibrations, mechanical shocks and likewise magnetic fields. Therefore, protected laboratories in which such disturbances are reduced to a minimum, are needed. Magnetic fields can be reduced by either passive shielding or active compensation, or the combination of both.
With Systron LabShield®, a mu-metal based shielding system is available to shield entire rooms against electromagnetic AC stray fields from electrical equipment such as transformers, cables, distribution panels or over head high-tension power lines. However, the system is also designed to shield DC stray fields from tram ways, moving vehicles or elevators.
Magnetically shielded room for electron microscope
   

 

Systron LabShield®, Mu-metal magnetically shielded TEM room Ebeam writer, Athena with active compensation system Omicron spin SEM, Lausanne with active compensation system Jeol JSM, Prag with compensation system FEI NOVA NanoSEM in magnetically shielded mu-metal room
TEM room, Dresden
Ebeam writer, Athena
Spin SEM, Lausanne
JSM 7001, Prag
Nova NANOSEM, Zürich


Systron LabShield® - TEM room:

Description

Mu-metal magnetically shielded TEM room

 
Research laboratory rooms for electron microscopes and other ebeam applications must meet the highest requirements regarding magnetic interference fields. The limit values which are defined by the microscopy manufacturers are a big challenge for the operators of the microscopes. Those who want to be part of the world's top research must definitely meet, or even exceed, these limits to guarantee a perfectly functioning microscope.
 
With the Systron LabShield® system, these even increasing requirements can be fulfilled. Systron individually designs the shielding measures, based on the proven shielding system Systron LabShield®Systron LabShield® is designed to attenuate static DC, slow varying DC shifts and AC stray fields.
One of the two magnetically shielded rooms at TU Dresden    

Example TEM room

Shielding performance TEM room

results systron permalloy shielded room3   Two rooms at the Technical University Dresden are shielded with the Systron LabShield® system, a permalloy based shielding system, especially designed to protect ebeam applications from magnetic stray fields. Since transmission electron microscopes (TEM's) have particularly high requirements regarding the residual magnetic fields, best possible measures were required. The manufacturer of the TEM's requested <20nT p-p at worst, but targetted <5nT p-p for slow varying DC shifts (<1Hz). The chart illustrates the results comparing a before and after measurment. The attenuation lies in the 27dB range, thus the room is well within the requested values.
Performance of magnetically shielded room    


Systron LabShield® - REM room:

Description

Electron microscopy facility

Electron microscope in magnetically shieldeElectron microscope in shielded room
 
Rooms for electron microscopes have to be protected against magnetic fields when external magnetic fields affect the operation of the microscopes. The supplier/manufacturer of the microscopes therefore specify the limit values, guaranteeing functionality at specified operation modes and specified optical resolution. Often fields can be sufficiently compensated with active compensation systems, however, some applications require passive room shields based on permalloy.
 
Stray fields, such as those caused by railways, tramways, high voltage power lines or electrical equipment are efficiently reduced with the passive permalloy based Systron LabShield® system.

Example REM room

Example

An electron microscope had to be moved to a new location. In order to find an appropriate room, site surveys were performed at several locations in question. Finally a room had be chosen, however, the magnetic field exceeded the specification of the microscope. The new location was surrounded by “in-house” interference sources such as an electric cable channel in the aisle in front of the laboratory, a power rail on the wall and an induction furnace in the adjacent production area. The customer tested various field reduction solutions and finally decided for a room shielding based on magnetically conductive plates. In particular, this solution was chosen because once the shielding plates are installed, no further maintenance is required.

Layout of REM room, magnetic field sources Induction furnace and bus bar Shielding work finished REM room finished, REM operational
Layout with sources of interfering fields
Sources of interference field: induction furnace
Shielding plates installed in REM room. Measering of shielding performance
Laboratory completely furnished

Active magnetic compensation:

Description

Magnetic active compensation systems were specifically developed to reduce low-frequency magnetic fields to the lowest possible. With compensation systems, interference limits of electron microscopes can be fulfilled or magnetic field interferences in bio magnetic examination rooms, EEG/ECG/EMG, can be prevented.

Compensation systems compensate low-frequency magnetic fields such as those from moving vehicles, elevators, railways, electrical equipment or other field sources. Interference fields are measured with a sensor and are actively compensated by counter fields generated in a 3 dimensional Helmholtz coil system.

Planning and Installation

 

3D model of active compensation system in TEM room

Planning and Installation

The planning of the installation of a compensation system requires some preparatory work. The assembly itself takes a total of 3 days and is usually carried out in two steps.

  • 1. Installation of the cable trays and coils. This work should preferably be carried out before the laboratory is furnished.
  • 2. After the commissioning of the microscope, the sensor is placed, coils are connected and the system is calibrated. After this, the performance will be checked by measurements and documented in a report.
3D-situation of compensation system  

Example tramway

Initial situation:
A new scanning electron microscope SEM Supra 55VP was installed in a laboratory in Vienna. Because of disruptions during the microscopic work, magnetic field measurements were carried out. These measurements showed that the slow varying DC shifts were outside the specifications. The source was a tramway passing by the building.

Solution:
In order to guarantee trouble-free operation, a magnetic field compensation system was installed. With the compensation system, the magnetic fields were lowered well below the specific values.

Supra 55VP with active compensation system   Proof of performance of active compensation system
 Supra 55VP with active compensation system   Left of graph, compensation “OFF and right, compensation “ON”

Example SEM and TEM next to each other

Initial situation:
At a University in Cologne a Philips CM 10 TEM had to be installed in one room and a LEO 430i SEM in the room next to it. The devices were moved from an old building into new laboratories. To eliminate the interferences of the nearby railway line (16,7Hz) and the tramway (DC), compensation systems were installed in both laboratories. However, if two compensation systems are being installed right next to each other, special care must be taken, as the systems might interfere with each other.

Solution:
In order to make sure that the compensation systems do not influence each other, certain minimum distances between the Helmholtz coils of both systems and the sensors must be maintained. The initial measure was to place the two microscopes as far from each other as possible. The size of the coil cage in one room was reduced so that the coils were not directly next to each other. The coils were relocated to about 1 m apart from the wall into the inside of the room. This allowed to achieve the minimum distance between both coil systems and sensors.

Floor plan of the two adjacent laboratories   Philips CM 10 TEM with sensor of compensation system   LEO 430i REM with sensor of compensation system
Floor plan of the two adjacent laboratories   Philips CM 10 TEM with sensor   LEO 430i REM with sensor

Freestanding frame construction

Initial situation:
After the commissioning of a Jeol SEM JSM 6490 in a laboratory in Jena, significant distortions were apparent during the microscopying. Measurements showed that these distortions were caused by the power cable installed under the ceiling. A relocation of the cable was not possible.

Solution:
Due to the very limited space and the unusual geometry of the microscopy room, the customer decided to install a free standing frame. On request of the customer, the frame was painted traffic red. The design should be an eye-catcher.

Fiber glass based frame for the coils   Mounting of the sensor holder on the ceiling
Frame construction made of GFRP profiles   Mounting of the sensor holder at the ceiling


Compensation system in magnetically shielded room:

Description

Low magnetic field rooms form the base for the operation of highly sensitive research tools. The interference limit of such equipment nowadays is as low as  < 20 nT peak-peak, or even < 5 nT peak-peak. Typically these values can hardly be reached with compensation systems, such that further measures are necessary.
Magnetically shielded room
 
In the new Binnig and Rohrer Nano Technology Centre, Rueschlikon, a combination of a mu-metal shielded room and active compensation system was installed to achieve lowest poosible values.
 

Requirements on the magnetic flux for the “Noise Free Labs":

  • BAC = < 5 nT (up to 2 kHz, integrated)
  • BDC = < 50 nT
“Noise Free Lab”, Binnig and Rohrer Nano Technology Center, Rueschlikon, Switzerland    

Low field rooms

Ebeam writer in magnetically shielded room
For the operation of a tool in a low field rooms, a combined solution of Systron LabShield®, and an active cancellation system was chosen. The Systron LabShield®, based on mumetal and aluminum, reduces low frequency magnetic fields in environments with interfering fields. With the addition of compensation systems a stable magnetic field is achieved for safe operation of the sensitive ebeam application. With this combination, AC and DC fields are reduced to lowest possible levels. The measured attenuation in the laboratories is for AC: approx. 40dB and for DC: approx. 32dB.
 
Ebeam writer, in "Noise Free Lab”  


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