Planning and Installation

Planning and Installation The planning of the mounting of the active magnetic field shielding is a preparatory work. The assembly itself takes a total of 3 days and is usually carried out in two steps. 1. Mounting of the cable channels and lay of the coils. This work should preferably be carried out before the assembly of the laboratory equipment and the installation of the microscope. 2. After the commissioning of the microscope, placing of the sensor, connecting the coils and calibrate the system. After this, the performance will be documented with measurements.

3D-situation active compensation system

Example tram

Initial situation:
A new scanning electron microscope Carl Zeiss SEM Supra 55VP was installed in a laboratory in Vienna. Because of disruptions during the microscopy work, magnetic field measurements were carried out. These measurements have shown that the DC magnetic fields were outside the specifications. The source was the tram that passes by the building.

Solution:
In order to guarantee trouble-free operation a magnetic field compensation system has been installed. This allowed to reduce the interference fields in the room well below the specific values.

Supra 55VP with active compensation system		Measured values compensation “OFF and compensation “ON”

Example of power distribution

Initial situation:
A new FEI TEM, Titan 80-300 was installed in a laboratory in Bern. After commissioning it was established, that the quality of the image doesn’t meet the expectations. With appropriate magnetic field measurements the disturbing influence of a nearby power distribution, which was not in operation at the time of the room measurements, could be evidenced.

Solution:
To eliminate the interference fields, an active compensation system has been installed. The problem of middle field sources is that the gradient at the location of the microscope is high and the fields are inhomogeneous. It is not easy to properly solve such situations with compensation systems. The aim of these being to compensate a maximum possible volume. In situations with a high gradient, however this is only possible to a limited extent.

Position of the electrical distribution		Red: Magnetic field sensor White: Compensation coils		Field strengths with compensation “OFF” and “ON”

cable channel in the floor

Initial situation:
An electron beam lithography device Electro Beam Writer RAITH 150 TWO has to be installed in a research center. Preliminary magnetic field measurements have revealed that the field strengths at the site of the lithography device are beyond the device specifications. With measurements it was found that the main power lines of the building are embedded in a channel in the floor. The channel crossed the room on the entire length.

Solution:
A magnetic field compensation system has been installed, to be able to use the lithography device in this room anyway. With the compensation, the field strengths could be reduced far enough to meet the specifications. The interference-free operation is therefore guaranteed.

Cable channel in the floor of the microscopy room		E-Beam writer Raith 150 two

Example REM’s next to each other

Initial situation:
In a University in Cologne a Philips CM 10 TEM has to be installed in one room and a LEO 430i REM in the room next to it. The devices are moved from an old building into new laboratories. To eliminate the interferences of the nearby railway line (16,7Hz) and the tram (DC), compensation systems have to be installed in both laboratories. If two compensation systems are being installed right next to each other, special points have to be considered, otherwise the systems would interfere with each other.

Solution:
In order for the compensation systems not to influence each other, certain minimum dimensions between the Helmholtz coils of the two systems and the sensors must be fulfilled. Initial measure is to place the two microscopes as far apart from each other as possible. The coil cage in one room was reduced so that the coils aren’t directly next to each other. The coils were relocated to about 1m off the wall into the inside of the room. This allowed to maintain the distance between the souelen-coils and the coil sensors.

Ground 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 disorders were apparent during the recording. Measurements have shown that these failures were cause by the ceiling mounted power cable. A transfer 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 go with a freestanding frame construction made of GFK. On request of the customer, the construction of the frame was painted traffic red. The design should be an eye-catcher.

Frame construction made of GFK profiles		Mounting of the sensor holder on the ceiling

Operation of Low Field Rooms

E-Beam writer, VISTEC in "Low Field Room™”

"Low Field Rooms™" are used for the reduction of low-frequency magnetic fields in environments with high interference field strengths, homogeneous and inhomogeneous fields. "Low Field Rooms” are based on a combination of mu-metal shielded rooms and compensation systems. The room shielding, based on nickel-iron (so-called “Mu- metal”), combined with aluminum, causes a basic reduction of external interference fields and homogenizes the field within the room. The active compensation reduces the rest of the field. In this combination, AC and DC fields are optimally limited. The measured attenuation in the "Low Field Rooms™" is, for AC: approx. 40dB, for DC: approx. 32dB. The attenuation however is dependent on various parameters such as room size, interference frequencies, field strengths, etc.