Object stages for in situ examination

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Several special purpose stages can be used for the 1172 and 1174 scanners. The stages are easily installed in place of the standard specimen holder, and take control signals and power from a small plug at the base of the sample stage mount. These special stages are controlled by software independent of the main scanner control program.

 

MICRO-POSITIONING STAGE

The micro-positioning stage helps to achieve exact positioning of small objects in the middle of the scanning field. Precise object centering improves all aspects of scan quality, enabling maximum magnification to be achieved and optimizing scan speed. This positioning stage has 5mm travel in the X and Y directions, and axial positioning is attained in a straightforward, user-friendly procedure, by reference to projection images.

 

MATERIAL TESTING STAGE

The SkyScan Material Testing Stage allows the user to combine micro-CT imaging with tensile and compression testing. During scanning the sample is subjected to a controlled load, while having the loading curve displayed on-screen in real time.

This material testing stage is specially designed for compression and tension testing using an accurate load cell and displacement sensor. The stage can be used in 2 modes: a continuous mode for compression or tension up to the maximum allowable load or until the maximum displacement; and a predefined mode in which the user can specify either the load or the displacement that should be reached. For compression the lower part of the stage will be moved upwards, for tension downwards. The loading curve is displayed on-screen in real time; units can be changed; load/displacement or stress/strain curves can be displayed and saved. The object can be held under a specific loading for micro-CT scanning.

The accuracy of the measurement and resolution will be around 0.5% of the load cell’s full scale. This is an important figure to bear in mind when choosing a load cell. The load cell’s range should be higher than the load the specimen will be exposed to. An “oversized” load cell will have a negative effect on the system’s sensitivity.

• Load ranges: 42N, 210N, 440N
• Displacement sensor accuracy: ± 0.01mm
• Load measurement accuracy: ± 1% of the full range
• Maximum object diameter : 20mm
• Maximum travel: 5.5mm
• Max object height for compression: 23mm
• Max object length for tensile tests: 18mm

The cooling stage keeps an object at a cooler-than-ambient or sub-zero temperature during imaging and micro-CT scanning. It contains a two-stage solid-state Peltier cooling system which keeps object temperature at up to 35-40C below ambient temperature. An internal microprocessor and a precision temperature sensor provide feedback to the stage control program for temperature stabilization during scanning at a pre-selected value, with 0.5C accuracy.

In the picture: left - a piece of ice inside the cooling stage; right - a 3D rendering of an ice crystal  scanned at -22C, 5µm voxel size.