Magnetic Particle Collection versus Magnet Quality
Executive Summary
We created a test bed for assessing the separation performance of magnetic particles with respect to field strength. Initially, there was no noticeable degradation associated with decreases in the magnetic field from 100% to 80%. However, as the collection rate slows a trend was revealed and a delay was shown to correlate with the decrease in field strength. Now, we have a guard band spec of greater than or equal to 80% of specified field strength! This helps increase the acceptance yield of magnets used for this application.
Challenge:
- Develop an application-specific method to assess magnet performance* with decreasing field strength and the effects on magnetic particle Collection
- Define a tolerance band for IQC by evaluating the performance of the current magnet with respect to magnetic field Evaluate multiple vendors for supplying the magnets
*Performance – Time required for a magnet to capture approximately 90% of available magnetic particles
Hypothesis:
- As the magnetic field decreases, the time necessary to capture the same amount of the magnetic particles will increase, requiring more time during particle transfer, resulting in longer processing time. If the magnetic field decreases sufficiently, it is possible, that the particle capture will never reach the desired amount
Performance assessed using optical analysis
- Video capture of the particles before, during, and after a test magnet had been moved into position and collection had begun
Image Processing
NOTE: Video is playing at 8X the actual speed to reduce file size. Refer to test results for actual times.
Results:
- Initially, there was no clear trend associated with decreases in the magnetic field from 100% to 80%. However, as the collection rate slows a trend was revealed and a delay was shown to correlate with the decrease in field strength. Therefore, the hypothesis that the time required to fully capture the particles is inversely proportional to the % of magnetic field strength has been confirmed.
Conclusions:
This data provides 2 big advantages:
- Increase the acceptance window for the purchased magnets so we don’t have to reject as many
- Optimize the exposure time of the magnetic field to target ~90% capture
Before, when we didn’t know how efficient the capture was, we set the exposure time to 120 seconds, knowing that was excessive. Now, based on the data, we can reduce the exposure time to as short as 40 seconds, a third of the original dwell!
And when time is money, every second counts.
If you want to discuss how Capstan Technologies, Inc. can help you with your benchtop lab tools and optical image processing, contact us any time at [email protected]
