IAD vs. Multi-Cavity Interference Filters
Awareness Technology uses Ion Assisted Deposition (IAD) filters which are more
expensive, but will give superior performance far longer than multi-cavity
filters, resulting in reduced service costs and down-time for filter
replacement.
Awareness Technology specializes in optical
design, and has always considered filter quality to be of major importance in
achieving photometric accuracy and, therefore, reliable test results. That is
why Awareness Technology chooses only Ion Assisted Deposition (IAD) filters when
manufacturing Stat Fax and ChemWell instruments. IAD filters are more
expensive, but will give superior performance far longer than multi-cavity
filters, resulting in reduced service costs and down-time for filter
replacement.
Before IAD technology was commercially available, Awareness Technology
used the best quality 3-cavity
sealed interference
filters on the market. In 1993, after extensive testing of regular production
lots of both types of filters, Awareness Technology
confidently made the change to superior filters; ones produced using IAD
technology.
What is IAD?
Prior to the 1990's, narrow-band interference filters were subject to instability and deterioration due to humidity, aging, and temperature changes, resulting in low peak transmittance and out-of-band transmittance ("leakage").
Filters manufactured using IAD technology and processes are vastly superior to sealed soft-coated interference filters especially in terms of stability and longevity.
IAD is an advanced coating process that yields
significant reduction in film porosity in an effort to solve the stability
problems inherent to soft coated filters. The principal function of IAD is to
bombard the coating material with accelerated ions to densify the coating.
An ion gun is directed at the substrate, and when energized, establishes a
plasma stream of high energy particles flowing toward the substrate. As the
accelerated ions collide with the coating material at the substrate, the coating
material is compacted creating a dense film structure.
Filters produced using IAD have demonstrated spectral shift characteristics
approaching and often achieving zero, comparing very favorably with the 10 to 20
nm shift typical of conventionally deposited coatings.
Testing
Both types
of filters were tested in an environmental test chamber (temperature and
humidity) that was designed to simulate MIL-STD-810C for the purpose of testing
the environmental integrity of the filters. Each day in the test chamber
corresponds to approximately 1 year of operation in extreme (high) temperature
and humidity. Filters were tested for 7 days and checked for delamination,
visible deterioration and %T changes periodically, with a final inspection and
assessment on day 7.
The
multi-cavity filters exhibited incipient delamination sometimes as early as the
third day in the test chamber, and most failed at the end of 7 days, either by
delamination or >10% increase in %T.
View Multi-cavity filter - clouded after 3 day test
View Multi-cavity filter - delaminated after 7 day test
Over the
course of 3 years, we continued environmental testing of filters from every
production lot. A sample filter was randomly selected and placed in the test
chamber. With very few exceptions, the IAD filters passed the tests of their
physical integrity, %T and exhibited no significant peak shift.
View IAD filter - after 7 day test
In another test, a
set of filters (340, 405, 450, 492, 545, 600 - IAD type) were placed outdoors
and exposed to direct sunlight, rain and temperature extremes typical of South
Florida. After 2 years, the filters had no significant change in physical
integrity, %T or peak shift.
Because we use
these higher quality, longer lasting, more expensive filters, we may not always
compete on price alone with companies selling cheap instruments with low quality
filters. When a competitor's instruments are brand new, their filters may give
adequate results, but as the filters deteriorate, results can become
unsatisfactory. It is important that customers realize the long-term value and
the advantages of IAD filters over the multi-cavity type.
