Final Report: Graded Interference Filter Spectrometer

EPA Contract Number: EPD07025
Title: Graded Interference Filter Spectrometer
Investigators: Cosgrove, Joseph
Small Business: Advanced Fuel Research Inc.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: March 1, 2007 through August 31, 2007
Project Amount: $69,976
RFA: Small Business Innovation Research (SBIR) - Phase I (2007) RFA Text |  Recipients Lists
Research Category: SBIR - Monitoring , Small Business Innovation Research (SBIR)


The release of volatile organic compounds (VOCs) can have negative impacts on the environment while also posing significant health and safety concerns. Many VOCs are cancer-causing in humans while others pose dangerous explosion hazards. VOCs are used or produced in a variety of industries including the chemical, automotive, and semiconductor industries. Although chemical recovery and waste treatment strategies are employed to reduce the emissions of VOCs, there is a strong need for a low-cost, compact sensor that can quickly and reliably identify leaks in the facility process line.

Infrared (IR) spectroscopy is widely recognized as a powerful and versatile method for compositional chemical analysis. However, conventional IR spectrometers are complex instruments that are expensive and physically bulky and involve moving mechanical parts, which must be maintained in careful alignment. Even the most portable commercially available IR spectrometers are too large for situations requiring maneuverability in tight spaces.

This program will develop an innovative IR spectrometer-based sensor for remote detection of VOCs. Key attributes are its “no-moving-parts” design and its eventual low-cost, handheld configuration. The basic design of the spectrometer involves the coupling of a 2-D array of Fabry-Perot etalons with an IR microbolometer focal plane array (FPA) detector. The novel etalon array or graded interference filter (GIF) consists of an array of optical coatings deposited on a low index, IR transparent substrate, such as potassium chloride (KCl), with thicknesses graded in a discrete manner. The etalon array can be fabricated by vacuum deposition of a high index of refraction material through a fixed shadow mask onto a movable substrate or through a movable shadow mask onto a stationary substrate. In assembling the spectrometer, each element of the array is aligned optically with a pixel (or group of pixels) in the FPA detector. The array of etalons is used to modulate the incident spectrum with a wavelength-periodic transmission function defined by the fringe pattern of each etalon. Using a sufficient number of etalons, each with its own detector, the measurements from the etalon array provide an interferogram that can be mathematically transformed to recover the original spectrum.

Summary/Accomplishments (Outputs/Outcomes):

The program successfully demonstrated that well-defined, discrete etalons could be deposited through a precisely controlled shadow mask. Germanium and tellurium were investigated as candidate etalon materials. The germanium-based etalons were shown to exhibit superior optical properties. A germanium GIF was fabricated and coupled to an uncooled, microbolometer focal plane IR camera for successful demonstration of low resolution IR transmittance measurements over a bandwidth of 990–1190 cm-1 (8.4–10.1 μm). This falls within the bandwidth of absorption for many VOCs. Continued improvements in the germanium quality, to be implemented in Phase II, will significantly enhance the performance of the GIF spectrometer, expanding the measurement bandwidth and increasing the instrument resolution.

A technology niche analysis by an independent third-party firm indicated a worldwide regional market for the GIF spectrometer sensor being developed in this program, with primary usage in the chemical and petrochemical industries. The primary competing technology to the sensor, identified by the third-party firm, is the FLIR IR camera. However, the GIF-based sensor being developed in this program offers the capability of identifying VOCs, which the FLIR system cannot. In addition, the targeted price for the GIF sensor is $15,000, significantly lower than the base price of $70,000 for the FLIR system. The third-party’s preliminary projection of gross revenues for the proposed technology, based on a unit price of $15,000, is approximately $11 million by 2010 and more than $40 million by 2013.


The Phase I program clearly established technical feasibility for the proposed sensor technology and proceeding to Phase II is called for. The Phase II program will have two major thrusts: (1) optimization of the germanium etalon quality through improvements in the deposition process, and (2) development of a high resolution handheld GIF spectrometer, with an expanded measurement bandwidth and automated signal processing.

Supplemental Keywords:

small business, SBIR, graded interference, filter, spectrometer, volatile organic compounds, EPA, VOCs, infrared spectrometer, microbolometer focal plane array, sustainable industry/business, RFA, technology for sustainable environment, sustainable environment, cleaner production/pollution prevention, environmental technology, infrared spectroscopy, air pollution control, VOC leak detection, emission controls, pollution prevention, sensors,, RFA, Sustainable Industry/Business, Sustainable Environment, cleaner production/pollution prevention, Technology for Sustainable Environment, environmental technology, air pollution control, emission controls, monitoring environmental emissions, infrared spectroscopy, VOC leak detection, pollution prevention