Grantee Research Project Results
Final Report: Field Deployable Mid-Infrared Spectrometer for Monitoring Volatile Organic Compound (VOC) Emissions from Concentrated Animal Feeding Operations (CAFOs)
EPA Contract Number: 68HERC21C0018Title: Field Deployable Mid-Infrared Spectrometer for Monitoring Volatile Organic Compound (VOC) Emissions from Concentrated Animal Feeding Operations (CAFOs)
Investigators: Walhof, Alexander C
Small Business: Firefly Photonics LLC
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2021 through August 31, 2021
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2021) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air Quality , SBIR - Air Monitoring and Remote Sensing
Description:
The purpose of this research was to demonstrate proof-of-concept for a low-cost, portable spectrometer system based on broadband mid-wave infrared (MWIR) light emitting diodes (LEDs) and uncooled superlattice photodetectors (PD) that can quantify type and concentration of volatile organic compound (VOC) and odor sources within concentrated animal feeding operations (CAFOs). VOC detection at CAFOs is often relegated to non-specific detection methods which are unable to determine the source of the emissions. Specific VOC detection requires sampling of air with cannisters and lab testing. Our approach intends to create a spectrometer-based VOC sensor that can specify and quantify concentration of VOCs allowing source identification in real time. Spectrometers based on thermal sources are inefficient, require long warm up times, and struggle with drift over the life of the sensor. A broadband, MWIR LED is more efficient, has sub- microsecond turn on, and is a stable, solid-state device. Firefly’s cascaded LED approach allows the LED to be well-tuned for battery use while generating light only in the spectral region of interest.
There were three research objectives for this Phase I project: (1) MBE growth of MWIR BBLEDs and BBPDs, (2) Integration of LED and PD with drive electronics, optics, a diffraction grating, and a long optical path length cavity into a benchtop spectrometer, and (3) Demonstration of lab-based detection utilizing the prototype spectrometer.
Summary/Accomplishments (Outputs/Outcomes):
A broadband MWIR LED (BBLED) was developed to be a solid-state light source for the spectrometer. The LED structure was designed to create room-temperature, broadband emission. Broadband LEDs were grown by molecular beam epitaxy (MBE), fabricated, and characterized. Broadband emission was observed from 2.5 to 5.5 µm. The LED’s electrical characteristics were demonstrated to be battery compatible. A cascaded superlattice broadband PD (BBPD) structure was similarly designed, grown by MBE, and fabricated.
Portable LED drive and PD sense electronics were developed and were implemented with data acquisition on a laptop via a USB oscilloscope. A long optical path length cavity was acquired and tested with Firefly’s devices, qualifying it for use in the spectrometer optical path. A MWIR- tuned diffraction grating’s dispersion power was measured in a simple set-up using a 3.3 µm LED.
Gas sensing capabilities were demonstrated using a non-dispersive IR approach. A single LED and PD were placed in a test gas chamber with the portable drive/sense electronics. Ethanol gas was introduced into the chamber via Tedlar bags with known concentration as calculated from the volume of liquid ethanol, the volume of the bag, and the ideal gas law. Experiments were also conducted with acetone. Measurements showed significant changes in signal but did not closely follow the Beer-Lambert absorption law due to parasitic losses.
Conclusions:
Significant progress was made towards development of a solid-state, MWIR spectrometer. The enabling component of a BBLED and BBPD was successfully grown and fabricated in a commercially compatible formfactors. The BBLED had sufficient output power for the application. Drive and sense electronics, a long optical path cavity, a diffraction grating all demonstrated expected performance and can be integrated into a benchtop spectrometer to complete the proof- of-concept. Discussions with commercialization partners in the spectrometer and gas sensing markets are ongoing.
The global portable spectrometer market was valued at $1.24 billion in 2017 and is expected to reach $2.15 billion by the 2023 with a CAGR of 10%. Increasing awareness about outdoor and indoor air pollution, and companion regulations protecting air quality issued by the U.S. EPA and Mine Safety and Health Administration (MSHA) are key factors driving market growth. Industrial applications such as real-time monitoring of pipelines, monitoring of benzene leaks, and remote monitoring of plant equipment are additional factors driving market growth. Firefly has secured purchase orders for LED components from a major gas sensor manufacturer and is in discussion with spectrometer manufacturers for Phase II commercialization.
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.