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Rice University Laser-based Air and Medical Sensors Powered by TI Digital Signal Controllers

Gas Sensing Technique Uses Laser-Based Electromagnetic Radiation For Airborne Chemical Analysis

Jul 20, 2005

HOUSTON, (July 20, 2005) – Helping to advance intelligent sensing applications, researchers at Rice University, Houston, TX have successfully tested laser-based air and medical sensors using Texas Instruments Incorporated (TI) (NYSE: TXN) 32-bit TMS320F28x™ digital signal processor (DSP)-based controllers to detect the presence of specific gases in concentrations in the range of parts per billion to (ppb) parts per trillion (ppt). Pulsed quantum cascade (QC) laser-based sensors use laser absorption spectroscopy to measure electromagnetic radiation for applications including spacecraft air quality monitoring, breath analysis to detect certain medical conditions, volcanic emission monitoring and networked air monitoring of combustion sources and noxious gasses in urban-industrial settings. TI’s highly integrated TMS320F2812 controller operates the lasers, converts and then processes the optical detector signals into highly precise measurements. For more information on intelligent sensing applications using TMS320C2000™ digital signal controllers and video on the Rice University laser-based sensors, see www.ti.com/c2000sensing.

DSPs Enable Innovation for Rice Team

The ability to perform extremely sensitive gas detections with smaller, cheaper instruments opened up a wide range of new applications for the Rice research team. Dr. Frank Tittel, the J.S. Abercrombie Professor in Electrical and Computer Engineering at Rice University, and his research team have worked with doctors at the Baylor College of Medicine in Houston to detect elevated levels of carbonyl sulfide that indicate problems with rejection of a lung transplant. The team is also working with the National Aeronautics and Space Agency (NASA) to measure the air quality in the space shuttle during missions. Another potential application under investigation is the use of the new generation of instruments to provide early warning of chemical or biological attack. Because the controller performs all processing required for the application independently, the device is appropriate for autonomous sensor networks. This autonomy is particularly valuable in multi-sensor applications or applications where it is not possible to have a human controller, as is the case in volcanic emissions monitoring networks.

Intelligent DSP-Based Sensing Plus TDLAS

The Rice researchers’ method is based on Tunable Diode Laser Absorption Spectroscopy (TDLAS), which uses a semiconductor laser as the excitation light source for the absorption spectroscopic measurement. Different types of molecule absorb light at different wavelengths, and the amount of light absorbed depends on the number of molecules in the light’s path. The device measures the change in the light intensity as it resonates with molecules’ absorption wavelengths. The F2812 controller’s 150 MIPS of DSP-enabled processing power performs calibration, filtering and numeric processing to precisely detect these intensity changes in real time. A technician can then monitor the concentration of molecules encountered in a person’s breath or in the air to detect the presence of a particular gas.

Why DSP / TDLAS Equals Ideal Solution for Rice Team

The conventional method of determining the composition of a gas is to run it through a laboratory instrument using a method like gas chromatography/mass spectroscopy (GC/MS). GC/MS separates the gas into its component parts and determines the composition of each component by splitting it into ions and measuring their various weights. The GC/MS approach and comparable technologies are accurate and sensitive, but are used mainly in a scientific laboratory because they require costly, bulky instruments and highly skilled technicians. Also, GC/MS is very time intensive, both in terms of preparing the sample for analysis and providing results. In contrast, by leveraging DSP-based technology and the TDLAS method, Rice researchers developed a more cost-effective laser sensor that can maintain a high level of precision for gas detection outside of a laboratory setting with a fast detection time of less than one second.

“TI’s F2812 controller not only gave us DSP-enabled real-time processing for increased sensitivity and more precise readings, but it also performed the functions of the PC and digital-to-analog converters (DAC), allowing us to replace these devices with a single chip,” said Dr. Tittel. “By lowering our component count, we reduced the laser sensor’s size and weight, and the cost of the associated electronics fell from thousands of dollars in the previous generation to the price of one C2000™ digital signal controller.”

After receiving data from the detector, the F2812 controller uses the on-chip analog-to-digital converter (ADC) to convert the detector signal and digitally averages a large number of samples in order to increase the signal-to-noise ratio. Then, the system processes the data and performs corrections before performing linear fits with data from a known sample of the target gas to determine the concentration. The F2812 offers 256 kilobytes of flash memory for storing the laser sensor program and booting the device. The Rice University team used TI’s Code Composer Studio™ software to program the F2812 controller, which made it possible to move through all phases of the development process within a single integrated development environment (IDE).

Pricing and Availability

The estimated commercial cost, according to Dr. Tittel, of producing the current design in volume is about $4,000, but it is expected that further improvements will reduce this figure by an order of magnitude. TI’s 32-bit F28x™ DSP-based controllers start at under $5 in volume and are available for sampling or volume quantities at www.ti.com/c2000.