Integrated Embedded Processor Based Laser Spectroscopic Sensor

• US 20120081708A1
• Filed: 12/14/2011
• Published: 04/05/2012
• Est. Priority Date: 09/07/2006
• Status: Active Grant

• Current Assignee: Rice University
• Original Assignee: Rice University
• Inventors: SO, Stephen, WYSOCKI, Gerard, FRANTZ, J. Patrick, TITTEL, Frank K.
• Granted Patent: US 8,334,980 B2
• Time in Patent Office: Days
• US Class Current: 356/432
• CPC Class Codes: G01N 2021/1708 with piezotransducers probes for investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves G01N29/24
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/39 using tunable lasers

Abstract

A novel low-power and compact laser spectroscopic sensor is described herein. Embodiments of the disclosed sensor utilize state-of-the-art microprocessors and digital processing techniques to reduce power consumption and integrate functions into a small device. In particular, novel software methods are disclosed which allow the use of low-power microprocessors which draw no more than about 0.02 W of power. Such low-power enables long battery life and allows embodiments of the sensor to be used in portable applications. In addition, the system architecture and methods described in this disclosure allow a single integrated embedded processor to control all the subsystems necessary for a laser spectroscopic sensor further reducing sensor size and power consumption. In addition, a power efficient method of calibrating a photoacoustic laser spectroscopic sensor is disclosed.

Claims

1. A method comprising:

generating a first waveform at a first modulation frequency using a direct digital synthesis (DDS) algorithm; and

dividing the first waveform into a plurality of second waveforms at a plurality of second modulation frequencies using a plurality of frequency dividers.

2. The method of claim 1, wherein the first waveform is generated using a software that is executed on a processor.

3. The method of claim 2, wherein the processor is a fixed point digital signal processor.

4. The method of claim 3, wherein the frequency dividers are hardware timers that are part of the processor.

5. The method of claim 4 further comprising detecting at least one of the second waveforms using a lock-in amplifier comprising a filter and a phase sensitive detector.

6. The method of claim 5, wherein a transimpedence preamplifier is used to detect the second waveform, wherein the transimpedence preamplifier is coupled to the lock-in amplifier.

7. The method of claim 1, wherein the second modulation frequencies comprise a light source modulation frequency that is used to control the frequency of a light source, a first in-phase modulation frequency and a first quadrature modulation frequency that are used to detect absorption of a first portion of the light source by a sample compound, and a second in-phase modulation frequency and a second quadrature modulation frequency that are used to detect absorption of a second portion of the light source by a reference concentration of the sample compound.

8. The method of claim 7, wherein a frequency initially used to modulate the light source is equal to about f, wherein the first modulation frequency is equal to or greater than about 12 f, wherein the light source modulation frequency is equal to about f, wherein additional timing waveforms comprise the first in-phase modulation frequency, the first quadrature modulation frequency, the second in-phase modulation frequency, and the second quadrature modulation frequency, wherein the first in-phase modulation frequency is equal to about 2 f, wherein the first quadrature modulation frequency is equal to about 2 f+90 degrees, wherein the second in-phase modulation frequency is equal to about 3 f, and wherein the second quadrature modulation frequency is equal to about 3 f+90 degrees.

9. The method of claim 7, wherein dividing the first waveform into the second waveforms is repeated until a signal level for detecting absorption of the first portion of the light source by the sample compound reaches a limit.

10. An apparatus comprising:

a light source;

a processor; and

a thermoelectric module coupled to the light source and the processor,

wherein the processor is a fixed point digital signal processor, and

wherein the processor is configured to use a control loop to control the thermoelectric module.

11. The apparatus of claim 10, wherein the control loop is a proportional loop, a proportional-integral loop, a proportional-derivative loop, or a proportional-integral-derivative loop.

12. The apparatus of claim 10, wherein the processor comprises an analog to digital converter and a digital to analog converter.

13. The apparatus of claim 10, wherein the thermoelectric module is controlled to adjust a wavelength of the light source, a wavelength modulation of the light source, or both.

14. The apparatus of claim 10, wherein the light source comprises a temperature sensor, and wherein the apparatus further comprises a current conveyor coupled to the temperature sensor and the processor.

15. The apparatus of claim 14, wherein the processor uses the current conveyor and a tunable reference current to detect and control the temperature of the light source_[GR1].

16. An apparatus comprising:

a light source; and

a processor configured to implement a method comprising;

dividing a first waveform into at least a second waveform having a lower frequency; and

filtering the second waveform to create a sinusoid;

attenuating the sinusoid using control signals from the processor; and

controlling a current fed to the light source using the attenuated sinusoid, thereby controlling a modulation of a light emitted from the light source.

17. The apparatus of claim 16 further comprising:

a detector; and

an amplifier coupled to the detector and the processor,

wherein the amplifier receives a signal from the detector, performs phase sensitive detection of the signal, and passes the signal to the processor.

18. The apparatus of claim 17, wherein the detector is an acoustic detector.

19. The apparatus of claim 17, wherein the detector comprises an absorption cell and a photodetector.

20. The apparatus of claim 17, wherein the processor, the light source, and the detector are mounted on a circuit board, and wherein the circuit board consumes a power less than about five watts (W).

21. The apparatus of claim 20 further comprising:

a wireless transmitter coupled to the processor; and

a power source coupled to the circuit board,

wherein the processor produces data associated with emission or uptake of a chemical, and

wherein the wireless transmitter transmits the data to a central location.