Integrated embedded processor based laser spectroscopic sensor

• US 8,334,980 B2
• Filed: 12/14/2011
• Issued: 12/18/2012
• Est. Priority Date: 09/07/2006
• Status: Expired due to Fees

• Current Assignee: Rice University
• Original Assignee: Rice University
• Inventors: So, Stephen, Wysocki, Gerard, Frantz, J. Patrick, Tittel, Frank K.
• Primary Examiner(s): Toatley, Gregory J
• Assistant Examiner(s): Underwood, Jarreas C
• Application Number:
  US13/325,568
• Publication Number:
  US 20120081708A1
• Time in Patent Office: 370 Days
• Field of Search: 356432-444
• 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;

dividing the first waveform into a plurality of second waveforms at a plurality of second modulation frequencies using a plurality of frequency dividers for phase sensitive detection at a plurality of harmonics; and

detecting at least one of the second waveforms using one or more lock-in amplifiers comprising a filter and a mixer;

wherein the first waveform is generated using hardware comprising a processor or comprising an integrated circuit,

wherein the frequency dividers comprise hardware timers that are part of the processor,

wherein a transimpedence preamplifier is used to detect the second waveform, and

wherein the transimpedence preamplifier is coupled to the lock-in amplifier.

2. The method of claim 1, wherein the processor is a fixed point digital signal processor.

3. 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 for phase sensitive detection at a plurality of harmonics, 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.

4. The method of claim 3, 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 12f, 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 2f, wherein the first quadrature modulation frequency is equal to about 2f +90 degrees, wherein the second in-phase modulation frequency is equal to about 3f, and wherein the second quadrature modulation frequency is equal to about 3f +90 degrees.

5. The method of claim 3, 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.

6. An apparatus comprising:

(a) a light source;

(b) a processor configured to implement a method comprising;

dividing a first digital 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;

(c) a communications device coupled to the processor comprising a wireless transmitter or comprising a bus link; and

(d) a power source coupled to a circuit board,

wherein the circuit board consumes a power less than about five watts (W) to generate the control signals,

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

wherein the communications device transmits the data to a central location.

7. The apparatus of claim 6 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.

8. The apparatus of claim 7, wherein the detector is an acoustic detector.

9. The apparatus of claim 7, wherein the detector comprises an absorption cell and a photodetector.

10. The apparatus of claim 6, wherein the attenuation is performed by a reference multiplying DAC.