NDIR glucose detection in liquids
A glucose sensor measures glucose molecules in vivo through use of NDIR in which scattering noise is reduced and Absorption Interference Noise (AIN) is suppressed with a reflection technique. Electronics are used to provide an output of glucose concentration glucose in a liquid sampling matrix after it has been determined that a calibration curve is valid after signal processing is used to obtain average ratio values for reflected signal/reference channels and interference/reference channel obtained after a pulsed beam from signal, interference and reference sources is directed at an inclined angle to a normal of a spot of the liquid sampling matrix. The signal, interference and reference sources are each pulsed at a preselected frequency of at least N Hz which is sufficiently fast so that a given molecule of glucose or interfering molecule will not pass in and out of the liquid sampling matrix within the preselected frequency.
1. An apparatus for determining a concentration of a targeted molecule M within a given time period in a liquid sampling matrix in which at least one interfering molecule M J coexists with the targeted molecule, comprising:
a signal source;
an interference source;
a reference source;
a multiplexer and a collimator configured to pulse infrared radiation from the signal source, the interference source and the reference source into a pulsed beam which is directed at an inclined angle (θ i ) to a normal of a spot of the liquid sampling matrix;
a detector configured to detect infrared radiation after it emerges from the spot as a pulsed signal and reference channel output and a pulsed interference signal and reference channel output from the pulsed beam after it penetrates into the spot;
signal processing for:
obtaining an average ratio value of R ave (t) for a first preselected period of time (“t”) from the pulsed signal and reference channel output, where R ave (t)=signal channel/reference channel output for the first preselected period of time, and
obtaining an average ratio value of R Jave (t 2 ) for a second preselected period of time (“t 2 ”) from the pulsed interference and reference channel output, where R Jave (t 2 )=interference channel/reference channel output for the second preselected period of time; and
electronics configured to use R Jave (t 2 ) to determine that a calibration curve is valid for the given time period and, if the calibration curve is valid, to calculate the concentration of the targeted molecule M in the liquid sampling matrix by use of R ave (t) and the calibration curve and provide the concentration of the targeted molecule M in the liquid sampling matrix as an output;
wherein the signal source emits radiation at a signal wavelength which is within a first absorption band of the targeted molecule M, the interference source emits radiation at an interference wavelength which is within a second absorption band of said at least one interfering molecule M J , and the reference beam emits radiation at a reference wavelength which is neutral and is not within either the first absorption band or the second absorption band;
wherein said at least one interfering molecule M J absorbs radiation at the signal wavelength;
wherein the signal source, the interference source and the reference source are each pulsed at a preselected frequency of at least N Hz which is sufficiently fast so that a given molecule of the targeted molecule M or said at least one interfering molecule M J will not pass in and out of the liquid sampling matrix within the preselected frequency.
2. The apparatus of claim 1 , wherein the pulsed beam is comprised of an alternate and sequential pulsing of a repeating pattern of the signal source, followed by the reference source, followed by the interference source, followed by the reference source.
3. The apparatus of claim 1 , wherein the pulsed beam is comprised of an alternate and sequential pulsing of a repeating pattern of the signal source, the reference source and the interference source.
4. The apparatus of claim 1 , wherein the frequency of N Hz is greater than 1.0 KHz with a duty factor of at least 10%.
5. The apparatus of claim 1 , wherein t=t 2 .
6. The apparatus of claim 1 , wherein the signal beam has a signal beam center wavelength of 1,150 nm (1.150μ) and the reference beam has a center wavelength of 1,064 nm (1.064μ).
7. The apparatus of claim 6 , wherein the interference beam has a center wavelength of 1,210 nm.
8. The apparatus of claim 7 , wherein the targeted molecule M is glucose, said at least one interfering molecule M J is comprised of a plurality of interfering molecules contained in a body interstitial fluid and radiation emerging from the spot is collected by a lens onto the detector.
9. An apparatus for determining a concentration of a targeted molecule M within a given time period in a liquid sampling matrix in which at least one interfering molecule M J coexists with the targeted molecule, wherein the targeted molecule M is glucose and said at least one interfering molecule M J is comprised of a plurality of interfering molecules contained in a body interstitial fluid, comprising:
a signal source;
an interference source;
a reference source;
a multiplexer and a collimator configured to pulse infrared radiation from the signal source, the interference source and the reference source into a pulsed beam which is directed at an inclined angle (θ i ) to a normal of a spot of the liquid sampling matrix;
a detector configured to detect infrared radiation after it emerges from the spot as a pulsed signal and reference channel output and a pulsed interference signal and reference channel output from the pulsed beam after it penetrates into the spot and radiation emerging from the spot is collected by a lens onto the detector;
signal processing for:
obtaining an average ratio value of R ave (t) for a first preselected period of time (“t”) from the pulsed signal and reference channel output, where R ave (t)=signal channel/reference channel output for the first preselected period of time, and
obtaining an average ratio value of R Jave (t 2 ) for a second preselected period of time (“t 2 ”) from the pulsed interference and reference channel output, where R Jave (t 2 )=interference channel/reference channel output for the second preselected period of time; and
electronics configured to use R Jave (t 2 ) to determine that a calibration curve is valid for the given time period and, if the calibration curve is valid, to calculate the concentration of the targeted molecule M in the liquid sampling matrix by use of R ave (t) and the calibration curve and provide the concentration of the targeted molecule M in the liquid sampling matrix as an output;
wherein the signal source emits radiation which has a signal beam center wavelength of 1,150 nm (1.150μ), the interference source emits radiation which has a center wavelength of 1,210 nm, and the reference beam emits radiation which has a center wavelength of 1,064 nm (1.064μ);
wherein said at least one interfering molecule M J absorbs radiation at the signal wavelength;
wherein the signal source, the interference source and the reference source are each pulsed at a preselected frequency of at least N Hz which is greater than 1.0 KHz with a duty factor of at least 10% and is sufficiently fast so that a given molecule of the targeted molecule M or said at least one interfering molecule M J will not pass in and out of the liquid sampling matrix within the preselected frequency.
10. The apparatus of claim 9 , wherein the pulsed beam is comprised of an alternate and sequential pulsing of a repeating pattern of the signal source, followed by the reference source, followed by the interference source, followed by the reference source.
11. The apparatus of claim 9 , wherein the pulsed beam is comprised of an alternate and sequential pulsing of a repeating pattern of the signal source, the reference source and the interference source.
12. The apparatus of claim 9 , wherein t=t 2 .