Breath acetone concentration detection device based on dual-modal detection of photoacoustic and absorption spectroscopy

Abstract

The present invention discloses a breath acetone concentration detection device based on photoacoustic and absorption spectroscopy dual-modal detection, comprising a deep ultraviolet light source, a lens collimation system, a spectroscopic system, a photoacoustic cell, an air chamber, and a photodetector coaxially arranged in sequence; the photoacoustic cell comprises a front window, a front buffer cavity, a photoacoustic cavity, a rear buffer cavity, and a rear window; the front buffer cavity is provided with a gas inlet to be measured; the rear buffer cavity is provided with a gas outlet; the photoacoustic cavity is provided with a sound pickup hole, and a microphone is provided outside the sound pickup hole; the air chamber mainly comprises a front window, a cylindrical cavity, a rear window, and an air inlet and an air outlet. The present invention uses a mechanical processing process to manufacture the aperture, the photoacoustic cell, and the air chamber, which can achieve better airtightness than 3D printing; and all components are fixed with a mechanical structure rather than glue, eliminating noise caused by glue absorbing light of the corresponding wavelength band of the light source, thereby improving detection accuracy; in addition, the overall cost of the system is low, which is conducive to productization.

Description

Technical Field

[0001] The present invention relates to the technical field of photoacoustic spectroscopy and absorption spectroscopy, and in particular to a breath acetone concentration detection device based on photoacoustic and absorption spectroscopy dual-modal detection. Background Art

[0002] Ketone bodies are the product of fat metabolism. Monitoring ketone body levels plays an irreplaceable and important role in areas such as fitness fat burning and diabetic ketoacidosis monitoring.

[0003] Among existing ketone monitoring technologies, the main medical testing methods are blood ketone testing and urine ketone testing. Both have high detection accuracy. However, urine ketone testing can only display monitoring results qualitatively or semi-quantitatively and cannot monitor β-hydroxybutyrate levels, which have the highest concentration during ketosis and are consistent with the condition. Test results are not available immediately. Blood ketone testing has the disadvantages of being expensive, complex, and invasive.

[0004] Medically, a statistical correlation between breath ketone levels and β-hydroxybutyrate levels has been demonstrated. Currently, most breath ketone meters on the market use electrochemical methods, whose results rely heavily on the performance of the core material. This results in low accuracy, poor stability (susceptible to interference from impurities and significant influence of material state changes), and a short instrument lifespan. Therefore, developing a high-precision, easy-to-use, and real-time ketone detection technology is crucial.

[0005] Photoacoustic spectroscopy (PAS) is a spectral analysis technique that utilizes the photoacoustic effect. Its measurement system primarily consists of a light source, a photoacoustic cell, a highly sensitive microphone or quartz tuning fork, and data processing circuitry. During detection, a beam of light is emitted into a gas detection chamber. As the light passes through the gas being measured, a reaction occurs between the light energy particles and the gas. The absorbed energy causes the temperature of the gas being measured to rise. Due to thermal expansion and contraction, the gas volume increases, and the pressure in the gas detection chamber rises. If the light source is periodically modulated before light emission, the gas pressure can be periodically varied, generating acoustic waves. Acoustic sensors detect the acoustic signals, allowing further analysis of the gas composition and concentration. This method offers high precision, fast response, and a wide dynamic measurement range, making it suitable for the development of small instruments.

[0006] However, existing photoacoustic spectroscopy detection devices are all made by 3D printing, which has poor airtightness. If the device is manufactured using a machining process, and the components are fixed with glue, the glue absorbs light and causes noise, resulting in inaccurate measurement results and low measurement accuracy. Therefore, there is an urgent need to develop a photoacoustic spectroscopy detection device with better airtightness and measurement accuracy.

[0007] Direct absorption spectroscopy (DAS) is an optical gas detection technology based on the Beer-Lambert law and is currently widely used in gas detection work in various fields. DAS systems are simple. They primarily consist of a light source, a gas chamber, and a photodetector. When incident light with a wavelength at the absorption peak of the gas to be measured passes through the absorbing gas, some of its energy is absorbed by the gas molecules, resulting in a decrease in the output light intensity. The degree of light intensity attenuation is related to the effective optical path and the concentration of gas molecules. To improve detection sensitivity, methods such as increasing the effective absorption optical path are often used, such as using a multi-ventilation gas chamber. DAS generally has the advantages of high detection sensitivity, extremely fast response speed, a simple system that is easy to miniaturize, and strong anti-interference capabilities. Summary of the Invention

[0008] The present invention aims to address the challenges of existing technologies by proposing a breath acetone concentration detection device based on dual-modal detection using photoacoustic and absorption spectroscopy. The device utilizes a machining process to fabricate the photoacoustic cavity, air chamber, and aperture to achieve improved airtightness. Mechanical structures are used to connect and secure the components, reducing noise caused by light absorption by glue, thereby achieving higher-precision detection.

[0009] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0010] A breath acetone concentration detection device based on dual-mode detection of photoacoustic and absorption spectroscopy includes a coaxially arranged LED, a lens collimation system, a spectroscopic system, a photoacoustic cell, a gas chamber, and a photodetector.

[0011] Sealing rings are placed before and after the air chamber window to enhance air tightness. The window adopts a high-reflection lens to increase the optical path and thus improve the detection sensitivity. A pressing structure is adopted instead of gluing to fix the window. The position and angle of the window can be fine-tuned by adjusting the depth of the fastening screws in different directions.

[0012] The photoacoustic cell includes a front window, a front buffer cavity, a photoacoustic cavity, a rear buffer cavity, and a rear window arranged in sequence; the front buffer cavity is provided with a gas inlet to be measured; the rear buffer cavity is provided with a gas outlet; the photoacoustic cavity is provided with a sound pickup hole, and a microphone is provided outside the sound pickup hole.

[0013] Furthermore, the detection device is further provided with an aperture and a rear window fixing piece;

[0014] The diaphragm is arranged between the lens collimation system and the photoacoustic cell and is in the form of a sheet. An aperture is provided in the center of the diaphragm for light to pass through. The outer ring is provided with a plurality of cage rod holes and fixing screw holes that pass through the outer ring. A first annular sealing ring positioning groove is provided on the rear side of the diaphragm. The first sealing ring positioning groove surrounds the diaphragm hole and is located inside the cage rod holes and fixing screw holes.

[0015] The front surface of the photoacoustic cell is provided with a first sealing ring and a window plate groove that matches the first sealing ring positioning groove. A cage rod hole and a fixing screw hole that match the diaphragm are provided outside the first sealing ring and the window plate groove. The diaphragm and the front surface of the photoacoustic cell are fixed by screws. A sealing ring is respectively provided in the first sealing ring positioning groove and the first sealing ring and the window plate groove. The front window plate is squeezed and arranged between the two sealing rings.

[0016] The rear window fixing plate is arranged behind the photoacoustic pool, and a through hole is provided in the center of the rear window fixing plate; a plurality of cage rod holes and fixing screw holes are provided on the outer ring, which pass through the front and back of the rear window fixing plate; a circular second sealing ring positioning groove is provided on the front side surface of the rear window fixing plate, and the second sealing ring positioning groove surrounds the through hole and is located inside the cage rod holes and the fixing screw holes;

[0017] The rear surface of the photoacoustic cell is provided with a second sealing ring and a window plate groove that matches the second sealing ring positioning groove, and a cage rod hole and a fixing screw hole that match the rear window fixing plate are provided on the outer side of the second sealing ring and the window plate groove, and the rear window fixing plate and the rear surface of the photoacoustic cell are fixed by screws; a sealing ring is respectively provided in the second sealing ring positioning groove and the second sealing ring and the window plate groove, and the rear window plate is squeezed and arranged between the two sealing rings;

[0018] The lens collimation system, the aperture and the photoacoustic cell are connected and fixed by a cage structure. Furthermore, the lens collimation system includes two convex lenses, with the front convex lens close to the LED; the two convex lenses have the same focal length, and the distance between them is equal to the focal length.

[0019] Furthermore, the sound pickup hole has a three-layer structure, which includes a sound conduction hole, a microphone placement hole and a threaded hole from the inside to the outside; the microphone is arranged in the microphone placement hole through a hollow screw, and the sound receiving end of the microphone is close to the sound conduction hole; a sealing ring is provided at the bottom of the hollow screw, and the hollow screw cooperates with the threaded hole to fix the microphone and tighten the sealing ring.

[0020] Furthermore, the photoacoustic cell, the air chamber and the aperture are all made of stainless steel by machining.

[0021] Furthermore, the LED is an ultraviolet LED with a spectral range of 250nm~290nm, and can also be replaced by a deep ultraviolet LD.

[0022] Furthermore, the signal from the microphone is output to a differential amplifier circuit and then connected to a computer via a lock-in amplifier; the lock-in amplifier is a DSP lock-in amplifier; the signal from the photodetector is directly output to a computer for processing and concentration inversion.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention simultaneously applies photoacoustic spectroscopy and direct absorption techniques to detect acetone in breath, and provides the acetone concentration through a weighted average method, thereby improving the accuracy and stability of detection.

[0025] 1. This invention utilizes machining rather than 3D printing to fabricate the photoacoustic cavity, air chamber, and aperture, resulting in improved airtightness. Furthermore, the device utilizes mechanical structures rather than glue to secure components, reducing noise caused by glue absorbing light within the corresponding wavelength band of the light source, thereby achieving higher-precision detection.

[0026] 2. This invention uses a UV-band LED as the light source. Impurities such as carbon dioxide and water in the gas being measured have little impact on the measurement results, thus eliminating interference from these gases to a certain extent. This invention can also use a UV-band LD as the light source. Although LDs offer superior performance to LEDs, deep-UV LDs are generally expensive, making them an alternative.

[0027] 3. The present invention uses LED as the light source, which is relatively cheap and helps reduce system costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 3 is a schematic structural diagram of a breath acetone concentration detection device based on photoacoustic and absorption spectroscopy dual-modal detection in an embodiment;

[0029] Figure 2 is a cross-sectional view of the photoacoustic cavity;

[0030] Figure 3 It is the front and back side view of the aperture;

[0031] Figure 4 This is the front and side view of the photoacoustic cell.

[0032] Figure 5 It is a cross-sectional view of the air chamber;

[0033] Figure 6 It is the front view of the fixing plate;

[0034] The reference numerals in the figure are: 1, LED; 2, lens collimation system; 3, front buffer chamber; 4, photoacoustic chamber; 5, rear buffer chamber; 6, front window; 7, rear window; 8, gas inlet to be measured; 9, gas outlet; 10, microphone; 11, LED driver; 12, lock-in amplifier; 13, data acquisition card; 14, computer; 15, aperture; 16, rear window fixing plate; 17, beam splitter; 18, reflector; 19, gas chamber; 20, photodetector; 21. Front window piece; 22. Rear window piece; 23. Threaded hole; 24. Microphone placement hole; 25. Sound conduction hole; 26. Sealing ring and window piece groove; 27. Cage rod hole; 28. Fixing screw hole; 29. ​​Aperture hole; 30. Sealing ring positioning groove; 31. Air chamber cavity; 32. Air inlet; 33. Air outlet; 34. Window piece fastening threaded hole; 35. Support rod fixing threaded hole; 36. Window fixing pressure piece; 37. Window fixing pressure piece through hole; 38. Pressure piece light hole. DETAILED DESCRIPTION

[0035] The present invention is described in detail with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following embodiments. That is, any simple equivalent changes and modifications made within the scope of the patent application of the present invention and the contents of the specification are still within the scope of the patent of the present invention.

[0036] It is worth noting that in the present invention, the words "front" and "rear" indicating the orientation are respectively defined as the front and back along the direction of the optical path, that is, the side close to the LED is the front side, and the side away from the LED is the rear side; the words "inside" and "outside" indicating the orientation are respectively defined as the directions close to and away from the axis of the LED, lens collimation system and photoacoustic cell.

[0037] In this embodiment, a breath acetone concentration detection device based on dual-modal detection using photoacoustic and absorption spectroscopy includes an LED 1, a lens collimation system 2, a beam splitter 17, a reflector 18, an aperture 15, an air chamber 19, a photodetector 20, a photoacoustic cell 4, a rear window fixing plate 16, a microphone 10, a differential amplifier circuit, a lock-in amplifier 12, and a computer 14. The LED 1, lens collimation system 2, aperture 15, and photoacoustic cell are coaxially arranged in sequence.

[0038] The LED 1 is a UV LED with a peak wavelength of 266 nm, a main spectral range of 250 nm to 290 nm, a peak power of 100 mW, and a divergence angle of approximately 90°. The lock-in amplifier 12 is a DSP lock-in amplifier with a frequency range of 1 mHz to 250 kHz.

[0039] The lens collimation system 2 consists of two convex lenses with a focal length of 25 mm. The distance between the two lenses is about 25 mm. The front lens is close to the LED, and the rear lens is close to the aperture. They are connected to the aperture photoacoustic cell with a cage structure. Experiments show that the focusing and collimation effect is best at this time.

[0040] The spectrometer 17 can split the ultraviolet light in a 1:1 ratio, and the reflectivity of the reflector 18 to the ultraviolet light can reach 99%.

[0041] The photoacoustic cell includes a front buffer chamber 3, a photoacoustic chamber 4 and a rear buffer chamber 5 which are coaxially arranged in sequence and are machined from stainless steel. The front buffer chamber 3 is provided with a gas inlet 8 to be measured, and a front window 6 is also provided on the front side of the front buffer chamber 3; the rear buffer chamber 5 is provided with a gas outlet 9, and a rear window 7 is also provided on the rear side of the rear buffer chamber 5. The photoacoustic chamber has a sound pickup hole.

[0042] The pickup hole has a three-layer structure. The sound conduction hole 25 is closest to the photoacoustic cavity, with a diameter of 1mm and a length of 0.3mm. Outside it is the microphone placement hole 24, with a diameter of 3mm, slightly larger than the diameter of the microphone 10. Outside it is a threaded hole 23 with M5 thread and a length of 8mm. The microphone 10 is placed in the microphone placement hole 24 through a hollow screw and a sealing ring. The sealing ring is set at the bottom of the hollow screw. The hollow screw fixes the position of the microphone 10 and squeezes the sealing ring, which has good airtightness.

[0043] The signal received by the microphone 10 is output to the differential amplifier circuit, and then connected to the data acquisition card 13 and the computer through the lock-in amplifier 12.

[0044] The aperture 15 is machined from stainless steel and has an aperture hole 29 at its center for light to pass through. The diameter of the aperture hole 29 is the same as that of the photoacoustic cavity 4. The outer ring is provided with four cage rod holes 27 and eight fixing screw holes 28 running through the front and back. A circular sealing ring positioning groove 30 is provided on the rear side of the aperture. The sealing ring positioning groove 30 surrounds the aperture hole 29 and is located inside the cage rod holes 27 and fixing screw holes 28.

[0045] The front surface of the photoacoustic cell is provided with a sealing ring and window piece groove 26 that matches the sealing ring positioning groove 30. The outer side of the sealing ring and window piece groove 26 is provided with a cage rod hole 27 and a fixing screw hole 28 that match the corresponding structure of the diaphragm 15. The diaphragm 15 and the front surface of the photoacoustic cell are fixed by eight M3 screws. A sealing ring is respectively provided in the sealing ring positioning groove 30 and the sealing ring and window piece groove 26. The front window piece is squeezed and arranged between the two sealing rings and connected in the order of sealing ring-front window piece 6-sealing ring, which has good airtightness.

[0046] The rear window fixing plate 16 secures the rear window 7. Its structure is similar to that of the aperture, but its through-hole diameter is 25 mm, slightly smaller than that of the rear window 7. Similarly, the rear surface of the photoacoustic cavity is equipped with a sealing ring and window slot 26, similar to those on the front surface. The rear window fixing plate 16 is also connected to the rear surface of the photoacoustic cavity via eight M3 screws in the order of sealing ring, window 7, and sealing ring.

[0047] The central cavity 31 of the air chamber 19 has a diameter of 12 mm and a length of 30 mm. The window has a diameter of 15 mm. The air inlet 32 ​​and outlet 33 are both M4 threaded holes, and the window fastening threaded hole 34 is also M4. The threaded hole 35 at the bottom of the air chamber for fixing the support rod is M6.

[0048] The window pressing piece 37 is 2 mm thick, and each piece has four through holes 38 with a diameter of 4 mm for M4 fixing screws to pass through, and a light hole 39 with a diameter of 12 mm is opened in the middle.

[0049] The photodetector 20 converts the received optical signal into an electrical signal and transmits it directly to the computer for processing, thereby completing the inversion of the acetone concentration.

[0050] The device also includes an LED driver 11, which is used to modulate the intensity of the light emitted by the LED 1. The intensity-modulated light passes through the lens collimation system 2 and the beam splitter 17 in sequence and is split into two. One part still passes through the aperture 15, the front window 6, the front buffer cavity 3, the photoacoustic cavity 4, the rear buffer cavity 5 and the rear window 7 in the original direction; the other part passes through the reflector 18, the air chamber 19 and the photodetector 20.

[0051] In this embodiment, the simulated resonant frequency of the acetone gas in the photoacoustic cell is 7585.8 Hz, while absorption spectroscopy techniques are generally unaffected by the light source modulation frequency. Therefore, a rectangular wave with a frequency of approximately 7585 Hz can be used to drive the LED, causing it to brighten and dim with the frequency. When bright, the gas in the cavity absorbs light, raising its temperature and increasing its pressure; when dim, the gas temperature and pressure decrease, generating a periodic acoustic wave signal. Comparative tests were performed using an existing photoacoustic cavity with a UV-curable adhesive fixed structure and the mechanical structure of the present invention. In the following tests, the acetone concentration of the gas to be measured was controlled by a valve and flowmeter on the gas pipeline, and a waste container was connected to the gas outlet of the rear buffer chamber.

[0052] When nitrogen gas is introduced into the photoacoustic cavity, which is fixed with UV-curing adhesive, the noise level is above 0.25 mV. After nitrogen gas is stopped, the noise level increases to 0.4 mV. After 300 ppm of acetone is introduced, there is no obvious signal.

[0053] When nitrogen is introduced into the photoacoustic cavity using the mechanical structure of the present invention, the noise level is 60 Ω. After 300 ppm of acetone is introduced, a signal of about 100 Ω is generated. After 150 ppm of acetone is introduced, a signal of about 80 Ω is generated. Compared with the photoacoustic cavity fixed with the UV-curing adhesive, the signal is obvious.

[0054] The present invention utilizes dual-mode detection of photoacoustic and absorption spectroscopy to detect breath acetone concentration. The aperture and photoacoustic cavity are manufactured using mechanical processing, achieving better airtightness than 3D printing. All components are fixed using mechanical structures rather than glue, eliminating noise caused by light absorption by glue and improving detection accuracy. Furthermore, the LED light source significantly reduces costs during mass production, facilitating the device's commercialization.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A breath acetone concentration detection device based on dual-modal detection of photoacoustic and absorption spectroscopy, characterized by: 1 UV LED The light is split into two paths, one for photoacoustic spectroscopy detection and the other for absorption spectroscopy detection. The photoacoustic spectroscopy device, which is machined from stainless steel, includes a lens collimation system and a photoacoustic cell coaxially arranged in sequence; the absorption spectroscopy detection device includes a lens collimation system, an air chamber, and a photodetector coaxially arranged in sequence. The photoacoustic cell comprises a front window, a front buffer cavity, a photoacoustic cavity, a rear buffer cavity, and a rear window, which are arranged in sequence; the front buffer cavity is provided with a gas inlet to be measured; the rear buffer cavity is provided with a gas outlet; the photoacoustic cavity is provided with a sound pickup hole, and a microphone is provided outside the sound pickup hole; The gas chamber is connected to the external gas to be measured, and adopts a back-and-forth reflection mechanism to increase the optical path and improve the sensitivity of the gas; The target gas concentrations detected by photoacoustic spectroscopy and absorption spectroscopy are respectively combined to obtain the acetone concentration through a weighted average algorithm. When the acetone concentration given by one detection mode exceeds the physiological limit of acetone exhaled by the human body, the other detection mode is automatically switched to output the acetone concentration.

2. The device for detecting breath acetone concentration based on dual-modal detection of photoacoustic and absorption spectroscopy according to claim 1, wherein: The detection device is further provided with an aperture and a rear window fixing plate; the detection device is provided with a spectroscopic lens for light splitting; The aperture is arranged between the lens collimation system and the photoacoustic cell, as well as between the reflector and the air chamber. It is sheet-shaped, with an aperture hole for light to pass through provided at its center. The outer ring is provided with a plurality of cage rod holes and fixing screw holes extending front to back. A first annular sealing ring positioning groove is provided on the rear side of the aperture. The first sealing ring positioning groove surrounds the aperture hole and is located inside the cage rod holes and fixing screw holes. The front surface of the photoacoustic cell is provided with a first sealing ring and a window plate groove that matches the first sealing ring positioning groove. A cage rod hole and a fixing screw hole that match the diaphragm are provided outside the first sealing ring and the window plate groove. The diaphragm and the front surface of the photoacoustic cell are fixed by screws. A sealing ring is respectively provided in the first sealing ring positioning groove and the first sealing ring and the window plate groove. The front window plate is squeezed and arranged between the two sealing rings. The rear window fixing plate is arranged behind the photoacoustic pool, and a through hole is provided in the center of the rear window fixing plate; a plurality of cage rod holes and fixing screw holes are provided on the outer ring, which pass through the front and back of the rear window fixing plate; a circular second sealing ring positioning groove is provided on the front side surface of the rear window fixing plate, and the second sealing ring positioning groove surrounds the through hole and is located inside the cage rod holes and the fixing screw holes; The rear surface of the photoacoustic cell is provided with a second sealing ring and a window plate groove that matches the second sealing ring positioning groove, and a cage rod hole and a fixing screw hole that match the rear window fixing plate are provided on the outer side of the second sealing ring and the window plate groove, and the rear window fixing plate and the rear surface of the photoacoustic cell are fixed by screws; a sealing ring is respectively provided in the second sealing ring positioning groove and the second sealing ring and the window plate groove, and the rear window plate is squeezed and arranged between the two sealing rings; The lens collimation system, the aperture and the photoacoustic cell are connected and fixed via a cage structure; Sealing rings are placed before and after the air chamber window to enhance air tightness. The window adopts a high-reflection lens to increase the optical path and thus improve the detection sensitivity. A pressing structure is adopted instead of gluing to fix the window. The position and angle of the window can be fine-tuned by adjusting the depth of the fastening screws in different directions.

3. The device for detecting breath acetone concentration based on dual-modal detection of photoacoustic and absorption spectroscopy according to claim 2, characterized in that: The lens collimation system includes two convex lenses, and the front convex lens is close to the LED; the two convex lenses have the same focal length, and the distance between them is equal to the focal length.

4. The device for detecting breath acetone concentration based on dual-mode detection of photoacoustic and absorption spectroscopy according to claim 1 The device is characterized by: The pickup hole has a three-layer structure, which includes a sound conduction hole, a microphone placement hole and a threaded hole from the inside to the outside; the microphone is arranged in the microphone placement hole through a hollow screw, and the sound receiving end of the microphone is close to the sound conduction hole; a sealing ring is provided at the bottom of the hollow screw, and the hollow screw cooperates with the threaded hole to fix the microphone and tighten the sealing ring.

5. The device for detecting breath acetone concentration based on dual-modal detection of photoacoustic and absorption spectroscopy according to claim 1, wherein: The photoacoustic cell, the air chamber and the aperture are all made by machining of stainless steel materials.

6. The device for detecting breath acetone concentration based on dual-modal detection of photoacoustic and absorption spectroscopy according to claim 1, characterized in that: The LED is an ultraviolet LED with a spectrum range of 250nm~290nm, or it can be replaced by an LD with the same wavelength range.

7. The device for detecting breath acetone concentration based on dual-mode detection of photoacoustic and absorption spectroscopy according to claim 1, characterized in that: The signal from the microphone is output to a differential amplifier circuit and then connected to a computer via a lock-in amplifier; the lock-in amplifier is a DSP lock-in amplifier; the signal from the photodetector is directly output to a computer for processing and concentration inversion.

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