A method for measuring the reflectivity of any material in air

Abstract

The present invention discloses a method for measuring the reflectivity of any material in the air, and the steps include: 1) selecting a detector whose inner wall is a highly reflective material and has an opening, and setting a signal collector and a light source through microholes on the inner wall, and placing the detector in a pure air light-proof environment; 2) using a selected pulse light source to illuminate the detector, using a signal collector to collect the waveform of the light signal size changing with time, and fitting the collected signal waveform to obtain the effective attenuation length λ1 of the photon in the detector; 3) covering the opening with the material to be measured, using the light source to illuminate the detector, using the signal collector to collect the light signal waveform, and fitting the collected signal waveform to obtain the effective attenuation length λ2 of the photon in the detector; 4) calculating the reflectivity f2 of the material to be measured according to the size of the detector and the size of the opening as well as λ1 and λ2. The present invention is simpler to operate and novel in principle than the existing measurement method, and has a strong application value.

Description

Technical Field

[0001] The present invention relates to a method for measuring the reflectivity of different materials in the air by measuring the attenuation of light intensity; a photosensitive element is used to collect signal changes in a detector with an inner wall made of a highly reflective material and an opening after being irradiated by pulsed light, and waveform signals of signal size changes over time when there is no reflective material at the opening and when the material to be tested is attached to the opening are respectively measured, so as to measure the reflectivity of different materials in the air by a simple and novel method. Background Art

[0002] At present, the reflectivity of non-mirror materials is mainly measured by light intensity comparison. For example, a standard colorimetric white plate with known reflectivity and the material to be tested are placed in the test window of a traditional integrating sphere instrument, and the reflectivity of the material to be tested is obtained by comparing the difference in integrated light intensity when the two materials are placed. Traditional integrating sphere instruments and other instruments that measure reflectivity require professionally manufactured standard instruments, which are expensive and have high requirements for measurement technology. The accuracy and preservation of the reflectivity of the standard colorimetric plate are likely to affect the measurement results of the reflectivity of the material to be tested. Summary of the invention

[0003] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a simple and novel method for measuring the reflectivity of any material in the air.

[0004] The technical solution of the present invention is:

[0005] A method for measuring the reflectivity of any material in the air, the steps comprising:

[0006] 1) Select a detector with an inner wall made of highly reflective material and an opening, set a signal collector and light source through the microholes on the inner wall, and place the detector in a pure air and light-proof environment;

[0007] 2) irradiating the detector with a selected pulse light source, collecting the optical signal waveform with the signal collector, and obtaining the effective attenuation length λ1 of the photon in the detector according to the collected signal waveform;

[0008] 3) Covering the opening with the material to be tested, irradiating the detector with the light source, collecting the optical signal waveform with the signal collector, and obtaining the effective attenuation length λ2 of the photon in the detector according to the collected signal waveform;

[0009] 4) Calculate the reflectivity f2 of the material to be tested according to the size of the detector and the size of the opening as well as λ1 and λ2. Further, the medium filled in the detector is pure air; in step 4), according to the formula Calculate the reflectivity f2 of the material to be tested; wherein r is the ratio of the area of ​​the opening to the inner wall area of ​​the detector, and L is the average optical path (average reflection step length) of a single reflection of the signal light emitted by the light source in the detector.

[0010] Furthermore, the single reflection average optical path L is calculated according to 4*(volume inside the detector) / (total area inside the detector).

[0011] Further, using N*e -t / τ Exponential fitting is used to obtain the waveform of the collected signal size changing with time to obtain the attenuation factor τ of the number of photons over time. The attenuation factor is multiplied by the speed of light to obtain the effective attenuation length of the photon in the detector; or the waveform of the collected signal size changing with time is multiplied by the speed of light to obtain the waveform changing with distance and then N*e is used to calculate the attenuation factor τ. -t / λ’ The effective attenuation length λ' is obtained by fitting; wherein N, τ, and λ are all parameters that can be directly fitted, and are respectively the number of photoelectrons collected by the signal collector at the initial moment of fitting, the effective attenuation time, and the effective attenuation length.

[0012] A method for measuring the reflectivity of any material in the air, the steps comprising:

[0013] 1) Select a detector whose inner wall is made of highly reflective material and has an opening, and set a signal collector and light source through the microhole on the inner wall, and place the detector in a pure air and light-proof environment; the average reflectivity of the inner wall except the opening is f1;

[0014] 2) Covering the opening with the material to be tested, irradiating the detector with the light source, collecting the optical signal waveform with the signal collector, and obtaining the effective attenuation length λ2 of the photon in the detector according to the collected signal waveform;

[0015] 3) Calculate the reflectivity f2 of the material to be tested according to the size of the detector, the size of the opening, f1 and λ2.

[0016] Furthermore, the reflectivity f2 of the material to be tested is calculated according to the formula 1 / λ2=-ln(f1*(1-r)+f2*r) / L; wherein r is the ratio of the area of ​​the opening to the inner wall area of ​​the detector, and L is the average optical path of a single reflection of the signal light emitted by the light source in the detector.

[0017] Furthermore, it is recommended that the ratio r of the area of ​​the opening to the inner wall area of ​​the detector be less than 5%.

[0018] Furthermore, there is no specific requirement for the reflectivity of the inner wall of the high-reflectivity material. In order to increase the data acquisition efficiency, it is recommended that the reflectivity of the high-reflectivity material is greater than 90% and is not a pure specular reflective material.

[0019] A method for measuring the reflectivity of an inner wall of a detector, the steps comprising:

[0020] 1) Select a detector whose inner wall is made of highly reflective material and whose light leakage opening area is known, and set a signal collector and light source through a microhole with negligible area on the inner wall, and place the detector in a pure air and light-proof environment;

[0021] 2) irradiating the detector with a selected light source, collecting the optical signal waveform with the signal collector, and obtaining the effective attenuation length λ1 of the photon in the detector by fitting the collected signal waveform;

[0022] 3) According to the formula The reflectivity f1 of the inner wall of the detector is calculated; wherein r is the ratio of the area of ​​the light leakage opening to the inner wall area of ​​the detector, and L is the average optical path of a single reflection of the signal light emitted by the light source in the detector.

[0023] The present invention develops a simple new measurement method for measuring the reflectivity of different materials in the air based on the reflection and attenuation principle of photons in a detector whose inner wall is made of highly reflective material and has an opening. It only needs to measure the waveform signal of the light intensity changing with time after the detector is irradiated by pulsed light when there is no material at the opening and when the material to be tested is attached to the opening. The reflectivity of the material can be obtained by combining the geometric dimensions of the detector.

[0024] The photons generated by the pulsed light are fully mixed after multiple reflections in the detector. The average distance L (average optical path for a single reflection, or average reflection step length) traveled by the photons for each reflection can be approximately calculated based on the volume and area, or can be measured according to the methods in Patents ZL201710398214.2 and ZL201710397900.8 or simulated by Geant4. The distance corresponding to the movement of a photon with a light speed of v in the detector for t time is x = light speed * t, and the number of reflections of the photon is x / L. The photons in the detector are mainly attenuated by the absorption of the inner wall of the detector and the absorption of the medium inside the detector. After the pulsed LED light is irradiated in the detector, the number of photons decays exponentially with time and distance. A photomultiplier tube (PMT) is used to collect the light signal in the detector through a small hole on the inner wall of the detector. After the photons are fully mixed after multiple reflections in the detector, the attenuation factor of the signal size received by the PMT that changes with time reflects the attenuation factor of the total number of photons in the detector with time, which is expressed as N*e -t / τ Exponential fitting is used to obtain the waveform of the signal size collected by the PMT that changes with time to obtain the attenuation factor τ of the number of photons over time, and multiply it by the speed of light to convert time into distance to obtain the effective attenuation length λ' of the photons in the detector. The waveform of the signal size that changes with time can also be multiplied by the speed of light to convert it into a waveform that changes with flight distance and then N*e -t / λ’The effective attenuation length λ' is obtained by fitting. Assume that there are N0 photons of a specific wavelength in the detector at a certain moment, the medium absorption length corresponding to this wavelength is λ, and the total reflectivity of the inner wall is f. Then the change in the number of photons with the movement distance of N0 photons moving x due to the absorption of the inner wall of the detector is N0*(f) x / L N0 photons travel a distance x, and the number of photons becomes N0*e simply due to the absorption of the medium. -x / λ . Under the combined action, the number of photons remaining after N0 photons move x distance in the detector is N0*e -x / λ *(f) x / L , which can also be expressed by the effective attenuation factor λ' as N0*e -x / λ’ Then e -x / λ’ =e -x / λ *(f) x / L (i.e., Formula 1), is transformed into 1 / λ'=1 / λ-ln(f) / L (i.e., Formula 2). If the detector is pure air, the absorption of light by the air can be ignored relative to the absorption of light by the inner wall of the detector, and Formula 2 becomes 1 / λ'=-ln(f) / L (i.e., Formula 3). If there are openings or black bodies in the inner wall of the detector in pure air with a proportion of r, and the average reflectivity of the remaining area is f1, all photons are absorbed when they hit the openings or the inner wall of the black body, then the total reflectivity f of the inner wall of the detector is f1 multiplied by its proportion of the inner wall (1-r), then Formula 3 becomes 1 / λ'=-ln(f1*(1-r)) / L (i.e., Formula 4). If there are r proportions of area reflectivity f2 in the inner wall of the detector in pure air, and the average reflectivity of the remaining area is f1, then the total reflectivity of the inner wall of the detector is f1*(1-r)+f2*r, then Formula 3 becomes 1 / λ'=-ln(f1*(1-r)+f2*r) / L (i.e., Formula 5). The average optical path of a single reflection and the residual area ratio r can be calculated based on the detector size. The reflectivity of different materials can be measured by measuring the effective attenuation factor of light in the detector and the detector size.

[0025] The present invention proves that a photomultiplier tube is used to collect the changes in pulsed light signals in a detector with an inner wall made of highly reflective material and an opening in pure air. The waveform signals of the PMT light intensity that changes with time when there is no material at the opening and when the material to be tested is attached to the opening are measured respectively, and the effective attenuation length is obtained by fitting. The average optical path of a single reflection is calculated according to the size of the detector, and the reflectivity of the material can be obtained: a small opening that occupies a proportion r of the inner wall area is opened in the detector, and a pulsed LED is irradiated inside. First, the PMT waveform when the inner wall has this known r-proportion opening is measured and fitted to obtain the effective attenuation length λ1, then 1 / λ1=-ln(f1*(1-r)) / L (i.e., Formula 6); then the opening is covered with other materials to be tested with any reflectivity, the PMT waveform is measured and fitted to obtain the effective attenuation length λ2, then 1 / λ2=-ln(f1*(1-r)+f2*r) / L (i.e., Formula 7). Combining the above two formulas, the reflectivity of the material to be tested at the opening can be obtained. (i.e., Formula 8), that is, as long as the PMT waveforms when there is no material at the opening and when the material to be tested is placed at the opening are respectively measured, the effective attenuation length is obtained by fitting, and L and r are calculated according to the detector size, the reflectivity of the material to be tested at the opening can be obtained. This method is still valid when there are other unknown light leakage areas or uneven reflectivity of the high-reflection inner wall of the detector. It is easy to operate and has strong practical value. At the same time, according to Formula 6, it can be obtained (i.e., Formula 9), that is, by measuring the light intensity attenuation in the detector with a certain light leakage ratio, the reflectivity of the inner wall of the detector outside the light leakage area can be measured.

[0026] This method is applicable to detectors of any shape. It is verified by Geant4 simulation, and the method is verified by a cylindrical detector with a diameter of 50 cm and a height of 50 cm and a cube detector with a length, width and height of 50 cm respectively. The inner wall of the simulated detector is a highly reflective material with a known opening of 15 cm*10 cm. The waveform of the instantaneous number of photons received by the PMT changing with time when there is no material at the opening or when the opening is covered with any reflective material is fitted to obtain the effective attenuation length, and L is calculated using 4*(volume inside the detector) / (total area inside the detector). According to formula eight, the reflectivity of any material covered by the opening can be measured, and the reflectivity of the inner wall with high reflectivity can also be measured according to formula nine.

[0027] Compared with the prior art, the present invention has the following positive effects:

[0028] This method cleverly achieves the measurement of the reflectivity of different materials in the air with a simple and novel method. When the reflectivity of all materials is unknown, the device can be built using the conditions available in an ordinary laboratory to measure the reflectivity of different materials. When there is unknown light leakage in the detector or the reflectivity of the inner wall is uneven, the reflectivity of the material to be measured at the opening can also be measured. The manufacturing process is simple and does not require a standard colorimetric plate. The present invention is simpler to operate and novel in principle than the existing measurement method, and has strong application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the method of the present invention;

[0030] Figure 2 To simulate a cubic cavity with a length, width and height of 50 cm, the inner wall is made of a material with a reflectivity of 98% and the top opening is 15 cm*10 cm. The number of photons received by the PMT changes with time*speed of light. The thick black line segment is Function fitting results.

[0031] Figure 3 To simulate a cubic cavity with a length, width and height of 50 cm, the inner wall is made of a material with a reflectivity of 98% and the upper opening of 15 cm*10 cm is covered with a material with a reflectivity of 50%. The number of photons received by the PMT changes with time*speed of light. The thick black line segment is Function fitting results.

[0032] Figure 4 To simulate a cubic cavity with a length, width and height of 50 cm, the inner wall is made of a material with a reflectivity of 98% and the upper opening of 15 cm*10 cm is covered with a material with a reflectivity of 90%. The number of photons received by the PMT changes with time*speed of light. The black thick line segment is Function fitting results.

[0033] Figure 5 To simulate the change of the number of photons received by the PMT over time when the cylindrical cavity with a diameter of 50 cm and a height of 50 cm is made of a material with a reflectivity of 98% and an opening of 15 cm*10 cm on the top, the black thick line segment is N0*e -x / τ1 Function fitting results.

[0034] Figure 6 To simulate the change of the number of photons received by the PMT over time when a cylindrical cavity with a diameter of 50 cm and a height of 50 cm is obtained, the inner wall is made of a material with a reflectivity of 98% and the upper opening of 15 cm*10 cm is covered with a material with a reflectivity of 10%. The black thick line segment is N0*e -x / τ2 Function fitting results. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with specific experiments, simulations and accompanying drawings.

[0036] The present invention uses the detector Geant4 simulation to prove that: using a photomultiplier tube to collect the pulse light signal changes in a detector with an opening and an inner wall made of a highly reflective material in pure air, respectively measuring the waveform signal of the light intensity changing with time when there is no material at the opening and when the material to be tested is attached to the opening, and calculating the average optical path of a single reflection according to the detector size, the reflectivity of the material can be obtained according to the light intensity attenuation formula. The method flow of the present invention is as follows Figure 1 shown.

[0037] The specific implementation method is shown in the following simulation verification scheme:

[0038] Cube cavity verification: simulate a cube cavity with a length, width and height of 50cm. The inner wall of the detector is made of Tyvek material with a reflectivity of 98%. The absorption length of light by the air inside the detector is set to 1000 meters. There is a small circular opening with a diameter of 1cm on the upper Tyvek for the photomultiplier tube cathode surface to receive photons, and there is another 10cm*15cm opening. According to the size of the detector, the average optical path of a single reflection is calculated as L = 4*volume / area = 0.333 meters, and the proportion r of the 10cm*15cm opening on the upper wall of the detector is 1%. Each simulation generates 100,000 photons within 10ns, and the number of photons received by the photomultiplier tube per unit time changes with time. When the time starting point is the case generation, set different random numbers for multiple simulations to improve the statistics. Simulate the change of the number of photons collected by the PMT with time when the reflectivity of the 10cm*15cm opening on the upper side is 0 and when the reflectivity is different. The abscissa time of the PMT time spectrum is multiplied by the speed of light to obtain the spectrum of the number of photons over time*speed of light, and the effective attenuation length λ' is obtained by fitting. Figure 2 The number of photons received by the PMT changes with time * speed of light when the reflectivity at the opening is 0. The thick black line segment is The effective attenuation length obtained by function fitting is 10.85 m. According to Formula 9, the reflectivity of the high-reflection material of the inner wall is calculated as f1=(exp(-0.333 / 10.85)) / (1-1%)=97.96%. Figure 3 When the reflectivity at the opening is 90%, the number of photons received by the PMT changes with time * speed of light. The effective attenuation length of light in the detector is fitted to be 15.55m. According to formula 8, the reflectivity of the material at the opening is calculated to be f2 = (exp(-0.333 / 15.55)-exp(-0.333 / 10.85)) / 0.01 = 90.38%. Figure 4The number of photons received by the PMT changes with time * speed of light when the reflectivity at the opening is 50%. The effective attenuation length of light in the detector is fitted to be 13.06m, and the reflectivity of the material at the opening is calculated to be f2 = (exp(-0.333 / 13.06)-exp(-0.333 / 10.85)) / 0.01 = 50.497%.

[0039] Cylindrical cavity verification: simulate a cylindrical cavity with a diameter of 50cm and a height of 50cm. The inner wall of the detector is made of Tyvek material with a reflectivity of 98%. The absorption length of light by the air inside the detector is set to 1000 meters. There is a small circular opening with a diameter of 1cm on the upper Tyvek for the photomultiplier tube cathode surface to receive photons, and there is also a 10cm*15cm opening. According to the size of the detector, the average optical path of a single reflection is calculated to be L=4*volume / area=0.333 meters, and the ratio of the 10cm*15cm opening on the upper detector wall is r 150 / (11780.962). Each simulation generates 100,000 photons within 10ns, and the number of photons received per unit time by the photomultiplier tube changes with time. When the time starting point is the case generation, set different random numbers for multiple simulations to improve the statistics. Figure 5 is the change of the number of photons received by the PMT over time when the reflectivity at the opening is 0. The black thick line segment is N0*e -x / τ1 Function fitting yields an effective decay time of 33.41 ns, which is multiplied by the light speed in vacuum to yield an effective decay length of 10.016 m. According to Formula 9, the reflectivity of the inner wall high reflective material is calculated as f1 = exp(-0.333 / 10.016) / (1-150 / 11780.962) = 97.98%. Figure 6 is the change of the number of photons received by the PMT over time when the reflectivity at the opening is 10%. The black thick line segment is N0*e -x / τ2 Function fitting yields an effective attenuation time of 34.81 ns, which is multiplied by the speed of light in a vacuum to yield an effective attenuation length of 10.4349 m. The reflectivity of the material at the opening is calculated according to Formula 8 as f2 = (exp(-0.333 / 10.4349)-exp(-0.333 / 10.016)) / (150 / 11780.962) = 10.15%.

[0040] This method still works when the material at the opening is changed to a material with a reflectivity of 5%, 99% or any other material. This method still works when the material at the opening is changed from diffuse reflection to specular reflection. This shows that this method can measure the reflectivity of materials with any reflectivity.

[0041] Alternatives

[0042] There are no specific requirements for the shape and size of the detector, as long as the volume and area can be measured and the data collection efficiency is high enough. There are no specific requirements for the reflectivity of the inner wall of the highly reflective material, but when the reflectivity is too low, the signal will decay too quickly and affect the data collection efficiency. It is recommended that the reflectivity of the inner wall high reflective material be greater than 90%. The inner wall high reflective material can be mainly diffuse reflective or mainly specular reflective, and it does not require absolute specular reflection. There are no requirements for the reflectivity and reflection model of the material to be tested attached to the opening. Any reflectivity is acceptable, and diffuse reflective materials or specular reflective materials are acceptable. When there is no material at the opening, the measurement can also be replaced by covering with black material with negligible reflectivity. A photomultiplier tube can be used as a photosensitive probe to collect signals in combination with any instrument that can collect waveforms, or other types of photosensitive probes can be used.

[0043] Although the specific embodiments of the present invention are disclosed for the purpose of illustration, the purpose is to help understand the content of the present invention and implement it accordingly, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the best embodiment, and the scope of the present invention is subject to the scope defined in the claims.

Claims

1. A method for measuring the reflectivity of any material in the air, the steps comprising: 1) Select a detector with an inner wall made of highly reflective material and an opening, set a signal collector and light source through the microholes on the inner wall, and place the detector in a pure air and light-proof environment; 2) irradiating the detector with a selected pulse light source, collecting the optical signal waveform with the signal collector, and obtaining the effective attenuation length λ1 of the photon in the detector according to the collected optical signal waveform; 3) Covering the opening with the material to be tested, irradiating the detector with the light source, collecting the light signal waveform with the signal collector, and obtaining the effective attenuation length λ2 of the photon in the detector according to the collected light signal waveform; 4) According to the size of the detector and the size of the opening as well as λ1 and λ2, the formula Calculate the reflectivity f2 of the material to be tested; wherein r is the ratio of the area of ​​the opening to the inner wall area of ​​the detector, and L is the average optical path of a single reflection of the signal light emitted by the light source in the detector; the single reflection average optical path L is calculated according to 4*(volume inside the detector) / (total area inside the detector).

2. The method according to claim 1, characterized in that The ratio r of the area of ​​the opening to the inner wall area of ​​the detector is less than 5%.

3. The method according to claim 1, characterized in that Use N*e -t / τ Exponential fitting is used to obtain the waveform of the collected signal size changing with time t to obtain the effective decay time τ of the photon number. The effective decay time τ is multiplied by the speed of light to obtain the effective decay length of the photon in the detector; or the waveform of the collected signal size changing with time t is multiplied by the speed of light to obtain the waveform changing with distance x and then N*e -x / λ’ The effective attenuation length λ' is obtained by fitting, wherein N, τ, and λ' are the number of photoelectrons collected by the signal collector at the initial moment of fitting, the effective attenuation time, and the effective attenuation length, respectively.

4. A method for measuring the reflectivity of any material in the air, the steps comprising: 1) Select a detector whose inner wall is made of highly reflective material and has an opening, and set a signal collector and light source through the microhole on the inner wall, and place the detector in a pure air and light-proof environment; the average reflectivity of the inner wall except the opening is f1; 2) Covering the opening with the material to be tested, irradiating the detector with the light source, collecting the light signal waveform with the signal collector, and obtaining the effective attenuation length λ2 of the photon in the detector according to the collected light signal waveform; 3) According to the size of the detector and the size of the opening as well as f1 and λ2, the reflectivity f2 of the material to be tested is calculated by the formula 1 / λ2=-ln(f1*(1-r)+f2*r) / L; wherein r is the ratio of the area of ​​the opening to the inner wall area of ​​the detector, and L is the average optical path of a single reflection of the signal light emitted by the light source in the detector; the single reflection average optical path L is calculated according to 4*(volume inside the detector) / (total area inside the detector).

5. The method according to claim 4, characterized in that The ratio r of the area of ​​the opening to the inner wall area of ​​the detector is less than 5%.

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