HK1211340B - Portable spectrometer - Google Patents

Description

Portable spectrometer

Technical Field

The present invention relates to a portable spectrometer, and more particularly, to a robust, high performance portable spectrometer requiring minimal power and size.

Background

In the last decade, near infrared spectroscopy (NIR) has been increasingly developed as an indispensable analytical tool for production and quality control in the pharmaceutical industry. Qualitative NIR inspection is often applied for identification control of raw material feed, while quantitative analysis of the final product is an important step in the pharmaceutical process chain. However, most pharmaceutical analyses are still performed by taking samples from the manufacturing site and shipping them to a remote quality control laboratory. This delay between sampling and the resulting results can limit the frequency of analysis and optimization of the production line. Thus, it is contemplated that new portable field instruments capable of rapid online or on-line analysis of processes may be employed as a key tool in furtherance of the increasing benefits of the pharmaceutical industry.

Early versions of compact spectrometers, such as those described in U.S. patent application publication No. 2012/0188541 to Ocean Optics, Inc, published on 26/7/2012 and U.S. patent application publication No. 2005/0007596 to Wilks Enterprise, Inc, published on 13/1/2005, attempted to minimize their footprint by providing a series of optical path folding mirrors. However, fold mirrors require a large number of calibration steps in production and do not provide a very robust structure for field application devices, thereby resulting in low or unexpected performance.

Historically, beam shaping or light redirection has been performed using light pipes, or light transmitting pipes. Examples include display engine technology for displays or front projection televisions, such as the technology disclosed in U.S. patent nos. 7,252,399 and 7,033,056 and U.S. patent application No. 2006/0044833. 6,420,708 to Wilks et al, 7/16/2002, discloses a spectrum analyzer that includes a rectangular light pipe or crystal for transmitting light to a sample, but not for shaping the reflected light to a filter.

6,473,165, 7,006,204, and 7,184,133 relate to automated verification systems in which the reflection of two separate beams of light at two different angles of incidence reflected from an optical interference security feature are measured and compared. A converging tapered light pipe for collecting and condensing light is disclosed.

It is an object of the present invention to overcome the disadvantages of the prior art by providing a high performance, rugged, portable, low power spectrometer for field sampling test devices that includes a broadband light source and detector array.

Summary of The Invention

Accordingly, the present invention relates to a portable spectrometer device comprising:

an illumination source for directing light towards the sample;

a Tapered Light Pipe (TLP) for collecting light that interacts with the sample at a first focal ratio and for transmitting light at a second focal ratio that is lower than the first focal ratio;

a Linear Variable Filter (LVF) for separating the collected light into spectra of constituent wavelength signals; and

a detector array comprising a plurality of pixels, each of the plurality of pixels being arranged to receive at least a portion of one of a plurality of constituent wavelength signals, providing a power reading at each constituent wavelength;

wherein the TLP includes a smaller first end for placement adjacent the sample, a wider and higher second end adjacent the LVF, and sidewalls diverging from the first end to the second end for mixing and propagating light across the LVF.

Brief description of the drawings

The invention will be described in more detail hereinafter with reference to the accompanying drawings, which represent preferred embodiments of the invention, and in which:

FIG. 1a is a schematic diagram of a spectrometer system according to the present invention;

FIG. 1b is a perspective view of the spectrometer of FIG. 1a positioned in a user's hand;

FIG. 1c is a perspective view of the spectrometer system of FIG. 1 a;

figures 2a and 2b are side views of two different embodiments of the portable spectrometer of figure 1 a;

FIG. 3 is a top view of one of the light sources of the portable spectrometer of FIG. 1 a;

FIG. 4 is a top view of the housing of the portable spectrometer of FIG. 1 a;

FIGS. 5a, 5b and 5c are isometric, side and top views, respectively, of a tapered light pipe of the spectrometer of FIG. 1 a;

FIG. 6 is a graph of transmission versus wavelength for a spectrometer with and without TLP;

FIGS. 7a and 7b show the incoming and outgoing beams of a standard TLP and the incoming and outgoing beams of a lensed TLP, respectively;

FIG. 8 is a graph of the transmittance versus wavelength for a spectrometer with and without a lensed TLP;

FIG. 9 is an isometric view of a TLP shield of the portable spectrometer of FIG. 1 a;

FIGS. 10a and 10b are graphs of response versus wavelength for spectrometers according to the present invention with and without a TLP shield, respectively;

FIG. 11 is a side view of the LVF of the portable spectrometer of FIG. 1 a;

FIG. 12 is a schematic diagram of the LVF and detector array of the portable spectrometer of FIG. 1 a;

FIGS. 13a and 13b are graphs of the response versus wavelength for a spectrometer with 750 μm and 200 μm gaps between the LVF of the present invention and the detector array, respectively;

FIG. 14 is a side view of an LVF and detector array configuration according to the present invention;

FIG. 15 is a schematic diagram of a wireless spectrometer system according to the present invention;

figure 16 is a schematic diagram of an alternative wireless spectrometer system according to the present invention.

Detailed Description

Referring to figures 1a, 1b, 1c, 2a and 2b, the compact spectrometer 1 according to the present invention is a very small, low cost, hand-held spectrometer, e.g. with a cell weight of less than 5 lbs, preferably less than 2 lbs, more preferably less than 0.5 lbs, ideally less than 100g, compact in volume, e.g. less than 6 inches x 2 inches, preferably less than 6 inches x 3 inches x 1 inches, more preferably less than 4 inches x 2 inches x 0.5 inches, the spectrometer being built around a filter 2, the filter 2 being mounted on a broadband detector array 3, the broadband detector array 3 having a width of, e.g., more than 500nm, preferably more than 600nm, most preferably more than 700nm, e.g. an indium gallium arsenide (InGaAs). The filter may be any form of spectrometer, for example diffraction based, phase holographic based, Frustrated Total Reflection (FTR) based or Linear Variable Filter (LVF) based, any form of instrument that requires a particular cone of incidence to be functional, but LVF is preferred.

LVF is a dielectric thin film Fabry-Perot (Fabry-Perot) bandpass filter deposited using electrical processes well known in the art to produce stable and reliable optical components. The filter coating in the LVF is intentionally tapered in one direction. Since the center wavelength of the bandpass filter is a function of the coating thickness, the peak transmission wavelength will vary continuously in the direction of the wedge. LVF is usually made of SiO₂And Ta₂O₅And the like, and is produced by adopting an ion-assisted physical vapor deposition technology to form a compact coating with high reliability and stability.

Ideally, the spectrometer 1 is fully USB powered, i.e. the spectrometer uses 2.5W or less of power, but spectrometers with wirelessly connected battery power supplies are also within the scope of the invention, as will be described in more detail below. The control system 4 is comprised of a processor and a suitable non-volatile memory and includes a suitable USB connector for receiving a USB cable 6 to enable data transfer between the control system 4 and a host control device 7 (e.g. a laptop, tablet or PDA etc.), the host control device 7 ideally being located within a protective cover 8. One or more free standing light sources 12 actuated by a switch 10 are employed to direct light onto a sample 15 to enable diffuse reflected, transmitted or interactive radiation to be collected by light collection optics, such as a TLP 11, for delivery to a filter, such as LVF 2.

To minimize the size and operating power consumption of the spectrometer 1 while maintaining robustness and high performance, a number of problems need to be addressed, including: 1) the efficiency of the optical path is made as high as possible; 2) TLP 11 is used in the optical path instead of fiber; 3) the LVF2 is placed close to the detector 3 to minimize the required optics; 4) the detector array 3 is not cooled to avoid the power requirements of the TE cooler; and 5) providing a light source 12 that consumes as little power as possible, yet can provide broadband illumination, such as in the Infrared (IR) region.

The spectrometer 1 according to the invention operates with a power consumption below 2.5W, even if the light source 12 comprises two or more lamps. For near infrared light, the light source 12 preferably consists of one or two on-board incandescent lamps (e.g., vacuum tungsten lamps) that provide broadband illumination, e.g., over 500nm, preferably over 700nm, and most preferably over 1000nm, throughout the effective range of the instrument (e.g., in the 900nm to 1700nm range or 900nm to 2150nm range for near infrared light). One lamp 12 suffices; however, two lamps 12 can add more light to the sample interaction, thereby making the integration time shorter. There are limitations in practical use; however, space conditions and USB or battery power may also be limited.

Referring to fig. 2a and 2b, the light source 12 generally has two configurations. In one configuration, the sample 15 is illuminated by aligned light from one, two or more light sources 12 at an acute angle to the normal to the sample 15 (e.g., at a 45 angle to the longitudinal axis LA of the TLP 11), and one end of the TLP 11 is placed at an equal distance between each lamp. The longitudinal axis LA of the TLP 11 is perpendicular to the LVF2 and the base of the detector array 3. In another arrangement, the sample 15 is flood illuminated. In both arrangements, the receiving end of the TLP 11 is arranged to receive light from the sample 15 that is incident substantially normally (i.e. in the direction of the longitudinal axis LA). The light source 12 is arranged to exclude specular reflections from the sample 15. 45 deg. illumination will diffuse the reflectance or transmittance reflectance measurements. Each light source 12 ideally comprises a vacuum tungsten lamp with a lens at the end for forming a 5mm, preferably 3mm or less spot on the sample 15. Referring to FIG. 4, the ends of the light source 12 and TLP 11 are ideally disposed inside a housing 20 extending outwardly from the body of the device 1. The housing 20 has an opening covered by a transparent protective window 21, such as sapphire blue, through which window 21 light is projected onto the sample 15, the reflected light being collected by the TLP 11. The housing 20 may protect the light source 12 from damage and prevent stray light from external sources from entering the end of the TLP 11. Both reflective and transmissive modes of the sample 15 placed between the source 12 and the TLP 11 are possible, as shown in fig. 2a and 2b, respectively.

The concept of a compact portable body can also include, but is not limited to, a small screen on the back for viewing the spectrum, a simple fool-proof interface, a battery, a memory card for storing the spectrum, a computer interface, a flash or onboard illumination source, and a framework for building, loading and post-processing data using onboard "applications".

A first embodiment of light source 12 employs a two-end lensed vacuum tungsten lamp to provide intense near-infrared illumination of sample 15. Ideally, the lamps are positioned so that light impinges on the sample 15 at an acute angle (e.g., 45 °) to the normal to the sample, while specularly reflected light will be reflected into the lamps on the opposite side. Ideally, a 3mm diameter spot is formed on the sample 15. Under normal conditions, no direct specular reflection will enter the entrance aperture of the TLP 11. This is still a viable lighting situation, but it has the disadvantage that the two beams will coincide at a position where the "depth of field" is about 500 μm. Many, if not most, near infrared measurements are made of light from the surface and within the sample, i.e., in some cases, the penetration depth can be up to 10 mm. Such illumination, while very effective in controlling specular reflection, produces variations in the resulting transmitted reflectance (transflection). This is a possible illumination arrangement if the sample 15 is only measured on its surface.

The light source 12 in the alternative embodiment employs flood lighting produced by a non-directional lamp. Flood illumination illuminates the sample 15 with non-collimated light, which alleviates the "depth of field" problem, i.e. for transmitted reflectance a depth of field of up to 10mm, rather than just surface measurements. Flood illumination also provides a greater flux of near infrared light to the sample 15 being measured. The additional degree of freedom comes at the cost of the need to control the parasitic specular reflection from the front protection window 21 of the spectrometer 1. This is accomplished by using a stepped shield 25 (see FIG. 9), which shield 25 severely limits the field of view seen by the entrance aperture of the TLP 11. Reducing the unwanted light from the lamps 12 into the TLP 11 is achieved by: adjusting the relative position of the lamp 12 and the entrance aperture of the protective cover 25, adjusting the approach distance of the protective cover 25 and the rear surface of the window 21, adjusting the thickness of the window 21, and applying a coating to the window 21 intended to minimize specular reflection, etc.

The TLP 11 is provided with light collection optics designed to deliver spectral light energy of any desired wavelength (i.e., light reflected from the lambertian scattering surface or the transmissive semi-transparent surface of the sample 15) to the entrance surface of the LVF2 for transmission to the detector array 3. For the filter/detector array assembly 2/3 to work efficiently, the maximum acceptance NA of light entering the LVF2 needs to be 0.2 or less. To achieve an acceptable NA, the output radiation pattern collected from the sample 15 under test requires a lens or a tapered light pipe. The tapered light pipe 11 may be solid (e.g., Schott N-BK7 glass) or hollow in structure, depending on the operating parameters of the spectral engine or spectrometer. The cone angle of the TLP 11 may be optimized for reflective or transmissive sampling and/or optical path length. The TLP 11 may or may not have a reflective coating applied for a hollow or solid design. The tapered and non-tapered light pipes may or may not have light recycling properties intended to enhance the signal from the sample. The spectrometer or spectral sensing will control the wavelength region targeted and ultimately dictate the light pipe design.

One specific example of a Tapered Light Pipe (TLP)11 is shown in figures 5a, 5b and 5c, which collects light from a lambertian light source at a first smaller end, i.e. light emitted by the lamp 12 that is reflected by a highly scattering surface (e.g. a solid or liquid sample 15) at a first focal ratio (e.g. f/1) and a cone angle of between 20 ° and 40 °, for example, but typically around 30 °, and mixes, disperses and shapes the reflected light to have a smaller focal ratio f/3, i.e. a cone angle of about 10 ° or less, that is required for the LVF2 within the spectrometer 1 to function better. The tapered light pipe 11 acts as a disperser (disperser) and a light shaping device with diverging side walls (e.g., 4) that disperse the light and enable the passage of electromagnetic waves from a larger second end (e.g., higher and wider ends) through the LVF2 from the lambertian illuminated surface. Accordingly, the TLP 11 enables the spectrometer 1 to sample light from a relatively large area, collecting light from any lambertian scattering surface, unlike other competing technologies, which typically use optical fibers to collect light from a smaller local area. In addition, the TLP 11 mixes and disperses light to accommodate the size of the LVF2 and the pixels in the pixel array 3. LVF2 can thus be optimized to accept light that deviates no more than 10 ° from the normal (i.e., normal to the coating surface and/or LVF substrate), thereby greatly improving resolution and performance.

The focal ratio is the ratio of the focal length of the telescope to its aperture, which is given by the focal length divided by the aperture. For example, a telescope with a focal length of 2032mm and an aperture of 8 inches (203.2mm) has a focal ratio of 10(2032/203.2 is 10), or f/10.

TLP 11 is a beam steering/shaping device that employs compound angles to slow the light cone from a first (fast) focal ratio (e.g., f/1) to a second lower (slower) focal ratio (e.g., f/3) and enables LVF2 to achieve performance requirements spectrally. This is achieved by controlling the aspect ratio of the entrance and exit apertures of the TLP 11. The length of the TLP 11 needs to be long enough to achieve sufficient mixing of the light and to obtain a suitable (slower) focal ratio over the exit aperture. Figure 6 shows the difference in transmission and wavelength (i.e. much less transmission, much wider wavelength) between spectrometers with and without TLP 11.

The entrance aperture of the TLP 11 closest to the lamp 12 has a smaller opening of 1.5mm to 2.5mm (preferably 2mm +/-0.1 mm). times.0.4 mm to 0.6mm (preferably 0.5mm +/-0.1 mm). The exit aperture near LVF2 has a larger opening 6mm to 7mm (preferably 6.6mm + -0.1mm) wide and 0.75mm to 1.25mm (preferably 1.0mm + -0.1mm) long. The TLP 11 has a length of 15mm to 25mm (preferably 20mm + -0.3 mm) and tapers in both height and width toward the inlet end. Accordingly, the taper angle is between 6 ° and 7 ° in width, and 12 ° to 13 ° in total, on each side of the longitudinal axis, and between 0.5 ° and 1 ° in height, and 1 ° to 2 ° in total, on each side of the longitudinal axis.

Disadvantageously, due to the TLP 11, the beams exiting the TLP 11 are no longer perpendicular to the LVF2, i.e. they are tilted at most to 6 ° at either end of the detector array 3 (see fig. 7 a). As a result, two adverse effects occur, which are more exacerbated at the ends of the detector array 3: 1) the central wavelength is shifted downwards; 2) there is a broadening of the bandwidth (resolution). The shorter, broader plot in figure 8 shows the performance of a spectrometer using a planar TLP 11.

Ideally, the addition of lensing elements within the TLP 11 to straighten the tilted beam may be accomplished by applying a lensing surface 23 to the TLP 11; however, it is also possible to add a separate lens and/or a lensed inlet to LVF 2. The oblique light at the edge of the detector array 3 can be straightened by a cylindrical lens 23, such as a lens made of typical optical materials with a sag of 0.5mm over a 6.4mm active area, which should enable the optimum performance of micro nir (micronir), such as linear wavelength spacing and optimum resolution, to be recovered. See the higher and narrower graph in fig. 8.

Referring to fig. 9, a TLP shield 25 is provided to support the TLP 11 and ensure that light reflected from the sample 15 is delivered to the entrance aperture of the TLP 11 at a suitable acceptance angle defined by a first focal ratio (e.g., f/1) and a cone angle of about 30 °, and that the field of view of the TLP 11 is delivered to the LVF2 at a desired second focal ratio (e.g., f/3) and a cone angle of about 10 °. The protective cover 25 includes a support portion 26 that supports at least the end of the TLP 11, and ideally supports the entire TLP 11 without introducing any strain, thereby protecting the TLP 11 from shock and vibration. The protective cover 25 also includes a spacer portion 27 that reduces the amount of light emitted by the lamps 12 that reaches the entrance aperture of the TLP 11 after being specularly reflected by the protective window 21 by accommodating the TLP 11 inside and separating the entrance end of the TLP 11 from the protective window 21. The spacer portion 27 is in direct contact with the entrance aperture of the TLP 11 and includes a plurality of stepped inner surfaces 28 having a plurality of planar rectangular steps 29 extending around the opening and perpendicular to the longitudinal axis LA of the TLP 11 to reduce near infrared light energy entering the TLP 11 at any other location (e.g., reflected from the entrance window). The sidewalls of the spacer portion 27 converge in a stepwise manner in length and width in the direction from the opening thereof to the opening of the TLP 11 provided in the protection cover 25. If light enters from elsewhere, the result will be a deterioration in the spectral performance of the system. The step 29, similar to the zoom bellows of an old dry plate camera, is very effective in blocking and capturing unwanted scattered light from entering the TLP 11. This allows for a higher Optical Density (OD) measurement in terms of transmission reflectance measurements, in addition to better utilization of detector dynamic range for the spectrometer 1.

If higher angular light flux enters the TLP 11 at the entrance aperture, the result will be: the spectral passband, second spectral peak, shoulder and base on the spectral curve will be broadened. The graphs in fig. 10a and 10b show the difference in laser line spectra between a conventional shield (fig. 10a) and the inventive shield 25 (fig. 10b), the resolution provided by the inventive shield 25 being much higher.

Referring to fig. 11 and 12, the LVF2 of the present invention receives the collected light from the TLP 11 and transmits individual wavelength bands that vary linearly in ascending or descending order across the length of the LVF 2. In the illustrated embodiment, LVF2 comprises a multilayer stack with a spacer layer 30 between first and second reflective layers 31 and 32 on a substrate 33, as is well known in the art. The first and second reflective layers 31 and 32 are deposited in a thickness gradient (converging or diverging) in cross section, whereby the thicker the filter, the longer the transmission wavelength. The graph of transmittance (%) versus wavelength shown includes wavelengths from 400 to 700; however, any wavelength range is possible.

The center wavelength varies continuously along the length of LVF2, so that the light impinging on a detector pixel is a superposition of the bandwidth emanating from each point on LVF2 that the pixel can "see" (set by the F/# of light). The center transmission wavelength varies linearly over the entire length of LVF 2. In the example, the leftmost end of LVF2 transmits only a narrow range of blue wavelengths (shorter wavelengths). During the movement to the right, LVF2 increases in thickness and transmits longer wavelengths. Finally at the rightmost end, only a narrow band of red light (longer wavelength) is transmitted.

LVF2 is designed to transmit one wavelength band at each position. These wavelength bands are designed to be roughly comparable to the desired total wavelength range divided by the number of pixels, but are typically somewhat smaller. For example, in the conventional 128-pixel spectrometer 1, the LVF2 is designed to transmit a wavelength band of about 1% of the center wavelength (10 nm in the case of a center wavelength of 1000 nm). One advantage of LVF technology is that the wavelength bands are not separated; in other words, light of each wavelength impinging on LVF2 will be "seen" somewhere on the detector plane.

Instead of a high power and bulky refrigeration system, a temperature feedback device 41, such as a thermistor, is ideally mounted in close proximity to the detector array 3. The temperature feedback device 41 may be a thermistor whose resistance varies with temperature, or may be a high-precision Integrated Circuit (IC) that outputs a known temperature-dependent voltage. The analog output of the temperature feedback device is read by the control system 4 CPU. The control system 4 may now perform a temperature adjustment process by accessing a look-up table or formula stored in non-volatile memory that corrects the initial measurement based on the temperature from the temperature feedback device to determine a temperature adjusted reading.

The dark current and the responsivity of the detector array 3 are both temperature dependent. Reproducible results can be obtained as long as the temperature is stable; however, the conventional wisdom holds that the temperature of the LVF2 and the detector array 3 should be as low as possible.

In all applications, the gap between LVF2 and detector array 3 is set to minimize the divergence of any wavelength of light beam emitted from LVF 2; for example to optimize the divergence of the beam to less than 3 pixels on the detector array 3. Another alternative is to separate the gaps to ensure that the beam size is not doubled between LVF2 and detector array 3.

Fig. 12 shows the importance of a small gap d between LVF2 and detector array 3. Assuming that the taper of the light provided by the TLP 11 is the same, the divergence S becomes d × tan9.59 ° when the light irradiates the LVF2, i.e., f/3 or 9.59 °. For a gap d of 150 μm, the divergence becomes 25 μm. Accordingly, a single line on LVF2 will form a line of one pixel width on detector array 3.

For a 150 μm gap, each "line" of light emanating from the LVF diverges at 9.59 to form a line 25 μm wide at the detector plane. This corresponds to the pixel pitch (50 μm). Thus, the wavelength sensitive response of each line on LVF2 is split between the two pixels in a weighted proportion. Accordingly, the use of a gap of less than 500 μm, preferably less than 200 μm, more preferably between 5 μm and 80 μm, is a preferred way to minimize the required optics and enable the device to be provided in a compact package.

Fig. 13a and 13b show the difference in spectral performance for gaps of 750 μm (fig. 10a) and 200 μm (fig. 10b), where a smaller 200 μm gap minimizes pixel crosstalk, spectral broadening, and platform bottoms (pedestals).

Ideally, LVF2 is as close as possible to detector array 3 to mitigate spectral cross talk between detector elements, as shown in fig. 14. Optimally, LVF2 is bonded directly to the pixels 52 of the detector array 3 using a light transmissive adhesive 51; however, the adhesive 51 also needs to have the following conditions: non-conductive or having dielectric properties; by obtaining good bond strength when the detector array 3 is subjected to induced strain or failure forces, thereby exhibiting neutrality to mechanical conditions; optically transmitting desired spectral components; eliminating reflections occurring at the air-glass interface; and has reasonable coefficient of thermal expansion properties to minimize stress on the detector pixels 52 during curing and thermal cycling. Accordingly, LVF2 may cause each pixel 52 of detector array 3 to respond ideally to a different wavelength.

For example, the internal electronics of the detector array 3, such as an InGaAs linear diode array, and the wires 53 are very sensitive to any conductive material, which can cause shorting, damage or damage to the detector pixels or the CMOS processing chip 54. In this example, the bonding material 51 to mitigate this problem is Epo-Tek 353ND^TMIt has the property of being heat curable but not curable with ultraviolet rays. In this example, thermal curing is acceptable because the coating on LVF2 that is directly adhered to pixels 52 of detector array 3 does not transmit ultraviolet energy. Furthermore, EP353ND (colorless or black) has excellent dielectric properties both before and after the curing process. Ideally, EP353ND colorless type can be used as the adhesive 51 between the LVF2 and the detector array 3 over a thickness of about 5 to 15 microns.

A "glass cover" 55, i.e. the substrate of LVF2, is provided over LVF2 covering most of the pixels 52 in the detector array 3, but not over the environmentally sensitive portion 53 of the sensor-carrying chip 54. However, the adhesive EP353ND can also take an opaque form, for example black, as the coating agent 56 for the entire inner envelope. Opaque adhesive 56 may act as an optical isolator or light absorbing encapsulant or spacer, surrounding LVF2 and covering the sensitive electronic components of detector array 3 within the package to minimize stray light issues. The adhesive coating 56 also acts as an environmental protectant of the electronic circuitry 53 within the package, eliminating the need for the currently required cover windows. Using the same material as the transparent adhesive 51 and the black coating material 56 provides advantages in terms of thermal, optical, and processing.

Thus, there are three factors that affect the resolution (wavelength range) seen by each pixel: first, the pixel width geometrically corresponds to the central wavelength range on LVF2, e.g. a 50 μm pixel sees a wavelength of 6.3nm in the case of LVF in the range 900-1700 nm. Second, LVF2 has an intrinsic bandwidth (e.g., 1% wide, or 9nm to 17nm, depending on location) determined by the combination of the design and the incident light cone angle. Third, the gaps and taper angles can create a confounding or weighting effect (e.g., 1 pixel wide, or an additional 6.3nm increase as a weighted average). The superposition of these factors results in the overall resolution of the instrument, which in our current instrument is 1.1%, for example.

Possible applications for the portable spectrometer 1 include in-situ threat detection; identification and validation of drugs, controlled substances and food products; forensic debate; process monitoring in the food industry (e.g. for moisture content in cereals); and identification of products for recycling and contaminant detection. Any object having a near infrared signal (structure) can be measured and determined.

In an alternative embodiment shown in fig. 15, the handheld compact spectrometer 1 includes an optical package coupled to a battery pack 59 and a bluetooth or WiFi chip 60 for communicating with a control device 7 (e.g., control hardware and software) located at a remote location.

The user will make a real-time prediction using the compact spectrometer 1 connected to an Android, Windows or apple iOS based device, i.e. the control device 7. Ideally, the control device 7 and the compact spectrometer 1 communicate via a USB cable 6 or a standalone bluetooth or WiFi connection (i.e. they are just two devices on this local area network). There is no cloud interface; the user will upload the method file 62 or app to the non-volatile memory of the control device 7 using a hard-coded method, the control device 7 is expected to control the compact spectrometer 1 and execute the saved method file 62. The method file 62 refers to a combination of pre-processing and spectral models derived from a spectral library that will give a prediction to the end user of the compact spectrometer 1. The method file 62 may contain more than one model if multiple results are required for the application. The method file 62 may also specify the desired configuration of the compact spectrometer, such as exposure time, number of scans to be used for averaging, or leave these settings as settings to be defined as part of the instrument setup protocol.

Preprocessing is mathematical data processing or processing techniques to remove various effects (e.g., baseline bias or sample light scattering) from a set of measured spectra. These techniques include derivation, stray, and baseline correction. The particular choice of pretreatment is chosen to improve discrimination, i.e., minimize differences between multiple spectra of the same material and maximize differences between spectra of different materials.

The spectral library is a series of spectral measurements of known "reference" materials, which may be a variety of different substances or variations of the same material type, stored in a non-volatile memory of the control device 7 or in a server 64 connected thereto. Examples may be a series of Near Infrared (NIR), Infrared (IR) or raman spectra of different white powder samples. The spectral library will be used to generate a "spectral model".

"spectral model" refers to a mathematical equation derived from a particular set of spectra. The model is typically a regression vector statistically derived from the spectral library, quantifying the similarity of an unknown spectrum to the spectrum in the library. For example, a "spectral model" may include the wavelength, amplitude, and spectral peak width for a given material. These wavelengths, amplitudes and widths are compared to the wavelengths, amplitudes and widths of the pre-processed spectra that have been measured. The results of this comparison can be interpreted qualitatively by the prediction engine 63 for Identification (ID) or "pass/fail" class applications, and quantitatively for determining purity or concentration.

The prediction engine consists of computer hardware and/or software stored in non-volatile memory on the control device 7. The determined parameter or result is referred to as "prediction". The predictions provided by the prediction engine 63 can be transmitted to the compact spectrometer 1 for viewing by a user or for easy viewing on a suitable graphical user interface on the control device 7. Alternatively, the predictions may be stored in non-volatile memory on the control device 7 or on the remote server 64 for later review.

Prediction engine 63 may predict in one of two ways: first, a simple method using known models and pre-processing can be performed directly within the spectrometer provider's software. Second, complex or third party proprietary methods may be uploaded in third party formats and the control device 7 will communicate with a third party prediction "engine" to make real time predictions. The third party engine will need to reside on the control device 7. Data reduction or projection techniques may include partial least squares, principal component analysis, principal component regression, partial least squares discriminant analysis, and cluster independent soft mode methods.

Some users may wish to keep a history of scans and predictions. To do this, the control device 7 will be provided with the ability to save the spectrum and predictions locally and synchronize them onto the server 64 when networked (e.g. over a USB, WiFi, bluetooth or 4G network). The control device 7 will also have the capability to receive an update method from the server 64 when synchronizing. It may be desirable in this context to employ a bar code reader to select the appropriate method.

The method software 62 will be able to send the unknown spectrum to the engineering design through the server 64 for further evaluation or calibration updates.

In addition to the save and execute method, the application method 62 on the control device 7 will be able to set and check the health of the spectrometer 1, e.g. to make reference measurements. The "diagnostic" capabilities of the compact spectrometer 1 will include measurements made in accordance with external wavelength accuracy standards (NIST 2036 or equivalent) and confirm that the instrument accuracy is intact. Photometric noise and linearity calculations also need to be performed. The diagnostic scan may be performed at initial startup or on demand by the user.

In another alternative configuration shown in fig. 16, the compact spectrometer 1 and the control device 7 are connected to each other and to a server 71 of the user through a wireless network 72. One example of such a system is a receiving dock located at a pharmaceutical company. The method files 62 and prediction engine 63 are stored on the server 71 instead of on the control device 7. In the infrastructure mode, the user will be able to (and may even be required to) scan the barcode 73 of the sample 15 to be analyzed. Software stored in non-volatile memory and executing on the control device 7 will use a bar code recognition algorithm on the pictures taken by the camera on the control device 7, use the bar code 73 to select the appropriate method from the server 71, and appropriately mark the recorded spectrum and results for display and storage. The user will then scan the material by pressing the integrated scan button of the compact spectrometer 1. The user may also wish to control the scanning from the control device 7. When the scan is complete, the user will look at the predicted result on the control device 7 and confirm the result based on the method. If the bar code integration is not in effect at the user site, the user should be able to select the appropriate method file from the list stored on the server 71 before using the compact spectrometer 1 for spectrum acquisition.

In one particular case in infrastructure mode, the operator can configure the compact spectrometer 1, including selecting a method, and then carry only the spectrometer 1 to scan the sample in a single pass/no pass evaluation. In this mode, the spectrometer 1 will communicate with the control device 7 and be triggered by the integrated scan button via the WLAN 72, providing audible, visual or tactile (vibration) feedback depending on the pass/fail result.

The method, spectrum and results will all be saved/stored on the user database server 71, not on the control device 7. Furthermore, the method may also be performed on a local cloud, i.e. the server 71, with the results being transmitted back to the control device 7, these being transparent to the user. A user with appropriate rights should be able to view the results from multiple compact spectrometers 1 and, through interaction with the local cloud, provide rights management for multiple users, such as the ability to generate or use only methods. In this case, it is necessary to use software conforming to part 11 of the 21 CFR; each user should have different "administrative" rights to enable a trained operator to use the compact spectrometer 1 only when it is licensed. Section 11 of 21CFR also provides a data verification mechanism in which any data cannot be deleted and changed without proper authorization. The local server 71 is expected to be an integral part of the 21CFR part 11 combiner.

In another configuration, highly targeted for compact spectrometer 1 applications, a cloud computing based core architecture is crucial. The core architecture and measurement process are similar to that shown in fig. 16.

The user of this configuration is a beginner, not necessarily having the experience of near infrared technology or spectrometer 1. The user only has to rely on the spectrometer 1 to provide an answer based on one very specific sampling and testing step. The typical term is "standard practice", SOP. Law enforcement personnel, hazardous article technicians or military personnel are preferred examples.

A sophisticated app on the control device 7 will guide the user in the initialization and configuration of the compact spectrometer 1. The app will download updates and methods as needed from the spectrometer provider's server 71 located in a remote and secure location, such as via one or more networks, such as the internet, and report diagnostic information onto the spectrometer provider server 71. In this configuration, the option is provided to: full characterization of the instrument and periodic verification as per baseline and zero will no longer necessarily need to be done on site, and setup can be done fully automatically.

In the "cloud operating mode," the spectrometer provider's personnel will be responsible for managing the method software 62 and monitoring system health and performance. The method software 62 will be owned and managed by the spectrometer 1 provider. Thus, any updates to the method software 62 need to be "pushed" to the local subscriber repository.

Similarly, the results and data produced by the spectrometer 1 will be transferred back to the server 71 of the spectrometer provider (or its partner) and archived for possible later use. The data returned from the end-user sample 15 to the spectrometer provider server 71 will be screened for statistical simplicity or uniqueness, depending on the results from the field and further analysis of the spectra uploaded by the methods applied at the spectrometer provider server 71. If the sample is considered unique when compared to the spectrometer provider's library, the spectrum will be marked as a possible addition to future method updates (and the user will be notified and asked to provide more information). In essence, this is the collection of unique samples for future addition to the model to account for any variability that the prior methods have not been able to account for.

Claims (21)

1. A portable spectrometer device comprising:

an illumination source for directing light towards the sample;

a TLP tapered light pipe for collecting light that interacts with the sample at a first focal ratio and for transmitting light at a second focal ratio that is lower than the first focal ratio;

a linear variable filter LVF for separating the collected light into spectra of component wavelength signals; and

a detector array comprising a plurality of pixels for providing a power reading for each constituent wavelength;

wherein each of the plurality of pixels is arranged to receive at least a portion of one of the constituent wavelength signals,

the TLP includes a smaller first end for placement near the sample, a wider and higher second end adjacent the LVF, and sidewalls diverging from the smaller first end to the wider and higher second end for mixing and propagating light across the LVF, and

the linear variable filter LVF and the detector array are separated by a gap comprising an optically clear adhesive.

2. The portable spectrometer device according to claim 1, wherein the TLP accepts light at a first focal ratio of f/1 and a cone angle between 20 ° and 40 ° and transmits the reflected light to the LVF at a second focal ratio slower than f/3 and a cone angle less than 10 °.

3. The portable spectrometer device according to claim 1, wherein the TLP includes a lensed exit face for straightening the tilted beam for delivery to the LVF.

4. The portable spectrometer device of claim 1, wherein the gap is less than 200 μm to improve spectral resolution.

5. The portable spectrometer device according to claim 1, wherein the gap ensures that a single line on the linear variable filter LVF forms a line of one pixel width on the detector array.

6. The portable spectrometer device of claim 1, wherein said Linear Variable Filter (LVF) is glued directly onto said detector array; and the optically clear adhesive has a thickness of 5 to 15 micrometers.

7. The portable spectrometer device as in claim 1, further comprising a tapered light pipe shield comprising a support portion for supporting the TLP and a spacing portion for spacing the TLP from the sample, thereby ensuring that light from the sample is delivered to the TLP at a desired acceptance angle defined by the first focal ratio f/1 and a cone angle of about 30 °.

8. The portable spectrometer device as in claim 7, wherein said spacing section comprises stepped inner walls to reduce specular light reaching said tapered light pipe TLP.

9. The portable spectrometer device of claim 1, further comprising a housing and a control system located within the housing, the control system comprising a processor, suitable non-volatile memory, and a USB connector for receiving a USB cable to enable data transfer between the processor and a host computer.

10. The portable spectrometer device of claim 1, further comprising a bluetooth or WIFI chip for communicating with a control device that sends the test steps and receives the test results.

11. The portable spectrometer device of claim 1, further comprising a battery or USB cable connector for providing less than 2.5W of power to the portable spectrometer device.

12. The portable spectrometer device according to claim 1, further comprising a housing for enclosing the illumination source, the TLP, the LVF and the detector array, wherein the housing has dimensions less than 2 inches by 2 inches.

13. The portable spectrometer device according to claim 12, wherein the weight of the housing, the illumination source, the TLP, the LVF and the detector array is less than 0.5 lbs.

14. The portable spectrometer device according to claim 1, wherein said illumination light source comprises at least one light source disposed at an acute angle to a longitudinal axis of said linear variable filter LVF for creating a spot on said sample, whereby light is reflected from said sample along said longitudinal axis into said linear variable filter LVF.

15. The portable spectrometer device according to claim 14, wherein each of said at least one light source arranged at an acute angle to the longitudinal axis of said linear variable filter LVF comprises a vacuum tungsten lamp with a lens at the end for forming a spot of less than 5mm on said sample.

16. The portable spectrometer device of claim 1, wherein the illumination source comprises two light sources; and one end of the TLP is placed between two of the light sources.

17. The portable spectrometer device of claim 1, further comprising a temperature feedback system for adjusting the power reading of each constituent wavelength signal based on ambient temperature.

18. A spectrometer system comprising:

the portable spectrometer device of claim 1;

a control device operably coupled with the portable spectrometer device for controlling the portable spectrometer device; and

a server operatively coupled with the portable spectrometer device and the control device via a wireless data network for storing spectra.

19. The spectrometer system of claim 18, wherein the control device is configured to receive the spectrum from the portable spectrometer device; comparing the spectrum to a library of spectra; and outputs the result of the comparison.

20. The spectrometer system of claim 18, wherein the server is configured to receive the spectrum from the portable spectrometer device; comparing the spectrum to a library of spectral models; and outputs the result of the comparison.

21. The spectrometer system of claim 20, wherein the server comprises a library of scan features and spectral models;

the control device includes a barcode reader, wherein in operation the barcode reader reads a barcode corresponding to the sample, the control device communicates information associated with the barcode to the server, and the server selects scan features and spectral models from the barcode for comparison that are included in the library of scan features and spectral models.