Moving Towards Ubiquitous Spectral Sensing

Transcription

1 Moving Towards Ubiquitous Spectral Sensing Deploying a -based approach for consumer-level pricing and scalability Ahmed Korayem Saïd Meet us at Laser World of Photonics Hall B2 Booth 340 Material analysis tools have long been an important asset for research and production in a range of domains and markets, and have transformed our knowledge, development and quality control capabilities over time. Academic teams use material analysis for assessing composition and detection of chemicals in disciplines ranging from archaeology to medicine, food analysis, agricultural research, and biotech. Company Si-Ware Systems Cairo, Egypt Material analysis for commercial production and quality control has become increasingly important over time as analysis equipment has moved from massive and expensive stand-alone units to more manageable benchtop apparati. The development of more compact tools has resulted in a proliferation of labs eager to provide their services for detection of chemicals and analysis of composition within samples sent to them. This equipment can include mass spectrometers, FTIR (Fourier transform infrared) spectroscopy, gas chromatography, and advanced imaging, among others. Still, despite increasing lab space and the growth of analysis services, many Si-Ware Systems (SWS) is an independent fabless semiconductor company that fosters silicon innovation through two main businesses ASIC Solutions and Optical Technology. The ASIC Solutions group provides custom ASIC development and supply, specializing in analog / mixed-signal and RF design. The Optical Technology group developed the world s first single-chip FT-IR spectrometer, NeoSpectra, that allows the creation of multiple optical components on silicon. A -based FT-NIR approach enables spectroscopy at a size and price point for consumer applications. Pictured: A prototype application for detecting gluten with a smartphone, using software developed by GreenTropism and a case developed by XPNDBLS. sectors face time-sensitive bottlenecks and high costs as they are forced to send factory floor or field samples to a thirdparty or central company lab while delaying processed food production, holding back on important medical decisions, keeping tankers of petrochemicals at the refineries, or watching crop planting windows shrink. Add to this the opportunity for consumer-based material analysis and the industry is seeing a woeful shortage of capability. While the consumer market has yet to be widely introduced to the benefits of material analysis, experts are seeing large possible markets for detection of chemicals in foodstuffs in retail environments, in particular for allergens such as nuts, gluten, dairy and caffeine, and for ripeness of perishables. Other consumer markets include non-invasive detection and analysis of body chemistry markers such as glucose. What the industry requires to make ubiquitous spectral sensing a reality is a spectrometer on a chip. This article maps out one path to get there. A versatile spectroscopy approach: near-infrared Near-infrared (NIR) spectroscopy is a well-established technique for material quantification and qualification in many applications. The principle behind NIR is to derive a spectral signature from a particular material by shining a broadband light on a sample and measuring its spectral response (Fig. 1). The spectral response is used to perform identification and / or quantification analysis using pre-developed analysis models. Unlike other material analysis approaches, NIR can provide accurate data immediately on multiple chemical and physical parameters at the same time, with little to no preparation of different sample types. In contrast to wet chemical and other conventional analysis methods, there is no need to wait for certain transformations to happen in the sample. The technique has been widely adopted for performing non-destructive 26 Optik&Photonik 3/ WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2 Spectroscopy material analysis tests in several domains, including food quality control, pharmaceutical purity, oil and gas composition, medical sample diagnostics and others. In an added benefit, NIR light can even pass through plastic and glass to analyze materials inside a container. NIR barriers to wide deployment However, while the benefits of NIR spectroscopy offer major advantages including rapid results and some portability for onsite use, technical and market barriers have constrained development of versatile tools for broader commercial use, not to mention consumer use. The obvious prerequisite for a consumer device or even any wider commercial deployment is miniaturization, for incorporation into a comfortable mobile device form factor. A second prerequisite is an affordable price point. NIR spectroscopy has indeed seen some significant advances in the last ten years equipment has evolved from larger benchtop devices costing more than $ 100,000 to in-line process analyzers priced at more than $ 50,000, and even some bulky handheld units hovering in the $ 30,000 range. However, even with present advances such as gratings and NIR modules suitable for B2B design-in, these devices still cost between $ 10,000 and $ 20,000 each and are only one part of a complete system. Clearly, more integration is necessary to achieve viable pricing. Finally, to truly enable consumer market penetration, the industry requires high volume scalability, so that NIR-based components and equipment can be produced quickly and reliably in the hundreds of thousands of units. Given the need for robust, high-accuracy optics and circuitry, there is no choice but to move towards semiconductor style manufacturing. In essence, spectrometers must be as cheap as chips. The question is what approach can get the industry to that point. New approaches to NIR spectrometry targeting market growth A number of techniques have been developed to achieve better integration and smaller form factors for a NIR device, including micromirror arrays, linear variable filters, tunable Fabry-Perot filters, and many others. These techniques have successfully helped with the miniaturization of spectrometers to unprecedented form factors and they offer decent performance that may be sufficient for some applications that require portability. However, there are still additional features that must be enabled in order to facilitate integration of NIR spectral sensors into ubiquitous devices designed for use by average, non-expert consumers. These needed features revolve around size and price reduction as well as increased scalability. Perhaps more importantly, the creation of a truly versatile spectrometer demands an increase in spectral ranges covered by a single spectral sensor. Without this capability the use of a NIR spectrometer will be limited only to a narrow range of spectral signatures that may be of no use to consumers. % Reflectance % Reflectance opens the door to consumerlevel size, cost, and scalability A promising approach is using (micro-electromechanical systems) for the development of a FT-NIR device that meets the major requirements outlined above. When it comes to a device with moving parts such as mirrors, is already well-positioned as a technology, with a validated track record, and holding a major advantage. enables miniaturization to chip scale, uses semiconductor style wafers and etching techniques for high volume batch-style production, and can offer pricing at the component level. Capitalizing on mature microfabrication infrastructures, many fabrication facilities are now well equipped to handle the production of -based components. The emergence of moving structures on a very small scale that can be supplied in high volumes and at low fructose no calorie sweetner normal sugar sucralose Wavelength (nm) plain Cerelac Cerelac with milk powdered milk Wavelength (nm) Fig. 1 Measurements: The upper image shows the ability to detect different kinds of sugars based on spectral signatures. The lower image for measurements conducted on Cerelac infant cereal shows the spectral signature for plain Cerelac and also the presence of plain milk and powdered milk in the mixture WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Optik&Photonik 3/

3 cost has opened the door to new untapped markets, which now can include spectrometry and material analysis. Today, sensors are found in almost every mobile device. Si-Ware Systems arrived at a approach through its extensive parallel work in, ASIC development and photonics, and through the creation of a proprietary technology called SiMOST (silicon micro optical systems technology) that enables the replication of semiconductor capabilities for the photonics industry. The technology pulls from a library of well-characterized and validated optical and mechanical components to design and fabricate optical benches on a single silicon chip. The team used SiMOST to develop a fully monolithic Michelson interferometer with moving mirrors. The Michelson interferometer, the core of any FT-NIR spectrometer, is an optical interferometer where a beamsplitter splits the incident beam into two paths: one of the beams is reflected by a moving mirror, and the other is used as a reference when reflected by a fixed mirror. The moving mirror controls the optical path, or simply the delay, of the first beam and thus the two reflected beams interfere, producing a pattern that corresponds to the spectral content of the input light. The latter is captured by the single photo detector generating an interferogram. The spectrum of the input light is directly generated by applying a Fourier transform over the interferogram. Like other devices, the 3-dimensional SiMOST spectrometer design is printed onto masks, which are used to pattern the design over silicon wafers by photolithography. Then the patterns are etched in layers, using batch processes, and finally the chips are diced and packaged, providing unprecedented economies of scale and the associated reduced costs. As shown in the scanning electron microscope photo of the miniaturized version of the Michelson interferometer (Fig. 2), all the optical components (fixed mirror, moving mirror, and beamsplitter) as well as the mechanical components (a comb drive micro-actuator) are integrated onto the single chip. The components are aligned using a single photolithography process and fabricated using a single deep reactive ion etching (DRIE) process. The dedicated ASIC chip complements the interferometer s function to create a full spectrometer. The ASIC generates the electrical signals that drive the micro-actuator. Additionally, the ASIC reads data from the photodetector and performs signal conditioning functions. It also operates digital signal processing techniques on the detector ASICs 18 mm glass lid 18 mm Fig. 3 Exploded view of the spectral sensor in a chip-scale package measured data (optical signal and mirror position) to generate the spectrum. In conventional FT-NIR spectrometers, the moving mirror s position is determined using a He-Ne laser system: By detecting the laser beam reflected by the moving mirror, the mirror s position can be accurately determined. The version uses a novel technique, operated by the ASIC chip, where the capacitance of the comb drive is sensed. This capacitance variation is directly related to the moving mirror s position. light source moving mirror motor beamsplitter fixed mirror photodetector discrete moving mirror i/p fiber actuator beamsplitter fixed mirror o/p fiber Fig. 2 A conventional Michelson interferometer and a -based interferometer on a chip 28 Optik&Photonik 3/ WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

4 Spectroscopy Performance advantages In contrast to spectrometer instruments based on grating / dispersive techniques, which require detector arrays that include a large number of detection elements (128, 256, 512 or 1024, depending on the required resolution), FT-NIR devices require only a single photo detector to capture the optical power. In conventional FT-NIR instruments, the operating wavelength range is gated by the materials of the beam splitter and the photodetector in use. In the version, the beam is split using a single medium interface (silicon / air). This offers a stable splitting ratio over a very wide spectral range. In this way the operating wavelength range depends only on the photodetector in use. Covering wide ranges at the higher end of the NIR spectrum (higher than 1,150 nm up to 2,500 nm) allows simultaneous measurement of different materials with high accuracy. In addition, it allows measuring samples in different form factors including particles, flat surfaces and even ground samples with no need for sample preparation. This wide range makes the technology suitable for adoption in many industries. The resolution at a given wavelength depends on the maximum achievable optical path difference (OPD) between the two beams. Thus an instrument s resolution is mostly contingent on the maximum travel range of the moving mirror. For a given actuator, the stroke of mirror can be adjusted by applying the appropriate electrical signal. Hence, resolution of the spectrometer can be easily adjusted. Chip-sized NIR spectral sensors: from design to reality To capitalize on the potential of this technology to allow for the smallest, lowest-cost, and most scalable NIR spectral sensor, Si-Ware developed a chip-sized spectral sensor module. The photodetector, the chip, and the ASIC chips have been housed under one roof in a single 18 mm 18 mm package. The smaller footprint enables the creation of new usage models and applications for spectroscopy (Fig. 4). Portable spectrometry, in-line process monitoring, wireless spectrometry networks under an IoT umbrella, and integration into mobile consumer devices Fig. 4 The NeoSpectra Micro spectral sensor for mobile device applications, scheduled for volume production this year. are just a few examples. Each of these usage models can include qualitative and / or quantitative analysis of materials in different sectors, from medical to industrial, food and beverage, forensics, and law enforcement applications. Use case: portable soil analysis As an example of a new usage model made possible by the smaller FT-NIR form factor, a company called SoilCares, in the Netherlands, has incorporated the FT-NIR-based spectrometer into a ruggedized portable instrument for field use, called the SoilCares Scanner (Fig. 5). The tool includes a wide steel tube to plunge into the soil to secure a representative sample. When the button is pushed the scanner activates, obtains the soil signatures and relays them via mobile phone to a cloud-based database for a determination on the amount of nitrogen, phosphorus, potassium, and many other ingredients contained in the soil. The SoilCares Scanner now eliminates the tedious and hectic procedure of collection and delivery of soil samples by enabling in-field soil analysis. The company sells the tool to farmers worldwide, including developing countries, so they can determine soil health and get recommendations for the most appropriate soil treatments from the company s extensive global soil database. Use case: oil & gas quality control An oil refinery needed to set up cost effective spot-checking on a refinery production line. Rather than having to send samples to an onsite or offsite lab, the company used a compact FT-NIR engine to create a portable instrument that can scan oil and gas samples at various stages of production to ensure the right blend and consistency WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Optik&Photonik 3/

5 Fig. 5 The SoilCares portable soil spectrometer, built around the -based FT-NIR spectral sensor, to measure soil quality based on nitrogen, phosphorus and potassium levels, as well as other soil conditions. Use case: medical A medical firm in Utah decided that there had to be a more convenient and more accurate way for prediabetic patients to ascertain glucose levels and potentially delay onset and progress of the disease. They saw significant potential using near FT-NIR spectroscopy to conduct instant urinalysis within a toilet a regularly used piece of equipment. Currently, consumers who suspect they might be prediabetic must actively take steps on their own to check glucose levels using a urine test strip or a blood glucose meter. These methods require people to alter their routines, can prove awkward and difficult to use on a regular basis, and are error-prone due to the inexact nature of the test material and technology. During development and testing the company captured urine samples in a toilet equipped with a one-millimeter slot that retained the sample through capillary forces. The slot was situated just above the water level in the toilet. A light source illuminated the sample in the slot and the FT-NIR device measured the glucose. The result was that after data filtering, the device was able to display either a target range of glucose or an optimized indication of sharp upward or downward trends. The integration of NIR spectral sensing in so-called smart toilets is expected to revolutionize the way patients can easily monitor certain health conditions. Consumer spectroscopy and the era of ubiquitous spectral sensing The development of versatile based FT-NIR spectrometers in cost-effective chip-scale packaging promises to open up vast new markets. The samples that have traditionally been analyzed in labs in many industries can now be analyzed in the field, in-line on the factory floor, or using consumer devices in homes or at point of sale. As spectral sensors hit component-level size and cost, OEMs have limitless opportunities to incorporate these devices in a wide range of environments and to enable always-on material analysis. Taking the use case of an in-field soil sensor one step farther, such spectrometers could be implanted in the soil at intervals across a farm, continuously transmitting soil health data. Many industries can benefit from always-on process and quality control. Pharmaceutical sector production requires adherence to strict standards, while pharmacies and consumers alike need to guard against counterfeit products as well as prescription filling mistakes. The food and beverage industry needs quality control at all points in production, and retailers must be vigilant to avoid tainted products. Similarly, as the medical industry makes strides in non-invasive detection of chemical body markers using spectroscopy, patients can expect to see a plethora of home use devices to assist in both disease control and preventative healthcare. In the consumer space, spectral sensors can be used in detection of unwanted chemicals and ingredients. The anticipated demand for scanning of foodstuffs by shoppers, either at the store or at home, is high. Many consumers are keen to find out about potential allergen content, whether dairy, nuts, gluten or shellfish traces, and to detect ripeness or spoilage. As industry and commerce try new applications, we can expect to see those applications made available to consumers farther down the road. The capability will be incorporated into dedicated mobile devices, home appliances such as ovens or microwaves, and even into smart phones. Until now, such applications have been hindered by the cost, size, and scalability of available spectral sensors. Today, FT-NIR spectral sensors overcome these limitations and open the door for the creation of applications that have never before existed. DOI: /opph Author Ahmed Korayem Saïd is Product Marketing Lead NeoSpectra, Si-Ware Systems. Ahmed received his BSc in electrical engineering from the French University in Egypt, and his MSc in electric and computer systems from the University of Pierre & Marie Curie (UPMC). He has served as technical marketing lead for the FT-IR spectral sensor NeoSpectra module and the chip-scale NeoSpectra Micro from R&D through volume production. He joined Si-Ware Systems upon receiving his degree and works closely with customers, product development engineers, and business development teams to align NeoSpectra s offerings with market requirements. Ahmed Korayem, 3, Khaled Ibn Al-Waleed street, Sheraton, Heliopolis, Cairo 11361, Egypt, office: , x180, ahmed.korayem@si-ware.com, 30 Optik&Photonik 3/ WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim