Article

Modeling of Infrared Gas Sensors Using a Ray Tracing Approach

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Abstract

Many gas molecules absorb electromagnetic radiation at characteristic wavelengths in the infrared region. This absorption can be used to identify defined substances like CO<sub>2</sub>, ammoniac, and so forth. A lot of different types of gas sensors are based on the principle of infrared absorption like photoacoustic sensors (e.g., Golay cells), dispersive infrared instruments (e.g., utilizing a diffraction grating), or Fourier transform infrared (FTIR) spectrometers. However, the most commonly used types of infrared absorbing gas sensors are nondispersive infrared (NDIR) sensors. Such a NDIR gas sensor consists of some basic function blocks, i.e., an IR-source, the sensor cell or optical path containing the sample gas, a gas specific filter, and an IR-detector. One of the central issues in the design of this kind of sensors is the geometry of the sensor cell. In this paper we investigate the use of statistic ray tracing to predict the efficiency of 3-D cell geometries for NDIR gas sensors. We demonstrate the feasibility of the method and show examples on how to apply it on given 3-D sensor models where we illustrate the agreement between simulated and measured gas response data.

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... Further miniaturisation may also result from work to include an high NA Fresnel lens [9] integrate and to integrate detectors and filters on a single base substrate [10] . There have been various studies to improve device performance using optical raytracing, aimed at providing longer optical pathlengths [11] and / or improving light collection efficiency [12,13] . However, none of this raytracing work has resulted in sensors as small as the pellistor format. ...
... We used the Zemax [16] commercial raytracing package for the design process. In common with Mayrwöger et al [11] , we required use of non-sequential raytracing in three dimensions, in which rays are permitted to strike any object, in any order. This feature increased processing time, such that it became impossible to use a number of automated optimisation and tolerancing features, however was essential for our design. ...
Article
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Non-dispersive infra-red (NDIR) gas detection has enjoyed a widespread uptake as a result of the development of sensors in the so-called pellistor format, consisting of a cylinder with external dimensions of 20 mm diameter x 16.5 mm height. We present a new design for such a sensor, making use of low-cost injection moulding technology. The new design pays particular attention to the problem of maintaining a high optical throughput while providing an acceptable optical pathlength for gas detection. A detailed analysis of the design is presented, with the results of optical raytracing, showing a raytrace estimate of 4% of the total emitted radiation reaching each of two separated detector elements and an optical pathlength of 32mm. The high throughput provides a number of advantages in helping to overcome detector noise in NDIR measurements. Finally, we show experimental results obtained with asmanufactured devices, demonstrating the superior signal to noise ratio achieved in measurement of carbon dioxide (CO2). We believe the optical efficiency of the device, and the improved signal to noise ratio that results from this, to be a record for a device of these dimensions.
... Various groups have reported studies of novel gas cell designs using a ray tracing approach. Mayrwöger et al have used the Zemax software package to evaluate 3 different cell designs including a hollow, internally reflective tube (25mm long x 3mm diameter), an internally reflective ellipsoid (principal axes 55 mm and 20 mm) and a spiral design within a cylinder of dimensions 30 mm diameter x 10 mm height [15]. Each design incorporated a standard microbulb and a single element detector within a 9 mm diameter TO-5 can. ...
... We used the Zemax [26] commercial raytracing package for the design process. In common with Mayrwöger et al [15], we required use of non-sequential raytracing in three dimensions, in which rays are permitted to strike any object, in any order. This feature increased processing time, such that it became impossible to use a number of automated optimisation and tolerancing features, however it was essential for our analysis. ...
Article
Non-dispersive infra-red (NDIR) gas detection has enjoyed widespread uptake as a result of development of devices in the standard miniature format for gas sensors, consisting of a cylinder with external dimensions of 20 mm diameter x 16.5 mm height. We present a new design for such a sensor, making use of low-cost injection moulding technology. The design pays particular attention to the problem of maintaining a high optical throughput while providing an acceptable optical pathlength for gas detection. A detailed analysis of the design is presented, with the results of optical raytracing, showing a raytrace estimate for 4% of the total emitted radiation reaching each of two separated detector elements and a pathlength of 32 mm. Finally, we show experimental results obtained with as-manufactured devices, with a short-term limit of detection for carbon dioxide (CO2) estimated at 1 ppm or a noise equivalent absorption (NEA) of 3 x 10(-5) AU.
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... The light concentration is generally enhanced by manipulating the optical cavity structure using commercial ray tracing software Tracepro as shown in Fig.1 and we designed the asymmetry gas cavity to reduce the dimension of gas sensor with deviation of the center of inner circle and outer circle [4,5]. ...
Article
Full-text available
Many gas molecules absorb electromagnetic radiation at characteristic wavelengths in the infrared region. This absorption can be used to identify defined substances like CO2, ammoniac, and so far. This study presents a comparative analysis of parameters of infrared radiation source and detector hardware that are most important for the creation of portable optical nondispersive infrared (NDIR) gas sensors. One of the central issues in the design of this kind of sensors is the geometry of the sensor cell. In this paper we investigate an asymmetry sensor cavity and predict the performance using Tracepro software. Then, the CO2 sensor is made and tested.
... Finally the resulting sensor performance is calculated. For a more detail description of the entire ray tracing process see [15]. ...
Article
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... To calculate the response to CO 2 and H 2 O of the total sensor system, we apply a ray tracing approach using a Monte-Carlo method [8] [9]. The modeled sample cell for the simulations is demonstrated in Fig. 4, in which the influence of the glass plate is included in model of the detector. ...
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Full-text available
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... Il existe différentes méthodes pour modéliser la source d'excitation des molécules de gaz. [83][84][85]. L'un des avantages de la cellule DHR, et nous le verrons dans le Chapitre 3, est que la génération de signal photoacoustique ne dépend pas fortement de la distribution spatiale de la source mais de l'énergie déposée dans la cellule [83]. Il est donc possible d'utiliser une distribution uniforme du dépôt d'énergie dans la cellule. ...
Thesis
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... Many gas molecules absorb electromagnetic radiation at characteristic wavelengths in the infrared region (Mayrwoger et al., 2010). This absorption can be used to identify defined substances like CO 2 , ammonia, and so forth. ...
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The paper reviews and discusses the opportunities and threats associated with the use of Liquefied Petroleum Gas and how to ameliorate the threats by the use of electronic gas detectors. Most developing countries now use Liquefied Petroleum Gas (LPG) as a source of fuel mainly for cooking in homes and premises to substitute for charcoal and firewood in response to the bid to save the planet from green gas effects. This paper looks at the opportunities and threats of the usage of LPG and serves as a prelude to a comprehensive paper, which proposes a design solution to the threats of having to live together with LPG gas cylinders at homes and elsewhere. This paper brings to light, the emerging issues with the use of LPG especially in homes and premises in Ghana. It also enumerates incidences of gas explosions due to LPG leakages and concludes with the evolution of gas detection from the use of canaries to gas sensors. The recommendation is to use appropriate electronic gas detectors to reduce the risks associated with the use of LPG especially in homes.
... Direct, gas-phase absorption measurements also remain promising if sensitivity and selectivity can be improved. One active area of research for NDIR sensing is minor modifications to the measurement cell shape to lengthen the effective path-length for the absorption measurement [88]. Han et al. recently have described a stair-tapered reflector cell that increased sensitivity by > 25% [89]. ...
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... So we research the effective temperature compensation method. The other issue is optical chamber, and therefore we compare and analyze the detecting performance in the conventional optical chambers covered with gold plating and chrome plating[7, 8]. ...
... Only reflection and refraction at locally plane interfaces are taken into account. The method of choice is the combination of raytracing with the Monte Carlo method [22,23]: a large number of rays are followed individually from their random generation at the light source to their exit of the domain. ...
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Thesis
Respiratory Carbon dioxide (CO2) contains substantial amount of information that can be used to diagnose and treat pulmonary diseases. Many devices have been developed for this purpose, such as capnography, vital monitor, peak flow meter, spirometer etc. There are many CO2 sensor are available in the market but among them NDIR based sensors are considered to be most inexpensive with its accuracy in terms of sensitivity and fast response time. There are commonly two types of technology available for detection; mainstream and sidestream. Mainstream technology is preferable than sidestream because sidestream is not applicable in intubated patients and at the same time it tends to give delay in detection due to longer transmission tube. Most of the NDIR CO2 sensor are being used for the environmental CO2 detection and there are very few mainstream NDIR based CO2 sensor are available in the market. These sensor have a vast number of advantages with some disadvantages as well; such as high response time, thermal noise, temperature increase and others. This project proposed the specification of the electrical circuit of the NDIR CO2 sensor combined with a gas chamber to detect human respiratory CO2. To determine the specification of the CO2 sensor circuit, the components value has been calculated and then the circuit design has been carried out by using Multisim Software. The overall CO2 sensor circuit has six circuit blocks named oscillator, driver circuit, preamplifier, voltage regulator, rectifier, LPF and each of the blocks were built and simulated in the Multisim software. After the simulation the circuit has been built on breadboard to test the output. An IR source from International Light Technologies (ILT) 4115-2A and pyroelectric photodetector L2100X2020 from laser component were used for this project as NDIR components. After the successful simulation from breadboard a gas acquisition cell has been designed to acquire the human CO2 gas. The design has been done by using Solid Works software and printed from a 3D printing machine. The material used for this chamber was ABS. After placing all the calculated components with the source and detector the output has been observed on the digital oscilloscope as a capnograph wave form showing the voltage range. These waveforms are being used in a capnometer determining respiratory diseases. The circuit shows a response time of 6 second with less noise and the waveform showed clear view of detected CO2 without any temperature increase.
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Lehrbuch der Experimentalphysik Band III Optik
  • H.-J Eichler
  • H Gobrecht
H.-J. Eichler and H. Gobrecht, Lehrbuch der Experimentalphysik Band III Optik. Berlin, Germany: de Gruyter, 1978, 7. Auflage.