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Plastic Encapsulated Optical Head for IR Gas Sensor

IP.com Disclosure Number: IPCOM000228760D
Publication Date: 2013-Jul-04
Document File: 6 page(s) / 244K

Publishing Venue

The IP.com Prior Art Database

Related People

Jonathan Stephen Mifsud: INVENTOR [+3]

Abstract

Photoacoustic spectroscopy is widely used to determine the concentration of the gas. In photoacoustic spectroscopy the photoacoustic sensor converts the optical energy of a modulated light into sound energy. Depending upon the concentration level of the gas a particular amount of the light radiations is absorbed by the gas and pressure fluctuations or sound is generated. These pressure fluctuations or sound waves are detected by the microphone and the corresponding concentration levels of the gases are determined. It can be noted that the detected level of gas is sensitive to noise generated due to external factors such as wind or vibrations as these may leading to additional pressure fluctuations. In the proposed solution, all the components are robustly sealed through a plastic injection molded body design which utilizes over-mold or two-shot injection molding techniques. The system helps in keeping away the system from most of the external factors such as vibration, wind and any leakage that contribute to pressure fluctuations or noise.

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Page 01 of 6

Plastic Encapsulated Optical Head for IR Gas Sensor

Jonathan Stephen Mifsud, Mike Poulter, Paul Westmarland

ABSTRACT

Photoacoustic spectroscopy is widely used to determine the concentration of the gas. In photoacoustic spectroscopy the photoacoustic sensor converts the optical energy of a modulated light into sound energy. Depending upon the concentration level of the gas a particular amount of the light radiations is absorbed by the gas and pressure fluctuations or sound is generated. These pressure fluctuations or sound waves are detected by the microphone and the corresponding concentration levels of the gases are determined. It can be noted that the detected level of gas is sensitive to noise generated due to external factors such as wind or vibrations as these may leading to additional pressure fluctuations. In the proposed solution, all the components are robustly sealed through a plastic injection molded body design which utilizes over-mold or two-shot injection molding techniques. The system helps in keeping away the system from most of the external factors such as vibration, wind and any leakage that contribute to pressure fluctuations or noise.


1. Introduction

In sites such as chemical plant or a manufacturing place there is always a threat of potential leakage of hazardous gases. In such a potential hazardous situation rapid detection and identification of hazardous gases is a top priority. Increasing speed and sensitivity of the detection is critical for hazardous-materials detection technology. A highly sensitive technique 'photoacoustic spectroscopy' is introduced for this purpose which measures the effect of the absorbed energy of light on a gas by measuring the resulting sound.


Page 02 of 6

Figure 1: A typical assembly of a photoacoustic spectroscope (source:

http://www.acoustics.org/press/148th/pedersen.html)

It is known that absorption spectrum for gases are distinct hence; details such as concentration and type of gas can be obtained easily. It is further observed that the photoacoustic spectroscope is highly sensitive to external sources of noise such as wind and vibration. Hence, the measurement should be free from any noise in order to indicate correct measurements.

In past, people tried to solve the problem by having a reference measurement. For instance, as shown in Figure 2, in one of the US Patent Applications US6006585A the photoacoustic spectroscope includes a separate reference cell. The reference cell has same size and dimensions to the measurement cell. The reference cell is free from the radiation used to detect the concentrations in the measurement cell. The signal which indicates only the gas concentration can be obtained by subtracting the reference cell's signals from the measurement cell's signals. The subtraction of signals makes sure that the signals due to external disturbances such as air and vibrations substantially cancel out.


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Figure 2: FIG. 3 of US6006585A

The above mention...