Vapor sensor

Install flammable and/or toxic vapor sensors where needed... 

Stitzel S. E., Stein D. R., Walt D. R., Enhancing vapor sensor discrimination by mimicking a canine nasal cavity flow environment, J. Am. Chem. Soc. 2003 125 3684-5. 

The major potential application of active carbon fibers is as an adsorbent in environmental control, as outlined in the previous section. However, there is a number of smaller scale, niche applications that seem to be particularly suited to ACF. These emerging applications include the use of ACF in medicine [111 (see also 59,60),112], as capacitors [113-119] and vapor sensors [120], and in refrigeration [121]. The first two of these applications are summarized below. However, there are not many detailed, publicly-available sources describing any of these applications, partly for commercial reasons and partly because the technology is emerging, so any summary is necessarily limited in scope. 

The contributed chapters are divided into three sections. The first section is dedicated to chemical vapor sensing. In the majority of the photonic vapor sensors described here, a layer of vapor sensitive material (polymer, ceramics, or colloidal... 

Gao, T. Gao, J. Sailor, M. J., Tuning the response and stability of thin film mesoporous silicon vapor sensors by surface modification, Langmuir. 2002, 18, 9953 9957... 

Chemical vapor sensors play an ever-increasing role in the environmental monitoring, homeland security, defense, and health care. The desirable characteristics of a chemical vapor sensor include ultrahigh sensitivity, specific and rapid response to certain vapor molecules, as well as the ability for on-the-spot chemical analysis, which usually requires the sensor to be small, portable, reusable, stable, robust, and cost effective. Toward this end, various sensing techniques have been studied... 

So far, there are four basic ring resonator configurations that can potentially be used as a vapor sensor, the first three of which are shown in Fig. 6.1. They include... 

Fig. 6.1 Various configurations of ring resonator vapor sensors...

Fig. 6.3 Four layer model for the OFRR vapor sensor. OD ring resonator outer diameter / polymer thickness d ring resonator wall thickness , n2, n2, and are the refractive indices for the medium inside (air), polymer, silica ring resonator, and medium outside (air), respectively...

Theoretical Analysis of the OFRR Chemical Vapor Sensor... 

For the OFRR-based vapor sensor, the ring resonator wall thickness has a significant impact on the sensor performance. Since the polymer layer is treated as the extension of the ring resonator, the relative thickness between the wall and the polymer determines the radial intensity distribution of the WGMs. As a result,... 

Smooth and uniform polymer surface after vacuum plays a key role to ensure good OFRR sensing performance. We have observed in experiments that toluene after vacuum is prone to leave a number of cavities of a few micrometers in diameter on the surface. These cavities will induce additional scattering loss for the WGMs in the OFRR, which greatly degrade the g-factor, and hence the detection limit of the OFRR vapor sensor. Moreover, these small cavities have different adsorption characteristics compared to smooth polymer surface. Vapor molecules may be retained for a longer time at the cavity, which increases the response time and recovery time. Acetone and methanol are found to be better candidates for solvents because they usually leave uniform and smooth surface after vacuum. 

In this part, we demonstrate OFRR s capability as a rapid chemical vapor sensor. During experiments, ethanol and hexane vapors are used as a model system and represent polar and nonpolar analytes, respectively. 

Fig. 6.14 (a) OFRR vapor sensor responses to DNT vapor samples extracted with various sampling time at room temperature, (b) Calibration curve of DNT mass extracted by on SPME fiber under various extraction times at room temperature... 

Aemecke MJ, Guo J, Sonkusale S, Walt DR (2009) Design, implementation, and field testing of a portable fluorescence-based vapor sensor. Anal Chem 81 5281-5290... 

Bulk sensors certainly have a role in chemical sensing of explosives, but the subject of this book is the other basic type sensor, one that seeks molecules released from the bulk of the explosive material in an object. We will refer to these as trace chemical sensors. They are sometimes called vapor sensors, but that seems a less accurate description when they are applied to explosive molecules, which may not always be found in a vapor state. As we shall see in Chapter 5, that requires us to understand where and how to look for these molecules. It will become apparent upon a little reflection that the two types of sensors are complementary and are best used in different situations. Furthermore, even when trace sensors are used, in some situations sampling of particles of soil or vegetation or sampling from surfaces may prove to be more productive that vapor sampling. For underwater sources the term vapor sensing is also inappropriate. 

The underwater sensor platform is derived from the Fido explosives vapor sensor, originally developed under the Defense Advanced Research Projects Agency (DARPA) Dog s Nose Program. The vapor sensor, whose operation is discussed in Chapters 7 and 9 and in other publications [7-9], was developed for the task of landmine detection. The underwater adaptation of the sensor is very similar to the vapor sensor. In the underwater implementation of the sensor, thin films of polymers are deposited onto glass or sapphire substrates. The emission intensity of these films is monitored as water (rather than air) flows past the substrate. If the concentration of TNT in the water beings to rise, the polymer will exhibit a measurable reduction in fluorescence intensity. The reduction in emission intensity is proportional to the concentration of target analyte in the water. Because the sensor is small, lightweight, and consumes little power, it proved to be ideal for deployment on autonomous platforms. 

EXPLOSIVES DETECTION USING ULTRASENSITIVE ELECTRONIC VAPOR SENSORS FIELD EXPERIENCE... 

---