175 research outputs found
Chemical event tracking using a low-cost wireless chemical sensing network
A recently developed low-cost light emitting diode (LED) chemical sensing technique is integrated with a Mica2Dot wireless communications platform to form a deployable wireless chemical event indicator network. The operation of the colorimetric sensing node has been evaluated to determine its reproducibility and limit of detection for an acidic airborne contaminant. A test-scale network of five similar chemical sensing nodes is deployed in a star communication topology at fixed points within a custom built Environmental Sensing Chamber (ESC). Presented data sets collected from the deployed wireless chemical sensor network (WCSN) show that during an acidic event scenario it is possible to track the plume speed and direction, and estimate the concentration of chemical plume by examining the collective sensor data relative to individual sensor node location within the monitored environment
Measurement of representative landfill gas migration samples at landfill perimeters: a case study
This paper describes the development of a fully integrated autonomous system based on existing infrared sensing technology capable of monitoring landfill gas migration (specifically carbon dioxide and methane) at landfill sites. Sampling using the described system was validated against the industry standard, GA2000 Plus hand held device, manufactured by Geotechnical Instruments Inc. As a consequence of repeated sampling during validation experiments, fluctuations in the gas mixtures became apparent. This initiated a parallel study into what constitutes a representative sample of landfill gas migration as reported to the Environmental Protection Agency. The work described in this paper shows that gas mixture concentrations change with depth of extraction from the borehole well, but with evidence of a steady state after a time
Monitoring of gas emissions at landfill sites using autonomous gas sensors
Executive Summary
This report details the work carried out during the Smart
Plant project (2005-AIC-MS-43-M4). As part of this
research, an autonomous platform for monitoring
greenhouse gases (methane (CH4), carbon dioxide
(CO2)) has been developed, prototyped and field
validated. The modular design employed means that the
platform can be readily adapted for a variety of
applications involving these and other target gases such
as hydrogen sulfide (H2S), ammonia (NH3) and carbon
monoxide (CO) and the authors are in the process of
completing several short demonstrator projects to
illustrate the potential of the platform for some of these
applications. The field validation for the greenhouse gas
monitoring platform was carried out at two landfill sites in
Ireland. The unit was used to monitor the concentration of
CO2 and CH4 gas at perimeter borehole wells. The final
prototype was deployed for over 4 months and
successfully extracted samples from the assigned
perimeter borehole well headspace, measured them and
sent the data to a database via a global system for mobile
(GSM) communications. The data were represented via
an updating graph in a web interface. Sampling was
carried out twice per day, giving a 60-fold increase on
current monitoring procedures which provide one gas
concentration measurement per month.
From additional work described in this report, a
number of conclusions were drawn regarding lateral
landfill gas migration on a landfill site and the
management of this migration to the siteâs perimeter.
To provide frequent, reliable monitoring of landfill gas
migration to perimeter borehole wells, the unit needs
to:
⢠Be fully autonomous;
⢠Be capable of extracting a gas sample from a
borehole well independently of personnel;
⢠Be able to relay the data in near real time to a base
station; and
⢠Have sensors with a range capable of adequately
monitoring gas events accurately at all times.
The authors believe that a unit capable of such
monitoring has been developed and validated. This
unit provides a powerful tool for effective management
of landfill site gases. The effectiveness of this unit has
been recognised by the site management team at the
long-term deployment trial site, and the data gathered
have been used to improve the day-to-day operations
and gas management system on-site.
The authors make the following recommendations:
1. The dynamics of the landfill gas management
system cannot be captured by taking
measurements once per month; thus, a minimum
sampling rate of once per day is advised.
2. The sampling protocol should be changed:
(i) Borehole well samples should not be taken
from the top of the well but should be
extracted at a depth within the headspace
(0.5â1.0 m). The measurement depth will be
dependent on the water table and headspace
depth within the borehole well.
(ii) The sampling time should be increased to 3
min to obtain a steady-state measurement
from the headspace and to take a
representative sample; and
(iii) For continuous monitoring on-site, the
extracted sample should be recycled back
into the borehole well. However, for
compliance monitoring, the sample should
not be returned to the borehole well.
3. Devices should be placed at all borehole wells so
the balance on the site can be maintained through
the gas management system and extraction
issues can be quickly recognised and addressed
before there are events of high gas migration to
the perimeter.
4. A pilot study should be carried out by the EPA
using 10 of these autonomous devices over three
to five sites to show the need and value for this
type of sampling on Irish landfill sites
Automatic reaction to a chemical event detected by a low-cost wireless chemical sensing network
A test-scale wireless chemical sensor network (WCSN) has been deployed within a controlled Environmental Chamber (EC). The combined signals from the WCSN were used to initiate a controllable response to the detected chemical event. When a particular sensor response pattern was obtained, a purging cycle was initiated. Sensor data were continuously checked against user-defined action limits, to determine if a chemical event had occurred. An acidic contaminant was used to demonstrate the response of the sensor network. Once the acid plume was simultaneously detected by a number of wireless chemical sensor nodes, an automatic response action, which was the purging of the EC with clean air, was initiated and maintained for a period of time until the WCSN indicated that normal status had been re-established
Additive BIO Fabrication: Impact, Opportunities and Challenges
In recent years we have outrun our ability to fabricate structures from the amazing materials that we can now create. While this can be said of many areas of materials research it is particularly so in the area of biomaterials. Here, we are often confronted with delicate compositions with nano- to microscopic features that will not survive the traditional (hammer and chisel) approach to fabrication. There is good reason why nature âgrowsâ complex, highly functional structures. Such structures with functionality determined by the spatial distribution of composition with nanodimensional resolution can not be chiselled from a slab of material.
Additive fabrication (AdFab), often referred to as 3D Printing, involves layer-by-layer deposition and fusion of materials to create customised structures. The structure to be produced can be conceptualised, manipulated and defined within a growing array of modelling environments; from conventional parametric Computer-Aided Design (CAD) solutions such as Solidworks⢠or ProEâ˘, through to free-form animation toolsets such as Autodesk 3ds Maxâ˘, and even free web-based applications like Tinkercad⢠(www.tinkercad.com). Once a design is completed, a file that describes the structuresâ surface geometry is generated and a set of digitised instructions then drives the printer to create the required structure layer by layer.
The fabrication process can involve several deposition modes. In fused deposition modelling / extrusion printing, a molten build material is deposited and solidified on cooling. For higher resolution structures (layer thicknesses as low as 16 Âľm), a fluid material precursor is ink-jetted onto a substrate and simultaneously transformed into a solid structure via a chemical reaction (UV induced polymerisation). Metal structures can be fabricated through a physical micron-scale welding process known as selective laser melting
The optimisation of a paired emitter-detector diode optical pH sensing device
With recent improvements in wireless sensor network hardware there has been a concurrent push to develop sensors that are suitable in terms of price and performance. In this paper a low cost gas sensor is detailed, and significant improvements in sensor characteristics have been achieved compared to previously published results. A chemical sensor is presented based on the use of low cost LEDs as both the light source and photodetector, coupled with a sensor slide coated with a pH sensitive colorimetric dye to create a simple gas sensor. Similar setups have been successfully used to detect both acetic acid and ammonia. The goal of this work was to optimise the system performance by integration of the sensing technique into a purposely deigned flowcell platform that holds the colorimetric slide and optical detector in position. The reproducibility of the sensor has been improved through this arrangement and careful control of deposited film thickness. The enhanced reproducibility between sensors opens the potential of calibration-free measurement, in that calibration of one sensor can be used to model the characteristics of all sensors in a particular batch
A printed bio-mimetic fish for the detection of chemical pollutants in water bodies
Monitoring of chemical contaminants within the Environment operates predominantly through manual gathering of samples, transportation to centralised laboratories, and analysed by means of sophisticated instruments. This process is expensive and therefore faces limitations under the demands of current and forthcoming bodies of legislation, e.g. the Water Framework Directive.
Recent technological breakthroughs have allowed for the realisation of static analytical systems capable of autonomously monitoring key chemical targets in situ. The challenge at present is to reduce the cost of such systems while meeting the demands of legislation. An alternative approach may exist in a moveable device capable of monitoring large water bodies using a single platform
A wearable electrochemical sensor for the real-time measurement of sweat sodium concentration
We report a new method for the real-time quantitative analysis of sodium in human sweat,
consolidating sweat collection and analysis in a single, integrated, wearable platform. This temporal
data opens up new possibilities in the study of human physiology, broadly applicable from assessing
high performance athletes to monitoring Cystic Fibrosis (CF) sufferers. Our compact Sodium Sensor
Belt (SSB) consists of a sodium selective Ion Selective Electrode (ISE) integrated into a platform that
can be interfaced with the human body during exercise. No skin cleaning regime or sweat storage
technology is required as the sweat is continually wicked from the skin to a sensing surface and from
there to a storage area via a fabric pump. Our results suggest that after an initial equilibration period,
a steady-state sodium plateau concentration was reached. Atomic Absorption Spectroscopy (AAS) was
used as a reference method, and this has confirmed the accuracy of the new continuous monitoring
approach. The steady-state concentrations observed were found to fall within ranges previously found
in the literature, which further validates the approach. Daily calibration repeatability (n 1â4 4) was
+/- 3.0% RSD and over a three month period reproducibility was +/- 12.1% RSD (n 1â4 56). As a further
application, we attempted to monitor the sweat of Cystic Fibrosis (CF) sufferers using the same device.
We observed high sodium concentrations symptomatic of CF ($60 mM Na+) for two CF patients, with
no conclusive results for the remaining patients due to their limited exercising capability, and high
viscosity/low volume of sweat produced
Video analysis of events within chemical sensor networks
This paper describes how we deploy video surveillance techniques to monitor the activities within a sensor network in order to detect environmental events. This approach combines video and sensor networks in a completely different
way to what would be considered the norm. Sensor networks
consist of a collection of autonomous, self-powered
nodes which sample their environment to detect anything
from chemical pollutants to atypical sound patterns which
they report through an ad hoc network. In order to reduce
power consumption nodes have the capacity to communicate
with neighbouring nodes only. Typically these communications
are via radio waves but in this paper the sensor nodes communicate to a base station through patterns emitted
by LEDs and captured by a video camera. The LEDs are chemically coated to react to their environment and on doing so emit light which is then picked up by video analysis.
There are several advantages to this approach and to demonstrate we have constructed a controlled test environment.
In this paper we introduce and briefly describe this
environment and the sensor nodes but focus mainly on the
video capture, image processing and data visualisation techniques
used to indicate these events to a user monitoring the
network
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