innovative ad-hoc wireless sensor networks

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INNOVATIVE AD-HOC WIRELESS SENSOR NETWORKS

TO SIGNIFICANTLY REDUCE LEAKAGES

IN UNDERGROUND WATER INFRASTRUCTURES

Daniele Trinchero(1), Riccardo Stefanelli(1), Luca Cisoni(1),Abdullah Kadri(2), Adnan Abu-Dayya(2) , Mazen Hasna(3) , Tamer Khattab(3)

(1)iXem Labs, Electronics Department, Politecnico di Torino, Torino, Italy(2)Qatar University Wireless Innovation Center, Doha, Qatar

(3)College of Engineering, Qatar University, Doha, QatarABSTRACT

This paper presents an ICT solution to overcome the

problem of water dispersion in water distribution networks.

Leakage prevention and breaks identification in water

distribution networks are fundamental for an adequate use

of natural resources. Nowadays, all over the world, water

wasting along the distribution path reaches untenable

percentages (up to 80 % in some regions). Since the pipes

are buried within the terrain, typically only relevant breaks

are considered for restorations: excavations are very

expensive and consequently the costs to identify the position

of the leakage or just the position of the pipe itself are too

high. To address this problem, and simplify the leakage

identification process, the authors have designed a wireless

network system making use of mobile wireless sensors able

to detect breaks and reveal unknown tracks and monitor the

pressure spectrum of the fluid flowing in the pipe. The

sensors transmit the acquired data from the terrain to the

surface by use of a wireless connection. On the surface

ground there are stations that receive the signal, process it,

and communicate with a central unit where necessary

intelligent signal processing techniques are used to detect

leakage sources. Compared to other leakage detection

solutions already available in the market (such as: Ground

penetrating radar (GPR), pure acoustic techniques and

tracer gases), the proposed technique appears very efficient

and much more inexpensive.

Keywords Wireless sensor networks, Ad-hocnetworks, RFIDs, Green technology, radio-acoustic sensors

1. INTRODUCTION

Breakdowns and damages in fluid distribution systems

represent a problem of growing importance, due to their

fundamental role as a primary good that water and gas

symbolize all over the world [1]. This problem is

emphasized by the progressive decrease of water resourcesnot only in Equatorial Countries, but also in Western ones.

All over the world, water distribution networks are typically

old and suffer from leakages and dispersions. . On the other

hand, gas infrastructures are less affected by damages and

falls, but the cost and the strategic value of the resourcemakes relevant the effect of even small, rare or distributed

damages.

The restoration of damaged pipelines, especially when

pipes are deployed under the ground surface, requires high

complexity, first of all because the exact paths are generally

unknown, and secondly because, even when the path is

known, it is difficult to identify the exact location of the

damage along the conduit. Therefore, despite these breaks

represent for companies that manage fluid transportation

infrastructures, and consequently for the social community,

a huge dispersion of primary resources, the renovations are

complex and require long times to reach an acceptable

solution. From the point of view of the costs, the first factor

is represented by the technological process needed toidentify the leakage. Hence, it is strongly related to time

drawbacks. As an example, the detection of failures using

advanced technologies may cost 3200 USD per kilometer

when it is easy to identify the break, up to 65000 USD per

kilometer if the damage occurs in a complex metropolitan

environment. In general, expenses increase with the

complexity of the urban scenario, because of indirect costs

generated primarily by the excavation process. Especially

when works concern relatively huge areas, there can be an

unbearable effect on traffic, public services and business

activities. All these costs can be lowered by refining the

identification techniques with more accurate approaches.

Several monitoring techniques are available in the literature[2], [3], [4], [5]. Among all these, tracer gases [6] and

ground penetrating radars (GPR) [7], [8] appear to be very

promising since they do not require any direct connectionbetween the pipe and the outside, but they are not able to

identify small leakages or to survey the pipe before strong

damages occur. Gas tracing makes use of special gas

mixture, a mix of hydrogen (5%) and nitrogen (95%), used

to identify the conduit leakages within the ground. The gas

is inserted in the pipeline and subsequently is investigatedfrom the exterior using special instruments able to detect

the concentration of gas in the environment. The system

requires service interruption (tracer gases must replace the

fluid normally conducted in the pipe) and is very expensive,due to the high cost of the gas itself, together with the gas

sensors on the ground surface. GPR, on the other hand, may

Authors thank the Qatar National Research Fund (QNRF) forfinancing the project, in the framework of the National PrioritiesResearch Program (NPRP)

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allow an easy estimation of unknown tube paths, but cannot

provide a comprehensive monitoring of small pipedamages.

An automatic system able to measure electromagnetic

parameters of oil field pipes automatically has been

developed [9], so that the correct interpretation of steel pipe

defects can be provided. The fault of steel products can bedetected based on the eddy current technique, and an

automatic measuring technique is used to correlate results.

This system is applicable only to steel pipes, since it is

based on the measurement of steel electromagnetic

properties.

Accurate techniques make use of acoustic sensors [10], able

to detect the acoustic noise typically produced by the

presence of water losses and generated by the pressure

gradient between the inner side and the outer side of the

pipeline. The noise can be monitored on the pipe, in the

ground or within the pipe itself. I.e., it is possible to apply a

correlation technique to two measured acoustic/vibration

signals on the pipe, on either side of a leak [11]. Thetechnique that makes use of geophones [12] requires an

operator with high professional background and good

expertise, in order to identify the acoustic noise produced

by losses in the framework of an external acoustic

background. For this reason, the technique is critical in

urban environments with high background noise.

Furthermore, it becomes even more critical in case of largelosses and fluids with low hydraulic pressure. An

alternative acoustic solution is based on a time-domain

technique that makes an analysis of the noise propagation

delay. For this purpose, two different sensors are applied on

the pipe surface in separate positions. Synchronizing the

sensors and calculating the time taken by the noise to reachthe two probes, it is possible to identify the position of the

damage. Depending on the mechanical properties of the

material used to construct the tube, the technique works on

distances ranging from 50 to 200 meters.

More recently, it has been possible to deploy microphones

in the pipe, processing the data on-site, without the need of

a further elaboration. The main drawback, in this case, is

represented by the need to keep the flow of the sensor under

control, to reconstruct its position and make correlations

between sensor position and the monitored acoustic

spectrum [13].

Apart from the last one, all the known acoustic techniquesnormally require a direct wired connection with the sensor

on or inside the tube. Therefore they are inappropriate to

investigate pipes networks over long distances.

Furthermore, they do not provide useful solutions for the

detection of underground paths. To overcome these

drawbacks, our group has recently proposed a system able

to detect breaks and reveal unknown tracks by monitoring

the acoustic spectrum of the noise produced by the fluid

flowing in the pipe [14]. It transmits the detected

information on a wireless channel, hence it does not require

a physical connection to the surface, it gives an accurate

detection of the leakage location; it allows an easy and

repeatable identification of the track.

2. AN APPROACH BASED ON WIRELESS SENSOR

NETWORKS

To simplify the construction and management of the

system, the architecture is based on the use of underground

mobile wireless sensor networks [14]. As shown in Fig.1,the suggested network is made up of ground stations,

collocated in fixed or even movable locations, in proximity

of known pipe crossing positions. The ground stations are

equipped with directive antennas, pointed towards the

terrain and communicating with mobile sensors that flowthrough the pipe network, transported by the liquid. These

sensors represent the core of the monitoring system. They

are made up of a hydrophone as a sensing unit, and a

radiofrequency or microwave radio as a transmitting unit.

The wireless component is able to connect to the ground

stations, even if it is collocated within the liquid, inside apipe interred in the terrain. Since the sensor is transported

by the liquid under normal working conditions, theproposed solution preserves water provisioning, without the

need to take the liquid out of the conduit. The flow of the

sensor is controlled by means of hydraulic tricks and kept

constant along the path. In this way it is possible to make

real time and continuous pressure acquisitions without the

use of wires or cables. Furthermore, when the sensor

intercepts a ground station, its position is identified and the

acquired spectra are correlated to leakage positions.

The proposed network scheme allows detecting breaks bymonitoring the spectrum of the fluid pressure, and revealing

unknown paths, by tracking the sensor movements. The

detected information is transmitted through wireless

channels; hence, a physical connection to the surface is notrequired. An accurate detection of the leakage position is

provided. An easy and repeatable identification of the track

is possible.

3. SENSOR CONFIGURATION

Fig. 1. Mobile Wireless Sensor Network applied to water pipessurvey. The ground stations are collocated in fixed or movable

positions, where the pipe crosses the normal direction to theground (typically, where manholes are located).

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The sensor must make a measurement of liquid pressure in

time domain, which is further processed in the frequencydomain, to recognize pipe damages or fluid leakages.

Hence, the general scheme of the wireless sensor unit isshown in Fig.2: the pressure is measured by means of a

standard hydrophone, interfaced with a digital acoustic

card. The card is controlled by a Single Board Computer(SBC), where the detected information is processed

electronically, digitalized, stored on a flash memory and

transmitted to the surface. Power supply is obtained from

standard rechargeable batteries.

4. SENSOR REALIZATION

Several prototypes were designed, working at different

frequency ranges, from 100 MHz to 2.4 GHz. Among all,three have been designed, at 180 MHz, 433 MHz and 700

MHz.

As a sensor, different acoustic transducers able to work

within water (hydrophones) were considered. Finally, a

miniaturized hydrophone with high sensitivity, -198 dB re

1V/Pa, was selected. Figure 3 shows the hydrophone,

which does not need a power supply in order to generate

acceptable signals based on the acoustic noise. Preliminary

experiments showed that the output signal amplitude ranges

between 10 mV and 100 mV based on the level of the

generated noise.

The microprocessor board hosts and manages the whole

mobile system. The main managing tasks are the control of

the interface with the hydrophone and the sampling

operation, the conversion of the acquired data from

analogue to digital, the storing, pre-processing and routing

of the data, the control of the RF board through the serialperipheral interface (SPI) interface, and the power control

of RF board through a specific and ad-hoc protocol.

Among the numerous of-the-shelf controllers capable to

perform most of these tasks, the PIC32 from Microchip

Technology Inc was chosen (see Fig.4 for reference). The

main features of the board are: 32-bit 80 MHz core

microprocessor, 16 channels 10-bit analog to digital

converter (ADC), 16-bit timer, several types of interfacing

protocols, 512 KB flash memory, 128 KB SRAM, etc.

The wireless transmission is realized by means of an RF

board operating on the industrial, scientific, medical (ISM)

band. The operating frequency was chosen, based on

previous results [6]. The highest transmission power is 27dBm. The module has input sensitivity level of -117 dBm

with high data rate up to 115.2 kbps. Also, it exhibits

analog and digital received signal strength indicator (RSSI).

The wireless protocol used between the transmitter, the

detection module, and the receiver, the gateway, is being

developed in such a way to reduce the overhead exists inother wireless chipsets available in the market. This is

required to minimize the time needed to send and receive

data. Consumed energy is a critical factor in the proposed

setup and reducing transmission time significantly

improves the system performance.

As far as the design activity concerns the realization of the

antenna, one must take into account that, in order to favor

the flow of the sensor within the pipelines, the sensor must

be as small as possible. Hence, the antenna must be

miniaturized, even if the selected frequency ranges would

require antennas with relevant dimensions (especially at

180 Mhz and 433 MHz) to optimize the transmission to the

surface. As a matter of fact, the antennas are much smaller

than the wavelength.

Being small, electrical antennas are not suitable for thedesired application, as they are inserted in conductive

media and consequently completely mismatched from the

surrounding environment. Hence, the use of magnetic

antennas (dipoles) is mandatory. Electrically smallmagnetic dipoles are characterized by very short

dimensions: their circumference C has to be less than one

Fig. 2. Block-diagram of the mobile wireless sensor unit.

Fig. 3. The hydrophone implemented in the wireless mobile unit

Fig. 4. The microcontroller board

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fifth of the wavelength and then the input impedance tends

to be a short circuit. For this reason they are completely

mismatched from the transmitter because of a very high

reactive part and a very low (almost zero) real part of the

input impedance.

Starting from results shown in Fig.5, the design of the

antenna is carried out by fixing the real part of the antenna

impedance at 50 Ohm, and consequently manipulating the

imaginary part by inserting in series to stubs with inputreactance equal to half the reactance of the antenna. The

geometrical result is shown in Fig.6 The insertion of the

stubs slightly modifies the impedance of the antenna, and

consequently their length must be re-adapted, following an

iterative algorithm.

6. CONCLUSIONS

The paper presents an innovative concept that uses mobile

wireless network technology to monitor pipes for water

provisioning. The numerical electromagnetic predictions, as

well as the experimental data, validate the proposed

approach and demonstrate its applicability on larger scales.

At the moment three different solutions have been

implemented. The one working at 750 MHz has been

already measured in a real scenario [14], it works well and

allows the use of more directive antenna over the groundsurface, minimizing the generation of noise. The second

one works at 433 MHz, and it has been presented here. The

third one works at 180 MHz, it is under construction now

and will be presented in future publications.

REFERENCES

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Detection Methods for Plastic Water Distribution Pipes. In

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[8] B.J. Allred and N.R. Fausey. G.P.R. Detection of DrainagePipes in Farmlands. In International Conference on GroundPenetrating Radar, Delft, Netherlands, 2004.

[9] J. Yin, J. Pineda de Gyves, M. Lu. An Automatic SystemMeasuring Electromagnetic Parameters for Oil Field Pipes.IEEE International Conference on Industrial Technology,

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[10] Hunaidi O., Wing C., Acoustical Characteristics of LeakSignals in Plastic Water Distribution Pipes, Journal of

Applied Acoustic, 1998.

[11] Y. Gao, M.J. Brennan, P.F. Joseph, J.M. Muggleton, and O.

Hunaidi. On the selection of acoustic/vibration sensors for

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[12] http://www.water-

technology.net/contractors/pipe_clean/pure_tech/.

[13] M. Thompson, M. L. Harper, The body is the sensor, Insight -Non-Destructive Testing and Condition Monitoring, Volume:

50, Issue: 2, pages: 98-99, 2008.

[14] D. Trinchero, R. Stefanelli, "Microwave Architectures forWireless Mobile Monitoring Networks Inside Water

Distribution Conduits," Micr. Theory and Tech., IEEE Trans.on, vol.57, no.12, pp.3298-3306, Dec. 2009

Fig. 5. . Real and Imaginary Parts of the input loop's impedance

versus its circumference normalized to the wavelenght (C/)

Fig. 6. A magnetic antenna with the matching circuit, specifically

designed for the described application, at 433 MHz

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