ORAL - International Conference of Agricultural Engineering

Manuscript Preparation Guidelines for CIGR-Ageng2012International Conference of Agricultural EngineeringTHE EFFECT ON WIRELESS SENSOR NETWORK COMMUNICATION WHENEMBEDDED IN BIOMASSJakob J. Larsen 1 *, Ole Green 1 , Esmaeil S. Nadimi 2 , Thomas S. Toftegaard 31 Department of Engineering, Aarhus University, Blichers Alle 20, 8830 Tjele, Denmark.2 Faculty of Engineering, Institute of Chemical Engineering, Biotechnology andEnvironmental Technology, University of Southern Denmark, Odense, Denmark.3Department of Engineering, Aarhus University, Ny Munkegade 120, 8000 Aarhus, Denmark.*Corresponding author. E-mail: JakobJuul.Larsen@agrsci.dkAbstractUsing wireless sensor networks (WSN) inside a heterogeneous biomass is challenging. Inthis article some of the challenges of deploying a WSN in a heterogeneous biomass, in thiscase silage, is handled. The permittivity of silage is measured using an open-ended coaxialprobe. Results were successfully obtained in the frequency range from 400 MHz to 4 GHz,but large variations suggested that a larger probe should be used for more stable results.The effect of silage on a helix and loop antenna was measured. Of the two antennas testedthe helix antenna was deemed best suited for deployment in biomass. Lastly it is suggestedthat taking the dielectric properties of silage into account during hardware development couldresult in much better achievable communication range.Key words: WSN; permittivity; detuning; biomass storage.1 IntroductionEfficient storage of farm produce is vital as improper storage causes product loss andtherefore also financial loss. Substantial losses can happen without it being easily detectable(McDonald et al. 1991). Current monitoring systems involve considerable extrapolation fromvery few samples (MacDonald et al. 2002).Wireless Sensor Network (WSN) technology could help change this and is now commonlyused in a variety of monitoring situations, but relatively few WSN applications have so farbeen developed which require signal transmission through complex materials with high watercontent. Recently Green (Green & Pranov 2008; Green 2010) suggested that WSN might besuitable for monitoring agricultural biomass and patented a suitable sensor (Green et al.2009) for use in silage. Green et al. (2009) indicated a great potential for quality optimizationand ensuring the quality. The sensors used in the experiment were limited to very shortcommunication ranges. No discussion was made on how to improve transmission distance,or which parameters to consider when designing sensors for embedding in biomass. Thisarticle tries to investigate the properties of silage that affects Radio Frequency (RF)communication and how big the effects are.In a heterogeneous material such as silage the RF-characteristics within a region of thematerial will be determined by the permittivity of that region. To estimate which challenges aWSN deployed in silage must face a method for measuring the complex permittivity isneeded. A variety of methods exist for this purpose (von Hippel 1954; Roberts & Von Hippel1946; Nelson 1973). For a high loss material such as silage (Stuchly & Stuchly 1980) is thesimplest and offer good accuracy.The aim of this study is to measure the RF properties of silage under normal storageconditions to gain a better understanding of how it will affect the radio communication of a