Bruce Grieve

Compact Patch Antenna Design for Outdoor RF Energy Harvesting in Wireless Sensor Networks

In this paper, two compact patch antenna designs for a new application - outdoor RF energy harvesting in powering a wireless soil sensor network - are presented. The first design is a low-profile folded shorted patch antenna (FSPA), with a small ground plane and wide impedance bandwidth. The second design is a novel FSPA structure with four pairs of slot embedded into its ground plane. Performance of both antennas was first simulated using CST Microwave Studio. Antenna prototypes were then fabricated and tested in the anechoic chamber and in their actual operating environment - an outdoor field. It was found that the FSPA with slotted ground plane achieved a comparable impedance bandwidth to the first design, with an overall size reduction of 29%. Simulations were also carried out to investigate the effects of different design parameters on the performance of the proposed slotted ground plane FSPA.

Electrochemical issues in impedance tomography

Linear ramp cyclic voltammetry and ac impedance spectroscopy have been used to investigate the electroactivity of Zeneca products and filtration solvents using platinum microelectrodes. Linear ramp cyclic voltammetry has been used to establish appropriate excitation potentials which will minimise electrochemical reactions associated with the product or the solvent during impedance process tomography measurements. Impedance spectroscopy has been used to resolve the electrochemical impedance and the geometric impedance of a small scale test rig. This technique offers a method of establishing the appropriate frequency range of the excitation potential for use in impedance tomography measurements.

Detecting filter-cake pathologies in solid–liquid filtration: semi-tech scale demonstrations using electrical resistance tomography (ERT)

Abstract Solid–liquid filtration monitoring by means of a single inexpensive 16-element ring sensor array for electrical resistance tomography (ERT) is described. The high sensitivity of the UMIST Mark 1b-E data acquisition system led to the unexpected finding that this tomography array can detect movement of the liquid level during filtration. This degree of sensitivity was also capable of detecting any tilt of the filter assembly, so that pathological behaviour due to malfunction or accidental displacement of the filter support plate could also be identified. Moreover, illustrative distortions of a filter cake formed by artificial surface depressions were readily observed in tomograms reconstructed by linear back projection. It is concluded that ERT has great potential for instrumenting and detecting ‘pathological’ behaviour of filtration processes in the pharmaceutical and fine chemicals industries.

Three-dimensional electrical impedance tomography applied to a metal-walled filtration test platform

The first true three-dimensional image reconstructions from a metal-walled vessel using electrical impedance tomography (EIT) are presented. Two image reconstruction techniques have been applied via relatively sophisticated FEM modelling of a bespoke laboratory test vessel from which data have been obtained using an EIT instrument designed to intrinsically safe requirements. A generalized Tikhonov regularization method is compared with the linear back-projection (LBP) technique. Subsequent image reconstructions strongly suggest that the LBP method when applied to a metal-walled vessel is highly sensitive to the level of detail within the FEM model. By comparison, the regularized technique is far less sensitive to the complexity of the modelled geometry. Additionally, unlike the LBP method, the regularization technique has been successful in accurately reconstructing multiple inhomogeneities within an aqueous system. A further experiment has shown similar sensitivity in a wetted powder-based system. It is concluded that EIT via a regularized difference imaging approach has significant potential for detecting 3D malformations and non-uniformities in industrial pressure filtration systems.

Towards process tomography for monitoring pressure filtration

This paper reports on progress towards the first continuous application of electrical impedance tomography to a production scale industrial process. It includes the design and implementation of the worlds first certified intrinsically safe electrical tomography system. Zener barrier (ZB) modules and intrinsically safe relays provide electrical isolation and the instrument is certified for operation in a Zone 0 environment. Two systems have been operating successfully on production pressure filters for two years. A sensor architecture has been implemented that is compliant with the process such that it is not detrimental to efficiency or the integrity of the associated vessel structure. The MATLAB-based EIDORS three-dimensional software toolkit has been employed to yield images from simulated data. To overcome problems that arise due to dramatic changes in the conductivity of materials in the vessel during the process, a new approach is introduced that proposes the use of dynamic sensitivity maps that evolve during the batch based on the predicted mean conductivity at each stage. Real data present challenges due to a number of factors, notably the ZB modules that are integral to the intrinsically safe instrumentation. However, a simple approach to data processing has yielded process relevant information using real tomographic data.

Investigation of PCB microstrip patch receiving antenna for outdoor RF energy harvesting in wireless sensor networks

In this paper the suitability of using a printed circuit board (PCB) microstrip patch receiving antenna for a novel application — RF energy harvesting to power a wireless soil sensor network deployed in an outdoor environment — is investigated. The performance of a conventional circular microstrip patch antenna using different microwave laminate substrates is evaluated in terms of return loss, radiation efficiency, and gain. Based on a chosen PCB material as the antenna substrate, an enhanced gain circular patch with a ring shaped parasitic radiator is presented. Simulations have been carried out using CST Microwave Studio to examine the antennas performance both in free air and in the presence of different soil conditions.

Localized multispectral crop imaging sensors: Engineering & validation of a cost effective plant stress and disease sensor

Close proximity hyperspectral and multispectral imaging of crops and soils offers significant potential to optimize sustainable intensification of arable produce and seeds breeding, through the real-time precision management of plant pathogens, viruses and pests and the non-destructive high throughput screening for beneficial crop traits. These opportunities have been recently reported and are the subject of ongoing R&D within industry and academia. The broad uptake of the technology by large commercial end-users, through integration with in-field and glasshouse machinery, is limited by cost and equipment reliability. It is further restricted by spectral and spatial resolution, power budget and size, when extending its applicability to consumer markets and small-holder farmers. This study verifies, for the first time, that multispectral sensor systems architectures, exploiting proprietary narrowband LEDs and silicon C-MOS imaging detectors, are capable of substituting for conventional and more expensive line-scanning hyperspectral imaging systems when operated in close proximity (c. 1-2m) of a crop canopy. This was achieved by comparing the data from a prototype version of the new LED-sensor system versus a reference laboratory hyperspectral imaging unit, which was previously developed for crop phenotyping, and the early detection of two fungal pathogen borne diseases in whole barley and sugar beet plants. The choice of crops and diseases replicates earlier studies, with the reference hyperspectral unit, and serves to demonstrate the generic applicability of the new LED-sensor system to cereal and tuber classes of crops. The results indicate that the new approach can deliver data of comparable quality to that of the reference system, for in-field duties, and offers the opportunity for higher sensitivity and spatial resolution. Future potential to apply the new multispectral, LED-based system within commercial products is then discussed.

Electrical impedance imaging of water distribution in the root zone

The paper describes a technique that is proposed for imaging water transport in and around the root zone of plants using distributed measurements of electrical impedance. The technique has the potential to analyse sub-surface phenotypes, for instance drought tolerance traits in crop breeding programmes. The technical aim is to implement an automated, low cost, instrument for high-throughput screening. Ultimately the technique is targeted at in-field, on-line, measurements. For demonstration purposes the present work considers measurements on laboratory scale rhizotrons housing growing maize plants. Each rhizotron is fitted with 60 electrodes in a rectangular array. To reduce electrochemical effects the capacitively coupled contactless conductivity (C4D) electrodes have an insulating layer on the surface and the resistance of the bulk material is deduced from spectroscopic considerations. Electrical impedance is measured between pairs of electrodes to build up a two-dimensional map. A modified electrical model of such electrodes is proposed which includes the resistive and reactive components of both the insulating layer and the bulk material. Measurements taken on a parallel-plate test cell containing water confirm that the C4D technique is able to measure electrical impedance. The test cell has been used to explore the effects of water content, compaction and temperature on measurements in soil. Results confirm that electrical impedance measurements are very sensitive to moisture content. Impedance fraction changes up to 20% are observed due to compaction up to a pressure of 0.21 kg cm -2 and a temperature fraction sensitivity of about 2%/??C. The effects of compaction and temperature are most significant under dry conditions. Measurements on growing maize reveal the changes in impedance across the rhizotron over a period of several weeks. Results are compared to a control vessel housing only soil. ?? 2014 IOP Publishing Ltd.

Capillary zone electrophoresis for the analysis of glycoforms of cellobiohydrolase

Cellobiohydrolase (CBH) is an important enzyme for the conversion of lignocellulosic biomass to ethanol. This work separated the glycoforms of CBH possessing different numbers of neutral mannoses using capillary zone electrophoresis (CZE) in a 50 mM, pH 7.5 phosphate buffer. The method analysed CBH in an intact form using a polyacrylamide coated fused silica capillary without requiring additives or labelling of the enzyme. The migration time of the major peak was found to be 21.6±0.1 min (n=3) and the approach is suitable for testing of batch-to-batch consistency of CBH. Ease-of-use, automation and speed are the other benefits due to which the use of CZE for analysing glycoforms of CBH was concluded to be ideal.

Supplemental Blue LED Lighting Array to Improve the Signal Quality in Hyperspectral Imaging of Plants

Hyperspectral imaging systems used in plant science or agriculture often have suboptimal signal-to-noise ratio in the blue region (400–500 nm) of the electromagnetic spectrum. Typically there are two principal reasons for this effect, the low sensitivity of the imaging sensor and the low amount of light available from the illuminating source. In plant science, the blue region contains relevant information about the physiology and the health status of a plant. We report on the improvement in sensitivity of a hyperspectral imaging system in the blue region of the spectrum by using supplemental illumination provided by an array of high brightness light emitting diodes (LEDs) with an emission peak at 470 nm.