Cost effective power amplifiers for pulsed NMR sensors

Sensors that measure magnetic resonance relaxation times are increasingly finding applications in areas such as food and drink authenticity and waste water treatment control. Modern permanent magnets are used to provide the static magnetic field in many commercial instruments and advances in electronics, such as field programmable gate arrays, have provided lower cost console electronics for generating and detecting the pulse sequence. One area that still remains prohibitively expensive for many sensor applications of pulsed NMR is the requirement for a high frequency power amplifier. With many permanent magnet sensors providing a magnetic field in the 0.25T to 0.5T range, a power amplifier that operates in the 10MHz to 20MHz rage is required. In this work we demonstrate that some low cost commercial amplifiers can be used, with minor modification, to operate as pulsed NMR power amplifiers. We demonstrate two amplifier systems, one medium power that can be constructed for less than Euro 100 and a second much high power system that produces comparable results to commercial pulse amplifiers that are an order of magnitude more expensive. Data is presented using both the commercial NMR MOUSE and a permanent magnet system used for monitoring the clog state of constructed wetlands

A Low Cost Magnetic Resonance Relaxometry Sensor

Magnetic resonance relaxometry, conducted by measuring relaxation parameters at different field strengths, has become an increasingly popular technique in recent years. This technique, known as field cycling, often uses expensive and large electromagnets. In this work we present a small, portable field cycling sensor. Fast field cycling is a technique that uses a varying magnetic field applied to a sample, polarising it at a high field, allowing it time to develop at a lower field and then collecting the data at the same initial high field. This causes changes in T1 and can reveal interesting proper ties of the samples not seen by traditional methods. A prototype portable magnetic resonance sensor that undertakes relaxometry measurements using fast field cycling has been developed using a combination of permanent magnets which has been used to conduct preliminary studies on a water sample. We demonstrate the effectiveness of this sensor by conducting measurements of T1 at different field strengths

Temperature dependence of magnetic resonance sensors for embedding into constructed wetlands

Constructed wetlands are an environmentally considerate means of water purification. Automating parameters such as heating and aeration may extend the lifetime of constructed wetlands and allow for superior waste-water treatment. One critical parameter to monitor in a wetland system is clogging of pores within the gravel matrix, as this limits the viable lifetime of the system. It has previously been observed in a laboratory setting that magnetic resonance (MR) relaxation measurements, T1 and T2eff, can be used to characterise the clogging state. Various open-geometry MR sensors have been constructed using permanent neodymium magnets with the view of long-term embedding as part of the EU FP7 project ARBI (Automated Reed Bed Installations). The ultimate aim is to monitor clogging levels over the lifetime of the reed bed using MR techniques. One issue with taking various MR measurements over such an extreme time scale, in this case years, is that temperature fluctuations will significantly alter the magnetic field strength produced by the sensors constituent magnets. While the RF transmit-receive circuit has been built so that MR can still be conducted at a range of frequencies without altering the tuning or matching of the circuit, this will result in poor RF excitation if the magnetic field strength shifts significantly. This work investigates the effect that temperature has on the a MR sensor intended for embedding, to determine whether received signal intensity is compromised significantly at large temperature changes

Low-cost magnetic resonance sensors for process monitoring in the food industry<span></span>

Low-cost magnetic resonance (MR) sensors have in recent years been used to investigate a number of systems by measuring the relaxation times T1 and T2eff. These measured parameters vary in line with changes in many systems giving the investigator a useful non-invasive probe. While the use of MR for in-line or on-line process monitoring in the food industry is not a novel concept, much of the work conducted previously has involved acquiring spatially resolved data which requires a magnetic resonance imaging system. These are both expensive to purchase and maintain, occupy large amounts of space and present problems with safety. In this work we show the value that a very inexpensive magnet and coil geometry (<€200) can bring to process monitoring. A MR sensor utilising an eight-element Halbach cylinder with internal diameter of 10mm has been constructed giving a highly uniform magnetic field yielding a strong signal-to-noise ratio. It is shown to be useful for assessing the relaxation times of a range of relevant samples

A magnetic resonance disruption (MaRDi) technique for the detection of surface immobilised magnetic nanoparticles

There are numerous assays that result in a surface with bound magnetic nanoparticles (MNP) whose number is proportional to the concentration of the analyte of interest. The techniques used to explore such assays are typically complex and costly. Since the presence of such MNP disrupts the pulsed magnetic resonance signal that would normally be detected from a fluid covering the surface, we present a measurement technique to quantify such assays. In this work we identify and characterise a suitable fluid for such measurements, namely 10 cSt viscosity PDMS oil of thickness 250 μm. We demonstrate that the Teff2 relaxation time from the PDMS reduces as the proportion of the surface area covered with MNP increases. Most significant however, is a linear decrease in the signal amplitude from the PDMS as a function of MNP coverage. This is observed both for the integral over 4096 echoes and also in the first echo promising simplified console electronics for rapid measurements

Non-invasive measurements of the dry solids content of whole potatoes using unilateral magnetic resonance: towards automation

Crisps or chips are considered a popular snack food around the world and at their most fundamental are potatoes which are sliced and then fried. It has been known for some time that during their production industrially, controlling the final oil content requires prior knowledge of the dry solids of the potatoes to modify the temperature and frying time to give the best product. The dry weight of a batch of potatoes is most commonly performed using a buoyancy measurement. In preliminary experiments, we have found evidence that such a measurement, whilst representative of the average dry solids, does not offer the most appropriate measurement since the variation within the batch is significant. We present an investigation into the properties of intact potatoes using magnetic resonance relaxation measurements and relate these to the dry solids content. This preliminary study will lay the groundwork for the development of an online process monitoring device based around a unilateral sensor to allow batch sorting of incoming potatoes

Magnetic resonance relaxation measurements using open-geometry sensors to assess the clog state of constructed wetlands

Monitoring the T1 relaxation of wetland clog matter has previously been identified as a gauge of its clogged state [1]. Magnetic resonance MR)sensors explored in other work have typically been of a bore-whole configuration, which may not be ideal in a wetland environment where the sensitive volume of the sensor may become physically clogged and therefore inoperable. This work investigates two open-geometry sensor designs and a short study is presented to determine the suitability of the sensors for monitoring the clog state of wetlands. It was shown that a bar magnet geometry has a higher stray field than that of the four magnet surface sensor also presented, leading to a prohibitively short T2eff. This means that the T1 values collected are notably shorter and not useful for distinguishing between clog state for the single magnet sensor. By contrast the four magnet surface sensor has a longer T2eff, making it more suitable for T1 measurements; where T1 = 915 ± 212 ms for a very thinly clogged sample, and T1 = 127 ± 27 ms for a heavily clogged sample. This offers a clearly resolvable difference in the T1 values allowing the clogging state to be easily determined and making this sensor the desirable choice for long-term embedding

Determining the clog state of constructed wetlands using an embeddable Earth's Field Nuclear Magnetic Resonance probe

The recent rise in interest of green technologies has led to significant adoption of the constructed wetland as a waste water treatment technique. This increased popularity has only been mired by the decline in operational lifetime of wetland units, leading to the need for more regular, time consuming, and expensive rejuvenation techniques to be performed than initially anticipated. To extend operational lifetimes and increase efficiency of wetland units, it is crucial to have an accurate method to determine the internal state of the wetland system. The most important parameter to measure within the reed bed is the clog state of the system, which is representative of the overall system health. In previous work, magnetic resonance (MR) measurements, parameters of T1 and T2eff, have been demonstrated as extremely powerful tools to determine the internal clog state of a wetland [1, 2]. Measurements have been performed in a laboratory setting, using low field permanent magnet arrangements. This work presents an Earth's Field Nuclear Magnetic Resonance (EFNMR) probe suitable for in situ measurements within constructed wetlands. We show T2eff and T1 measurements using the EFNMR probe. T1 values are shown to be sensitive to the change in the clog state with 1498 ms for the thickly clogged sample and 2728 ms for the thinly clogged sample. T2eff values are shown to be marginally more sensitive to clog state with 630 ms for a thickly clogged sample and 1212 ms for the thinly clogged sample. This gives distinguishable variation within both parameters suggesting that this probe is suitable for embedding into an operational constructed wetland. This work was conducted as part of an EU FP7 project to construct an Automated Reed Bed Installation, "ARBI"

Advances in clog state monitoring for use in automated reed bed installations

Constructed wetlands are a popular form of waste-water treatment that have proliferated across Europe and the rest of the world in recent years as an environmentally conscious form of waste water treatment. The ability to monitor the conditions in the bed and control input factors such as heating and aeration may extend the lifetime of the reed bed substantially beyond the ten year lifetime normally reached. The Autonomous Reed Bed Installation (ARBI) project is an EU FP7 initiative to develop a reed bed with automated control over input parameters based on readings taken from embedded sensors. Automated remedial action may improve bed treatment efficiency, and prolong the life of the bed and avoiding the need to refurbish the bed, which is both time consuming and costly. One critical parameter to observe is the clog state of the reed bed, as this can severely impact on the efficiency of water treatment to the point of the bed becoming non-operable. Magnetic resonance (MR) sensors can be a powerful tool in determining clogging levels, and has previously been explored in the literature. This work is based on a conference paper (2nd International Conference "Water resources and wetlands", 2014) and details magnetic sensors suitable for long-term embedding into a constructed wetland. Unlike previous studies this work examines a probe embedded into a wetland

Advances in automated reed bed installations

Constructed wetlands are a popular form of waste-water treatment that have proliferated across Europe and the rest of the world in recent years as an environmentally conscious alternative to chemical treatments. The ability to monitor the conditions in the bed and control input factors such as heating and aeration may extend the lifetime of the reed bed substantially beyond the ten year lifetime normally reached. The Autonomous Reed Bed Installation (ARBI) project is an EU FP7 initiative to develop such a bed. One critical parameter to observe is the clog state of the reed bed, as this can severely impact on the efficiency of water treatment. Magnetic resonance (MR) sensors can be a powerful tool in determining clogging levels (Analyst 2011, 136, 2283-2286) and allow automated remedial action to be taken against the bed improving treatment efficiency, prolonging the life of the bed and avoiding the need to refurbish the bed, which is both time consuming and costly. This work details magnetic sensors suitable for long-term embedding into a constructed wetland