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@INPROCEEDINGS{Windt:1032518,
      author       = {Windt, Carel},
      title        = {{E}ngineering for mobility and ease of use: small-scale
                      devices for {NMR} sensing and {NMR} imaging of plants in the
                      field},
      reportid     = {FZJ-2024-06307},
      year         = {2024},
      abstract     = {In this contribution we present the development of mobile
                      NMR sensors and MR imagers for measuring plants in the
                      field. A prerequisite for the systems whas that they be
                      based on permanent magnets, to minimize power consumption,
                      and that the air gap should be wide and freely accessible.
                      This should allow measurements of branches and stems of
                      field grown plants, but also allow objects such as leaves
                      and cereal spikes to be illuminated inside the magnet. An
                      open C-shaped magnet design was chosen, a type of magnet
                      that can be both affordable and easy to build. To permit
                      operation under variable environmental conditions, both
                      temperature stable and temperature stabilized versions were
                      constructed. In order to maximize space for plants, pole gap
                      width of the magnet and resilience against handling were
                      prioritized over homogeneity and field strength. For the
                      imagers, to overcome the adverse effects of short T2* that
                      may result from these design choices, multi-spin echo
                      imaging strategies were employed with short echo times and
                      high spectral widths [1]. To achieve microscopic resolution
                      under these constraints requires fast switching field
                      gradients, driven by strong and fast gradient amplifiers.
                      While small-scale spectrometers and RF amplifiers are
                      readily available, appropriate small-scale gradient
                      amplifiers or designs thereof currently are not. We
                      therefore constructed a small, 3-channel gradient amplifier
                      on the basis of a conventional current-controlled AB
                      amplifier design. Tailored to small low-impedance gradient
                      coils the amplifiers could remain small, suitable for
                      battery driven operation and still meet our requirements
                      regarding switching speed, power and duty cycle. The
                      finished gradient amplifier weighed 5 kg and was capable
                      of delivering 40 A gradient pulses of up to 6 ms in
                      duration, sufficient for micro imaging and flow mapping.
                      With all components built onto an aluminum hand trolley, the
                      entire imaging setup weighed 45 kg and was small enough to
                      fit into a car [2]. For an MR imager such a system already
                      is small, mobile and relatively low in complexity. However,
                      without imaging and tailored for use as a time domain NMR
                      (TD-NMR) relaxometer, such systems can become simpler,
                      smaller and more affordable still. The limiting factor then
                      becomes the design of the TD-NMR experiment and the
                      subsequent data analysis. Key is to tailor the method for a
                      single, well-defined application: this way TD-NMR can
                      become simple and fast, and suitable for non-expert
                      operators with minimal training. An example of this approach
                      is the Solid-Fat Content determination, currently the gold
                      standard method to determine the ratio between liquid oil
                      and solid fat in mixtures, or to measure moisture or lipid
                      contents in dry seeds [3]. For living plant tissues we
                      developed a similarly simplified TD-NMR method, to estimate
                      total proton density (linearly correlated to fresh weight)
                      and solid proton density (linearly correlated to solid
                      matter content) in samples with a moisture content of
                      between 15 and $100\%$ [4]. For further details on this
                      method also see Woertche et al, this abstract book. Mobile
                      relaxometry, in this manner, becomes a valuable tool to
                      non-invasively monitor plant water content as a function of
                      drought, or to characterize dry matter accumulation (yield
                      development) in grain crops.},
      month         = {Aug},
      date          = {2024-08-26},
      organization  = {16th International Bologna Conference
                       Magnetic Resonance in Porous Media
                       (MRPM16), Tromso (Norway), 26 Aug 2024
                       - 30 Aug 2024},
      subtyp        = {After Call},
      cin          = {IBG-2},
      cid          = {I:(DE-Juel1)IBG-2-20101118},
      pnm          = {2171 - Biological and environmental resources for
                      sustainable use (POF4-217)},
      pid          = {G:(DE-HGF)POF4-2171},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/1032518},
}