The beginnings of compact NMR can be traced to the introduction of tabletop relaxometers for food quality control and materials testing in the early 1970ies [1]. Mobile NMR started even earlier in the 1950ies with the exploration of earth-field NMR for well logging [2]. It received a decisive boost with the introduction of permanent magnets in 1980 [3], which enabled the sensitive volume to be localized in the stray field of the magnet. A derivative of this development are small stray-field devices for materials testing [4], one of which is the NMR-MOUSE [5]. Efforts to shape the stray magnetic field benefitted the development of compact centerfield magnets for benchtop NMR spectroscopy with fields sufficiently homogeneous to resolve the chemical shift of protons in liquids [6]. Miniaturizing the electronics and the magnet even further pushes the application of handheld centerfield relaxometers [7] and miniature magnetic resonance sensors [8]. Such sensors are particularly useful for rapid testing of short-lived and degradable products [9]. The development of compact and mobile NMR is reviewed from a personal perspective and concluded with a recent study of an antique, late-Roman burial chamber in Trier, where moisture flux towards the surface of a naturally wet wall has been estimated based on NMR depth profiles and Fick’s first law [10].

References
[1]    B. Blümich, Low-field and benchtop NMR, J. Magn. Reson. 306 (2019) 27.
[2]    R.H. Varian, Apparatus and method for identifying substances, US patent 3,395,337, 1952.
[3]    J.A. Jackson, L.J. Burnett, J.F. Harmon, Remote (inside-out) NMR. III. Detection of nuclear magnetic resonance in a remotely produced region of homogeneous magnetic field, J. Magn. Reson. 41 (1980) 411.
[4]    G.A. Matzkanin, J.D. King, W.L. Rollwitz, Nondestructive measurement of moisture in concrete bridge decks using pulsed NMR, Proc. 13th Symp. on NDE, 1981 April 21–23, San Antonio, Texas, 1981, p. 454.
[5]    G. Eidmann, R. Savelsberg, P. Blümler, B. Blümich, The NMR MOUSE, a mobile universal surface explorer, J. Magn. Reson. A122 (1996) 104.
[6]    B. Blümich, K. Singh, Desktop NMR and its applications from materials science to organic chemistry, Angew. Chem. Int. Ed. Eng. 57 (2018) 6996.
[7]    N. Sun, S. Ham, Handheld NMR systems and their applications for biomolecular sensing, in: D. Issadore, R.M. Westervelt (Eds.), Point-of-Care Diagnostics on a Chip, Springer, Berlin, 2013, p. 177.
[8]    M. Kern, J. Wrachtrup, and J. Anders, Toward Scalable Quantum Sensors: Devices and Technologies Enabling the Next Generation of Precision Measurement, IEEE Electron Devices Magazine 3 (2025) 2.
[9]    M.P. Augustine, K. Straetkvern, M. Nguyen, M. Johnston, B. Blümich, Relaxation in water from different sources in Rome: Field testing a portable, center-field relaxometer, manuscript in preparation
[10]    C. Golini, Q. Yang, M. Waldecker, et al., Investigation of the late-Roman burial chamber at Reichertsberg in Trier by NMR depth profiling, Solid-State Nucl. Magn. Reson. xx (2026) xxx.