Single-sided Magnet

The Single-Sided Magnet project focuses on the development and application of a unilateral (single-sided) Nuclear Magnetic Resonance (NMR) device. This innovative NMR system was devised to non-invasively determine the ripeness of watermelons by correlating T2 relaxation times with sugar content in the fruit. The primary objective was to enable easy and accurate assessment of fruit quality without causing any damage to the samples.

The device comprises a wooden box with dimensions of 18" x 18" x 12". At the core of the system is a barrel magnet, which sits beneath an RF coil located at the center of the box. The barrel magnet's design is axially magnetized, resembling a hollow right circular cylinder. This configuration generates a magnetic field with a saddle point, creating a sensitive region where NMR experiments can be performed. The sweet spot for these measurements is about 8mm long, axially centered 17mm above the magnet, allowing the device to probe just inside the rind of the fruit.

One of the significant advantages of the barrel magnet over traditional NMR devices is its capability to measure long T2 components with minimal diffusive attenuation due to magnetic field gradients. This feature is particularly advantageous compared to other unilateral NMR instruments like MOUSE, which typically have large B0 gradients. The barrel magnet's design allows for a larger depth of investigation, facilitating a broader range of applications.

The construction of the barrel magnet involved the use of NdFeB blocks arranged in columns, which were later refined into a solid annular magnet composed of inexpensive magnetic rings polarized perpendicular to the plane of the rings. Two compact versions of the barrel magnet, referred to as Magnets A and B, were developed. Magnet A was extensively characterized for its field and performance in unilateral NMR applications, while Magnet B was incorporated into a mobile system used in various practical scenarios.

In addition to measuring the sweetness of watermelons, the Single-Sided Magnet has been employed by the University of California at Davis, Food Science Department, to test the quality of tomato sauce in barrels, specifically to detect rancidity. This application highlights the versatility and practicality of the device in the food industry.

Furthermore, the project's scope includes exploring the theoretical and experimental aspects of the barrel magnet. Detailed studies on the magnet's construction, the design of RF coils, and the experimental methods used to characterize the magnet's performance have been conducted. These studies aim to optimize the magnet's design for various unilateral NMR applications, ensuring reliable and accurate measurements.

Overall, the Single-Sided Magnet project represents a significant advancement in unilateral NMR technology. Its applications in non-invasive fruit quality assessment and food safety testing demonstrate its potential to impact various industries positively. The continued development and refinement of this technology hold promise for broader applications in fields requiring non-destructive testing and quality control.

ABQMR Single-sided Magnet Publications:

S. Utsuzawa and E. Fukushima, "Unilateral NMR with a barrel magnet," J. Magn. Reson. 282, 104-113 (2017).

E. Fukushima, Jasper A. Jackson, Unilateral magnet having a remote uniform field region. U.S.Patent No. 6,489,872; December 3, 2002.