A novel high-gradient permanent magnet for the profiling of planar films and coatings.

The design and construction of a low-cost, permanent magnet is described. The magnet is intended for applications which require a large static gradient, such as those for which stray field imaging or fringe field diffusometry are conventionally employed. The magnet has been designed using the scalar potential method. Particular features of the magnet include a field profile such that ||B || is constant in the horizontal plane and such that B is horizontal at the midpoint between the poles. There is a vertical, and therefore orthogonal, strong gradient, G, in ||B ||. The ratio G/ ||B || is constant within a large volume and so allows measurements at a range of gradient strengths. It is this ratio which governs the shape of the pole-pieces. The constructed magnet has a typical operating field of 0.8 T, gives a gradient of 20 Tm-1, and has a useable interpole access of 20 mm. Field plot data show values consistent with the theory. In particular ||B || has a curvature of less than +/-5 microm over a 5 x 5 mm area at the target field. The magnet is most suitable for the one-dimensional profiling of thin planar samples. As an example of the magnet's use, a profile of a sandwich structure made of several polymer layers is shown. In addition, a set of one-dimensional profiles of an alkyd coating, recorded during solvent loss and cross-linking, is presented. This example demonstrates quantitative T2 measurements at a resolution of 6.5 microm across a 70-microm-thick film.

Tibial physeal closure and genu recurvatum after femoral fracture: occurrence without a tibial traction pin.

Two cases of premature closure of the anterior portion of the proximal tibial physis with associated genu recurvatum deformity in adolescent males who had sustained a closed femur fracture are reported. In both cases, physeal closure occurred without use of a proximal tibial traction pin. In one patient, treatment included distal femoral pin traction; the other patient was treated with skin traction followed by spica cast. We believe that development of recurvatum of the tibia after femoral fracture in children is not necessarily iatrogenic and related to a tibial traction pin, but instead may result from physeal injury incurred at the time of the original trauma.