Published | Reviewed
Size a 1 T Halbach cylinder, see when geometry crosses a practical boundary, and use the evidence-backed report to decide whether to quote, simulate, or switch architectures.
1.0 T
target bore
2.4x
typical ratio
Jul 19
published/reviewed
Practical for small-to-mid bores when the design includes high-coercivity grade selection, segmented geometry, field mapping, shimming, and a controlled assembly plan. Not practical as a raw magnet order based on the ideal equation alone.
A 1 T bore field is physically achievable with NdFeB Halbach cylinders, especially for small and mid-size bores. The practical limit is usually coercivity, segmentation, fixture safety, and shimming rather than the ideal equation alone.
The ideal field equation is logarithmic, so every field increase demands a disproportionate outer-radius increase. Bore diameter and target uniformity therefore dominate mass and assembly effort.
High-Br grades reduce size on paper, but high-opposing-field regions can require SH, UH, or EH-class demagnetization curves. Do not freeze N52 or N50 without a demag review at operating temperature.
Material mass is only a screening variable. Segmented blocks, coatings, non-magnetic assembly fixtures, thermal control, shims, mapping, freight, and acceptance testing can exceed raw magnet cost.
The quick sizer starts from the ideal infinite dipole Halbach cylinder relationship, then applies a fill factor for segmentation and tolerances. It is a screening tool, not a substitute for segmented 3D FEA or supplier material curves.
Bore radius, outer radius, and axial length set most of the mass and finite-length penalty.
Br reduces size, but coercivity and temperature margin decide whether the design survives operation.
Segment angles, gaps, end effects, shims, and acceptance maps must be modeled before procurement.
Example ratios below use a high-coercivity NdFeB baseline with a 0.90 practical fill factor. Exact values move with supplier grade, segment count, gaps, and operating temperature.
| Target field | Rout / Rin | Magnet volume vs 0.5 T | Decision signal |
|---|---|---|---|
| 0.5 T | 1.55x | 1.0x | Sensor fixtures and compact demonstrators |
| 1.0 T | 2.40x | 3.4x | Practical concept range for many small bores |
| 1.5 T | 3.71x | 9.1x | Review geometry, demag, and assembly early |
| 2.0 T | 5.75x | 22.9x | Usually not a permanent-magnet-only target |
This static snapshot mirrors the calculator default so the sizing logic remains readable in server-rendered HTML and AI summaries.
| Metric | Value | Engineering takeaway |
|---|---|---|
| Default inputs | 1.00 T target, 25 mm bore radius, 120 mm length, N42UH, 0.90 fill factor | Small-bore 1 T screening case before segmented 3D FEA. |
| Outer geometry | 60.0 mm outer radius / 119.9 mm outer diameter | The radius ratio is 2.40x, inside the concept-sizing range. |
| NdFeB mass | 8.40 kg material estimate | Assembly tooling and field mapping still need separate budget. |
| Material-only range | $792 - $1,425 | Excludes segmentation, coating, shims, QA, freight, and fixtures. |
| Review flag | Engineering review | Length / outer diameter is near 1.0x, so end effects must be modeled. |
The page uses public engineering references for the ideal relationship, portable Halbach context, NMR frequency conversion, magnet grade data, and temperature drift. Final design values must come from current supplier datasheets and project-specific FEA.
Journal of Applied Physics, 2008
Analytical Halbach-cylinder field model, segmentation effects, and optimization limits.
Magnetic Resonance in Medicine / PubMed Central, 2018
Portable MRI evidence that Halbach layouts can trade magnet mass, openness, and field homogeneity.
NIST Physical Measurement Laboratory
Reference for converting a 1 T field into proton resonance frequency context.
Arnold Magnetic Technologies
Representative Br, coercivity, and grade-selection data; final builds still need supplier-specific BH curves.
Arnold Magnetic Technologies technical paper
Temperature coefficient context for permanent magnet field drift and thermal compensation planning.
Trigger: 1 T target with standard high-Br grades or elevated temperature
Request supplier BH curves, model segment corners in FEA, and evaluate SH/UH/EH grades before purchase.
Trigger: Short axial length relative to the outer diameter
Use the calculator as screening only, then model end effects and define the usable uniform region.
Trigger: Large segmented blocks, high mass, or tight bore access
Design non-magnetic fixtures, staged insertion tooling, retention features, and written assembly procedures.
Trigger: NMR, MRI, calibration, or spectroscopy requirements
Budget for passive shims, field mapping, thermal enclosure, and acceptance tests in ppm or percent terms.
Use a permanent magnet Halbach when you need zero-hold-power field generation, compact packaging, and a fixed field profile. Use another architecture when adjustability, large access, or safety shutdown matters more than power consumption.
Better for tunable field strength, repeated experiments, and emergency de-energizing. Expect power, heat, cooling, and iron yoke tradeoffs at 1 T.
Better when high homogeneity, large bore, or field above the practical permanent-magnet range dominates the requirement. Cost and infrastructure are the tradeoffs.
Permanent magnets do not require cooling to hold field, but precision systems still need temperature compensation because NdFeB output drifts with operating temperature.
A 1 T Halbach array is not a generic magnet block purchase. The correct answer depends on the usable volume, allowed drift, homogeneity target, access path, and safety envelope.
A 1 T field places proton resonance near 42.58 MHz, which is useful for compact NMR architectures.
Halbach permanent magnets are proven in portable and low-field MRI research because they reduce cryogen and power needs.
Small 1 T bores can be useful for Hall sensors, magnetoresistive devices, material exposure tests, and compact physics experiments.
Yes, a 1 T bore field is achievable in a NdFeB Halbach cylinder when the bore is not too large and the outer radius, grade, segmentation, and shimming plan are realistic. The ideal equation is only the first screening step.
N52 has higher remanence, so it looks compact in an ideal model. A 1 T array can expose segments to strong reverse fields, so a high-coercivity grade is often a better baseline until a demagnetization model proves otherwise.
Ratios below about 3.2 are usually reasonable for concept sizing. Ratios near 4.0 or above become heavy and hard to assemble, and the calculator flags them as a boundary condition.
No. The estimate is material-only screening. Machined wedges, coatings, non-magnetic fixtures, shims, field mapping, thermal control, packaging, and acceptance testing can dominate the final project cost.
The central field can be useful, but homogeneity depends on axial length, segmentation count, magnet tolerances, bore access, and shimming. NMR or MRI use requires explicit ppm or percent uniformity targets.
Only for very small demonstrators with low stored magnetic energy. Most 1 T engineering builds need CNC non-magnetic metals or composite retention structures sized for assembly and operating loads.
It does not need electric power or cryogens to hold the field, but it may need thermal control. NdFeB remanence changes with temperature, and high-stability instruments need compensation or enclosure design.
No. It can inform portable or low-field architecture decisions, but clinical MRI performance depends on patient access, gradients, RF coils, shielding, uniformity, and regulatory validation.
Use an electromagnet when you need frequent field changes, switch-off safety, wide access, or a field profile that is easier to tune with coils than with permanent magnets.
The next deliverable should be a segmented 3D model with material curves, thermal assumptions, field map targets, assembly sequence, and a quote package for magnet and fixture suppliers.
If you are evaluating motor architectures, check our [Axial Flux Halbach Array Calculator](/learn/axial-flux-halbach-array) to estimate back-iron mass savings and flux concentration for axial gap topologies.
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