Six Questions to Take Into Your Next PEMF Sales Meeting

If you're about to spend a few thousand dollars on a PEMF device and the spec sheets all start to blur together, you don't need to become an expert in electromagnetics. You need six questions, and the discipline to ask all of them.

You've sat through meetings with a friendly rep, a glossy brochure, one big peak Gauss number on the front page, and a lot of confidence. By the end of the meeting, you've heard a lot, and you still can't tell whether the device will deliver what you need. These questions close that gap. Each one targets a number that the brochure either left off or rounded into uselessness. We'll provide a recognizable pattern for what a good answer for each looks like.

Question 1. Where was the peak measured?

How far was the probe from the coil face when the measurement was recorded? A reading taken right at the surface and a reading taken at body distance from the same coil can differ by a factor of ten or more. A peak Gauss number with no measurement standoff stated is just a number.

A good answer sounds like this. "Peak measured on the surface with a calibrated axial Hall probe directly on the disc face, at the highest power setting."

A bad or missing answer sounds like this. "It's up to 7,000 Gauss." No location, no probe, no standoff, no setting. A real measurement always comes with the conditions that produced it. If a vendor can't give you those conditions, the number isn't telling you what they think it is.

Question 2. Is the peak number a single point, or a profile?

Is that headline number from a single tiny spot on the coil, or does it describe what the field is doing across the whole face? Peak alone tells you the maximum the coil can do somewhere. A profile tells you what the coil does everywhere. Two coils can share the same peak value while producing very different treatment results.

A good answer sounds like this. "We publish the mirrored falloff profile from one edge of the coil through the center to the other edge, with the 50 percent and 10 percent thresholds marked." That gives you the therapeutic core (the zone where the field is at or above 50 percent of peak) and the effective field radius (where the useful field tapers off below 10 percent).

A bad or missing answer sounds like this. "It's X Gauss." No profile, no scan, no idea where the field goes after the peak. You're being handed the highest reading the coil can produce, with no description of what it does anywhere else.

Question 3. What's the coil geometry inside the applicator?

How is the coil built inside the housing? The size of the housing is a separate question. A pancake coil is a flat spiral, and its field peaks at the geometric center. A donut coil is wound in a ring, and its field peaks in a ring around the center, producing broader, more even coverage across the face. Two discs of identical outer diameter can be constructed differently and behave very differently in clinical use.

A good answer sounds like this. "It's a pancake coil inside a 380mm (15 in) diameter disc. Peak field is at the center, falling off symmetrically toward the edges."

A bad or missing answer sounds like this. "It's a 380mm (15 in) disc." That tells you the size of the housing. It tells you nothing about the field shape inside it.

Question 4. What's the rise time or slew rate?

How quickly does each pulse climb to its peak? By Faraday's law, what stimulates tissue is the rate of change of the magnetic field, not the peak field itself. A 1,500 Gauss pulse with a sharp rising edge can deliver more stimulus than a 7,000 Gauss pulse that ramps up slowly. So the peak is only half the story. The slope is the other half.

A good answer sounds like this. "Slew rate is 140 G per microsecond at top setting. Rise time is 160 microseconds. We capture the actual oscilloscope waveform at every power setting and publish those traces."

A bad or missing answer sounds like this. "The peak is 7,000 Gauss." No time-domain data. You can't tell whether the pulse is sharp or soft. A sharp low-Gauss pulse and a soft higher-Gauss pulse can be summarized the same way on a brochure, and you wouldn't be able to tell them apart.

Question 5. On a multi-coil mat, do the coils fire together or one at a time?

When the mat has several coils embedded in it, do they all fire simultaneously at full strength, or does the device cycle through them one at a time? This is a decisive question for mats, because "rated intensity per coil" means very different things in those two cases. A mat that fires its eight coils sequentially at "full intensity per coil" puts full intensity on any given square inch for only one-eighth of the session. A mat that fires all eight in parallel keeps every square inch at full intensity the whole time.

A good answer sounds like this. "All coils fire simultaneously at rated intensity. Every square inch of the mat receives full peak Gauss for the entire session."

A bad or missing answer sounds like this. "Each coil produces X Gauss." A per-coil number with no firing scheme. You can't tell whether you're getting continuous coverage or a rotating spotlight, and the difference is easily a factor of eight in delivered energy per square inch.

Question 6. Are unit tolerances disclosed?

Does the manufacturer acknowledge that no two production units are identical? Is the variation published? Every electronic device varies a little from the next one off the assembly line. A spec sheet that prints a single exact number with no tolerance is either oversimplified or hasn't been measured across enough units to know.

A good answer sounds like this. "Peak field is 7,000 Gauss plus or minus 30 percent across production units."

A bad or missing answer sounds like this. "Peak field is 7,000 Gauss." Implied to be exact for every unit shipped, which is almost certainly not true. The absence of a tolerance is itself a tell. Either the variation hasn't been measured, or it has been measured and isn't being shown.

What a vendor's six answers actually tell you

A vendor who can answer all six clearly has nothing to hide and has done the engineering work behind the marketing. A vendor who answers three and hedges on three has told you which parts of the device they're confident in and which they're not. A vendor who can't answer any of them isn't being dishonest, but they're selling a product they haven't fully characterized, which means you'd be buying it on faith.

Use our example reports as your gauge

The fastest way to understand a good answer is to see it broken down into simple, easy-to-read graphs and charts that clearly visualize a detailed analysis. Gauss Labs publishes complete example reports for a device analysis, a pancake accessory, and a donut accessory. They show all six questions answered in detail, with the actual measurements, charts, and tolerances. Read one, and the pattern of a real answer feels obvious.

You don't have to be an expert in electromagnetics to make a smart purchase when buying a PEMF device. You need six answers. The vendors who can give them go on the shortlist. The vendors who can't have just told you something useful about themselves.