Read range, antennas and band geometry

Area is what couples

Inductive coupling depends on how much of the reader's field passes through the loop inside the credential. A card-sized antenna encloses a large area and therefore captures a lot; a wristband antenna, constrained to the width of a band or the size of a small faceplate, encloses far less. That difference is physics rather than quality, and no chip specification compensates for it. A band that reads on contact where a card read at four centimetres is behaving exactly as expected.

Orientation matters more than distance at close range

The coupling depends on the angle between the credential's coil and the reader's field. Flat and parallel is best; edge-on can drop to nothing. Guests naturally present a wrist at an angle, especially at a lock reader mounted vertically on a door, so a band that measures well on a bench can behave inconsistently in service. Where a band has an obvious face — a faceplate, a lock, a moulded module — guests orient it correctly without being told, which is a real argument for constructions with a visible front.

The wearer is part of the circuit

A wrist behind the antenna changes its tuning. So does water on the band, a wet sleeve, and to a much greater degree any metal nearby — a watch, a bracelet, a metal reader housing. The band that was measured on a desk is not the band that arrives at the door. This is why commissioning should be done with a band on a wet wrist in the actual position guests use, rather than with a sample held in the hand.

How to fix a marginal read

In order of cost: reposition or re-aim the reader; raise the reader's power if the platform allows; change the presentation instruction given to guests; change the band construction to one with a larger or better-placed antenna. Replacing the chip is almost never the answer and is usually the first thing suggested. If a read is marginal at commissioning it will be a complaint in August, so it is worth solving before the season rather than during it.