Out in Front: August 15, 1996

Two companies have devised ways to foil counterfeiters who forge money and high-value items, such as drugs and aircraft parts. The scheme involves two elements: giant magnetoresistive (GMR)-effect sensors from NVE Inc and irregularly shaped and sized, microscopic particles, called "Microtaggants," from Microtrace. NVE offers several standard parts and can tailor the devices' properties to your applications.

The sensors resemble ICs, and the manufacturing process is similar to IC fabrication. One form of the sensors comprises a Wheatstone bridge. Two of the bridge's resistors are exposed to an external magnetic field, and layers of high-permeability material beneath and atop the other two resistors shield them from the external field. Some sensors combine signal-conditioning circuits in the same package with the resistive sensing elements. The sensors cost less than $3 (1000) and often resemble eight-pin SOICs. GMR devices sensitively measure small magnetic fields that need not vary as a function of time. Only a few types of magnetic sensors measure fields that hold constant with time, and most such sensors are relatively insensitive.

Microtaggants normally comprise magnetic and colored layers. The particles' color codes, which resemble the codes on resistor bodies, usually identify the manufacturer of a substance—a hazardous material, for example—with which the Microtaggants mix. A GMR sensor that is near an item having Microtaggants reads a "signature." No two items have the same signature. A computer-based system algorithmically derives a serial number from an item's unique signature and prints the number either on the coded item or on an accompanying certificate of authenticity. An item is genuine only if the serial number and the signature match.

Microtaggants are available in many forms, including inks and adhesive labels. Depending on the form and the number of units to be coded, Microtaggants cost fractions of cents to a few cents per item you code.

—by Dan Strassberg

NVE Nonvolatile Electronics Inc, Eden Prairie, MN. (800) 467-7141, fax (612) 996-1600, info@nve.com, http://www.nve.com.

Microtrace Inc, Minneapolis, MN. (612) 784-9725, fax (612) 784-3787.