There is a large difference in frequency dependent, complex electrical permittivity between genuine and counterfeit documents, including paper currency. Genuine bills have a substantially different complex permittivity which is distinct from the permittivity of counterfeit bills. The invention broadly measures the complex permittivity, .epsilon., of the `paper` bills to determine if the bill(s) is genuine or counterfeit. In one aspect, the present invention comprises a device and method for determining the genuineness of a document by measuring the complex permittivity based on the frequency dependent dielectric properties of the document. The complex electric permittivity of a dielectric material is typically read by measuring complex impedance using a capacitor to sense material properties. The document may include an enhanced region comprising an additive that establishes a known permittivity in the enhanced region. For example, the enhanced region may be established by using a "smart ink" that is applied to the document, or a dopant that may be built into the document itself. The "smart ink" or dopant may include carbon nanotubes, barium titanate, barium strontrium, or in general ferroelectric materials having a relatively high permittivity and a ferroelectric transition point that is above room temperature (e.g., lithium niobate, rochelle salt, sodium niobate, lithium tantalate). To determine the authenticity of the document, the permittivity of the enhanced region is measured. Advantageously, providing the enhanced region changes the local properties of the document to prevent document counterfeiting.

A currency identification system comprising at least two laterally displaced scanheads, one or more laterally moveable scanheads, or at least two laterally displaced sensors of a linear scanhead. The scanheads or sensors are positioned so as to permit scanning along at least two segments on a first side of a bill. The scanheads or sensors are capable of detecting characteristic information from the bill along the segments and generating corresponding output signals representing variations in the detected characteristic information from which scanned patterns of characteristic information may be generated. The system also comprises a pattern generator for generating at least one scanned pattern from the output signals, the scanned pattern representing analog variations in the characteristic information along a segment of the bill. The system also comprises a memory for storing at least one master pattern associated with each genuine bill which the system is capable of identifying, the master pattern representing analog variations in characteristic information along a segment of an associated genuine bill. The system further comprises a signal processor for performing a pattern comparison wherein at least one of the scanned patterns or portions thereof is compared with at least one of the master patterns or portions thereof. The signal processor generates an indication of the identity of the bill based on the pattern comparison when the bill is one that the system is capable of identifying.

An improved method of generating a master pattern corresponding to a given denomination for use in a discrimination system capable of discriminating among currency bills of different denominations. The method comprises the steps of generating a plurality of component patterns for a given denomination by scanning at least one genuine bill of the given denomination and generating a master pattern for the given denomination. The master pattern is derived from an average of the component patterns. The component patterns represent analog variations in characteristic information detected from a genuine bill during scanning. The master pattern represents an average of analog variations of the characteristic information for the given denomination.

An improved method of generating modified scanned or master patterns for use in a discrimination system capable of identifying one or more currency bills. Each of the scanned and master patterns comprises a sequence of data values representing analog variations of characteristic information along a segment of a bill and each pattern has a leading end and a trailing end. Each of the data values has an associated sequence position. The modified scanned or master patterns are generated by designating either the scanned pattern or the master pattern for modification and inserting a predetermined number, R, of data values at either the trailing end of the sequence of data values of the designated pattern when the modification is performed in the forward direction or the leading end of the sequence of data values of the designated pattern when the modification is performed in the backward direction. This modification effectively removes R data values from the leading or trailing end of the designated pattern. Either the last R data values of the designated pattern are set equal to the last R data values of the non-designated pattern when the modification is performed in the forward direction or the first R data values of the designated pattern are set equal to the first R data values of the non-designated pattern when the modification is performed in the backward direction. Alternatively, the modified master patterns are generated by inserting R data samples at the leading or trailing ends of the master patterns and by setting the first R or last R data samples of the modified master pattern equal to zero.

An improved method of generating a master pattern corresponding to given denomination for use in a discrimination system capable of discriminating among currency bills of different denominations. The master pattern is stored in a memory for subsequent comparison to a pattern generated from a bill under test. The method comprises the steps of generating a plurality of component patterns for a given denomination by scanning a genuine bill of the given denomination and generating a master pattern for the given denomination. The master pattern is derived from an average of the component patterns. The component patterns represent and approximate analog amplitude variations in characteristic information detected from a genuine bill during scanning. Each of the component patterns comprises a plurality of sample values. Each sample value is proportional to the detected characteristic information.