On different tag reader architectures for bistable microwires

Abstract

A bistable microwire reader is an inductive type sensor that measures the fast magnetic flux reversals in ferromagnetic microwires having predominant longitudinal magnetisation. The signal processing in such readers is a challenging problem due to short induced pulses, pile up effect, pickup noise, and ringing distortion in the pickup coils. In our present work, analog and digital reading schemes for multi-bit tags made of several bistable microwires have been proposed. The performance of an analog reader can be sufficient for well separated pulses. However, the digital algorithms deliver a clearer output signal with better pulse resolution in the case of the pulse pile up effect. In turn, this enables reliable code recognition. Here, two digital algorithms have been tested. The digital low-pass Gauss filter effectively suppresses the pickup noise and ringing oscillations. The deconvolution algorithm constitutes the inverse task with respect to the convolution operator defining the pickup voltage output. This algorithm recovers the initial pulse profiles and provides the highest possible resolution of a pulse series. The obtained results will be useful for the creation of a robust reader for bistable microwire tags that can be implemented in recycling projects, marking of items, and fraud protection.