Liquid and moisture sensing by ultra-wideband pseudo-noise sequence signals

Abstract

The use of ultra-wideband signals for moisture sensing by electromagnetic wave interaction provides more information on the material under test compared to single tone or narrowband approaches, regarding spatial and frequency dependent phenomena. Current activities to regulate the emission of electromagnetic waves in the spectral band up to 10 GHz for sensor applications open new perspectives for microwave moisture sensing. Therefore, improved and cost effective ultra-wideband measurement principles will become more and more interesting. The use of short pulses or swept sine waves are classic approaches to cover a large spectral band. However, this paper deals with some variants of an alternative method, which applies pseudo-random codes, namely M-sequences, to stimulate the test objects. The method permits monolithic integration of the RF-electronics in SiGe technology. The signal generation and data capturing are referred to a common stable single tone clock and they are controlled by steep trigger signals. This provides for very stable operation, which allows for measurements in both time and frequency domain. Two versions of an M-sequence approach will be considered and their functioning will be demonstrated by means of simple measurement examples.