Viscosity is an important quality factor for providing food products with quantifiable attributes. A governing law, based on elastic model with the boundary condition of solid particles suspended in liquid, was derived for correlating apparent viscosity with the ultrasound velocity in a liquid food. This law indicates that apparent viscosity varies quadrically with the ultrasound velocity. Experiments were conducted to estimate apparent viscosities of orange and tomato juices using pulse-echo method. The results are in agreement with the governing law proposed. Data analysis demonstrates that the increase of solid particles in the juices increased both the apparent viscosity and ultrasound velocity. This is believed due to the effects of friction between the solid and liquid, and of bulk modulus stiffening.
Detection of small objects, those that lie on the bottom or stick to the wall of containers, constitutes a challenging issue for ultrasonic detection techniques. This is because echo signals from the object are fused with that of the inner surface of the container when subjected to ultrasound scanning. This study proposes a maximum component integration method based on the short‐time Fourier transform algorithm to detect these objects. Experiments were conducted using glass fragments of about 2 × 2 × 2 mm3 to test the proposed method. Compared with other signal‐processing methods (statistical calculations, backscattered amplitude integral and maximum frequency calculation), this method is able to make selective and full use of multiecho information, and hence demonstrated to have improved detection ability to the extent that it can detect small glass fragments contained inside glass containers. Principles are introduced for choosing the optimized WINDOW size and signal size to be processed when applying this method.
A conceptual design of an online ultrasonic system for bottled beverages’ quality control and monitoring is presented. The design consists of being able to measure ultrasound propagation velocities of beverages in each glass bottle without needing to know its diameter and wall thickness. This was achieved using simultaneously both ultrasound pulse/echo and thru-transmission signals. The ultrasound velocity is then correlated with the beverage’s, viscosity, which is an index of quality. The design also includes: (1) an online transducer alignment technique using a mechanism of frequency shift in spectrum of an ultrasonic pulse signal according to incident angle, and (2) a signal processing method using a slide window technique suitable for automatic separation and recognition of narrowly spaced pulse signals. Experiments were conducted to evaluate the design. Results of beverage viscosity/velocity correlation, frequency shift due to transducer alignment, and ultrasound velocity measurement in real bottles are reported.
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