Using intelligent materials and sensors to monitor the safety of concrete structures is a hot topic in the field of civil engineering. In order to realize the omni-directional monitoring of concrete structural damage, the authors of this paper designed and fabricated an embedded annular piezoelectric ultrasonic sensor using the annular piezoelectric lead zirconate titanate (PZT) ceramic as a sensing element and epoxy resin as the matching and the backing layers. The influence of different matching and backing layers thickness on the acoustic characteristic parameters of the sensor were studied. The results show that the resonant frequency corresponding to the axial mode of annular piezoelectric ceramics moves toward the high frequency direction with the decrease of the height of piezoelectric ceramics, and the radial vibration mode increases as well as the impedance peak. With the thickness of the backing layer increases from 1 mm to 2 mm, the radial resolution of the annular piezoelectric ultrasonic sensor is enhanced, the pulse width is reduced by 39% comparing with the sensors which backing layer is 1 mm, and the head wave amplitude and −3 dB bandwidth are increased by 61% and 66%, respectively. When the matching layer thickness is 3 mm, the sensor has the highest amplitude response of 269 mV and higher sensitivity.

In this paper, the authors analyse the propagation of surface Love waves in an elastic layered waveguide (elastic guiding layer deposited on an elastic substrate) covered on its surface with a Newtonian liquid layer of finite thickness. By solving the equations of motion in the constituent regions (elastic substrate, elastic surface layer and Newtonian liquid) and imposing the appropriate boundary conditions, the authors established an analytical form of the complex dispersion equation for Love surface waves. Further, decomposition of the complex dispersion equation into its real and imaginary part, enabled for evaluation of the phase velocity and attenuation dispersion curves of the Love wave. Subsequently, the influence of the finite thickness of a Newtonian liquid on the dispersion curves was evaluated. Theoretical (numerical) analysis shows that when the thickness of the Newtonian liquid layer exceeds approximately four penetration depths 4δ of the wave in a Newtonian liquid, then this Newtonian liquid layer can be regarded as a semi-infinite half-space. The results obtained in this paper can be important in the design and optimization of ultrasonic Love wave sensors such as: biosensors, chemosensors and viscosity sensors. Love wave viscosity sensors can be used to assess the viscosity of various liquids, e.g. liquid polymers.