This paper presents a miniaturized patch antenna sensor for structural crack sensing, and the patch antenna sensor can be interrogated wirelessly. The proposed patch antenna sensor can detect the expansion of structural crack through relative movement between antenna components, and the relationships between the antenna resonant frequency and the crack width were studied. By using Rogers RO3010 laminate with high dielectric constant as the dielectric substrate of the antenna, the size of the proposed antenna sensor is significantly reduced, and higher sensing sensitivity is achieved. Furthermore, the wireless interrogation methods of the patch antenna sensor were also studied. The resonant frequency of the patch antenna sensor was wirelessly interrogated using linearly polarized wide-band antennas. Compared with the previous patch antenna sensor, the overall area of the proposed antenna sensor has been reduced to 33.4%, and the miniaturized patch antenna sensor shows a sensing sensitivity of 116.1 MHz/mm, which is 2.6 times higher than the previous patch antenna sensor. A series of simulations and experiments have demonstrated the feasibility of the proposed patch antenna sensor for structural crack sensing and the effectiveness of wireless interrogation methods.

This article presents a novel passive patch antenna sensor for simultaneous crack and temperature sensing, and the antenna sensor has the ability of temperature self-compensation. The passive patch antenna sensor consists of an underlying patch and an overlapping sub-patch. The off-center feeding activates resonant modes in both transverse and longitudinal directions. The resonant frequency shift in transverse direction is used for environmental temperature sensing, while the structural crack width can be sensed by the longitudinal resonant frequency shift after temperature compensation. Furthermore, the unstressed design of the antenna can also eliminate the issue of incomplete strain transfer ratios. In this article, the relationships between the antenna resonant frequencies, the environmental temperature, and the structural crack width were studied. Simulations were conducted to determine the optimal off-center fed distance of the patch antenna sensor. Furthermore, a series of experimental tests were also conducted, where the passive patch antenna was fabricated and installed on the concrete components as well as an actual building. Continuous monitoring was performed for several days to test the temperature sensing ability of the passive patch antenna, and the sensed crack width after temperature compensation was compared with the actual results. The results of these experiments demonstrate the feasibility of using the passive patch antenna for simultaneous temperature and crack sensing.

Bolts are widely used in civil engineering, and the detection of bolt loosening is of great significance to ensure the safety of a structure. This paper introduces a new method for detecting bolt loosening using a customized detachable strain sensor based on a patch antenna. A patch antenna with overlapping sub-patch is proposed to measure the longitudinal elongation of the entire bolt shaft, indicating the loosening state of the bolt. When the bolt is fastened, the elongation of the bolt under tension will change the combined length of the underlying patch and the radiation sub-patch, consequently increasing or decreasing the resonant frequency of the antenna. The resonant frequency of the antenna can be measured by the vector network analyzer. Furthermore, with wireless interrogation of the strain sensor based on the patch antenna, the proposed method can also be used in the wireless detection of bolt loosening. The authors conducted a finite element analysis of the bolt and the electromagnetic simulations of the antenna. They designed the detection sensor and conducted a series of experimental tests to demonstrate how a bolt under different applied preloads can be effective and feasible under the proposed method.

The south building of Huadong Hospital is a well-known historic building in Shanghai, China. In August 2021, the building was lifted by 1.30 m to correct the subsidence caused by long-term use and to expand the usable space of the building. To ensure structural safety during uplifting of the historic building, a structural health monitoring system is devised to monitor the overall status of the structure and the state of critical components. The structural health monitoring system comprises sensor, data acquisition, and data management systems. The content that is monitored includes vertical displacement, horizontal displacement, inclination, differential settlement, cracks, strains, and acceleration. The overview and uplifting scheme of the historic building are first introduced. The monitoring system’s design and sensor installation are then thoroughly discussed, followed by monitoring data analysis to investigate the state of the structure before and after uplifting. Furthermore, a structural safety assessment based on multisource monitoring data and neural networks is conducted. Huadong Hospital’s south building is currently the largest uplifted historic building in terms of construction area in China. The building’s structural health monitoring system played an exemplary and promoting role in structural health monitoring during uplifting of historic buildings, and it also has referential significance for similar engineering projects.

This paper presents an off-center fed patch antenna for simultaneous crack and temperature sensing. The antenna sensor consists of an off-center fed underlying patch and an overlapping sub-patch. The bottom copper sheet of the sub-patch is tightly attached to the underlying radiation patch allowing the electric current to flow through the integrated patch. The off-center feeding can activate the resonant modes in both transverse and longitudinal directions. The transverse resonant frequencies of the combined patch are utilized for temperature sensing. Therefore, the crack width sensed by the longitudinal frequency shift can be adjusted, eliminating the temperature effect. In addition, this unstressed structure of the combined patch can avoid the issues of incomplete strain transfer ratio and the insufficient bonding strength of a monolithic antenna. The authors developed theoretical relationships between the antenna resonant frequencies, the temperature, and the crack width. They also developed simulations of the off-center fed patch antenna sensor as well as a series of experimental tests to demonstrate the feasibility of the proposed sensor for simultaneous crack and temperature sensing.