In this research, two radiofrequency identification (RFID) antenna sensor designs are tested for compressive strain measurement. The first design is a passive (battery-free) folded patch antenna sensor with a planar dimension of 61mm × 69mm. The second design is a slotted patch antenna sensor, whose dimension is reduced to 48mm × 44mm by introducing slots on antenna conducting layer to detour surface current path. A three-point bending setup is fabricated to apply compression on a tapered aluminum specimen mounted with an antenna sensor. Mechanics-electromagnetics coupled simulation shows that the antenna resonance frequency shifts when each antenna sensor is under compressive strain. Extensive compression tests are conducted to verify the strain sensing performance of the two sensors. Experimental results confirm that the resonance frequency of each antenna sensor increases in an approximately linear relationship with respect to compressive strain. The compressive strain sensing performance of the two RFID antenna sensors, including strain sensitivity and determination coefficient, is evaluated based on the experimental data.
In this work, a slotted patch antenna is employed as a wireless sensor for monitoring structural strain and fatigue crack. Using antenna miniaturization techniques to increase the current path length, the footprint of the slotted patch antenna can be reduced to one quarter of a previously presented folded patch antenna. Electromagnetic simulations show that the antenna resonance frequency varies when the antenna is under strain. The resonance frequency variation can be wirelessly interrogated and recorded by a radiofrequency identification (RFID) reader, and can be used to derive strain/deformation. The slotted patch antenna sensor is entirely passive (battery-free), by exploiting an inexpensive offthe- shelf RFID chip that receives power from the wireless interrogation by the reader.
This research investigates the field performance of a mobile sensor network designed for structural health monitoring.
Each mobile sensing node (MSN) is a small magnet-wheeled tetherless robot that carries sensors and autonomously
navigates on a steel structure. A four-node mobile sensor network is deployed for navigating on the top plane of a space
frame bridge. With little human effort, the MSNs navigate to different sections of the steel bridge, attach
accelerometers, and measure structural vibrations at high spatial resolution. Using high-resolution data collected by a
small number of MSNs, detailed modal characteristics of the bridge are identified. A finite element model for the bridge
is constructed according to structural drawings, and updated using modal characteristics extracted from mobile sensing
For application in structural health monitoring, a folded patch antenna has been previously designed as a wireless sensor
that monitors strain and crack in metallic structures. Resonance frequency of the RFID patch antenna is closely related
with its dimension. To measure stress concentration in a base structure, the sensor is bonded to the structure like a
traditional strain gage. When the antenna sensor is under strain/deformation together with the base structure, the antenna
resonance frequency varies accordingly. The strain-related resonance frequency variation is wirelessly interrogated and
recorded by a reader, and can be used to derive strain/deformation. Material properties of the antenna components can
have significant effects on sensor performance. This paper investigates thermal effects through both numerical
simulation and temperature chamber testing. When temperature fluctuates, previous sensor design (with a glass
microfiber-reinforced PTFE substrate) shows relatively large variation in resonance frequency. To improve sensor
performance, a new ceramic-filled PTFE substrate material is chosen for re-designing the antenna sensor. Temperature
chamber experiments are also conducted to the sensor with new substrate material, and compared with previous design.