Haiying Huang

Exploiting a patch antenna for strain measurements

The feasibility of applying patch antennas for strain measurement is investigated. The resonance frequency of a patch antenna is determined by the size of its metallic patch. An applied strain changes the dimensions of the metallic patch, resulting in a shift in the antenna resonant frequency. Therefore, the applied strains can be measured from the changes in antenna resonant frequency. A dual-frequency patch antenna was designed and fabricated using conventional photolithography techniques. The application of the patch antenna for strain measurement was evaluated by bonding the patch antenna to an aluminum cantilever beam and applying loads at the free end of the cantilever beam. The shifts of the return loss S11 curves under loads were correlated to the strains experienced by the patch antenna. The strain sensitivity of the antenna obtained from experimental measurements agreed well with the analytical prediction.

Wireless interrogation of passive antenna sensors

Recently, we discovered that the resonant frequency of a microstrip patch antenna is sensitive to mechanical strains or crack presence in the ground plane. Based on this principle, antenna sensors have been demonstrated to measure strain and detect crack in metallic structures. This paper presents a wireless method to remotely interrogate a dual-frequency antenna sensor. An interrogation horn antenna was used to irradiate the antenna sensor with a linear chirp microwave signal. By implementing a light-activated switch at the sensor node and performing signal processing of the backscattered signals, the resonant frequencies of the antenna sensor along both polarizations can be measured remotely. Since the antenna sensor does not need a local power source and can be interrogated wirelessly, electric wiring can be eliminated. The sensor implementation, the signal processing and the experimental setup that validate the remote interrogation of the antenna sensor are presented. A power budget model has also been established to estimate the maximum interrogation range.

Flexible Wireless Antenna Sensor: A Review

This review paper summarizes a new flexible sensor concept based on the microstrip patch antenna technology. The principle of the patch antenna as a sensing element and the wireless interrogation of the antenna sensors are presented first, followed by the description of the antenna design and fabrication using flexible film components. The applications of the flexible antenna sensor for wireless strain sensing and crack detection are presented. The design and testing of inserting a flexible layer to improve the reliability of the flexible antenna sensor is also discussed. Because the flexible antenna sensors can be wirelessly interrogated with ultra-low power consumption and can be frequency division multiplexed, the complexity of implementing a large sensor array is greatly reduced.

Detecting crack orientation using patch antenna sensors

Crack orientation is a very important parameter for structural integrity analysis. Even though many sensors have been developed to detect crack presence and length, very few sensors can detect crack orientation. Recently, we have demonstrated a patch antenna sensor that can detect crack propagation with sub-millimeter resolution. In this paper, the capability of the antenna sensors for crack orientation detection is studied. An antenna sensor with a rectangular antenna patch radiates at two fundamental modes. The effect of a ground-plane crack on these two resonant frequencies depends on its orientation. Hence, the crack orientations can be monitored by analyzing the crack-induced shifts of both antenna resonant frequencies. The principle of operation will be discussed first, followed by detailed descriptions on the numerical simulation, sensor fabrication, experimental procedure, results and analysis. Simulation as well as experimental results confirmed that the antenna sensor is capable of providing quantified information about the crack orientation.

Broadband electrical impedance matching for piezoelectric ultrasound transducers

This paper presents a systematic method for designing broadband electrical impedance matching networks for piezoelectric ultrasound transducers. The design process involves three steps: 1) determine the equivalent circuit of the unmatched piezoelectric transducer based on its measured admittance; 2) design a set of impedance matching networks using a computerized Smith chart; and 3) establish the simulation model of the matched transducer to evaluate the gain and bandwidth of the impedance matching networks. The effectiveness of the presented approach is demonstrated through the design, implementation, and characterization of impedance matching networks for a broadband acoustic emission sensor. The impedance matching network improved the power of the acquired signal by 9 times.

An Antenna Sensor for Crack Detection and Monitoring

A major goal of structural health monitoring (SHM) is crack detection and monitoring. Because cracks are localized defects, quantifying the sizes and locations of the cracks would require placing many sensors over a large area. We present a crack sensor that is suitable for densely distributed sensor network because they can be remotely interrogated and do not need any wiring for data transmission or power supply. A rectangular patch antenna, consisting of a metallic patch on one side of a dielectric substrate and a ground plane on the other side of the substrate, is studied in this paper for crack detection and monitoring. The presence of a crack in the ground plane of the antenna changes its conductivity, which in turn reduces the resonant frequency of the antenna sensor. Experimental results demonstrated that the antenna sensor can monitor crack growth with sub-millimeter spatial resolution. Detailed experimental set-up and measurement results are presented.

The effect of actuator bending on Lamb wave displacement fields generated by a piezoelectric patch

A Lamb wave is a special type of elastic wave that is widely employed in structural health monitoring systems for damage detection. Recently, piezoelectric (piezo) patches have become popular for Lamb wave excitation and sensing because one piezo patch can serve as both the actuator and the sensor. All published work has assumed that the Lamb wave displacement field generated by a piezo patch actuator is axi-symmetric. However, we observed that piezo sensors placed at equal distances from the piezo patch actuator displayed different responses. In order to understand this phenomenon, we used a laser vibrometer to measure the full-field displacements around a circular piezo actuator noncontactly. The displacement fields excited by the piezo patch actuator are found to be directional, and this directionality is also frequency dependent, indicating that the out-of-plane bending dynamics of the piezo actuator may play an important role in the Lamb wave displacement fields. A simulation model that incorporates the bending deformation of the piezo patch into the calculations of the Lamb wave generation is then developed. The agreement between the simulated and measured displacement fields confirmed that the directionality of the Lamb wave displacement fields is governed by the bending deformation of the piezo patch actuator.

Simulation, implementation, and analysis of an optical fiber bundle distance sensor with single mode illumination

A simulation model for an optical fiber bundle distance sensor with a single mode fiber as the illumination fiber and a multimode fiber as the receiving fiber is presented. Approximating the illumination light exiting the single mode fiber as having a Gaussian intensity profile, a closed-form solution of the reflected light coupled into the receiving fiber was derived. A distance sensor was implemented and the measured sensor outputs were compared with the simulation data to verify the theoretical model. The performance of the distance sensor with different design parameters was analyzed. Design guidelines for achieving desired sensor performances are suggested.

Optical fiber corrosion sensor based on laser light reflection

The development of an optical fiber corrosion sensor based on the principle of light reflection is presented in this paper. The sensor consists of an optical fiber reflection sensor and a tube/film subassembly formed by welding a sacrificial metallic film to a steel tube. One side of the sacrificial metallic film is finely polished and is isolated from the environment while the other side is exposed to the corrosive environment. The corrosion pits initiated at the exposed film surface slowly penetrate the sacrificial film as the exposure time increases. The corrosion pits that reach the polished surface reduce the surface reflectivity of the polished surface. This decrease in reflectivity is detected by the optical fiber reflectivity sensor. To interrogate multiple sensors at one time, a sensor multiplexing scheme was implemented. The principles of operation, packaging, and characterization of the corrosion sensors are presented.

Development of an in-fiber white-light interferometric distance sensor for absolute measurement of arbitrary small distances

The fabrication, implementation, and evaluation of an in-fiber white-light interferometric distance sensor that is capable of measuring the absolute value of an arbitrary small distance are presented. Taking advantage of the mode-coupling effect of a long-period fiber grating, an additional cavity distance is added to the optical path difference of the distance sensor; therefore, it can generate a sufficient number of fringes for distance demodulation even if the free-space cavity distance is very small. It is experimentally verified that the distance sensor is capable of measuring small distances that are beyond the capability of a Fabry-Perot interferometric distance sensor.