Ali Daliri

Utilising microstrip patch antenna strain sensors for structural health monitoring

In this article, the feasibility of using a circular microstrip patch antenna to measure strain and the effects of different materials on sensitivity of the patch antenna are investigated. Also, the effect of strain direction on the frequency shift is studied. The theoretical model shows a linear relationship between strain and the shift in the resonant frequency of the antenna in any material. Both finite element analysis (FEA) and experimental tests have been undertaken to corroborate the relationship between strain and frequency shift. In addition, a new antenna sensor based on a meandered microstrip patch antennas has been designed and tested to overcome the shortcomings of the circular patch. The meandered circular microstrip patch antenna exhibited a threefold increase in sensitivity and a fivefold reduction in its physical size, when compared to the simple circular patch. The ultimate intention of this work is to configure antennas for the detection of relatively small damage zones in structures and to do so wirelessly.

Split-Ring Slot in the Broad-Wall of a Rectangular Waveguide

Recently the Slotted Waveguide Antenna Stiffened Structure (SWASS) was introduced, where an antenna array is incorporated as an integrated part of a load bearing structure. The array element spacing and individual radiating element sizes play a critical role in the overall mechanical strength of the structure. These parameters are constrained by Slotted Waveguide Antenna (SWA) array design, and the coupling of the waveguide electromagnetic fields to the radiating apertures. In this letter, the radiation characteristics of a split-ring slot in the broad-wall of a rectangular waveguide are investigated for the first time. The simulated and measured results show that the split-ring slot radiates a linearly polarized wave with a total efficiency and realized gain close to those of conventional rectangular slots. The proposed split-ring slot has an outer diameter of 0.186 λ0, a significant size reduction compared to a traditional 0.5 λ0 rectangular slot and the previous limit of 0.25 λ0 for metamaterial loaded rectangular slots. The reduced aperture size of the split-ring slot alleviates the impact of the radiating elements on the mechanical strength of the structure.

A slot spiral in carbon-fibre composite laminate as a conformal load-bearing antenna

Conformal load-bearing antenna structures, which afford load-bearing structures with radar capability, are a promising technology to reduce weight and drag of air vehicles. This article presents an investigation of the mechanical and electromagnetic performance of slot log-spiral antenna in carbon-fibre composite structures. Compared with traditional rectangular slots, equiangular slot spiral antenna is found to offer broader bandwidth and better mechanical strength. Through experimental testing and finite element analyses, a new tip design is proposed that can significantly reduce the stress concentration of the non-load-bearing log-spiral antenna. Results of mechanical tests also show that the compressive strength of a carbon-fibre composite plate featuring a spiral slot is comparable with that pertinent to a plate with a circular hole of the same size. Filling the slots with epoxy resin can further enhance the compressive strength.

Quality Factor Effect on the Wireless Range of Microstrip Patch Antenna Strain Sensors

Recently introduced passive wireless strain sensors based on microstrip patch antennas have shown great potential for reliable health and usage monitoring in aerospace and civil industries. However, the wireless interrogation range of these sensors is limited to few centimeters, which restricts their practical application. This paper presents an investigation on the effect of circular microstrip patch antenna (CMPA) design on the quality factor and the maximum practical wireless reading range of the sensor. The results reveal that by using appropriate substrate materials the interrogation distance of the CMPA sensor can be increased four-fold, from the previously reported 5 to 20 cm, thus improving considerably the viability of this type of wireless sensors for strain measurement and damage detection.

Strain measurement in composite materials using microstrip patch antennas

In this paper the feasibility of using a circular microstrip patch antenna to detect strain in composite plates and the effects of different materials on sensitivity of the patch antenna are investigated. Also the effect of strain direction on the frequency shift is studied. The theoretical model shows a linear relationship between strain and the shift in the resonant frequency of the antenna in any material. A circular microstrip patch antenna is designed and fabricated to work at 1.5GHz and attached to three different materials for testing. Both Finite Element Analysis (FEA) and experimental tests have been undertaken to corroborate the relationship between strain and frequency shift. The ultimate intention of this work is to configure antennas for the detection of relatively small damage zones in structures and to do so wirelessly

A Spiral Shaped Slot as a Broad-Band Slotted Waveguide Antenna

The utility of slotted waveguide antennas would be maximized if the bandwidth of the radiating elements matched that available in the waveguide. This was achieved using a spiral shaped slot cut through the broad-wall of a rectangular waveguide. The predicted total e-ciency and peak realized gain were relatively uniform across the entire bandwidth. The current distribution around the slot was predicted to be similar to that around a conventional, center fed, slot spiral antenna, indicating similarity of radiation mechanisms. Finally, the antenna patterns for spiral shaped slots in waveguides manufactured from copper and carbon flbre reinforced polymer (CFRP) were shown to be similar to that predicted.

FEA Evaluation of the Mechanical and Electromagnetic Performance of Slot Log-Spiral Antennas in Conformal Load-Bearing Antenna Structure (CLAS)

Conformal load-bearing antenna structures (CLAS) have been attracting the attention of aerospace industries in recent years. This type of multifunctional structures combines the features of conventional antennas with load-bearing capacity and has important applications in military and commercial airplanes especially for Unmanned Aerial Vehicles (UAVs). Equiangular slot spiral antennas are an alternative to traditional rectangular slots because of its wideband radiation characteristics. However, the mechanical characteristics of such a spiral antenna integrated into a structure are so far largely unexplored. In this paper, the electromagnetic (scattering parameter, radiation pattern and gain) and mechanical properties (stress concentration factor (SCF)) of spiral antennas is investigated using finite element analysis (FEA). The results lead to a recommendation for using this type of antenna for future CLAS concepts.Copyright

Subwavelength spiral slotted waveguide antenna

Integrating antennas into a load-bearing airframe structure has the potential for profound improvements in the capability of military and commercial airplanes, by allowing for substantially increased radiator and array size with reduced weight or drag penalties. Reducing the size of array elements can significantly improve the mechanical performance of the loadbearing antenna. The novel single element spiral slot cut in the broad-wall of a WR-90 rectangular waveguide proposed in this paper is smaller than a quarter of the operating wavelength (half of the size of a conventional rectangular slot). The small antenna element enables a slotted waveguide array to be realized without significantly degrading the mechanical performance in load bearing applications. The proposed spiral slot is compared with conventional rectangular slots and exhibits comparable performance in terms of total efficiency (representing coupling from waveguide mode to the slot) and peak realized gain. Total efficiency and peak realized gain of the spiral slot in travelling wave mode are significantly higher than those of a quarter wavelength rectangular slot element which has near zero radiation. The simulated results were validated by manufacturing the spiral slot placed on the broad-wall of a rectangular waveguide. Realized gain patterns of the spiral slot measured at the design frequency corroborate reasonably with the simulations.

Multidirectional Circular Microstrip Patch Antenna Strain Sensor

In this paper, a new design for microstrip patch antenna strain sensors is proposed. The new antenna sensor works based on the meandered microstrip patch antennas. It is threefold more sensitive than previously proposed circular microstrip patch antenna strain sensors. Also, the overall physical dimension of the new antenna sensor is reduced by the factor of five. The current sensor is able to detect strain in all directions. In order to design the antenna sensor, two available commercial FEM software packages ANSYS™ and HFSS™ are used. Both experimental and FEM results corroborate the multidirectional feature of the new antenna sensor. Also, the effect of the hole size in the structure (for coaxial connection to the antenna) on the antenna performance has been studied. Based on the results obtained, the antenna sensor can be recommended for use in structural health monitoring for strain-based damage detection in aerospace structures.Copyright

Spiral slotted waveguide antenna array

Slotted waveguide antenna stiffened structure (SWASS) integrates the slotted waveguide antennas (SWAs) into the carbon fiber reinforced polymer (CFRP) composites in airplane skins. SWASS utilizes conventional half-wavelength rectangular slots as elements of the SWA array. Size of the rectangular slots is an important factor affecting the mechanical performance of the SWASS and restricting its application. Subwavelength spiral slots are recently proposed to replace the rectangular slots and consequently improve the SWASS mechanical performance. In this paper, a four element array using subwavelength spiral slots is presented which demonstrates the feasibility of using such slots for SWASS application.