Trang T. Thai

Design and Analysis of Microstrip Bi-Yagi and Quad-Yagi Antenna Arrays for WLAN Applications

In this letter, the design of a microstrip bi-Yagi and microstrip quad-Yagi array antenna is presented. These designs are a derivative of the original microstrip Yagi antenna array and can achieve a high gain and a high front-to-back (F/B) ratio in comparison to the conventional microstrip Yagi structure first proposed by Huang in 1989. The proposed Bi-Yagi and quad-Yagi antenna arrays can also achieve a higher gain (3-6 dB) than the conventional microstrip Yagi array. Simple fabrication techniques can be used with these designs due to the placement of the feeding network on the same layer with the antenna elements. Furthermore, simulations and measurements demonstrate with very good agreement that the proposed arrays can achieve a gain as high as 15.6 dBi (compared to a gain of 10.7 dBi that is achieved by the microstrip Yagi antenna array) while maintaining an F/B ratio that is relatively high.

Design and Development of a Novel Compact Soft-Surface Structure for the Front-to-Back Ratio Improvement and Size Reduction of a Microstrip Yagi Array Antenna

In this letter, a novel antenna structure based on a microstrip Yagi array antenna and a soft surface (SS) ring is proposed, that enables a highly directional gain in addition to an improved front-to-back (F/B) ratio of more than 20 dB. The SS ring is shown to be capable of greatly improving the performance while miniaturizing the designs size by half. The implementation of the SS ring to a microstrip Yagi array antenna is demonstrated to verify its functionality in suppressing surface waves, showing that an improvement of at least 3 dB in the F/B ratio can be obtained. The design is investigated at the center frequency of 5.8 GHz; however, the structure can be easily scaled to other frequency ranges. A design analysis is performed to give insight into the operational mechanism of the SS ring and the critical dimensions that affect the SS structure surrounding the antenna array. In addition, measurements are presented to validate the results obtained via simulation. The principles established in this letter can be applied to other planar antenna designs.

RFID-Based Sensors for Zero-Power Autonomous Wireless Sensor Networks

Radio frequency identification (RFID) technology has enabled a new class of low cost, wireless zero-power sensors, which open up applications in highly pervasive and distributed RFID-enabled sensing, which were previously not feasible with wired or battery powered wireless sensor nodes. This paper provides a review of RFID sensing techniques utilizing chip-based and chipless RFID principles, and presents a variety of implementations of RFID-based sensors, which can be used to detect strain, temperature, water quality, touch, and gas.

Novel Design of a Highly Sensitive RF Strain Transducer for Passive and Remote Sensing in Two Dimensions

A novel design of a highly sensitive wireless passive RF strain transducer is presented based on a patch antenna loaded with an open loop that is capable of sensing strain independently in two directions. An original idea of utilizing a cantilever at the gap of the open loop significantly improves the sensitivity of resonant frequency shifts. The frequency shifts in two distinct resonant modes are detected based on two dominant orthogonal modes of the patch resonators. In measurements, the prototypes achieved a sensitivity of 2.35% frequency shift per 1% strain, more than twice that of existing strain transducers of the same class. In simulations, the new design achieved a theoretical sensitivity up to four times as high as existing designs of RF passive wireless strain transducers. The ground plane allows for the sensitivity of the sensor to be independent from the applied surface. An implementation example of the passive remote sensing system based on the proposed strain transducer is also discussed as a proof-of-concept case. Based on calculations, the interrogation method in the example shows a radar cross section fluctuation of 3.8 dB corresponding to the strain induced at the sensor.

Design and Development of a Novel Passive Wireless Ultrasensitive RF Temperature Transducer for Remote Sensing

A wireless, passive, and ultrasensitive temperature transducer is presented in this paper. The transducer consists of split ring resonators loaded with micro-bimorph cantilevers, which can potentially operate up to millimeter-wave frequencies (above 30 GHz). As the temperature changes, the bimorph cantilevers deflect and result in a shift of the resonant frequency of the split rings. A design is proposed, that has a maximum sensitivity of 2.62 GHz/μm, in terms of frequency shift per deflection unit, corresponding to a sensitivity of 498 MHz/°C for an operating frequency around 30 GHz, i.e., a frequency shift of 1.6% per °C. Theoretically, its about two orders of magnitude higher than the existing sensors observed in the same class. This sensor design also offers a high Q factor and is ultra-compact, enabling easy fabrication and integration in micro-electromechanical systems technology. Depending on the choice of materials, the proposed designs can also be utilized in harsh environments. As a proof of concept, a prototype is implemented around 4.7 GHz which exhibits a frequency shift of 0.05%/°C, i.e., 17 times more sensitive than the existing sensors.

Nanotechnology Enables Wireless Gas Sensing

In this paper different topologies of CNT-based RF passive gas sensors are presented, particularly focusing on wireless transducers, which can directly indicate gas concentration through the change of easy to-monitor RF parameters. CNTs feature numerous unique properties that could potentially enable the next generation of gas sensors with sensitivities better by 1-2 orders of magnitude with respect to existing ones.

A novel passive wireless ultrasensitive RF temperature transducer for remote sensing

A wireless passive ultrasensitive temperature transducer is presented in this paper. The transducer consists of micro bimorph cantilevers (Aluminum-Silicon) and split ring resonators, operating at millimeter wave frequencies around 30 GHz. As the temperature changes, the bilayer cantilevers deflect and thus alter the resonant frequencies of the resonators. The design achieves a sensitivity of 1.05 GHz/um with respect to cantilever deflection, corresponding to a sensitivity of 150 MHz/°C, three orders of magnitude higher than existing passive wireless temperature sensors. The sensor design has high Q factor, is ultra-compact, easily fabricated and integrated with other passive sensors in sensing networks. Depending on material choices, the proposed design can also be utilized in harsh environments. To demonstrate the proof-of-concept, scaled designs around 4 GHz are presented, utilizing Aluminum-PET (Polyethylene terephthalate) bilayer cantilevers, achieves a sensitivity of 2.14 MHz/°C.

Wireless sensing and identification of passive electromagnetic sensors based on millimetre-wave FMCW RADAR

The wireless measurement of various physical quantities from the analysis of the RADAR Cross Sections variability of passive electromagnetic sensors is presented. A millimetre-wave Frequency-Modulated Continuous-Wave RADAR is used for both remote sensing and wireless identification of sensors. Long reading ranges (up to some decameters) may be reached at the expense of poor measurement resolution (typically 10%).

Design of a highly sensitive wireless passive RF strain transducer

A highly sensitive wireless passive radio frequency strain transducer is designed and developed based on a patch antenna loaded with an open loop. A novel idea of utilizing a cantilever at the gap of the open loop significantly improves the sensitivity of resonant frequency shifts. The ground plane allows the sensitivity of the sensor to be independent from the applied surface. A proof-of-concept prototype is fabricated and the measurements successfully validate the operation principle.

Graphene enhanced wireless sensors

In this paper we demonstrate the design and development of a family of low-cost, self-powered, wireless sensor solutions utilizing both analog and digital principles. The sensors will utilize Graphene-based thin films integrated directly into the structure. For an immediately deployable digital sensing solution compatible with current commercial technologies we will utilize the Intel WISP platform, which can be read with current COTS products. Our thin films are produced from water-based, inkjet printed graphene oxide (GO) on paper/Kapton, developed using both conventional thermal and laser reduction techniques. In addition to reporting the first ever integration of inkjet-printed water soluble GO inks into low cost, flexible RF electronics, we also bring gas sensing capabilities to RFID tags relying on purely wireless digital transmission. The introduction of low cost, mass producible, eco-friendly, reduced graphene oxide (RGO) films on paper substrates lays the foundation for the development of a wide range of new low-cost, high performance Graphene-based electronic devices.