Daniela Staiculescu

A Novel Conformal RFID-Enabled Module Utilizing Inkjet-Printed Antennas and Carbon Nanotubes for Gas-Detection Applications

This letter introduces for the first time the integration of a conformal radio frequency identification (RFID) antenna with a single-walled carbon nanotube (SWCNT) composite in a chipless RFID node for toxic gas detection. The electrical performance characterization of the inkjet-printed SWCNT film is also reported for the first time up to 1 GHz. The whole module is realized by inkjet printing on a low-cost paper-based substrate, and the RFID tag is designed for the European UHF RFID band. The electrical conductivity of the SWCNT film changes in the presence of very small quantities of toxic gases like ammonia and nitrogen oxide, resulting in the variation of the backscattered power level, which can be easily detected by the RFID reader to realize reliable wireless toxic gas sensing.

Design rule development for microwave flip-chip applications

This paper presents a novel experimental approach for the analysis of factors to be considered when designing a flip-chip package. It includes the design of an experiment and statistical analysis of the outputs and uses both test-structure measurements and full-wave simulation techniques in the 1-35-GHz frequency range. The most significant factors are found to be, from the most to least important, the length of the area where the device and substrate overlap (referred to as conductor overlap), the bump diameter, and the width of the coplanar-waveguide transmission-line launch. These results are valid for conductor overlaps between 300-500 /spl mu/m. For a lower value (120 /spl mu/m), the significance level of the overlap decreases and the bump height also becomes significant. Test-structure measurements in the 120-200-/spl mu/m overlap range validate this result and demonstrate the decrease in the significance level. The substrate thickness in the 10-25-mil interval is found to be statistically insignificant, therefore, it can be eliminated from further analysis. This approach provides a foundation for development of a set of design rules for RF and microwave flip-chip similar to RF integrated-circuit design rules.

Conformal Magnetic Composite RFID for Wearable RF and Bio-Monitoring Applications

This paper introduces for the first time a novel flexible magnetic composite material for RF identification (RFID) and wearable RF antennas. First, one conformal RFID tag working at 480 MHz is designed and fabricated as a benchmarking prototype and the miniaturization concept is verified. Then, the impact of the material is thoroughly investigated using a hybrid method involving electromagnetic and statistical tools. Two separate statistical experiments are performed, one for the analysis of the impact of the relative permittivity and permeability of the proposed material and the other for the evaluation of the impact of the dielectric and magnetic loss on the antenna performance. Finally, the effect of the bending of the antenna is investigated, both on the S-parameters and on the radiation pattern. The successful implementation of the flexible magnetic composite material enables the significant miniaturization of RF passives and antennas in UHF frequency bands, especially when conformal modules that can be easily fine-tuned are required in critical biomedical and pharmaceutical applications.

Wideband scalable electrical model for microwave/millimeter wave flip chip interconnects

We present a method for developing fully scalable lumped element models for flip chip interconnects. Measurements of test structures and full wave simulations are used to generate circuit models for various single bump configurations. Furthermore, regression models are developed for scaling the values of the elements with the physical attributes of the circuit. First, the method is validated using only two factors, then the model is extended to more inputs related to the bump geometry and placement. The values of L and C in a simple /spl pi/ model have been scaled with the conductor overlap, the distance from the ground bump to the edge of the ground plane, the width of the CPW launch, the bump height and diameter. Explicit formulas are obtained for L and C as a function of those variables. It has been found that the value of the inductance varies with the conductor overlap, bump height and diameter, while the capacitance is mostly affected by conductor overlap. This paper presents the first fully scalable model for microwave flip chip technology.

Modeling and sensitivity analysis of circuit parameters for flip-chip interconnects using neural networks

This paper presents a neural network-based technique for modeling and analyzing the electrical performance of flip-chip transitions. A lumped element model using a simple pi equivalent circuit is used to characterize the electrical properties of the flip-chip bond. Statistical experimental design is used to extract the electrical parameters for flip-chip characterization from measurements and full-wave simulations up to 35 GHz. The extracted data is used to train back-propagation neural networks to obtain an accurate model of the pi equivalent circuit components and s-parameters as a function of layout parameters. The prediction error of the models is less than 5%. The models are used to obtain response surfaces for the entire range of variation of layout parameters. The neural network models are subsequently used to perform sensitivity analysis. All electrical parameters are shown to be sensitive to conductor overlap. The inductance and capacitance of the pi equivalent circuit are sensitive to the bump height. However, the return loss (S11) is insensitive to the change in bump height. The coplanar waveguide width has a significant impact on the s-parameters, as it affects the matching of flip-chip transitions

Design and optimization of 3-D compact stripline and microstrip Bluetooth/WLAN balun architectures using the design of experiments technique

In this paper, various architectures of three-dimensional compact microwave balanced to unbalanced (balun) transformers for Bluetooth/WiFi antenna applications are successfully designed and optimized using the design of experiments (DOE) approach. Two different multilayer topologies, one microstrip and one stripline, are investigated on low temperature co-fired ceramic (LTCC) substrate. The design goals for both baluns are perfectly balanced outputs from 2 to 3 GHz and a resonant frequency of exactly 2.4 GHz. It is demonstrated, using only eight simulations, that perfectly balanced outputs are not possible under the given conditions in the case of the microstrip balun. Nevertheless, the stripline balun can be optimized due to its almost symmetrical structure, and both simulations and measurement results verify the conclusions. The DOE method is very simple to implement and gives a clear understanding of the system behavior at the beginning of the design process, reducing the amount of work required for achieving the design goals by orders of magnitude compared to the widely used trial-and-error approach. The matching and unique measurement issues regarding the calibration, placement of probes and the de-embedding of the microstrip to coplanar waveguide transitions are discussed in detail for the optimized stripline balun. This technique can be easily applied to the fast and efficient optimization of complicated radiation structures, such as reconfigurable or multilayer multiband antenna arrays.

Design rule development for microwave flip chip applications

This paper presents a novel approach for analysis of factors to be considered when designing a flip chip package. It includes the design of an experiment and statistical analysis of the outputs. The most significant factors are found to be, from most to least important, the length of the area where the device and the substrate overlap (referred to as conductor overlap), the bump diameter and the width of the coplanar waveguide transmission line launch. These results are valid for conductor overlaps between 300 and 500 /spl mu/m. For a lower overlap value (120 /spl mu/m), the bump height also becomes significant. The substrate thickness in the 10 to 25 mil interval is found to be statistically insignificant, and therefore can be eliminated from further analysis.

Ni-Au surface finish effects on RF performance

We present a simplified analysis of the Nickel-Gold surface finish effects on microstrip conductive losses for boards with different Ni thickness and Ni/Au finish chemistries. Otherwise identical test structures were fabricated with various Ni/Au finishes and different thicknesses. The conductive loss has been extracted from Q measurements on series microstrip resonators. A theoretical model for conductor loss of a two metal layer system has also been proposed. The theoretical approach has been supported with measurement results. For a specific frequency, conductive loss shows an S-curve behavior with Ni thickness.

Full wave analysis and development of circuit models for flip chip interconnects

This paper presents a full electromagnetic wave analysis at bump interconnects in flip chip packages. From measurement and simulation, a simple and accurate lumped element model has been developed for such flip chip interconnects. Based on our analysis, we provide basic design guidelines for flip-chip operation to 20 GHz.

Design and development of compact conformal RFID antennas utilizing novel flexible magnetic composite materials for wearable RF and biomedical applications

This paper reports the first conformal RFID antenna printed on a flexible magnetic composite material for the UHF frequency band. The target applications are wearable RFIDs and bio-monitoring wireless probes. The successful implementation of the flexible magnetic composite material allows the tag miniaturization and provides excellent electrical performance in the 480 MHz band. First, the material is chosen for optimal electric and magnetic losses, then the antenna is designed for both the non-magnetic material and the magnetic one to prove the miniaturization. Finally, the effect of bending the antenna on the measured return loss performance is investigated.