Stylianos D. Assimonis

Design and Optimization of Uniplanar EBG Structures for Low Profile Antenna Applications and Mutual Coupling Reduction

We present a series of designs for uniplanar electromagnetic bandgap structures for antennas and microwave circuits. The proposed, easy to fabricate configurations, are based solely on metallic surfaces on layer interfaces, without the use of vias or other kinds of vertical connections. Their use in low profile antenna applications and mutual coupling reduction of planar radiating elements is investigated through an efficient and versatile technique, since the only information needed is the reflection phase and the dispersion diagram of the unit cell.

Computational Investigation and Design of Planar EBG Structures for Coupling Reduction in Antenna Applications

The uniplanar cross-like compact EBG structure is thoroughly assessed by means of a computational FEM-based eigenvalue analysis. A careful inspection of the dispersion diagram reveals the existence of a nearly-TEM mode that compromises the bandgap behavior, a fact that is also confirmed in coupling performance investigations. The structure is then modified and optimized to maximize the resulting bandgap zone, for mutual coupling reduction in WiMAX MIMO arrays.

A Family of Ultra-Thin, Polarization-Insensitive, Multi-Band, Highly Absorbing Metamaterial Structures

The systematic design of size-conflned, polarization- independent metamaterial absorbers that operate in the microwave regime is presented in this paper. The novel unit cell is additionally implemented to create e-cient multi-band and broadband structures by exploiting the scalability property of metamaterials. Numerical simulations along with experimental results from fabricated prototypes verify the highly absorptive performance of the devices, so developed. Moreover, a detailed qualitative and quantitative analysis is provided in order to attain a more intuitive and sound physical interpretation of the underlying absorption mechanism. The assets of the proposed concept, applied to the design of difierent patterns, appear to be potentially instructive for various EMI/EMC conflgurations.

Two-parameter Nyquist pulses with better performance

We present three novel Nyquist (intersymbol interference free) pulses that outperform two sophisticated pulses reported in literature by Bealieu et al. and Assalini and Tonello. The pulses are based on the concept of inner and outer functions, which was recently explored by the authors. Apart from requiring only two design parameters, the proposed pulses offer an enhanced error performance for various values of roll-off factor and timing jitter along with a smaller maximum distortion.

Sensitive and Efficient RF Harvesting Supply for Batteryless Backscatter Sensor Networks

This work presents an efficient and high-sensitivity radio frequency (RF) energy harvesting supply. The harvester consists of a single-series circuit with one double diode on a low-cost, lossy FR-4 substrate, despite the fact that losses decrease RF harvesting efficiency. The design targeted minimum reflection coefficient and maximum rectification efficiency, taking into account not only the impedance matching network, but also the rectifier microstrip trace dimensions and the load. The simulated and measured rectenna efficiency was 28.4% for -20-dBm power input. In order to increase sensitivity, i.e., ability to harvest energy and operate at low power density, rectennas were connected in series configuration (voltage summing), forming rectenna arrays. The proposed RF harvesting system ability was tested at various input power levels, various sizes of rectenna arrays, with or without a commercial boost converter, allowing operation at RF power density as low as 0.0139 μW/cm2. It is emphasized that the boost converter, whenever used, was self-started, without any additional external energy. The system was tested in supplying a scatter radio sensor, showing experimentally the effect of input power density on the operational cold start duration and duty cycle of the sensor.

Parametric Construction of Improved Nyquist Filters Based on Inner and Outer Functions

In this paper, we explore the concept of inner and outer functions to come up with two novel parametric families of Nyquist pulses. Aside from requiring only two design parameters, the proposed pulses yield an enhanced performance compared to the sophisticated flipped-inverse hyperbolic secant (asech) pulse, that was recently presented in the literature. While the construction of parametric families originates from the work of Beaulieu and Damen, the usage of inner and outer functions guarantees a higher flexibility in the choice of the composite family members. The proposed pulses may have a slower decay rate than the well-known raised-cosine (RC) pulse, but exhibit a more pronounced decrease in the amplitudes of the two largest sidelobes and this accounts for their improved robustness to error probabilities. In the following, it is clearly demonstrated that a lower bit error rate (BER), compared to the existing pulses, can be achieved for different values of the roll-off factor and timing jitter. Moreover, a smaller maximum distortion along with a more open eye diagram are attained as well.

Efficient RF harvesting for low-power input with low-cost lossy substrate rectenna grid

An efficient, low-cost and low-complexity rectenna-grid is analyzed, fabricated and measured, for low-power RF input and RF density. The design consists of two single series rectifier circuits that add the currents from each diode, in order to increase the offered power at the load. Despite the fact that a lossy and low-cost FR-4 substrate was used, the rectenna-grid offers 200 μW at load for 1 μW=cm2 ambient power density, while for 0.01 μW=cm2 the power at load reaches 0.8 μW. Furthermore, RF-to-DC rectification efficiency of 20.5% and 35.3% is achieved at -20 and -10 dBm power input, respectively. Measurements of the proposed RF harvester agree well with simulations. Finally, the rectenna was connected to a DC-to-DC converter and the open voltage was increased from 298 mV to 1.4 V, charging a 1 mF capacitor at 37 min. The stored energy could supply a sensor in a wireless network, with consumption 20 mW, rate 1 kbps and word-length of 20 bits.

Soil Moisture Scatter Radio Networking With Low Power

A low-cost (6 Euro per sensor), low-power (in the order of 200 μW per sensor), with high communication range (on the order of 250 m), scatter radio sensor network is presented, for soil moisture monitoring at multiple locations. The proposed network utilizes analog frequency modulation in a bistatic network architecture (i.e., the emitter and reader are not colocated), while the sensors operate simultaneously, using frequency-division multiple access. In contrast to prior art, this paper utilizes an ultralow-cost software-defined radio reader and offers custom microstrip capacitive sensing with simple calibration, as well as modulation pulses for each scatter radio sensor with 50% duty cycle; the latter is necessary for scalable network designs. The overall root mean squared error below 1% is observed, even for the range of 250 m. This is another small (but concrete) step for the adoption of scatter radio technology as a key enabling technology for scalable, large-scale, low-power, and cost environmental sensor networking.

Energy harvesting with a low-cost and high efficiency rectenna for low-power input

In this paper a low-complexity, low-cost and high efficiency rectenna is analyzed, fabricated and measured, for low input power. Even though the configuration employs a low-cost, lossy substrate and a low-complexity rectifier circuit with a single diode, the rectenna efficiency reaches 20% and 37% at -20 and -10 dBm, respectively. Measurements agree well with simulations.

Soil moisture wireless sensing with analog scatter radio, low power, ultra-low cost and extended communication ranges

The measurement of the soil moisture is critical in agriculture. In this work a joint analog design of wireless transmitter with scatter radio and capacitive sensor for soil moisture is presented. The design is based on a custom microstrip capacitor, exploits bistatic analog scatter radio principles and is able to wirelessly convey soil moisture percentage by mass (% MP) with RMS error of 1.9%, power consumption and communication range on the order of 100 uWatts and 100 meters, respectively. It is tailored for ultra-low cost (5 Euro per sensor) agricultural sensor network applications for soil moisture.