Hervé Aubert

Design and Implementation of Two-Layer Compact Wideband Butler Matrices in SIW Technology for Ku-Band Applications

The design and realization of a novel wideband two-layer 4 × 4 Butler matrix in substrate integrated waveguide (SIW) technology are addressed. The two-layer SIW design is exploited through a two-fold enhancement approach. The two-layer topology is first explored in a simple matrix layout with minimum number of components. A space saving design is then proposed making optimum use of the two-layer topology and the SIW technology leading to a significant size reduction. A two-level, low-loss, wideband SIW transition is designed and optimized using its equivalent circuit model. The two corresponding Butler matrix prototypes are optimized, fabricated and measured. Measured and simulated results are in good agreement. Isolation characteristics better than -15 dB with input reflection levels lower than - 12 dB are experimentally validated over 24% frequency bandwidth centered at 12.5 GHz. Measured transmission magnitudes and phases exhibit good dispersive characteristics of 1 dB, around an average value of -6.8 dB, and 10° with respect to the theoretical phase values, respectively, over the entire frequency band. The impact of the measured transmission phases and magnitudes on the radiation pattern of a 4-element antenna array is also investigated.

Scale-Changing Technique for the Electromagnetic Modeling of MEMS-Controlled Planar Phase Shifters

A scale changing approach is proposed for the electromagnetic modeling of phase-shifter elements used in reconfigurable microelectromechanical system (MEMS)-controlled reflectarrays. Based on the partition of the discontinuity plane in planar sub-domains with various scale levels, this technique allows the computation of the phase shift from the simple cascade of networks, each network describing the electromagnetic coupling between two scale levels. The high flexibility of the approach associated with the advantages of the integral equations formulations renders this original approach powerful and rapid. The scale-changing technique allows quasi-instantaneous computing of the 1024 phase shifts achieved by ten RF-MEMS switches distributed on the phase-shifter surface. Moreover, the proposed approach is much better than the finite-element-method-based software in time costing. Experimental data are given for validation purposes

Radio frequency pressure transducer

A novel system is reported here for the pressure measurement at microwave and millimetre-wave frequencies. This method consists in using a radio frequency transducer based on RF resonator. Accurate determination of the pressure is expected.

Pressure micro-sensor based on Radio-Frequency transducer

A new type of pressure micro-sensors is reported in this communication. It is based on the use of a Radio-Frequency transducer. The pressure to be measured is applied on a silicon membrane located in the close vicinity of a coplanar millimeter-wave resonator: when varying the applied pressure, the distance between the membrane and the planar resonator is modified and consequently, the resonant frequency of the cavity changes. From the measurement of the resonant frequency the applied pressure is derived. Coplanar technology has been chosen because, on the one hand, it confers a better sensitivity to the pressure cell compared to the microstrip technology and, on the other hand, it does not require backside technological processing. In the millimeter frequency range, HFSS simulation results predict a good sensitivity of the resonant frequency to the applied pressure. Very first prototypes of the original pressure micro-sensor based on Radio-Frequency transducer were micro-machined and the obtained measured performances are presented here. Experimental results confirm the expected sensitivity of this new type of pressure micro-sensors.

Microwave Power Harvesting for Satellite Health Monitoring

This paper addresses the microwave energy harvesting on board of geostationary satellites for health satellite monitoring. To prove the feasibility of such a concept, we investigated the electromagnetic environment existing on antenna panels. Based on established cartographic maps, three designs of rectennas are proposed. Measured dc powers ranging from 0.256 to 1.28 mW can be harvested for electric field levels ranging from 91 to 121 V/m and by using very simple and compact designs. The harvesting structures consist of only one Schottky diode per rectenna and present a total surface of 2.4 cm 2. They are suitable for powering the new generation of ultra-low power transceivers, thus enabling autonomous wireless power networks for satellite health monitoring.

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.

Novel Microfluidic Structures for Wireless Passive Temperature Telemetry Medical Systems Using Radar Interrogation Techniques in Ka-Band

We present a new miniaturized (below 1 mm3) temperature sensor based on microfluidic technology and radar passive interrogation principles, which can be easily applied for temperature telemetry for medical applications. The chipless microsystem is made up of a planar-gap capacitor with a microchannel located in between its plates. The temperature-dependent expansion/shrinkage of the water inside the microchannel modifies in a monotonic way the liquid level across the capacitor. The resulting change in the effective permittivity modifies the capacitance value in a temperature-dependent way. The first prototypes of the temperature microsensor were micromachined and integrated with an antenna, while the ambient temperature was remotely measured using frequency-modulated continuous-wave (FMCW) radar interrogation principles at 29.75 GHz. Preliminary measurement results demonstrated a 0.4 dBm/°C sensitivity over a 9°C temperature range (24°C-33°C).

EQUIVALENT ELECTRICAL CIRCUIT FOR DESIGNING MEMS-CONTROLLED REFLECTARRAY PHASE SHIFTERS

This article presents an equivalent electrical circuit for designing Radio-Frequency MEMS-controlled planar phase shifter. This kind of phase shifters has recently been incorporated in reconflgurable re∞ectarrays. The proposed equivalent circuit depends on the number, the ON/OFF state and the locations of the switches inside the unit cell. Such equivalent circuit is used for determining, with a little computational efiort, the two important design parameters i.e., the number and the locations of RF-MEMS switches in the phase shifter cell. These two design parameters then allow a designer to design a phase shifter cell having a linear distribution of a given number of phases over 360 - phase range at a single desired frequency.