Nahid Vahabisani

Compact MEMS-Based Ultrawide-Band CPW Band-Pass Filters With Single/Double Tunable Notch-Bands

In this paper, novel ultrawide-band (UWB) band-pass filters with single and double tunable notch-bands are described. To the best of our knowledge, this is the first MEMS-based UWB filter reported with double tunable notch-bands. In this design, a new configuration of μ-strip coupled lines integrated with the MEMS capacitor is developed and used for tuning. The proposed structure is analyzed by considering the LC equivalent circuit of the MEMS capacitor and it is shown that an extra transmission zero (notch-band) is realized at its resonance. Each notch-band frequency can be independently tuned up to 1 GHz using MEMS capacitors actuation, while the filter performance across its ultrawide pass-band remains unchanged. The proposed filter is suitable for UWB applications when flexible interference blockage is required.

Monolithic Millimeter-Wave MEMS Waveguide Switch

Here, for the first time, a monolithic wafer-level micro-electro-mechanical systems (MEMS) waveguide switch for millimeter-wave application is presented. The switch is based on the monolithic integration of MEMS actuators (cantilever beams) inside the waveguide channel. The highly deflected beams are electrostatically actuated to provide on and off states. In the off state, the beams are pushing against the upper inner wall of the waveguide to provide a short circuit, while the actuators are rolled flat to allow for maximum signal propagation during the on state. The switch illustrates an excellent wideband RF performance, with an insertion loss as low as 0.2 dB in the on state, and isolation of better than 22 dB in the off state, for the entire 60-75 GHz frequency band. A low-loss waveguide to CPW transition is also designed and integrated with the switch, which exhibits less than 1.1 dB loss for a back-to-back configuration across the band, and enables the on-wafer characterization of the entire structure.

A novel ultra wideband (UWB) filter with double tunable notch-bands using MEMS capacitors

This paper presents a novel UWB filter with double tunable notch bands on coplanar technology. Each notch-band frequency can be independently tuned using MEMS capacitors while the filter performance across its ultra-wide pass band remains unchanged. The measured results indicate up to 1GHz independent tuning range for each notch frequency. To our knowledge, this is the first UWB filter reported with double tunable notch bands. In addition, a high impedance resonator has been incorporated and a size reduction of up to 66% has been achieved compared to its conventional half wavelength counter parts. The proposed filter is suitable for ultra wide band applications when flexible interference blockage is required.

A new wafer-level CPW to waveguide transition for millimeter-wave applications

A novel wafer-level coplanar waveguide (CPW) line to rectangular waveguide transition for millimeter-wave communication is presented in this paper. A metalized probe is adopted to couple the signal from the CPW to waveguide. Unlike the previous designs which are mostly based on capacitive coupling, the proposed CPW to waveguide transition is based on inductive coupling and offers the capability of monolithic fabrication of the transition on a wafer. Thus, the transition can be easily integrated with any micro-fabricated waveguide device and provides amenable option of having waveguide integration.

Microfluidically Reconfigurable Rectangular Waveguide Filter Using Liquid Metal Posts

In this letter, the integration of microfluidically controlled liquid metal with WR42 rectangular waveguide to implement reconfigurable band-reject/band-pass filter is introduced. Here, microfluidic channels carrying liquid metal are used to realize off-centered adjustable partial/full-height circular posts at the dominant T E10 mode. First, a liquid metal post is partially inserted into the waveguide to create a tunable transmission zero over a 2.9 GHz rejection tuning range (18.20 GHz to 21.10 GHz). Next, the band-reject element (partial-height post) is used in conjunction with another microfluidic metal post to design a reconfigurable 1-pole band-pass filter with a transmission zero in the stop-band. The filter is configured for two states. The measured insertion loss of the filter at J0 is 2.3 dB and 2.8 dB while the return loss is better than 20 dB and 30 dB for State 1 and State 2 respectively.

A Microwave Ring Resonator Sensor for Early Detection of Breaches in Pipeline Coatings

A planar microwave resonator sensor is designed, customized, and fabricated to detect coating breaches in industrial steel pipelines. The sensor, which utilizes a ring-shaped resonator to maximize the sensitivity at its core, is tuned to 2.5 GHz with a quality factor of 280. In the setup, the sensor is grounded to a piece of steel pipeline with an Epoxy-100 coating, which provides the substrate beneath the microstrip structure. It is demonstrated that any change in the gap height between the substrate layer and the pipeline, from 0 to 3.5 mm, produces a significant resonant frequency variation and bandwidth change in the sensors response. The sensor structure demonstrates sensitivity and selectivity to air and water penetration to the breach. The sensor structure described in this work is a compact, low-cost solution and has potential for further miniaturization in mobile applications which may serve as a method for pipeline breach detection.

Monolithic Wafer-Level Rectangular Waveguide and Its Transition to Coplanar Waveguide Line Using a Simplified 3-D Fabrication Process

In this paper, we are introducing a new category of wafer-level micromachined rectangular waveguide devices and illustrate a new transition of these devices to Coplanar Waveguide (CPW) lines for millimeter-wave applications. The 3-D fabrication process used in this paper utilizes a combination of thin film and thick film processes and produces a simple three-mask fabrication process. As a result, all the on-wafer elements such as the waveguide, the CPW lines, and their transition are simultaneously fabricated, which eliminates the ever-existing requirement of hybrid assembly of the waveguide parts. A metalized post is employed to couple the signal from the CPW line to the waveguide. Unlike the previous designs that are mostly based on capacitive coupling, the proposed CPW to waveguide transition is based on inductive coupling, which simplifies the fabrication requirements and improves the performance. Here, the entire back-to-back structure is designed, fabricated, and measured on a 10 mm2 wafer area. A wide-band RF performance is measured for the proposed waveguide structure. Our measured results show an insertion loss of as low as 1 dB at 72 GHz range. The proposed technique to realize wafer-level waveguides has great potential to include a variety of waveguide topologies including bends and arcs. Besides, this method allows for further expansion of the topic to integrate MEMS components inside the waveguide.

Study of Contact Resistance for Curled-Up Beams in Waveguide Switch

In this letter, we are proposing a new technique to determine the contact resistance of the curled up beams in RF MEMS waveguide switches. Unlike the previous studies on the contact resistance of RF MEMS switches, here the contact resistance is measured at the “OFF” state of the switch with no dc voltage applied. The presented concept has been analyzed theoretically and verified by simulations and experimental data, illustrating less than 10% error. This study provides a measure for estimating the contact resistance of the emerging RF and millimeter-wave MEMS waveguide switches and paves the way for commercialization of such devices.

A Fully 3-D Printed Waveguide and Its Application as Microfluidically Controlled Waveguide Switch

This paper reports the design, fabrication, and characterization of a fully 3-D printed waveguide (WG) and a microfluidically controlled WG switch, operating at K-band. The WG body is printed using a benchtop 3-D printer with thermoplastic substrate acrylonitrile butadiene styrene, and the conductive layer is incorporated using the same printer by automated deposition of conductive silver ink. The measured total insertion loss of the 3-D printed WG is in good match with the simulations showing better than 0.11 dB/cm for the entire K-band. The 3-D printed WG is characterized, and its attenuation and propagation constants are computed for the K-band using a multiline technique. In addition, microfluidically controlled eutectic gallium-indium and galistan liquid metals are integrated with the 3-D printed WG, and a novel reflective WG switch is implemented. The insertion loss and isolation of the switch are measured to be better than 0.5 dB and better than 15 dB for the entire K-band, respectively. Furthermore, the switchs performance with respect to changes in ambient temperature has been studied. To the best of our knowledge, this is the first time that fused deposition modeling printing and automated ink dispensing is used to fabricate fully 3-D printed WGs, and a 3-D printed WG switch is developed, exhibiting the potential of such technology for rapid prototyping of RF devices.

Realization of a new class of monolithic RF MEMS waveguide switches for millimeter-wave applications

A new category of monolithic RF MEMS waveguide switches for the millimeter-wave application is presented in this paper. The switches are based on monolithic integration of highly deflected RF MEMS actuators (cantilever beams) inside the waveguide channel. The waveguide structure and the MEMS components are simultaneously fabricated using a monolithic 8-mask fabrication process. It is shown that the actuators in the UP state virtually generate a conductive wall that can be used to reroute the signal and design various waveguide switch structures. When the actuators are pulled down, they coincide with the inner wall of the waveguide and are completely removed from the signal path. To prove the concept, a monolithic waveguide “Short” using the curled-up MEMS actuators is fabricated and the results are compared to a solid wall for the frequency band of 60 GHz-75 GHz. The idea is then generalized to show the feasibility of multiport structures such as C-type switch.