Kagan Topalli

Frequency Tunable Microstrip Patch Antenna Using RF MEMS Technology

A novel reconfigurable microstrip patch antenna is presented that is monolithically integrated with RF microelectromechanical systems (MEMS) capacitors for tuning the resonant frequency. Reconfigurability of the operating frequency of the microstrip patch antenna is achieved by loading it with a coplanar waveguide (CPW) stub on which variable MEMS capacitors are placed periodically. MEMS capacitors are implemented with surface micromachining technology, where a 1-mum thick aluminum structural layer is placed on a glass substrate with a capacitive gap of 1.5 mum. MEMS capacitors are electrostatically actuated with a low tuning voltage in the range of 0-11.9 V. The antenna resonant frequency can continuously be shifted from 16.05 GHz down to 15.75 GHz as the actuation voltage is increased from 0 to 11.9 V. These measurement results are in good agreement with the simulation results obtained with Ansoft HFSS. The radiation pattern is not affected from the bias voltage. This is the first monolithic frequency tunable microstrip patch antenna where a CPW stub loaded with MEMS capacitors is used as a variable load operating at low dc voltages

A tunable multi-band metamaterial design using micro-split SRR structures

This paper presents the results of a feasibility study for the design of multi-band tunable metamaterials based on the use of micro-split SRR (MSSRR) structures. In this study, we have designed and constructed a conventional split-ring resonator (SRR) unit cell (type A) and two modified SRR unit cells having the same design parameters except that they contain two (type B) or four (type C) additional micro-splits on the outer square ring, along the arm having the main split. Transmission characteristics of the resulting MSSRR cells are obtained both numerically and experimentally and compared to those of the ordinary SRR unit cell. It is observed that the presence of the additional micro-splits leads to the increase of resonance frequency by substantial amounts due to the series capacitance effect. Next, we have designed and constructed 2 x 2 homogeneous arrays of magnetic resonators which consist of the same type of cells (either A, or B, or C). Such MSSRR blocks are found to provide only a single frequency band of operation around the magnetic resonance frequency of the related unit cell structure. Finally, we have designed and constructed 2 x 2 and 3 x 2 inhomogeneous arrays which contain columns of different types of metamaterial unit cells. We have shown that these inhomogeneous arrays provide two or three different frequency bands of operations due to the use of different magnetic resonators together. The number of additional micro-splits in a given MSSRR cell can be interactively controlled by various switching technologies to modify the overall metamaterial topology for the purpose of activating different sets of multiple resonance frequencies. In this context, use of electrostatically actuated RF MEMS switches is discussed, and their implementation is suggested as a future work, to control the states of micro-splits in large MSSRR arrays to realize tunable multi-band metamaterials.

A Monolithic Phased Array Using 3-bit Distributed RF MEMS Phase Shifters

This paper presents a novel electronically scanning phased-array antenna with 128 switches monolithically implemented using RF microelectromechanical systems (MEMS) technology. The structure, which is designed at 15 GHz, consists of four linearly placed microstrip patch antennas, 3-bit distributed RF MEMS low-loss phase shifters, and a corporate feed network. MEMS switches and high-Q metal-air-metal capacitors are employed as loading elements in the phase shifter. The system is fabricated monolithically using an in-house surface micromachining process on a glass substrate and occupies an area of 6 cm times 5 cm. The measurement results show that the phase shifter can provide nearly 20deg/50deg/95deg phase shifts and their combinations at the expense of 1.5-dB average insertion loss at 15 GHz for eight combinations. It is also shown by measurements that the main beam can be steered to required directions by suitable settings of the RF MEMS phase shifters.

Pirani Vacuum Gauges Using Silicon-on-Glass and Dissolved-Wafer Processes for the Characterization of MEMS Vacuum Packaging

This paper presents the design and implementation of Pirani vacuum gauges for the characterization of vacuum packaging of microelectromechanical systems (MEMS). Various Pirani vacuum gauges are fabricated with two different standard in-house fabrication processes, namely the silicon-on-glass (SOG) process and dissolved-wafer process (DWP). The Pirani gauges utilize meander-shaped suspended silicon coils as the heaters and two isolated silicon islands in the close proximity of the heater that function as dual-heat sinks to enhance the sensitivity and dynamic range as compared to a microbridge with a single heat sink. The gauges are designed to occupy an area of 4 mm × 1.5 mm. The DWP Pirani gauge fabricated with a structural thickness of 14 mum and a gap of 2 mum shows a measured sensitivity of 4.2×10⁴ (K/W)/Torr in a dynamic range of 10-2000 mTorr. The SOG Pirani gauge fabricated with a structural thickness of 100 mum and a gap of 3 mum shows a lower measured sensitivity of 3.8×10³ (K/W)/Torr in a dynamic range of 50-5000 mTorr; however, the 100 mum-thick structural layer results in a much more robust process against stress-based deformations in suspended silicon compared to the DWP Pirani gauges. Each gauge is used to monitor the pressure of a different packaging approach. The DWP Pirani gauge is used to detect the pressure of a wafer-level vacuum package, where the pressure inside the cavity is measured to be about 2.4 mTorr. The SOG Pirani gauge is used the monitor the pressure inside a hybrid platform package which is vacuum-sealed using a projection welder, where the pressure is measured to be about 1400 mTorr. These measurements verify that the DWP and SOG Pirani gauges can be used for the characterization of wafer-level or hybrid platform vacuum packages for MEMS devices.

Low-Loss Ku-Band Artificial Transmission Line With MEMS Tuning Capability

An artificial transmission line unit cell is presented based on the so-called composite right/left handed transmission line. It is implemented on a microelectromechanical system process on glass, and is suitable for applications such as reconfigurable leaky-wave antennas and series feed networks. The device presents state-of-the-art performance in terms of differential phase shift over losses (38deg/dB at 14 GHz) and quasi-zero drive power consumption. It is monolithic and has a total footprint of 4 mm2.

A monolithic phased array using 3-bit DMTL RF MEMS phase shifters

This paper presents a phased array system designed at 15 GHz employing 3-bit distributed MEMS transmission line (DMTL) type phase shifters which are monolithically integrated with the feed network of the system and the radiating elements on the same substrate. The phase shifter can give 0deg-360deg phase shift with 45deg steps at 15 GHz which is used to obtain various combinations of progressive phase shift in the excitation of radiating elements. The phased array is composed of four linearly placed microstrip patch antennas. In order to monolithically integrate the patch antennas and phase shifters, tapered lines with low return loss from microstrip to coplanar waveguide (CPW) have been designed. The design of the phased array system and its components is given. Since the DC biasing schema of a MEMS system is also an important issue in terms of the RF losses, the paper also addresses the effect of the bias lines on the loss characteristics of the phase shifters. Moreover, the process steps, which are used in the fabrication of the phased array, are also summarized

Reconfigurable Nested Ring-Split Ring Transmitarray Unit Cell Employing the Element Rotation Method by Microfluidics

A continuously tunable, circularly polarized X-band microfluidic transmitarray unit cell employing the element rotation method is designed and fabricated. The unit cell comprises a double layer nested ring-split ring structure realized as microfluidic channels embedded in Polydimethylsiloxane (PDMS) using soft lithography techniques. Conductive regions of the rings are formed by injecting a liquid metal (an alloy of Ga, In, and Sn), whereas the split region is air. Movement of the liquid metal together with the split around the ring provides 360 ° linear phase shift range in the transmitted field through the unit cell. A circularly polarized unit cell is designed to operate at 8.8 GHz, satisfying the necessary phase shifting conditions provided by the element rotation method. Unit cell prototypes are fabricated and the proposed concept is verified by the measurements using waveguide simulator method, within the frequency range of 8-10 GHz. The agreement between the simulation and measurement results is satisfactory, illustrating the viability of the approach to be used in reconfigurable antennas and antenna arrays.

A Reconfigurable RF MEMS Triple Stub Impedance Matching Network

This paper presents a reconfigurable triple stub impedance matching network using RF MEMS technology centered at 10GHz. The device is capable of covering impedances on the whole Smith Chart. The device structure consists of three variable length stubs which are designed as distributed MEMS transmission lines and two lambdag/8 length CPW transmission lines connecting the stubs. The variable length stubs are implemented with 12 MEMS switches over CPW lines and CPW lines connecting the switches. lambdag/8 spacing between the stubs is selected to obtain a uniform distribution of the impedance points on the Smith Chart. Initial measurement results of the fabricated structure show a good agreement with the simulation results

Dual-frequency reconfigurable slot dipole array with a CPW-based feed network using RF MEMS technology for X- and ka-band applications

In recent years there is a growing interest to combine various wireless applications in a single system for miniaturization purposes. A reconfigurable MEMS antenna that can operate in multi- frequencies is an appropriate way of reducing system volume. The monolithic integration of tunable MEMS components with antennas can also reduce parasitic effects, the losses, and packaging costs. Moreover an array of these types of antennas can offer solutions for the systems requiring high antenna gains. This paper presents a 4-element linear array of dual-frequency slot dipole antennas whose resonant frequencies are controlled via MEMS switches placed on the slots. The corporate feed network of the array is realized with coplanar wave transmission (CPW) lines. A CPW-based feed network has advantages over a microstrip feeding network, such as low radiation losses, less dispersion, easier in combining active devices for active array implementation, and the possibility of connecting shunt lumped without the need of via holes through the substrate. The CPW-based feed network in this paper includes properly designed T-junctions, chamfered corners, and dual-frequency impedance transformers in order to match the input impedance at the resonant frequency of the antennas. The proposed array structure, reconfigurable slot dipole antenna, and the details about the dual-frequency impedance transformer are presented in the following sections.

All-Silicon Ultra-Broadband Infrared Light Absorbers

Absorbing infrared radiation efficiently is important for critical applications such as thermal imaging and infrared spectroscopy. Common infrared absorbing materials are not standard in Si VLSI technology. We demonstrate ultra-broadband mid-infrared absorbers based purely on silicon. Broadband absorption is achieved by the combined effects of free carrier absorption, and vibrational and plasmonic absorption resonances. The absorbers, consisting of periodically arranged silicon gratings, can be fabricated using standard optical lithography and deep reactive ion etching techniques, allowing for cost-effective and wafer-scale fabrication of micro-structures. Absorption wavebands in excess of 15 micrometers (5–20 μm) are demonstrated with more than 90% average absorptivity. The structures also exhibit broadband absorption performance even at large angles of incidence (θ = 50°), and independent of polarization.