Rodica Ramer

Electric field tunable ferrite-ferroelectric hybrid wave microwave resonators: Experiment and theory

The electric field tuning characteristics of a combined microwave resonator based on ferrite-ferroelectric layered structure have been studied in a wide range of bias magnetic fields. The combined ferrite-ferroelectric resonator was composed of two rectangular resonators fabricated from a ceramic barium strontium titanate (BST) slab and a single-crystal yttrium iron garnet (YIG) film. The in-plane dimensions for the YIG and BST resonators were chosen to be equal in order to maximize the electromagnetic coupling between their main modes and reduce spurious influence of their higher order modes. A tuning range of 100MHz for the resonator frequency was realized at 5GHz through the variation of magnetic permeability and dielectric permittivity of the YIG-BST structure. A theory for the hybrid wave excitations, based on a coupled-mode approach, has been developed and provides good description of the data.

Scalable RF MEMS Switch Matrices: Methodology and Design

This paper proposes new solutions for implementing wideband large switch matrices. These solutions are based on crossbar and L-shaped topologies. This paper introduces a high-performance wideband switch cell to build up scalable NtimesN switch matrices and gives an account of the design, fabrication, and characteristics of the switch cell and a 3times3 crossbar switch matrix. The chosen design procedure is seen to be appropriate since it produces valid measured results. In addition, this paper presents an RF microelectromechanical systems L-shaped switch matrix, which indicates less variation of characteristics for certain types of connectivity. It also demonstrates that for a 4times4 switch matrix, there is a 50% improvement in insertion loss and phase-shift variation.

Monolithic crossbar MEMS switch matrix

This paper presents a novel approach to implement RF MEMS large size switch matrices. The concept is based on the implementation of a crossbar switch matrix and the introduction of unique switch cells that can be easily used to expand the matrix size. A six-mask fabrication process is adapted to fabricate the proposed four-port switch cell as well as the switch matrix samples. The switch cell has two operational states: thru and turn. This allows the cell to be easily integrated in the form of a crossbar switch matrix. Novel series contact cantilever beams have been used to implement the entire structure. The measured results for the entire switch cell show excellent insertion loss of 0.5dB, return loss of better than −20dB and isolation of −25dB for the thru path. The turn state of the switch shows a good performance of 0.4dB insertion loss, −18dB return loss and better than −25dB isolation for the frequency band of interest. A 3×3 switch matrix is implemented that shows 98% size reduction in comparison with the previously reported RF MEMS switch matrices.

RF MEMS Switchable Interdigital Bandpass Filter

By taking advantage of the MEMS contact type switches in tunable filters, a new method that allows both the adjustment of resonant frequency and the input/output and inter-resonator coupling is presented. A three-pole filter capable to switch to three different states is designed using this method. The measured center frequency for each state is 8, 9, and 10 GHz (25% tuning) with a constant bandwidth of around about 1 GHz. The measured insertion loss of the filter is better than 3.5 dB for all three states.

Novel Beam Design for Compact RF MEMS Series Switches

This paper presents two novel integrated RF MEMS series contact switches for broadband applications. The proposed designs are based on cantilever and clamped-clamped beams that can be easily integrated in large multi-port structures. A novel set of dimples are integrated in the cantilever type switch to prevent the unwanted warpage of the beam resulting from the residual stress of the fabrication process. The switches are fabricated using a metal based six-mask process. The results illustrate smooth beams with excellent RF performance. The cantilever beam switch shows an actuation voltage of 60 V with better than a 0.35 dB insertion loss and a 24 dB return loss up to 40 GHz. The isolation of the switch is 22 dB for all the frequency band of interest. The clamped-clamped beam switch results are also presented indicating enhanced isolation of 26 dB up to 40 GHz with 0.5 dB insertion loss.

Cluster head selection using decision trees for Wireless Sensor Networks

Wireless sensor network (WSN) is the hot research topic in the civil as well as military applications. Researchers are working in this area to boost it up according to the current needs and requirements. An efficient way to enhance the lifetime of the WSN is to partition the network into distinct clusters with a high-energy node called gateway as cluster-head. In this paper we present the cluster head selection scheme based on four major factors. We are using decision tree algorithm to select the best node as a cluster head. Simulation results show that the performance of this scheme is better than the cluster head selection using both the AHP (analytical hierarchy process) and the LEACH (low energy adaptive clustering hierarchy).

Cantilever beam designs for RF MEMS switches

This paper presents the design, modeling, fabrication and measurements of two novel radio frequency microelectromechanical systems (RF MEMS) switches. Two new non-standard cantilever beams have been designed in order to validate the mathematical model developed for the calculation of the spring constant and to verify the fabrication parameters. The mechanical modeling is based on the Euler?Bernoulli beam equations. The fabricated switches using these cantilever beams exhibit 19 V and 23 V actuation voltages. The fabrication consists of a six-mask all-metal process. A unique dry-release technique is also described. The RF simulations and measurements of these switches are finally presented. The isolation is better than 23 dB and 27 dB and the return loss is better than 19 dB and 18 dB, from 0 to 40 GHz. The insertion loss is 1.15 dB and 1.3 dB for the two designs, respectively, for all frequency bands of interest.

A novel RF MEMS switch with novel mechanical structure modeling

A novel RF MEMS contact-type switch for RF and microwave applications is presented. The switch is designed with special mechanical structures for stiffness enhancement. A method of using dimple lines to reduce the stress sensitivity of a beam is shown with complete mathematical modeling and finite element mechanical simulation. A complete mathematical model is developed for the proposed switch. Limited fabrication resolution and non-uniformities in layer thickness and stress were taken into consideration for this design, concomitantly with the preservation of device miniaturization and functionalities. The novel mechanical modeling of the switch leads to the estimation of the actuation voltage and shows simplification from previously published analysis. The measured actuation voltage and RF performance of the novel RF MEMS switch are also reported. The switch actuated at 20 V achieved better than 22 dB return loss and less than 0.7 dB insertion loss in on state from dc–40 GHz; it provided better than 30 dB isolation in off state.

Compact microstrip resonators for 900 MHz frequency band

A technique to reduce the size of planar resonators is investigated using a transmission line model and a finite-difference time-domain (FDTD) method. New miniaturized square microstrip resonators are proposed for 900 MHz band. The resonators offer low impedance sections leading to a better handling of power. The feasibility of compact filters using the proposed resonators is demonstrated. The input/output coupling lines of a two-pole filter have been positioned in a way that produces a filter response with transmission zeros on the both sides of the pass-band. Sharper skirts and higher out-of-band rejection are obtained for four-pole filters with cross-coupled resonators.

Quasi centralized clustering approach for an energy-efficient and vulnerability-aware routing in wireless sensor networks

In this paper, we propose a Quasi-Centralized Clustering Approach (QCCA), in which Wireless Sensor Network (WSN) partition into disjoint and equal-sized cells. Each cell has a powerful node, which acts as a cluster head. Hence, we consider a heterogeneous cluster-based WSN, which consists of two types of nodes: powerful clusterheads and ordinary sensor nodes. It leverages the advantages of small transmit distances for most nodes, requiring only a few nodes to transmit far distances to the base station. It completely eliminates redundant transmissions by ensuring, via carrier sensing (CSMA-CA), only one head sensor in each cell transmits and communicates with the sink, which can be either mobile or stationary. This approach reduces both energy consumption and communication bandwidth requirements, and prolongs the lifetime of the WSN. Simulation results show that a large amount of energy is saved using this strategy.