Cyrus Shafai

A Resonant Micromachined Magnetic Field Sensor

The design, modeling, and simulation of a novel micromachined magnetic field sensor are discussed. The sensor uses an electrostatic resonator whose fundamental resonant frequency is modified by a Lorentz force generated from the interaction of the sensor structure and the present magnetic field. The sensor was fabricated in a standard bulk micromachining process without the need for any additional processing steps. Since the sensor does not employ any magnetic materials, it does not exhibit hysteresis. A comprehensive model of the sensor behavior is derived which encompasses the interactions of the involved physical domains. Validity of the modeling results was verified by finite-element simulations, and later, through experiments. The sensitivities of the fabricated sensors are in the range of 48-87 Hz/T, depending on sensor structure and dimensions. The design of the sensor allows for its fabrication in many standard microelectromechanical system processes and is compatible with CMOS processes. The theoretical minimum detectable signal with current devices is on the order of 217 nT. Methods to improve the sensitivity of the current sensors are suggested. A linear response to a wide range of magnetic fields makes this design suitable for applications where large fields need to be measured with high resolution.

Thin films with nanometer-scale pillar microstructure

Thin films possessing microstructure composed of isolated vertical pillars were deposited by glancing angle deposition (GLAD) without the need for subsequent etch processing. The GLAD technique uses substrate rotation and oblique angle flux incidence to deposit a porous columnar thin film with engineered microstructures. Thin films with a pillar microstructure were fabricated from a variety of metals, metal oxides and fluorides, and semiconductors. The rate and incident angle of vapor flux, as well as the substrate rotation speed during deposition, were found to critically affect pillar microstructure. Thin films with pillar diameters and densities as low as 30 nm and 3 pillars per μm 2 , respectively, were deposited. The low stress, high surface area, and porous nature of these films suggests use of pillar microstructure films in optical, chemical, biological, mechanical, magnetic, and electrical applications.

Filter-Antenna Module Using Substrate Integrated Waveguide Cavities

A design procedure for filter-antenna modules based on substrate integrated waveguide cavities is presented in this letter. The filter-antenna module is modeled as an asynchronously tuned coupled-resonator circuit in which the last resonator also contains the radiating element. The design of the filter-antenna module is based on the classical process applied to obtain filters through the use of coupled resonators. The designed filter-antenna module is manufactured and measured, obtaining the following: a central frequency (fo) of 1.94 GHz, a -3-dB fractional band- width (FBW) of 5.57%, a gain (G) of 4.87 dBi, a front-to-back ratio (FTBR) of 25.60 dB, and a co-to-cross-polarization ratio of 22.86 dB in the direction of maximum radiation. The integration of the filter and the antenna into just one module leads to a reduction of size and weight in the RF front-end, while the implementation by means of the substrate integrated waveguide technique makes the integration with planar circuits easier.

Analysis and Design of a Micromachined Electric-Field Sensor

In this paper, the design and experimental results for a novel micromachined electric-field sensor are presented. The operation of the sensor is based on chopping an incident field with a shutter and measuring the induced charge on two sets of electrodes situated below the shutter. Employing of thermal actuators to move the shutter allows for substantial reduction in drive-signal amplitude as compared to electrostatic actuators which has consequently resulted in less interference from the drive signal. Moreover, the drive and sense signals are separated in the frequency domain owing to the inherent nonlinearity of thermal actuators, further improving the accuracy and resolution of the measurements. The relatively small displacements produced by thermal actuators are mechanically amplified using a novel lever mechanism. The sensor is capable of measuring fields as small as 42 V/m using actuation signals on the order of 60 mV.

Microstrip phase shifter using ground-plane reconfiguration

In this paper, a new reconfigurable microstrip structure is presented where line impedance can be actively controlled to induce phase shift on a transmission-line signal. Micromachining is used to fabricate thin-film copper membranes in the ground plane below the transmission line. Actuation of these membranes enables control of transmission-line to ground-plane spacing and, thus, the line capacitance. The performance of this reconfigurable microstrip transmission line as a phase shifter is investigated between 5-32 GHz for a variety of membrane geometries. A phase shift of up to -32.1/spl deg/ at 15.00 GHz is achieved by actuating an array of five 4.3-mm-diameter membranes beneath a 30-/spl Omega/ microstrip line. A single 10.0-mm-diameter membrane achieved a phase shift of -25.57/spl deg/ at 15.05 GHz on a 50-/spl Omega/ line, while a 10.4-mm membrane achieved a phase shift of -55.5/spl deg/ at 14.25 GHz on a 30-/spl Omega/ line. Both single and multiple series ground-plane membranes are possible, and they can be activated with discrete or continuous control signals, individually or together. Discrete and continuous phased array beam steering are, therefore, feasible.

Micromachined Electric-Field Sensor to Measure AC and DC Fields in Power Systems

This paper describes a new type of electric field sensor fabricated using micromachining technology. This micromachined sensor is dramatically smaller than conventional field mills, possessing a field chopping shutter measuring only 1mm2. The shutter is moved using thermal actuators, thereby eliminating the wear and tear associated with rotating and moving elements of field mills. The sensor requires minimal operating power, with the shutter being driven by a 75mV drive signal while consuming only 70W. The field chopping shutter operates at ~4200Hz, enabling the measurement of both ac and dc fields. Two sets of sense electrodes enable differential field measurement, thereby not requiring a reference ground potential. The sensor has a linear response to electric field amplitude and has demonstrated capable of measuring a dc field as small as 42V/m. This miniature sensor is the smallest sensor with such a resolution for use in power engineering applications.

X-Band Tunable Frequency Selective Surface Using MEMS Capacitive Loads

A tunable frequency selective surface (FSS) based on slotted ground is presented. Tuning of the resonance frequency is achieved by using a metallic MEMS bridge over the slot. The bridge acts as a capacitive load, increasing the equivalent capacitance, and so decreasing the resonance frequency. Electromagnetic and electromechanical simulations are performed to investigate the designed FSS. S-parameter measurements of the FSS unit cell are performed in a waveguide simulator, showing more than 1.7 GHz frequency shift in the X-band, achieved by using only one MEMS bridge. A measured bandwidth of 400 MHz at the resonance frequency of 9.59 GHz is achieved. The designed MEMS bridge benefits from an unconventional method of using SU-8 as the sacrificial layer, resulting in low loss at high frequencies (3.2 dB loss at the resonance frequency of 9.59 GHz). Devices with different heights of the MEMS bridge were fabricated to study the variation in the resonance frequency. The MEMS bridge was tested at fixed heights. Simulated and measured results show excellent agreement. An FSS array is designed based on the FSS unit cell results. The design procedure to maximize the quality factor and controllable frequency range, and improve the radiation characteristics of the FSS array is discussed. Further simulations are performed to examine the performance of the FSS array with regards to grating lobes, oblique incidence and tunability.

Fabrication and optimization of a conducting polymer sensor array using stored grain model volatiles.

During storage, grain can experience significant degradation in quality due to a variety of physical, chemical, and biological interactions. Most commonly, these losses are associated with insects or fungi. Continuous monitoring and an ability to differentiate between sources of spoilage are critical for rapid and effective intervention to minimize deterioration or losses. Therefore, there is a keen interest in developing a straightforward, cost-effective, and efficient method for monitoring of stored grain. Sensor arrays are currently used for classifying liquors, perfumes, and the quality of food products by mimicking the mammalian olfactory system. The use of this technology for monitoring of stored grain and identification of the source of spoilage is a new application, which has the potential for broad impact. The main focus of the work described herein is on the fabrication and optimization of a carbon black (CB) polymer sensor array to monitor stored grain model volatiles associated with insect secretions (benzene derivatives) and fungi (aliphatic hydrocarbon derivatives). Various methods of statistical analysis (RSD, PCA, LDA, t test) were used to select polymers for the array that were optimum for distinguishing between important compound classes (quinones, alcohols) and to minimize the sensitivity for other parameters such as humidity. The performance of the developed sensor array was satisfactory to demonstrate identification and separation of stored grain model volatiles at ambient conditions.

An Ultra Wideband (UWB) Mixer with 0.18UM RF CMOS Technology

In this paper a CMOS down-conversion mixer for UWB applications is presented. The mixer circuit, designed using a standard 0.18mum RF CMOS technology, is an integral part of an entire UWB transceiver chip, working at the 3.1-10.6 GHz frequency range. The core of the mixer has been designed based on Gilbert cell architecture and uses a current injection method for increasing the linearity. For matching of RF and LO inputs to 50Omega a wideband matching circuit, using passive on-chip components, has been designed which provides a good match over the entire frequency range. A simple buffer is incorporated at the IF output. The simulated conversion gain of the mixer is greater than 10dB. The 1dB compression point, referred to input, is -10dBm and the IIP3 point is 4dBm. The RF return-loss is well below -10dB. Also, the LO-IF isolation is greater than -30dB, while the NF is about 10dB. The DC power consumption of the mixer is only 10mW. All characteristics are achieved for the entire frequency range of 3.1-10.6 GHz and meet the UWB standard requirements. In the paper it is shown that this mixer, which uses only a 1.8V supply, has considerable advantages over previously published mixers designed for this purpose

A frequency-tunable mechanically actuated microstrip patch antenna

A frequency-tunable microstrip patch antenna with a stacked air-glass substrate is presented in this paper. Adjusting the air-gap height between the patch and ground plane varies the antennas effective dielectric constant, resulting in a shift in resonant frequency. Ensemble simulations and experimental results are presented for the bulk-machined model. Microstrip patch antennas of frequencies ranging between 5 GHz to 20 GHz exhibited frequency shifts of up to 12%. The 8.8 GHz antenna tested experienced a frequency shift of nearly 400 MHz (8.47 GHz to 8.79 GHz).