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An on-body antenna, comprised of two closely-spaced antiphase patch elements, for microwave imaging may provide enhanced signal penetration into the tissue. By further integrating a 180-degree on-chip power splitter with the dual antiphase patch antenna element, a low-profile miniaturized antenna, integrated into a single 18.5 mm × 10 mm × 1.6 mm circuit board assembly, is designed and evaluated both numerically and experimentally. This is the smallest on-body antenna known to the authors for the given frequency band. This linearly polarized antenna may potentially serve as a building block of a dense antenna array for prospective high-resolution microwave imaging. A 2.4 GHz band was chosen as the design target. The final antenna size was a compromise between the miniaturization, the SNR (Signal-to-Noise Ratio), and the targeted antenna bandwidth (2.3–2.5 GHz). The effect of surface waves (the secondary radiating components) was also factored in the design consideration, while maximizing the detected signals’ SNR.

On-body antennas for use in microwave imaging (MI) systems can direct energy around the body instead of through the body, thus degrading the overall signal-to-noise ratio (SNR) of the system. This work introduces and quantifies the usage of modern metal-backed RF absorbing foam in conjunction with on-body antennas to dampen energy flowing around the body, using both simulations and experiments. A head imaging system is demonstrated herein but the principle can be applied to any part of the body including the torso or extremities. A computational model was simulated numerically using Ansys HFSS. A physical prototype in the form of a helmet with embedded antennas was built to compare simulations with measured data. Simulations and measurements demonstrate that usage of such metal-backed RF-absorbing foams can significantly reduce around-body coupling from Transmit (Tx) and Receive (Rx) antennas by approximately 10 dB. Thus, the overall SNR of the MI system can be substantially improved using this low-cost and affordable method.

Die optische Datenübertragung in Glasfasernetzen bildet das Rückgrat der weltweiten Kommunikation. Auch wenn zur Kommunikation zunehmend breitbandige mobile Endgeräte eingesetzt werden, benötigt das weltweite Kommunikationsnetz leistungsfähige faseroptische Kernnetze. Die Übertragungssysteme haben zurzeit je nach Übertragungslänge eine maximale Kapazität von etwa 1 bis 5 Terabit/s und verwenden eine Datenrate von maximal 40 Gigabit/s in einem einzelnen Wellenlängenkanal. Im Labor konnten in einem Kanal schon 2,56 Terabit/s übertragen werden. Das ist der aktuelle Geschwindigkeitsweltrekord.

Extensive work at PMRC has established a clear correlation between green-state density and electric conductivity of P/M parts. By monitoring a static electric current flow through the pre-sintered P/M sample and recording the voltage response over its surface, sufficient information can be gathered to predict the density profile throughout the sample volume. In this paper, the formulation and implementation of a novel numerical forward and inverse formulation will be presented that is capable of relating DC voltage measurements to green-state density distributions. It will be shown that this methodology is applicable to both lubricated and lubricant-free compacts. We will present a general forward solution that enables the calculation of three-dimensional surface voltages for a given set of boundary conditions and a known conductivity/density distribution throughout the P/M sample. This formulation is particularly useful for the development of new sensors and measurement arrangements, since it permits the optimization of current injection patterns and voltage probe locations. Our novel inverse solution adjusts the conductivity/density profile so as to determine the conductivity distribution that matches most closely a given set of voltage data on the surface. Practical measurements with a range of green-state P/M samples will underscore the success and usefulness of this modeling approach.

A new design approach for the construction of gradient coils for magnetic resonance imaging is presented. The theoretical formulation involves a constraint cost function between the desired field in a particular region of interest in space and an almost arbitrarily defined surface that carries the current configuration based on Biot‐Savart's integral equation. An appropriate weight function in conjunction with linear approximation functions permits the transformation of the problem formulation into a linear matrix equation whose solution yields discrete current elements in terms of magnitude and direction within a specified coil surface. Numerical predictions and comparisons with practical measurements for the Gx, Gy, Gz gradient coils underscore the success of this approach in terms of achieving highly linear fields while maintaining low parasitic fields and low inductances. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 26B: 67–80, 2005.

A new approach to design uniplanar gradient coils for magnetic resonance imaging (MRI) is presented. The theoretical formulation involves a constraint cost function between the desired field in a particular region of interest in space and the current-carrying coil plane based on Biot-Savart's integral equation. An appropriate weight function in conjunction with linear approximation functions allows the transformation of the problem formulation into a linear matrix equation in which its iterative solution yields discrete current elements in terms of magnitude and direction within the prescribed coil plane. These current elements can be synthesized into an overall practical wire configuration by suitably adding individual wire loops. Numerical predictions and practical testing for a Gy gradient coil underscore the success of this approach in terms of achieving a highly linear field while maintaining low parasitic fields. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 20B: 17–29, 2004

The method of lines is described as a novel and powerful way to analyze radio frequency (RF) coils for high-field magnetic resonance imaging. Originally developed for optical and microwave circuits, this method enables a full-wave solution to Maxwell's field equations without the computational burden of pure finite element or finite difference methods. Because only two of the three geometric dimensions are discretized, while seeking an analytic solution in the remaining space dimension, an efficient solution can be obtained at reasonable geometric restrictions. After outlining the theoretical formulation and the computer implementation of this technique, we will apply it to the modeling of microstrip RF transverse electromagnetic resonator coils at 200 and 400 MHz as well as a high-pass shielded birdcage resonator and a single-loop surface coil. With single-frequency solutions obtainable within 5–10 s on a personal computer, the approach proves highly suitable as a design tool and for rapid prototyping. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 16B: 22–37, 2003

Ongoing research at Worcester Polytechnic Institute (WPI) has recently resulted in the development of an electrostatic multipin instrument capable of testing green-state compacts directly after compaction. By monitoring a steady electric current flow through the sample and recording the voltages over the surface valuable information is gathered, leading to the prediction of the structural health of the green-state parts. Whereas our prior work concentrated on the detection of surface-breaking and subsurface defects, which requires the determination of large differences in material properties over small flaw sizes, the results presented in this paper aim at the density prediction throughout the volume of the sample. This requires the detection of small changes in material properties over large regions. A physical model and a mathematical formulation are reported, which are capable of relating green-state density changes to electric conductivity in the presence of various lubricant concentrations. Preliminary electrostatic measurements of cylindrical compacts have thus far confirmed the theoretical model assumptions, showing that the electric conductivity follows a complex graphical behavior that is determined by the type and concentration of the lubricant. Specifically, the green state conductivity increases as the sample density increases up to values of approximately 6.9 to 7.0 g/cm3. Any further density increase, however, results in a decrease in conductivity.

In this research we discuss an electrostatic measurement approach whereby electric current is injected into green-state compacts and the resulting surface voltages are recorded in an effort to determine density distributions. We present results for pure iron powder with and without lubricants compacted to various densities and their corresponding measured conductivity values, thereby clearly establishing correlation between these two entities. The electric conductivity recordings will ultimately be utilized to infer density distributions throughout the green-state P/M compact. The constant current is injected through point and aperture electrodes, and voltages are recorded along the surface of the compact. To gain confidence in the underlying physical concepts, the recorded voltages of the controlled cylindrical samples are compared with a mathematical Green's function model involving an analytical electrostatic solution of Poisson's equation.

Olfactory cues can elicit intense emotional responses. This study used fMRI in male common marmoset monkeys to identify brain areas associated with sexual arousal in response to odors of ovulating female monkeys. Under light anesthesia, monkeys were secured in a specially designed restrainer and positioned in a 9.4 T magnetic resonance spectrometer. When fully conscious, they were presented with the scents of both ovariectomized and ovulating monkeys. The sexually arousing odors of the ovulating monkeys enhanced signal intensity in the preoptic area and anterior hypothalamus compared to the odors of ovariectomized monkeys. These data corroborate previous findings in monkeys based on invasive electrical lesion and stimulation techniques and demonstrate the feasibility of using non-invasive functional imaging on fully conscious common marmosets to study cue-elicited emotional responses.

This letter describes the effect of a heavy current pulse, of approximately 10 kA, produced by a charge capacitor bank, on a small volume of liquid metal, confined in a cylindrical container (tube diameter is 1 cm and tube length is about 10 cm). The liquid metal contamination implies the presence of microscopic nonconducting particles. Theoretical consideration shows that a typical heavy current pulse of 15 msec duration leads to extremely large Lorentz force, due to the appearance of a self-induced magnetic field. Even though the particle contaminants are of micron size they can be moved by this force to macroscopic distances. Such a motion phenomenon can be used in the development of a cleanliness control system.

This paper investigates electrostatic voltage distributions around a surface-breaking flaw due to an injected current of known strength. The direct 3-D solution of the voltage behavior over the flawed surface is obtained numerically by the use of a boundary integral formulation. A novel iteration method is applied to solve the resulting electrostatic integral equation for the unknown surface voltage distribution. In addition to investigating the sensitivity of different flaw sizes to the observed surface voltage distribution, important issues such as suitable probe spacing and current flow orientation are studied. For sufficiently small surface-breaking flaws, a simple image source model is developed to evaluate the voltage response of hairline cracks. The model is tested by comparing it with the developed numerical solution. Experiments aimed at establishing the validity of the modeling approach show remarkable agreement with the theoretical model.

This paper investigates electrostatic voltage distributions around a surface-breaking flaw due to an injected current of known strength. The direct 3-D solution of the voltage behavior over the flawed surface is obtained numerically by the use of a boundary integral formulation. A novel iteration method is applied to solve the resulting electrostatic integral equation for the unknown surface voltage distribution. In addition to investigating the sensitivity of different flaw sizes to the observed surface voltage distribution, important issues such as suitable probe spacing and current flow orientation are studied. For sufficiently small surface-breaking flaws, a simple image source model is developed to evaluate the voltage response of hairline cracks. The model is tested by comparing it with the developed numerical solution. Experiments aimed at establishing the validity of the modeling approach show remarkable agreement with the theoretical model.

We demonstrate 160Gbit/s return-to-zero (RZ) differential quarternary phase-shift keying (DQPSK) signal transmission over a 110km single-mode fiber by taking advantage of mid-span optical phase conjugation (OPC). The technique is based on nonlinear wavelength conversion by cascaded second harmonic and difference frequency generation in a Ti:PPLN waveguide. Error-free operation with a negligible optical signal-to-noise ratio penalty for the signal after the OPC transmission without and with polarization scrambling was achieved. The results also show the polarization insensitivity of the OPC system using a polarization diversity scheme.

A theoretical study was conducted using a multiple-voltage probe sensor for detecting nonconducting inclusions in conducting media. Results show that the multiple-voltage probe sensor is capable of providing precise quantitative measurements of submerged nonconducting objects if the surface voltage response has a standard two-peak form. The standard response is observed for well-localized non-slender single inclusions below the sensor surface. In this case, the peak separation distance is associated with the inclusion depth whereas the peak magnitude is associated with the inclusion volume. Linear dependencies of the inclusion depth and the inclusion volume are observed for a wide variety of inclusion shapes. The predefined form of the surface voltage response makes it feasible to identify useful signal responses at very high noise levels. This is accomplished by using a 2D neural network classifier, based on the probabilistic neural network. A reasonable recognition error of less than 20 % is obtained if the signal-to-noise ratio is larger than or equal to 1/10. A metal casting example shows that the multiple-voltage probe sensor can measure inclusion concentrations in hot conducting melts (gas bubbles and sludge) with inclusion radii in the range from 100 to 1000 μm. In contrast to existing particle counter technology, this sensor construction is simple to construct and does not require special aperture and vacuum treatment.