Pascal Leuchtmann

Resolution and contrast in Kelvin probe force microscopy

The combination of atomic force microscopy and Kelvin probe technology is a powerful tool to obtain high-resolution maps of the surface potential distribution on conducting and nonconducting samples. However, resolution and contrast transfer of this method have not been fully understood, so far. To obtain a better quantitative understanding, we introduce a model which correlates the measured potential with the actual surface potential distribution, and we compare numerical simulations of the three-dimensional tip–specimen model with experimental data from test structures. The observed potential is a locally weighted average over all potentials present on the sample surface. The model allows us to calculate these weighting factors and, furthermore, leads to the conclusion that good resolution in potential maps is obtained by long and slender but slightly blunt tips on cantilevers of minimal width and surface area.

Analysis and Simulation of a 1-18-GHz broadband double-ridged horn antenna

A 1-18-GHz broadband double-ridged horn antenna with coaxial input feed section is investigated. For the ridged horn antenna it is found that the radiation pattern, contrary to common belief, does not maintain a single main lobe in the direction of the horn axis over the full frequency range. Instead, at frequencies above 12 GHz, the main lobe in the radiation pattern starts to split into four large side lobes pointing in off-axis directions with a dip of up to 6 dB between them along the main axis. Although this type of horn is the preferred test antenna, which is in common use for over four decades, no explanation for this unwanted behavior was found in the open literature. To investigate this phenomenon in detail, a method of moments approach has been adopted to simulate the complete antenna system. The simulations are in good agreement with the measurements over the 1-18-GHz operational bandwidth and indicate that the use of this type of horn antenna in EMC applications remains questionable.

A generalized local time-step scheme for efficient FVTD simulations in strongly inhomogeneous meshes

A new generalized local time-step scheme is introduced to improve the computational efficiency of the finite-volume time-domain (FVTD) method. The flexibility of unstructured FVTD meshes is fully exploited by avoiding the disadvantage of a single short time step in the entire mesh. The great potential of this scheme is fully revealed in the FVTD simulation of electromagnetic (EM) problems with both large and fine structures in close proximity. The scheme is based on an automatic partition of the computational domain in subdomains where local time steps of the type 2/sup /spl lscr/-1//spl Delta/t(/spl lscr/=1,2,3,...) can be applied without violating the stability condition. Interfaces between subdomains are reduced to a generic two-level system which requires a very limited number of time interpolations during the FVTD iteration, therefore resulting in a very simple and robust technique. The application of local time stepping to three-dimensional EM problems demonstrates a significant speed-up of the computation without compromising the accuracy of the results.

A flexible wearable antenna

The paper describes the development of a flexible wearable antenna used in military and police work. The design is based on numerical simulations using commercial software. Simulations taking into account the curved-surface profile of the antenna and differently sized human bodies are presented. Experimentally obtained return loss and radiation patterns are shown in comparison with the computed results. Measured return loss better than 7 dB has been achieved across the frequency band of 360-460 MHz. The superiority of the antenna with respect to conventionally used antennas in the abovementioned applications is demonstrated.

Spectrum of corrugated and periodically loaded waveguides from classical matrix eigenvalues

The paper presents a rigorous full-wave analysis of propagation in corrugated and periodically loaded waveguides. The propagation constants are determined from the classical eigenvalues of a canonical matrix eigenvalue problem instead of a determinant. The entries of the matrix are computed only once per frequency point. The entire k/sub 0/-/spl beta/ diagram of a corrugated circular waveguide, a circular waveguide periodically loaded with dielectric disks, and a rectangular waveguide periodically loaded with capacitive irises are determined and compared with results of other researchers. Excellent agreement is documented in each case.

Direct Conversion of Free Space Millimeter Waves to Optical Domain by Plasmonic Modulator Antenna

A scheme for the direct conversion of millimeter and THz waves to optical signals is introduced. The compact device consists of a plasmonic phase modulator that is seamlessly cointegrated with an antenna. Neither high-speed electronics nor electronic amplification is required to drive the modulator. A built-in enhancement of the electric field by a factor of 35 000 enables the direct conversion of millimeter-wave signals to the optical domain. This high enhancement is obtained via a resonant antenna that is directly coupled to an optical field by means of a plasmonic modulator. The suggested concept provides a simple and cost-efficient alternative solution to conventional schemes where millimeter-wave signals are first converted to the electrical domain before being up-converted to the optical domain.

Pin gap investigations for the 1.85mm coaxial connector

This paper presents a detailed investigation of the influence of pin gap size on the S-parameters of the 1.85 mm connector. In contrast to earlier publications connector geometry is simulated with all chamfers, gaps and contact fingers. Simulation results are verified by cross-checking between finite element frequency domain and finite difference time domain methods. Based on reliable simulation results, a very fast tool was developed to calculate S-parameters for a given connector geometry. This was done using database and interpolation techniques. The most important result is that very small pin gaps in conjunction with large chamfers have a drastic impact on connector S-parameters for frequencies above 50 GHz.

Enhanced field simulations and measurements of the ESD calibration setup

Simulating the complete electromagnetic field of the calibration setup for ESD testing holds two major difficulties: (A) the relevant dimensions of the setup are both very small (millimeters) and very large (meters); and (B) the time behavior of an ESD pulse is rather fast (subnanoseconds). In the first part of this paper we present new ideas to overcome these problems. The second part deals with measurements of the target current and field quantities. A new target with flat frequency responses is used in order to overcome the drawbacks of the widely used Pellegrini target which has a resonance at 3 GHz. Comparisons between measurements and simulations are also presented.

Comprehensive analysis and simulation of a 1-18 GHz broadband parabolic reflector horn antenna system

A 1-18 GHz parabolic reflector horn antenna system featuring a broadband double ridged primary horn with a coaxial feed line is investigated. For the ridged horn antenna it is found that the radiation pattern, contrary to common belief, does not maintain a single main lobe in the direction of the horn axis over the whole frequency range. Instead, at frequencies above 12 GHz the main lobe in the radiation pattern starts to split into four lobes pointing in off-axis directions with a dip of up to 6 dB between them along the center axis. To investigate this phenomenon in detail, a combined method of moments and physical optics approach has been adopted to simulate the complete antenna system.

Plasmonic Organic Hybrid Modulators—Scaling Highest Speed Photonics to the Microscale

Complementing plasmonic slot waveguides with highly nonlinear organic materials has rendered a new generation of ultracompact active nanophotonic components that are redefining the state of the art. In this paper, we review the fundamentals of this so-called plasmonic- organic-hybrid (POH) platform. Starting from simple phase shifters to the most compact IQ modulators, we introduce key devices of high-speed data communications. For instance, all-plasmonic Mach-Zehnder modulators (MZMs) are reviewed and long-term prospects are discussed. This kind of modulator already features unique properties such as a small footprint (<; 20 μm2), a large electro-optic bandwidth (> 110 GHz), a small energy consumption (~25 fJ/b), a large extinction ratio (> 25 dB) in combination with a record small voltage-length product of 40 Vμm. Finally, as an example for seamless integration we introduce novel plasmonic IQ modulators. With such modulators we show the generation of advanced modulation formats (QPSK, 16-QAM) on footprints as small as 10 μm × 75 μm. This demonstration ultimately shows how plasmonics can be used to control both phase and amplitude of an optical carrier on the microscale with reasonably low losses.