Tunable liquid crystal phase shifter for microwave frequencies

A tunable phase shifter using liquid crystal (LC) is presented. The device is fabricated in a fashion similar to LC displays which makes fabrication very simple compared, for example, to MEMS approaches. At the targeted operation frequency of 20 GHz the device offers a performance of above 60 differential phase shift per dB insertion loss and a minimum tuning speed of 340 ms.     

Electrically tunable split-ring resonators at microwave frequencies based on barium-strontium-titanate thick films

Split-ring resonators (SRRs) implemented using ferroelectric materials to modify their resonance frequency by means of a tuning voltage are presented for the first time. SRRs have been used to load a microstrip transmission line on a multilayered substrate including a thick film of barium-strontium-titanate (BST) to obtain a tunable stopband response. The characteristics of the BST layer allow the application of 140 V as tuning voltage to obtain frequency tunability values of around 12.5 . The applied technology is suitable for the fabrication of cost-effective and reliable planar microwave devices.     

Analysis of viscous losses in the chemical interface layer of Love wave sensors

Love waves have been introduced as highly effective devices for liquid-sensing applications. For chemical sensors, a microacoustic delay line featuring a multilayered waveguide supporting a generalised Love wave mode can be used in an oscillator setup. The top layer of the waveguide is a chemical interface, which selectively adsorbs certain target molecules in the adjacent liquid. The increase in mass density caused by adsorption can be detected as changes in the oscillation frequency. Commonly used interface materials show viscoelastic losses leading to an unwanted damping of the wave. To keep the signal-to-noise ratio high, the total insertion loss of the delay line should be kept as low as possible. Furthermore, it must not exceed a certain value to allow the electronic circuitry to sustain the oscillation. We analyzed the viscoelastic losses, which strongly depend on the frequency being used. By means of the proposed theoretical approach, the maximum thickness of the interface layer can be determined not to exceed the losses that can be handled by the driving electronics.     

<Emphasis Type="Italic">t</Emphasis>-Private and <Emphasis Type="Italic">t</Emphasis>-Secure Auctions

In most of the auction systems the values of bids are known to the auctioneer. This allows him to manipulate the outcome of the auction. Hence, one might be interested in hiding these values. Some cryptographically secure protocols for electronic auctions have been presented in the last decade. Our work extends these protocols in several ways. On the basis of garbled circuits, i.e., encrypted circuits, we present protocols for sealed-bid auctions that fulfill the following requirements： 1） protocols are information-theoretically t-private for honest but curious parties; 2） the number of bits that can be learned by malicious adversaries is bounded by the output length of the auction; 3） the computational requirements for participating parties are very low： only random bit choices and bitwise computation of the XOR-function are necessary. Note that one can distinguish between the protocol that generates a garbled circuit for an auction and the protocol to evaluate the auction. In this paper we address both problems. We will present a t-private protocol for the construction of a garbled circuit that reaches the lower bound of 2t ＋ 1 parties, and Finally, we address the problem of bid changes in an auction. a more randomness efficient protocol for （t ＋ 1）^2 parties     

A Compact Two-dimensional Power Divider for a Dielectric Rod Antenna Array Based on Multimode Interference

In this work, multimode interference is investigated for the design of a two-dimensional fully dielectric power divider, well suited for the usage of dielectric waveguides. Most important, power division is achieved in a single device without the need of cascading multiple dividers. This allows to design a very compact and lightweight power divider, well applicable for dielectric rod antenna arrays. As a proof of concept for the used technique, a 16-way power divider with 4 × 4 output ports, made out of Rexolite, is realized, working in a frequency range between 90 and 105 GHz. For the S-parameter measurements, a special measurement setup, including a modular pin probe technique as well as radiation taper for waveguide termination, is proposed. The measurements are in good agreement with the simulations with a power split of ??15 dB for all output ports within the desired frequency range. This is equal to an additional insertion loss of 3 dB. To demonstrate the usability for antenna arrays, a fully dielectric rod antenna array is realized based on the proposed power divider. With this array, a gain of 22.5 dBi at 97.5 GHz was achieved.     

Private Computation: k-Connected versus 1-Connected Networks

We study the role of connectivity of communication networks in private computations under information theoretical settings in the honest-but-curious model. We show that some functions can be 1-privately computed even if the underlying network is 1-connected but not 2-connected. Then we give a complete characterisation of non-degenerate functions that can be 1-privately computed on non-2-connected networks. Furthermore, we present a technique for simulating 1-private protocols that work on arbitrary (complete) networks on k-connected networks. For this simulation, at most additional random bits are needed, where L is the number of bits exchanged in the original protocol and n is the number of players. Finally, we give matching lower and upper bounds for the number of random bits needed to compute the parity function on k-connected networks 1-privately, namely random bits for networks consisting of n players.     

Integration of impedance spectroscopy sensors in a digital microfluidic platform

Digital microfluidics combines the advantages of a low consumption of reagents with a high flexibility of processing fluid samples. For applications in life sciences not only the processing but also the characterization of fluids is crucial. In this contribution, a microfluidic platform, combining the actuation principle of electrowetting on dielectrics for droplet manipulations and the sensor principle of impedance spectroscopy for the characterization of the fluid composition and condition, is presented. The fabrication process of the microfluidic platform comprises physical vapor deposition and structuring of the metal electrodes onto a substrate, the deposition of a dielectric isolator and a hydrophobic top coating. The key advantage of this microfluidic chip is the common electric nature of the sensor and the actuation principle. This allows for fabricating digital microfluidic devices with a minimal number of process steps. Multiple measurements on fluids of different composition (including rigid particles) and of different conditions (temperature, sedimentation) were performed and process parameters were monitored online. These sample applications demonstrate the versatile applications of this combined technology.     

Compact and Sensitive Millimetre Wave Detectors Based on Low Barrier Schottky Diodes on Impedance Matched Planar Antennas

Compact and highly responsive millimeter wave planar Schottky detectors are proposed for uni-planar and low-cost fabrication. For optimum power transfer, the zero-bias Schottky diodes are impedance matched by the antenna design itself, with an established meander dipole and a new folded dipole type. In particular, up to 200GHz, the folded dipole exhibits a single responsivity peak, notably beneficial for communications. The realized detectors exhibit an outstanding system RF voltage responsivity of up to 16005mV/mW at 87.8GHz without lenses or pre amplification. In addition, an excellent NEP level is demonstrated by the detectors with 0.39pW/ \(\sqrt {\text {Hz}}\) .