Liquid crystals (LCs) promise to be suitable passive tunable material for microwave devices with excellent features concerning tunability and losses. In order to optimize the synthesis of LCs and the design of tunable microwave devices based on them, LCs have to be characterized at microwaves. For a microwave analysis between 360 MHz-23 GHz, use was made of a broad-band characterization method with a two-port coaxial line, temperature controlled within -7/spl deg/C and 115/spl deg/C. Two LCs are investigated: K15, as a quasi-standard, and MDA-03-2838, as a novel mixture with increased dielectric anisotropy and reduced microwave losses tan/spl delta/.

We present the characterization of a Zero-bias Schottky diode-based Terahertz (THz) detector up to 5.56 THz. The detector was operated with both a table-top system until 1.2 THz and at a Free-Electron Laser (FEL) facility at singular frequencies from 1.9 to 5.56 THz. We used two measurement techniques in order to discriminate the sub-ns-scale (via a 20 GHz oscilloscope) and the ms-scale (using the lock-in technique) responsivity. While the lock-in measurements basically contain all rectification effects, the sub-ns-scale detection with the oscilloscope is not sensitive to slow bolometric effects caused by changes of the IV characteristic due to temperature. The noise equivalent power (NEP) is 10 pW/$\sqrt{\mathrm{Hz}}$ in the frequency range from 0.2 to 0.6 THz and 17 pW/$\sqrt{\mathrm{Hz}}$ at 1.2 THz and increases to 0.9 $\mathsf{\mu }$W/$\sqrt{\mathrm{Hz}}$ at 5.56 THz, which is at the state of the art for room temperature zero-bias Schottky diode-based THz detectors with non-resonant antennas. The voltage and current responsivity of ∼500 kV/W and ∼100 mA/W, respectively, is demonstrated over a frequency range of 0.2 to 1.2 THz with the table-top system.

Relative humidity (RH) sensors are fabricated based on anti-corrosive gold electrodes surface acoustic wave (SAW) resonators, which are covered with photolithographically patterned polyvinyl-alcohol (PVA) films in micrometer resolution. The patterned films enable RH sensors conveniences of measurement and integration with clean contact pads, and facilitate the sensor design with various patterns for different applications requirements. Two RH sensors with almost the same PVA film thickness but different patterns are investigated. The sensor with the PVA film patterned only on the reflectors of the SAW resonator has larger RH operation range, higher maximum reflection, and narrower relative bandwidth. In comparison, the sensor shows higher sensitivity when the PVA film is only open at interdigital transducer pads.

A novel mass flow detector has been developed using an open cylindrical resonator based on two microstrip patch couplers. The directivity of the couplers provides a compact sensor design without loss of sensitivity. The design of a particulate mass flow detector and the algorithm to detect the average solids concentration is shown. Spatial filtering velocimetry is applied to a microstrip patch sensor in order to detect the average particulate velocity. The simultaneous detection of the velocity and the solids/air concentration from a single measurement, ensure a true mass flow detector. Subsequently, free fall measurements as well as measurements in a self contained material flow measuring system were carried out in order to prove the concept.

When operating Schottky diodes and rectifying field-effect transistors in the saturation regime, where they show a sublinear response to incident THz power, they can be used as fast autorcorrelators yielding information on the pulse envelope. We report on autocorrelation measurements at 3.41 THz of high-power THz pulses for determination of the pulse duration and pulse structure. By fringe-resolved measurements, the THz frequency of the pulse is also obtained. We develop a theoretical model for the rectification process and compare the performance of an antenna-coupled Schottky diode to a large-area field-effect transistor rectifier. While the Schottky diode saturates earlier and can therefore be used for autocorrelation measurements at lower input power, antenna-less large-area field-effect transistors can be used for highest power levels-even at free electron lasers-and turn out to be very robust.