Flexible strain sensors

In one embodiment, a flexible strain sensor includes a flexible substrate having a top surface and a layer of piezoresistive amorphous carbon formed on the top surface of the substrate.Board of Regents, University of Texas Syste

Passive wireless antenna sensor for strain, temperature, crack and fatigue measurement

An apparatus and method is provided for monitoring a condition of a structure using a passive wireless antenna sensor having a known resonant frequency when mounted on the structure. A series of radio frequency signals are transmitted with sweeping frequencies around the known resonant frequency to the passive wireless antenna sensor. The passive wireless antenna sensor includes a dielectric substrate disposed between an antenna pattern and a ground plane such that a change in the condition of the structure will cause a change in one or more characteristics of the passive wireless sensor. A signal is received from the passive wireless antenna sensor and a resonant frequency of the passive wireless antenna sensor is determined based on the received signal. The determined resonant frequency is then compared to the known resonant frequency, whereby a change in the resonant frequency indicates a change in the condition of the structure.Board of Regents, University of Texas Syste

Probe modeling for millimeter-wave integrated-circuit horn antennas

Integrated-circuit probe-excited horn-antenna arrays etched in silicon are well developed. They are a very promising class of antenna arrays for milli-meter and submillimeter applications. Further development of this technology involves integrating mixers and amplifiers into the antenna arrays. In an effort to develop an antenna-mixer array based on the existing technology, various antenna probes inside the pyramidal horns have been examined on scaled model-horns at the microwave frequencies. In this paper, modeling results and design principles of these antenna probes have been presented, which include the resonant impedance, the operating frequency, and the bandwidth of the horn antennas. These measurement results provide a guideline in designing probes for millimeter/submillimeter-wave integrated-circuit horn-antenna-mixer arrays

Microswitch beam-steering grid

We propose new microswitch beam-steering grids to operate at 90 GHz and 240 GHz. The microswitch beam-steering grid has potential advantages over mechanical-scanning devices or active beam-steering reflectors based on diode grids such as lower loss and simple control circuits. Simulations predict that a 4-bit controlled 10-layer microswitch beam-steering grid can have phase-shift resolution of 22.5° with a loss of 1.6 dB and a maximum phase error of 5° at 240 GHz

A terahertz grid frequency doubler

We present a 144-element terahertz quasi-optical grid frequency doubler. The grid is a planar structure with bow-tie antennas as a unit cell, each loaded with a planar Schottky diode. The maximum output power measured for this grid is 24 mW at 1 THz for 3.1-μs 500-GHz input pulses with a peak input power of 47 W. An efficiency of 0.17% for an input power of 6.3 W and output power of 10.8 mW is measured. To date, this is the largest recorded output power for a multiplier at terahertz frequencies. Input and output tuning curves are presented and an output pattern is measured and compared to theory

Metal mesh couplers using evanescent waves at millimeter and submillimeter wavelengths

A metal mesh evanescent wave coupler which makes use of coupling of evanescent waves between a metal mesh and a tuning dielectric plate, has been developed as a quasioptical component for millimeter and submillimeter wavelengths. The coupling coefficient of the capacitive evanescent wave coupler can be changed more than 70 % by moving the silicon plate only 60 μm at around 53 GHz. The transmission properties of the evanescent wave couplers depending on the mesh period and the silicon plate thickness have been studied

Metal mesh couplers using optical tunneling effect at millimeter and submillimeter wavelengths

A new metal mesh coupler that makes use of a tunneling effect of evanescent waves between a metal mesh and a dielectric plate, has been proposed as a quasi-optical component for millimeter and submillimeter wavelengths. Theoretical calculation and experimental measurement performed from 40 GHz to 60 GHz show that the transmittance of the coupler can be changed more than 50 % for the variation of a spacing less than 0.18 mm between a capacitive mesh and a silicon plate at around 57 GHz

A 100-element HBT grid amplifier

A 100-element 10-GHz grid amplifier has been developed. The active devices in the grid are chips with heterojunction-bipolar-transistor (HBT) differential pairs. The metal grid pattern was empirically designed to provide effective coupling between the HBTs and free space. Two independent measurements, one with focusing lenses and the other without, were used to characterize the grid. In each case, the peak gain was 10 dB at 10 GHz with a 3-dB bandwidth of 1 GHz. The input and output return losses were better than 15 dB at 10 GHz. The maximum output power was 450 mW, and the minimum noise figure was 7 dB. By varying the bias, a signal could be amplitude modulated with a modulation index as large as 0.65. Tests show that the grid was quite tolerant of failures-the output power dropped by only 1 dB when 10% of the inputs were detuned. The grid amplifier is a multimode device that amplifies beams of different shapes and angles. Beams with incidence angles up to 30° were amplified with less than a 3-dB drop in gain