The effectiveness of the developed front-end on blocking the communication link of a commercial drone vehicle has been demonstrated in this work. A jamming approach has been taken in a broadband fashion by using GaN HEMT technology. Equipped with a modulated-signal generator, a broadband power amplifier, and an omni-directional antenna, the proposed system is capable of producing jamming signals in a very wide frequency range between 0.1 - 3 GHz. The maximum RF output power of the amplifier module has been software-limited to 27 dBm (500 mW), complying to the legal spectral regulations of the 2.4 GHz ISM band. In order to test the proof of concept, a real-world scenario has been prepared in which a commercially-available quadcopter UAV is flown in a controlled environment while the jammer system has been placed in a distance of about 10 m from the drone. It has been proven that the drone of interest can be neutralized as soon as it falls within the range of coverage (∼3 m) which endorses the promising potential of the broadband jamming approach.
In this paper, we present a millimeter wave radar system which will enhance the performance of infrared cameras used for fire-fighting applications. The radar module is compact and lightweight such that the system can be combined with inertial sensors and integrated in a hand-held infrared camera. This allows for precise distance measurements in harsh environmental conditions, such as tunnel or industrial fires, where optical sensors are unreliable or fail. We discuss the design of the RF front-end, the antenna and a quasi-optical lens for beam shaping as well as signal processing and demonstrate the performance of the system by in situ measurements in a smoke filled environment.
Martina Baeumler, Michael Dammann, Matthias Wespel, Roshna George, Helmer Konstanzer, Stephan Maroldt, Vladimir Polyakov, Stefan Müller, Wolfgang Bronner, Peter Brückner, Fouad Benkhelifa, Patrick Waltereit, Rüdiger Quay, Michael Mikulla, Joachim Wagner, Oliver Ambacher, Andreas Graff, Frank Altmann, Michél Simon-Najasek, Martino Lorenzini, Martin Fagerlind, Paul van der Wel, Thomas Roedle
Long-term stability and reliability of AlGaN/GaN high electron mobility transistors (HEMT) can be validated by various stress tests which allow studying the physical mechanisms responsible for degradation. As the electroluminescence (EL) intensity is related to the kinetic energy and density of the channel electrons accelerated in the electric field, both local current and electric field changes can result in an increase or decrease of the EL intensity. The electric field distribution in source drain direction peaks at the drain side edge of the gate foot and the field plates. It is strongly dependent on the gate design and the passivation /semiconductor interface trap density. Although the spatial resolution of the electroluminescence microscopy (ELM) set-up is limited to a few microns, the technique allows to monitor submicron changes in the device geometry and hence to identify elevated electric field peaks being responsible for the acceleration of the degradation process. ELM also benefits from the fact that submicron imperfections at the Schottky interface of the gate electrode result in strong local current variations. It has been used to selectively identify suitable positions for further failure analysis of focused ion beam prepared cross sections by scanning and transmission electron microscopy. Process induced imperfections as voids at the Schottky interface after stress have been localized.
KEYWORDS: Radar, Optical spheres, Antennas, Extremely high frequency, Amplifiers, Digital signal processing, Signal attenuation, Receivers, Doppler effect, Warfare
Small and fast objects, for example bullets of caliber 5 to 10 mm, fired from guns like AK-47, can cause serious problems to aircrafts in asymmetric warfare. Especially slow and big aircrafts, like heavy transport helicopters are an easy mark of small caliber hand fire weapons. These aircrafts produce so much noise, that the crew is not able to recognize an attack unless serious problems occur and important systems of the aircraft fail. This is just one of many scenarios, where the detection of fast and small objects is desirable. Another scenario is the collision of space debris particles with satellites.
We investigate the influence of the epitaxial layer roughness on the far-field profile of the optical mode in gallium Nitride-based, c-plane ridge waveguide laser diodes. Occasionally, we observe long-range growth instabilities leading to a periodical modulation of the surface. Amplitude and period of this surface roughness is typically on the order of a few 10nm and 20 μm, respectively. Using different characterization techniques, we investigate the influence of the surface roughness on the vertical mode profile along the fast axis in the far-field, in particular the contribution of light scattering at the rough waveguide interfaces, as well as that of substrate modes.
We present tunable lenses based on aluminum nitride membranes. The achievable tuning range in the refractive power is 0 to 25 dpt with an external pressure load of ≤20 kPa . The lenses are manufactured using MOEMS technology. For 500-nm-thick membranes with a diameter of 3 mm, a spherical deflection profile is found. The system provides good long-term stability showing no creep or hysteresis. A model for the refractive power versus applied pressure is derived and validated experimentally. Based on this model, design guidelines are discussed. One essential parameter is the residual stress of the aluminum nitride layer that can be controlled during deposition.
A millimeter-wave spectroscope for the detection of triatomic gases has been constructed and characterized for frequencies between 230 and 325 GHz (H-band). The achieved results demonstrate a high sensitivity and low threshold detection. A circular lensed horn antenna transmits millimeter- waves into a gas-filled vacuum tube and excites triatomic gas molecules to a higher energy level, if the rotational resonance frequency of the molecule matches with the excitation frequency. At the other end of the tube a second lensed horn antenna receives the propagated electromagnetic wave and the millimeter-wave power is measured by a heterodyne receiver. By sweeping the radiated transmit frequency, the molecules' specific absorption can be detected. The measured absorption results are superimposed by standing wave effects within the tube. To eliminate the standing wave effects, spectroscopy on the basis of rotational spontaneous millimeter-wave emission was examined. This kind of spectroscopy decouples the transmitted from the received signal, whereby independent excitation and detection of the molecules are realized. The use of additional absorbers at the end of the gas tube decreases the decay time of the radiated wave inside the gas cell. In this paper, the detection of spontaneous emission of triatomic gas molecules with the use of a pulse-controlled transmitter and receiver is shown. Optimizations improved the stability and reproducibility of the measurements, and the detection threshold of nitrous oxide could be decreased to a ratio of 1/400. Furthermore, the implementation of a differential measurement method reduces the measurement time by a factor of 150 and simultaneously decouples of environmental influences.
We introduce sputtered aluminum nitride thin films for tunable micro-optics. During lens fabrication, AlN is deposited on a silicon substrate. Silicon is structured by using DRIE, which allows fabrication of circular, rectangular and irregular membrane shapes. In this contribution, we present the design, fabrication and characterization of AlN membranes for tunable cylindrical lenses. An optimized “dogbone” membrane is presented, which deflects cylindrically and has a small footprint. Compared to conventional rectangular membranes the optically useful area is doubled. The load deflection characteristic is investigated and basic relations between the refractive power and applied pressure are found. The relation can be used for tailoring the membrane properties, i.e. their residual stress, for a specific application. According to this calculation, a refractive power of 25 dpt with a lens aperture of 3x3 mm2 is achieved for 12 kPa of applied pressure. The cylindrical deflection of the “dogbone” membrane is measured. The maximum shape difference in measured to be 270 nm.
The use of millimeter-waves for imaging purposes is becoming increasingly important, as millimeter-waves can
penetrate most clothing and packaging materials, so that the detector does not require physical contact with
the object. This will offer a view to the hidden content of e.g. packets or bags without the need to open
them, whereby packaging and content will not be damaged. Nowadays X-ray is used, but as the millimeter-wave
quantum energy is far below the ionization energy, it is less harmful for the human health. In this paper we report
an active millimeter-wave imaging tomograph for material analysis and concealed object detection purposes. The
system is build using in-house W-band components. The object is illuminated with low-power millimeter-waves
in the frequency range between 89 and 96GHz; mirrors are used to guide and focus the beam. The object is
moved through the focus point to scan the object pixel by pixel. Depending on the actual material some parts
of the waves are reflected, the other parts penetrate the object. A single-antenna transmit and receive module
is used for illumination and measurement of the material-specific reflected power. A second receiver module
is used to measure the transmitted wave. All information is processed for amplitude and phase images by a
computer algorithm. The system can be used for security, such as detecting concealed weapons, explosives or
contrabands at airports and other safety areas, but also quality assurance applications, e.g. during production
to detect defects. Some imaging results will be presented in this paper.
At this paper we report on a W-band direct detection radiometer cascading a single-pole four-throw switch with
integrated 50 Ω load as a reference noise source, a 3 x 20 dB low-noise amplifier chain, and a broadband Schottky-diode
detector. All components are designed and fabricated in 100 nm metamorphic high electron mobility transistor
(mHEMT) technology and use waveguide packaging. By using 2 channels of the switch module the Dicke-principle is
implemented to drastically reduce the inherent amplifier noise. The multi-throw switch insertion loss is less than 3.5 dB
on the chip level and 4.4 dB on the module level. The entire W-band direct detection radiometer chain is also integrated
on a single chip and packaged into a waveguide module, which was successfully tested and is now ready for system
integration.
Step-structured thermo-mechanical actuators based on aluminum nitride (AlN) thin films and their application in
refractive beam steering are investigated. The actuators will tilt a suspended plate and deform a liquid surface to realize a
micro-prism. Arrays of tunable micro-prisms will increase the resolution of compound eye systems. A numerical
actuator description is presented and the beam geometry is investigated, considering achievable tilt angles and actuator
linearity. For an accurate design, the coefficient of thermal expansion (CTE) of AlN is determined, while measuring the
bow of a coated silicon substrate at different temperatures. For a temperature difference of 300 K, the results show a
maximum tilt angle of 7.1 °, which is independent of actuator length. Furthermore, the fabrication process is introduced
and the nano-crystalline structure of AlN at facets, which are caused by pre-structured substrates, is investigated.
We present design and realization concepts for thin compound eye cameras with enhanced optical functionality. The
systems are based on facets with individually tunable focus lengths and viewing angles for scanning of the object space.
The active lens elements are made of aluminum nitride (AlN)/nanocrystalline diamond (NCD) membranes. This material
system allows slow thermally actuated elements with a large deformation range as well as fast piezoelectric elements
with a smaller deformation range. Due to the extreme mechanical stability of these materials, we are able to realize
microoptical components with optimum surface qualities as well as an excellent long-term stability.
We use facets of microlenses with 1 mm in diameter and a tunable focusing power to compensate for the focus shift for
different viewing angles during the scanning procedure. The beam deflection for scanning is realized either by laterally
shifting spherical elements or by a tunable microprism with reduced aberrations. For both actuators we present a design,
fabrication concept and first experimental results.
Recent advances in MMIC-based solutions dedicated to imaging and sensing applications in the atmospheric windows located around 140, 200 and 300 GHz are presented. The MMICs comprise the individual components of a typical architecture of heterodyne analog frontends, and their combination into MMICs performing several functionalities or with full receiver capability. We discuss low-noise amplifiers up to 300 GHz, frequency multipliers and mixers operating up to 300 GHz, a power amplifier MMIC achieving more than 11 dBm of output power at 140 GHz, and a 200 GHz multi-functional, heterodyne receiver MMIC driven by a subharmonic local oscillator signal with low power requirements.
A millimeter-wave imaging system has been developed operating at a center frequency of 94 GHz. The system has a
single stationary mounted transmit and receive lensed horn antenna and two moving mirrors in x and y. The beam is
generated by a FMCW-radar module. The final beam aperture is an off-set parabolic mirror which focuses the beam to a
small spot at 2 m distance. Key component of the FMCW radar module is a MMIC, which includes a VCO, a
MPA/HPA, two Lange-couplers, an LNA , a Wilkenson splitter, and an I/Q-mixer. This MMIC is fabricated using IAF's
100 nm metamorphic HEMT process.
We report on MMIC-based analog frontend components for imaging radar and radiometry at high millimeter-wave frequencies. The MMICs are realized in our metamorphic HEMT technology. In W-band, the focus is on analog frontends with multi-pixel capability. A compact four-channel receiver module based on four single-chip heterodyne receiver MMICs achieves a noise figure of 4.2 dB and a conversion gain of 7 dB. A W-band five-to-one switch MMIC with less than 3.5 dB insertion loss addresses four antenna ports and uses an integrated reference termination for pixel normalization. Both components operate in a frequency range from 75 to 100 GHz, making them suitable for broadband imaging systems with high geometrical resolution. After an overview of MMIC amplifier performance over the entire millimeter-wave frequency range, we present a chip set for imaging radar at 210 GHz, comprising linear and frequency-translating circuits.
There is a high demand for compact low-cost ozone (O3) sensors. It has been shown that indium oxide (In2O3) thin films
grown by metal-organic vapor-phase epitaxy (MOVPE) act as an O3 sensitive material, which can be activated at roomtemperature
by ultraviolet (UV) light. In the present work we integrated the In2O3 sensing thin film and an (AlGaIn)N
based near-UV LED back-to-back on a single sensor chip. The integrated In2O3 film-LED sensor was exposed to varying
ozone concentrations ranging from 38 ppb to 726 ppb and found to be sensitive to even the lowest O3 concentration.
Tapered diode lasers combine high output power and a beam quality near to the diffraction limit resulting in very high
brightness. Therefore, they are finding use in a wide range of applications today, such as pumping of rare-earth-doped
fibre amplifiers, tunable frequency doubling of diode lasers for blue-green outputs, and non linear spectroscopy. Due to
increasing brightness and lifetime tapered lasers even become attractive for material processing and for telecom
applications like pumping of Er-doped fiber amplifiers or raman amplifiers.
In order to further enhance the brightness of tapered diode lasers the output power has to be increased while
simultaneously the beam quality has to be kept near the diffraction limit. For this purpose we have grown low modal
gain, single quantum well InGaAs/AlGaAs devices emitting at 976 nm by molecular beam epitaxy. The lateral design of
the investigated laser diodes consists of a tapered section and a ridge-waveguide section. Since it has been shown by
previous simulations and experiments that longer tapered sections allow higher output power with unchanged beam
quality, we use tapered section lengths of 2000 μm, 3000 μm and 4000 μm. The beam quality parameter M2 and output
powers as well as the nearfields of the different structures were carefully investigated. For longer devices we reach an
optical output power of more than 10 W per single emitter in continuous wave mode (cw) without any distinct thermal
rollover.
InN, a novel semiconductor material, is used as THz surface emitter. The material is irradiated with fs-laser pulses at 1060 nm and 800 nm and the emitted ultrashort THz pulses are measured by phase sensitive detection. Pulsforms, amplitudes and spectra are compared to the THz emission of p-doped InAs, the standard material for THz surface emission.
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