MHz System Research Articles

Archaeological geophysics: 3D imaging of the Muweilah archaeological site, United Arab Emirates

The sand-covered Muweilah archaeological site in the United Arab Emirates (UAE) is a unique Iron Age site, and has been subject to intensive investigations. However, excavations are time consuming and may require twenty years to complete. Thus geophysical surveys were undertaken with the objective of characterising the site more expeditiously. This paper presents preliminary results of these surveys.Ground penetrating radar (GPR) was tested as a primary imaging tool, with an ancillary shallow time domain EM (MetalMapper) system. Dense 3D GPR datasets were migrated to produce horizontal (plan view) depth slices at 10 cm intervals, which is conceptually similar to the archaeologists’ excavation methodology. The objective was to map all features associated with anthropogenic activity. This required delineating extensive linear and planar features, which could represent infrastructure. The correlation between these and isolated point reflectors, which could indicate anthropogenic activity, was then assessed. Finally, MetalMapper images were used to discriminate between metallic and non-metallic scatterers.The moderately resistive sand cover allowed GPR depth penetration of up to 5 m with a 500 MHz system. GPR successfully mapped floor levels, walls, and isolated anthropogenic activity, but crumbling walls were difficult to track in some cases. From this study, two possible courtyard areas were recognised. The MetalMapper was less successful because of its limited depth penetration of 50 cm. Despite this, the system was still useful in detecting modern-day ferruginous waste and bronze artefacts.The results (subject to ongoing ground-truthing) indicated that GPR was optimal for sites like Muweilah, which are buried under a few metres of sand. The 3D survey methodology proved essential to achieve line-to-line correlation for tracking walls. In performing the surveys, a significant improvement in data quality ensued when survey areas were flattened and de-vegetated. Although MetalMapper surveys were not as useful, they certainly indicated the value of including other geophysical data to constrain interpretation of complex GPR features.

Snow Mass Quantification and Avalanche Victim Search by Ground Penetrating Radar

Ground penetrating radar (GPR) systems can be used in many applications of snow and ice research. The information from the GPR is used to identify and interpret layers, objects and different structures in the snow. A commercially available GPR system was further developed to work in the rough environment of snow and ice. The applied GPR is a 900 MHz system that easily reaches snow depths of up to 10 meters. The system was calibrated in the course of several manual snow depth measurements during each survey. The depth resolution depends on the snow type and is around ±0.1 m. The GPR system is carried alongside a line of interest and is triggered by an odometer wheel at regular adjustable steps. All equipment is mounted in a sledge and is pulled by a snowmobile over the snow surface. This setup allows for an efficient coverage of several kilometers of terrain profiles. The radar profiles give a real time two-dimensional impression of structures and objects and the interface between snow and the underlying ground. The actual radar profile is shown on a screen on the sledge allowing the immediate marking of objects and structures. During the past three years the instrument was successfully used for the study of snow distributions, for the detection of glacier crevasses under the snow cover, and for the search of avalanche victims in avalanche debris. The results show the capability of the instrument to detect persons and objects in the snow cover. In the future, this device may be a new tool for avalanche rescue operations. Today, the size and weight of the system prevents the accessing of very steep slopes and areas not accessible to snowmobiles. Further developments will decrease the size of the system and make it a valuable tool to quantify snow masses in avalanche release zones and run-out areas.

A hybrid fingerprint matcher

Most fingerprint matching systems rely on the distribution of minutiae on the fingertip to represent and match fingerprints. While the ridge flow pattern is generally used for classifying fingerprints, it is seldom used for matching. This paper describes a hybrid fingerprint matching scheme that uses both minutiae and ridge flow information to represent and match fingerprints. A set of 8 Gabor filters, whose spatial frequencies correspond to the average inter-ridge spacing in fingerprints, is used to capture the ridge strength at equally spaced orientations. A square tessellation of the filtered images is then used to construct an eight-dimensional feature map, called the ridge feature map. The ridge feature map along with the minutiae set of a fingerprint image is used for matching purposes. The proposed technique has the following features: (i) the entire image is taken into account while constructing the ridge feature map; (ii) minutiae matching is used to determine the translation and rotation parameters relating the query and the template images for ridge feature map extraction; (iii) filtering and ridge feature map extraction are implemented in the frequency domain thereby speeding up the matching process; (iv) filtered query images are catched to greatly increase the one-to-many matching speed. The hybrid matcher performs better than a minutiae-based fingerprint matching system. The genuine accept rate of the hybrid matcher is observed to be ∼10% higher than that of a minutiae-based system at low FAR values. Fingerprint verification (one-to-one matching) using the hybrid matcher on a Pentium III, 800 MHz system takes ∼1.4 s , while fingerprint identification (one-to-many matching) involving 1000 templates takes ∼0.2 s per match.

A 40–80 MHz system for phase rotation and cooling

In this note a scheme for the collection, phase rotation and cooling of muons for a neutrino factory is reported. The scheme is sufficiently generic to be site independent also if some particular choices are influenced by the CERN design. The system discussed in this note is worked on as a possible alternative to the induction linac scheme. The results presented assume the following overall set-up: the proton driver is constituted by a 2.2GeV superconducting linac followed by an accumulator and compressor ring; the muon re-circulator and decay ring are assumed as described in PJK scenario.

A video system capable of simulating Landsat TM 5, 4, 3 imagery

This article describes a multispectral digital video imaging system that produces imagery similar to Landsat Thematic Mapper (TM) Bands 5, 4, 3. The system is comprised of two charge coupled device (CCD) analog video cameras, one tube analog video camera, and a computer equipped with an image digitizing board. The two CCD cameras are sensitive to visible/near-infrared wave-lengths and are equipped with visible red (0.625–0.635 μm) and NIR (0.845–0.857 μm) narrowband filters, respectively. The third camera is sensitive to visible/NIR/middle-infrared The third camera is sensitive to visible/NIR/middle-infrared wavelengths (MIR) (0.40–2.20 μm) and was equipped with an MIR (1.631–1.676 μm) narrowband filter. The computer is a Bi-Link Pentium 90 MHz system that has an RGB image grabbing board with 640 × 480 pixel resolution. The MIR, NIR, and red image signals from the cameras are subjected to RGB inputs of the computer digitizing board, thus giving a false color composite digital image similar in color rendition to TM 5, 4, 3 satellite imagery. The computer hard disk can store 1000 false color composite images. Image esults showed this system to have potential for a variety of remote sensing applications including detection of plant species and distinguishing among vegetation cover types.

Meteor observations by the Arecibo 430 MHz incoherent scatter radar. II. Results from time-resolved observations

Abstract The paper discusses an incoherent scatter radar (ISR) power profile interference detection and meteor filtering technique and presents the meteor interference statistics derived from the Arecibo 430 MHz ISR. The statistics obtained from the Arecibo ISR are comparable with the meteor statistics obtained by other radar and optical techniques. Using the hourly rate of meteor flux, the average visual magnitude of the meteors i s estimated to be as faint as + 14, probably, the faintest ever reported. For low echo meteors, the mean ablation height exhibits a logarithmic relationship with the returned power below 105 km. However, once the echo power exceeds a certain threshold, the mean height remains constant at 107 km for all meteors irrespective of their returned power. The unique aspect of the meteor trails reported here is that they are observed in the radial direction of the radar beam. The lack of aspect sensitivity and the high meteor rate detected by the Arecibo 430 MHz system seem to suggest that the scattering mechanism in the UHF range of frequencies may be different from the mechanism operating at VHF. Some future prospects of exploiting; meteor trails to study the neutral wind and other aspects of the meteor region are also proposed.

NMR

Magnex Scientific has introduced the MRCA 800 MHz magnet system. The system can provide a central magnetic field of 18.8 Tesla and has a nominal room-temperature bore diameter of 51 mm. As the name suggests, the unit is a stable 800 Mhz system that operates in a conventional (non-pumped) cryostat at a liquid-helium temperature of 4.2 K. The MRCA 800 Mhz could form part of the set-up for a variety of high-resolution NMR techniques.

Design and implementation of MPEG-2/DVB scrambler unit and VLSI chip

This paper describes the MPEG-2/DVB scrambler unit (DVB-SU) and VLSI chip developed for ETRI's conditional access system (CAS) for a digital broadcasting system. The DVB-SU is designed and implemented based on an ASIC, FPGAs and a DSP. The ASIC, compliant with the EP-DVB common scrambling specification, is a 128-pin MQFP type and operates with a 50 MHz system clock; it has features of flexible conditional access handling and interfaces with a commercial MPEG-2 multiplexer in compliance with the MPEG-2 system specification (ISO/IEC 13818). It has been integrated as a part of a conditional access sub-system for a digital broadcasting system and conforms so that it meets all the initial objectives and performance requirements.

High Deposition Rate a-Si:H for the Flat Panel Display Industry

AbstractHigh deposition rates and good quality electrical properties and thickness uniformities over large areas are required for all three films (SiNx, a-Si:H and n+ a-Si:H) composing the thin film transistors (TFTs) for the AMLCD industry, while maintaining high tool up-time and low particle formation. Generally these conditions have been achieved for most single-panel multichamber PECVD systems; however, it has become increasingly apparent that a compromise is drawn between the TFT mobility and the deposition rate of the a-Si:H layer. Thus it becomes essential to clearly assess the industry requirements for both deposition rates as well as TFT performance for the different device structures used for AMLCDs, and to discover and control these underlying material properties.The TEL VHF (40/60 MHz) PECVD system produces high quality, low defect density a- Si:H at deposition rates exceeding 1500 Å/min when analyzed by FTIR, CPM, photo and dark conductivity. Even though the low deposition rate a-Si:H exhibits very similar bulk properties, higher mobility TFTs are produced with a-Si:H deposited at lower RF power. Having both a high ion flux and low ion energy in the SiH4 discharge are likely the most critical conditions for controlling the a-Si:H quality and thus the TFT mobility. Increasing the RF frequency enhances both of these effects, as well as provides a higher deposition rate for a given power density and a higher power threshold for particle/powder formation. For these reasons it is likely a 40/60 MHz plasma will produce better performing TFTs for a given deposition rate when compared with a conventional 13.56 MHz system. Other process conditions such as diluting the SiH4 in H2 or Ar also seem to play an important role in the optoelectronic properties of the a-Si:H film and ultimately the TFT performance.

High frequency endosonography of gastrointestinal arteries: Potential and limitations defined in vitro

Objective: Severe arterial bleeding from the gastrointestinal (GI) wall usually arises from submucosal or subserosal arteries. Endosonography (EUS) is a method which can image small structures like GI wall vessels and, thus, has potential for improving the diagnosis and directing the therapy of vascular disorders of the β tract. Furthermore, ultrasonography is increasingly used in open and laparoscopic surgery to detect arteries, thereby possibly reducing bleeding complications. The aim of this study was to evaluate the ability of two different ultrasound (US) systems to image small arteries in the submucosa, subserosa and mesentery in vitro. Methods: A special system was used which allowed the ultrasound images to be precisely compared with histology of the same area of tissue. US images were made with an 8.5 MHz linear array and a 20 MHz single crystal US probe. Fifty measurements were obtained from 48 porcine and human GI arteries. All arteries were localized in the submucosa, subserosa or mesentery. Two of these arteries were also partly located in the mucosa and muscularis propria, respectively. Results: The arteries had an internal diaméter between 0.04 and 2.20 mm (median 0.25 mm) on histology. Both US systems could display arteries with a diameter as small as 0.1 mm, but arteries less than 0.20 mm in diameter were better resolved with the 20 MHz system than by the 8.5 MHz system. Arteries with diameters less than 0.1 mm could not be reliably distinguished from artifacts. Arterial lumens were anechoic, thus giving a good contrast to the echogenic submucosa and subserosal fat. The two arteries in the mucosa and muscularis propria could not be seen on US images due to their similar hypoechoic appearance. Conclusions: These findings indicate that small gastrointestinal arteries can be defined in vitro using ultrasound frequencies between 8.5 MHz and 20 MHz. Further studies with ultrasonography done in vivo are needed to define their potential clinical role.

Meteor observations by the Arecibo 430 MHz incoherent scatter radar—I. Results from time-integrated observations

The paper discusses an incoherent scatter radar (ISR) power profile interference detection and meteor filtering technique and presents the meteor interference statistics derived from the Arecibo 430 MHz ISR. The statistics obtained from the Arecibo ISR are comparable with the meteor statistics obtained by other radar and optical techniques. Using the hourly rate of meteor flux, the average visual magnitude of the meteors i s estimated to be as faint as + 14, probably, the faintest ever reported. For low echo meteors, the mean ablation height exhibits a logarithmic relationship with the returned power below 105 km. However, once the echo power exceeds a certain threshold, the mean height remains constant at 107 km for all meteors irrespective of their returned power. The unique aspect of the meteor trails reported here is that they are observed in the radial direction of the radar beam. The lack of aspect sensitivity and the high meteor rate detected by the Arecibo 430 MHz system seem to suggest that the scattering mechanism in the UHF range of frequencies may be different from the mechanism operating at VHF. Some future prospects of exploiting; meteor trails to study the neutral wind and other aspects of the meteor region are also proposed.

Fundamental limits for linearity of CATV lasers

We have considered nonlinear distortions in a subcarrier multiplexed optical transmission system arising from carrier heating effects in the source laser. We included two sources of carrier heating: free-carrier absorption of the coherent radiation in the cavity, and the power flux into the active layer, associated with the input current. Resulting from the very existence of modulated optical and electrical signals, these effects cannot be avoided in any laser structure. Simple analytic expressions have been derived for the intermodulation distortion in multichannel single-mode lasers. For an 80-channel 60-540 MHz system with 3% optical modulation depth per channel, the composite second-order (CSO) distortion brought about by the hot-carrier effects is near the tolerance limit for CATV systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Second- and third-order harmonic distortion in DFB lasers

The second- and third-order harmonic distortion in distributed feedback (DFB) lasers is simulated using a time domain large signal dynamic model. The effects of the longitudinal spatial hole burning, nonlinear gain, spontaneous emission, and current leakage are included in the model. Composite second-order (CSO) and composite triple beat (CTB) are calculated for an 80 channel 60-540 MHz system with 3% modulation depth in each channel. The simulation results are compared with the experimental harmonic distortion measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Correction of mixer nonlinearity in quadrature modulators

Baseband preconditioning is used to partially cancel third order nonlinearities in mixers. Calibration is by means of a simple diode detector, but requires the presence of a carrier leak signal. The technique led to an improvement of 8dB in IM3 for a 900 MHz system.

Computer simulation of a direct sequence spread spectrum cellular radio architecture

A computer simulation study to evaluate the channel capacity of a direct sequence spread spectrum cellular radio architecture which is based on code division is described. The cellular radio architecture utilizes the processing gain provided by a wideband multipath RAKE receiver to suppress multicell/multiuser interference. As a result, the same piece of radio spectrum can be reused in every cell. We use a step-by-step approach to verify the basic idea behind the spread spectrum cellular radio architecture. Computer simulations are used to calculate the distributions of signal-to-reference ratio (SIR). From SIR distributions, one can easily calculate the channel capacity of the cellular radio architecture. Technical requirements to fulfil potential system performance are also discussed. Finally, an 800 MHz system example is given for cellular mobile radio telephone application. >

Combined treatment with interstitial hyperthermia and interstitial radiotheraphy in an animal tumor model

An interstitial hyperthermia system operating at 27 MHz has been developed at the Dr. Daniel den Hoed Cancer Center. To test this system in combination with interstitial radiotherapy and to study the interactions of interstitial radiotherapy and interstitial hyperthermia, animal experiments were performed using rhabdomyosarcoma type R1 transplanted in the flanks of female Wag/Rij rats. Using the 27 MHz system, it appeared feasible to obtain hyperthermic temperatures. In this experiment a thermal dose of 44°C for 30 minutes was delivered by controlling the temperature at the periphery of the tumor to 44°C. The interstitial heating applicators were inserted in four standard afterloading catheters implanted with a fixed spacing of 7 mm; the same catheters were used for the radioactive sources for interstitial radiotherapy treatment following the interstitial hyperthermia sessions. Interstitial radiotherapy was given by means of four Ir 192 wires with an average activity of 4.5 · 10 7 Bq/cm. Minimum tumor doses of 20 to 115 Gy with a mean dose rate of 47 cGy/hour were applied. Interstitial hyperthermia alone resulted in a growth delay (GDI) of 6 ± 2 days without significant reduction of tumor volume. The 50% tumor cure dose after interstitial radiotherapy alone was 95 ± 9 Gy. Combination of interstitial hyperthermia and interstitial radiotherapy resulted in reduction of the 50% tumor cure dose to 48 ± 13 Gy. The dose-effect data for cure for these modalities are compared to existing data for external irradiation and external hyperthermia in the same tumor model. It was found that the addition of hyperthermia to different modes of irradiation, that is, either to single dose or protracted radiotherapy, results in a common level of radiosensitivity through impaired repair of sublethal damage. This study demonstrates the feasibility of the 27 MHz heating system in achieving hyperthermic temperatures; in the combined modality experiments a thermal enhancement factor of 2.0 ± 0.3 (mean ± standard deviation) was observed.

An ultrasonic method for measuring tissue displacement: technical details and validation for measuring myocardial thickening

We have developed a method for measuring myocardial thickening from a single ultrasonic transducer attached to the epicardium. Displacement of the underlying myocardial tissue is measured by following the phase of the echoes within a sample volume range-gated across the myocardium. The output is in the form of an analog signal. To verify the accuracy, resolution, and limitations of the system, we derived the equations relating the position of a reflector to the phase of its echo and compared the system output in vitro to a known input using a single moving target and a random distribution of scatterers, and in vivo to that of an ultrasonic transit-time dimension gauge. The results demonstrate that the 10 MHz system can accurately follow the motion of single or multiple targets with a resolution of 0.02 mm. In 25 dogs myocardial thickening measured with the displacement system compared favorably in both waveform and magnitude with thickening measured by the two-crystal transit-time method. Applications for the displacement method include: quantification of regional ventricular function in animal models of cardiovascular diseases, measurement of endocardial to epicardial differences in the deformation of regional myocardium during the cardiac cycle, and evaluation of regional cardiac function in patients during and after corrective cardiac surgery.

Special architecture for high-performance scan conversion

This paper describes the design of a scan-line converter engine as preprocessor for a Hidden Surface removal and Shading Processor (HSSP). The HSSP is a special-purpose processor based on the 3-dimensional (3-D) scan-line z-buffer algorithm. Scan-line conversion is the transformation of polygon data into segment data, suitable for the HSSP. It consists of two separate processes: the generation of segment data from polygon data, and the sorting of segment data for each scan-line. For both processes, architectures are proposed: a parallel architecture for segment data generation, which computes one segment in 6 clock cycles, and a RISC-oriented architecture for the scan-line algorithm which finds a segment in 3 clock cycles. Simulation results show that the overall performance is 3.3 ∗10 6 segments/s for a 20 MHz system.

Applications for optical current and voltage sensors

The construction and use of optical sensors for the measurement of electric current and voltage is described. The voltage sensor uses the electrooptic effect of Bi 4(GeO 4) 3. The range is ±6 kV with a signal-to-noise ratio of 1500 for a 10 MHz system. The temperature stability is better than 5% in the range 20 – 85 °C. Both fibre and bulk optical current sensors were investigated. The range, signal-to-noise ratio and temperature stability of the bulk sensor depend on the Faraday rotator used. Typical values are 2 kA, 2000 and 2.5% respectively. The use of the fibre current sensor as a fast lightning detector is demonstrated. The voltage and bulk current sensors are applied in a transformer protection system.

Maintenance of Helium Microwave-Induced Plasmas at Powers of Greater Than a Kilowatt for Chemical Analysis

A description of a helium kilowatt-plus microwave-induced plasma (KiP-MIP) system is presented. The output of a 2450 MHz system, with root mean square powers of up to 2.7 kW, are directed to a plasma torch within a TMoloresonator. The system is utilized to maintain plasmas of argon, nitrogen and helium; the latter showing unique potential for chemical analysis. Power waveforms and their effects on the plasmas are illustrated with “unfiltered” and “filtered” systems. Reflected and forward power are observed as the magnitude of the applied power is varied and the slide tuner is adjusted. Preliminary spectra from aqueous chloride and bromide are presented.