Continuous Exposure of Chicks and Rats to Electromagnetic Fields

Growth rate and feed consumption depressions were observed in groups of 25 day-old male chicks when exposed in metal cage environments to the following CW fields: 1) a UHF wave at 880 MHz in a very low-Q cavity resonator energized by a 220-mW power source (values of electric field square E/sup 2/ divided by the intrinsic impedance of free space /spl eta/ = 377 /spl Omega/ were measured resulting in a maximum value of 550 /spl mu/W/cm/sup 2/ with a "hot spot" of 900 /spl mu/W/cm/sup 2/); 2) a VHF wave at 260 MHz in a very low-Q cavity resonator, energized by a 220-mW power source (values of E/sup 2/ / /spl eta/ were not measured, but the values should have been similar to those measured in the UHF facility); 3) an extremely low frequency (ELF) electric field at either 45 or 60 Hz with calculated electric field strength of 3500 V/m; 4) an ELF magnetic field at either 45 or 60 Hz with 1.3 G was measured. Adrenal glands of chicks exposed to the 880-MHz wave were compared with those from control chicks. Smaller adrenals were observed in the treated group of birds. Growth depression was also observed in rats exposed to the UHF field at 880 MHz. Mean adrenal weights of the treated and control rats did not differ significantly; however, spleen and thymus weights of the treated rats were notably larger. Potential causes of the growth responses observed are discussed.     

Determination of Power Absorption in Man Exposed to High Frequency Electromagnetic Fields by Thermographic Measurements on Scale Models

When the body of man, small compared to a wavelength, is exposed to high frequency (HF) electromagnetic (EM) fields, the absorbed power density patterns and total absorbed power may be approximated by the simple superposition of the internal electric fields obtained from the quasistatic coupling characteristics of the electric and magnetic field components determined independently. These characteristics were obtained for full scale man by thermographic studies of power absorption in scale models of man exposed to fields at frequencies scaled up inversely proportional to the model size. A VHF resonant cavity was used to provide the necessary field strengths for producing measurable power absorption patterns under simulated HF exposure conditions. The results indicate that peak power absorption densities as high as 5.63 W/kg can be produced in man exposed to 10 mW/cm2 31 MHz radiation fields. The results show that the absorption decreases as the square of the frequency as predicted by theory for frequencies below 31 MHz.     

Full characterization of packaged Er-Yb-codoped phosphate glass waveguides

We present a procedure for the characterization of packaged Er-Yb-codoped phosphate glass waveguides. The procedure is based on precise measurements of the output optical powers when the waveguide is diode-laser pumped at 980 nm. The dependence of these optical powers on the input pump power is then fitted to the results from a numerical model that describes in detail the propagation of the optical powers inside the waveguide. The best fit is obtained for the following parameters: the signal wavelength scattering losses are /spl alpha/(1534)=8.3/spl times/10/sup -2/ dB/cm, the Yb/sup 3+/ absorption and emission cross sections (/spl ap/980 nm) are 5.4/spl times/10/sup -25/ m/sup 2/ and 7.0/spl times/10/sup -25/ m/sup 2/, the Er/sup 3+/ absorption and emission cross sections (/spl ap/980 nm) are 1.6/spl times/10/sup -25/ m/sup 2/ and 1.2/spl times/10/sup -25/ m/sup 2/, the Yb/sup 3+/--Er/sup 3+/ energy-transfer coefficient is 1.8/spl times/10/sup -23/ m/sup 3//s and the cooperative-upconversion coefficient is 8/spl times/10/sup -25/ m/sup 3//s. An approximate method is introduced that allows the determination of the absorption and emission cross section distributions for the erbium /sup 4/I/sub 13/2//spl hArr//sup 4/I/sub 15/2/ transition from the amplified spontaneous emission power spectrum.     

Thin-film persistent current switch

We have developed a fast, low power heat switch for switching a niobium thin film between the normal and superconducting state. The sputtered niobium film (400 nm thick, 100 /spl mu/m wide) has a critical current density of 5/spl times/10/sup 10/ Am/sup -2/. Switching is produced by joule heating a small section of the niobium film with a titanium thin-film resistor. With the heat switch in vacuum, the minimum heater power needed to switch to the normal state was 4.5/spl times/10/sup -5/ W. A simple three-dimensional thermal model shows that the minimum power is primarily determined by the thermal conductivity of the substrate. We have achieved response times less than 10/sup -6/ s.     

Nonuniform Layer Model of a Millimeter-Wave Phase Shifter

The electromagnetic wave propagation of millimeter waves in dielectric waveguides with thin surface plasma layers is characterized. The phase and attenuation of a 94-GHz wave are computed for various surface plasma layer thicknesses as a function of earner density levels. The electron/hole pairs generated in the vicinity of the dielectric waveguide surface by photo excitation are assumed to have an exponential profile due to either carrier diffusion or the exponential absorption of the optical field. Field computations made for a uniform plasma layer are compared with those of the nonuniform plasma to illustrate the effects of the exponential tails of the carrier profiles on both the phase and attenuation of the millimeter wave. The thin plasma layers slightly affect the field profile of the transverse electric modes (fields polarized parallel to the plasma layer). The transverse magnetic fields are highly distorted at plasma densities greater than 10/sup 16/ cm/sup -3/.     

Influence of surface defect charge at AlGaN-GaN-HEMT upon Schottky gate leakage current and breakdown voltage

The relation between Schottky gate leakage current and the breakdown voltage of AlGaN-GaN high-electron mobility transistors (HEMTs) is discussed based on the newly introduced simple, yet useful, surface defect charge model. This model represents the leakage current caused by the positive charge in the surface portion of AlGaN layer induced by process damage such as nitrogen vacancies. The new model has been implemented into a two-dimensional device simulator, and the relationship between the gate leakage current and the breakdown voltage was simulated. The simulation results reproduced the relationship obtained experimentally between the leakage current and the breakdown voltage. Further simulation and experiment results show that the breakdown voltage is maintained even if the defect charge exists up to the defect charge density of 2.5/spl times/10/sup 12/ cm/sup -2/, provided the field plate structure is adopted, while the breakdown voltage shows a sudden drop for the defect density over 5/spl times/10/sup 11/ cm/sup -2/ without the field plate. This result shows that the field plate structure is effective for suppressing the surface charge influence on breakdown voltage due to the relaxation of the electric field concentration in the surface portion of the AlGaN layer.     

Computation of the Electromagnetic Fields and Induced Temperatures Within a Model of the Microwave-Irradiated Human Eye

The electromagnetic fields within a detailed model of the human eye and its surrounding bony orbit are calculated for two different frequencies of plane-wave irradiation: 750 MHz and 1.5 GHz. The computation is performed with a finite-difference algorithm for the time-dependent Maxwell's equations, carried out to the sinusoidal steady state. The heating potential, derived from the square of the electric field, is used to calculate the temperatures induced within the eyeball of the model. This computation is performed with the implicit alternating-direction (IAD) algorithm for the heat conduction equation. Using an order-of-magnitude estimate of the heat-sinking capacity of the retinal blood supply, it is determined that a hot spot exceeding 40.4/spl deg/C occurs at the center of the model eyeball at an incident power level of 100 mW/cm/sup 2/ at 1.5 GHz.     

W-band investigation of material parameters, SAR distribution, and thermal response in human tissue

This investigation is divided into three parts. First, the W-band dielectric properties of different biological tissues are determined. Then, the electromagnetic field in the human eye and skin is simulated for plane-wave exposure. An analytical method is used to investigate the specific absorption rate (SAR) inside a layered model of the human skin between 3-100 GHz. Furthermore, the SAR inside a detailed model of the human eye is investigated numerically by the finite-difference time-domain method for a frequency of 77 GHz. Maximum local SAR values of 27.2 W/kg in skin tissue and 45.1 W/kg in eye tissue are found for 77 GHz and an incident power density of 1 mW/cm/sup 2/. In the third part of the investigation, the temperature changes of superficial tissue caused by millimeter-wave irradiation are measured by a thermal infrared imaging system. The exposure setup is based on a horn antenna with a Gunn oscillator operating at 15.8-dBm output power. The measurements showed a maximum temperature increase of 0.7/spl deg/C for a power density of 10 mW/cm/sup 2/ and less than 0.1/spl deg/C for 1 mW/cm/sup 2/, both in human skin (in vivo), as well as in porcine eye (in vitro). The comparison of the temperature measurements with a thermal bio-heat-transfer simulation of a layered skin model showed a good agreement.     

Photoresponse of (In,Ga)N-GaN multiple-quantum-well structures in the visible and UVA ranges

Characterization and analysis of photoresponse in p-n diodes with embedded (In,Ga)N-GaN multiple-quantum-well (MQW) structures are reported. Their dependence on the number of wells and In composition are considered. The influence of device structure on electric fields in the active region and on device responsivity has also been studied. Theoretical considerations as well as photocapacitance and photocurrent measurements show that the position of quantum wells (QWs), either in the quasi-neutral region or in the space charge region, is a critical factor in the collection efficiency. Hence, device photoresponse is not proportional to the number of QWs in photovoltaic mode. Present p-MQW-n devices show a promising performance as UVA and visible photodetectors, with detectivities, D/sup */, higher than 1.2/spl times/10/sup 12/ cm/spl middot/Hz/sup 1/2//spl middot/W/sup -1/ and rejection ratios higher than 10/sup 3/.     

Very High Sensitivity Heterodyne Detection of X-Band Radiation with Neon Indicator Lamps

Very high sensitivity with simple inexpensive commercial neon glow lamps designed for indicator-lamp applications is observed at X band in synchronous detection. Typical minimum detectable signals with 10-nW-order local-oscillator powers are 10/sup -17/ W /spl dot/ Hz/sup -1/ or lower. This is equivalent to 10/sup -22/ W /spl dot/Hz/spl -1/ with 1-mW local-oscillator power. As such lamps can be used without damage in high microwave fields, they can be used in principle with appropriate local-oscillator power levels to reach ideal microwave noise equivalent power (NEP) limits. The low NEP and noise figure result from the high responsivities of such devices which are due to high internal signal gain. Experimental results correlate well with the enhanced-ionization collision-rate detection model.     

Absorption and light scattering in InGaN-on-sapphire- and AlGaInP-based light-emitting diodes

Different experimental and simulation techniques aiming at a better understanding of lateral mode absorption in light-emitting diodes (LEDs) are presented in this paper. A measurement of transmitted power versus propagation distance allows us to derive the absorption losses of LED layer structures at their emission wavelength. Two models for the observed intensity distribution are presented: one is based on scattering, whereas the other relies on selective absorption. Both models were applied to InGaN-on-sapphire-based LED structures. Material absorption losses of 7 cm/sup -1/ for the scattering model and 4 cm/sup -1/ for the absorbing-layer model were obtained. Furthermore, these values are independent of the emission wavelength of the layer structure in the 403-433-nm range. The losses are most likely caused by a thin highly absorbing layer at the interface to the substrate. In a second step, interference of the modal field profile with the absorbing layer can be used to determine its thickness (d=75 nm) and its absorption coefficient (/spl alpha/ /spl ap/ 3900 cm/sup -1/). This method has also been tested and applied on AlGaInP-based layer structures emitting at 650 nm. In this case, the intensity decay of /spl alpha/=30 cm/sup -1/ includes a contribution from the absorbing substrate.     

UV-induced index changes in Undoped Fluoride glass

Undoped fluoride glass slides have been exposed to pulsed 193-nm ultraviolet (UV) irradiation. Their absorption changes have been measured to evaluate UV-induced index changes using Kramers-Kronig relation. A layer-peeling polishing technique was applied to characterize the local UV-induced index change of highly absorbing glass. Index changes up to 1.75/spl times/10/sup -4/ have been evaluated with this method in fluorozirco-aluminate glass. Fluoroaluminate and fluorozirconate glass showed only small index changes of about 2.0/spl times/10/sup -6/ and 2.6/spl times/10/sup -6/ at a wavelength of 1550 nm.     

Human Whole-Body Radiofrequency Absorption Studies Using a TEM-Cell Exposure System

A system has been constructed for measuring radiofrequency absorption in the human body resulting from exposure to high-frequency (HF) electromagnetic radiation. The exposure chamber is a 6.1 X 7.3 X 13.0-m rectangular-coaxial transverse-electromagnetic (TEM) cell. The absorbed power, determined from signal-averaged measurements of incident, reflected, and transmitted power, is measured to a precision of 0.06 percent of incident power (0.003 dB in insertion loss). A detailed analysis of systematic errors in the method has shown that a directional-coupler directivity approaching 50 dB is necessary for high accuracy in absorbed-power measurements and that any dielectric-loading effect of the subject on the cell absorption is undetectable. The total systematic error in determining absorption rate per unit exposure rate is about +-35 percent of the measurement. Operating frequencies are currently limited to the 3 to 20-MHz range due to the occurrence of the first cell resonance, associated with the TE/sub 01/ mode, at 20.7 MHz. The first set of human whole-body absorption results is presented for three subjects exposed in free space to 11 µW/cm/sup 2/ at 18.5 MHz in six different body orientations with respect to the TEM wave. The measured absorption rates for the two principal E orientations are larger than the published predictions by a factor of 2 to 3.     

Reduction of off-current in self-aligned double-gate TFT with mask-free symmetric LDD

In this work, the lateral electric field distribution in the channel of a double-gate TFT is studied and compared with that of a conventional single-gate TFT. The double-gate TFT is predicted to suffer from a more severe anomalous off-current than the single-gate TFT. A smart double-gate TFT technology is proposed to decrease the off-current. The unique feature of the technology is the lithography independent formation of the self-aligned double-gate and the symmetric lightly doped drain (LDD) structures. With the LDD applied, the anomalous off-current of the fabricated double-gate TFT is reduced by three orders of magnitude from the range of 10/sup -9/ A//spl mu/m to 10/sup -12/ A//spl mu/m. The on/off current ratio is increased by three orders of magnitude accordingly from around 10/sup 4/ to 10/sup 7/.     

Optical and electrical properties of nanostructured metal-silicon-metal photodetectors

We report an experimental evaluation of the performance of silicon (Si) photodetectors incorporating one-dimensional (1-D) arrays of rectangular and triangular-shaped nanoscale structures within their active regions. A significant (/spl sim/2/spl times/) enhancement in photoresponse is achieved in these devices across the 400- to 900-nm spectral region due to the modification of optical absorption properties that results from structuring the Si surface on physical optics scales smaller than the wavelength, which both reduces the reflectivity and concentrates the optical field closer to the surface. Both patterned (triangular and rectangular lineshape) and planar Ni-Si back-to-back Schottky barrier metal-semiconductor-metal photodetectors on n-type (/spl sim/5/spl times/10/sup 14/ cm/sup -3/) bulk Si were studied. 1-D /spl sim/50-250-nm linewidth, /spl sim/1000-nm depth, grating structures were fabricated by a combination of interferometric lithography and dry etching. The nanoscale grating structures significantly modify the absorption, reflectance, and transmission characteristics of the semiconductor: air interface. These changes result in improved electrical response leading to increased external quantum efficiency (from /spl sim/44% for planar to /spl sim/81% for structured devices at /spl lambda/=700 nm). In addition, a faster time constant (/spl sim/1700 ps for planar to /spl sim/600 ps for structured at /spl lambda/=900 nm) is achieved by increasing the absorption near the surface where the carriers can be rapidly collected. Experimental quantum efficiency and photocurrents results are compared with a theoretical photocurrent model based on rigorous coupled-wave analysis of nanostructured gratings.     

Blue energy upconversion emission in thulium-doped-SiO/sub 2/-P/sub 2/O/sub 5/ channel waveguides excited at 1.064 /spl mu/m

Blue energy upconversion emission in Tm/sup 3+/-doped SiO/sub 2/-P/sub 2/O/sub 5/ channel waveguides off-resonance pumped by infrared radiation is reported. The waveguide samples were excited by a single continuous-wave laser source at 1.064 /spl mu/m. Two distinct blue emission signals around 450 and 480 nm, in addition to red at 660 nm and near-infrared at 800-nm less intense emissions were observed. The upconversion excitation mechanism was assigned to stepwise multiphoton absorption processes followed by nonradiative multiphonon-assisted relaxation processes. Infrared-to-blue conversion efficiencies with respect to the absorbed pump power of /spl sim/6.0/spl times/10/sup -7/ for this off-resonance pumping scheme was measured. The dependence of the infrared-to-blue upconversion mechanism upon the excitation power and thulium content is also examined.     

Midinfrared holmium fiber lasers

The use of the high-power Tm/sup 3+/-doped silica fiber laser as a pump source for Ho/sup 3+/-doped silica and Ho/sup 3+/-doped fluoride fiber lasers for the generation of 2.1-/spl mu/m radiation is demonstrated. The Ho/sup 3+/-doped silica fiber laser produced a maximum output power of 1.5 W at a slope efficiency of /spl sim/82%; one of the highest slope efficiencies measured for a fiber laser. In a nonoptimized but similar fiber laser arrangement, a Ho/sup 3+/-doped fluoride fiber laser produced an output power of 0.38 W at 2.08 /spl mu/m at a slope efficiency of /spl sim/50%. A Raman fiber laser operating at 1160 nm was also used to pump a Ho/sup 3+/-doped fluoride fiber laser operating at a wavelength of 2.86 /spl mu/m. An output power of 0.31W was produced at a slope efficiency of 10%. The energy transfer upconversion process that depopulates the lower laser level in this case operates at a higher efficiency when the pump wavelength is closer to the absorption peak of the /sup 5/I/sub 6/ energy level, however, this energy transfer process does not impede to a great extent the performance of the Ho/sup 3+/-doped fluoride fiber laser based on the /spl sim/2.1/spl mu/m laser transition.     

A 10-Gb/s receiver with series equalizer and on-chip ISI monitor in 0.11-/spl mu/m CMOS

A 10-Gb/s receiver is presented that consists of an equalizer, an intersymbol interference (ISI) monitor, and a clock and data recovery (CDR) unit. The equalizer uses the Cherry-Hooper topology to achieve high-bandwidth with small area and low power consumption, without using on-chip inductors. The ISI monitor measures the channel response including the wire and the equalizer on the fly by calculating the correlation between the error in the input signal and the past decision data. A switched capacitor correlator enables a compact and low power implementation of the ISI monitor. The receiver test chip was fabricated by using a standard 0.11-/spl mu/m CMOS technology. The receiver active area is 0.8 mm/sup 2/ and it consumes 133 mW with a 1.2-V power supply. The equalizer compensates for high-frequency losses ranging from 0 dB to 20 dB with a bit error rate of less than 10/sup -12/. The areas and power consumptions are 47 /spl mu/m /spl times/ 85 /spl mu/m and 13.2 mW for the equalizer, and 145 /spl mu/m /spl times/ 80 /spl mu/m and 10 mW for the ISI monitor.     

Electroabsorption modulation at 1.3 /spl mu/m on GaAs substrates using a step-graded low temperature grown InAlAs buffer

We have achieved quantum confined Stark effects (QCSE) on In/sub 0.38/Ga/sub 0.62/As-In/sub 0.38/Al/sub 0.62/As multiple-quantum-well (MQW) structures, operating at 1.3 /spl mu/m grown on GaAs substrates. A quantum confined Stark shift of the exciton absorption peak of 47 meV was obtained with an applied electric field of 190 KV/cm, measured on surface normal PIN diodes. The structure is grown by MBE on a novel three-stage, compositionally step graded, In/sub x/Al/sub 1-x/As buffer, doped with Si to 5/spl middot/10/sup 17//cm/sup 3/, on an n-type GaAs substrate. The total thickness of the buffer is 0.3-0.6 mm, which is considerably smaller than that of linearly graded buffer layers. This structure can be used in both waveguide modulators and surface normal F-P type modulators on GaAs substrates.     

Design criteria of high-Voltage lateral RESURF JFETs on 4H-SiC

Integrated power electronics on SiC have great potential in future power electronics applications. In this paper, a novel vertical channel lateral junction field-effect transistor structure with reduced surface electric field effect is proposed for the first time on 4 H-SiC to address existing challenges in lateral power devices on SiC. Based on an experimentally proven channel design, the detailed design procedure of such a device has been investigated. Design criteria to optimize device forward blocking as well as conduction characteristics are studied. Parameter tolerance and design windows are discussed considering practical issues in device fabrication. Designs that will lead to an optimized tradeoff between device breakdown voltage and specific on-resistance are shown. With an 8-/spl mu/m-long drift region, a 1535-V breakdown voltage and 3.24 m/spl Omega//spl middot/cm/sup 2/ specific on-resistance can be achieved. This represents a figure-of-merit of 737 MW/cm/sup 2/, about 100 times higher than that of the best normally off lateral power devices reported in the literature. The proposed device can be an attractive candidate for power integrated circuit on SiC.