A highly integrated FPGA-based nuclear magnetic resonance spectrometer

The digital circuits required for a nuclear magnetic resonance (NMR) spectrometer, including a pulse programmer, a direct digital synthesizer, a digital receiver, and a PC interface, have been built inside a single chip of the field-programmable gate-array (FPGA). By combining the FPGA chip with peripheral analog components, a compact, laptop-sized homebuilt spectrometer has been developed, which is capable of a rf output of up to 400 MHz with amplitude-, phase-, frequency-, and pulse-modulation. The number of rf channels is extendable up to three without further increase in size.     

High power solid state rf amplifier for proton accelerator

A 1.5 kW solid state rf amplifier at 352 MHz has been developed and tested at RRCAT. This rf source for cw operation will be used as a part of rf system of 100 MeV proton linear accelerator. A rf power of 1.5 kW has been achieved by combining output power from eight 220 W rf amplifier modules. Amplifier modules, eight-way power combiner and divider, and directional coupler were designed indigenously for this development. High efficiency, ease of fabrication, and low cost are the main features of this design.     

L波段雷达功率放大器设计和优化

设计一种L波段雷达功率放大器.对功率放大器的输出功率、脉冲顶降、热设计等关键参数进行了理论分析,结合电路输出功率的仿真结果对功率放大器的工作效率以及输出功率的带内波动进行评估.研究了脉冲顶降对输出信号的品质影响,探讨了功率放大器热设计的半定量的制约问题.给出系统主要参量的优化设计方法,完成了L波段雷达功率放大器的样机制...     

含氮固体物质的核四极共振远程探测仪

本文介绍一台结构简单，造价低廉的１４Ｎ核四极共振远程探测仪。它利用脉冲傅立叶变换技术，将获得的核自由感应衰减信号或回波信号进行相干累加以提高信噪比。整个系统分硬件和软件两部分。前者由射频脉冲放大器（有效值功率输出约３００Ｗ）、探头、接收机和ＩＢＭ—ＰＣ机构成。后者由ＰＣ机上的脉冲序列程序和数字信号处理程序组成。利用这台谱仪，能够在几十秒时间内得到距离探头线圈１０厘米以内的典型含氮化合物的核四极共振谱     

A repeater type biotelemetry system for use on wild big game animals.

A repeater type telemetry system was developed and field tested on a wild elk near laramie, Wyoming, in the summer of 1973. The telemetry system consisted of the following: (a) a heat flow rate sensing implanted transmitter, (b) a repeater type neck collar and (c) a portable receiving station consisting of a receiver, decoding circuitry and analog chart recorder. The transmitter in (a) produced relatively low frequency rf pulses whose repetition rate was directly proportional to heat flow rate through the hide of the animal. In (b), the pulses from the implant are sensed and retransmitted using a relatively high power, high frequency transmitter. A second rf pulse was generated whose pulse spacing was related to animal activity. Details of circuit design and performance are given. Field experience has shown that this method is extremely useful for the monitoring of biological data from secretive big game animals such as elk.     

Repetitive sub-gigawatt rf source based on gyromagnetic nonlinear transmission line

We demonstrate a high power repetitive rf source using gyromagnetic nonlinear transmission line to produce rf oscillations. Saturated NiZn ferrites act as active nonlinear medium first sharpening the pumping high voltage nanosecond pulse and then radiating at central frequency of about 1 GHz: shock rise time excites gyromagnetic precession in ferrites forming damping rf oscillations. The optimal length of nonlinear transmission line was found to be of about 1 m. SINUS-200 high voltage driver with Tesla transformer incorporated into pulse forming line has been designed and fabricated to produce bursts of 1000 pulses with 200 Hz repetition rate. A band-pass filter and mode-converter have been designed to extract rf pulse from low-frequency component and to form TE(11) mode of circular waveguide with linear polarization. A wide-band horn antenna has been fabricated to form Gaussian distribution of radiation pattern. The peak value of electric field strength of a radiated pulse at the distance of 3.5 m away from antenna is measured to be 160 kV/m. The corresponding rf peak power of 260 MW was achieved.     

Hot-electron bolometer terahertz mixers for the Herschel Space Observatory

We report on low noise terahertz mixers (1.4-1.9 THz) developed for the heterodyne spectrometer onboard the Herschel Space Observatory. The mixers employ double slot antenna integrated superconducting hot-electron bolometers (HEBs) made of thin NbN films. The mixer performance was characterized in terms of detection sensitivity across the entire rf band by using a Fourier transform spectrometer (from 0.5 to 2.5 THz, with 30 GHz resolution) and also by measuring the mixer noise temperature at a limited number of discrete frequencies. The lowest mixer noise temperature recorded was 750 K [double sideband (DSB)] at 1.6 THz and 950 K DSB at 1.9 THz local oscillator (LO) frequencies. Averaged across the intermediate frequency band of 2.4-4.8 GHz, the mixer noise temperature was 1100 K DSB at 1.6 THz and 1450 K DSB at 1.9 THz LO frequencies. The HEB heterodyne receiver stability has been analyzed and compared to the HEB stability in the direct detection mode. The optimal local oscillator power was determined and found to be in a 200-500 nW range.     

A broadband Fourier transform microwave spectrometer based on chirped pulse excitation

Designs for a broadband chirped pulse Fourier transform microwave (CP-FTMW) spectrometer are presented. The spectrometer is capable of measuring the 7-18 GHz region of a rotational spectrum in a single data acquisition. One design uses a 4.2 Gsampless arbitrary waveform generator (AWG) to produce a 1 mus duration chirped pulse with a linear frequency sweep of 1.375 GHz. This pulse is sent through a microwave circuit to multiply the bandwidth of the pulse by a factor of 8 and upconvert it to the 7.5-18.5 GHz range. The chirped pulse is amplified by a traveling wave tube amplifier and broadcast inside the spectrometer by using a double ridge standard gain horn antenna. The broadband molecular free induction decay (FID) is received by a second horn antenna, downconverted, and digitized by a 40 Gsampless (12 GHz hardware bandwidth) digital oscilloscope. The second design uses a simplified pulse generation and FID detection scheme, employing current state-of-the-art high-speed digital electronics. In this spectrometer, a chirped pulse with 12 GHz of bandwidth is directly generated by using a 20 Gsampless AWG and upconverted in a single step with an ultrabroadband mixer. The amplified molecular emission is directly detected by using a 50 Gsampless digital oscilloscope with 18 GHz bandwidth. In both designs, fast Fourier transform of the FID produces the frequency domain rotational spectrum in the 7-18 GHz range. The performance of the CP-FTMW spectrometer is compared to a Balle-Flygare-type cavity-FTMW spectrometer. The CP-FTMW spectrometer produces an equal sensitivity spectrum with a factor of 40 reduction in measurement time and a reduction in sample consumption by a factor of 20. The CP-FTMW spectrometer also displays good intensity accuracy for both sample number density and rotational transition moment. Strategies to reduce the CP-FTMW measurement time by another factor of 90 while simultaneously reducing the sample consumption by a factor of 30 are demonstrated.     

A detector for the pulsed nuclear quadrupole resonance spectrometer

An increase in the sensitivity of a pulse-type detector for the nuclear quadrupole resonance spectrometer has been attained by optimizing the delay time for switching on the receiver after termination of an excitation pulse and by using an original circuit of the synchronous detector with a high dynamic range of 100 dB. The sensitivity of the nuclear quadrupole resonance spectrometer improved by using the developed detector is about twice as great as the spectrometer sensitivity before its upgrading. The spectrometer is capable of detecting 0.5 g of sodium nitrite.     

转轴扭矩红外遥测系统

用微处理器结合数字电位器、运放、A／D等组成信号调理电路，解决传感器信号的采集及零点校准的自动实现等问题；微处理器再结合与门将所采集的扭矩信号转换、调制成已调波，已调波经功率放大后驱动一组相互并联的红外LED，发出同步的脉冲光信号；红外LED沿转轴圆周均布，使均布角小于红外LED的散射角，从而使地面上的接收器可接收到连续的脉冲光信号，实现转轴扭矩信号的红外遥测。接收器中使用多只红外一体化接收头，使遥测系统的可靠性得到讲一步提高。     

A plasma cathode for a radio-frequency gun

A plasma ferroelectric cathode is used to form electron beams with a high pulse charge and a high charge in an electron bunch in an rf electron gun of a 10-cm wavelength range. The design of the cathode is described, and the results of calculations of the densities of the cathode-emitted and the gun-outputted currents are presented. The operation of the cathode in the rf gun was studied experimentally: the electron energy, the pulse current, and the transverse emittance of the beam were measured. The electron beam obtained at the output of the single-resonator gun had a pulse current of up to 10 A, a pulse duration of 60 ns, and an electron energy of ?500 keV. The normalized beam emittance was 40 mm mrad.     

An ESN-STM spectrometer for single spin detection

We have designed and built an ESN-STM spectrometer dedicated to single electron spin detection. Our spectrometer couples a home-made STM with a Real-Time Spectrum Analyzer. The head of the spectrometer allows routine imaging of molecules deposited on surfaces with high tunnelling current set point. In order to provide a maximal ESN-STM signal power transfer from the source (i.e. tunnelling junction) to the amplifier stage we have developed an impedance matching circuit between the tunnelling junction and impedance of RF signal amplifier. Our impedance matching circuit is based on application of a wide-spectrum amplifier equipped with FET transistor. In order to validate the usefulness of our ESN-STM spectrometer tests of sensitivity are presented. The main advantage of our spectrometer is the fact that it allows the collection of spin spectra from every single point of the topography image.     

Fast recovery, high sensitivity NMR probe and preamplifier for low frequencies

The design of a probe-preamplifier combination which reduces the NMR receiver recovery time following a pulse by a factor of at least twenty at 5 MHz is described. The preamplifier, which has a noise figure of 1.3 dB, employs negative feedback to damp the probe coil (a typical effective Q is 7), but maintains the signal-to-noise ratio that one would expect from an undamped coil. In addition, the use of a short phase-inverted pulse following the main transmitter pulse serves to reduce drastically the ring-down of the probe for those high voltages where the preamplifier is inoperative. Optimum utilization of transmitter power in achieving fast pulse rise times is also discussed, as well as elimination of 'phase-glitch' by proper tuning and the use of a broadband transmitter.     

A low-frequency NMR probe

A probe for a low-frequency pulse NMR spectrometer with crossed coils has been designed. The probe is based on operational amplifiers and has an operating frequency of 3.6 MHz, a gain of 43 dB, and a noise factor of 1.8 dB. The damping unit of the pickup coil, which is integrated into the probe, reduces the complete recovery time of the receiving section of the spectrometer down to 15 μs.     

Development and application of setup for ac magnetic field in neutron scattering experiments

We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm(3) and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed.     

Note: Ultra-high frequency ultra-low dc power consumption HEMT amplifier for quantum measurements in millikelvin temperature range

We have presented theory and experimentally demonstrated an efficient method for drastically reducing the power consumption of the rf/microwave amplifiers based on HEMT in unsaturated dc regime. Conceptual one-stage 10 dB-gain amplifier showed submicrowatt level of the power consumption (0.95 μW at frequency of 0.5 GHz) when cooled down to 300 mK. Proposed technique has a great potential to design the readout amplifiers for ultra-deep-cooled cryoelectronic quantum devices.     

Direct coupling of pulsed radio frequency and pulsed high power in novel pulsed power system for plasma immersion ion implantation

A novel power supply system that directly couples pulsed high voltage (HV) pulses and pulsed 13.56 MHz radio frequency (rf) has been developed for plasma processes. In this system, the sample holder is connected to both the rf generator and HV modulator. The coupling circuit in the hybrid system is composed of individual matching units, low pass filters, and voltage clamping units. This ensures the safe operation of the rf system even when the HV is on. The PSPICE software is utilized to optimize the design of circuits. The system can be operated in two modes. The pulsed rf discharge may serve as either the seed plasma source for glow discharge or high-density plasma source for plasma immersion ion implantation (PIII). The pulsed high-voltage glow discharge is induced when a rf pulse with a short duration or a larger time interval between the rf and HV pulses is used. Conventional PIII can also be achieved. Experiments conducted on the new system confirm steady and safe operation.     

A probe and amplifier of a <Emphasis Type="Italic">Q</Emphasis>-meter for recording electron paramagnetic resonances at 300 MHz

A probe with a high-frequency amplifier of a continuous-wave Q-meter-type electron paramagnetic resonance (EPR) spectrometer operating at 300 MHz is described. The probe is inductively connected with both an exciting high-frequency generator and the amplifier. The amplifier is matched to the probe for obtaining a minimum noise figure of 2.9 dB. The single-scan EPR line with a 1.7-G width and 3 × 10¹⁸ resonant paramagnetic centers is recorded with a signal-to-noise ratio of about 260.     

A high-power pulse amplifier for radar and navigation systems

A high-power pulse amplifier intended for pulse excitation of microwave generators on 3A750, 3A762, 3A765, and 3A766 diodes is described. An advantage of the amplifier is that its output voltage is independent of the load resistance owing to a low output resistance of ～0.05 Ω. The performance characteristics of the amplifier are as follows: a maximal output voltage of 120 V, a maximal output pulse current of 25 A, a pulse rise time of 10 ns, amplified-pulse durations of 20 to 300 ns, and a gain of 35 dB.     

Relativistic electron diffraction at the UCLA Pegasus photoinjector laboratory

Electron diffraction holds the promise to yield real-time resolution of atomic motion in an easily accessible environment like a university laboratory at a fraction of the cost of fourth-generation X-ray sources. Currently the limit in time-resolution for conventional electron diffraction is set by how short an electron pulse can be made. A very promising solution to maintain the highest possible beam intensity without excessive pulse broadening from space charge effects is to increase the electron energy to the MeV level where relativistic effects significantly reduce the space charge forces. Rf photoinjectors can in principle deliver up to 10(7)-10(8) electrons packed in bunches of approximately 100-fs length, allowing an unprecedented time resolution and enabling the study of irreversible phenomena by single-shot diffraction patterns. The use of rf photoinjectors as sources for ultrafast electron diffraction has been recently at the center of various theoretical and experimental studies. The UCLA Pegasus laboratory, commissioned in early 2007 as an advanced photoinjector facility, is the only operating system in the country, which has recently demonstrated electron diffraction using a relativistic beam from an rf photoinjector. Due to the use of a state-of-the-art ultrashort photoinjector driver laser system, the beam has been measured to be sub-100-fs long, at least a factor of 5 better than what measured in previous relativistic electron diffraction setups. Moreover, diffraction patterns from various metal targets (titanium and aluminum) have been obtained using the Pegasus beam. One of the main laboratory goals in the near future is to fully develop the rf photoinjector-based ultrafast electron diffraction technique with particular attention to the optimization of the working point of the photoinjector in a low-charge ultrashort pulse regime, and to the development of suitable beam diagnostics.