Amplitude Of Radio Frequency Signal Research Articles

Maintenance-free wireless multi-functional sensing enabled by electrostatic generator

Conventional self-powered sensor nodes rely on commercial sensing and wireless modules, making it difficult to achieve both long-range and real-time sensing, due to the limited energy harvested from the environment and the module’s high-power consumption. To solve this problem, a universal paradigm for self-powered sensor nodes with real-time, long-range and multi-functional sensing capability was proposed, which is achieved by low-power signal modulation using an electrostatic generator and a surface acoustic wave resonator (SAWR)-based transmitter. Once the sensor node is mechanically stimulated, the generator triggers the transmitter to generate radio frequency (RF) signals, containing both the generator’s motion status which encodes the RF signal amplitude to binarized 1/0 and the information sensed by SAWR which modulates the RF signal frequency. Based on the paradigm, we demonstrated simultaneous and continuous monitoring of wind speed and temperature from two sensor nodes located over 100 m, opening up new possibilities for maintenance-free wireless sensing.

전자전 다중 위협 재밍을 위한 멀티빔 송수신장치용 광대역 고출력 송수신모듈 개발

An eight-channel transmit/receive module (TRM) was designed for a wideband electronic warfare multiple threat jamming transceiver. In the system, the TRM amplifies a multijamming signal from a multibeam transceiver module and a small radio frequency (RF) signal from an antenna. In TX mode, it has an output power of more than 43 dBm for a continuous wave. In RX mode, it has a gain of more than 10 dB and noise figure of less than 5 dB. The voltage standing wave ratio is less than 2:1, and the TX and RX path isolation is 50 dBc or more. The RF signal amplitude and phase variation are less than 2 dB and 10°, respectively. True time delay and a digital attenuator are used to compensate for the signal amplitude and phase for each channel.

A Feedback Control Method to Maintain the Amplitude of the RF Signal Applied to Ion Traps

For high-fidelity quantum operations in ion traps, it is important to maintain the secular frequency of the trapped ions at a constant value. The radial secular frequency is proportional to the amplitude of the radio frequency (RF) signal applied to ion traps. Owing to the changes in the ambient temperature of a helical resonator and the minute vibration of the optical table, the amplitude can vary. Recently, a method for reducing the fluctuation in the RF signal amplitude, using a commercial universal proportional-plus-integral (PI) controller, has been introduced, which, in turn, reduces the secular frequency drift of the trapped ions. The method improves the capability to maintain the secular frequency at a constant value. However, the structure of the controller is fixed; thus, the control method cannot be changed to suit different experimental conditions, and the different feedback configuration cannot be implemented to increase the resolution. In this paper, we develop a field-programmable gate array (FPGA)-based feedback controller that allows the implementation of various automatic control methods and feedback configurations. In our experiments, the fluctuation in the amplitude of the RF signal was 1.806% using a commercial universal PI controller. The fluctuation was reduced to 0.099% using the developed FPGA-based PI controller, and to 0.102% using the developed FPGA-based lag compensator. By employing the developed FPGA control method, many other automating control methods can be applied to achieve a stable and high-performance control of the secular frequency.

Angling for angles

Researchers from Australia have presented their novel technique to estimate incoming radio-frequency (RF) signal angles of arrival (AOA), irrespective of the RF signal amplitude. Experimental results show that the AOA measurement can be achieved between 0°–63° with less than 3° of errors for a 15 GHz signal at varying power levels. Identifying the location of an object is extremely important for a number of different applications, including navigation, wireless communication and electronic warfare. The process of identifying an object involves a transmitter, for example a mobile phone or a radar unit, that transmits an RF signal, and a detector device to measure the RF signal. The RF signal reflects off an object and towards the detector. The detector unit can identify the difference in time or phase for the arriving RF signal to when it was transmitted – the angle of arrival. The AOA can then be used to identify the object's location. Chan (left) and Chen (right), authors of the published submission. Correlation between estimated (Y) and actual (X) AOA. The deviation above 60° can clearly be seen. Schematic of the proposed system. Using microwave photonics, the AOA of high-frequency RF signals can be determined, with a reduction in electromagnetic interference as well as system size, weight and power consumption. There are drawbacks to using microwave photonics, however, in that a calibration process involving measuring either system output power at a 0° AOA, or measuring the incoming RF signal amplitude, is necessary to eliminate the RF signal amplitude dependence in the system output prior to measuring the AOA. The work of Chan and Chen is useful because it allows for a measurement of the AOA without the need for measuring the incoming RF signal amplitude, simplifying the process. The new technique works by using a continuously laser-generated wave of light, which is split equally between two modules. Each module comprises one dual-drive Mach Zehnder modulator, an optical bandpass filter and a photodetector. After some phase shifting, the photodetectors eventually generate two DC photocurrents, which can be used to calculate a K value which is a function of the RF signal phase difference. K can then be used to derive the AOA without the need for information about the input RF signal amplitude. Further experiments were carried out using the system. An RF signal of 15 GHz was generated by a microwave signal generator, producing two RF signals with 3.2 dBm power level after the initial splitting between the two modules. It was found that the methodology performed well when the actual AOA was between 0° and ∼60°. The experiment was also repeated with different signal powers of −0.3 dBm and −3.6 dBm, with accurate results being obtained, proving that the AOA can be estimated independent of the RF signal amplitude. With a larger optical carrier suppression, it should be possible to accurately measure the RF signal AOA beyond 60°.

Technique to eliminate RF signal amplitude dependence in AOA measurement

A technique to estimate an incoming radio frequency (RF) signal angle of arrival (AOA) irrespective of the RF signal amplitude is presented. It is based on measuring the DC voltage at the output of two modules where each of them consists of an optical modulator, an optical filter and a photodetector. An RF signal amplitude-independent AOA can be obtained from the ratio of the two DC voltages. Experimental results are presented that demonstrate 0°–63° AOA measurement with <3° errors for an RF signal with three different power levels of 3.2, −0.3 and −3.6 dBm into the modulator.

Ripple Suppression in Broadband Microwave Photonic Phase Shifter Frequency Response

This paper presents a detailed investigation on the cause of ripples in the frequency response of a microwave photonic phase shifter implemented using a 90° hybrid coupler. It was found that an unwanted radio frequency (RF) modulation sideband is generated at the modulator output due to the 90° hybrid coupler amplitude and phase imbalance. This resulted in phase shifter output RF signal amplitude variation and phase deviation. Experimental results demonstrated that incorporating an optical filter in the phase shifter structure can reduce the amplitude variation and phase deviation from 4.2 dB to 2.2 dB and from ±12° to ±3.8°, respectively, over a wide frequency range. A comparison of the loss and the dynamic range of the microwave photonic phase shifter implemented using a 90° hybrid coupler with a conventional fiber optic link is also presented.

Highly flexible optical Nyquist pulses generation based on dual-parallel Mach–Zehnder modulator and intensity modulator

A new scheme for highly flexible optical Nyquist pulses generation is proposed by using a dual-parallel Mach–Zehnder modulator (DPMZM) and an intensity modulator (IM) without any external optical filter. The optical Nyquist pulses generator includes two stages. At the first stage, 2-, 3-, or 5-carrier light sources with two different frequency spacing are generated by utilizing a DPMZM. At the second stage, the light source used as seed light is then sent to IM, and two forms of optical frequency combs with spectral line flatness of less than 0.7 dB can be finally obtained by simply adjusting the DC bias and amplitude of radio frequency signal applied to IM. Ideal sinc-shaped Nyquist pulses are also generated in the time domain with bandwidth from 75 to 225 GHz and repetition rate from 40 to 80 ps. Simulation results show the high flexibility, effectiveness, and practicability of the proposed scheme, which can be applied to future high-capacity optical transmission systems.

Optical frequency comb generation based on dual-parallel Mach–Zehnder modulator and intensity modulator with RF frequency multiplication circuit

A new method of generating optical frequency comb by cascading a single dual-parallel Mach–Zehnder modulator and two intensity modulators is proposed. The intensity modulators are modulated by a frequency multiplication circuit of radio frequency. Theoretical model of the system is derived, and optical frequency comb with ultra-flatness and high side-mode suppression ratio can be obtained. The study results show that 72-line optical frequency comb with spectrum power variation of 0.26 dB, SMSR of 21 dB and frequency space of 4 GHz is gotten easily by adjusting the amplitude of radio frequency signal and the direct current bias of the modulators. The simulation result is in good agreement with the theoretical analysis model.

Chip-Based Brillouin Processing for Phase Control of RF Signals

Manipulating radio frequency (RF) signals in integrated photonic devices has recently emerged as a new paradigm for wireless communications, enabling high-frequency signal processing and broadband frequency agility in miniaturized photonic platforms. These advances are crucial for space and airborne applications which are weight and size sensitive. Recent progress in on-chip stimulated Brillouin scattering (SBS) using high gain has shown great potentials for RF photonic signal processing, owing to its inherent advantages of high resolution, high reconfigurability, and flexible programmability. On-chip SBS serves as a versatile and high-performance toolbox to process and manipulate the amplitude and phase of RF signals in the optical domain. In this paper, we provide a brief overview of recent advances achieved using SBS in planar waveguides, with a focus on applications requiring phase control of RF signals, including phase shifters, delay lines, and separate carrier tuning. We introduce a power-efficient scheme based on the concept of phase amplification to improve Brillouin-based phase processing capability.

Carotid artery intima-media thickness measurement in children with normal and increased body mass index: a comparison of three techniques

BackgroundCommon carotid artery intima-media thickness is a marker of subclinical atherosclerosis. In children, increased intima-media thickness is associated with obesity and the risk of cardiovascular events in adulthood.ObjectiveTo compare intima-media thickness measurements using B-mode ultrasound, radiofrequency (RF) echo tracking, and RF speckle probability distribution in children with normal and increased body mass index (BMI).Materials and methodsWe prospectively measured intima-media thickness in 120 children randomly selected from two groups of a longitudinal cohort: normal BMI and increased BMI, defined by BMI ≥85th percentile for age and gender. We followed Mannheim recommendations. We used M’Ath-Std for automated B-mode imaging, M-line processing of RF signal amplitude for RF echo tracking, and RF signal segmentation and averaging using probability distributions defining image speckle. Statistical analysis included Wilcoxon and Mann-Whitney tests, and Pearson correlation coefficient and intra-class correlation coefficient (ICC).ResultsChildren were 10–13 years old (mean: 11.7 years); 61% were boys. The mean age was 11.4 years (range: 10.0–13.1 years) for the normal BMI group and 12.0 years (range: 10.1–13.5 years) for the increased BMI group. The normal BMI group included 58% boys and the increased BMI group 63% boys. RF echo tracking method was successful in 79 children as opposed to 114 for the B-mode method and all 120 for the probability distribution method. Techniques were weakly correlated: ICC=0.34 (95% confidence interval [CI]: 0.27–0.39). Intima-media thickness was significantly higher in the increased BMI than normal BMI group using the RF techniques and borderline for the B-mode technique. Mean differences between weight groups were: B-mode, 0.02 mm (95% CI: 0.00 to 0.04), P=0.05; RF echo tracking, 0.03 mm (95% CI: 0.01 to 0.05), P=0.01; and RF speckle probability distribution, 0.03 mm (95% CI: 0.01 to 0.05), P=0.002.ConclusionThough techniques are not interchangeable, all showed increased intima-media thickness in children with increased BMI. RF echo tracking method had the lowest success rate at calculating intima-media thickness. For patient follow-up and cohort comparisons, the same technique should be used throughout.

Radio Frequency Beamforming Based on a Complex Domain Frontend

The state-of-the-art phased array-based digital beamforming systems suffer from disadvantages of high power consumption, high cost, and system complexity due to the massive use of transmitter/receiver (T/R) modules and high-speed digital and digital–analog mixed devices. In this paper, we point out that by proposing a new concept “complex domain” radio frequency (RF) frontend, the relatively slowly changed waveform delay information required to accomplish adaptive beamforming can be separated from wideband RF signals, based on which a self-contained beamforming system can be implemented with a low-speed baseband. By introducing vector RF multipliers in the proposed frontend, the amplitude and phase of RF signals can be simultaneously controlled by the real and imaginary parts of complex numbers, such that beamforming algorithms derived in complex domain can be directly applied without any form of transformation. By doing so, the massive use of conventional T/R modules and high-speed baseband devices can be avoided. Theoretical analysis and experimental demonstration based on commercial components have validated the proposed approach. Our method is able to significantly simplify the realization and decrease the cost of wideband digital beamforming systems, and can be widely used in low cost, power efficient beamforming applications.

FPGA-based amplitude and phase detection in DLLRF

The new generation particle accelerator requires a highly stable radio frequency (RF) system. The stability of the RF system is realized by the Low Level RF (LLRF) subsystem which controls the amplitude and phase of the RF signal. The detection of the RF signal's amplitude and phase is fundamental to LLRF controls. High-speed ADC (Analog to Digital Converter), DAC (Digital to Analog Converter) and FPGA (Field Programmable Gate Array) play very important roles in digital LLRF control systems. This paper describes the implementation of real-time amplitude and phase detection based of the FPGA with an analysis of the main factors that affect the detection accuracy such as jitter, algorithm's defects and non-linearity of devices, which is helpful for future work on high precision detection and control.

Partial discharge current pulses in SF6 and the effect of superposition of their radiometric measurement

The practical advantages of employing non-contact radio frequency (RF) methods for detecting partial discharges (PDs) in high voltage equipment have led to significant effort being focused on the diagnosis of electrical plants using RF techniques. This has particularly been the case for gas insulated substations, which use sulphur hexafluoride (SF6) as an insulating medium. One of the most important challenges facing RF diagnostics is the problem of relating the RF emissions to some measure of severity of the PD. Previous work has established that the amplitude or energy of RF signals radiated from a PD source is strongly dependent on the rate of change of current in the PD pulse. In this paper, measurements of PD current pulses in SF6 are presented for a point-plane configuration using an extremely wide bandwidth (13 GHz) measurement system. By this means, PD pulse shapes have been recorded with better resolution than has previously been possible and rise times have been measured with a high degree of accuracy. The results show a considerable variation in pulse shape, with the minimum rise time measured being 35 ps. With this high time-domain resolution, we have been able to distinguish features within the PD pulses that will affect the energy of the radiated RF signal. In particular, the current pulses tend to occur in bursts of up to ten individual pulses in as little as 1 ns, which will excite multiple RF signals in rapid succession. The effect of superposition of RF waveforms has been investigated by studying the variation in detected RF energy with respect to the time delay between PD pulses. It was found that when two PDs occur within a short period (< 150 ns) the combined energy of the resulting RF pulse has the potential to vary by ±30% of that resulting from two equivalent PD pulses with a wider pulse spacing (≫ 150 ns). In terms of a practical monitoring system concerned with order-of-magnitude variations; this is not considered to pose a major problem for the RF technique.

Trial of a quantitative method for evaluating hemangioma of the liver and hepatocellular carcinoma using a radio-frequency signal.

In recent years, advances in ultrasonographic techniques have allowed the detection of even small hepatocellular carcinomas. However, many cases do not show distinctive ultrasonographic features. A quantitative ultrasonographic procedure for making the diagnosis would therefore be desirable. It is recognized that radio-frequency (RF) signals from hepatic tumors conform to the K distribution. The K distribution is used for the characterization of the statistical properties of backscattering signals from heterogeneous regions. In this study, RF signals were acquired from hemangioma of the liver (hemangioma) and hepatocellular carcinoma (HCC), and parameters of the K distribution, i.e., φ (the mean square of the amplitude of RF signals) and α (the number of effective scatterers), were calculated for the quantitative ultrasonographic evaluation of hepatic tumors. This study included 10 nodules of 10 patients with hemangioma and 27 nodules of 24 patients with HCC. The A-mode RF signals passing through the hepatic tumors were acquired with an Aloka SSD-1000 ultrasound system, and measurement units comprising 279 points were set on the RF signals corresponding to the tumor lesion. The parameters of the K distribution that were most consistent with the histogram were calculated and assessed. With regard to φ, the values were high in hemangioma, and there was a significant (P < 0.05) difference in the φ value between hemangioma and HCC. On the other hand, there was no significant difference in the α value between hemangioma and HCC. The α values of hemangioma were equivalent to those of HCC, while the φ values for hemangioma were higher than those for HCC. It was deduced from these observations that a situation in which an electron beam is likely to scatter exists in the tumor. This is also consistent with the pathological findings reported from previous studies. The use of these parameters is expected to allow quantitative ultrasonographic evaluation of hepatic tumors.

Microembolic signal description: a reappraisal based on a customized digital postprocessing system

The high variability in presence and signature of microembolic signals (MES), detected with transcranial Doppler sonography (TCD) in the middle cerebral artery (MCA), cannot be explained with the currently available published data. We applied customized postprocessing on the radiofrequency (RF) signal of a standard TCD system. The spatial resolution was on the order of 2 mm, depending only on the length of the ultrasound (US) burst emitted. The amplitude of clutter-filtered RF signals was color-coded and plotted as a function of time and depth (range 30 mm). Additionally, 128 point fast Fourier transforms (FFTs) (50% temporal overlap) were calculated, visualizing both the background Doppler spectrum and the MES. We evaluated 122 gaseous MES from two patients during cardiac surgery and 52 particulate MES from four patients after carotid endarterectomy. Both MES categories showed comparable properties: they appeared in the RF amplitude plot as rather straight lines of increased intensity, indicating that the velocity remained approximately the same while they passed the US beam. The velocity calculated from the amplitude plot never exceeded that of the background Doppler spectrum. Various “MES patterns” could be identified with respect to the depth range at which the MES were visible. A quarter of the gaseous MES changed their direction at a specific depth, suggesting that the MES entered a branch ( e.g., an M2 artery or the anterior cerebral artery). In the FFT analysis, these MES contained both positive and negative frequencies. It is concluded that MES show consistent signature patterns in the amplitude-time plots and that the previously reported variability of MES appearance in conventional Doppler systems is an artefact caused by relatively large signal amplitudes and sample volumes. (E-mail: Max@fknf.azm.nl)