Generation Of Intermodulation Products Research Articles

A New Varactor-Tuned 5.8 GHz Dielectric Resonator Band-Stop Filter for ITS and C-V2X Coexistence with Vehicular DSRC

In this paper, we introduce an electronically tuneable band-stop filter based on a dielectric resonator, along with its design principles and equivalent circuit model aimed at the coexistence of intelligent transport systems (ITS) and cellular vehicle-to-everything (C-V2X) communications operating at 5.9 GHz, with the widely spread vehicular dedicated short range communications (DSRC) at 5.8 GHz. The proposed architecture involves a dielectric resonator coupled via a microstrip transmission line to a planar ring resonator. The resonance is electronically tuned by varying the bias voltage of a varactor diode placed in the ring. This design is analyzed theoretically and experimentally. For validation, a filter operating at 5.8 GHz was designed. The prototype is capable of enhancing coexistence exhibiting to features. First, when inserted into the ITS transmitter chain, it reduces unwanted transmitter emissions in the out-of-band spectrum occupied by the DSRC carriers in the 5.8 GHz frequency band of at least 25 dB, with a minimal insertion loss at 5. 9 GHz of 1.6 dB; secondly, when inserted in the ITS receiver chain, it exhibits high linearity that prevents the generation of intermodulation products falling into the filter pass band. The prototype features more than 21 dBm of third-order input intercept points, and a tuning range of 26 MHz while maintaining a minimal loaded Q factor of 93. The prototype is discussed regarding the detailed equivalent circuit parameter extraction and their dependency upon the control voltage.

Ultrasonic time reversal on defects in carbon fibre reinforced polymer using chirp-coded ultrasound in complex media

Various nonlinear methods have been investigated in recent years offering improvements of over conventional B-mode in medical imaging and non-destructive testing (NDT) [1]. The most common include harmonic and overtone generation, inter-modulation product generation and resonant frequency shift, also known as Nonlinear Elastic Wave Spectroscopy (NEWS) methods. Furthermore, new optimized excitations such as Nonlinear Time Reversal (TR) based methods are needed and, thanks to the analysis of symmetry properties of cross-correlation generated functions, a wide range of innovation are classified within TR-NEWS methods [2]. This work proposes to unite the frequency-modulated constant-wave scatterer localization with TR-NEWS principles to enable the localization of scatterers distant from the transducers and the analysis of their nonclassical nonlinearity which often can be caused by microdamage or cracking. In this paper, using the found frequency of the defect, the delayed TR–NEWS can be leveraged to periodically excite the damaged region with the focused ultrasound. Resonance excitation results show potential for enhancing the wave motion more than a simple focused waves [3]. Thanks to the complexity of the acoustical propagation in a complex medium, the physical interpretation of the cross-correlation function used during the TR-NEWS analysis can be easily understood in terms of the acoustic energy focused in space and in time.

Frequency Mixing Magnetic Detection Scanner for Imaging Magnetic Particles in Planar Samples.

The setup of a planar Frequency Mixing Magnetic Detection (p-FMMD) scanner for performing Magnetic Particles Imaging (MPI) of flat samples is presented. It consists of two magnetic measurement heads on both sides of the sample mounted on the legs of a u-shaped support. The sample is locally exposed to a magnetic excitation field consisting of two distinct frequencies, a stronger component at about 77 kHz and a weaker field at 61 Hz. The nonlinear magnetization characteristics of superparamagnetic particles give rise to the generation of intermodulation products. A selected sum-frequency component of the high and low frequency magnetic field incident on the magnetically nonlinear particles is recorded by a demodulation electronics. In contrast to a conventional MPI scanner, p-FMMD does not require the application of a strong magnetic field to the whole sample because mixing of the two frequencies occurs locally. Thus, the lateral dimensions of the sample are just limited by the scanning range and the supports. However, the sample height determines the spatial resolution. In the current setup it is limited to 2 mm. As examples, we present two 20 mm × 25 mm p-FMMD images acquired from samples with 1 µm diameter maghemite particles in silanol matrix and with 50 nm magnetite particles in aminosilane matrix. The results show that the novel MPI scanner can be applied for analysis of thin biological samples and for medical diagnostic purposes.

Frequency Mixing Magnetic Detection Scanner for Imaging Magnetic Particles in Planar Samples

The setup of a planar Frequency Mixing Magnetic Detection (p-FMMD) scanner for performing Magnetic Particles Imaging (MPI) of flat samples is presented. It consists of two magnetic measurement heads on both sides of the sample mounted on the legs of a u-shaped support. The sample is locally exposed to a magnetic excitation field consisting of two distinct frequencies, a stronger component at about 77 kHz and a weaker field at 61 Hz. The nonlinear magnetization characteristics of superparamagnetic particles give rise to the generation of intermodulation products. A selected sum-frequency component of the high and low frequency magnetic field incident on the magnetically nonlinear particles is recorded by a demodulation electronics. In contrast to a conventional MPI scanner, p-FMMD does not require the application of a strong magnetic field to the whole sample because mixing of the two frequencies occurs locally. Thus, the lateral dimensions of the sample are just limited by the scanning range and the supports. However, the sample height determines the spatial resolution. In the current setup it is limited to 2 mm. As examples, we present two 20 mm × 25 mm p-FMMD images acquired from samples with 1 µm diameter maghemite particles in silanol matrix and with 50 nm magnetite particles in aminosilane matrix. The results show that the novel MPI scanner can be applied for analysis of thin biological samples and for medical diagnostic purposes.

Design, development and testing of multi-functional non-linear ultrasonic instrumentation for the detection of defects and damage in CFRP materials and structures

Abstract A multi-functional non-linear ultrasonic testing approach is presented for in situ and ex-situ detection of a variety of defects (e.g. micro-cracking, delamination and disbonding) induced by various damage mechanisms (stress, impact, heat) in CFRP materials and structures. Such multi-functionality is provided via programmable and re-configurable instrumentation that incorporates a wide range of non-linear ultrasonic testing regimes, including harmonic and overtone generation, inter-modulation product generation, resonant frequency shift and pulse-inversion techniques. The capabilities of this multi-functional approach to defect detection are demonstrated by examining CFRP samples subjected to various forms of damage, specifically stress, impact and heat induced damage. We show that the multi-functional non-linear approach is well-suited to the detection of such forms of damage and that the pulse-inversion technique, largely ‘ignored’ in the CFRP literature, potentially provides a powerful, but as yet un-tapped, simple and effective route to the defect and damage detection.

Multipulse technique exploiting the intermodulation of ultrasound waves in a nonlinear medium

In recent years, the nonlinear properties of materials have attracted much interest in nondestructive testing and in ultrasound diagnostic applications. Acoustic nonlinear parameters represent an opportunity to improve the information that can be extracted from a medium such as structural organization and pathologic status of tissue. In this paper, a method called pulse subtraction intermodulation (PSI), based on a multipulse technique, is presented and investigated both theoretically and experimentally. This method allows separation of the intermodulation products, which arise when 2 separate frequencies are transmitted in a nonlinear medium, from fundamental and second harmonic components, making them available for improved imaging techniques or signal processing algorithms devoted to tissue characterization. The theory of intermodulation product generation was developed according the Khokhlov-Zabolotskaya-Kuznetsov (KZK) nonlinear propagation equation, which is consistent with experimental results. The description of the proposed method, characterization of the intermodulation spectral contents, and quantitative results coming from in vitro experimentation are reported and discussed in this paper.

Analysis of phase and intermodulation distortion of a travelling-wave tube

Phase and intermodulation distortion in travelling-wave tubes are investigated using lagrangian large signal theory. The generation mechanism of phase distortion is explained clearly from the behaviours of bunched electrons in the phase of the slow-wave circuit voltage, and the principle to construct the most effective circuit taper to decrease the phase distortion with a high efficiency is found. By investigating the correlation of intermodulation products with phase distortion and the RF modulation of the electron beam, the in-phase component of the fundamental modulation with respect to the circuit voltage is found to dominate the generation of intermodulation products. The circuit pitch tapers are designed to decrease phase and intermodulation distortion, and to increase the efficiency of the travelling-wave tube.

Validation of a nonlinear transistor model by power spectrum characteristics of HEMT's and MESFET's

The bias dependence of the power output spectrum and the generation of intermodulation products from different HEMT's and MESFET's at large signal excitation is studied and compared with simulated values. An extended HEMT/FET model suitable for small and and negative V/sub ds/ (with a drain voltage dependence of the peak transconductance in the unsaturated drain current region, and at negative drain voltage), is also proposed. Good agreement between simulated and measured power spectrum up to at least the fourth harmonic is demonstrated for HEMT and MESFET devices from different manufacturers. Measured and simulated intermodulation products are also in good agreement, which confirm the validity of the model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effect of acoustic diffraction and acoustic attenuation on the dynamic range of acoustooptic Bragg cells

A three-dimensional model for the propagation of finite acoustic waves in nonlinear media is developed. This model implicitly includes the effects of acoustic attenuation and divergence due to diffraction. The generation of intermodulation products in the case of a two-tone input signal is numerically analyzed. It is found that acoustic diffraction can have a significant effect on the dynamic range of a Bragg cell if the acoustic field extends well into the Fraunhofer region. Inclusion of the effect of diffraction in the model predicts a dynamic range that can be considerably larger than the value obtained by using the infinite plane wave assumption. It is shown that acoustic attenuation significantly reduces the level of the acoustic intermodulation products relative to the level of the fundamental modes. This also increases the dynamic range. The influence of these effects on design considerations for Bragg cells is discussed.

Identification of passive intermodulation product generation on microwave reflecting surfaces

New developments in the adaptation of microwave holographic imaging to assess the intermodulation product (IMP) performance of microwave reflectors are described. In particular, a method of assessment of reflecting materials such as wire meshes and carbon fibres that have the potential to generate IMP signals across large areas is given. Identification and location of the apparent IMP sources are provided.

Intermodulation distortion in optical amplifiers from carrier-density modulation

We present a theoretical model describing the generation of intermodulation products (IMPs) in semiconductor optical amplifiers by signal-induced carrier-density modulation. The IMPs depend strongly on the linewidth-enhancement factor and the ratio of output intensity to the saturation intensity of the amplifier. Calculation of the total intermodulation penalty for multichannel amplifier applications is possible using the expressions presented.

Interference Effects of Hard Limiting in PN Spread-Spectrum Systems

It is shown that the use of a hard limiter in PN spread-spectrum systems leads to the generation of intermodulation products which become narrow-band signals after the despreading process in the PN receiver. The analysis treats the situation where a bandpass limiter is inserted into the transmission path of the PN signal prior to the PN receiver. The input to the bandpass limiter is the superposition of the PN signal with white Gaussian noise and one interferer. This interferer may be either a narrow-band signal or another wide-band PN signal. It is found that the amplitudes of the resulting narrow-band intermodulation products are independent of the spread-spectrum processing gain and of the type of interference. A complete loss of the antijamming capability may thus result even with extremely large `processing gain'.

Nonlinearities in Metal Contacts at Microwave Frequencies

Generation of intermodulation products arising from nonlinearities at metal-to-metal contacts for microwave frequencies has been investigated. Detailed studies concentrated on the intermodulation products generated at contacting faces between both similar and dissimilar metals, and included contact materials of copper, beryllium-copper, brass, oxygen-free nickel, mild steel, stainless steel, aluminium, and twelve home-made steels with various compositions. The surface properties of the materials were found to be of prime importance. Measurements were carried out at frequencies around 1.5 GHz. The variations of the 3rd- and 5th-order intermodulation product levels with power levels of the fundamental signals and with the axial force applied to the contact were studied.

Coaxial Cables as Sources of Intermodulation Interference at Microwave Frequencies

Intermodulation interference arising from nonlinearities in braided coaxial cables at microwave frequencies is discussed. Detailed investigations have been carried out using a large number of commercially available and specially constructed cables to isolate and assess the relative contributions of different parameters of coaxial cables responsible for the generation of intermodulation products (IP's) at L-, S-, and C-band frequencies centered on 1.5, 3, and 5 GHz. Ambient temperature in the case of polythene dielectric cables and oxides on copper-wire braids affect considerably the IP's generated in a coaxial cable.

A Brief Survey of Intermodulation Due to Microwave Transmission Components

The phenomenon of intermodulation product generation in coaxial connectors, circulators, and waveguide joints is discussed.Annotated referrals are made to prior experimental works. Anomalies encountered by the various researchers are presented.

Nonlinear effects in coaxial cables at microwave frequencies

A study of the generation of intermodulation products due to nonlinearities in braided coaxial cables at L-, S-and C-band frequencies is in progress and some results are presented. The different cable parameters responsible for intermodulation products at microwave frequencies have been examined and their relative contributions towards the total nonlinearities assessed.

Visibility of Noise on Television Pictures

IN investigations of the visibility of random noise in television pictures1,2, it has been found that for narrow-band noise which is just visible the required noise power increases by about 20 db. as the centre frequency is raised from 0.15 to 2 Mc./s. For frequencies between 2 and 3 Mc./s., the noise power remains nearly constant1, or shows a small fall2. It has been suggested1 that this may be because of the generation of intermodulation products of low-frequency noise, due to the non-linearity of the voltage/brightness characteristic of the television tube. These low-frequency products should be much easier to see than the original high-frequency noise. It follows that the non-linearity should also affect visibility of noise if a sinusoidal signal, together with noise, is applied to the tube control-grid. In this case, sum and difference frequencies of the signal and noise should be produced. An experiment which appears to demonstrate the expected intermodulation effect has been carried out.