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Standoff Acoustic Modulation of Radio Frequency Signals in a Log-Periodic Dipole Array Antenna
Abstract
An acoustic tone isonifying an antenna is shown to produce radio frequency (RF) distortion in a log-periodic dipole array. This distortion is capable of interfering with a sensitive receiver. The passive distortion produces two sidebands, the powers of which have a 1:1 relationship with both the RF and acoustic tone, but have nonmonotonic behavior with respect to RF and acoustic frequency.
... Thus, micro-scale petrophysical techniques can partially remedy such limitations in sampling and allowing the direct determination in anisotropy, deformability and brittleness of target reservoirs by combining seismic imaging with logging information Wang et al., 2018). Dipole array acoustic logging effectively evaluates mechanical parameter profiles, yielding estimates of elastic modulus and Poisson ratio (Wetherington, 2012) -but sometimes with significant uncertainties. The anisotropy of shale mechanical properties is the result of the combination of organic and clay mineral orientation, brittle mineral composition, pore-fracture development, and other factors (Weijermars et al., 2020;Wild and Amman, 2018). ...
Mechanical properties of shales are key parameters influencing hydrocarbon production – impacting borehole stability, hydraulic fracture extension and microscale variations in in situ stress. We use Ordovician shale (Sichuan Basin, China) as a type-example to characterize variations in mineral particle properties at microscale including particle morphology, form of contact and spatial distribution via mineral liberation analysis (MLA) and scanning electron microscopy (SEM). Deformation-based constitutive models are then built using finite element methods to define the impact of various architectures of fracture and mineral distributions at nanometer scale on the deformation characteristics at macroscale. Relative compositions of siliceous, calcareous and clay mineral particles are shown to be the key factors influencing brittleness. Shales with similar mineral composition show a spectrum of equivalent medium mechanical properties due to differing particle morphology and mineral heterogeneity. The predominance of small particles and/or point-point contacts are conducive to brittle failure, in general, and especially so when quartz-rich. Fracture morphology, length and extent of filling all influence shale deformability. High aspect-ratio fractures concentrate stress at fracture tips and are conducive to extension, as when part-filled by carbonate minerals. As fracture spacing increases, stress transfer between adjacent fractures weakens, stress concentrations are amplified and fracture extension is favored. The higher the fractal dimension of the fracture and heterogeneity of the host the more pervasive the fractures. Moreover, when fractures extend, their potential for intersection and interconnection contributes to a reduction in strength and the promotion of brittle failure. Thus, these results provide important theoretical insights into the role of heterogeneity on the deformability and strength of shale reservoirs with practical implications for their stimulation and in the recovery of hydrocarbons from them.
... 5 If the acoustic transmission is a steady tone, the surface of the target vibrates sinusoidally. 6 Since the time derivative of the phase of Erefl is generally nonzero, the perturbation imparted by the acoustic source on the target, as a result of moving the target toward and away from the radar receiver sinusoidally, is frequency modulation (FM). ...
Acoustic-electromagnetic (EM) interaction is evaluated for metallic and electronic target detection. The transmitter consists of a radar-wave generator emitting a single EM frequency and an acoustic-wave generator emitting a single acoustic frequency. The EM wave and the acoustic wave interact at the target. The target reradiates a new EM wave, which consists of the original EM wave modulated by the acoustic wave. This reradiated wave is captured by the radar’s receive antenna. The presence of measurable EM energy at any discrete multiple of the audio frequency away from the original radio-frequency (RF) carrier indicates target detection. Proof-of-concept detection is demonstrated for purely metallic and RF electronic targets within the near field of an ultra-wideband radar antenna operating in the ultra-high frequency band.
... 4,5 Tx RF Because of these interactions and the radar-reflective nature of electronics and metals, the target radiates a new EM wave that consists of the original EM wave modulated by the acoustic wave. 6,7 The new EM wave contains a set of frequencies, fRF ± n·faudio, where n is any positive integer. This acousto-EM response is captured by the radar's receive (Rx) antenna. ...
A novel technique for exciting radar targets with acoustic and electromagnetic (EM) energy simultaneously is presented. The technique exploits the interaction between the two forms of energy at the target, in a well-controlled acoustic and EM environment, to evaluate the feasibility of standoff acoustic-radar detection of each target. Data recorded on three electronic radar targets and three metallic clutter items, probed by audible acoustic frequencies and UHF radio frequencies, successfully demonstrate acousto-EM interaction.
This paper investigates the generation of passive intermodulation (PIM) in coaxial connectors during vibration. A series of experiments were designed and the simulation model and method were proposed for understanding these phenomena. We found that PIM is mainly influenced by the contact stress and contact surface roughness during vibration. Thus, a power spectral density method is presented to identify the roughness parameter of contact surface based on the Weierstrass–Mandelbrot model, and the simulation model and method were verified by the relative experiments. Eventually, some suggestions for engineering application were provided.
The radio signal transmitted from a vibrating antenna is modulated producing spectral content that can interfere with a nearby receiver. The additional spectral content is centered at the transmitted RF signal, and with chaotic vibrations, the spectrum has significant content beyond the fundamental frequency of vibration. Thus, the effect of vibration on co-site interference is much greater than expected. A controlled experiment using a monopole antenna driven at 900 MHz and vibrating at 150 Hz has significant RF spectral content extending to 5 kHz.
The essence of radar, radio and wireless sensor engineering is extracting small information-bearing signals. This is notoriously difficult and engineers compensate by transmitting high power signals, reducing range, and spacing wireless systems in frequency and time. New understandings of passive intermodulation distortion, thermal effects, time-frequency effects, and noise are presented. It is seen that the familiar frequency-domain-based abstractions have missed important underlying physics. Through greater understanding, RF engineers can develop microwave systems with far lower levels of distortion and noise.
A resonant antenna displays passive intermodulation related to antenna vibrations at levels that impact communications systems. A non-resonant antenna was immune to structure vibrations. Both antennas were of solid construction with thick metalization and did not exhibit electro-thermal passive intermodulation distortion previously observed with microstrip structures. The ultimate dynamic ranges of two antennas are explored using a measurement system with a dynamic range of 98 dB at one hertz offset from a 30 dBm, 500 MHz transmit signal. This increased to 140 dB when the separation increased to 100 Hz.
The limitations of existing counter-mine technology have motivated the development of an acousto-electromagnetic technique for detecting landmines and other buried objects (Lawrence, D. and Sarabandi, K., IEEE Trans. on Antennas and Propag., vol.49, p.1382-92, 2001). This hybrid method exploits the acoustic resonance of an object to discriminate it from soil, plant matter, rocks, and other clutter that cause false alarms for GPR. An object is distinguished based on the Doppler signature imparted to radar signals scattering off the object's vibrating surface. We investigated whether small vibrations in objects can be detected by a sensitive Doppler radar. Objects with known acoustic resonant frequencies (tuning forks) were excited (by a speaker), and their Doppler signatures measured using a CW radar system. In the resulting Doppler return, the carrier signal is frequency modulated by a pure tone. Our Doppler radar succeeded in detecting resonant tuning forks even when the vast majority of the receive power was clutter. The primary limitation on our system's performance was not the sensitivity of the radar, but rather the ability to couple acoustic energy into the forks from a remote source.
Laboratory results, obtained with a novel setup for a corrected
co-channel distortion ratio, validate the idea that no matter the notch
width, a conventional noise-power-ratio test produces optimistic
small-signal in-band distortion measurements, when compared to a
hypothetical continuous spectrum excitation test by the authors. This
paper also generalizes previous memoryless mildly nonlinear behavior
predictions to saturated and frequency-dependent regimes. Finally, a
close agreement between measurement results and harmonic-balance
simulated data provided an alternative means of corrected co-channel
power-ratio evaluation
The idea of using acoustically induced Doppler spectra as a means of target detection and identification is introduced. An analytical solution for the calculation of the bistatic scattered Doppler spectrum from an acoustically excited, vibrating, metallic, circular cylinder is presented. First, the electromagnetic scattering solution of a slightly deformed circular cylinder is obtained using a perturbation method. Then, assuming the vibration frequency is much smaller than the frequency of the incident electromagnetic wave, a closed form expression for the time-frequency response of the bistatic scattered field is obtained which can be used directly for estimating the Doppler spectrum. The acoustic scattering solution for an incident acoustic plane wave upon a solid elastic cylinder is applied to give the displacement of the cylinder surface as a function of time. Results indicate that the scattered Doppler frequencies correspond to the mechanical vibration frequencies of the cylinder, and the sidelobe Doppler spectrum level is, to the first order, linearly proportional to the degree of deformation and is a function of bistatic angle. Moreover, the deformation in the cylinder, and thus the Doppler sidelobe level, only becomes sizeable near frequencies of normal modes of free vibration in the cylinder. Utilizing the information in the scattered Doppler spectrum could provide an effective means of buried object identification, where acoustic waves are used to excite the mechanical resonances of a buried object.
This paper investigates rotor modulation on the gain and input
impedance of an antenna mounted on a helicopter's fuselage. The rotor
blades, which are rotating about an axis with a given angular velocity,
continuously modulate the signal transmitted by the antenna and
adversely affect the established communication links. In this study,
particular emphasis is placed on wire antennas operating within the HF
and VHF bands. Specifically, the Doppler spectrum of the magnitude and
phase of the radiated field from a vertical and a horizontal short
dipole underneath the rotors is computed and analyzed. The variation of
the corresponding antenna gain as a function of rotor angle and
frequency is also investigated. The same type of analysis is then
extended to a 14-ft towel-bar antenna mounted on the tail boom of a 10:1
scaled helicopter model. In addition to gain, the variation of input
impedance versus angle and frequency is computed within the HF band.
Finally, the bit error rate (BER) assuming a quadrature phase-shift
keying (QPSK) modulation is evaluated assuming linearly and circularly
polarized receiving antennas
An automated analog canceller is presented that uses feedforward cancellation in a bridge configuration. A minimum of 70 dB of analog cancellation is obtained. The canceller is used to construct an intermodulation distortion measurement system achieving up to 120 dBc of intermodulation dynamic range in two-port transmission testing and 140 dBc of intermodulation dynamic range in one-port reflection testing for frequency separations of at least 1 kHz. At a two-tone frequency separation of 1 Hz, the respective dynamic ranges are at least 94 and 111 dBc. The relationship of cancellation performance and dynamic range is examined in terms of application-specific definitions of dynamic range. The system is then used to measure passive intermodulation distortion using a two-tone test with a tone frequency separation from 1 Hz to 100 MHz.
A measurement technique is proposed which exploits the standing wave in a microstrip resonator to more thoroughly measure passive nonlinearities. The measurement technique is demonstrated to be able to measure the difference between current induced and voltage induced passive nonlinearities. By placing the device under test in a resonator three times higher voltage and current magnitudes are created compared to traveling wave passive intermodulation measurement systems. This increases the effective power only at the device under test and increases the measurement sensitivity of the original traveling wave measurement system. Based on our measurements we project the ability to characterize devices at -196 dBc, a 29 dB improvement over the original system.
An analytic formulation of dynamic electro-thermally induced nonlinearity is developed for a general resistive element, yielding a self-heating circuit model based on a fractional derivative. The model explains the 10 dB/decade slope of the intermodulation products observed in two-tone testing. Two-tone testing at 400 MHz of attenuators, microwave chip terminations, and coaxial terminations is reported with tone spacing ranging from 1 to 100 Hz.
The long-tail transient responses of a bandpass network to pulsed and switched-tone stimuli are examined and a time-domain closed-form expression of the envelope response is developed. It is shown that the long-tail response leads to interference in frequency-hopping communication systems. Interference, and in particular co-site interference, can result in any radar, communication, or RF sensor system becoming exposed to unintentional pulsed RF signals. In the experimental study, 900-MHz Chebyshev bandpass filters are considered.
In this paper a method to overcome the insufficient dynamic range of RF measurement instruments, i.e. signal generators and spectrum analyzers, for distortion measurements on feedforward and other highly linear amplifiers, is discussed. A circuit board is designed, built and verified. Its performance is found to be superior to traditional methods using filters, both from a technical performance and flexibility standpoint as well as from an economic view. ACLR measurements for WCDMA signals can be done well below -70 dBc using the produced circuit board.
A theoretical treatment of distributed electro-thermally induced intermodulation distortion is developed for microstrip transmission lines. The growth of passive intermodulation distortion (PIM) along the length of a line is derived accounting for both loss and electrical dispersion. PIM dependencies on width, length, thickness, and substrate parameters are analyzed leading to design guidelines for low distortion lines. Single metal silver transmission lines are fabricated on sapphire and fused-quartz substrates to isolate the electro-thermal effect and validate the model. Electro-thermal PIM is measured in a two-tone test with tone separation ranging from 4 Hz to 10 kHz.
This paper presents an intermodulation distortion measurement system based on automated feedforward cancellation that achieves 113 dB of broadband spurious-free dynamic range for discrete tone separations down to 100 Hz. For 1-Hz tone separation, the dynamic range is 106 dB, limited by carrier phase noise. A single-tone cancellation formula is developed requiring only the power of the probing signal and the power of the combined probe and cancellation signal so that the phase shift required for cancellation can be predicted. The technique is applied to a two-path feedforward cancellation system in a bridge configuration. The effects of reflected signals and of group delay on system performance is discussed. Spurious frequency content and interchannel coupling are analyzed with respect to system linearity. Feedforward cancellation and consideration of electromagnetic radiation coupling and reverse-wave isolation effects extends the dynamic range of spectrum and vector analyzers by at least 40 dB. Application of the technique to the measurement of correlated and uncorrelated nonlinear distortion of an amplified wideband code-division multiple-access signal is presented.
The central theme of this dissertation is the study of passive nonlinearities in electromagnetic transmit/receive systems such as radar sensing and wireless communications systems. Passive intermodulation (PIM) is a form of nonlinear distortion that is caused by the electromagnetic nonlinearity of passive wireless system components. The vast majority of passive components are normally considered to have a linear electrical response under small excitation values. However, these passive components have trace levels of nonlinearity which cause a small amount of intermodulation distortion in high-power transmit/receive systems. This distortion can, in certain cases, fall into a transmitting device's receive band. This causes significant interference and limits the sensitivity and range of the system. The results of our study have given a better understanding of the causes and behavior of passive intermodulation in wireless systems and components, particularly coaxial connectors. Theoretical advances we have made toward this end include a point-source model of PIM sources, as well as a circuit-level model of the interaction between the passive nonlinearity and the surrounding linear impedances in a circuit. Both of these models achieve much higher agreement with experiment than has previously been attained and grant deep insights into the nature of the underlying nonlinear mechanisms that generate PIM distortion. On the more practical side, we have developed two new methods of mitigating PIM distortion: one in which the nonlinear distortion is cancelled by a specially engineered source of PIM distortion, and the other (specific for ferromagnetic nonlinearities) which relies on the imposition of an external magnetic field.
A frequency agile feedforward noise cancellation system (FFCS) concept was developed to increase the isolation between the transmitter and receiver which share a common antenna in a frequency division duplex (FDD) radio front-end. A cancellation performance of 50 dB was achieved in a bandwidth of 4.5 MHz. The performance was maintained throughout a tuning bandwidth of 25 MHz, centered at 836.5 MHz. The FFCS has applications in communication systems requiring tunable notch filters with wideband performance. The research on the FFCS is aimed at developing technology to complement a cellular base station (BTS) duplexer of reduced order and reduced size and capable of operating in any CDMA cellular bands. The FFCS component is envisioned as enabling technology to implement frequency agile duplexers.
The use of sound as a means to gather information about our environment has been developed with limited scope over the past several decades. The primary application of this technology has been ultrasound and ultrasonic ranging. Recent developments in nonlinear acoustics have proven that two-tone measurements and directional high frequency parametric arrays can extract much more information about the size, shape, and density of objects under inspection. However, acoustic measurements are difficult to make in the laboratory environment due to excessive ambient noise. For these reasons, the Electronics Research Laboratory at NC State University has constructed an acoustic-RF anechoic chamber as a means to make these measurements and further research in nonlinear acoustics and acoustic detection and imaging.
A hybrid technique is presented that simultaneously uses both
electromagnetic and acoustic waves in a synergistic manner to detect
buried land mines. The system consists of an electromagnetic radar and
an acoustic source. The acoustic source causes both the mine and the
surface of the earth to be displaced. The electromagnetic radar is used
to detect these displacements and, thus, the mine. An experimental and
numerical model for the system has been developed
In this paper, a short-circuit transmission line method is proposed for passive intermodulation (PIM) evaluation of metallic materials. The method is introduced as a current-based PIM evaluation method that is effective for characterization of metallic materials and electrical contacts. The impedance matching condition is not required for a device under test. Therefore, its shape can be advantageously chosen arbitrarily. The proposed method realizes quantitative characterization of metallic materials, and demonstrates that characterizing the materials in terms of applied current density is effective to provide a fair assessment for material choice. Using the proposed method, copper foils with arbitrary width and thickness were evaluated without any effects on characteristic impedance. The proposed method is applicable to actual microwave components such as SMA connectors. The paper presents that the PIM level obtained using the proposed method is 18 dB higher than that in the conventional impedance-matched line method. As a result, a clear interpretation from the proposed method to the matched line method is also presented.
Measurement of ultra low passive 51
- A Christianson
- W Chappell
A. Christianson and W. Chappell, " Measurement of ultra low passive 51, no. 7, pp. 1499–1507, Jul. 2003.