@article{elbadry_wetherington_zikry_2022, title={Electromagnetic Finite-Element Modeling of Induction Effects for Buried Objects in Magnetic Soils}, volume={60}, ISSN={["1558-0644"]}, url={https://doi.org/10.1109/TGRS.2021.3124839}, DOI={10.1109/TGRS.2021.3124839}, abstractNote={A frequency-based finite element (FE) framework has been developed to predict and understand the response of an electromagnetic induction (EMI) sensor due to buried targets. The EMI sensor is used to detect buried targets in magnetic nonconducting soils. The framework was verified with an analytical model that utilizes dipole approximations. The framework was then used to predict the electromagnetic (EM) response due to interrelated stimuli and properties. The results indicate that the sensor was not sensitive to small variations (0–200 mm) in the standoff height and lateral positions, and only showed a significant change in the response due to stand-off variations that were greater than 200 mm. This low sensitivity to minor variations in standoff height and lateral position signify that there are critical distances related to the EM response of buried objects. The response to different target conductivities and permeabilities was also investigated for steel and aluminum targets. The lower conductivity steel targets had EM responses, where the inductive limit was reached at higher frequencies than the higher conductivity aluminum targets. Variations in target permeabilities for steel showed that as permeabilities increased, the frequencies at which the inductive limit was reached also increased. This verified predictive approach can provide a methodology to characterize the EM response of buried objects for a broad class of buried object EM properties, geometries, and input stimuli.}, journal={IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Elbadry, Mohamed H. and Wetherington, Josh and Zikry, Mohammed A.}, year={2022} }
 @inproceedings{shityoy_schuchinsky_steer_wetherington_2014, title={Characterisation of nonlinear distortion and intermodulation in passive devices and antennas}, DOI={10.1109/eucap.2014.6902055}, abstractNote={The paper presents a conceptual discussion of the characterisation and phenomenology of passive intermodulation (PIM) by the localised and distributed nonlinearities in passive devices and antennas. The PIM distinctive nature and its impact on signal distortions are examined in comparison with similar effects in power amplifiers. The main features of PIM generation are discussed and illustrated by the example of PIM due to electro-thermal nonlinearity. The issues of measurement, discrimination and modelling of PIM generated by nonlinearities in passive RF components and antennas are addressed.}, booktitle={2014 8th european conference on antennas and propagation (eucap)}, author={Shityoy, A. and Schuchinsky, A. G. and Steer, M. B. and Wetherington, J. M.}, year={2014}, pages={1454–1458} }
 @inproceedings{steer_wetherington_wilkerson_2013, title={Investigation of close-in passive intermodulation distortion on antennas}, DOI={10.1109/aps.2013.6711784}, abstractNote={Passive intermodulation distortion (PIM) generated on antennas is experimentally investigated and shown to agree with calculations based on an electro-thermal origin. Two-tone testing is used in the investigations with tone spacings ranging from 3 Hz to 100 kHz. The two-tone measurement system has a minimum spurious-free dynamic range of 125 dB at 3 Hz tone separation. Results show that at least some of the PIM generated by an antenna is due to electro-thermal effects but it is apparent that there are sources of PIM that cannot be described by electro-thermal effects alone.}, booktitle={2013 ieee antennas and propagation society international symposium (apsursi)}, author={Steer, M. B. and Wetherington, J. M. and Wilkerson, J. R.}, year={2013}, pages={2251–2252} }
 @article{wetherington_steer_2013, title={Sensitive Vibration Detection Using Ground-Penetrating Radar}, volume={23}, ISSN={["1558-1764"]}, DOI={10.1109/lmwc.2013.2284779}, abstractNote={A high-dynamic-range vibration detection system is presented based on analog cancellation. The prototype system operates at 900 MHz and is shown to detect vibrational displacement as low as 11 nm for a rectangular aluminum plate at a standoff distance of 2 m. By operating at a lower frequency than previous radar vibrometers, the system gains ground-penetrating capability and is shown to detect vibrations through 13 cm of sand. A fundamental relationship is introduced relating the minimum detectable vibration displacement to the standoff distance and system dynamic range.}, number={12}, journal={IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS}, author={Wetherington, Joshua M. and Steer, Michael B.}, year={2013}, month={Dec}, pages={680–682} }
 @inproceedings{wetherington_steer_2012, title={Characterization of the dynamic range of a single aperture communications system}, DOI={10.1109/inmmic.2012.6331945}, abstractNote={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.}, booktitle={2012 Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits (INMMIC)}, author={Wetherington, J. M. and Steer, M. B.}, year={2012} }
 @article{wetherington_steer_2012, title={Robust Analog Canceller for High-Dynamic-Range Radio Frequency Measurement}, volume={60}, ISSN={["0018-9480"]}, DOI={10.1109/tmtt.2012.2189230}, abstractNote={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.}, number={6}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Wetherington, Joshua M. and Steer, Michael B.}, year={2012}, month={Jun}, pages={1709–1719} }
 @article{wetherington_steer_2012, title={Standoff Acoustic Modulation of Radio Frequency Signals in a Log-Periodic Dipole Array Antenna}, volume={11}, ISSN={["1536-1225"]}, DOI={10.1109/lawp.2012.2210692}, abstractNote={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.}, journal={IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS}, author={Wetherington, Joshua M. and Steer, Michael B.}, year={2012}, pages={885–888} }
 @inproceedings{steer_wilkerson_kriplani_wetherington_2012, title={Why it is so hard to find small radio frequency signals in the presence of large signals}, DOI={10.1109/inmmic.2012.6331916}, abstractNote={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.}, booktitle={2012 Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits (INMMIC)}, author={Steer, M. B. and Wilkerson, J. R. and Kriplani, N. M. and Wetherington, J. M.}, year={2012} }