Frank Djuth - Academia.edu (original) (raw)
Papers by Frank Djuth
2008 IEEE Ultrasonics Symposium, 2008
ABSTRACT
IEEE Ultrasonics Symposium, 2004
(1-x)PbYb12/Nb12/Nb12/O3-xPbTiO3 (PYbN-PT, x=0.5) thin films were investigated for high frequency... more (1-x)PbYb12/Nb12/Nb12/O3-xPbTiO3 (PYbN-PT, x=0.5) thin films were investigated for high frequency transducer applications in this work. Firstly, highly [001] oriented LaNiO3 (LNO) thin films were prepared on Si [001] substrates by a simple metal organic decomposition technique. The room temperature resistivity of the LNO thin films was 0.65 mΩ·cm. Then PYbN-PT thin films were deposited onto the LNO/Si substrates by sol-gel
Two-dimensional images of F- and E- layers have been obtained using the technique called radio-in... more Two-dimensional images of F- and E- layers have been obtained using the technique called radio-induced aurora (RIA). This technique makes the plasma layers glow in the ionosphere glow when being stimulated by high power radio waves. Normally the irregularities in the ionosphere do not radiate strong enough visible emissions to be observed from the ground. Experiments at Arecibo Observatory in
The Astrophysical Journal, 1975
... Printed in USA DETECTION OF NUCLEAR GAMMA RAYS FROM THE GALACTIC CENTER REGION RC HAYMES, GD ... more ... Printed in USA DETECTION OF NUCLEAR GAMMA RAYS FROM THE GALACTIC CENTER REGION RC HAYMES, GD WALRAVEN, CA MEEGAN, RD HALL ... A power-law continuum was observed and several spectral lines were detected for the first time, at energies close to ...
Bulletin of the …, 1974
... R. C . HAYMES , G . D . WALRAVEN , C . A . NEEGAN , R . D. HALL , F . T . DJIJTH , and D . H ... more ... R. C . HAYMES , G . D . WALRAVEN , C . A . NEEGAN , R . D. HALL , F . T . DJIJTH , and D . H . SHELTON , Rice Univ.', On 1974 April 2, during a balloon' flight conducted in Argentina, a 0.03 MeV - 12.1 NeV differential energy spectrum was measured from GX 1+4 for a total of ...
Journal of Geophysical Research: Space Physics, 1985
Experiments were performed at Arecibo, Puerto Rico, to investigate the evolution times of 3‐m fie... more Experiments were performed at Arecibo, Puerto Rico, to investigate the evolution times of 3‐m field‐aligned Striations produced in the ionosphere by powerful high‐frequency (HF) radio waves. The results of this investigation are now summarized. First, the striations' rise times are dependent on the HF electric field. The E region data suggest that this dependence is nonlinear. Second, the threshold value of the HF electric field required to produce detectable Striations was experimentally determined. At threshold the component of the HF electric field perpendicular to the geomagnetic field is calculated to be 0.09 V/m in the F region and 0.37 V/m in the E region. Third, both the E and the F region data verify theoretical predictions that the Striations' decay times are directly proportional to the electron diffusion across B. Finally, a one‐to‐one correspondence between the growth of the 3‐m Striations and the decline of the HF‐enhanced plasma line during overshoot is someti...
Journal of Geophysical Research: Space Physics, 2007
Incoherent scatter radar (ISR) power profile observations at Arecibo Observatory (AO) have reveal... more Incoherent scatter radar (ISR) power profile observations at Arecibo Observatory (AO) have revealed long vertical wavelength (>100 km) quasi-coherent waves with periods of 1hourthatareobservedtobenearlycontinuouslypresentovertwo1 hour that are observed to be nearly continuously present over two 1hourthatareobservedtobenearlycontinuouslypresentovertwo35-hour geomagnetically quiet observation periods. When properly filtered, results from both 22-23 March 2004 and 5-6 June 2005 provide unambiguous views of these waves. The waves are strong throughout the F region, often spanning 160 to above 500 km in altitude and are present day and night in the F2 layer. Filtering techniques that were used to better reveal the waves are extensively discussed. Barometric pressure and imager data, both of which were taken on site at Arecibo, are used to provide further insight into the nature of these waves. These waves may be linked to high-latitude medium-scale traveling ionospheric disturbances (MSTIDs) observed with the superDARN radar network and associated with E region auroral electrojet source(s) that are quasi-coherent under geomagnetic quiet conditions. As auroral-zone MSTIDs are believed to dissipate before reaching Arecibo latitudes (Vadas, 2007), various alternative sources including weather patterns are explored.
Journal of Geophysical Research: Space Physics, 2010
Wave‐like disturbances in electron density ne have been observed in the thermosphere above Arecib... more Wave‐like disturbances in electron density ne have been observed in the thermosphere above Arecibo Observatory, Puerto Rico throughout its 45 year history. However, only recently has it become evident that these waves are continuously present in the Arecibo thermosphere. The wave characteristics are fairly constant between day and night and from season to season. High‐resolution electron density measurements obtained by applying the coded long‐pulse radar technique to photoelectron‐enhanced Langmuir waves are presented. These new observations strongly suggest that the perturbations in electron density are the result of internal acoustic‐gravity waves (AGWs) propagating through the Arecibo thermosphere. The AGWs appear to be broadbanded in wave number space. The downward phase trajectories of Δne/ne between 400 and 120 km combined with the low horizontal phase velocities obtained from airglow measurements support the idea that the AGWs are not ducted but rather are locally produced. ...
Journal of Geophysical Research, 1984
Backscatter from quasi-periodic inhomogeneities in the electron density, generated by a powerful ... more Backscatter from quasi-periodic inhomogeneities in the electron density, generated by a powerful ionospherically reflected wave, has been observed at Arecibo. The backscatter was more intense by about 40 dB than that observed earlier by other workers at higher latitudes. It is suggested that the anomalous ionospheric absorption was greater in the earlier experiments. Backscatter from quasi-periodic inhomogeneities in the electron density of the ionospheric F region, generated by a powerful standing wave, was observed and interpreted by Belikovich et al. [1975, 1977, 1978]. The present brief report describes similar observations on April 15, 1983, at the Arecibo Observatory. The observations were preliminary in nature; potential applications as a diagnostic method for the ionospheric plasma are beyond the scope of the present work. Continuous wave (CW) transmissions near 5.1 MHz with an equivalent power of about 20 MW were made in the ordinary magnetoionic mode at Islote, about 17 km from the Arecibo Observatory. The inhomogeneities generated by such transmissions were detected, using scatter echoes from pulsed transmissions in the extraordinary mode at a frequency near 5.7 MHz, with a pulse length of 20 tts, an interpulse period (IPP) of 20 ms or 40 ms, and an equivalent power of about 20 MW, also at Islote. The scatter echoes were received at the ^recibo Observatory using the 305-m reflector. Perfect synchronization of the clocks at Islote and at the Arecibo Obser
Journal of Geophysical Research: Space Physics, 1986
The temporal development of the so‐called HF‐enhanced plasma line (HFPL) has been studied in deta... more The temporal development of the so‐called HF‐enhanced plasma line (HFPL) has been studied in detail using the high‐power high‐frequency (HF) facility located near Arecibo, Puerto Rico. Observations were made with the Arecibo 430‐MHz radar. In the current work, attention is focused on the evolution of the HFPL spectrum subsequent to the onset of the HF wave in the F region plasma. The development of the HFPL spectrum is examined for several different HF pulse lengths and HF duty cycles. In this regard, low duty cycles with long HF‐off periods tend to consistently produce a different spectral evolution than high duty cycles with short HF‐off periods. Broad, diffuse HFPL spectra are observed with low HF duty cycles, whereas sharply defined nonlinear Landau damping cascades develop at high duty cycles. Under a variety of observing conditions, the Arecibo HFPLs are found to develop dominant decay line peaks within a few milliseconds of HF turn‐on in the plasma. In addition, at early time...
Ferroelectrics, 2010
Development of PMN-PT single crystal/epoxy 1-3 composites for high-frequency ultrasonic transduce... more Development of PMN-PT single crystal/epoxy 1-3 composites for high-frequency ultrasonic transducers application is presented. The composite was fabricated by using a DRIE dry etching process with a 45% volume fraction of PMN-PT. A 35 MHz ultrasound flat transducer was fabricated with the composite, which was found to have an effective electromechanical coupling coefficient of 0.81, an insertion loss of 18 db, and a-6 dB bandwidth as high as 100%. Tungsten wire phantom image shows that the transducer had an axial resolution of 30 μm, which was in good agreement with the theoretical expectation. The initial results showed that the PMN-PT/ epoxy 1-3 composite has many attractive properties over conventional piezoelectric materials for medical imaging applications.
Radio Science, 2009
We present polar mesospheric radar observations at three frequency bands (MF/HF/VHF) and eight ra... more We present polar mesospheric radar observations at three frequency bands (MF/HF/VHF) and eight radar frequencies: 2.43, 3.3, 4.53, 4.9, 7.6, 28, 50, and 139 MHz, in order to better understand the well known but still not fully understood Polar Mesosphere Summer Echoes (PMSE). The echo morphology at the different frequencies is described by means of case studies where PMSE events were observed concurrently using at least two radar systems deployed over the Alaskan central region. The identity of MF and HF radar echoes as PMSE is resolved for the first time by means of simultaneous measurements made with VHF radars, the reference sensors employed traditionally for PMSE studies. On the basis of echo duration and radar reflectivity estimates, we suggest that low‐power HF radars would be more appropriate for PMSE monitoring. This is confirmed by a radar target analysis of turbulent scattering mechanisms in the polar summer mesosphere. MF radars show highly organized PMSE layers quite oft...
Earth, Moon, and Planets, 2015
Unfortunately, in the original publication of this article, Eq. (1) has been incorrectly publishe... more Unfortunately, in the original publication of this article, Eq. (1) has been incorrectly published. Correct Eq. (1) is given below: x 2 r ¼ x 2 pe þ sin 2 hx 2 ce þ 3k 2 AE jT e m e ; ð1Þ The online version of the original article can be found under
Ultrasonics, 2006
A modified sol-gel method is used to prepare PZT thick film on Pt-coated silicon substrate. A new... more A modified sol-gel method is used to prepare PZT thick film on Pt-coated silicon substrate. A new method of vacuum filling sol-gel precursor solution is introduced to improve film quality. The effects of the filling on PZT thick film structure and ferroelectric properties are discussed. The fabrication of a high frequency transducer with the PZT film as the actuating layer is described. The performance of the transducer is measured and results show that the transducer backed by E-Solder without a matching layer has a center frequency of 103 MHz and a bandwidth of 70%. Beam profile measurements show that the transducer has an axial resolution of 9.2 microm and a lateral resolution of 33 microm.
2007 IEEE Ultrasonics Symposium Proceedings, 2007
ABSTRACT
2008 IEEE Ultrasonics Symposium, 2008
ABSTRACT
IEEE Ultrasonics Symposium, 2004
(1-x)PbYb12/Nb12/Nb12/O3-xPbTiO3 (PYbN-PT, x=0.5) thin films were investigated for high frequency... more (1-x)PbYb12/Nb12/Nb12/O3-xPbTiO3 (PYbN-PT, x=0.5) thin films were investigated for high frequency transducer applications in this work. Firstly, highly [001] oriented LaNiO3 (LNO) thin films were prepared on Si [001] substrates by a simple metal organic decomposition technique. The room temperature resistivity of the LNO thin films was 0.65 mΩ·cm. Then PYbN-PT thin films were deposited onto the LNO/Si substrates by sol-gel
Two-dimensional images of F- and E- layers have been obtained using the technique called radio-in... more Two-dimensional images of F- and E- layers have been obtained using the technique called radio-induced aurora (RIA). This technique makes the plasma layers glow in the ionosphere glow when being stimulated by high power radio waves. Normally the irregularities in the ionosphere do not radiate strong enough visible emissions to be observed from the ground. Experiments at Arecibo Observatory in
The Astrophysical Journal, 1975
... Printed in USA DETECTION OF NUCLEAR GAMMA RAYS FROM THE GALACTIC CENTER REGION RC HAYMES, GD ... more ... Printed in USA DETECTION OF NUCLEAR GAMMA RAYS FROM THE GALACTIC CENTER REGION RC HAYMES, GD WALRAVEN, CA MEEGAN, RD HALL ... A power-law continuum was observed and several spectral lines were detected for the first time, at energies close to ...
Bulletin of the …, 1974
... R. C . HAYMES , G . D . WALRAVEN , C . A . NEEGAN , R . D. HALL , F . T . DJIJTH , and D . H ... more ... R. C . HAYMES , G . D . WALRAVEN , C . A . NEEGAN , R . D. HALL , F . T . DJIJTH , and D . H . SHELTON , Rice Univ.', On 1974 April 2, during a balloon' flight conducted in Argentina, a 0.03 MeV - 12.1 NeV differential energy spectrum was measured from GX 1+4 for a total of ...
Journal of Geophysical Research: Space Physics, 1985
Experiments were performed at Arecibo, Puerto Rico, to investigate the evolution times of 3‐m fie... more Experiments were performed at Arecibo, Puerto Rico, to investigate the evolution times of 3‐m field‐aligned Striations produced in the ionosphere by powerful high‐frequency (HF) radio waves. The results of this investigation are now summarized. First, the striations' rise times are dependent on the HF electric field. The E region data suggest that this dependence is nonlinear. Second, the threshold value of the HF electric field required to produce detectable Striations was experimentally determined. At threshold the component of the HF electric field perpendicular to the geomagnetic field is calculated to be 0.09 V/m in the F region and 0.37 V/m in the E region. Third, both the E and the F region data verify theoretical predictions that the Striations' decay times are directly proportional to the electron diffusion across B. Finally, a one‐to‐one correspondence between the growth of the 3‐m Striations and the decline of the HF‐enhanced plasma line during overshoot is someti...
Journal of Geophysical Research: Space Physics, 2007
Incoherent scatter radar (ISR) power profile observations at Arecibo Observatory (AO) have reveal... more Incoherent scatter radar (ISR) power profile observations at Arecibo Observatory (AO) have revealed long vertical wavelength (>100 km) quasi-coherent waves with periods of 1hourthatareobservedtobenearlycontinuouslypresentovertwo1 hour that are observed to be nearly continuously present over two 1hourthatareobservedtobenearlycontinuouslypresentovertwo35-hour geomagnetically quiet observation periods. When properly filtered, results from both 22-23 March 2004 and 5-6 June 2005 provide unambiguous views of these waves. The waves are strong throughout the F region, often spanning 160 to above 500 km in altitude and are present day and night in the F2 layer. Filtering techniques that were used to better reveal the waves are extensively discussed. Barometric pressure and imager data, both of which were taken on site at Arecibo, are used to provide further insight into the nature of these waves. These waves may be linked to high-latitude medium-scale traveling ionospheric disturbances (MSTIDs) observed with the superDARN radar network and associated with E region auroral electrojet source(s) that are quasi-coherent under geomagnetic quiet conditions. As auroral-zone MSTIDs are believed to dissipate before reaching Arecibo latitudes (Vadas, 2007), various alternative sources including weather patterns are explored.
Journal of Geophysical Research: Space Physics, 2010
Wave‐like disturbances in electron density ne have been observed in the thermosphere above Arecib... more Wave‐like disturbances in electron density ne have been observed in the thermosphere above Arecibo Observatory, Puerto Rico throughout its 45 year history. However, only recently has it become evident that these waves are continuously present in the Arecibo thermosphere. The wave characteristics are fairly constant between day and night and from season to season. High‐resolution electron density measurements obtained by applying the coded long‐pulse radar technique to photoelectron‐enhanced Langmuir waves are presented. These new observations strongly suggest that the perturbations in electron density are the result of internal acoustic‐gravity waves (AGWs) propagating through the Arecibo thermosphere. The AGWs appear to be broadbanded in wave number space. The downward phase trajectories of Δne/ne between 400 and 120 km combined with the low horizontal phase velocities obtained from airglow measurements support the idea that the AGWs are not ducted but rather are locally produced. ...
Journal of Geophysical Research, 1984
Backscatter from quasi-periodic inhomogeneities in the electron density, generated by a powerful ... more Backscatter from quasi-periodic inhomogeneities in the electron density, generated by a powerful ionospherically reflected wave, has been observed at Arecibo. The backscatter was more intense by about 40 dB than that observed earlier by other workers at higher latitudes. It is suggested that the anomalous ionospheric absorption was greater in the earlier experiments. Backscatter from quasi-periodic inhomogeneities in the electron density of the ionospheric F region, generated by a powerful standing wave, was observed and interpreted by Belikovich et al. [1975, 1977, 1978]. The present brief report describes similar observations on April 15, 1983, at the Arecibo Observatory. The observations were preliminary in nature; potential applications as a diagnostic method for the ionospheric plasma are beyond the scope of the present work. Continuous wave (CW) transmissions near 5.1 MHz with an equivalent power of about 20 MW were made in the ordinary magnetoionic mode at Islote, about 17 km from the Arecibo Observatory. The inhomogeneities generated by such transmissions were detected, using scatter echoes from pulsed transmissions in the extraordinary mode at a frequency near 5.7 MHz, with a pulse length of 20 tts, an interpulse period (IPP) of 20 ms or 40 ms, and an equivalent power of about 20 MW, also at Islote. The scatter echoes were received at the ^recibo Observatory using the 305-m reflector. Perfect synchronization of the clocks at Islote and at the Arecibo Obser
Journal of Geophysical Research: Space Physics, 1986
The temporal development of the so‐called HF‐enhanced plasma line (HFPL) has been studied in deta... more The temporal development of the so‐called HF‐enhanced plasma line (HFPL) has been studied in detail using the high‐power high‐frequency (HF) facility located near Arecibo, Puerto Rico. Observations were made with the Arecibo 430‐MHz radar. In the current work, attention is focused on the evolution of the HFPL spectrum subsequent to the onset of the HF wave in the F region plasma. The development of the HFPL spectrum is examined for several different HF pulse lengths and HF duty cycles. In this regard, low duty cycles with long HF‐off periods tend to consistently produce a different spectral evolution than high duty cycles with short HF‐off periods. Broad, diffuse HFPL spectra are observed with low HF duty cycles, whereas sharply defined nonlinear Landau damping cascades develop at high duty cycles. Under a variety of observing conditions, the Arecibo HFPLs are found to develop dominant decay line peaks within a few milliseconds of HF turn‐on in the plasma. In addition, at early time...
Ferroelectrics, 2010
Development of PMN-PT single crystal/epoxy 1-3 composites for high-frequency ultrasonic transduce... more Development of PMN-PT single crystal/epoxy 1-3 composites for high-frequency ultrasonic transducers application is presented. The composite was fabricated by using a DRIE dry etching process with a 45% volume fraction of PMN-PT. A 35 MHz ultrasound flat transducer was fabricated with the composite, which was found to have an effective electromechanical coupling coefficient of 0.81, an insertion loss of 18 db, and a-6 dB bandwidth as high as 100%. Tungsten wire phantom image shows that the transducer had an axial resolution of 30 μm, which was in good agreement with the theoretical expectation. The initial results showed that the PMN-PT/ epoxy 1-3 composite has many attractive properties over conventional piezoelectric materials for medical imaging applications.
Radio Science, 2009
We present polar mesospheric radar observations at three frequency bands (MF/HF/VHF) and eight ra... more We present polar mesospheric radar observations at three frequency bands (MF/HF/VHF) and eight radar frequencies: 2.43, 3.3, 4.53, 4.9, 7.6, 28, 50, and 139 MHz, in order to better understand the well known but still not fully understood Polar Mesosphere Summer Echoes (PMSE). The echo morphology at the different frequencies is described by means of case studies where PMSE events were observed concurrently using at least two radar systems deployed over the Alaskan central region. The identity of MF and HF radar echoes as PMSE is resolved for the first time by means of simultaneous measurements made with VHF radars, the reference sensors employed traditionally for PMSE studies. On the basis of echo duration and radar reflectivity estimates, we suggest that low‐power HF radars would be more appropriate for PMSE monitoring. This is confirmed by a radar target analysis of turbulent scattering mechanisms in the polar summer mesosphere. MF radars show highly organized PMSE layers quite oft...
Earth, Moon, and Planets, 2015
Unfortunately, in the original publication of this article, Eq. (1) has been incorrectly publishe... more Unfortunately, in the original publication of this article, Eq. (1) has been incorrectly published. Correct Eq. (1) is given below: x 2 r ¼ x 2 pe þ sin 2 hx 2 ce þ 3k 2 AE jT e m e ; ð1Þ The online version of the original article can be found under
Ultrasonics, 2006
A modified sol-gel method is used to prepare PZT thick film on Pt-coated silicon substrate. A new... more A modified sol-gel method is used to prepare PZT thick film on Pt-coated silicon substrate. A new method of vacuum filling sol-gel precursor solution is introduced to improve film quality. The effects of the filling on PZT thick film structure and ferroelectric properties are discussed. The fabrication of a high frequency transducer with the PZT film as the actuating layer is described. The performance of the transducer is measured and results show that the transducer backed by E-Solder without a matching layer has a center frequency of 103 MHz and a bandwidth of 70%. Beam profile measurements show that the transducer has an axial resolution of 9.2 microm and a lateral resolution of 33 microm.
2007 IEEE Ultrasonics Symposium Proceedings, 2007
ABSTRACT