Ahmed Salim | Johns Hopkins University School of Medicine (original) (raw)

Papers by Ahmed Salim

Biosensors, 2021

Glucose-monitoring sensors are necessary and have been extensively studied to prevent and control... more Glucose-monitoring sensors are necessary and have been extensively studied to prevent and control health problems caused by diabetes. Spoof localized surface plasmon (LSP) resonance sensors have been investigated for chemical sensing and biosensing. A spoof LSP has similar characteristics to an LSP in the microwave or terahertz frequency range but with certain advantages, such as a high-quality factor and improved sensitivity. In general, microwave spoof LSP resonator-based glucose sensors have been studied. In this study, a millimeter-wave-based spoof surface plasmonic resonator sensor is designed to measure glucose concentrations. The millimeter-wave-based sensor has a smaller chip size and higher sensitivity than microwave-frequency sensors. Therefore, the microfluidic channel was designed to be reusable and able to operate with a small sample volume. For alignment, a polydimethylsiloxane channel was simultaneously fabricated using a multilayer bonding film to attach the upper si...

Sensors (Basel, Switzerland), Jan 15, 2018

Metamaterial elements/arrays exhibit a sensitive response to fluids yet with a small footprint, t... more Metamaterial elements/arrays exhibit a sensitive response to fluids yet with a small footprint, therefore, they have been an attractive choice to realize various sensing devices when integrated with microfluidic technology. Micro-channels made from inexpensive biocompatible materials avoid any contamination from environment and require only microliter-nanoliter sample for sensing. Simple design, easy fabrication process, light weight prototype, and instant measurements are advantages as compared to conventional (optical, electrochemical and biological) sensing systems. Inkjet-printed flexible sensors find their utilization in rapidly growing wearable electronics and health-monitoring flexible devices. Adequate sensitivity and repeatability of these low profile microfluidic sensors make them a potential candidate for point-of-care testing which novice patients can use reliably. Aside from degraded sensitivity and lack of selectivity in all practical microwave chemical sensors, they r...

Sensors, 2016

In this paper, a complementary split-ring resonator (CSRR)-loaded patch is proposed as a microflu... more In this paper, a complementary split-ring resonator (CSRR)-loaded patch is proposed as a microfluidic ethanol chemical sensor. The primary objective of this chemical sensor is to detect ethanol's concentration. First, two tightly coupled concentric CSRRs loaded on a patch are realized on a Rogers RT/Duroid 5870 substrate, and then a microfluidic channel engraved on polydimethylsiloxane (PDMS) is integrated for ethanol chemical sensor applications. The resonant frequency of the structure before loading the microfluidic channel is 4.72 GHz. After loading the microfluidic channel, the 550 MHz shift in the resonant frequency is ascribed to the dielectric perturbation phenomenon when the ethanol concentration is varied from 0% to 100%. In order to assess the sensitivity range of our proposed sensor, various concentrations of ethanol are tested and analyzed. Our proposed sensor exhibits repeatability and successfully detects 10% ethanol as verified by the measurement setup. It has created headway to a miniaturized, non-contact, low-cost, reliable, reusable, and easily fabricated design using extremely small liquid volumes.

Sensors (Basel, Switzerland), Jan 7, 2018

Microwave resonators working as sensors can detect only a single analyte at a time. To address th... more Microwave resonators working as sensors can detect only a single analyte at a time. To address this issue, a TE-mode substrate-integrated waveguide (SIW) resonator is exploited, owing to its two distinct regions of high-intensity electric fields, which can be manipulated by loading two chemicals. Two microfluidic channels with unequal fluid-carrying capacities, engraved in a polydimethylsiloxane (PDMS) sheet, can perturb the symmetric electric fields even if loaded with the two extreme cases of dielectric [ethanol (E), deionized water (DI)] and [deionized water, ethanol]. The four layers of the sandwiched structure considered in this study consisted of a top conductive pattern and a bottom ground, both realized on a Rogers RT/Duroid 5880. PDMS-based channels attached with an adhesive serve as the middle layers. The TE-mode SIW with empty channels resonates at 8.26 GHz and exhibits a -25 dB return loss with an unloaded quality factor of Q ≈ 28. We simultaneously load E and DI and dem...

INFOCOMP Journal of Computer Science, 2015

Energy consumption and prolonging network lifetime are a primary challenge in many studies on Wir... more Energy consumption and prolonging network lifetime are a primary challenge in many studies on Wireless Sensor Networks (WSN). Thus, since radio communication and routing protocol transmission are in general the main cause of power consumption, different techniques proposed in lit- erature to improve energy efficiency have mainly focused on l imiting transmission/reception of data. To this aim, we propose an adaptive and efficient technique base d on compressive sensing for improving the performance of routing in wireless sensor network. The performance of our technique is evaluated by applying it to PEGASIS (power efficient gathering in senso r information systems), which is one of the most popular protocols for routing in wireless sensor network. A comparison of PEGASIS and PE- GASIS with Huffman coding shows the advantage of the proposed technique in terms of reducing the energy consumption and network lifetime.

International Journal of Computer Applications, 2014

Compressive sensing(CS) is an emerging research field that has applications in signal processing,... more Compressive sensing(CS) is an emerging research field that has applications in signal processing, error correction, medical imaging, seismology, and many more other areas. CS promises to efficiently reconstruct a sparse signal vector via a much smaller number of linear measurements than its dimension. In order to improve CS reconstruction performance, this paper present a novel reconstruction greedy algorithm called the Enhanced Orthogonal Matching Pursuit (E-OMP). E-OMP falls into the general category of Two Stage Thresholding(TST)-type algorithms where it consists of consecutive forward and backward stages. During the forward stage, E-OMP depends on solving the least square problem to select columns from the measurement matrix. Furthermore, E-OMP uses a simple backtracking step to detect the previous chosen columns accuracy and then remove the false columns at each time. From simulations it is observed that E-OMP improve the reconstruction performance better than Orthogonal Matching Pursuit (OMP) and Regularized OMP (ROMP).

An international partnership to help the poor gain sustained access to improved water supply and ... more An international partnership to help the poor gain sustained access to improved water supply and sanitation services

International Journal of Mental Health Systems, 2011

BACKGROUND: The Zanzibar Ministry of Health and Social Welfare, concerned about mental health in ... more BACKGROUND: The Zanzibar Ministry of Health and Social Welfare, concerned about mental health in the country, requested technical assistance from WHO in 1997. AIMS: This article describes the facilitation over many years by a WHO Collaborating Centre, of sustainable mental health developments in Zanzibar, one of the poorest countries in the world, using systematic approaches to policy design and implementation.

Biosensors, 2021

Glucose-monitoring sensors are necessary and have been extensively studied to prevent and control... more Glucose-monitoring sensors are necessary and have been extensively studied to prevent and control health problems caused by diabetes. Spoof localized surface plasmon (LSP) resonance sensors have been investigated for chemical sensing and biosensing. A spoof LSP has similar characteristics to an LSP in the microwave or terahertz frequency range but with certain advantages, such as a high-quality factor and improved sensitivity. In general, microwave spoof LSP resonator-based glucose sensors have been studied. In this study, a millimeter-wave-based spoof surface plasmonic resonator sensor is designed to measure glucose concentrations. The millimeter-wave-based sensor has a smaller chip size and higher sensitivity than microwave-frequency sensors. Therefore, the microfluidic channel was designed to be reusable and able to operate with a small sample volume. For alignment, a polydimethylsiloxane channel was simultaneously fabricated using a multilayer bonding film to attach the upper si...

Sensors (Basel, Switzerland), Jan 15, 2018

Metamaterial elements/arrays exhibit a sensitive response to fluids yet with a small footprint, t... more Metamaterial elements/arrays exhibit a sensitive response to fluids yet with a small footprint, therefore, they have been an attractive choice to realize various sensing devices when integrated with microfluidic technology. Micro-channels made from inexpensive biocompatible materials avoid any contamination from environment and require only microliter-nanoliter sample for sensing. Simple design, easy fabrication process, light weight prototype, and instant measurements are advantages as compared to conventional (optical, electrochemical and biological) sensing systems. Inkjet-printed flexible sensors find their utilization in rapidly growing wearable electronics and health-monitoring flexible devices. Adequate sensitivity and repeatability of these low profile microfluidic sensors make them a potential candidate for point-of-care testing which novice patients can use reliably. Aside from degraded sensitivity and lack of selectivity in all practical microwave chemical sensors, they r...

Sensors, 2016

In this paper, a complementary split-ring resonator (CSRR)-loaded patch is proposed as a microflu... more In this paper, a complementary split-ring resonator (CSRR)-loaded patch is proposed as a microfluidic ethanol chemical sensor. The primary objective of this chemical sensor is to detect ethanol's concentration. First, two tightly coupled concentric CSRRs loaded on a patch are realized on a Rogers RT/Duroid 5870 substrate, and then a microfluidic channel engraved on polydimethylsiloxane (PDMS) is integrated for ethanol chemical sensor applications. The resonant frequency of the structure before loading the microfluidic channel is 4.72 GHz. After loading the microfluidic channel, the 550 MHz shift in the resonant frequency is ascribed to the dielectric perturbation phenomenon when the ethanol concentration is varied from 0% to 100%. In order to assess the sensitivity range of our proposed sensor, various concentrations of ethanol are tested and analyzed. Our proposed sensor exhibits repeatability and successfully detects 10% ethanol as verified by the measurement setup. It has created headway to a miniaturized, non-contact, low-cost, reliable, reusable, and easily fabricated design using extremely small liquid volumes.

Sensors (Basel, Switzerland), Jan 7, 2018

Microwave resonators working as sensors can detect only a single analyte at a time. To address th... more Microwave resonators working as sensors can detect only a single analyte at a time. To address this issue, a TE-mode substrate-integrated waveguide (SIW) resonator is exploited, owing to its two distinct regions of high-intensity electric fields, which can be manipulated by loading two chemicals. Two microfluidic channels with unequal fluid-carrying capacities, engraved in a polydimethylsiloxane (PDMS) sheet, can perturb the symmetric electric fields even if loaded with the two extreme cases of dielectric [ethanol (E), deionized water (DI)] and [deionized water, ethanol]. The four layers of the sandwiched structure considered in this study consisted of a top conductive pattern and a bottom ground, both realized on a Rogers RT/Duroid 5880. PDMS-based channels attached with an adhesive serve as the middle layers. The TE-mode SIW with empty channels resonates at 8.26 GHz and exhibits a -25 dB return loss with an unloaded quality factor of Q ≈ 28. We simultaneously load E and DI and dem...

INFOCOMP Journal of Computer Science, 2015

Energy consumption and prolonging network lifetime are a primary challenge in many studies on Wir... more Energy consumption and prolonging network lifetime are a primary challenge in many studies on Wireless Sensor Networks (WSN). Thus, since radio communication and routing protocol transmission are in general the main cause of power consumption, different techniques proposed in lit- erature to improve energy efficiency have mainly focused on l imiting transmission/reception of data. To this aim, we propose an adaptive and efficient technique base d on compressive sensing for improving the performance of routing in wireless sensor network. The performance of our technique is evaluated by applying it to PEGASIS (power efficient gathering in senso r information systems), which is one of the most popular protocols for routing in wireless sensor network. A comparison of PEGASIS and PE- GASIS with Huffman coding shows the advantage of the proposed technique in terms of reducing the energy consumption and network lifetime.

International Journal of Computer Applications, 2014

Compressive sensing(CS) is an emerging research field that has applications in signal processing,... more Compressive sensing(CS) is an emerging research field that has applications in signal processing, error correction, medical imaging, seismology, and many more other areas. CS promises to efficiently reconstruct a sparse signal vector via a much smaller number of linear measurements than its dimension. In order to improve CS reconstruction performance, this paper present a novel reconstruction greedy algorithm called the Enhanced Orthogonal Matching Pursuit (E-OMP). E-OMP falls into the general category of Two Stage Thresholding(TST)-type algorithms where it consists of consecutive forward and backward stages. During the forward stage, E-OMP depends on solving the least square problem to select columns from the measurement matrix. Furthermore, E-OMP uses a simple backtracking step to detect the previous chosen columns accuracy and then remove the false columns at each time. From simulations it is observed that E-OMP improve the reconstruction performance better than Orthogonal Matching Pursuit (OMP) and Regularized OMP (ROMP).

An international partnership to help the poor gain sustained access to improved water supply and ... more An international partnership to help the poor gain sustained access to improved water supply and sanitation services

International Journal of Mental Health Systems, 2011

BACKGROUND: The Zanzibar Ministry of Health and Social Welfare, concerned about mental health in ... more BACKGROUND: The Zanzibar Ministry of Health and Social Welfare, concerned about mental health in the country, requested technical assistance from WHO in 1997. AIMS: This article describes the facilitation over many years by a WHO Collaborating Centre, of sustainable mental health developments in Zanzibar, one of the poorest countries in the world, using systematic approaches to policy design and implementation.