Terahertz communication: detection and signal processing.

The development of 6 G networks has promoted related research based on terahertz communication. As submillimeter radiation, signal transportation via terahertz waves has several superior properties, including non-ionizing and easy penetration of non-metallic materials. This paper provides an overview of different terahertz detectors based on various mechanisms. Additionally, the detailed fabrication process, structural design, and the improvement strategies are summarized. Following that, it is essential and necessary to prevent the practical signal from noise, and methods such as wavelet transform, UM-MIMO and decoding have been introduced. This paper highlights the detection process of the terahertz wave system and signal processing after the collection of signal data.

Photoacoustic Imaging with Capacitive Micromachined Ultrasound Transducers: Principles and Developments.

Photoacoustic imaging (PAI) is an emerging imaging technique that bridges the gap between pure optical and acoustic techniques to provide images with optical contrast at the acoustic penetration depth. The two key components that have allowed PAI to attain high-resolution images at deeper penetration depths are the photoacoustic signal generator, which is typically implemented as a pulsed laser and the detector to receive the generated acoustic signals. Many types of acoustic sensors have been explored as a detector for the PAI including Fabry-Perot interferometers (FPIs), micro ring resonators (MRRs), piezoelectric transducers, and capacitive micromachined ultrasound transducers (CMUTs). The fabrication technique of CMUTs has given it an edge over the other detectors. First, CMUTs can be easily fabricated into given shapes and sizes to fit the design specifications. Moreover, they can be made into an array to increase the imaging speed and reduce motion artifacts. With a fabrication technique that is similar to complementary metal-oxide-semiconductor (CMOS), CMUTs can be integrated with electronics to reduce the parasitic capacitance and improve the signal to noise ratio. The numerous benefits of CMUTs have enticed researchers to develop it for various PAI purposes such as photoacoustic computed tomography (PACT) and photoacoustic endoscopy applications. For PACT applications, the main areas of research are in designing two-dimensional array, transparent, and multi-frequency CMUTs. Moving from the table top approach to endoscopes, some of the different configurations that are being investigated are phased and ring arrays. In this paper, an overview of the development of CMUTs for PAI is presented.

A novel field emission microscopy method to study field emission characteristics of freestanding carbon nanotube arrays.

Field emission (FE) uniformity and the mechanism of emitter failure of freestanding carbon nanotube (CNT) arrays have not been well studied due to the difficulty of observing and quantifying FE performance of each emitter in CNT arrays. Herein a field emission microscopy (FEM) method based on poly(methyl methacrylate) (PMMA) thin film is proposed to study the FE uniformity and CNT emitter failure of freestanding CNT arrays. FE uniformity of freestanding CNT arrays and different levels of FE current contributions from each emitter in the arrays are recorded and visualized. FEM patterns on the PMMA thin film contain the details of the CNT emitter tip shape and whether multiple CNT emitters occur at an emission site. Observation of real-time FE performance and the CNT emitter failure process in freestanding CNT arrays are successfully achieved using a microscopic camera. High emission currents through CNT emitters causes Joule heating and light emission followed by an explosion of the CNTs. The proposed approach is capable of resolving the major challenge of building the relationship between FE performance and CNT morphologies, which can significantly facilitate the study of FE non-uniformity, the emitter failure mechanism and the development of stable and reliable FE devices in practical applications.

Numerical and experimental study of radiation induced conductivity change of carbon nanotube filled polymers.

Measuring the conductivity changes of sensing materials to detect a wide range of radiation energy and dosage is one of the major sensing mechanisms of radiation sensors. Carbon nanotube (CNT) filled composites are suitable for sensing radiation because of the extraordinary electrical properties of CNTs and the CNT-network formed inside the polymer matrix. Although the use of CNT-based nanocomposites as potential radiation sensing materials has been widely studied, there is still a lack of theoretical models to analyze the relationship between electrical conductivity and radiation dosages. In this article, we propose a 3D model to describe the electrical conductivity of CNT-based nanocomposites when being irradiated by ionizing radiation. The Monte Carlo method has been employed to calculate radiation intensity, CNT concentration and alignment's influence on the electrical conductivity. Our simulation shows a better agreement when CNT loading is between the percolation threshold and 3% volume fraction. Radiation experiments have been performed to verify the reliability of our model to illustrate a power function relationship between the electrical conductivity of a CNT-filled polymer and radiation intensity. In addition, the predicted alignment to obtain the best sensitivity for radiation sensing has been discussed to help with CNT-network building in the fabrication process.

Internal Model-Based Robust Tracking Control Design for the MEMS Electromagnetic Micromirror.

The micromirror based on micro-electro-mechanical systems (MEMS) technology is widely employed in different areas, such as scanning, imaging and optical switching. This paper studies the MEMS electromagnetic micromirror for scanning or imaging application. In these application scenarios, the micromirror is required to track the command sinusoidal signal, which can be converted to an output regulation problem theoretically. In this paper, based on the internal model principle, the output regulation problem is solved by designing a robust controller that is able to force the micromirror to track the command signal accurately. The proposed controller relies little on the accuracy of the model. Further, the proposed controller is implemented, and its effectiveness is examined by experiments. The experimental results demonstrate that the performance of the proposed controller is satisfying.

PMMA/MWCNT nanocomposite for proton radiation shielding applications.

Radiation shielding in space missions is critical in order to protect astronauts, spacecraft and payloads from radiation damage. Low atomic-number materials are efficient in shielding particle-radiation, but they have relatively weak material properties compared to alloys that are widely used in space applications as structural materials. However, the issues related to weight and the secondary radiation generation make alloys not suitable for space radiation shielding. Polymers, on the other hand, can be filled with different filler materials for reinforcement of material properties, while at the same time provide sufficient radiation shielding function with lower weight and less secondary radiation generation. In this study, poly(methyl-methacrylate)/multi-walled carbon nanotube (PMMA/MWCNT) nanocomposite was fabricated. The role of MWCNTs embedded in PMMA matrix, in terms of radiation shielding effectiveness, was experimentally evaluated by comparing the proton transmission properties and secondary neutron generation of the PMMA/MWCNT nanocomposite with pure PMMA and aluminum. The results showed that the addition of MWCNTs in PMMA matrix can further reduce the secondary neutron generation of the pure polymer, while no obvious change was found in the proton transmission property. On the other hand, both the pure PMMA and the nanocomposite were 18%-19% lighter in weight than aluminum for stopping the protons with the same energy and generated up to 5% fewer secondary neutrons. Furthermore, the use of MWCNTs showed enhanced thermal stability over the pure polymer, and thus the overall reinforcement effects make MWCNT an effective filler material for applications in the space industry.

Facile microfluidic channels for acoustophoresis on a budget.

Acoustophoresis is a powerful yet gentle technique for manipulating cells and particles that has quickly earned a place in the lab-on-a-chip toolkit. However, traditional construction techniques for acoustophoretic resonators have typically required prohibitively expensive and laborious processing methods. Here, we propose a highly cost-effective and cleanroom-free construction technique for transversal acoustophoretic resonators. Channels with two different widths of 750 and 300 µm were constructed using a simple glass and polyimide sandwiching technique. Half and full wavelength resonators were then established using 1 and 5 MHz ultrasound respectively and polystyrene beads were successfully manipulated in both types of resonators. This construction technique was then utilized to demonstrate a bifurcation and trifurcation microchannel with 600 µm widths and 2.5 MHz ultrasound. Our approach addresses some of the key drawbacks of acoustophoretic devices by drastically simplifying the fabrication and prototyping of transversal resonators and will assist in expanding this technology from laboratory benches and into the broader market.

Quantitative detection of pre-ovulatory luteinizing hormone surges in urine using the microfluidic vertical agitation approach.

Identifying the time of ovulation is an important process for women seeking and avoiding pregnancy. Luteinizing hormone (LH) plays an important role in ovulation, which is very important in the reproductive mechanism. Therefore, detecting the LH level is of great importance in monitoring ovulation. In this study, sensitive, rapid and selective electrochemical biosensors were developed to detect LH quantitatively from human urine samples and to monitor the ovulation period. Isopotential region and current density optimization studies revealed that sensors with an electrode width and spacing of 1 mm had the optimum performance. Electrochemical impedance spectra evidenced immobilization of DSP self-assembled monolayers and anti-LH-beta antibody on the surface. While the mobile phone vibrator led to a 3.5-fold enhancement in response signals, the agitation system developed resulted in a 10-fold improvement. The sensors displayed detection limits of 1.02 and 1.53 mIU/ml in the range of 0-40 mIU/ml LH concentration obtained using two statistical approaches. Additionally, the sensors showed no cross-reactivity to hCG, which is very similar in structure and is widely reported to have high cross-reactivity.

Design and fabrication of carbon nanotube field-emission cathode with coaxial gate and ballast resistor.

A low density vertically aligned carbon nanotube-based field-emission cathode with a ballast resistor and coaxial gate is designed and fabricated. The ballast resistor can overcome the non-uniformity of the local field-enhancement factor at the emitter apex. The self-aligned fabrication process of the coaxial gate can avoid the effects of emitter tip misalignment and height non-uniformity.

Fabrication of electro-microfluidic channel for single cell electroporation.

The point of this paper is to demonstrate the use of a quick and cheap fabrication method to realize a laser-ablated microfluidic channel for single cell electroporation. Traditional lithography of microchannel with electrode in MEMS applications has always been complicated. Here, we introduce a new methodology of fabricating microchannel with electrical functionalities achieved through a fast and cheap process. In the present methodology, the microchannel pattern is cut out of polyimide, bonded to two ITO-coated substrates using Teflon as an adhesion layer. ITO as conductive material enables electric field in the channel and its optical transparency allows microscopy techniques to be utilized in characterizing the behavior of the microfluidic chip. The performance of the chip was tested on irreversible single-cell scale electroporation which requires relatively high voltages. CHO cells, as mammalian cells, were passed through the microchannel to experience electric field. Cells were loaded with a fluorogenic dye, Calcein AM, and the electroporation of each was individually recorded in real-time via fluorescent microscopy. The results show promising performance of the electric microchannel in electroporation. By customizing of ITO electrodes and the design of microchannel pattern, utilization and integration of the proposed electrical microchannel in variety of other MEMS-based devices are achievable.

In vitro clearance and hemocompatibility assessment of ultrathin nanoporous silicon membranes for hemodialysis applications using human whole blood.

BACKGROUND/AIMS: Recent advances in nanotechnology have made it possible to mass-produce ultrathin silicon membranes with pore sizes in the range of nanometers. In this study, we investigate the possibility of employing ultrathin nanoporous silicon membranes with pore diameters of 5 and 20 nm for dialysis of human whole blood by performing in vitro clearance and hemocompatibility assessments. METHODS: A mini blood dialyzer is fabricated by mounting nanoporous silicon membranes on a Teflon structure. Clearance is calculated based on the concentration of sodium, chloride, ionized calcium, total CO2, glucose, creatinine and hematocrit measured before and after dialysis. Blood activation is assessed by flow cytometry. RESULTS: Blood contact with the nanoporous membranes induces considerable leukocyte activation. Coating of the membranes with polyethylene glycol significantly improves hemocompatibility without blocking the nanopores. CONCLUSION: Silicon nanoporous membranes are potential candidates for fabrication of miniaturized blood dialyzers. Their mechanical strength and hemocompatibility can be further improved.

Flexible Multi-Element Photothermoelectric Detectors Based on Spray-Coated Graphene/Polyethylenimine Composites for Nondestructive Testing.

Photothermoelectric (PTE) detectors receive much attention owing to the superiority of self-powered, non-bias input, and friendly ambient environments, facilitating abundant prospective applications in industrial inspection, medical diagnostics, homeland security, and wearable Internet of Things. However, many drawbacks of currently applicable PTE materials, involving unstable material oxidation, an uncontrollable fabrication process, and unscalable manufacturing, hinder the development of industrial productions. Herein, we demonstrate a vertical graphene/polyethylenimine composite PTE detector fabricated with an optimized spray-coating method in compact alignment on various surfaces, achieving a significant photovoltage detectivity and responsivity of 6.05 × 107 cm Hz1/2 W-1 and 2.7 V W-1 response at a 973 K blackbody temperature radiation (2.98 µm peak wavelength). In addition, the long-term stability and resistible concave and convex bending flexibility are presented. Furthermore, a nondestructive testing system is established and verified through high-spatial-resolution and high-penetration illustration. Overall, the spray-coated and flexible PTE graphene/polyethylenimine multi-elements with broadband infrared absorption compatibility and stable energy conversion are promising candidates for future health monitoring and wearable electronics.

An infrared photothermoelectric detector enabled by MXene and PEDOT:PSS composite for noncontact fingertip tracking.

Photothermoelectric (PTE) detectors functioning on the infrared spectrum show much potential for use in many fields, such as energy harvesting, nondestructive monitoring, and imaging fields. Recent advances in low-dimensional and semiconductor materials research have facilitated new opportunities for PTE detectors to be applied in material and structural design. However, these materials applied in PTE detectors face some challenges, such as unstable properties, high infrared reflection, and miniaturization issues. Herein, we report our fabrication of scalable bias-free PTE detectors based on Ti3C2 and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) composites and characterization of their composite morphology and broadband photoresponse. We also discuss various PTE engineering strategies, including substrate choices, electrode types, deposition methods, and vacuum conditions. Furthermore, we simulate metamaterials using different materials and hole sizes and fabricated a gold metamaterial with a bottom-up configuration by simultaneously combining MXene and polymer, which achieved an infrared photoresponse enhancement. Finally, we demonstrate a fingertip gesture response using the metamaterial-integrated PTE detector. This research proposes numerous implications of MXene and its related composites for wearable devices and Internet of Things (IoT) applications, such as the continuous biomedical tracking of human health conditions.

System design of large-area vertical photothermoelectric detectors based on carbon nanotube forests with MXene electrodes.

Photothermoelectric (PTE) detectors that combine photothermal and thermoelectric conversion have emerged in recent years. They can overcome bandgap limitations and achieve effective infrared detection. However, the development of PTE detectors and the related system design are in the early phases. Herein, we present vertical PTE detectors utilizing the active layer of carbon nanotube forests with MXenes acting as top electrodes. The detector demonstrates its capacity for sensitive infrared detection and rapid infrared response. We also investigated the relationship between photoresponse and different MXene electrode types as well as their thickness, which guides the PTE detector configuration design. Furthermore, we packed the PTE detectors with a polytetrafluoroethylene (PTFE, Teflon) cavity. The photoresponse is improved and the degradation is significantly delayed. We also applied this PTE detector system for non-destructive tracking (NDT) applications, where the photovoltage mapping pattern proves the viability of the imaging track. This work paves the way toward infrared energy harvesters and customized industrial NDT measurement.

A precise and rapid early pregnancy test: Development of a novel and fully automated electrochemical point-of-care biosensor for human urine samples.

Human chorionic gonadotropin (hCG), a glycoprotein hormone secreted from the placenta, is an important biomarker for pregnancy. In this study, we designed a precise, rapid and fully automatic device with an electrochemical point-of-care biosensor capable of quantitative hCG detection from human urine samples for early pregnancy detection. Gold and Ag/AgCl electrodes, whose structure with optimum isopotential region and current density, were simulated using COMSOL Multiphysics® software and custom-made from Flex Medical. The sensing surface was fabricated with DSP self-assembled monolayers (SAMs) and covalently immobilized anti-hCG-beta antibody. The detection method involved a sandwich assay using anti-hCG alpha-HRP. Based on an automated agitation design implemented in our device, the surface reaction rate is significantly improved comparing to routinely performed sandwich assays, and therefore a rapid detection of very low concentration can be achieved. Electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) measurements were used to characterize the immobilization of the antibodies and to determine the sensor activities respectively. The sensors displayed a limit of detection (LOD) of 2.17 mIU/ml within established clinical hCG levels for early detection of pregnancy. They responded very well to hCG, but not to luteinizing hormone (LH), which has a high degree of cross-reactivity with hCG. The results showed that the immunosensor has high specificity, good reproducibility, and long-term stability for the detection of hCG in urine samples.

Integration of nanoparticle cell lysis and microchip PCR for one-step rapid detection of bacteria.

This paper describes an integrated microchip system as an efficient and cost-effective solution involving Nanotechnology and Lab-on-a-Chip technology for the rapid detection of bacteria. The system is based on using surface-modified gold nanoparticles for efficient cell lysis followed by microchip PCR without having to remove the nanoparticles from the PCR solution. Poly(quaternary ammonium) modified gold nanoparticles are used to provide a novel and efficient cell lysis method without the need to go through time-consuming, expensive and complicated microfabrication processes as most of current cell lysis methods for Lab-on-a-Chip applications do. It also facilitates the integration of cell lysis and PCR by sharing the same reaction chamber as PCR uses. It is integrated with a prototype microchip PCR system consisting of a physical microchip PCR device and an automated temperature control mechanism. The research work explores solutions for the problem of PCR inhibition caused by gold nanoparticles as well as for the problem of non-specific PCR amplification in the integrated microchip system. It also explores the possibility of greatly reducing PCR cycling time to achieve the same result compared to the protocol for a regular PCR machine. The simplicity of the setup makes it easy to be integrated with other Lab-on-a-Chip functional modules to create customized solutions for target applications.

Antibacterial properties of poly(quaternary ammonium) modified gold and titanium dioxide nanoparticles.

We report excellent antibacterial effect induced by amine-functionalized gold and titanium dioxide nanoparticles without external excitations. The idea originates from the excellent antibacterial property of quaternary ammonium salts. The effects of poly(quaternary ammonium) and polyacrylate sodium functional groups as nanoparticle surfactants are compared to show that poly(quaternary ammonium) functional groups are the main cause of the induced antibacterial effect. 99.999% of E. coli can be destructed in 10 minutes by simply mixing bacteria with nanoparticle dispersions. The effect of nanoparticle concentrations on the antibacterial property is evaluated. Time required to significantly suppress bacteria growth is studied. The result indicates that the excellent antibacterial property can be introduced to any nanomaterials by using poly(quaternary ammonium) functional groups as surfactants. The engineered nanoparticles can find enormous applications such as self-cleaning surfaces, waste water treatment, Lab-on-a-Chip devices and many more.

Improvement of field emission performances by DMSO and PEDOT:PSS treated freestanding CNT clusters.

In this paper, we present two methods to improve the field emission (FE) performance of vertically aligned carbon nanotube emitters that are treated with dimethyl sulfoxide (DMSO) solution and poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) solution, respectively, and compared their performances. Both treatments force CNTs to be bundled into clusters, but the formed structures are very different. After treatment, both methods reduced the threshold electric field due to the reduction in screening effects, whereas the PEDOT:PSS treatment significantly reduced the threshold field to far lower than that of DMSO treatment. In addition, the FE efficiency and lifetime of treated CNT emitters are significantly improved. For both treated emitters, there is only slight degradation of the emission current after 80 hours of continuous FE at around 50 µA. In addition, the uniformity of both treated CNT emitters is improved which enables more CNTs to contribute to the overall current emission. This, in turn, lowers the current emitted by individual CNTs, and thereby increases the lifetime of the emitters. Therefore, this study demonstrates that these simple treatment methods of bundling CNTs into unique cluster-structures significantly improve the lifetime of FE and make them excellent candidates for large currents and long-term FE.

Simulation of a Miniature Linear Ion Trap with Half-Round Rod Electrodes.

The miniaturization of ion trap mass analyzers is an important direction in the development of mass spectrometers. In this work, we proposed two models of miniaturized HreLIT with a field radius of about 2 mm based on the existing research on conventional HreLIT and other ion traps, one with ions ejection slits on one pair of electrodes only (2-slit model) and the other with the same slits on all electrodes (4-slit model). The relationship of mass resolution with r/rx and the "stretch" distance of electrodes in the ejection direction is investigated by theoretical simulations. Trends of electric fields inside the ion traps were discussed as well. The comparable maximum resolution is observed at r/rx = 2/1.4 in both models, but stretching simulations revealed that the peak resolution of the 2-slit model was higher than that of the other model by about 8%. The highest value of 517 was obtained when stretching 1.1 mm. Furthermore, the resolution of ions with m/z = 119 could exceed 1000 when the scan rate was reduced to 800 Th/s. The mass spectrometry capability of miniature HreLIT has been confirmed theoretically, and it laid the foundation for the subsequent fabrication with MEMS technology.

Study of a novel cell lysis method with titanium dioxide for Lab-on-a-Chip devices.

In this paper, a novel method is proposed and demonstrated to be able to lyse gram-negative (E. coli) bacteria cells for Lab-on-a-Chip applications. The proposed method incorporates using titanium dioxide particles as photocatalysts and a miniaturized UV LED array as an excitation light source to perform cell lysis on microchips. The experimental result demonstrates the feasibility of the proposed prototype device. The working device suggests an inexpensive, easy to be fabricated and effective way for microchip cell lysis. The miniaturized UV LED array and the microchip with a reaction chamber can be easily integrated with other functional components to form a customized whole Lab-on-a-Chip system.