Microwave shielding and DC Electrical Properties of Carbon Black Loaded Rubber Nano-Composites

Abstract

In this work, ten carbon black (CB) loaded elastic acrylonitrile butadiene rubber (NBR) nano-composites have been prepared to be used in microwave shielding applications. The DC electric properties of these CB loaded NBR composites have been studied. The evolution of DC conductivity of CB loaded NBR composites with loading level revealed S-shapes curve in accordance with the percolation theory. The current (I)-voltage (V) relations have been studied for these samples at room temperature. All CB loaded NBR composite samples showed Ohmic behavior with the exception of two samples namely CB30 and CB40 in which space charge limited conduction is obvious. Microwave shielding has been calculated from the transmittance data measured using terahertz time domain spectroscopy (THz-TDS) technique. The analysis of microwave shielding data revealed that the sample CB70 has the highest shielding effectiveness. The results of the microwave shielding effectiveness of CB loaded NBR composites were correlated to their DC electric conductivities. Results showed that there is a strong relationship between the DC electric conductivity of the samples and their activity regarding microwave shielding effectiveness. The current investigation of microwave shielding properties of CB loaded NBR composites magnifies the importance of DC electric conduction losses as a major mechanism for microwave shielding.

http://www.jmest.org/wp-content/uploads/JMESTN42350842.pdf

TPS Spectra 3000, (TeraView, UK) was used for measuring transmittance of the samples in the frequency range 10-1000 GHz

ASSESSMENT METHODS FOR COMPOSITE AEROSPACE STRUCTURES

Summary:
In this paper result of detection and localization of artificially initiated delaminations in small carbon fibre reinforced polymer CFRP and glass fibre reinforced polymers GFRP samples were presented. The first method was electromechanical impedance method (EMI). This method utilizes electromechanical coupling of piezoelectric transducer with host structure. Due to this coupling mechanical resonances of structure can be seen in electrical impedance characteristic of piezoelectric transducer. Instead of electrical impedance other parameters such as resistance, conductance, admittance or susceptance are very often utilized. In the research real part of electrical impedance (resistance) was measured. Delamination in CFRP sample caused frequency shift of certain resonance frequencies visible in resistance characteristic. The second method was a laser vibrometry. It is a noncontact technique that allows to measure vibration of structure excited by piezoelectric transducer. During research standing waves (vibration–based method) and propagating waves (guided waves–based method) were registered for CFRP sample. In the vibration–based method, the frequency shifts of certain resonance frequencies were analyzed. In guided waves-based technique, the interaction of elastic waves with delamination can be seen in the RMS energy map. The third method is Terahertz spectroscopy. The device uses an electromagnetic radiation in the terahertz range (0.1–3 THz). The spectrometer is equipped with moving table that allows for XY scanning of large objects. During research the scanning heads working in reflection mode were utilized and the measurements were taken for GFRP sample with delamination. During research time signals as well as sets of signals creating B–scans and C–scans were analysed. The obtained results showed that the THz spectroscopy technique can detect and visualize delamination between the GFRP layers.

Teraview's TPS Spectra 3000 was used in these investigations

http://www.dem.ist.utl.pt/smart2015/files/SMART_2015_Proceedings/PDF/Papers/SMART2015_053.pdf

Microelectromechanically tunable multiband metamaterial with preserved isotropy

Abstract

We experimentally demonstrate a micromachined reconfigurable metamaterial with polarization independent characteristics for multiple resonances in terahertz spectral region. The metamaterial unit cell consists of eight out-of-plane deformable microcantilevers placed at each corner of an octagon ring. The octagon shaped unit cell geometry provides the desired rotational symmetry, while the out-of-plane movable cantilevers preserves the symmetry at different configurations of the metamaterial. The metamaterial is shown to provide polarization independent response for both electrical inductive-capacitive (eLC) resonance and dipolar resonance at all states of actuation. The proposed metamaterial has a switching range of 0.16 THz and 0.37 THz and a transmission intensity change of more than 0.2 and 0.7 for the eLC and dipolar resonances, respectively for both TE and TM modes. Further optimization of the metal layer thickness, provides an improvement of up to 80% modulation at 0.57 THz. The simultaneously tunable dual band isotropic metamaterial will enable the realization of high performance electro-optic devices that would facilitate numerous terahertz applications such as compressive terahertz imaging, miniaturized terahertz spectroscopy and next generation high speed wireless communication possible in the near future.

All THz transmission spectra measured in this paper were acquired using TeraView's TPS Spectra 3000.

http://www.nature.com/srep/2015/150626/srep11678/full/srep11678.html

Influence of terahertz waves on the penetration in thick FRP composite materials

Kwang-Hee Im¹, David K. Hsu², Chien-Ping Chiou², Daniel J. Barnard², In-Young Yang³ and Je-Woong Park⁴


Abstract

Fiber reinforced plastics (FRP) are increasingly utilized in engineering structures because of their performance and fabrication advantages. With this increased utilization, a technique to gage quality and further characterize the materials would be beneficial. The nondestructive applications for Terahertz (T-ray) methods have also experienced increased utilization for evaluating engineering materials and will be reported on here in applications for the inspectionand characterization of FRP materials used in wind energy components. First, refraction and transmission T-ray modes are used to determine the refractive index (n) of a glass fiber reinforced plastic (GFRP) reference sample, and extended for calculating the refractive indicesfor a sample of GFRP, balsa and epoxy. Additionally, carbon fiber reinforced plastic (CFRP) samples were evaluated with respect to fiber directions versus T-ray electric field polarization direction to evaluate the level of penetration of T-ray energy due to the fiber orientation dependent conductivity of this composite material. Finally, an evaluation of T-ray data was made to evaluate resonance effects, where the resonance frequency was found to agree with that expected from reflections from individual plies in thick GFRP laminates.

This study was performed using TeraView's CW Spectra 400 system. (TeraView, Cambridge, UK)

Full Article: http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4865010

Detailed non-destructive evaluation of UHMWPE composites in the terahertz range

Optical and Quantum ElectronicsDOI 10.1007/s11082-013-9836-4

N. Palka, D. Miedzinska

Abstract

We report on the terahertz analysis of an internal structure of an ultra-high molecular weight polyethylene (UHMWPE) composite material, which is based on the HB10-tape from Dyneema®. This type of composite is very hard and resistant and therefore it is often used to manufacture personal armors such as bulletproof vests and helmets. The multilayer structure of the UHMWPE composite was investigated by means of a raster scanning time domain spectroscopy technique in a reflection configuration. The mechanism of the formation of many shifted in time THz pulses (reflected from the internal layers of the sample) originates from the periodic modulation of the refractive index along the propagation of the radiation. This modulation is connected with alternate layers of fibers, each having different direction (perpendicular to each other). As a result we obtained the detailed three dimensional profile of the 3.3-mm thick sample with all 74 layers clearly visible. Thicknesses of all layers, having around 45 μm each, were determined. Moreover, it is also possible to identify internal defects i.e. delaminations in the internal structure of this composite material.

This study was performed using TeraView's TPS Spectra 3000 system, with the XY Reflectance imaging module. (TeraView, Cambridge, UK)


Source: http://link.springer.com/article/10.1007%2Fs11082-013-9836-4/fulltext.html

Generation THz - an article from Dr Axel Zeitler

Original article from:
http://www.scienceomega.com/article/881/generation-thz

Dr Axel Zeitler, of the University of Cambridge’s Department of Chemical Engineering and Biotechnology, looks at the dramatic progress made in terahertz research in recent years…

Terahertz radiation has excellent potential to help with the understanding of fundamental and exciting new challenges at the interface between physics, materials chemistry and the life sciences. Examples include fields as diverse as non-destructive testing of composite materials such as wind turbine blades, semiconductor quality control and intraoperative probes for breast cancer surgery. However, light located in this range of the electro-magnetic spectrum was very difficult to generate until quite recently, and so the full potential of these exciting applications is only just starting to emerge.

There can be no doubt that the main reasons for the surge in interest in performing spectroscopy at terahertz frequencies were the development of ultrafast lasers and the discovery of the Auston switch. These technologies made it possible to provide light at terahertz frequencies (a frequency of 1 THz equals a wavelength of 0.3 mm) in a relatively simple way. They enabled the development of a new generation of spectrometers in the early 1990s that were able to generate and detect pulses of coherent terahertz radiation with previously unprecedented ease and sensitivity. Today, most of the research in terahertz spectroscopy and imaging is carried out using such time-domain spectrometers. Terahertz time-domain spectroscopy (THz-TDS), therefore, is currently the main focus of research activities in the terahertz community.

There is no commonly agreed definition of the upper and lower frequency limits of terahertz (THz) radiation. Its spectral range overlaps with the far infrared at the higher frequency end and the microwave region at lower frequencies. The term thus refers to a relatively narrow part of the electro-magnetic spectrum. Despite this narrowness, which it shares, for example, with visible light, terahertz radiation is of great importance in terms of fundamental research as well as in technology and the life sciences. And yet, whilst nobody would question the importance of research involving radiation such as visible light, until recently research into terahertz radiation has been relatively obscure.

Terahertz radiation has unique properties in that it easily penetrates through most polymeric and ceramic materials and is therefore an exciting new tool to study such materials, which are often opaque at visible frequencies. This transparency of terahertz radiation to non-polar and non-metallic materials motivates the use of terahertz radiation in security screening and industrial quality control applications. As well as being a non-destructive probe of materials in organic molecular crystals such as drug molecules, terahertz radiation has the important property of interacting with vibrational modes that extend across large domains of a crystal lattice. This makes terahertz spectroscopy unique: even though it is possible to excite molecules using a variety of energies, it is only through the careful selection of the low energy in the terahertz range that it is possible to selectively excite crystal lattice vibrations and study in a unique way the presence and nature of interactions between molecules.

A wide range of further significant microscopic physical phenomena can be found in the terahertz regime. Bulk dielectric relaxations and intermolecular motions occur in this spectral range. Critical frequencies for Debye relaxation processes in many liquids fall into the terahertz regime. Pure rotational transitions occur when polar gases are stimulated by terahertz radiation. Moderately doped semiconductors have their plasma frequencies and damping rates defined between 0.1 and 2THz.

Terahertz research continues to mature at rapid pace and commercial instrumentation is now readily available. This has made it possible for the field to expand from a niche technology in semiconductor physics to an exciting mainstream research and sensing platform with a broad variety of applications, from fundamental research to industrial process control.


Dr Axel Zeitler
Head Terahertz Application Group
Department of Chemical Engineering and Biotechnology
University of Cambridge
www.ceb.cam.ac.uk/axel.zeitler

Over the years TeraView has successfully collaborated with Dr. Zeitler at the Department of Chemical Engineering and Biotechnology, University of Cambridge. Dr. Zeitler purchased a TPI imaga 2000 and is currently working with TeraView on advancing the industrial applications of terahertz technology into process control, manufacturing and real-time data generation in industrial conditions.

The collaboration between Dr. Zeitler and TeraView goes back many years as he completed his PhD Thesis Physical Characterisation of Pharmaceutical Solids by Terahertz Pulsed Spectroscopy and Imaging, working with TeraView's Applications Group lead by Dr Phil Taday. 

For a full list of his publications visit: http://www.researcherid.com/rid/B-4885-2008