Ionica Cristea

Development of SAW filters based on GaPO 4

The results of research into Surface Acoustic Wave — SAW — devices have been recognized for their efficiency and versatility in the electrical signals processing [1], [3]. Actual progress in the industrial application of piezoelectric materials such as Lithium Niobate (LiNbO<inf>3</inf>), Langasite (LGS), Lanthanum-Gallium Silicate La<inf>3</inf>Ga<inf>5</inf>SiO<inf>14</inf> and Gallium Orthophosphate (GaPO<inf>4</inf>), allows the manufacturing of devices with performances, which overcome the limits obtained with quartz crystals [2]. The single crystal materials have a long term high stability — near to infinite — and moreover, some of these have an excellent behavior with temperature variation, as is the case of GaPO<inf>4</inf> [4]. Today, GaPO<inf>4</inf> with its properties is by far the best suited piezoelectric material to be used in sensor applications for machine monitoring and pressure measurements, at high temperatures. SAW microdevices based on GaPO<inf>4</inf> operate at temperatures of up to 800°C. We have developed five SAW filters based on GaPO<inf>4</inf>. The paper describes the steps to solve the problems regarding the use of GaPO<inf>4</inf> substrates for the development of SAW filters. In the 3rd chapter of the paper are given some experimental results obtained with Network Analyzer.

Recent developments in surface acoustic wave sensors

Surface Acoustic Wave sensors - SAW have been recognized for their efficiency and versatility in the electrical signals processing. The majority of results reported till the present, regarding SAW sensors, have been used Rayleigh SAW, on the principle of delay line. Reflexive delay line can be used for passive sensing and remote control. In the paper is presented a short introduction regarding the actual level of SAW devices development and their applications. A comparative study in connection with diversity of piezoelectric materials used for SAW devices manufacturing, (Quartz, LiNbO3, LGS with emphasis on GaPO4) evidence the advantages of GaPO4. The development directions of SAW sensor devices are shown: telecommunication, RFID SAW systems, SAW devices for remote monitoring, SAW sensors for early cancer diagnostics. Some applications of SAW sensor devices with GAPO4 are presented in the directions: remote monitoring and identification of gas. Some conclusions regarding trends in the development of SAW sensor devices are presented in the end of the work.

Comparative study of GaPO 4 , langasite, and LiNbO 3 properties with application in Surface Acoustic Waves microdevices

The results of research into Surface Acoustic Wave — SAW — devices have been recognized for their efficiency and versatility in the electrical signals processing. Actual progress in the industrial application of piezoelectric materials such as Lithium Niobate (LiNbO3), Langasite (LGS), Lanthanum-Gallium Silicate La3Ga5SiO14 and Gallium Orthophosphate (GaPO4), allows the manufacturing of devices with performances, which overcome the limits obtained with quartz crystals. One of the most important applications of SAW microdevices is passively, wirelessly interrogating systems. Today, GaPO4 with its properties is by far the best suited piezoelectric material to be used in sensor applications for machine monitoring and pressure measurements, at high temperatures. SAW microdevices based on GaPO4 operate at temperatures of up to 800°C. In this paper is presented a short introduction regarding the actual level of SAW microdevices development. We discuss our investigations as a comparative study of GaPO4, Langasite, and LiNbO3, regarding their properties. Each has unique strengths and weaknesses giving advantages in different applications. Conclusions regarding trends in the development of SAW sensor devices with novel materials are presented in the end of the work.

Characterization of chemical microsensors in SAW systems

Between other sensing and identification technologies that of Surface Acoustic Waves, (SAW), is a unique sensing system. The principal advantage to most SAW systems is that they can use two or three SAW sensors and compare the measurements between them, providing a good accuracy. We have carried out the design of both piezoelectric substrate and interdigital transducers, (IDTs), and has tested them in a delay line mode operation. The measurement of changes in the surface waves characteristics were materialized by applying of a radio frequency electric field to the piezoelectric crystal by means of IDTs. The finger width of the IDTs was measured by high accuracy optical coherent method. The results are presented in the work. The potential development of microsensors as an array of four or five miniature sensors, sensitive to Werent chemicals may be used as mobile chemical detecting units carried by remote control vehicles to the site chemical contamination.

Development of optoelectronics in Politehnica University of Bucharest

Optoelectronics is facing with an ever dynamic increasing in our lives. We feel a growing demand for specialists in design and operation of optoelectronic systems. In accord with this demand Politehnica University of Bucharest (PUB) has introduced optoelectronics curricula since 1992 year. The theoretical courses are covered by laboratory activities, to provide the students with actual experience of optoelectronic systems. Some experiments are presented in this paper. To get a good efficiency of experiments, the student should study Laboratory guide manual, before entering the laboratory. PUB in collaboration with SPIE organization is intending to develop an integrated optoelectronics laboratory for education ofoptoelectronics specialization students with the following principles: define the educational goals and experimental laboratory courses to fulfill the objectives, design the instrumentation and systems to enable practical, experimental investigation and measurements; elaboration of experimental algorithms and laboratory guide for students, which include exercises and problems with responses connected with real world of optoelectronics specialists demand. This paper focuses on the presentation of laboratory courses that would be developed a meaningful understanding of optoelectronic devices, and systems.

Laser Characterization of the Periodic Line-Space Micro/Nano Structures

Recent advances in micro/nanotechnology devices have demonstrated periodic line-space structure with dimensions of order less than ten nm. Laser scatterometry is a noncontact measurement method for collecting and analyzing of scattered light from the structures. Methods using laser scatterometry can characterize periodic line-space structures. The objective of this paper is three-fold: (1) characterization of laser beam quality which is used for optical metrology; (2) optical characterization of periodic line-space structures; (3) some conclusions regarding experimental results are presented.

Terpolymer polyrotaxanes: a promising supramolecular system as electron-transporting materials for optoelectronics

Optical, electrochemical and surface-morphological properties of three terpolymer polyrotaxanes (1a, 1b and 1c) composed of 2,7-dibromo-9,9-dicyanomethylenefluorene encapsulated into γ-cyclodextrin (γCD), β- or γ-persilylated cyclodextrin (PS-γCD, PS-γCD) cavities (acceptor) and 4,4′-dibromo-4′′-methyltriphenylamine (donor) randomly distributed into 9,9-dioctylfluorene conjugated chains have been evaluated and compared to those of the reference 1. The role of the encapsulation on the thermal stability, solubility, film forming ability and transparency was also investigated. High fluorescence efficiency, almost identical normalized absorbance maximum in solution and solid-states of 1a, 1b and 1c provides the lower aggregation tendency. The fluorescence lifetimes (τ) of 1a, 1b and 1c follow a mono-exponential decay with a value τ = 1.11, 1.03 and 1.14 ns, compared with the neat 1, where a bi-exponential decay was identified. AFM studies reveal a smooth and homogenous surface morphology for polyrotaxanes than that of the reference. The electrochemical data provided that the investigated compounds exhibited n- and p-doping processes. The HOMO/LUMO energy levels 1a, 1b, 1c and 1 and in combination with the work function of anodic ITO glass substrates coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (-5.2 eV) and cathodic Ca (-2.8 eV) or Al (-2.2 eV) indicate that the compounds are electrochemically accessible as electron-transporting materials.

Antenna for passive RFID tags

Minuscule devices, called RFID tags are attached to objects and persons and emit information which positioned readers may capture wirelessly. Many methods of identification have been used, but that of most common is to use a unique serial number for identification of person or object. RFID tags can be characterized as either active or passive [1,2]. Traditional passive tags are typically in “sleep” state until awakened by the reader’s emitted field. In passive tags, the reader’s field acts to charge the capacitor that powers the badge and this can be a combination of antenna and barcodes obtained with SAW( Surface Acoustic Wave) devices [1,2,3] . The antenna in an RFID tag is a conductive element that permits the tag to exchange data with the reader. The paper contribution are targeted to antenna for passive RFID tags. The electromagnetic field generated by the reader is somehow oriented by the reader antenna and power is induced in the tag only if the orientation of the tag antenna is appropriate. A tag placed orthogonal to the reader yield field will not be read. This is the reason that guided manufacturers to build circular polarized antenna capable of propagating a field that is alternatively polarized on all planes passing on the diffusion axis. Passive RFID tags are operated at the UHF frequencies of 868MHz (Europe) and 915MHz (USA) and at the microwave frequencies of 2,45 GHz and 5,8 GHz . Because the tags are small dimensions, in paper, we present the possibility to use circular polarization microstrip antenna with fractal edge [2].

Preparation and characterization of Ga2O3and GaN nanoparticles

In this communication, we present results on preparation of GaN nanoparticles by conversion of Ga2O3 nanocrystals in a flow of NH3 and H2. The monoclinic Ga2O3 nanoparticles have been prepared by hydrothermal method with gallium nitrate and sodium hydroxide as precursors. Ga2O3 nanowires are produced with increasing the duration of the hydrothermal process up to 24 hours. The production of β-phase Ga2O3 has been confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. According to XRD, Raman and FTIR spectra, wurtzite type GaN nanocrystals with an average size of 28.6 nm are obtained by nitridation of Ga2O3 nanoparticles. Doping of Ga2O3 nanomaterial with Eu3+ ions in the hydrothermal process is demonstrated, and the emission spectra of this Eu-doped nanomaterial are compared with those of Eu-doped nanoparticles prepared previously by solid state reactions.

Atomic absorption spectrophotometry for the analysis of metal contents in tobacco samples

Spectroscopy is one of the most important tools for studying the structures of atoms and molecules. Paper underlines the procedures required for the determination of metal contents in tobacco samples. Sampling procedures, sample preparation, and atomic absorption instrumentation requirements are presented. Particular attention is given to the determination of metals as Pb, Cr, Li, Cu, Au, Co using atomic absorption spectroscopy. A dual-beam Atomic Absorption Spectrophotometer was used for the measurements. The concentration of these metals in five different tobacco samples is given.