Alexandru Craciun

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.

Optical measurements for excitation of CdTe quantum dots

The paper presents the experimental results obtained using a laboratory setup installation for fluorescence excitation of CdTe QDs used as biomarkers for clinical diagnostics. Quantum Dots (QDs) made of Cadmium Telluride (CdTe), are highly fluorescent and they are used as robust biomarkers. Generally, QDs are referred to as the zero-dimensional colloidal crystals that possess strong size dependence and multi-colored luminescence properties. Along with its intrinsic features, such as sharp and symmetric emission, photo-stability and high quantum yields, QDs play a vital role in various applications, namely the identification of the chemical moieties, clinical diagnostics, optoelectronics, bio-imaging and bio-sensing1.

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.

Integration of optoelectronics and SAW technology

The number of radio frequency surface acoustic wave (SAW) filters produced presently exceeds 3 billion per year. The demand for high-frequency SAW filters for telecommunications and remote sensing, has led to extensive research, focusing on new SAW microdevices. SAW devices have shown compact structures, small size, low cost, high sensitivity and fast response. The need of miniaturized systems, with high sensitivity and low energy has motivated the need to integrate on the same substrate all the structure of SAW device and connecting electronic circuits. As a consequence, many types of methods of both constructive and operating characterization of SAW devices have been developed. This paper provides a short introduction regarding the developed level of SAW microdevices and describes the results of literature investigation research of optoelectronic techniques for constructive characterization of SAW microdevices. Further research will be done into the determination of SAW parameters such as the amplitude of surface wave, the velocity of wave propagation on the surface of the piezoelectric substrate. Substrates of quartz, lithium tantalite (LiTaO3) and lithium niobate (LiNbO3), are piezoelectric materials commonly used in manufacturing of SAW devices, but these materials are not compatible with the integrated circuit (IC) technology. Three optoelectronic measurement techniques are known for detection of surface acoustic waves: diffraction grating technique, the knife-edge technique, and the detection of ultrasonic vibrations using optical interferometry. The research work given in this paper concentrates on describing of optoelectronic techniques used for constructive characterization of SAW microdevices. Finally, we try to draw some conclusion where: optoelectronic techniques are predicted to be one of the fundamental measurement methods for measurement of future SAW microdevices.

Method for the quantitative determination through fluorescence of biosurfaces

In recent years, the development of new and simple methods for characterization of biosurfaces for rapid detection of acute myocardial infarction (AMI) is a constant concern in the immunochromatographic tests [3]. The method used in the present assays can easily detect AMI markers within 15 minutes, with moderate sensitivity and specificity. The article shows a quick method of characterization with help of the fluorescence detection using quantum dots (QDs) of cadmium telluride (CdTe), binding molecules with biological samples [2,4]. This method provides a faster AMI biomarker detection and can have higher sensitivity and specificity. For quantitative determination through fluorescent of biosurfaces we realized both biosurfaces and apparatus of fluorescence.

Optoelectronic module for quantification of biomarkers based on fluorescence

The paper presents an optoelectronic module for quantification of biomarkers based on fluorescence, intended to be used for detection of acute myocardial infarction (AMI). The basic principles of fluorescence microscopy have been used for designing this module, taking into account that the fluorophores used to mark the detection antibodies are quantum dots (QD) made of cadmium telluride (CdTe) with the emission wavelengths in the range of 510 nm - 700 nm and that excitation wavelengths needed are around either 405 nm or 475 nm.

Recent developments on surface acoustic wave (SAW) sensors for harsh conditions

The results of research into Surface Acoustic Waves (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 piezoelectric performances, which overcome the limits obtained with quartz crystals. 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. 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 micro devices based on GaPO4 operate at temperatures of up to 8000C. For a particular case, of harsh-environment applications, additional challenges need to be overcome, relating to substrate integrity and operation, thin film electrode fabrication, device packaging, and sensor interrogation. This paper reviews the novel progres in the area of (SAW) sensors for harsh conditions.

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].

Characterization of SAW filters based on GaPO4

The results of research into Surface Acoustic Wave – SAW – filters have been recognized for their efficiency and versatility in the electrical signals processing 1,3. Gallium Orthophosphate (GaPO4) is a relative new material, which has a long term high stability and, moreover, has an excellent behavior with temperature variation 2,3. The characterization of SAW filters based on GaPO4 is uses the comparative analysis of simulated results of parameters, with different software programs, which were developed for designing of these filters. Simulation covers the determination and analysis of the characteristics of this filter, namely, mechanical parameters (constructive) and operational parameters in comparison with the design data. In order to obtain the parameters of SAW filters we have used the algorithms and software for modelling, simulation. The paper presents several versions of software programs, in Matlab and Microsoft Visual C#, for the design of GaPO4 SAW filters and their interpretation. These modeling, simulations were performed successively by each program, until we set the parameters of SAW filter. By the comparison of the data obtained with each program, we have improved the constructive dimensions of fingers, we obtained the desired parameters. With this data, we realised SAW filters based on GaPO4, and with the help of the Network Analyzer we measured parameters of the filter, which are presented in the paper2,10.