Direct comparison of the gravimetric responsivities of ZnO-based FBARs and SMRs

Film bulk acoustic resonators (FBARs) and solidly mounted resonators (SMRs) have the potential to significantly improve upon the sensitivity and minimum detection limit of traditional gravimetric sensors based on quartz crystal microbalances (QCMs) and surface acoustic wave resonators (SAWs). To date, neither FBAR nor SMR devices have been demonstrated to be superior to the other; hence the choice between them depends primarily on the users' ability to design/fabricate membranes and/or Bragg reflectors. In this work, it is shown that identically designed FBAR and SMR devices resonating at the same frequency exhibit different responsivities to mass loadings, Rm, and that the SMRs are less responsive than the FBARs. For the specific device design and resonant frequency (~2 GHz) of the resonators presented here, the FBARs' mass responsivity is ~20% greater than that of the SMRs', and although this value is not universal for all possible device designs, it clearly shows that FBAR devices should be favoured over SMRs in gravimetric sensing applications where the FBARs' fragility is not an issue. Numerical calculations based on Mason's model offer an insight into the physical mechanisms behind the greater FBARs responsivity, and it was shown that the Bragg reflector has an effect on the acoustic load at one of the facets of the piezoelectric films which is in turn responsible for the SMRs' lower responsivity to mass loadings. © 2013 Elsevier B.V.

A theory of slow feature analysis for transformation-based input signals with an application to complex cells

We develop a group-theoretical analysis of slow feature analysis for the case where the input data are generated by applying a set of continuous transformations to static templates. As an application of the theory, we analytically derive nonlinear visual receptive fields and show that their optimal stimuli, as well as the orientation and frequency tuning, are in good agreement with previous simulations of complex cells in primary visual cortex (Berkes and Wiskott, 2005). The theory suggests that side and end stopping can be interpreted as a weak breaking of translation invariance. Direction selectivity is also discussed. © 2011 Massachusetts Institute of Technology.

3 Gbit/s LED-based step index plastic optical fiber link using multilevel pulse amplitude modulation

Multilevel PAM is investigated for a LED-based SI-POF link. Using PAM-8, transmission at a record 3 Gbit/s is demonstrated for a maximum length of 25 m step index POF with offline post-receiver processing. © 2013 OSA.

Characterization of the surface acoustic wave devices based on ZnO/nanocrystalline diamond structures

Nanocrystalline ZnO films with strong (0002) texture and fine grains were deposited onto ultra-nanocrystalline diamond (UNCD) layers on silicon using high target utilization sputtering technology. The unique characteristic of this sputtering technique allows room temperature growth of smooth ZnO films with a low roughness and low stress at high growth rates. Surface acoustic wave (SAW) devices were fabricated on ZnO/UNCD structure and exhibited good transmission signals with a low insertion loss and a strong side-lobe suppression for the Rayleigh mode SAW. Based on the optimization of the layered structure of the SAW device, a good performance with a coupling coefficient of 5.2% has been realized, promising for improving the microfluidic efficiency in droplet transportation comparing with that of the ZnO/Si SAW device. An optimized temperature coefficient of frequency of -23.4 ppm°C-1 was obtained for the SAW devices with the 2.72 μm-thick ZnO and 1.1 μm-thick UNCD film. Significant thermal effect due to the acoustic heating has been redcued which is related to the temperature stability of the ZnO/UNCD SAW device. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhancement of microfluidic efficiency with nanocrystalline diamond interlayer in the ZnO-based surface acoustic wave device

Ultra-smooth nanocrystalline diamond (UNCD) films with high-acoustic wave velocity were introduced into ZnO-based surface acoustic wave (SAW) devices to enhance their microfluidic efficiency by reducing the acoustic energy dissipation into the silicon substrate and improving the acoustic properties of the SAW devices. Microfluidic efficiency of the ZnO-based SAW devices with and without UNCD inter layers was investigated and compared. Results showed that the pumping velocities increase with the input power and those of the ZnO/UNCD/Si devices are much larger than those of the ZnO/Si devices at the same power. The jetting efficiency of the droplet was improved by introducing the UNCD interlayer into the ZnO/Si SAW device. Improvement in the microfluidic efficiency is mainly attributed to the diamond layer, which restrains the acoustic wave to propagate in the top layer rather than dissipating into the substrate. © 2013 Springer-Verlag Berlin Heidelberg.

Sensors based on SAW and FBAR technologies

Over the last few years a number of sensing platforms are being investigated for their use in drug development, microanalysis or medical diagnosis. Lab-on-a-chip (LOC) are devices integrating more than one laboratory functions on a single device chip of a very small size, and typically consist of two main components: microfluidic handling systems and sensors. The physical mechanisms that are generally used for microfluidics and sensors are different, hence making the integration of these components difficult and costly. In this work we present a lab-on-a-chip system based on surface acoustic waves (for fluid manipulation) and film bulk acoustic resonators (for sensing). Coupling surface acoustic waves into liquids induces acoustic streaming and motion of micro-droplets, whilst it is well-known that bulk acoustic waves can be used to fabricate microgravimetric sensors. Both technologies offer exceptional sensitivity and can be fabricated from piezoelectric thin films deposited on Si substrates, reducing the fabrication time/cost of the LOC devices. © 2013 SPIE.

A single FBAR-based temperature and pressure sensors

A novel temperature and pressure sensor based on a single film bulk acoustic resonator (FBAR) is designed. This FBAR support two resonant modes, which response opposite to the change of temperature. By sealed the back cavity of a back-trench membrane type FBAR with silicon wafer, an on-chip single FBAR sensor suitable for measuring temperature and pressure simultaneously is proposed. For unsealed device, the experimental results show that the first resonant mode has a temperature coefficient of frequency (TCF) of 69.5ppm/K, and the TCF of the second mode is -8.1ppm/K. After sealed the back trench, it can be used as a pressure sensor, the pressure coefficient of frequency (PCF) for the two resonant mode is -17.4ppm/kPa and -6.1 ppm/kPa respectively, both of them being more sensitive than other existing pressure sensors. © 2013 Trans Tech Publications Ltd, Switzerland.

3 Gbit/s LED-based step index plastic optical fiber link using multilevel pulse amplitude modulation

Multilevel PAM is investigated for a LED-based SI-POF link. Using PAM-8, transmission at a record 3 Gbit/s is demonstrated for a maximum length of 25 m step index POF with offline post-receiver processing. © 2013 OSA.

Evaluation of bimetallic catalysts for the growth of carbon nanotube forests

We systematically study the growth of carbon nanotube forests by chemical vapor deposition using evaporated monometallic or bimetallic Ni, Co, or Fe films supported on alumina. Our results show two regimes of catalytic activity. When the total thickness of catalyst is larger than nominally 1nm, bimetallic catalysts tend to outperform the equivalent layers of a single metal, yielding taller forests of multi-walled carbon nanotubes (CNTs). In contrast, for layers thinner than ~1nm, bimetallic catalysts are notably less active than individually. However, the amount of small diameter and single-walled CNTs is significantly increased. This possible transition at ~1nm might be related to different catalyst composition after annealing, depending whether or not the films overlap during evaporation and alloy during catalyst formation. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-power ultrafast solid-state laser using graphene based saturable absorber

We demonstrate a graphene based saturable absorber mode-locked Nd:YVO4 solid-state laser, generating ~14nJ pulses with ~1W average output power. This shows the potential for high-power pulse generation. © 2011 Optical Society of America.

High-power ultrafast solid-state laser using graphene based saturable absorber

We demonstrate a graphene based saturable absorber mode-locked Nd:YVO4 solid-state laser, generating ~14nJ pulses with ~1W average output power. This shows the potential for high-power pulse generation. © 2011 Optical Society of America.

Molecular cloning and characterization of common carp (Cyprinus carpio L.) TCR gamma and CD3 gamma/delta chains

Partial cDNA sequences of TCR gamma and CD3 gamma/delta were isolated from the thymus of common carp (Cyprinus carpio L.) by the method of suppression subtractive hybridization (SSH). Subsequently the full length cDNAs of carp TCR gamma and CD3 gamma/delta were obtained by means of 3' RACE and 5' RACE, respectively. The full length of carp TCR gamma chain is 1368 bp and encodes 326 amino acids including a signal peptide region of 19 amino acids and a transmembrane region of 23 amino acids at the C-terminal region from aa 291 to 313. The V region of carp TCR gamma contains 109 amino acids, the core motif FGXG in J segment was also found in carp TCR gamma. The C region of carp TCR gamma contains the characteristic CX6PX6WX45C motif. The CP region of carp TCR C gamma contains 37 amino acids. The full length of carp CD3 gamma/delta is 790 bp and encodes 175 amino acids including a signal peptide region of 17 amino acids and a transmembrane region of 23 amino acids from aa 93 to 115. Similar to other known CD3 gamma/delta s, four cysteine residues in the extracellular domain and an immunoreceptor tyrosine-based activation motif ITAM (YxxL/Ix6-8YxxL/I) in the intracellular domain are also included in carp CD3 gamma/delta. Differing from other known CD3 gamma/delta s, carp CD3 gamma/delta tacks the CXXCXE motif in the extracellular domain. RTPCR analysis demonstrated that the expression of TCR gamma gene was mainly in the thymus and gill of 6-month carp, but in 18-month carp, TCR gamma gene was detected in all the examined tissues. The expression of CD3 gamma/delta gene was detected in all examined tissues of 6 and 18-month carp; among them, the highest expression level was in the thymus of 6-month carp. In situ hybridization showed that CD3 gamma/delta-expressing cells were widely distributed in the head kidney, spleen and kidney of carp, whereas in the thymus, they were densely distributed in the lymphoid outer zone and scattered in the epithelioid inner zone. (c) 2007 Published by Etsevier Ltd.

High-power ultrafast solid-state laser using graphene based saturable absorber

We demonstrate a graphene based saturable absorber mode-locked Nd:YVO4 solid-state laser, generating ~14nJ pulses with ~1W average output power. This shows the potential for high-power pulse generation. © 2011 Optical Society of America.