Reflection properties and defect formation in photonic crystals

Cataloged from PDF version of article.We have investigated the surface reflection properties of a layer‐by‐layer photonic crystal. By using a Fabry–Perot resonant cavity analogy along with the reflection‐phase information of the photonic crystal, we predicted defect frequencies of planar defectstructures. Our predictions were in good agreement with the measureddefect frequencies. Our simple model can also predict and explain double defect formation within the photonic band gap

Micro motion amplification – A Review

Many motion-active materials have recently emerged, with new methods of integration into actuator components and systems-on-chip. Along with established microprocessors, interconnectivity capabilities and emerging powering methods, they offer a unique opportunity for the development of interactive millimeter and micrometer scale systems with combined sensing and actuating capabilities. The amplification of nanoscale material motion to a functional range is a key requirement for motion interaction and practical applications, including medical micro-robotics, micro-vehicles and micro-motion energy harvesting. Motion amplification concepts include various types of leverage, flextensional mechanisms, unimorphs, micro-walking /micro-motor systems, and structural resonance. A review of the research state-of-art and product availability shows that the available mechanisms offer a motion gain in the range of 10. The limiting factor is the aspect ratio of the moving structure that is achievable in the microscale. Flexures offer high gains because they allow the application of input displacement in the close vicinity of an effective pivotal point. They also involve simple and monolithic fabrication methods allowing combination of multiple amplification stages. Currently, commercially available motion amplifiers can provide strokes as high as 2% of their size. The combination of high-force piezoelectric stacks or unimorph beams with compliant structure optimization methods is expected to make available a new class of high-performance motion translators for microsystems

A new detection method for capacitive micromachined ultrasonic transducers

Cataloged from PDF version of article.Capacitive micromachined ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They consist of many small circular membranes that are connected in parallel. In this work, we report; a new detection method for cMUTs. We model the membranes as capacitors and the interconnections between the membranes as inductors. This kind of LC net-work is called an artificial transmission line. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the frequency of the signal through it. By measuring the electrical length of the artificial line at a high RF frequency (in the gigahertz range), the vibrations of the membranes can be detected in a very sensitive manner. Far the devices we measured, we calculated the minimum detectable displacement to be in the order of 10(-5) Angstrom/root Hz with a possible improvement to 10(-7) Angstrom/root Hz

A sensitive detection method for capacitive ultrasonic transducers

Cataloged from PDF version of article.We report a sensitive detection method for capacitive ultrasonic transducers. Detection experiments at 1.6 MHz reveal a minimum detectable displacement around 2.5 x 10(-4) Angstrom/root Hz. The devices are fabricated on silicon using surface micromachining techniques. We made use of microwave circuit considerations to obtain a good displacement sensitivity. Our method also eliminates the dependence of the sensitivity on the ultrasound frequency, allowing the method to be used at low audio frequency and static displacement sensing applications. (C) 1998 American Institute of Physics

Resonant cavity-enhanced detectors embedded in photonic crystals

The resonant-cavity-enhanced (RCE) effect is demonstrated by placing microwave detectors in a layer-by-layer photonic crystal. The output of a network analyzer was used as the microwave source, and the output was fed to a horn antenna to obtain EM waves. The crystal was then replaced in the beam-path of the EM wave, and the electric field inside the cavity was measured by a probe that consisted of a monopole antenna. The output of the antenna was measured by use of two different techniques: network analyzer and microwave detector within the cavity

Resonant cavity enhanced detectors embedded in photonic crystals

Cataloged from PDF version of article.We report a resonant cavity enhanced (RCE) detector built around a three-dimensional photonic band gap crystal. The RCE detector was built by placing a monopole antenna within the localized modes of planar and boxlike defectstructures. The enhanced electric field around these defectstructures were then measured by a microwave detector and a network analyzer. We measured a power enhancement factor of 3450 for planar cavity structures. A Fabry–Perot cavity model was used to understand and predict resonant cavity enhancement in this structure. The tuning bandwidth of the RCE detector extends from 10.5 to 12.8 GHz, which corresponds to the full photonic band gap by the crystal. These RCE detectors have increased sensitivity and efficiency when compared to conventional detectors, and can be used for various applications. © 1998 American Institute of Physic

Guiding and bending of photons via hopping in three-dimensional photonic crystals

A new mechanism to manipulate the propagation of electromagnetic waves in 3D photonic crystals is proposed and demonstrated. Photons hop from one evanescent defect mode to the next one regardless of the direction of propagation. A complete (near 100%) transmission along a straight path and around sharp corners were observed experimentally. The measured dispersion relation of the waveguiding band agrees well with the results of the classical wave analog of tight-binding method

Propagation of photons by hopping: A waveguiding mechanism through localized coupled cavities in three-dimensional photonic crystals

A new type of waveguiding mechanism in three-dimensional photonic band-gap structures is demonstrated. Photons propagate through strongly localized defect cavities due to coupling between adjacent cavity modes. High transmission of the electromagnetic waves, nearly 100%, is observed for various waveguide structures even if the cavities are placed along an arbitrarily shaped path. The dispersion relation of the waveguiding band is obtained from transmission-phase measurements, and this relation is well explained within the tight-binding photon picture. The coupled-cavity waveguides may have practical importance for development of optoelectronic components and circuits. ©2000 The American Physical Society

Towards a procedure-optimised steerable catheter for deep-seated neurosurgery

In recent years, steerable needles have attracted significant interest in relation to minimally invasive surgery (MIS). Specifically, the flexible, programmable bevel-tip needle (PBN) concept was successfully demonstrated in vivo in an evaluation of the feasibility of convection-enhanced delivery (CED) for chemotherapeutics within the ovine model with a 2.5 mm PBN prototype. However, further size reductions are necessary for other diagnostic and therapeutic procedures and drug delivery operations involving deep-seated tissue structures. Since PBNs have a complex cross-section geometry, standard production methods, such as extrusion, fail, as the outer diameter is reduced further. This paper presents our first attempt to demonstrate a new manufacturing method for PBNs that employs thermal drawing technology. Experimental characterisation tests were performed for the 2.5 mm PBN and the new 1.3 mm thermally drawn (TD) PBN prototype described here. The results show that thermal drawing presents a significant advantage in miniaturising complex needle structures. However, the steering behaviour was affected due to the choice of material in this first attempt, a limitation which will be addressed in future work

Tight-Binding Description of the Coupled Defect Modes in Three-Dimensional Photonic Crystals

We have experimentally observed the eigenmode splitting due to coupling of the evanescent defect modes in three-dimensional photonic crystals. The splitting was well explained with a theory based on the classical wave analog of the tight-binding (TB) formalism in solid state physics. The experimental results were used to extract the TB parameters. A new type of waveguiding in a photonic crystal was demonstrated experimentally. A complete transmission was achieved throughout the entire waveguiding band. We have also obtained the dispersion relation for the waveguiding band of the coupled periodic defects from the transmission-phase measurements and from the TB calculations