Input impedance matching of acoustic transducers operating at off-resonant frequencies

The input impedance matching technique of acoustic transducers at off-resonant frequencies is reported. It uses an inherent impedance property of transducers and thus does not need an external electric matching circuit or extra acoustic matching section. The input electrical equivalent circuit includes a radiation component and a dielectric capacitor. The radiation component consists of a radiation resistance and a radiation reactance. The total reactance is the sum of the radiation reactance and the dielectric capacitive reactance. This reactance becomes zero at two frequencies where the impedance is real. The transducer size can be properly chosen so that the impedance at one of the zero-crossing frequencies is close to 50 Ω, the output impedance of signal generators. At this off-resonant operating frequency, the reflection coefficient of the transducer is minimized without using any matching circuit. Other than the size, the impedance can also be fine tuned by adjusting the thickness of material that bonds the transducer plate to the substrates. The acoustic impedance of the substrate and that of the bonding material can also be used as design elements in the transducer structure to achieve better transducer matching. Lead titanate piezoelectric plates were bonded on Lucite, liquid crystal polymer (LCP), and bismuth (Bi) substrates to produce various transducer structures. Their input impedance was simulated using a transducer model and compared with measured values to illustrate the matching principle.     

Coupling-loss reduction of a vertically coupled microring resonator filter by spot-size-matched busline waveguides

To improve the input-output coupling loss of a vertically coupled microring resonator filter, we fabricated microring resonators on an antiresonant reflecting optical waveguide (ARROW) with a large spot size and on the rectangular busline waveguide with a spot-size transformer. The spot size and the tapered structure were optimally designed from the viewpoint of spot-size matching to single-mode fibers and the reduction of radiation loss. Clear dropping responses were demonstrated for the ARROW-based microring resonator filters, and the coupling loss was successfully reduced by 22 dB.     

Binary image encryption based on interference of two phase-only masks

Optical image encryption based on interference has attracted a lot of attention recently. The technique employs two pure phase masks derived from the complex field of the image in the Fresnel diffraction domain. The image decryption procedure can be carried out by inverse Fresnel transformation of the summation of two pure phase masks. However, the silhouette of the original image, which is recovered by either of the two phase-only masks, impedes the application of this technique. In this paper, a very simple method for binary image encryption based on interference of two phase-only masks is proposed without any silhouette problem. The binary image in combination with a random phase mask is separated into two phase-only masks directly, and the decryption by summation of the two masks can be performed digitally or optically. In this paper, the encryption and decryption processes are analyzed, after which both the optical simulation and the experimental results based on single-beam holography are given to demonstrate the feasibility of the encryption method. As information nowadays is mainly digitized into binary codes, the proposed encryption method may find applications in the information processing field.     

Simultaneous enhanced photon capture and carrier generation in Si solar cells using Ge quantum dot photonic nanocrystals

We propose a novel solar cell structure with photonic nanocrystals coupled to quantum dots (QDs) for advanced management of photons and carriers. The photonic nanocrystals at the surface create an extra interaction between the photons and the QDs, which promotes light trapping. Photo-generated carriers can be efficiently transported by preparing vertically aligned QDs with electronic coupling. Implementation of the proposed structure was realized in crystalline Si solar cells with Ge QDs by development of a simple and practical formation method based on a wet chemical process without any lithography techniques. The wet process utilizes a periodically modulated etching rate induced by self-organized Ge QDs. The effectiveness of the proposed solar cell was demonstrated by the marked increase of the absolute conversion efficiency when compared with the control crystalline Si solar cells. It is found that light trapping by the photonic nanocrystals has a larger contribution to the efficiency improvement than the contributions from the carrier transport of the vertically aligned QDs.     

Using H3+ and H2D+ as probes of star-forming regions

The H3+ and H2D+ ions are important probes of the physical and chemical conditions in regions of the interstellar medium where new stars are forming. This paper reviews how observations of these species and of heavier ions such as HCO+ and H3O+ can be used to derive chemical and kinematic properties of nearby pre-stellar cores and the cosmic ray ionization rate towards more distant regions of high-mass star formation. Future prospects in the field are outlined at the end.     

Direct growth of core-shell SiC-SiO(2) nanowires and field emission characteristics

A simple, direct synthesis method was used to grow core-shell SiC-SiO(2) nanowires by heating NiO-catalysed silicon substrates. A carbothermal reduction of WO(3) provided a reductive environment and carbon source to synthesize crystalline SiC nanowires covered with SiO(2) sheaths at the growth temperature of 1000-1100?°C. Transmission electron microscopy showed that the SiC core was 15-25?nm in diameter and the SiO(2) shell layer was an average of 20?nm in thickness. The thickness of the SiO(2) shell layer could be controlled using hydrofluoric acid (HF) etching. Field emission results of core-shell SiC-SiO(2) and bare SiC nanowires showed that the SiC nanowires coated with an optimum SiO(2) thickness (10?nm) have a higher field emission current than the bare SiC nanowires.     

Determination of small angular displacement by moiré fringes of matched radial-parallel gratings

We investigate the properties of the moiré fringes of matched radial-parallel (MRP) gratings that are useful for the fine visual indication of angular displacements. Moiré patterns formed by overlapping two different MRP gratings of angular pitches, P(theta) and P(theta)? (相似文献   

Microscopic measurement of cellular infiltration in the rheumatoid arthritis synovial membrane: a comparison of semiquantitative and quantitative analysis

BACKGROUND: A significant proportion of burn patients with inhalation injuries incur difficulties with airway protection, dysphagia, and aspiration. In assessing the need for intubation in burn patients, the efficacy of fiberoptic laryngoscopy was compared with clinical findings and the findings of diagnostic tests, such as arterial blood gas analysis, measurement of carboxyhemoglobin levels, pulmonary function tests, and radiography of the lateral aspect of the neck. OBJECTIVE: To determine if these patients were at risk for aspiration or dysphagia, barium-enhanced fluoroscopic swallowing studies were performed. DESIGN: Prospective study. SETTINGS: Burn intensive care unit in an academic tertiary referral center. MAIN OUTCOME MEASURES: Need for endotracheal intubation and potential for aspiration. RESULTS: Six (55%) of 11 patients had clinical findings and symptoms that indicated, under traditional criteria, endotracheal intubation for airway protection. Visualization of the upper airway with fiberoptic laryngoscopy obviated the need for endotracheal intubation in all 11 patients. These patients also failed to evidence an increased risk of aspiration or other swallowing dysfunction. CONCLUSIONS: In comparison with other diagnostic criteria, fiberoptic laryngoscopy allows differentiation of those patients with inhalation injuries who, while at risk for upper airway obstruction, do not require intubation. These patients may be safely observed in a monitored setting with serial fiberoptic examinations, thus avoiding the possible complications associated with intubation of an airway with a compromised mucosalized surface. In these patients, swallowing abnormalities do not manifest.