In many commercial, industrial, and military applications, supplying power to electronics through a thick metallic barrier without compromising its structural integrity would provide tremendous advantages over many existing barrier-penetrating techniques. The Faraday shielding presented by thick metallic barriers prevents the use of electromagnetic power-transmission techniques. This work describes the electrical optimization of continuouswave power delivery through thick steel barriers using ultrasound. Ultrasonic channels are formed by attaching pairs of coaxially-aligned piezoelectric transducers to opposite sides of thick steel blocks. The thickness of the steel considered is on the order of, or greater than, one quarter wavelength of the acoustic power signal inside of steel, requiring the use of wave propagation theory to properly analyze the system. A characterization and optimization methodology is presented which measures the linear two-port electrical scattering parameters of the transducersteel-transducer channel. Using these measurements, the simultaneous conjugate impedance-matching conditions at both transducers are calculated, and electrical matching-networks are designed to optimize the power transfer from a 50Ω power amplifier on one side of the steel block to a 50Ω load on the opposite side. In addition, the impacts of, and interactions between, transducer and steel geometries are discussed, and some general guidelines for selecting their relationships are presented. Measurements of optimized systems using transducers designed to resonate at 1 MHz with diameters from 12.7 mm to 66.7 mm, and steel block thicknesses from 9.5 mm to 63.5 mm, reveal power transfer efficiencies as high as 55%, and linear delivery of 81 watts through an optimized channel.
This paper demonstrates automatic recognition of vocalizations of four common bird species (herring gull [Larus argentatus], blue jay [Cyanocitta cristata], Canada goose [Branta canadensis], and American crow [Corvus brachyrhynchos]) using an algorithm that extracts frequency track sets using track properties of importance and harmonic correlation. The main result is that a complex harmonic vocalization is rendered into a set of related tracks that is easily applied to statistical models of the actual bird vocalizations. For each vocalization type, a statistical model of the vocalization was created by transforming the training set frequency tracks into feature vectors. The extraction algorithm extracts sets of frequency tracks from test recordings that closely approximate harmonic sounds in the file being processed. Each extracted set in its final form is then compared with the statistical models generated during the training phase using Mahalanobis distance functions. If it matches one of the models closely, the recognizer declares the set an occurrence of the corresponding vocalization. The method was evaluated against a test set containing vocalizations of both the 4 target species and 16 additional species as well as background noise containing planes, cars, and various natural sounds.
Traditionally, power transfer through thick metallic barriers has required physical penetrations and wire feed-throughs, which reduces structural integrity and limits the environmental isolation provided by the barrier. The Faraday shielding presented by these barriers, however, prevents efficient transfer of electromagnetic power, limiting many RF coupling techniques. More recently, the use of ultrasound has been shown as an effective non-destructive technique for transmitting large amounts of power (100s of watts) through solid metallic mediums. By using two coaxially aligned piezoelectric transducers loaded onto opposite sides of the barrier through an acoustic couplant, an ultrasonic channel is formed through which efficient power delivery is possible. This work presents finite element modeling and simulations that help characterize the impacts of many mechanical design factors on the power transfer efficiency of these ultrasonic channels, including: transducer-wall coupling effects, transducer and wall resonance modes, transducer dimensions, and barrier composition and dimensions. Physical channel measurements are also presented to show the strong correlation between the finite element simulations and the systems modeled.
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