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A simple method for measuring the directivity of an ultrasound receiver is described. The method makes use of a custom-designed laser ultrasound source which generates a large diameter (>1 cm) broadband monopolar plane wave with a continuous frequency content extending from $\le 330~{\mathrm {kHz}}$ to $\approx 80~{\mathrm {MHz}}$ . The plane wave is highly uniform in amplitude (±5% over >8...
We explore the frequency dependence of piezoceramic disc transducers bonded to plates. For some transducer dimensions, the frequency response shows a sharp peak. This behavior is inconsistent with the use of short pulses or broadband chirps for flaw localization. We use finite element simulation to show that the highly resonant behavior is caused by a high-strain region immediately beneath the transducer...
To reduce harmonics in the AC voltage signal, a precise bound-pass RC filter named `waveform purer' is designed with a double-T network in the negative feedback loop. This filter keeps fundamental frequency unvaried, in both phase and amplitude, but greatly reducing harmonics. Related principles are discussed, including the `bridge balance principle' of double-T network and the `three time constants...
The state of the art in millimeter-wave detection and imaging using Sb-heterostructure detectors has been advanced recently with demonstration of excellent low-noise performance through the use of very thin (< 15 Aring) tunnel barriers. This reduction in tunnel barrier thickness improves the noise by reducing the thermal noise associated with the junction resistance, Rj. However, the thinner barrier...
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