Active control of hysteretic base-isolated structures via delayed signals

Postprint (published version

Combinational logic for generating gate drive signals for phase control rectifiers

Control signals for phase-delay rectifiers, which require a variable firing angle that ranges from 0 deg to 180 deg, are derived from line-to-line 3-phase signals and both positive and negative firing angle control signals which are generated by comparing current command and actual current. Line-to-line phases are transformed into line-to-neutral phases and integrated to produce 90 deg phase delayed signals that are inverted to produce three cosine signals, such that for each its maximum occurs at the intersection of positive half cycles of the other two phases which are inputs to other inverters. At the same time, both positive and negative (inverted) phase sync signals are generated for each phase by comparing each with the next and producing a square wave when it is greater. Ramp, sync and firing angle controls signals are than used in combinational logic to generate the gate firing control signals SCR gate drives which fire SCR devices in a bridge circuit

Virtual-detector synthetic aperture focusing technique with application in in vivo photoacoustic microscopy

In this study, we introduce a synthetic aperture focusing technique which employs a virtual detector concept, combined with coherence weighting, to extend the depth of focus for an in-vivo photoacoustic microscopy system. This technique treats the transducer's focal point as a virtual point detector of photoacoustic signals, delays adjacent scan lines relative to the virtual detector, and then sums the delayed signals to achieve focusing in the out-of-focus region. In addition, a coherence factor among the delayed signals for each synthesized imaging point is used as a weighting factor to further improve the focusing quality. Images of an Intralipid phantom containing a carbon fiber show how this technique improves the -6 dB lateral resolution from 49-379 μm to 46-53 μm and increases the SNR by 0-29 dB, depending on the distance from the ultrasonic focal point. In vivo experiments show that this technique also provides a clearer tumorassociated angiogenesis in the mouse's scalp. The extended depth of focus for the photoacoustic microscopy system enables 3D reconstruction of the vascular network for the study of tumor angiogenesis