College of Engineering

ECE Ph.D. Research Presentation: Mr. Robert C. Randall

Date(s): 12/7/2012 10:40 AM - 12/7/201211:10 AM
Location: Lester W. Cory Conference Room, SENG, Room 213A
Contact: Honggang Wang 508-999-8469

Topic: “Motional Current Velocity Control”

Presenter: Mr. Robert C. Randall, ECE Ph.D. Student, University of Massachusetts Dartmouth

Advisor: Dr. David A. Brown

A SONAR array’s radiation pattern is affected by the acoustic interactions, which may limit the effectiveness of beamforming algorithms when transmitting. A negative feedback system with a velocity sense signal fed back to the power amplifier can mitigate the array interactions proportional to the loop gain, and be effective across a broad frequency range without requiring a priori knowledge of the input signals. The velocity feedback signal for piezoelectric loads may be obtained by the motional current that is proportional to the velocity of the transducer. This approach may be used as a virtual massless accelerometer (or velocimeter) if the transducer’s electrical branch admittance is estimated correctly. The transducer’s coupling coefficient, mechanical Q, and a priori estimate of the blocked capacitance fundamentally limits both the maximum stable loop gain, and the output velocity gain and phase tracking relative to the amplifier’s input voltage. The array equations governing the acoustical outputs are presented, both with and without motional current velocity control. Class D switching amplifiers can achieve greater than 90% efficiency, and are increasingly being used to drive SONAR arrays. When a velocity control system is used with a Class D amplifier, feedback stability becomes a significant concern due to obtaining the feedback signal after the amplifier’s LC output filter. The array equations are still obtained by converting the amplifier into a Thevenin equivalent force and output impedance, which now includes the amplifier’s output filter and the synthesized impedance due to the velocity control loop.

Robert C. Randall is currently a Senior Electrical Engineer at Raytheon Integrated Defense Systems in Portsmouth, Rhode Island where he has been working since 2006. His expertise is in the areas of FPGA design for Xilinx devices, embedded real-time systems, Class-D power amplifiers, and digital feedback and control of piezoelectric sonar devices. Robert is a Doctoral Candidate for the PhD in Electrical Engineering concentrating on Acoustics and Amplifier Design at the Electroacoustics Research Laboratory (ATMC) at the University of Massachusetts Dartmouth. Robert Randall earned his BS in Electrical Engineering in 2003 and MS in Computer Engineering in 2009 also from UMass Dartmouth.

The seminar is open to the public free of charge.

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