The experimental setup with eight horn loudspeakers and a microphone positioned inside the reverberation chamber. (Credit: BYU)

Researchers are investigating the use of time reversal (TR) signal processing to focus waves sound with high amplitudes in a room. In biomedical applications, focused ultrasound can be used in lithotripsy procedures for treating kidney stones or to target brain tumors.

TR focuses waves to a selected location that converge from all directions to produce a virtual source of spherical waves and then diverge from that location. To generate the acoustic waves and capture the results, they use arbitrary waveform generator (AWG) cards and a digitizer card from Spectrum Instrumentation.

An experimental setup consisted of eight coaxial compression drivers with horns attached. One GRAS free-field microphone with a specified dynamic range upper limit of 175 dB was used in conjunction with a preamplifier for the measurements. The signals used for the experiments are created in MATLAB and output via two, 4-channel Spectrum M2i.6022-exp 20 MS/s AWG cards. The output from the Spectrum AWG is amplified with two, 4-channel Crown CT4150 amplifiers. The signal acquisition from the microphone is done with one, 4-channel Spectrum M2i.4931-exp 16-bit digitizer card running with a sampling frequency of 50 kHz.

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