Techniques, systems, and devices are disclosed for ultrasound diagnostics using spread spectrum, coherent, frequency- and/or phase-coded waveforms. In one aspect, a method includes synthesizing individual orthogonal coded waveforms to form a composite waveform for transmission toward a biological material of interest, in which the synthesized individual orthogonal coded waveforms correspond to distinct frequency bands and include one or both of frequency-coded or phase-coded waveforms; transmitting a composite acoustic waveform toward the biological material of interest, where the transmitting includes transducing the individual orthogonal coded waveforms into corresponding acoustic waveforms to form the composite acoustic waveform; receiving acoustic waveforms returned from at least part of the biological material of interest corresponding to at least some of the transmitted acoustic waveforms that form the composite acoustic waveform; and processing the received returned acoustic waveforms to produce an image of at least part of the biological material of interest.