The ultrasound detector is the heart of a photoacoustic imaging system. In photoacoustic imaging of the breast
there is a requirement to detect tumors located a few centimeters deep in tissue, where the light is heavily attenuated.
Thus a sensitive ultrasound transducer is of crucial importance. As the frequency content of photoacoustic
waves are inversely proportional to the dimensions of the absorbing structures, and in tissue can range from hundreds
of kHz to tens of MHz, a broadband ultrasound transducer is required centered on an optimum frequency.
A single element piezoelectric transducer structurally consists of the active piezoelectric material, front- and
back-matching layers and a backing layer. To have both high sensitivity and broad bandwidth, the materials,
their acoustic characteristics and their dimensions should be carefully chosen. In this paper, we present design
considerations of an ultrasound transducer for imaging the breast such as the detector sensitivity and frequency
response, which guides the selection of active material, matching layers and their geometries. We iterate between
simulation of detector performance and experimental characterization of functional models to arrive at an
optimized implementation. For computer simulation, we use 1D KLM and 3D finite-element based models. The
optimized detector has a large-aperture possessing a center frequency of 1 MHz with fractional bandwidth of
more than 80%. The measured minimum detectable pressure is 0.5 Pa, which is two orders of magnitude lower
than the detector used in the Twente photoacoustic mammoscope.