  This work studies the adverse effects, as regards noise, of immersing in
water an integrating line piezoelectric detector devoted to optoacoustic
imaging. We found that the sensor, in conjunction with the acoustic coupling
medium (water), behaves as a resonant dielectric antenna. This phenomenon
limits the performance of the system because it efficiently captures unwanted
electromagnetic signals. The requirement of good acoustic coupling between the
water and the sensor precluded the use of a standard metallic shielding
enclosure. Therefore, we resorted to a silver-paint based electrical shield
deposited on the detector. This easy-to-implement and low-cost solution
significantly increases the signal to noise ratio and does not degrade the
acoustic performance. The noise reduction allows the use of a better
transimpedance amplifier with higher gain and bandwidth; thus achieving a very
sensitive, low-noise detection system.
