A Tactile Sensor for Ultrasound Imaging Systems

Medical ultrasound systems are capable of monitoring a variety of health conditions while avoiding invasive procedures. However, this function is complicated by ultrasound contrast of the tissue varying with contact pressure exerted by the probe. The knowledge of the contact pressure is beneficial for a variety of screening and diagnostic procedures involving ultrasound. This paper introduces a solid-state sensor array, which measures the contact pressure distribution between the probe and the tissue marginally affecting the ultrasound imaging capabilities. The probe design utilizes the dielectrostriction mechanism, which relates the change in dielectric properties of the sensing layer to deformation. The concept, structure, fabrication, and performance of this sensor array are discussed. The prototype device is highly tolerant to overloads (>1 MPa tested) and provides stress measurements in the range of 0.14-10 kPa. Its loss of ultrasound transmissivity is less 3 dB at 9-MHz ultrasound frequency. This performance is satisfactory for clinical and biomedical research in ultrasound image formation and interpretation, however, for commercial product, a higher ultrasound transmissivity is desired. Directions for improving the sensor ultrasound transparency and electrical performance are discussed. The sensor array described in this paper has been specifically developed for ultrasound diagnosis during breast cancer screening. However, the same sensing mechanism, the similar configuration, and the sensor array structure can be applied to other applications involving ultrasound tools for medical diagnostics.