Ultrasonic probe, Signal to noise ratio, Multilayer piezoelectric ceramic, Electric impedance, Co-firing multilayer method
We have developed an ultrasonic probe employing a multilayer piezoelectric ceramic in order to improve the signal-to-noise (S/N) ratio. The S/N ratio is degraded when the impedance of the probe rises excessively in relation to the combined impedance of the cable and receiver circuits. An improvement in the S/N ratio is particularly important for Doppler mode ultrasonography. This is because the echo from blood cells is weaker than that from tissues, and the impedance of a phased array probe, which is mainly used with the Doppler mode, is larger than that of a linear array probe. The impedance of a probe using n layers of ceramic can be reduced to 1/n2 when compared with a single layer ceramic, thus permitting the S/N ratio to be raised. A co-firing multilayer method has been introduced in order to produce a multilayer ceramic with a high adhesive strength. The quantity of the ceramic powder mixed into the internal electrode ink and the thickness of the internal electrode layer were optimized. The new multilayer ceramic was applied to small-phased array probes for neonatal and pediatric use. As a result, the S/N ratio was improved by as much as 8.2 dB over that of conventional probes.