Noise Modelling and Comparison of P(VDF-TrFE) and PZT-5A Piezoelectric Hydrophones for Thermoacoustic Sensing

Thermoacoustic signals, as in photoacoustic imaging or ionoacoustic range verification, are of a few millipascals, and the noise-equivalent pressure (NEP) of receiver and readout decides whether they are detectable. This work presents a frequency-domain noise model of immersed piezoelectric hydrophones read by a charge amplifier, applied to a P(VDF-TrFE) copolymer and a PZT-5A ceramic of identical geometry. A distributed Mason/KLM model gives the charge sensitivity, the matching layer and, via the Nyquist theorem at its electrical port, the thermal noise of the thickness mode while a multi-branch network adds the in-plane modes. Over 1 kHz–1 MHz ionoacoustic bandwidth the NEP is 47.6 mPa rms for the copolymer and 123.7 for PZT-5A. As sensors they are within 0.3 dB; the 8.3 dB difference comes from the ceramic capacitance, which multiplies the amplifier voltage noise. A k-Wave study of a 200 MeV proton beam at 54 mGy per pulse gives signal-to-noise ratios of 30.5 and 22.1 dB and range errors of 0.06 and 0.33 mm.