An amplifier circuit to be used in a sonar, the amplifier circuit comprising: a transducer having an impedance characteristic, the impedance characteristic comprising a resonance frequency, and an anti-resonance frequency higher than the resonance frequency; and a matching circuit connected to the transducer, the matching circuit comprising a capacitive component and an inductor, characterised in that: the capacitive component is connected in parallel with the transducer and the inductor is connected in series with the parallel connection of the capacitive component and the transducer; and the capacitance of the capacitive component and the inductance of the inductor are selected such that: the impedance characteristic of the transducer connected to the matching circuit has a first resonance frequency and a second resonance frequency higher than the first resonance frequency, wherein the first resonance frequency is a first local minimum in the impedance characteristic of the transducer connected to the matching circuit and the second resonance frequency is a second local minimum in the impedance characteristic of the transducer connected to the matching circuit; and the impedance characteristic of the transducer connected to the matching circuit further has an anti-resonance frequency between the first resonance frequency and the second resonance frequency, the anti-resonance frequency being a local maximum in the impedance characteristic. a transducer having an impedance characteristic, the impedance characteristic comprising a resonance frequency, and an anti-resonance frequency higher than the resonance frequency; and a matching circuit connected to the transducer, the matching circuit comprising a capacitive component and an inductor, characterised in that: the capacitive component is connected in parallel with the transducer and the inductor is connected in series with the parallel connection of the capacitive component and the transducer; and the capacitance of the capacitive component and the inductance of the inductor are selected such that: the impedance characteristic of the transducer connected to the matching circuit has a first resonance frequency and a second resonance frequency higher than the first resonance frequency, wherein the first resonance frequency is a first local minimum in the impedance characteristic of the transducer connected to the matching circuit and the second resonance frequency is a second local minimum in the impedance characteristic of the transducer connected to the matching circuit; and the impedance characteristic of the transducer connected to the matching circuit further has an anti-resonance frequency between the first resonance frequency and the second resonance frequency, the anti-resonance frequency being a local maximum in the impedance characteristic. the capacitive component is connected in parallel with the transducer and the inductor is connected in series with the parallel connection of the capacitive component and the transducer; and the capacitance of the capacitive component and the inductance of the inductor are selected such that: the impedance characteristic of the transducer connected to the matching circuit has a first resonance frequency and a second resonance frequency higher than the first resonance frequency, wherein the first resonance frequency is a first local minimum in the impedance characteristic of the transducer connected to the matching circuit and the second resonance frequency is a second local minimum in the impedance characteristic of the transducer connected to the matching circuit; and the impedance characteristic of the transducer connected to the matching circuit further has an anti-resonance frequency between the first resonance frequency and the second resonance frequency, the anti-resonance frequency being a local maximum in the impedance characteristic. the impedance characteristic of the transducer connected to the matching circuit has a first resonance frequency and a second resonance frequency higher than the first resonance frequency, wherein the first resonance frequency is a first local minimum in the impedance characteristic of the transducer connected to the matching circuit and the second resonance frequency is a second local minimum in the impedance characteristic of the transducer connected to the matching circuit; and the impedance characteristic of the transducer connected to the matching circuit further has an anti-resonance frequency between the first resonance frequency and the second resonance frequency, the anti-resonance frequency being a local maximum in the impedance characteristic.