Method and apparatus for transmitting ultrasound pulses and receiving echo signals at a harmonic of the transmission frequency

A method for transmitting ultrasound pulses and receiving echo signals at a harmonic of the transmission frequency comprising the following steps:

• generating a signal for exciting a plurality of transducers for transmitting at least one ultrasound pulse at a basic transmission frequency;
• receiving a reflection echo of said at least one ultrasound pulse at a harmonic of the frequency of the at least one ultrasound pulse;
• removing any contributions to the harmonic frequency in the signal for exciting;
• filtering the signal for exciting by using a transmitting resonant circuit having a resonance frequency which is adjusted to the basic transmission frequency, wherein an assembly of the plurality of transducers and a cable connecting said plurality to a transmitter that is constructed and arranged for performing said generating step is constructed and arranged as said transmitting resonant circuit;
• and
• inserting an inductance in series between the cable and the transmitter for adjusting the resonance frequency to the basic transmission frequency;
• connecting said plurality of transducers to a receiver through a receiving resonant circuit;
• calibrating said receiving resonant circuit to the second harmonic of the basic transmission frequency;
• and
• configuring said receiving resonant circuit for operating upon reception, in a resonant circuit mode with predetermined resistance and capacitance values.

An apparatus constructed and arranged for transmitting ultrasound pulses at a transmission frequency and receiving echo signals at a harmonic of said transmission frequency, said apparatus comprising:

• a transmitter constructed and arranged for generating electric signals for exciting at least one transducer for transmitting ultrasound pulses at a predetermined basic frequency;
• a transducer constructed and arranged for picking up reflected echo signals at a harmonic frequency of said ultrasound pulses;
• a receiver connected to said transducer for receiving electric signals from said transducers;
• means for removing contributions of harmonic components in said transmitted ultrasound pulses, said means including a resonant circuit which is a part of the connection of said transducer to the transmitter, said resonant circuit having a resonance frequency which is set to the basic frequency of the transmitted ultrasound pulses, wherein said resonant circuit includes the combination of said transducer and a connecting cable which connects the transducer to the transmitter;
• a variable inductance positioned in series between the connecting cable and the transmitter for adjusting the frequency of the resonant circuit to the basic frequency;
• and
• means for automatically adjusting the variable inductance based on electrical characteristics of the resonant circuit.

An apparatus for transmitting ultrasound pulses and receiving echo signals comprising:

• a transmitter constructed and arranged for generating electric signals for exciting at least one transducer for transmitting ultrasound pulses at a predetermined basic frequency;
• a transducer constructed and arranged for picking up reflected echo signals at a harmonic frequency of said ultrasound pulses;
• a receiver connected to said transducer for receiving electric signals from said transducer;
• a resonant circuit through which said transducer is coupled to the receiver, said resonant circuit having a resonance frequency which is set to a harmonic or sub-harmonic frequency of the basic frequency of the transmitted pulses;
• means for transmitting, for each line of view, at least two successive identical or phase-inverted transmission pulses;
• and
• means for combining the received reflection echoes, caused by said two pulses in the form of a subtraction or a sum of the two reflection echoes respectively, such as a summer or subtracting circuit, said transducer being coupled to the transmitter through a resonant circuit calibrated to the fundamental frequency of the transmitted pulses.