Ultrasonic transducer having impedance matching layer

A resonant type tranducer providing a narrowband, high output or high sensitvity signal to a radiation medium, said resonant transducer comprising:

• a vibrator body comprising piezoelectric or electrostrictive material having a first acoustic impedance associated with a resonant frequency;
• and
• a matching layer for acoustically matching said vibrator body at resonance to said radiation medium, said matching layer comprising:
• a first layer of material of thickness t1 and acoustic impedance Z1 and having an inner surface coupled to a front surface of said vibrator body;
• and
• a second layer of material of thickness t2 and acoustic impedance Z2 and having an outer surface coupled to said radiation medium, wherein the acoustic impedance Z2 is greater than the first acoustic impedance Z1 so as to provide a combined impedance of the matching layer at the front surface of the vibrator body which is less than the acoustic impedance of the radiation medium.

A resonant type transducer for producing and/or detecting ultrasound energy in an adjacent radiation medium, said radiation medium having an acoustic impedance associated therewith, said transducer comprising:

• a vibrator body comprising piezoelectric or electrostrictive material and having a first impedance associated with a resonance frequency that is less than that of said acoustic impedance of said radiation medium, said vibrator body having a front surface and a rear surface;
• a backing layer disposed at said rear surface of said vibrator body for absorbing ultrasound energy from the vibrator body;
• and
• a matching layer having a first surface coupled to said front surface of said vibrator body and a second surface coupled to said radiation medium for communicating ultrasound energy therebetween,
• wherein said matching layer has an acoustic impedance less than the acoustic impedance of the radiation medium and greater than sad first impedance at said resonance frequency of said vibrator body.

A resonant type transducer for producing and/or detecting ultrasound energy in an adjacent radiation medium, said radiation medium having an acoustic impedance associated therewith, said transducer comprising:

• a vibrator body comprising piezoelectric or electrostrictive material and having a first impedance associated with a resonance frequency that is less than that of said acoustic impedance of said radiation medium said vibrator body having a front surface through which ultrasound energy is transferred to said radiation medium;
• a backing layer disposed at said rear surface of said vibrator body for absorbing ultrasound energy from the vibrator body;
• and
• a matching layer for acoustically matching said vibrator body at said resonance frequency to said radiation medium said matching layer comprising:
• a first layer of material of thickness t1 and acoustic impedance Z1, said first layer having a first surface coupled to said front surface of said vibrator body, and a second surface;
• a second layer of material of thickness t2 and acoustic impedance Z2 greater than Z1, said second layer having a first surface coupled to said second surface of said fis layer, and a second surface coupled to said radiation medium,
• wherein said first and second layers are adapted to provide an effective impedance of the matching layer at the front surface of said vibrator body that is less than the acoustic impedance of the radiation medium and greater that of said vibrator body impedance at said resonance frequency.