Composite transducer structure

An ultrasonic transducer in which a plurality of elements are employed alternate ones of which are utilized as transmitters and receivers and having the same area but in which the transmitter elements are composed of material having a high transmit sensitivity while the receiver elements are composed of a material having a high receive sensitivity.

BACKGROUND OF THE INVENTION 
This invention relates to ultrasonic imaging, or doppler and more 
particularly to an improved transducer structure useful in ultrasonic 
imaging or doppler, especially in the area of medical diagnosis. 
Ultrasonic transducers are well known in the art and a large variety of 
shapes and sizes have been proposed. One particularly useful configuration 
for medical diagnosis is an annular array wherein one or more ring shaped 
transducing elements are arranged in concentric fashion about an axis in 
order to pulse energy into a body and to receive the reflected energy from 
internal organs. An example of such a transducer may be found in the 
Specht et al. U.S. Pat. No. 4,241,611, issued Dec. 30, 1980. This patent 
also notes that one of the rings may be dedicated to transmit energy while 
the remainder of the rings may be used to receive energy. Also, if the 
transmit ring is a separate ring, it can then be made of a different 
material which is more efficient as a transmitter than as a receiver. The 
Dorr et al. U.S. Pat. No. 3,327,286 issued June 30, 1967 also shows a 
sonic transducer having two annular elements one of which is a transmitter 
and the other of which is a receiver. 
The difficulty with the prior art has been the problem of obtaining 
increased sensitivity without having beam pattern degradation. More 
specifically, it is desirable to have a beam pattern which is 
substantially symmetrical at all depths at which the transducer is to be 
used. I have determined that one way of obtaining this desired beam 
pattern is to construct a transducer array in which alternate ones of the 
transducer elements transmit radiation while the opposite alternate ones 
receive the reflected radiation and the area of all of the elements is 
substantially the same. Furthermore, by constructing a tranducer in this 
manner and utilizing a material for the transmitting elements which is 
chosen for high transmit sensitivity and utilizing a different material 
chosen for high receive sensitivity for the receiving elements an increase 
of sensitivity results. 
SUMMARY OF THE INVENTION 
The present invention increases the sensitivity of an ultrasonic transducer 
without losing beam pattern symmetry by utilizing elements which are 
alternately arranged as transmitters and receivers, all of which are of 
substantially the same area in order to obtain a good beam pattern and in 
which the transmitters are composed of material which has a high transmit 
sensitivity while the receivers are composed of a slightly different 
material which has a high receive sensitivity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 and 2 show an ultrasonic transducer 10 consisting of a plurality of 
transducing elements 12, 13, 14, 15, 16, and 17, arranged as concentric 
rings in an annular array. The area of each of the elements is 
substantially the same as can be seen in FIGS. 1 and 2 by the fact that 
the width of the elements decreases as the distance from the center 
increases. 
Alternate ones of the elements, e.g., 12, 14, and 16 are connected together 
by conductor 18 to a transmitter 20. The other alternate ones of the 
elements, e.g., 13, 15, and 17 are connected together by a conductor 22 to 
a receiver 24. Upon a signal from transmitter 20 elements 12, 14, and 16 
transmit a pulse of ultrasonic energy in a general direction shown by 
arrow 26 to a remotely located object such as the internal parts of a 
body. Reflections from the internal parts are received by elements 13, 15, 
and 17 and are presented to receiver 24 for use thereby in an imaging 
system (not shown) which may be like that described in the James M. 
Gessert co-pending application, Ser. No. 173,874, filed July 30, 1980. 
Since the area of elements 12, 13, 14, 15, 16, and 17 are substantially 
the same, the beam pattern of the energy transmitted and received by the 
transducer 10 remains symmetric throughout the range of depth for which 
the transducer is to be used. In order to increase sensitivity, however, 
elements 12, 14, and 16 are made from a material which has high transmit 
sensitivity even though such material may have a low receive sensitivity 
while elements 13, 15, and 17 are made from a material which has high 
receive sensitivity even though such material may have a rather low 
transmit sensitivity. By this means the transmitter sensitivity is 
increased and the receiver sensitivity is increased without a loss of beam 
pattern symmetry. An example of a material having high transmit 
sensitivity is lead zirconate lead titinate (PZPT) comprising 
approximately fifty-three percent lead zirconate and approximately 
forty-seven percent lead titinate and which utilizes a lanthanum oxide 
dopant. An example of a material having high receive sensitivity is PZPT 
consisting of about sixty-five percent lead zirconate and about 
thirty-five percent lead titinate with a niobium oxide dopant. Other 
materials will occur to those skilled in the art. 
While the present invention has been shown in connection with an annular 
array of transducing elements, it should be understood that a linear array 
in which alternate elements are transmitters and receivers but in which 
all of the elements have the same area and in which the receivers and 
transmitters utilize high receive sensitivity and high transmit 
sensitivity materials respectively could be employed. I therefore do not 
wish to be limited by the disclosures used in connection with the 
preferred embodiment, but wish to be limited only by the following claims.