Transducer arrays

For conventional probes, acoustic verification aims at characterizing the beam pattern, beam crossing, beam angle, sensitivity, etc., which are key characteristics in the acoustic interaction between acoustic beam and defect. For array transducers, obviously, it is also a meaning to check the acoustic capabilities of the probe. That is to valid a domain (angle beam, focus, etc.) in which the probe can operate satisfactorily. 

FIGURE 6.7 Intracardiac ultrasound (A) shows the left atrium (LA) imaged from a phased array transducer in the right atrium. A contour of the LA is incorporated into an electroanatomical map (B) and also merged with a preacquired Computed tomographic angiogram. 

In using a diode-array transducer, the slit width of the spectrometer is usually adjusted so that the image of the entrance slit just fills the surface area of one of the diodes that make up Ihe array. Thus, the information obtained is equivalent lo that recorded during scanning with a traditional spectrophotometer. With the array, however, information about the entire spectrum is accumulated essentially simultaneously and in discrete Clements rather than in a continuous way. 

Micru-Faraday Array Transducer. Recently, a new type of array transducer for mass spectrometry has been introduced lhal shows promise for the simultaneous detection of ions at the focal plane of Maltauch-Merzog-type mass spectrometers and other similar applications. An image of the prototype Faraday cup... 

PVDF is generally an ideal material for transducers operating at frequencies above 0.5 MHz in hydrophones and pulse echo probes for medical and nonmedical testing. A 64-element linear array transducer has been produced that, operating at 5 MHz, offers a wide-bandwidth pulse response, sharp ultrasonic field distribution, and a high energy conversion efficiency. 

An improvement over the individual transducers is thephased-array transducer systems that may have many elements (e.g., from 16 to over 128 elements) in a linear arrangement [23,27]. The phased-array electronic systems will pulse multiple small (e.g., 1 mm wide) elements in a timed sequence to create an ultrasonic beam with directional or focused properties based on the time phasing of the transducer pulses... 

Another model-free method for active damage detection is based on directional transducers. For passive sensing. Section 16.9 has already discussed the use of directional strain rosettes (both piezo and optical) to effectively detect an acoustic source without the need for a structural model. For active sensing, directional transmission as well as reception of guided wave can be achieved with phased-array transducers. 

Yasuda K, Ogawa M, Sato A et al (2004) Newly developed ultrasound endoscope with an electronic radial array transducer. Dig Endo 16 [Suppl] 219-222... 

Mechanical Steering. The simplest method of beam steering is to use a mechanism to reorient a transducer (usually a circular aperture) to a predetermined set of orientations so as to capture the required two-dimensional data set. This approach was dominant at first however, in the last 15 years, electronically steered systems have become, by far, the most popular. Mechanical systems usually use either a single-element transducer or an annular array transducer (Fig. 25.8). Tlie former will have a fixed focus while the latter does allow the focal point to be moved electronically. This will be discussed more fiilly later. 

Complying with the current specification leads to increased requirements for ultrasonic transducers, emphasising the potential interest of array-transducers. 

Qiu Y, et al. Screen-printed ultrasonic 2-D matrix array transducers for microparticle manipulation. Ultrasonics 2015 62 136-46. 

A variety of linear-array transducers is currently available in the frequency range used for penile imaging. Selection of the most appropriate transducer primarily depends on the frequency, but is also related to other factors. Compared with small transducers, for instance, larger probes tend to have a large near-field beam width leading to a poor lateral resolution at shallow depths. 

Fig. 19.3a,b. Sonourethrography. Normal appearance of the urethra in sagittal (a) and transversal (b) scans. The urethra distended hy the saline solution appears as an anechoic tubular structure well depicted with linear array transducer using direct skin contact on the ventral surface of the penis and with trans-scrotal and perineal scanning for bulbar urethra... 

The multiple tilted-array transducer (Lee, Kim, and Tsai, 1979), where an array of standard IDTs with staggered center frequencies are tilted toward each other in order to satisfy the Bragg condition at each frequency (Fig. 3.15). 

The Phase-array transducer (Nguyen and Tsai, 1977) that consists of several IDT segments with one period displacement (phase difference) between adjacent segments, using frequency control SAW beam steering (Fig. 3.16). 

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