|
 Contact
Phased Array Transducers
Contact phased array transducers
are the most commonly used, as their wide variety enables them to
be used for many different applications.
They also allow to generate variable angle refracted beam without
wedge, which helps to solve size problems for reduced access applications.
 Principle
Contact phased array transducers typically combine
electronic beam steering and focusing.
To avoid grating lobes, they require a relatively small inter-element
pitch.
For linear arrays, the number of elements is typically less than
128, and even 64, as electronic scanning is not often used.
Matrix arrays require 2D sampling, which can easily require up to
256 elements or more.
 Advantages
These transducers can work with angles and electronically-adaptable
focusing depths, i.e. without changing or moving the transducer.
This allows, in particular:
- a smaller number of probes to be used,
- faster inspection.
They also allow a refracted, non-zero incidence
beam to be generated without using a wedge, which opens new possibilities
for when there is no room to use a wedge.
Types of Probes
Contact phased array transducers
can be classified according to three criteria that can be combined
totally independently.
The type of array
- Linear arrays
(1D) allow a beam to be driven on a plane
- Matrix arrays (2D)
allow 3D steering
The coupling mode
Direct contact, removable or integrated
wedge (See below)
The principle of emission-reception
Single-unit or separated transmitter-receiver
(TRL/SE probes)
| Direct
Contact, Integrated or Removable Wedge?
Contact transducers can integrate a non-removable wedge,
can be adapted to different removable wedges, or can be used
in direct contact without a wedge.
Direct contact
In some cases, contact transducers can be used without a
wedge, for example, if there is not enough space available,
or to avoid interference echoes from the wedge.
In this configuration, the unseen area below the surface is
larger because of the ringing of the excitation signal. Furthermore,
deflection without grating lobes at high angles will require
smaller spacing, and consequently a larger number of elements.
Finally, in this case, shear waves cannot be generated by
mode conversion at the interface between the wedge and the
part to be inspected.
Hard face
Wear and tear on the front face may have unexpected effects
on probes, such as water penetration or modification of electroacoustical
properties.
Conversely, placing a protective layer may alter the pulse
length and sensitivity due to the additional interface.
For this reason, IMASONIC has implemented a new hard face
material that combines appropriate acoustical impedance for
high energy transfer and ten times higher resistance to wear
than a conventional front face.
 Integrated
wedges
An integrated wedge allows a transducer to be more compact
and often better adapted to industrial conditions. The coupling
between the active part and the wedge is guaranteed by being
glued during manufacturing.
Thus it is constant and homogeneous, requires no maintenance
and guaran- tees a high level of performance.
 Removable
wedges
Removable wedges have great flexibility and enable the same
transducer to be used in several different configurations.
They can also be replaced easily if they show wear or are
damaged. |
|
