·Table of Contents
·Methods and Instrumentation
Development of Acoustic Emission Sensors with Required CharacteristicsA.A.Bazhenov, V.I.Yarovikov
Russian Federal Nuclear Center - All-Russian Research Institute of Experimental Physics, Sarov,
|Fig 1: Typical pulse characteristic of transducer AII206 (a) and its spectrum (b)|
Fig. 2 shows frequency responses of transducers AII205 and for comparison those of a widely used in practice analogue R6 (Physical Acoustics Corp., USA) obtained on metrological facility IIfAII-PM (Dal'standard, Khabarovsk, Russia) acted upon by Releight waves (test unit material is steel 30X13).
|Fig 2: Typical frequency response of transducers AII205 and R6 on exposure to Releight waves|
Fig. 3 presents frequency responses of the same transducers on exposure to longitudinal waves obtained on metrological facility IIfAII-PM (Dal'standard, Khabarovsk, Russia) with a specific acoustic impedance at the point of the transducer mounting z = 31.106 kg/m2.s.
|Fig 3: Typical frequency response of transducers AII205 and R6 on exposure to longitudinal waves|
Designing of vibroacoustic transducers, operating in a resonance mode, in low ultrasound area, involves some features related to large longitudinal and transverse size of a sensing element and variations in frequency response.
|Type of the received wave||volumetric (longitudinal) and surface waves with a comb periodic structure (Lambar, Releight waves)|
|Type of a sensitive element||elongated cylinder||short cylinder||ring||disk|
|Operating frequency range, kHz||20 - 100||50 - 200||100 - 500||100 - 900||300 - 1000|
|Average electroacoustic transformation coefficient, dB ref to V/m/s||55||55||54||53||50|
|Operating temperature range, °C||-60...+100|
|Electric capacitance, pF||200||250||400||500||400|
|Average resonance frequency, kHz||60||90||180||-|
|Variations in frequency response, dB||±4||+10 |
|Method of the electric signal output||coaxial|
|Type of the used piezoceramics||PZT-19|
|Type of the protector material||high-strength ceramics (Chilymin)|
|Type of the body material||stainless steel||titanium alloy|
|Cable lead out of the body||from the side|
|Method of the body sealing||epoxy adhesive|
|Attachment to an object||By glue or using contact liquid with simultaneous compression against the object under control|
|Overall dimensions, mm||Æ36´32||Æ32´28||Æ16´15||Æ22´15||Æ16´15|
The problem of these transducers development was solved by mathematics simulation and optimization of design parameters of piezoceramic sensitive elements. Available approximate calculation techniques for such transducers do not enable to have the problem completely solved. Using known methods of piezoelements mated fields [6-9], in the context of deformed media mechanics, a new technique has been developed based on the calculation of the piezoelement electroelasticity at volumetrically stressed sensitive elements (SE), with regard to volumetric waves reflection and passage through the transducer design elements [2-4]. This technique offers some significant distinctions such as consideration of all components of the
piezoelement strain tensor, including those which under specific boundary conditions may be zero, as well as considering input circuit parameters of amplifying-transforming equipment.
The proposed technique offers versatility physical evidence, it provides convenient computational algorithm and optimization based upon the requirement of a specific task (obtaining predetermined electroacoustic transformation coefficient, shape and variations of the frequency response).
This technique is used to calculate sensitive elements of any complex shape (disks, rings, multilayer plates, sectional rods, etc.).
As optimization techniques of AE transducers parameters, may serve synthesis of a required frequency response from different modes of the piezoelement vibration (in longitudinal and lateral directions), suppression or isolation of certain oscillation modes, etc. To illustrate the computational technique Fig. 4 shows calculated and experimental frequency responses of the acoustic emission transducer AII203 acted, upon by longitudinal waves.
|Fig 4: Calculated and experimental characteristics of acoustic emission transducer AII203 acted upon by longitudinal waves, and its external view|
|© AIPnD , created by NDT.net|||Home| |Top||