Design and development of ultrasonic bipolar square-wave pulser for non-destructive testing of concrete structures

Abstract

This paper provides design and development details of the generation of bipolar High Voltage (HV) square wave pulses for the excitation of low frequency ultrasonic transducers. Such a circuit is required for the purpose of ultrasonic inspection of components, particularly where high energy is required to insonify the attenuative medium, such as concrete. A HV (±350 V) square wave pulse has been generated by an ultrafast complementary Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) pair, which is driven by high speed MOSFET drivers. The generated bipolar square wave pulse has been utilized to energize a 108 kHz ultrasonic transducer to operate in the pulse-echo mode for the evaluation of a concrete test block. The receiver amplifier filters the received low-amplitude echo signals, which are reflected back from a discontinuity, and amplifies further for signal to noise ratio enhancement. The pulser board designed has been tested and evaluated for its functionality to measure ultrasonic velocity in the highly attenuative concrete medium up to a depth of 1 m. The measured value of acoustic velocity was compared with the value obtained from the commercially available ultrasonic pulse velocity instrument, and the values obtained are within ±5%.

Embedded system for ultrasonic imaging of under-water concrete structures

“…In most of the NDT applications, spike pulser is employed for the generation of ultrasound because of its wide band response [19,20]. For the imaging system described in this paper, the bipolar pulser with narrow-band response has been utilized, which provides comparatively higher energy for the same voltage rating of spike pulser and provides higher sensitivity to smaller discontinuities in thick concrete structures, submerged in water, for PE mode [21].…”

“…Figure 2(a) shows a schematic block diagram of the newly designed ultrasonic tone burst bipolar pulser which consists of: transistor-transistor logic (TTL) buffers to drive the trigger pulses suitable for MOSFET drivers, followed by them are the MOSFET drivers which drive gate of the Power MOSFETs with HV bipolar pulse for the energisation of the ultrasonic transducer [21]. The trigger pulses have been generated in a sequential manner through FPGA, with user selectable pulse widths (PW) of 1 to 20 μs with pulse repetition frequency (PRF) of 20 Hz to 50 Hz.…”

Ultrasonic Imaging of Concrete/ RCC Structures using Immersion Technique

“…The technique is completely contactless as ultrasonic immersion transducers with fixed stand-off distance are employed. The four-channel imaging system consists of four-channel high voltage (HV) toneburst square-wave bipolar pulser [10], four-channel pre-amplifiers with maximum gain of 66 dB for each pre-amplifier and a common main amplifier with 66 dB gain; multi-channel data acquisition module which includes in-house developed 100 MSPS, 8 bits high speed digitizer, commercially available Spartan 6 FPGA module which controls the entire system and USB controller module for the communication with computer; immersion type four transducers and an automated X-Y scanner mounted onto 300 mm (L) x 300 mm (W) x 500 mm (D) deep water tank for maneuvering the transducers in the water-tank during the inspection. confirms the presence of identical diameter steel bars embedded inside the concrete.…”