Comparison of optimisation strategies for the improvement of depth detection capability of Pulse-Compression Thermography

In Pulse Compression Thermography, the impulse response of the sample under test is retrieved pixelwise by applying a proper matched filter on the set of acquired thermal images obtained by stimulating the system with a heat source amplitude-modulated by a proper coded signal. Linear frequency modulated chirp signals and binary codes are the most employed coded excitations, and to improve the detection capability of the technique, a non-linear frequency modulated chirp signal can be used to deliver more energy to the sample in a frequency range of interest. In this work, we report the application of an exponential chirp to modulate the heating source and we compare it with a standard linear chirp excitation. To do a fair comparison, various windowing functions have been applied on the matched filters to reduce range sidelobes, thus enhancing the retrieved impulse response quality. It is shown that the combined use of an exponential chirp and an appropriate matched filter obtained by exploiting the Reactance Transform window, provides a faithful reconstruction of the sample impulse response and an enhanced signal-to-noise ratio with respect to the use of linear chirp. This has been demonstrated on a 3D-printed polymethylmethacrylate (PMMA) sample containing sixteen flat-bottom holes of different depths

Modified FMCW scheme for improved ultrasonic positioning and ranging of unmanned ground vehicles at distances < 50 mm

Unmanned ground vehicles (UGVs) find extensive use in various applications, including that within industrial environments. Efforts have been made to develop cheap, portable, and light-ranging/positioning systems to accurately locate their absolute/relative position and to automatically avoid potential obstacles and/or collisions with other drones. To this aim, a promising solution is the use of ultrasonic systems, which can be set up on UGVs and can potentially output a precise reconstruction of the drone’s surroundings. In this framework, a so-called frequency-modulated continuous wave (FMCW) scheme is widely employed as a distance estimator. However, this technique suffers from low repeatability and accuracy at ranges of less than 50 mm when used in combination with low-resource hardware and commercial narrowband transducers, which is a distance range of the utmost importance to avoid potential collisions and/or imaging UGV surroundings. We hereby propose a modified FMCW-based scheme using an ad hoc time-shift of the reference signal. This was shown to improve performance at ranges below 50 mm while leaving the signal unaltered at greater distances. The capabilities of the modified FMCW were evaluated numerically and experimentally. A dramatic enhancement in performance was found for the proposed FMCW with respect to its standard counterpart, which is very close to that of the correlation approach. This work paves the way for the future use of FMCWs in applications requiring high precision

Ultrasonic propagation in highly attenuating insulation materials

Experiments have been performed to demonstrate that ultrasound in the 100−400 kHz frequency range can be used to propagate signals through various types of industrial insulation. This is despite the fact that they are highly attenuating to ultrasonic signals due to scattering and viscoelastic effects. The experiments used a combination of piezocomposite transducers and pulse compression processing. This combination allowed signal-to-noise levels to be enhanced so that signals reflected from the surface of an insulated and cladded steel pipe could be obtained

Ultrasonic NDE of thick polyurethane flexible riser stiffener material

Ultrasonic signals at frequencies below 1 MHz have been used for the NDE of thick polymer samples. Coded signals such as chirps and bipolar Golay codes, together with pulse compression and signal processing, have been used to penetrate into thick sections of attenuating polypropylene riser stiffener material, using piezocomposite transducers to provide the required bandwidth. It is shown that this approach can be used to detect manufacturing defects such as air bubbles in flexible riser stiffeners, which might compromise their performance in the offshore oil and gas environments

Trapped air metamaterial concept for ultrasonic sub-wavelength imaging in water

Funding for this work was provided through the UK Engineering and Physical Sciences Research Council (EPSRC), Grant Numbers EP/N034163/1, EP/N034201/1 and EP/N034813/1.Acoustic metamaterials constructed from conventional base materials can exhibit exotic phenomena not commonly found in nature, achieved by combining geometrical and resonance effects. However, the use of polymer-based metamaterials that could operate in water is difficult, due to the low acoustic impedance mismatch between water and polymers. Here we introduce the concept of “trapped air” metamaterial, fabricated via vat photopolymerization, which makes ultrasonic sub-wavelength imaging in water using polymeric metamaterials highly effective. This concept is demonstrated for a holey-structured acoustic metamaterial in water at 200–300 kHz, via both finite element modelling and experimental measurements, but it can be extended to other types of metamaterials. The new approach, which outperforms the usual designs of these structures, indicates a way forward for exploiting additive-manufacturing for realising polymer-based acoustic metamaterials in water at ultrasonic frequencies.Publisher PDFPeer reviewe

A pharmacoeconomic analysis from Italian guidelines for the management of prolactinomas

Background: Prolactinoma, the most common pituitary adenoma, is usually treated with dopamine agonist (DA) therapy like cabergoline. Surgery is second-line therapy, and radiotherapy is used if surgical treatment fails or in relapsing macroprolactinoma. Objective: This study aimed to provide economic evidence for the management of prolactinoma in Italy, using a cost-of-illness and cost-utility analysis that considered various treatment options, including cabergoline, bromocriptine, temozolomide, radiation therapy, and surgical strategies. Methods: The researchers conducted a systematic literature review for each research question on scientific data- bases and surveyed a panel of experts for each therapeutic procedure's specific drivers that contributed to its total cost. Results: The average cost of the first year of treatment was euro2,558.91 and euro3,287.40 for subjects with micro- prolactinoma and macroprolactinoma, respectively. Follow-up costs from the second to the fifth year after ini- tial treatment were euro798.13 and euro1,084.59 per year in both groups. Cabergoline had an adequate cost-utility profile, with an incremental cost-effectiveness ratio (ICER) of euro3,201.15 compared to bromocriptine, based on a willingness-to-pay of euro40,000 per quality-adjusted life year (QALY) in the reference economy. Endoscopic sur- gery was more cost-effective than cabergoline, with an ICER of euro44,846.64. Considering a willingness-to-pay of euro40,000/QALY, the baseline findings show cabergoline to have high cost utility and endoscopic surgery just a tad above that. Conclusions: Due to the favorable cost-utility profile and safety of surgical treatment, pituitary surgery should be considered more frequently as the initial therapeutic approach. This management choice could lead to better outcomes and an appropriate allocation of healthcare resources

A metallic additively manufactured metamaterial for enhanced monitoring of acoustic cavitation‐based therapeutic ultrasound

The combination of ultrasound and microbubbles allows treatment of indications that would be impossible or too risk adverse with conventional surgery. During treatment, subharmonic and ultraharmonic components that can only be generated from microbubbles are of great interest for intraoperative monitoring. However, the microbubble emissions are several orders of magnitude lower in power compared to that of the fundamental frequency component from the ultrasound applicator, resulting in a low signal‐to‐noise ratio (SNR) for monitoring. A 3D acoustic metamaterial (AMM) immersed in water is proposed for suppressing unwanted ultrasound waves, which allows the improved sensitivity for detecting weak microbubble emissions. Numerically, the importance of shear waves on the AMM transfer properties is highlighted, though only longitudinal ultrasound waves are transmitted through water. Experimentally, the design is implemented in titanium using additive manufacturing, with an attenuation level of 40 dB at the fundamental frequency. Consequently, the application of the AMM efficiently improves the SNR for subharmonic and ultraharmonic microbubble emissions by 11.8 and 11.9 dB, respectively. The subharmonic components originally overwhelmed by noise are recovered. This is the first time that AMMs have been applied to passive acoustic monitoring and this work stands to improve treatment outcomes from cavitation‐mediated focused ultrasound therapy

Acoustic metamaterials for medical ultrasound and non-destructive evaluation

This thesis shows both the use of acoustic metamaterials and coded waveforms for Non-Destructive Testing (NDT) applications. The exotic features of the acoustic metamaterials have been exploited for imaging a sub-wavelength object at frequencies into the middle audible – low ultrasonic range, thus beating the so-called diffraction limit. This has been investigated by means of both Finite Element Modelling and a series of experiments. These demonstrate that acoustic metamaterials fabricated using additive manufacturing with a polymer substrate can be used successfully for imaging a subwavelength object within a frequency range that was not previously explored. The experimental setup made use of coded waveform excitation for characterising the performance of these metamaterials in the frequency domain. Such broadband excitations waveforms can be exploited together with advanced signal processing techniques such as Pulse Compression (PuC) to enhance the Signal-to-Noise Ratio (SNR). Hence, a first step toward the realization of an acoustic metamaterial device that can be used with coded waveforms and PuC has been investigated. Parallel research on the optimal use of coded signals with PuC techniques has been carried out. The main characteristics of several widely-used coded waveforms and advanced algorithms have been reported. Their features have been investigated numerically so as to provide a benchmark for choosing an optimal coded waveform and pulse compression algorithm for a given NDT application. In addition, the improvement in inspection capabilities given by these advanced signal processing techniques has been tested using real industrial NDT applications in highly scattering and attenuating samples. This has been done by programming a tailored post-processing/imaging algorithm for each specific application. Furthermore, a portable instrumentation system is described, which is capable of providing a performance comparable to standard bench-top PuC instruments. Finally, an innovative strategy for using coded signals and PuC in active thermography inspection has been investigated. This results in an enhanced defect discrimination in challenging materials with respect to the standard PuC thermography procedure