ABSTRACT
This paper describes the design and performance of a phase demodulation scheme based on software-defined radio (SDR), applied in heterodyne interferometry. The phase retrieval is performed in real time by means of a low-cost SDR with a wideband optoelectronic front-end. Compared to other demodulation schemes, the system is quite simpler, versatile, and of lower cost. The performance of the demodulator is demonstrated by measuring the displacement per volt of a thin-film polymeric piezoelectric transducer based on polyvinylidene fluoride for ultrasonic applications. We measured displacements between 3.5 pm and 122 pm with 7% relative uncertainty, in the frequency range from 20 kHz to 1 MHz.
ABSTRACT
This paper describes the design and performance of a low-noise and high-speed optical sensor that provides two output signals in quadrature from the simultaneous detection of four phase-shifted interferograms. The sensor employs four high-speed photodiodes and high-speed, low-noise transimpedance amplifiers. The optical and electronic design was optimized for high-speed displacement measurement interferometry, over a broad range of operating frequencies. Compared to other experimental schemes, the sensor is simpler and of lower cost. The performance of the sensor is demonstrated by characterizing a piezoelectric transducer for ultrasonic applications. We measured displacements between 38 pm and 32 nm with 6% relative uncertainty, in the frequency range from 1 to 2 MHz.
ABSTRACT
The scope of this work is to present a phase demodulator that enables the recovery of temporal phase information contained in the phase difference between two signals with different polarizations. This demodulator is a polarization interferometer that may consist only of a uniaxial crystal slab and a polarizer sheet. The phase shift between two orthogonal components of the electric field is translated into space by means of birefringent crystals, which act as demodulators or phase analyzers with great robustness. The experimental scheme utilized is based on a simple conoscopic interference setup. Each portion of the space in which the interference pattern is projected contains not only the unknown temporal phase we want to recover, but also a phase shift due to the uniaxial crystal itself. The underlying idea is developing simultaneous phase shifting with uniaxial crystals. Thus, different phase recovery techniques can be applied in order to maximize their ability to track high-speed signals. Depending on the characteristics of the fringe pattern, it will permit phase recovery via different classical procedures. In order to prove the demodulator under different experimental and signal processing schemes, we employed it for wave plate characterization. The results obtained not only allow some wave plate features such as axes determination and retardance to be characterized, but also prove the working principle and capabilities of the demodulator.
ABSTRACT
Atopic dermatitis (AD) is the most common chronic inflammatory skin disease worldwide. Its severity is assessed using scores that rely on visual observation of the affected body surface area, the morphology of the lesions and subjective symptoms, like pruritus or insomnia. Ideally, such scores should be complemented by objective and accurate measurements of disease severity to standardize disease scoring in routine care and clinical trials. Recently, it was shown that raster-scanning optoacoustic mesoscopy (RSOM) can provide detailed three-dimensional images of skin inflammation processes that capture the most relevant features of their pathology. Moreover, precise RSOM biomarkers of inflammation have been identified for psoriasis. However, the objectivity and validity of such biomarkers in repeated measurements have not yet been assessed for AD. Here, we report the results of a study on the repeatability of RSOM inflammation biomarkers in AD to estimate their precision. Optoacoustic imaging analysis revealed morphological inflammation biomarkers with precision well beyond standard clinical severity metrics. Our findings suggest that optoacoustic mesoscopy may be a good choice for quantitative evaluations of AD that are inaccessible by other methods. This could potentially enable the optimization of disease scoring and drug development.
ABSTRACT
A method for calibration of ultrasonic sensors for optoacoustics that provides both frequency response and sensitivity is presented. In order to obtain the bandwidth and the frequency response of an uncalibrated sensor, a point source with broadband spectra generated by a laser-induced bubble on a copper wire submerged in water is employed. On the other hand, the sensitivity measurement relies on the spatial symmetry of the pressure pulse and on a calibrated transducer. Therefore, two sensors are employed to detect the pressure pulse at the same distance from the source. The symmetry of the acoustic field that arrives at both transducers is adjusted and verified by means of an optical interferometer that provides a null signal when the copper wire is placed at the right position. The method is tested on the characterization of a thin-film polymeric piezoelectric transducer with a cylindrical focused shape.
ABSTRACT
We present a method to generate sub-microsecond quasi-unipolar pressure pulses. Our approach is based on the laser irradiation of a thin copper wire submerged in water. The acoustic waveforms were recorded using two different, well characterized, wideband detection techniques: piezoelectric and optical interferometry. The results show that the irradiated target behaves as an omnidirectional source. Moreover, the peak pulse pressure linearly depends on the laser fluence and the source size. From the results, we propose an empirical equation for the spatial and temporal profile of the pressure pulse. The method has several advantages: ease of implementation, high repeatability, wide ultrasonic bandwidth and quasi-unipolar time profile. These features lead to potential applications of this acoustic source in ultrasonic characterization such as transducer systems, materials or passive devices.