Testing the equivalence principle via the shadow of black holes

Funding: H.Z. acknowledges support from the USTC fellowship for international visiting professors and from Shanghai Astronomical Observatory. This work is sup- ported in part by the NSFC (No. 11722327, No. 11653002, No. 11961131007, No. 11725312, No. 11421303), by the CAST (No. 2016QNRC001), by the National Youth Talents Program of China, and by the Fundamental Research Funds for Central Universities. The work of D.A.E. is supported in part by the Foundational Questions Institute.We study the equivalence principle, regarded as the cornerstone of general relativity, by analyzing the deformation observable of black hole shadows. Such deformation can arise from new physics and may be expressed as a phenomenological violation of the equivalence principle. Specifically, we assume that there is an additional background vector field that couples to the photons around the supermassive black hole. This type of coupling yields impact on the way the system depends on initial conditions and affects the black hole shadow at different wavelengths by a different amount, and therefore observations of the shadow in different wavelengths could constrain such couplings. This can be tested by future multiband observations. Adopting a specific form of the vector field, we obtain constraints on model parameters from Event Horizon Telescope observations and measurements of gas/stellar orbits.Publisher PDFPeer reviewe

High Frequency Needle Ultrasonic Transducers Based on Lead-Free Co Doped Na0.5Bi4.5Ti4O15 Piezo-Ceramics

This paper describes the design, fabrication, and characterization of tightly focused (ƒ-number close to 1) high frequency needle-type transducers based on lead-free Na0.5Bi4.5Ti3.975Co0.025O15 (NBT-Co) piezo-ceramics. The NBT-Co ceramics, are fabricated through solid-state reactions, have a piezoelectric coefficient d33 of 32 pC/N, and an electromechanical coupling factor kt of 35.3%. The high Curie temperature (670 °C) indicates a wide working temperature range. Characterization results show a center frequency of 70.4 MHz and a −6 dB bandwidth of 52.7%. Lateral resolution of 29.8 μm was achieved by scanning a 10 μm tungsten wire target, and axial resolution of 20.8 μm was calculated from the full width at half maximum (FWHM) of the pulse length of the echo. This lead-free ultrasonic transducer has potential applications in high resolution biological imaging

Ultrahigh Frequency Ultrasonic Transducers Design with Low Noise Amplifier Integrated Circuit

This paper describes the design of an ultrahigh frequency ultrasound system combined with tightly focused 500 MHz ultrasonic transducers and high frequency wideband low noise amplifier (LNA) integrated circuit (IC) model design. The ultrasonic transducers are designed using Aluminum nitride (AlN) piezoelectric thin film as the piezoelectric element and using silicon lens for focusing. The fabrication and characterization of silicon lens was presented in detail. Finite element simulation was used for transducer design and evaluation. A custom designed LNA circuit is presented for amplifying the ultrasound echo signal with low noise. A Common-source and Common-gate (CS-CG) combination structure with active feedback is adopted for the LNA design so that high gain and wideband performances can be achieved simultaneously. Noise and distortion cancelation mechanisms are also employed in this work to improve the noise figure (NF) and linearity. Designed by using a 0.35 μm complementary metal oxide semiconductor (CMOS) technology, the simulated power gain of the echo signal wideband amplifier is 22.5 dB at 500 MHz with a capacitance load of 1.0 pF. The simulated NF at 500 MHz is 3.62 dB

Characterizing mechanical change in metals using amplitude-modulated diffuse ultrasound

International audienceIn this article, we present an ultrasonic method based on diffuse ultrasound with successive excitation amplitudes. This method provides amplitude-dependent parameters of diffuse ultrasound using coda wave interferometry, and these parameters can be used to characterize mechanical change in metallic materials. The localized mechanical change caused by an instantaneous 400°C thermal shock in a meter-scale aluminum alloy slab was characterized by measuring the diffuse-wave velocity change and decorrelation coefficient as functions of the excitation amplitude. The potential mechanisms and spatial distribution that cause the observed amplitude-dependent diffuse waveform modification are discussed. Combining the method presented here with complementary approaches will enhance the ability to nondestructively detect early-stage damage in the laboratory or in the field

Ultrahigh Frequency Ultrasonic Transducers (150MHz) Based on Silicon Lenses

Acoustic microscopes and acoustic tweezers have great value in the application of microparticle manipulation, biomedical research and non-destructive testing. Ultrahigh frequency (UHF) ultrasonic transducers act as the key component in acoustic microscopes, and acoustic tweezers and acoustic lenses are essential parts of UHF ultrasonic transducers. Therefore, the preparation of acoustic lenses is crucial. Silicon is a suitable material for preparing acoustic lenses because of its high acoustic velocity, low acoustic attenuation and excellent machinability. In previous research, silicon lenses were mainly prepared by etching. However, etching has some drawbacks. The etching of large sizes is complex, time-consuming and expensive. Furthermore, vertical etching is preferred to spherical etching. Thus, a new method of ultra-precision machining was introduced to prepare silicon lenses. In this paper, silicon lenses with an aperture of 892 μm and a depth of 252 μm were prepared. Then, UHF ultrasonic transducers with a center frequency of 157 MHz and a −6-dB bandwidth of 52% were successfully prepared based on silicon lenses. The focal distance of the transducers was 736 μm and the F-number was about 0.82. The transducers had a lateral resolution of 11 μm and could distinguish the 13 μm slots on silicon wafers clearly

A Survey on Analog-to-Digital Converter Integrated Circuits for Miniaturized High Resolution Ultrasonic Imaging System

As traditional ultrasonic imaging systems (UIS) are expensive, bulky, and power-consuming, miniaturized and portable UIS have been developed and widely utilized in the biomedical field. The performance of integrated circuits (ICs) in portable UIS obviously affects the effectiveness and quality of ultrasonic imaging. In the ICs for UIS, the analog-to-digital converter (ADC) is used to complete the conversion of the analog echo signal received by the analog front end into digital for further processing by a digital signal processing (DSP) or microcontroller unit (MCU). The accuracy and speed of the ADC determine the precision and efficiency of UIS. Therefore, it is necessary to systematically review and summarize the characteristics of different types of ADCs for UIS, which can provide valuable guidance to design and fabricate high-performance ADC for miniaturized high resolution UIS. In this paper, the architecture and performance of ADC for UIS, including successive approximation register (SAR) ADC, sigma-delta (Σ-∆) ADC, pipelined ADC, and hybrid ADC, have been systematically introduced. In addition, comparisons and discussions of different types of ADCs are presented. Finally, this paper is summarized, and presents the challenges and prospects of ADC ICs for miniaturized high resolution UIS

Fabrication and Characterization of High-Frequency Ultrasound Transducers Based on Lead-Free BNT-BT Tape-Casting Thick Film

A lead-free 0.94(Na0.5Bi0.5) TiO3-0.06 BaTiO3 (BNT-BT) thick film, with a thickness of 60 μm, has been fabricated using a tape-casting method. The longitudinal piezoelectric constant, clamped dielectric permittivity constant, remnant polarization and coercive field of the BNT-BT thick film were measured to be 150 pC/N, 1928, 13.6 μC/cm2, and 33.6 kV/cm, respectively. The electromechanical coupling coefficient kt was calculated to be 0.55 according to the measured electrical impedance spectrum. A high-frequency plane ultrasound transducer was successfully fabricated using a BNT-BT thick film. The performance of the transducer was characterized and evaluated by the pulse-echo testing and wire phantom imaging operations. The BNT-BT thick film transducer exhibits a center frequency of 34 MHz, a −6 dB bandwidth of 26%, an axial resolution of 77 μm and a lateral resolution of 484 μm. The results suggest that lead-free BNT-BT thick film fabricated by tape-casting method is a promising lead-free candidate for high-frequency ultrasonic transducer applications

Thermal Performance Optimization Simulation Study of a Passive Solar House with a Light Steel Structure and Phase Change Walls

Phase change materials are used in passive solar house construction with light steel structure walls, which can overcome the problems of weak heat storage capacity and poor utilization of solar heat and effectively solve the thermal defects of light steel structure walls. Based on this, on the basis of preliminary experimental research, this study further carried out theoretical analysis and simulation research on the thermal performance of a light steel structure passive solar house (Trombe form) with PCM walls. Through the heat balance analysis of heat transfer in the heat collecting partition wall, the theoretical calculation formula of the phase change temperature of the PCM was obtained, and it verified theoretically that the phase change temperature value should be 1–3 °C higher than the target indoor air temperature. The evaluation index “accumulated daily indoor temperature offset value” was proposed for evaluating the effect of phase change materials on the indoor temperature of the passive solar house, and “EnergyPlus” software was used to study the influence of the phase change temperature, the amount of material, and the thickness of the insulation layer on the indoor air temperature in a natural day. The results showed that there was a coupling relationship among the performance and between of the thickness of the PCM layer and the phase change temperature. Under typical diurnal climate conditions in the northern Tibetan Plateau of China, the optimal combination of the phase change temperature and the layer thickness was 17 °C and 15 mm, respectively. Especially at a certain temperature, excessive increases in the thickness of the phase transition layer could not improve the indoor thermal environment. For this transition temperature, there exists an optimal transition layer thickness. For a Trombe solar house, the thickness of the insulation layer has an independent impact on indoor temperature compared to other factors, which has an economic value, such as 50 mm in this case. In general, this paper studied the relationship between several important parameters of the phase change wall of a solar house by using numerical simulation methods and quantitatively calculated the optimal parameters under typical meteorological conditions, thus providing a feasible simulation design method for similar engineering applications

Recent Development and Perspectives of Optimization Design Methods for Piezoelectric Ultrasonic Transducers

A piezoelectric ultrasonic transducer (PUT) is widely used in nondestructive testing, medical imaging, and particle manipulation, etc., and the performance of the PUT determines its functional performance and effectiveness in these applications. The optimization design method of a PUT is very important for the fabrication of a high-performance PUT. In this paper, traditional and efficient optimization design methods for a PUT are presented. The traditional optimization design methods are mainly based on an analytical model, an equivalent circuit model, or a finite element model and the design parameters are adjusted by a trial-and-error method, which relies on the experience of experts and has a relatively low efficiency. Recently, by combining intelligent optimization algorithms, efficient optimization design methods for a PUT have been developed based on a traditional model or a data-driven model, which can effectively improve the design efficiency of a PUT and reduce its development cycle and cost. The advantages and disadvantages of the presented methods are compared and discussed. Finally, the optimization design methods for PUT are concluded, and their future perspectives are discussed