Wavefront Synthesis Research Articles

A far-field super-resolution imaging method based on phase constructive

Super-resolution imaging under passive illumination is always a crucial issue to be addressed. Because the wavefront of an incoherent light field is not easily detected, it is hard to achieve super-resolution imaging by synthetic aperture under passive illumination. In this work, we proposed a super-resolution method based on phase constructive. We use a quadrature phase-shifting algorithm to retrieve the wavefront from a series of correlation patterns and reconstruct the super-resolution image with a wavefront synthesis algorithm. A simulation result verifies the effectiveness of our proposed method with a USAF-1951 target as the object.

Faithful Wavefront Synthesis for Holography Using Light Field and Depth Information

Faithful Wavefront Synthesis for Holography Using Light Field and Depth Information

A region based random multi-pixel search algorithm to improve the binary hologram reconstruction quality

Direct binary search (DBS) is an effective method for the generation of binary computer-generated holograms (CGHs), which has been widely used in wavefront synthesis, optical tweezers and 3D display. However, the correlation of pixels in holograms is neglected in DBS, resulting the algorithm easily converging to local minimum and leading to an unsatisfactory reconstruction quality. To ameliorate this disadvantage, we proposed a new algorithm by randomly selecting multiple related pixels in the same region to generate hologram. Compared with DBS, the mean square error (MSE) of reconstructed image in simulation has declined from 844.85 to 445.74, the peak signal to noise ratio (PSNR) has increased from 18.86 to 21.64 and structural similarity (SSIM) has increased from 0.336 to 0.459. The reconstructed image in experiment shows fewer noise points and clearer outline. Both the numerical and experimental results demonstrate that the reconstruction quality can be improved by this algorithm, which will exhibit great applications in the fields of data storage, microscopy, and true sense dynamic 3D display.

Scalable non-mode selective Hermite–Gaussian mode multiplexer based on multi-plane light conversion

Non-mode-selective (NMS) multiplexers (muxes) are highly desirable for coherent power combining to produce a high-power beam with a shaped profile (wavefront synthesis) from discrete, phase-locked emitters. We propose a design for a multi-plane light conversion (MPLC)-based NMS mux, which requires only a few phase masks for coherently combining hundreds of discrete input beams into an output beam consisting of hundreds of Hermite–Gaussian (HG) modes. The combination of HG modes as a base can further construct a beam with arbitrary wavefront. The low number of phase masks is attributed to the identical zero-crossing structure of the Hadamard-coded input arrays and of the output HG modes, enabling the practicality of such devices. An NMS mux supporting 256 HG modes is designed using only seven phase masks, and achieves an insertion loss of − 1.6 dB , mode-dependent loss of 4.7 dB, and average total mode crosstalk of − 4.4 dB . Additionally, this design, featuring equal power for all input beams, enables phase-only control in coherent power combining, resulting in significant simplifications and fast convergence compared with phase-and-amplitude control.

Active noise control based on wavefront synthesis for a sound passing through an open window

Active noise control based on wavefront synthesis for a sound passing through an open window

Experimental analysis of the instantaneous mechanical torque applied to objects by means of acoustic beams

In this work, we quantify the mechanical torque and the angular momentum transferred by an acoustic beam (AB) to disk-like samples of flat surface and chiral objects. Also, two types of acoustic beams are generated, i.e., quasi-planar and helical beams. To produce the AB, we have fabricated a multitransducer of 123 ultrasonic elements (40 kHz) deployed on a triangular lattice which allows us an electronic wavefront synthesis by modifying the phase of each emitter. The samples to be freely rotated are supported at its center of mass by a sharp tip of a thin metallic needle vertically located at the geometrical center of the multitransducer. The instantaneous angular response of samples of different size, made of cork and plastic, was extracted using a fixed video camera. The instantaneous torque exerted on each sample and the transferred angular momentum are estimated by fitting the output of a dynamic model of the sample behavior to empirical data. The experimental apparatus proves to be useful to estimate the acoustic torque induced by AB on objects and its dependency on the geometries of the samples and the AB wavefront, their relative size and the intensity of the acoustic beam.

Basic Study on Active Noise Control Based on Wavefront Synthesis

Basic Study on Active Noise Control Based on Wavefront Synthesis

Perception of a virtual violin radiation in a wave field synthesis system

A method to synthesize the sound radiation characteristics of musical instruments in a wave front synthesis system is proposed and tested. Radiation patterns of a violin are measured with a circular microphone array which consists of 128 pressure receivers. For each critical frequency band one exemplary radiation pattern is decomposed to circular harmonics of order 0 to 64. So the radiation characteristic of the violin is represented by 25 complex radiation patterns. On the reproduction side, these circular harmonics are approximated by 128 densely spaced monopoles by means of 128 broadband impulses. An anechoic violin recording is convolved with these impulses, yielding 128 filtered versions of the recording. These are then synthesized as 128 monopole sources in a wave front synthesis system and compared to a virtual monopole playing the unfiltered recording. The subjects perceive the tone color of the recreated virtual violin as being dependent on the listening position and report that the two source ty...

Perceptually motivated sound field synthesis for music presentation

The conceptualization and implementation of a psychoacoustic sound field synthesis system for music is presented. Critical bands, the precedence effect, and integration times of the auditory system as well as the radiation characteristics of musical instruments are implemented in the signal processing. Interaural coherence, masking and auditory scene analysis principles are considered as well. The sound field synthesis system creates a natural, spatial sound impression and precise source localization for listeners in extended listening area, even with a low number of loudspeakers. Simulations and a listening test provide a proof of concept. The method is particularly robust for signals with impulsive attacks and quasi-stationary phases as in the case of many instrumental sounds. It is compatible with many loudspeaker setups, such as 5.1, ambisonics systems and loudspeaker arrays for wave front synthesis. The psychoacoustic sound field synthesis approach is an alternative to physically centered wave field synthesis concepts and conventional stereophonic sound and can benefit from both paradigms. Additional psychoacoustic quantities that have the potential to be implemented in the presented and other audio systems are discussed.

Reflective metasurface lens with an elongated needle-shaped focus

Novel multifocal flat metasurface (MS) lenses are developed using two techniques: (i) polarization diversity, and (ii) annular segmentation of the lens aperture. The polarization-diversity technique enables overall lens aperture reuse, thus doubling the number of foci through the simultaneous focusing of two orthogonal linearly polarized incident beams at two distinct foci using the lens aperture. The annular-segmentation technique, on the other hand, is independent of incident beam polarization and is only based on dividing the lens aperture into concentric annular segments that converge different portions of the illuminating beam at different foci. The total number of foci can be further increased by combining the polarization-diversity and the annular-segmentation techniques. Subsequently, the concept of multifocality is further extended to design a novel flat lens with an overall single needle-like focal region with elongated depth of focus (DOF) without loss of lateral resolution. To this goal, we design a multifocal lens with overlapping profiles of foci superposed into a single elongated needle-shaped focal region. Using the combination of polarization-diversity and annular-segmentation techniques, we develop a novel MS flat lens made of Y-shaped nanoantennas, whose polarization-dependent reflection phase and amplitude can be controlled independently via their geometrical parameters. Via numerical calculations, we demonstrate that the proposed MS lens has an overall single focal region with an extremely long DOF of about 74.1 λ, a lateral full width at half maximum varying in the range of 1.37 λ to 2.8 λ, and a numerical aperture of about 0.26 (considering the center of the focal region as the effective focal point). Here, the MS lens’s capability to synthesize extremely long DOF is conceptually demonstrated without resorting to time-consuming and complicated wavefront synthesis methods. The engineering of focal intensity profiles with flat MSs may introduce significant advancement in nanoimaging, many areas of microscopy, and ophthalmic applications.

Global active noise control based on wavefront synthesis

Global active noise control based on wavefront synthesis

Method And Apparatus For Reproducing Audio Signal

An audio signal is supplied to a loudspeaker array to perform wavefront synthesis. A virtual sound source is produced at an infinite distance using wavefront synthesis. A propagation direction of a sound wave emitted from the virtual sound source is changeable.

Sound Field Reproduction by Wavefront Synthesis Using Directly Aligned Multi Point Control

In this paper, we present a comparative study on directly aligned multi point controlled wavefront synthesis (DMCWS) and wave field synthesis (WFS) for the realization of a high-accuracy sound reproduction system, and the amplitude, phase and attenuation characteristics of the wavefronts generated by DMCWS and WFS are assessed. First, in the case of DMCWS, we derived an optimal control-line coordinate based on a numerical analysis. Next, the results of computer simulations revealed that the wavefront in DMCWS has wide applicability in both the spatial and frequency domains with small amplitude and phase errors, particularly above the spatial aliasing frequency in WFS, and we clarified that the amplitude error in DMCWS has similar behavior to the well-known approximate expression for spatial decay in WFS; this implies the ease of taking into account estimating the amplitude error in DMCWS. Finally, we developed wavefront measurement system and measured a DMCWS wavefront using our wavefront measurement system and algorithm. The results of measurements clarified the frequency characteristics of a loudspeaker. Also, DMCWS has wide applicability in frequency domains in actual environments. From these findings, we concluded the advantageousness of DMCWS compared with WFS.

Research trends of wave front synthesis technologies

Research trends of wave front synthesis technologies

Imaging tissue and wavefront control: Application to acousto‐optics and photoacoustics

Although optical waves do not exhibit the same ability to be manipulated as e.g. electromagnetic waves up to a few GHz or acoustic waves, for which field emitters‐detectors are available, various tools are nevertheless available in the optical domain which open the path to tricks which can be used in the context of sound‐light detection. In the purely optical domain, one knows the impact of deformable mirrors led to adaptive optics which is now coupled to OCT for retinal examination. Real time holography leads to complex wavefront synthesis and are useful in acousto‐optics (AO) to monitor very complex speckle field distributions. Phase conjugation which is in certain conditions equivalent to time reversal, starts to be used for wavefront retrieval after propagation in turbid media, one can think to use it for AO signal monitoring; moreover matrices of spatial light modulators allow to control light not only spatially but also in the frequency domain and open the field to new astonishing experiments. We will discuss a few applications and perspectives offered by these new devices to the field of biomedical imaging.

Wavefront synthesis using wideband constant delay IIR filters

With a view to realizing sound image shifting with a linear speaker array and a two-dimensional digital filter, wavefront synthesis by using low-order low-pass broadband constant delay IIR filters as the one-dimensional filters connected to each speaker is proposed. In the constant delay IIR filter, a bandpass MFD polynomial with a constant delay region wider than the low-pass MFD polynomial in the denominator is used. The amplitude has a flat low range at the set of complex mirror image zeros. As a result of multiple zeros at z = −1 and a set of real image zeros in the neighborhood, a bandwidth equal to the constant delay bandwidth as well as a stopband are formed. For wavefront synthesis, even and odd order constant delay filters and integer delay terms are used to provide the specified delay. The formation of a virtual sound source is confirmed by means of a low-order design example. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 88(10): 1–11, 2005; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/ecjc.20165

Sound field control and reproduction by wave front synthesis considering human hearing sense

Sound field control and reproduction by wave front synthesis considering human hearing sense

A contoured-beam horn-reflector antenna designed by plane wave synthesis

A satellite reflector antenna having a main beam and subbeam often enables us to illuminate the service area effectively. We present a new reflector-shaping design method for a contoured-beam antenna producing such beams by means of wave front synthesis. We determine the shape of the wave front associated with the main beam and then superimpose a plane wave associated with the subbeam onto it on the antenna aperture. The reflector is shaped to attain such a combined wave front by the optical path law. This method is applied to shape a 30/20-GHz horn-reflector antenna, whose diameter is 950 mm and flare angle (full) is 40°, and the fundamental properties of this method are investigated. It is found that this method is effective for producing a contoured-beam composed of a main beam and a subbeam. As an application, we design a contoured-beam horn-reflector antenna illuminating Japanese territory by means of the plane wave synthesis. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(2): 62–71, 2001

For A Better Acoustical Environment. 5. Wave-front Synthesis by Loudspeaker Array.

For A Better Acoustical Environment. 5. Wave-front Synthesis by Loudspeaker Array.

Sound field reproduction using wavefront synthesis based on the four microphones measurements

Reverberation time, distribution of sound pressure, intelligibility, and/or other parameters are used in sound room evaluation. But characteristics of room acoustics are complex, and often quite different impressions are received from rooms that have nearly the same parameters. These differences might come from the difference of spatial information, especially in early reflection periods. Thus a four-microphone method is proposed to measure spatial information of the room. Here, the sound field reproduction using the wavefront synthesis [A. J. Berkhout, J. Acoust. Soc. Am. 93(5) (1993) and Y. Yamasaki, J. Acoust. Soc. Jpn. 10(2) (1989)] based on the four-point measurement is discussed.