A system and method for micro-metalens based super resolution imaging using bulk ultrasonics

Abstract

The present invention discloses a system (100) and method (900) for micro-metalens based super resolution imaging using bulk ultrasonics. The system provides micron- scale resolution using linear bulk ultrasonic scanning in the 'through-transmission' mode. The system (100) comprises an ultrasonic transmitter unit (102), a nano-motion scanning stage (104), a sample holder (106), at least one sample (108), a metalens (110), a laser unit (112), a receiver unit (114), and a user device (116). The ultrasonic transmitter unit (102) comprises a fingertip transducer, which is integrated with a pulser. The ultrasonic transmitter unit (102) is connected to the computer-controlled nano-motion scanning stage (104) which supports the sample holder (106) holding the at least one sample (108) and the micro-metalens (110) for imaging. The receiver unit (114) detects the out-of-plane displacement from the at least one sample (108) and turns it into an ultrasonic signal using the receiver unit (114). Signals are then processed for sub-wavelength imaging by the user device (116).

Description

[0001] Description

[0002] Title of Invention : | A SYSTEM AND METHOD FOR MICROMETALENS BASED SUPER RESOLUTION IMAGING USING BULK ULTRASONICS

[0003] Technical Field

[0004] [1] The field of invention generally relates to a system for material diagnostics at greater depths with high resolution using Fabry-Perot type ultrasonic-micro- metalenses. More specifically, it relates to a system and method to overcome the limitations of expensive and radiation-prone electromagnetic techniques by utilizing ultrasonic waves and innovative micro-metalens technology for subwavelength resolution imaging in material inspection and diagnostics.

[0005] Background Art

[0006] [2] Evaluation of materials at significant depths with high resolution remains one of the most persistent challenges in scientific inquiry. Across critical domains including quantum materials, high-energy physics, nuclear power generation, aviation, and biomedical diagnostics, the inspection and qualification of bulk components with microscopic defect features present formidable hurdles. While electromagnetic methods like radiographic (X-ray) testing offer high resolution, their penetration in solids is limited, and they often involve ionizing radiation, rendering them expensive and restricting their widespread application.

[0007] Ultrasound presents a promising alternative due to its better penetration of thicker samples, cost-effectiveness, and non-ionizing nature. However, conventional ultrasounds have limitations in imaging microscopic defect features due to longer wavelengths.

[0008] [3] Currently, existing systems rely heavily on electromagnetic methods such as radiographic testing or conventional ultrasound techniques for material inspection. While these methods offer some degree of resolution, they face challenges in penetrating deep within solid materials to identify microscopic defects accurately. Moreover, the ionizing radiation associated with electromagnetic methods poses risks and regulatory hurdles, while conventional ultrasound's limited applicability for imaging small defect features hampers its effectiveness in critical applications.

[0009] [4] Other existing systems have tried to overcome the limitations of conventional ultrasound, by developing techniques like scanning acoustic microscopy (SAM) to provide better resolution at elevated frequencies. However, SAM is constrained to surface imaging, limiting its usefulness for inspecting defects deep within solid materials. Similarly, approaches like near-field scanning and time reversal techniques aimed at overcoming the diffraction limit have been hindered by issues such as signal noise and post-processing complexities. Although advancements in metamaterial lenses have shown promise in achieving subwavelength resolution, their practical applicability for imaging microscopic defects within bulk materials remains limited, especially in critical applications where feature dimensions are on the micron-scale.

[0010] [5] Thus, in light of the challenges posed by current methods and the limitations of existing systems, it is implied that there is a need for a system and method that can evaluate materials at greater depths with high resolution, which is reliable and does not suffer from the problems discussed above.

[0011] Object of Invention

[0012] [6] The principal object of this invention is to provide a system for micro-metalens- based super-resolution imaging using bulk ultrasonics.

[0013] [7] A further object of the invention is to provide a system for super-resolution imaging, detailing a setup comprising an ultrasonic transmitter unit, nano-motion scanning stage, sample holder, sample, metamaterial lens, receiver unit, and user device.

[0014] [8] Another object of the invention is to provide a system developed for superresolution imaging, demonstrating micrometer-scale resolution using bulk ultrasonics by incorporating an ultrasonic transducer attached to a nano-motion scanning stage, an acrylic tank for sample placement, and a micro-metalens for imaging, all arranged to facilitate through-transmission ultrasonic scanning.

[0015] [9] A further object of the invention is to provide micro-metalens fabricated by careful selection of geometric parameters.

[0010] Another object of the invention is to configure a user device for analyzing A- scan data, filtering ultrasonic signals, and plotting B-scan results showcasing defect separation resolution.

[0016]

[0011] A further object of the invention is to demonstrate a defect separation resolution down to 50 pm for the first time in the world for the bulk ultrasonic regime achieved using the microfabricated metalens.

[0017] Brief Description of Drawings

[0018]

[0012] This invention is illustrated in the accompanying drawings, throughout which, like reference letters indicate corresponding parts in the various figures.

[0019]

[0013] The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0020] Fig. 1a

[0021]

[0014] [Figure 1 a] depicts / illustrates a schematic of the system for micron-scale imaging using linear bulk ultrasonics, in accordance with an embodiment of the present disclosure;

[0022] Fig. 1b

[0023]

[0015] [Figure 1 b] depicts / illustrates a pictorial representation of the actual experimental system for demonstrating micron-scale sub-wavelength imaging, in accordance with an embodiment of the present disclosure;

[0024] Fig. 2a

[0025]

[0016] [Figure 2a] depicts / illustrates a schematic illustration of through-transmission ultrasonic scanning of silicon sample with sub-wavelength defects by micro-focal LDV and micro-metalenses, in accordance with an embodiment of the present disclosure;

[0026] Fig. 2b

[0027]

[0017] [Figure 2b] depicts / illustrates a pictorial representation of the actual experimental configuration, in accordance with an embodiment of the present disclosure.

[0028] Fig. 3a

[0018] [Figure 3a] depicts / illustrates a graphical representation of modulus of transmission coefficient versus parallel momentum (x-axis) and frequency (y-axis), in accordance with an embodiment of the present disclosure.

[0029] Fig. 3b

[0030]

[0019] [Figure 3b] depicts / illustrates a graphical representation of modulus of zeroorder transmission coefficient evaluated for 3 different frequencies, in accordance with an embodiment of the present disclosure.

[0031] Fig. 4a

[0032]

[0020] [Figure 4a] depicts / illustrates a pictorial representation of micro fabricated metalens, top coated with a thin layer of gold for high reflectivity for micro-focal ultrasonic laser reception, in accordance with an embodiment of the present disclosure.

[0033] Fig. 4b

[0034]

[0021] [Figure 4b] depicts / illustrates a pictorial representation of micro fabricated metalens, bottom view showing metamaterial mesh with scale; and SEM images of mesh, in accordance with an embodiment of the present disclosure.

[0035] Fig. 4c

[0036]

[0022] [Figure 4c] depicts / illustrates a pictorial representation of bottom view of micro fabricated metalens, in accordance with an embodiment of the present disclosure.

[0037] Fig. 4d

[0038]

[0023] [Figure 4d] depicts / illustrates a pictorial representation of side view of micro fabricated metalens, in accordance with an embodiment of the present disclosure.

[0039] Fig. 5

[0040]

[0024] [Figure 5] depicts / illustrates a graphical representation of an example time trace or ‘A-scan’ from the experiment with and without microfabricated metalens (the first arrival of the received signal is windowed for further analysis), in accordance with an embodiment of the present disclosure.

[0041] Fig. 6

[0025] [Figure 6] depicts / illustrates a graphical representation of ‘B-scan’ results based on post processed ultrasonic data obtained from a linear scan experiment across the sample by the laser Doppler Vibrometer (LDV) in spatial steps of 10 pm, demonstrating a defect separation resolution down to 50 pm for the first time in the world for the bulk ultrasonic regime achieved using the microfabricated metalens (rectangular box denotes defect locations), in accordance with an embodiment of the present disclosure.

[0042] Fig. 7

[0043]

[0026] [Figure 7] depicts / illustrates a pictorial representation of a Finite Element (FE) model considered for finding the resolution limit, in accordance with an embodiment of the present disclosure.

[0044] Fig. 8a, 8b, and 8c

[0045]

[0027] [Figure 8a, 8b, and 8c] depict simulation and experimental graphical representation of amplitude across B-scans showing resolution at resonant frequencies, in accordance with an embodiment of the present disclosure, in accordance with an embodiment of the present disclosure; and

[0046] Fig. 9

[0047]

[0028] [Figure 9] depicts / illustrates a method for micro-metalens based super resolution imaging using bulk ultrasonics, in accordance with an embodiment of the present disclosure.

[0048] Statement of Invention

[0049]

[0029] The present invention discloses a system and method for micro-metalens based super resolution imaging using bulk ultrasonics.

[0050]

[0030] Further, the system comprises at least one ultrasonic transmitter unit to transmit bulk ultrasonic waves.

[0051]

[0031] Furthermore, the system comprises a pulser integrated with the at least one ultrasonic transmitter unit to excite the bulk ultrasonic waves.

[0052]

[0032] Subsequently, the system comprises a sample holder configured to accommodate at least one sample.

[0033] Additionally, the system comprises the at least one sample placed within the sample holder to receive the bulk ultrasonic waves from the ultrasonic transmitter unit.

[0053]

[0034] Furthermore, the system comprises at least one micro-metalens positioned above the sample and aligned to receive the transmitted bulk ultrasonic waves for structured wave manipulation, wherein at least one micro-metalens possess a structured arrangement of microscopic holes.

[0054]

[0035] Subsequently, the system comprises at least one nano-motion scanning stage configured to support the sample holder, the sample, and the micro-metalens.

[0055]

[0036] Additionally, the system comprises at least one receiver unit configured to detect out-of-plane displacement from the sample and convert the out-of-plane displacement into at least one ultrasonic signal.

[0056]

[0037] Thereafter, the system comprises at least one user device configured to process the ultrasonic signal to provide the super resolution imaging.

[0057] Detailed Description

[0058]

[0038] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and / or detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0059]

[0039] The present invention discloses a system and method for micro-metalens based super resolution imaging using bulk ultrasonics. This system offers micron- scale resolution through linear bulk ultrasonic scanning in the 'through- transmission' mode. It comprises an ultrasonic transmitter unit integrated with a pulser, a computer-controlled nano-motion scanning stage supporting the sample holder and the micro-metalens for imaging, a receiver unit detecting out-of-plane displacement from the sample and converting it into an ultrasonic signal, and a user device for signal processing.

[0060]

[0040] The system facilitates micrometer (or ‘micron’)-scale imaging with commercial ultrasonic probes at frequencies in the range of a few MHz, using novel microstructured metalenses aided by custom-developed sub-micron spot size laser reception. The fingertip transducer excited by the ultrasonic pulser unit generates the bulk ultrasonic waves with a central frequency of approximately 2.08MHz.

[0061] Further, the system demonstrates an extraordinary resolution down to 50 microns (~ A / 75) for the first time in the ultrasonic regime, with excitation frequencies in the bulk regime. Thus, the invention provides a pathway for micrometalens enhanced ultrasound to emerge as an alternative to expensive and radiation- prone electromagnetic techniques.

[0062]

[0041] Figure 1 a depicts / illustrates a schematic of the system 100 for micron-scale imaging using linear bulk ultrasonics, in accordance with an embodiment of the present disclosure.

[0042] The system 100 comprises at least one ultrasonic transmitter unit 102, at least one nano-motion scanning stage 104, at least one at least one sample holder 106, at least one sample 108, at least one micro-metalens 110, at least one laser unit 112, at least one receiver unit 114, and at least one user device 1 16.

[0063]

[0043] The nano-motion scanning stage 104 is configured to support the sample holder 106, micro-metalens 110.

[0064]

[0044] The sample holder 106 is configured to accommodate at least one sample 108.

[0065]

[0045] The sample 108 is placed within the sample holder 106 to receive the bulk ultrasonic waves from the ultrasonic transmitter unit 102.

[0066]

[0046] The micro-metalens 110 is positioned above sample 108 and aligned to receive the transmitted bulk ultrasonic waves for structured wave manipulation. The micro-metalens 110 possess a structured arrangement of microscopic holes.

[0067]

[0047] The receiver unit 114 is configured to detect out-of-plane displacement from sample 108 and convert the out-of-plane displacement into an ultrasonic signal.

[0068]

[0048] The user device 116 is configured to process the ultrasonic signal to provide the super resolution imaging.

[0069]

[0049] Figure 1 b depicts / i llustrates a pictorial representation of the actual experimental system 100 for demonstrating micron-scale sub-wavelength imaging, in accordance with an embodiment of the present disclosure.

[0070]

[0050] In an embodiment, the ultrasonic transmitter unit 102 comprises a fingertip transducer, which is integrated with a pulser. The ultrasonic transmitter unit 102 is connected to the computer-controlled nano-motion scanning stage 104 which supports a sample holder 106, the sample 108, and the micro-metalens 110 for super resolution imaging.

[0071]

[0051] In an embodiment, the sample 108 used is a silicon sample with wire defects.

[0072]

[0052] The receiver unit 114 detects any out-of-plane displacement from the sample 108 and turns it into an ultrasonic signal using the receiver unit 114. These ultrasonic signals are then processed for sub-wavelength imaging by the user device 116.

[0053] Figure 2a depicts / illustrates a schematic illustration 200 of through- transmission ultrasonic scanning of silicon sample 108 with sub-wavelength defects, by a micro-focal LDV 202 and micro-metalenses 110, in accordance with an embodiment of the present disclosure.

[0073]

[0054] The ultrasonic transmitter unit 102 is firmly attached to the nano-motion scanning stage 104. The nano-motion scanning stage 104 itself accommodates an acrylic tank 204 and support structure. The sample 108 is placed in the tank 204 filled with water, and the micro-metalens 110 is axially oriented above.

[0074]

[0055] Upon initiation of the ultrasonic transmitter unit 102, ultrasound waves propagate vertically, traversing through the tank 204 containing water and silicon sample 108 wire defects. Finally, the ultrasonic waves exit the system 100 via the micro-metalens 110 that possess a structured arrangement of microscopic holes / channels.

[0075]

[0056] In an embodiment, the bulk ultrasonic waves propagate via the micro- metalens that possess a structured arrangement of microscopic holes.

[0076]

[0057] In an embodiment, a commercial ‘fingertip contact’ longitudinal ultrasonic probe (Olympus: V133-RM) 206, having a frequency tuned to 2.25 MHz with element size 0.25 inch, is excited by an ultrasonic pulser unit (Ritec 4000 RPR) in the ultrasound transmitter unit 102, while the nano-motion scanning stage 104 is linked to the motion controllers that are controlled by the user device 116.

[0077]

[0058] In an embodiment, the user device 116 is configured with an in-house custom-created software program created using (but not limited to) LabVIEW. The micro-focal ultrasonic laser unit 112 is required to measure the spontaneous displacement caused by the ultrasonic wave field propagating out of the plane from the top surface of the micro-metalens 110 and transmitted to the receiver unit (Optec AIR -522-TWM) 114. The data acquisition unit (DAQ) (Nl PXI-1033) unit 118 acquires the time domain ultrasonic A-scan signal through the custom- created LabVIEW program. For every reception point multiple frames of A-scan signals were averaged to remove the noise and saved in a dedicated directory for post processing and analysis.

[0078]

[0059] The sample holder 106 and miniature water tank 204 were fabricated using 3D printing and arranged in a configuration illustrated in Figure 2a. The geometric characteristics of the micro-metalens 110, such as the hole length, width, and periodicity were carefully selected to satisfy the necessary conditions for optimal functionality.

[0079] Optimization condition Dimension Actual Dimension equivalent to wavelength (X)

[0080] Hole length (L): (2m-l) x (Xwater / 4) X water / 4 180 pm

[0081] [ 'm' must be integer

[0082] Hole width (<p) water / n | 'n' must be X water / 66 10 pm integer & 10

[0083] Periodicity (A): 2p X water / n | 'A' 2 x (X water / 66) 20 pm must be even multiples of X In

[0084] Table 1 . Optimal geometric parameters of micro-metalens

[0085]

[0060] Figure 2b depicts / illustrates a pictorial representation of actual experimental configuration, in accordance with an embodiment of the present disclosure, in accordance with an embodiment of the present disclosure.

[0086]

[0061] The 2.25 MHz longitudinal ultrasonic transducer, as depicted in Figure 2b, has a diameter of 10 mm. It was excited with a 3 cycle Hanning windowed tone burst signal using an ultrasonic pulser specifically tuned to a wideband signal supporting the 1 st Fabry-Perot. The wave propagates within the tank 204, traversing the water medium, interacting with the sub-wavelength spaced defects in the silicon sample 108 and emerging via the water-filled micro-metalens 110. The wavefield then propagates further through a 20 pm thick silicon substrate coated with an 80 nm layer of gold for enhanced reflectivity enabling measurements by a micro-focal LDV 202. The time domain analog voltage output of the laser ultrasonic receiver unit is acquired in synchrony using a data acquisition (DAQ) card, which is connected to the user device 116.

[0087]

[0062] In an embodiment, a program in LabVIEW is used to regulate the scanning procedure and store the A-scan signal for each reception point 208. Further, as the sample 108 surface is not completely orthogonal to the micron scale beam, the micro focal LDV 202 loses focus when it is moved during scanning. This is resolved by adding an auto-focusing algorithm to the LabVIEW code controlling the nano-stage manipulators. The laser spot focus is maintained via continuous monitoring the auxiliary output that is optimal for the focusing of the laser. The main program created using incorporates a local search algorithm that seeks out the optimal value of the auxiliary output by adjusting the vertical axis of the nano stage manipulator and focusing the laser spot prior to acquiring the time domain A-scan signal.

[0088]

[0063] Figure 3a depicts / illustrates a graphical representation of modulus of transmission coefficient versus parallel momentum (x-axis) and frequency (y- axis), in accordance with an embodiment of the present disclosure.

[0089]

[0064] The dimensions of the holey structured metalens 110 are meticulously optimized to achieve a transmission coefficient with a modulus of unity for a wide range of wave vectors, encompassing both propagating and evanescent wave modes. They are verified by plotting the dispersion signatures (see Figure 3a) obtained for a squared holey structure having holes of width (a) equal to 10 pm, periodicity (A) equal to 20 pm, and length of 180 pm obtained for the zero-order transmission coefficient for an elastic plane wave of parallel momentum k\\ = / kf- + k , written as equation (1 ): where qzh = (2n - 1) x TT / 2) ; k0= z is the wave vector of the propagating fundamental waveguide mode; |S00| = and Y = ,k° . AKkOz- Kkz||

[0090]

[0065] In figure 3a, at the Fabry-Perot resonance modes (m=1 ,2,3), the flatness of the dispersion curves is clearly observed.

[0091]

[0066] Figure 3b depicts / illustrates a graphical representation of modulus of zeroorder transmission coefficient evaluated for 3 different frequencies, in accordance with an embodiment of the present disclosure.

[0092]

[0067] The first corresponds to the half of the 1 st Fabry-Perot resonant frequency and the remaining three correspond to the three lowest Fabry-Perot resonant frequencies (m=1 ,2,3).

[0068] Figure 4 depicts / illustrates a pictorial representation of the fabricated micro- metalens accompanied by Scanning Electron Microscopy (SEM) images, verifying the structural integrity post-fabrication.

[0093]

[0069] Figure 4a illustrates a pictorial representation of micro fabricated metalens, top coated with a thin layer of gold for high reflectivity for micro-focal ultrasonic laser reception.

[0094]

[0070] Figure 4b illustrates a pictorial representation of micro fabricated metalens, bottom view showing metamaterial mesh with scale, and SEM images of mesh.

[0095]

[0071] Figure 4c illustrates a pictorial representation of the bottom view of micro fabricated metalens, in accordance with an embodiment of the present disclosure.

[0096]

[0072] Figure 4d illustrates a pictorial representation of side view of micro fabricated metalens, in accordance with an embodiment of the present disclosure.

[0097]

[0073] A holey structured metalens 110 with optimized dimensions is microfabricated using the standard deep reactive ion etching (DRIE) procedure on the silicon substrate.

[0098]

[0074] Figure 5 depicts / illustrates a graphical representation of an example time trace or ‘A-scan’ from the experiment with and without microfabricated metalens 110 (the first arrival of the received signal is windowed for further analysis), in accordance with an embodiment of the present disclosure.

[0099]

[0075] The length of the holes in the micro-metalens 110 is designed in adherence to the Fabry-Perot resonance criteria of (2n-1 ) x(A / 4). Water is introduced into the holes as part of the experimental procedure. The microfabricated metalens 110 effectively retains water within its cavity due to its inherent hydrophilic properties imbued via a suitable thermal oxidation process. Ultrasonic waves propagate through silicon sample 108, interacting with the synthetic defects, and are detected by the micro-focal LDV 202. The defect resolvability is validated by performing a scan on the silicon sample 108 both with and without the presence of a micro metalens 110. The ultrasonic signal in the time domain (or ‘A-scan’) for each scanning point is processed and plotted as a function of the scan length, with the first arriving ultrasonic burst appearing in a windowed format as depicted in Figure 5.

[0100]

[0076] Figure 6 depicts / illustrates a graphical representation of ‘B-scan’ results based on post processed ultrasonic data obtained from a linear scan experiment across the sample 108 by the micro focal LDV 202 in spatial steps of 10 pm, demonstrating a defect separation resolution down to 50 pm for the first time in the world for the bulk ultrasonic regime achieved using the microfabricated metalens 110 (rectangular box denotes defect locations), in accordance with an embodiment of the present disclosure.

[0101]

[0077] The A-scan data for the ultrasonic inspection of 2 slits (not limited) type defects spatially separated by 50 pm are analyzed to demonstrate subwavelength resolution using the micro-metalenses 110. Further, the first arrival of the pulse is windowed from the A-scan, which is obtained from the receiver. The propagating components are eliminated by filtering the windowed signal up to the cut-off frequency, as indicated in table 2. Next, from the Fast Fourier Transform (FFT), the low frequency component in the frequency spectrum is masked by zero. Thereafter, by the inverse FFT technique the time domain signal is recovered. For every A-scan, this procedure is repeated. Finally, B-scan is plotted from all the recovered and processed A scans. The cut-off frequency of the high pass filter is chosen to leave out the low-frequency propagation modes and restore the defect-range wavelengths of the evanescent waves (see Table 2). p > Bulk long wave velocity in Silicon cut-off 2xDistance b / w linear def ects where the bulk longitudinal ultrasonic wave velocity in silicon <100> wafer is -8000 m / s and the distance between defects in this case, is 50 pm. Figure 6 presents ‘B-Scan’ results based on post processed ultrasonic data obtained from a linear scan experiment across the at least one sample 108 by the micro focal LDV 202 in spatial steps of 10 pm. These results demonstrate a defect separation resolution down to 50 pm for the first time in the world for the bulk ultrasonic regime achieved using the microfabricated metalens 1 10. Parameters Value

[0102] Filter mode: High-Pass

[0103] Filter type: Butterworth

[0104] Order: 1

[0105] Cut-off Defect Wavelength Chosen cut-off frequencies: resolution equivalent frequency frequencies

[0106] 50 pm 80 MHz 60 MHz

[0107] Table 2. High-pass filter settings

[0108]

[0078] The invention experimentally demonstrated the development of system and application of a microfabricated metalens 110, to achieve an extraordinary resolution of ~ A / 75 down to 50 pm utilizing a 2.25 MHz commercially available bulk ultrasonic transducer. Achieving such fine resolution at bulk ultrasonic frequencies makes this novel approach innovative for practical inspections, enabling a potential route to inspect finer features deep inside materials, thus matching the capabilities of electromagnetic techniques.

[0109]

[0079] Figure 7 depicts / illustrates a pictorial representation of a Finite Element (FE) model considered for finding the resolution limit, in accordance with an embodiment of the present disclosure.

[0110]

[0080] The resolution limit of the micro-metamaterial is determined to be 20 pm, which corresponds to the periodicity of the micro-holes. The metamaterial lens, with its holey structure, enhances resolution by amplifying evanescent waves through Fabry-Perot resonant modes.

[0111]

[0081] The FE model consists of a water medium where ultrasonic waves are excited at the bottom boundary using a 3-cycle Hanning windowed tone burst signal centered at 2.08 MHz. The micro-metamaterial (Micro MM) structure, positioned between the excitation source and the receiver, contains a series of slits with varying sizes and center-to-center distances, as detailed in Table 3. The at least one receiver is located 200 pm from the defect location, where acoustic pressure variations are recorded as A-scans. These A-scans are post-processed into B- scans to evaluate resolution.

[0112]

[0082] The model employs 4-noded quadrilateral meshing with a seed size of 2.5 pm (approximately Aw / 300 for 2.08 MHz in water) to ensure accurate wave propagation simulation. Each micro-hole is modeled as a water column with a length of 180 pm, a diameter of 10 pm, and a periodicity of 20 pm. The acoustic elements are assigned properties of water, with a density of 1000 kg / m3and a bulk modulus of 2.2 GPa. The explicit FE algorithm is used for wave propagation analysis, running for a total simulation time of 20 ps to capture longitudinal waves effectively.

[0113] Center to center Size of slits(0)

[0114] (50 Micro-meter) (25 Micro-meter)

[0115] 4 Asi (2.08 MHz) / 130 Asi (2.08 MHz) / 190

[0116] (30 micrometer) (20 micrometer)

[0117] Table 3: Parameter studied for resolution limit.

[0118]

[0083] Figures 8a, 8b, and 8c depict simulation and experimental graphical representation of amplitude across Brightness-scans showing resolution at resonant frequencies, in accordance with an embodiment of the present disclosure, in accordance with an embodiment of the present disclosure.

[0119]

[0084] Figure 8a depicts both simulated and experimental B-scan results for slits spaced 200 pm apart, showing good agreement between experimental and simulated results. The rectangular boxes denote the slit placement.

[0120]

[0085] Figure 8b depicts the simulated and experimental B-scan results for 100 pm spaced slits, revealing finer resolution details.

[0121]

[0086] Figure 8c depicts simulation-based B-scan results for slits spaced 50 pm apart, showing successful resolution. Additionally, it highlights the lack of resolution for slits measuring 20 pm, indicating the system's resolution limit.

[0087] Figure 9 depicts / illustrates a method for micro-metalens based super resolution imaging using bulk ultrasonics, in accordance with an embodiment of the present disclosure.

[0122]

[0088] The method 900 begins with transmitting bulk ultrasonic waves by at least one ultrasonic transmitter unit 102, as depicted at step 902. Subsequently, the method 900 discloses exciting the bulk ultrasonic waves by using a pulser integrated with the at least one ultrasonic transmitter unit 102, as depicted at step 904. Thereafter, the method 900 discloses accommodating at least one sample 108 by a sample holder 106, as depicted at step 906. Subsequently, the method 900 discloses receiving the bulk ultrasonic waves from the ultrasonic transmitter unit 102 by the sample 108 placed within the sample holder 106, as depicted at step 908. Subsequently, the method 900 discloses receiving the transmitted bulk ultrasonic waves for structured wave manipulation by at least one micro-meta lens 110 positioned and aligned above the sample 108, as depicted at step 910. Subsequently, the method 900 discloses supporting the sample holder 106 by at least one nano-motion scanning stage 104, the micro-metalens 110, as depicted at step 912. Thereafter, the method 900 discloses detecting out-of-plane displacement from the sample 108 by at least one receiver unit 114 and converting the out-of-plane displacement into at least one ultrasonic signal, as depicted at step 914. Thereafter, the method 900 discloses processing the ultrasonic signal by at least one user device 116 for providing the super resolution imaging, as depicted at step 916.

[0123]

[0089] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and / or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described here.]

Claims

Claims

1. A system (100) for micro-metalens (110) based super resolution imaging using bulk ultrasonics, the system (100) comprising: at least one ultrasonic transmitter unit (102) to transmit bulk ultrasonic waves; a pulser integrated with the at least one ultrasonic transmitter unit (102) to excite the bulk ultrasonic waves; a sample holder (106) configured to accommodate at least one sample (108); the sample (108) placed within the sample holder (106) to receive the bulk ultrasonic waves from the ultrasonic transmitter unit (102); at least one micro-metalens (110) positioned above the sample (108) and aligned to receive the transmitted bulk ultrasonic waves for structured wave manipulation, wherein the micro-metalens (110) possess a structured arrangement of microscopic holes; at least one nano-motion scanning stage (104) configured to support the sample holder (106), the micro-metalens (110); at least one receiver unit (114) configured to detect out-of-plane displacement from the sample (108) and convert the out-of-plane displacement into at least one ultrasonic signal; and at least one user device (116) configured to process the ultrasonic signal to provide the super resolution imaging.

2. The system (100) as claimed in claim 1 , wherein the ultrasonic transmitter unit (102) comprises a fingertip transducer excited by an ultrasonic pulser unit to generate the bulk ultrasonic waves with a central frequency of approximately 2.08MHz, and wherein the at least one ultrasonic transmitter unit (102) is connected to the computer-controlled nano-motion scanning stage (104) for the super resolution imaging.

3. The system (100) as claimed in claim 1 , wherein the nano-motion scanning stage (104) is operatively linked to motion controllers, wherein the motion controllers are controlled by at least one user device (116) to achievesuper-resolution imaging by regulating the movement of the at least one nano-motion scanning stage (104), wherein the at least one nano-motion scanning stage (104) comprises: an acrylic tank, configured to accommodate the sample (108), wherein sample (108) is placed inside the acrylic tank filled with water; and a support structure configured to support the micro-metalens (110) in a fixed position above the sample, wherein the micro-metalens (110) is positioned axially above the acrylic tank.

4. The system (100) as claimed in claim 1 , wherein the receiver unit (114) comprises a micro-focal laser doppler vibrometer (LDV) to measure ultrasonic displacement field.

5. The system (100) as claimed in claim 1 , wherein the micro-metalens (110) comprises a structured arrangement of microscopic holes or channels configured to enhance ultrasonic wave transmission and resolution.

6. The system (100) as claimed in claim 1 , wherein the micro-metalens (110) is fabricated using deep reactive ion etching (DRIE) on a silicon substrate and possesses hydrophilic properties for water retention, wherein the micro-metalens (110) comprises a holey structure that enhances resolution by amplifying evanescent waves through metamaterial-based Fabry-Perot resonant modes, and wherein the micro-metalens (110) is developed to achieve a resolution of ~ A / 75 down to 50 pm by utilizing a 2.25 MHz bulk ultrasonic transducer.

7. The system (100), as claimed in claim 1 , wherein at least one user device (116) is programmed with a software application to acquire, store, and analyze time-domain ultrasonic A-scan signals.

8. The system (100) as claimed in claim 1 , wherein the user device (116) processes the ultrasonic signal to: acquire the time-domain ultrasonic A-scan signals through a data acquisition unit (DAQ) synchronized with the scanning;post-process the acquired A-scan signals to remove noise and extract defect data; perform signal analysis on the processed signals to achieve super resolution imaging by filtering propagating components, masking low-frequency components in frequency spectrum, and recovering the time-domain signal; plot B-scan results based on the post-processed defect data obtained from a linear scan experiment across the sample (108); and provide a defect separation resolution down to 50 pm.

9. The system (100) as claimed in claim 1 , wherein at least one laser unit is configured for micro-focal ultrasonic laser reception, wherein at least one laser unit measures spontaneous displacement caused by ultrasonic wave field propagating out of the plane from the top surface of the micro-metalens (1 10) and transmitted to the at least one receiver unit (1 14).

10. A method (900) for micro-metalens (110) based super resolution imaging using bulk ultrasonics, the method (900) comprising: transmitting bulk ultrasonic waves by the ultrasonic transmitter unit (102); exciting the bulk ultrasonic waves by using a pulser integrated with the ultrasonic transmitter unit (102); accommodating at least one sample (108) by a sample holder (106); receiving the bulk ultrasonic waves from the ultrasonic transmitter unit (102) by the sample (108) placed within the sample holder (106); receiving the transmitted bulk ultrasonic waves for structured wave manipulation by the micro-metalens (110) positioned and aligned above the sample (108), wherein the micro-metalens (1 10) possess a structured arrangement of microscopic holes; supporting the sample holder (106) by at least one nano-motion scanning stage (104), the micro-metalens (1 10); detecting out-of-plane displacement from the sample (108) by at least one receiver unit (1 14) and converting the out-of-plane displacement into at least one ultrasonic signal; andprocessing the ultrasonic signal by the user device (116) for providing the super resolution imaging.

11. The method (900) as claimed in claim 10, comprising providing the at least one ultrasonic transmitter unit (102) comprises a fingertip transducer excited by an ultrasonic pulser unit to generate the bulk ultrasonic waves with a central frequency of approximately 2.08MHz, and wherein the at least one ultrasonic transmitter unit (102) is connected to the computer- controlled nano-motion scanning stage (104) for the super resolution imaging.

12. The method (900) as claimed in claim 10, comprising operatively linking at least one nano-motion scanning stage (104) to motion controllers, wherein the motion controllers being controlled by at least one user device (116) to achieve super-resolution imaging by regulating the movement of the at least one nano-motion scanning stage (104), wherein the at least one nano-motion scanning stage (104) comprises: accommodating by an acrylic tank the sample (108), wherein the sample(108) is placed inside the acrylic tank with water on top; and supporting by a support structure the at least one micro-metalens (110) in a fixed position above the sample, wherein the micro-metalens (110) is positioned axially above the acrylic tank.

13. The method (900) as claimed in claim 10, comprising providing the receiver unit (114) comprises a micro-focal laser doppler vibrometer (LDV) for measuring ultrasonic displacement field.

14. The method (900) as claimed in claim 10, comprising providing the micro-metalens (110) comprises a structured arrangement of microscopic holes or channels for enhancing ultrasonic wave transmission and resolution.

15. The method (900) as claimed in claim 10, comprising fabricating the micro-metalens (110) using deep reactive ion etching (DRIE) on a silicon substrate and possesses hydrophilic properties for water retention, wherein the micro-metalens (110) comprises a holey structure that enhances resolution by amplifying evanescent waves through metamaterial-based Fabry-Perot resonant modes, andwherein the at least one micro-metalens (1 10) is developed to achieve a resolution of ~ A / 75 down to 50 pm by utilizing a 2.25 MHz bulk ultrasonic transducer.

16. The method (900) as claimed in claim 10, comprising programming the user device (1 16) with a software application for acquiring, storing, and analyzing time-domain ultrasonic A-scan signals.

17. The method (900) as claimed in claim 10, comprising processing the ultrasonic signal comprising: acquiring the time-domain ultrasonic A-scan signals through a data acquisition unit (DAQ) synchronized with the scanning; post-processing the acquired A-scan signals to remove noise and extract defect data; performing signal analysis on the processed signals to achieve super resolution imaging by filtering propagating components, masking low- frequency components in frequency spectrum, and recovering the timedomain signal; plotting B-scan results based on the post-processed defect data obtained from a linear scan experiment across the sample (108); and providing defect separation resolution down to 50 pm

18. The method (900) as claimed in claim 10, comprising receipting micro-focal ultrasonic laser by at least one laser unit, wherein at least one laser unit measures spontaneous displacement caused by the ultrasonic wave field propagating out of the plane from the top surface of the at least one micro- metalens (110) and transmitted to the at least one receiver unit (1 14). i

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