Tip Geometry Research Articles

Parametric Experimental Studies on Supersonic Flow Unsteadiness over a Hemispherical Spiked Body

Experimental studies are carried out to investigate the effects of the geometrical parameters with a drag reducing spike on a hemispherical forebody in a supersonic freestream of at 0 deg angle of attack. The spike length (, 1.0, 1.5, 2.0), spike stem diameter (, 0.12, 0.18), and spike tip shapes are varied, and their influence on the time-averaged and time-resolved flowfield is examined. When increases, a significant reduction in drag is achieved at , whereas the variation in has only a minor effect. The intensity of the shock-related unsteadiness is reduced with an increase in from 0.06 to 0.18, whereas changes in have a negligible effect. The effects of spike tip geometry are studied by replacing the sharp spike tip with a hemispherical one having three different base shapes (vertical base, circular base, and elliptical base). A hemispherical spike tip with a vertical base is performing better by reducing and flow unsteadiness. The dominant spatiotemporal mode arising due to the shock-related unsteadiness is represented through modal analysis of time-resolved shadowgraph images, and the findings are consistent with the other measurements.

Vortex induced vibrations of wind turbine blades: Influence of the tip geometry

The present investigation used numerical simulations to study the vortex induced vibrations (VIVs) of a 96 m long wind turbine blade. The results of this baseline shape were compared with four additional geometry variants featuring different tip extensions. The geometry of the tip extensions was generated through the variation of two design parameters: the dihedral angle bending the blade out of the rotor plane and the sweep angle bending the blade in the rotor plane. The applied numerical methods relied on a fluid structure interaction (FSI) approach, coupling a computational fluid dynamics solver with a multi-body structural solver. The methodology followed for locating VIV regions was based on the variation of the inclination angle. This variable was defined as the angle between the freestream velocity and the blade axis, being 0° when these vectors were normal and positive when a velocity component from tip to root was introduced. For the baseline geometry, the FSI simulations predicted significant blade vibrations for inclination angles between 47.5° and 60° with a maximum peak-to-peak amplitude of 2.3 m. The installation of the different tip extensions on the blade geometry was found to significantly modify the inclination angles where VIV was observed. In particular, the simulations of three of the tip designs showed a shifting of several degrees for the point where the maximum vibrations were recorded. For the specific tip geometry where only the sweep angle was taken into account, a total mitigation of the VIV was observed.

Su1299 COMPARISON OF THE PERFORMANCE OF 2 CORE BIOPSY NEEDLES FOR ENDOSCOPIC ULTRASOUND-GUIDED LIVER BIOPSY

Endoscopic ultrasound-guided fine needle biopsy of the liver (EUS-LB) is a safe and effective technique to assess liver histology. EUS-LB is commonly performed using a 19-gauge fine needle biopsy (FNB). Two popular models used for EUS-LB differ in tip geometry. One has a 3-planed, Franseen-style tip with symmetric cutting surfaces (Acquire; Boston Scientific; Marlborough, MA). The other has a 2-pronged, fork-tip with asymmetric cutting surfaces (SharkCore; Medtronic; Sunnyvale, CA). Herein, we compare these two needles with respect to safety and tissue yield in EUS-LB. This is a retrospective analysis of all patients referred for EUS-LB between January 2017 and May 2019. All EUS-LB were performed using 19G Franseen or fork-tip needles, but the specific model selection, biopsy location, and number of passes were at endoscopist’s discretion. EUS-LB was performed via one pass, one actuation, wet suction technique without on-site cytopathology. All endoscopists grossly evaluated the specimen procured from each pass to determine whether another pass was needed. One hundred sixteen patients underwent EUS-LB. Franseen and fork-tip needles were employed in 71 and 89 cases respectively. Baseline patient characteristics were similar between the cohorts. Overall, both needles yielded comparable results with respect to aggregate length (29.5 vs 27mm, p=0.39), longest intact core (16.7 vs 19.8mm, p=0.10) and complete portal tracts (18.1 vs 16.9, p=0.47). However, more passes were performed with fork-tip (146) compared to Franseen needles (100), with a mean of 1.64 vs 1.41 (p=0.02). When only single pass biopsies were examined (46 Franseen, 39 fork-tip), the Franseen needle yielded statistically greater aggregate length (34.4 vs 27.1mm, p=0.05) and longest intact core (23.1 vs 17.5mm, p=0.01). Four EUS-LB procedures (2.5%) resulted in samples that were inadequate for histologic diagnosis (Franseen-1.4%, fork-tip-3.4%; p=NS). Adverse events after EUS-LB consisted of two cases of post-procedural bleeding (1.3%) not requiring intervention; one after Franseen (1.4%) and one after fork-tip FNB (1.1%; p=NS). Both Franseen and fork-tip fine needle biopsy needles appear safe and effective for endoscopic ultrasound-guided liver biopsy. However, fewer passes are needed and more tissue is procured in a single pass when using the Franseen model.Figure 1Comparison of results of endoscopic ultrasound-guided liver biopsy using the Franseen and Fork-tip needle systems between all samples (above) and single-pass only samples (below). Metrics examined were aggregate length (mm), longest intact core (mm) and complete portal tracts.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Dynamic coupling between particle-in-cell and atomistic simulations.

We propose a method to directly couple molecular dynamics, the finite element method, and particle-in-cell techniques to simulate metal surface response to high electric fields. We use this method to simulate the evolution of a field-emitting tip under thermal runaway by fully including the three-dimensional space-charge effects. We also present a comparison of the runaway process between two tip geometries of different widths. The results show with high statistical significance that in the case of sufficiently narrow field emitters, the thermal runaway occurs in cycles where intensive neutral evaporation alternates with cooling periods. The comparison with previous works shows that the evaporation rate in the regime of intensive evaporation is sufficient to ignite a plasma arc above the simulated field emitters.

A Robust RCSA-Based Method for the In Situ Measurement of Rotating Tool-Tip Frequency Response Functions

AbstractMeasuring rotating tool-tip frequency response functions (FRFs) is difficult because of the fluted tip geometry. The methods based on receptance coupling substructure analysis (RCSA) can obtain rotating tool-tip FRFs with a few tests. Existing RCSA-based methods require at least one smooth rod for measurement and then mathematically calculate the desired rotating tool-tip FRFs. However, involving the inverse of the experimentally obtained FRFs matrix, these methods are susceptible to the measurement noise in the rotating structure. In addition, the inconsistency between the holder–tool and holder–rod connections is another uncertainty which impacts accuracy. This paper presents a robust RCSA-based method to obtain rotating tool-tip FRFs. It is found that tool-tip FRFs can be calculated from another point FRFs on the same assembly. Then, one point on the smooth cylindrical shank of the tool is selected for measurement. The measured FRFs, along with those from the theoretical tool model, calculate the rotating tool-tip FRFs. Compared with the previous methods, the proposed one does not require inverting the measured FRFs matrix, inherently avoiding amplification of measurement noise. Since the tool replacement is no longer required, in situ measurement is achieved to ensure the same holder–tool connection throughout the procedure. The proposed method is first validated in a numerical case and then verified experimentally by a commercial hammer and laser vibrometer. Both results show that the method is insensitive to the measurement noise and can obtain rotating tool-tip FRFs with considerable accuracy.

Quantitative determination of the interaction potential between two surfaces using frequency-modulated atomic force microscopy.

The interaction potential between two surfaces determines the adhesive and repulsive forces between them. It also determines interfacial properties, such as adhesion and friction, and is a key input into mechanics models and atomistic simulations of contacts. We have developed a novel methodology to experimentally determine interaction potential parameters, given a particular potential form, using frequency-modulated atomic force microscopy (AFM). Furthermore, this technique can be extended to the experimental verification of potential forms for any given material pair. Specifically, interaction forces are determined between an AFM tip apex and a nominally flat substrate using dynamic force spectroscopy measurements in an ultrahigh vacuum (UHV) environment. The tip geometry, which is initially unknown and potentially irregularly shaped, is determined using transmission electron microscopy (TEM) imaging. It is then used to generate theoretical interaction force–displacement relations, which are then compared to experimental results. The method is demonstrated here using a silicon AFM probe with its native oxide and a diamond sample. Assuming the 6-12 Lennard-Jones potential form, best-fit values for the work of adhesion (Wadh) and range of adhesion (z0) parameters were determined to be 80 ± 20 mJ/m2 and 0.6 ± 0.2 nm, respectively. Furthermore, the shape of the experimentally extracted force curves was shown to deviate from that calculated using the 6-12 Lennard-Jones potential, having weaker attraction at larger tip–sample separation distances and weaker repulsion at smaller tip–sample separation distances. This methodology represents the first experimental technique in which material interaction potential parameters were verified over a range of tip–sample separation distances for a tip apex of arbitrary geometry.

Mathematical Modeling of the Interaction between a Single-Walled Nanotube Tip and a Biological Surface

The vibration characteristics of arbitrarily oriented tips made of single-walled carbon nanotubes (SWCNT) applied to biological surfaces of arbitrary scale were studied. A mathematical model was established linking the parameters of the SWCNT tip with its vibration characteristics using d’Alembert’s principle. Modeling was used to study the effects of tip rigidity and geometry on the tip position in three-dimensional space, related to applied aspects of biology.

Accurate tip characterization in critical dimension atomic force microscopy

A new method for accurately characterizing the tip geometry of critical dimension atomic force microscopy (CD-AFM) has been introduced. A sample type IVPS100-PTB whose line features have vertical sidewall, round corner with a radius of approx. 5 ∼ 6 nm and very low surface roughness has been applied as the tip characterizer. The geometry of the line features has been accurately and traceably calibrated to the lattice constant of crystal silicon. In this paper, detailed measurement strategies and data evaluation algorithms have been introduced, particularly concerning several important influence factors such as the line width roughness of the tip characterizer, measurement noise, measurement point density, and the calculation of the averaged tip geometry. Thorough experimental studies have been carried out, indicating high measurement accuracy of the developed method. For instance, tip geometry of a probe type CDR120 with a nominal tip diameter of 120 nm is reconstructed using two different tip characterizers before, during and after it is applied for a calibration of a user sample. The agreement of all 20 obtained tip profiles reaches 0.4 nm, confirming the high measurement stability, low tip wear as well as the high measurement consistency between two tip characterizers. Furthermore, the results of a nanofeature of the user sample after correcting the tip contribution show a repeatability of approximately 0.3 nm when it is repeatedly measured by a same tip, and a reproducibility of 0.9 nm when it is measured using two different tips, confirming the good performance of the tip correction method as well.

Characterisation of aeroelastic harvester efficiency by measuring transient growth of oscillations

With growing demand for small autonomous electrical devices, such as those in wireless sensor networks, energy harvesting has attracted interest with the promise of low maintenance and sustainable power sources. Galloping energy harvesters utilise the fluid-structure interaction to transform kinetic energy in fluid flow into electrical energy. The performance of galloping energy harvesters depends on the geometry of the tip, with the structure of the flow around the tip defining the nature of fluid-structure interaction and hence the potential efficiency of the device.In this work the curved blade tip geometry is investigated. To experimentally characterise the performance of the harvester, a method utilising the free oscillation transient is developed. The method avoids implementation of a transduction mechanism and hence optimisation of the associated parameters. The developed method is generic and can be applied to other energy generators.The power coefficient of curved blades of different curvatures is measured and the optimal range identified. The maximum coefficient of performance of the curved blade harvester occurs at tip speed ratios from 0.32 to 0.74 and reaches 0.08, which is 3 to 4 times lower than Savonius turbines, the best performing devices at similar Reynolds numbers. The square prism geometry is used as a comparator and found to have a coefficient of performance 10 times less than the curved blade. Flow visualisations confirm the curved blade to act as an airfoil in the highest performing cases, hence future tip shapes should be developed to promote flow attachment.

Nanoscale dielectric grating polarizers tuned to 4.43 eV for ultraviolet polarimetry.

Transmissive dielectric wire grid polarizers tuned to 4.43 eV (Mg II line, 280 nm), an important diagnostic line for solar physics, are presented in this communication. The polarizers are based on TiO2 gratings and designed with a period of ∼140 nm (7143 lines/mm), 40 nm line width (duty cycle of 0.286), and 100 nm line height. Several gratings are fabricated through electron beam lithography combined with reactive ion etching, whereby two parameters in the nanofabrication process are explored: e-beam dosage on the photoresist and TiO2 etching time. Polarization of samples is optically characterized using a spectroscopic ellipsometer in transmission mode, achieving the best result with an extinction ratio of ∼109 and a transmittance of 16.4% at the target energy of 4.43 eV. The shape of the gratings is characterized through atomic force microscopy (AFM) and scanning electron microscopy (SEM); the measured AFM profiles are distorted by the tip geometry, hence a simple deconvolution procedure is implemented to retrieve the real profile. By analysing the AFM and SEM profiles, we find that the real shapes of the different gratings are close to the design, but with a larger duty cycle than the intended value. With the real grating geometry, an improved model of the best sample was built with a finite-difference time-domain (FDTD) method that matches the result obtained through optical characterization.

Quasi-periodic migration of single cells on short microlanes.

Cell migration on microlanes represents a suitable and simple platform for the exploration of the molecular mechanisms underlying cell cytoskeleton dynamics. Here, we report on the quasi-periodic movement of cells confined in stripe-shaped microlanes. We observe persistent polarized cell shapes and directed pole-to-pole motion within the microlanes. Cells depolarize at one end of a given microlane, followed by delayed repolarization towards the opposite end. We analyze cell motility via the spatial velocity distribution, the velocity frequency spectrum and the reversal time as a measure for depolarization and spontaneous repolarization of cells at the microlane ends. The frequent encounters of a boundary in the stripe geometry provides a robust framework for quantitative investigations of the cytoskeleton protrusion and repolarization dynamics. In a first advance to rigorously test physical models of cell migration, we find that the statistics of the cell migration is recapitulated by a Cellular Potts model with a minimal description of cytoskeleton dynamics. Using LifeAct-GFP transfected cells and microlanes with differently shaped ends, we show that the local deformation of the leading cell edge in response to the tip geometry can locally either amplify or quench actin polymerization, while leaving the average reversal times unaffected.

Liquid-Superrepellent Bioinspired Fibrillar Adhesives.

Bioinspired elastomeric fibrillar surfaces have significant potential as reversible dry adhesives, but their adhesion performance is sensitive to the presence of liquids at the contact interface. Like their models in nature, many artificial mimics can effectively repel water, but fail when low-surface-tension liquids are introduced at the contact interface. A bioinspired fibrillar adhesive surface that is liquid-superrepellent even toward ultralow-surface-tension liquids while retaining its adhesive properties is proposed herein. This surface combines the effective adhesion principle of mushroom-shaped fibrillar arrays with liquid repellency based on double re-entrant fibril tip geometry. The adhesion performance of the proposed microfibril structures is retained even when low-surface-tension liquids are added to the contact interface. The extreme liquid repellency enables real-world applications of fibrillar adhesives for surfaces covered with water, oil, and other liquids. Moreover, fully elastomeric liquid-superrepellent surfaces are mechanically not brittle, highly robust against physical contact, and highly deformable and stretchable, which can increase the real-world uses of such antiwetting surfaces.

An adaptive finite element model for steerable needles

Penetration of a flexible and steerable needle into a soft target material is a complex problem to be modelled, involving several mechanical challenges. In the present paper, an adaptive finite element algorithm is developed to simulate the penetration of a steerable needle in brain-like gelatine material, where the penetration path is not predetermined. The geometry of the needle tip induces asymmetric tractions along the tool–substrate frictional interfaces, generating a bending action on the needle in addition to combined normal and shear loading in the region where fracture takes place during penetration. The fracture process is described by a cohesive zone model, and the direction of crack propagation is determined by the distribution of strain energy density in the tissue surrounding the tip. Simulation results of deep needle penetration for a programmable bevel-tip needle design, where steering can be controlled by changing the offset between interlocked needle segments, are mainly discussed in terms of penetration force versus displacement along with a detailed description of the needle tip trajectories. It is shown that such results are strongly dependent on the relative stiffness of needle and tissue and on the tip offset. The simulated relationship between programmable bevel offset and needle curvature is found to be approximately linear, confirming empirical results derived experimentally in a previous work. The proposed model enables a detailed analysis of the tool–tissue interactions during needle penetration, providing a reliable means to optimise the design of surgical catheters and aid pre-operative planning.

An Investigation of Tooth Tip Leakages in Gerotor Pumps: Modeling and Experimental Validation

Abstract Gerotors are inexpensive positive displacement pumps commonly used in hydrostatic transmissions, fuel injection, and automotive lubrication systems. In these pumps, leakages at the tooth tips of the gears are the major source of volumetric losses that prevents their usage in high pressure applications. However, due to the curvature of typical gear profiles, the flow relations available in the literature do not accurately model this leakage flow. In this paper, a novel tooth tip leakage flow model is developed based on dimensional analysis. Key geometric and flow parameters are identified and a set of computational fluid dynamics (CFD) simulations are conducted on the tooth tip geometry to establish the flow relationship. This relationship is first verified with the analytical formulation derived from Reynolds equation. Then, an experimental setup is designed to reproduce the flow conditions at the tooth tip of gerotors. Experiments are conducted for a range of geometric and flow parameters, and results from the experiments are used to validate the proposed leakage flow model. The tooth tip leakage flow model developed and validated in this work is valuable for pump designers in determining the impact of gear geometry and clearances on volumetric performance of the pump. Moreover, the model can be readily used in any lumped parameter based simulation tool permitting a fast and accurate prediction of the tooth tip leakage flow and hence the volumetric efficiency of the unit.

RELATIVE CASING MOTION EFFECT ON SQUEALER TIP COOLING PERFORMANCE AT TIGHT TIP CLEARANCE

Abstract The effect of relative motion between the casing and turbine blade tip has been recognized as an important factor for tip aerothermal performance evaluation. Tight tip clearance is becoming one of the main objectives of engine manufacturers. This paper provides some insights on the topic that the impact of casing motion on the blade tip thermal performance could be different between nominal and tight tip clearances. A typical squealer tip geometry was employed, with coolant holes on the cavity floor near the pressure side rim. Three tip clearances, 1.1%, 0.6% and 0.2% of the span, are compared. The CFD method was validated against experimental data in the previous study. The results suggest that, in the tight tip situation, the effect of casing motion on cooling efficiency and flow structure is distinguished from the larger clearance situations. The scraping effect drives the leakage flow towards the blade suction surface, inducing high thermal load at tight clearance. The findings in this study highlight the importance of relative casing motion, especially at tight clearance.

Abstract No. 504 Ex vivo evaluation of the effect of multiple electrode radiofrequency needle tip convergence on size of ablation zone

Radiofrequency ablation (RFA) is an established therapy for treatment of malignancy in several organs, including the liver. One commonly used system, the Cool-tip Cluster Electrode, uses three parallel needles fixed in a triangular geometry. However, upon insertion, the final geometry of the needle tips can vary. In the case of converging needles, ablation volumes have been anecdotally observed to be smaller than expected. The study objective is to determine whether needle tip convergence significantly affects ablation zone in a bovine liver model. Cool-tip Cluster Electrodes were used to perform RFA in an ex vivo bovine liver using a 3D-printed guide to produce: no, partial or full convergence of the electrode needle tips. Ablation time was 12 minutes. Cone beam computed tomography scans were obtained to verify needle positions. Time to first roll off and period between roll-offs was recorded. Gross pathology was performed to estimate ablation zone volumes. Preliminary results from the initial pilot experiment found partial needle tip convergence decreased ablation zone volume by 6.13 cm3 (40.3%), time to first roll-off by 5.16 minutes (36.1%), and average time between roll-offs by 16 seconds (25.5%) compared to no convergence. Full convergence resulted in ablation zone volume decrease by 10.3 cm3 (67.7%), time to first roll-off decreased by 5.45 minutes (39.5%), and the average time between roll-offs decreased by 13 seconds (31.4%) compared to no convergence. Preliminary results suggest significant decrease in ablation volume and faster roll-off as the electrode tips increasingly converge. Further experiments are planned to test the study hypothesis with statistical significance. If confirmed, these results suggest confirmation of needle tip geometry prior to ablation should be performed clinically in order to ensure adequate ablation volumes when using Cool-tip Cluster electrodes.Tabled 1Distance Between Electrodes (mm)Diameter of Ablation Zone (cm)Ablation Volume (cm3)Time to First Roll-Off (min)Average Time Between Roll-Offs (sec)44.415.218.535133.49.083.373802.54.913.0835 Open table in a new tab

A Novel Vortex Identification Technique Applied to the 3D Flow Field of a High-Pressure Turbine

Abstract The efficiency of modern axial turbomachinery is strongly driven by the secondary flows within the vane or blade passages. The secondary flows are characterized by a complex pattern of vortical structures that origin, interact, and dissipate along the turbine gas path. The endwall flows are responsible for the generation of a significant part of the overall turbine loss because of the dissipation of secondary kinetic energy and mixing out of nonuniform momentum flows. The understanding and analysis of secondary flows requires a reliable vortex identification technique to predict and analyze the impact of specific turbine designs on the turbine performance. However, the literature shows a remarkable lack of general methods to detect vortices and to determine the location of their cores and to quantify their strength. This paper presents a novel technique for the identification of vortical structures in a general 3D flow field. The method operates on the local flow field, and it is based on a triple decomposition of motion proposed by Kolář. In contrast to a decomposition of velocity gradient into the strain and vorticity tensors, this method considers a third, pure shear component. The subtraction of the pure shear tensor from the velocity gradient remedies the inherent flaw of vorticity-based techniques, which cannot distinguish between rigid rotation and shear. The triple decomposition of motion serves to obtain a 3D field of residual vorticity whose magnitude is used to define vortex regions. The present method allows to locate automatically the core of each vortex, to quantify its strength, and to determine the vortex bounding surface. The output may be used to visualize the turbine vortical structures for the purpose of interpreting the complex three-dimensional viscous flow field and to highlight any case-to-case variations by quantifying the vortex strength and location. The vortex identification method is applied to a high-pressure turbine with three optimized blade tip geometries. The 3D flow field is obtained by computational fluid dynamics (CFD) computations performed with Numeca FINE/Open. The computational model uses steady-state Reynolds-averaged Navier–Stokes (RANS) equations closed by the Spalart-Allmaras turbulence model. Although developed for turbomachinery applications, the vortex identification method proposed in this work is of general applicability to any three-dimensional flow field.

Drilling Tool Geometry Effects on the Hole Quality of Glare

Recently machining of hybrid stacking materials are much interested and challenging in manufacturing domains. Mostly, drill hole quality depends the machining parameters and type of cutting tool. This work investigates the experimental study for effects of drill bit geometry on hole quality of glass laminate aluminum reinforced epoxy (GLARE). GLARE have manufactured by alternative stacking of aluminum (AA7475) and glass fiber (E-glass)/epoxy composite through compression molding machine. Machining of GLARE by using of Computer numerical controller. Hole quality were studied with the aid of optical microscopic. Results show that a drill tip geometry to promote the reduction of delamination and structural damage. Superior hole quality is achieved with 2 fluted drill bit than 3 fluted drill bit.

Uncertainty quantification of the effects of squealer tip geometry deviation on aerothermal performance

The first-stage rotor squealer tip is a key area in gas turbine for both aerodynamic performance and blade cooling tasks, which should be carefully designed. However, harsh operating conditions near the rotor squealer tip can cause the geometry of the squealer tip to degrade, and manufacturing inaccuracies can also cause the squealer tip geometry to deviate from the ideal design. These geometry deviations would change the flow field near the blade tip, which will influence the thermal and aerodynamic performance. Thus, it is important to quantitatively investigate the effects of squealer tip geometry deviation on the aerothermal performance. In this paper, a typical transonic first-stage turbine is employed, and three important geometric features of squealer tip, the tip clearance height (H), the squealer depth (D), and the squealer edge chamfer (R), are selected. An uncertainty quantification process is performed to study the effect of deviation of H, D, and R on the aerothermal performance. Many cases with different geometry features are checked in the current study using 3D Reynolds-averaged Navier–Stokes simulations. A parameter sensitivity analysis using Sobol Indice method is carried out to identify the key parameters to aerothermal performance of the squealer tip. The uncertainty quantification results show that the existence of the tip chamfer reduces the size of separation bubble and the dwelling range of the scraping vortex, thus, the blockage effect of the leakage flow is weakened, which results in larger amount of leakage flow and more mixing loss of squealer tips with edge chamfer than those without edge chamfer. The results of the parameter sensitivity analysis show that the height of tip clearance is the main factor that affects the aerodynamic performance of the squealer tip. This work provides a certain guiding direction for the optimization design of the turbine groove tip.

Needle deflection and tissue sampling length in needle biopsy

This study investigates the effect of needle tip geometry on the needle deflection and tissue sampling length in biopsy. Advances in medical imaging have allowed the identification of suspicious cancerous lesions which then require needle biopsy for tissue sampling and subsequent confirmatory pathological analysis. Precise needle insertion and adequate tissue sampling are essential for accurate cancer diagnosis and individualized treatment decisions. However, the single-bevel needles in current hand-held biopsy devices often deflect significantly during needle insertion, causing variance in the targeted and actual locations of the sampled tissue. This variance can lead to inaccurate sampling and false-negative results. There is also a limited understanding of factors affecting the tissue sampling length which is a critical component of accurate cancer diagnosis. This study compares the needle deflection and tissue sampling length between the existing single-bevel and exploratory multi-bevel needle tip geometries. A coupled Eulerian-Lagrangian finite element analysis was applied to understand the needle-tissue interaction during needle insertion. The needle deflection and tissue sampling length were experimentally studied using tissue-mimicking phantoms and ex-vivo tissue, respectively. This study reveals that the tissue separation location at the needle tip affects both needle deflection and tissue sampling length. By varying the tissue separation location and creating a multi-bevel needle tip geometry, the bending moments induced by the insertion forces can be altered to reduce the needle deflection. However, the tissue separation location also affects the tissue contact inside the needle groove, potentially reducing the tissue sampling length. A multi-bevel needle tip geometry with the tissue separation point below the needle groove face may reduce the needle deflection while maintaining a long tissue sampling length. Results from this study can guide needle tip design to enable the precise needle deployment and adequate tissue sampling for the needle biopsy procedures.