arXiv subjects

Ian Anderson

Publications and source records attributed to Ian Anderson.

At least 19 recordsLinked to original sources

arXiv2026

13,000-Fold Frequency Down Conversion From 280 MHz to 21 kHz Using Mechanical Frequency Combs

Optical frequency combs bridge the microwave and terahertz regimes by down-converting terahertz optical energy into microwave signals. A photodetector converts the comb's equally spaced lines, generated through optical nonlinearities, into a low-frequency tone at their spacing. Here, we present the first mechanical version of this process, using mechanical frequency combs to downconvert energy over 4 orders of magnitude, from the MHz to kHz regime. Thin-film lithium niobate (LN) is used to design an acoustic resonator with a wide range of mode frequencies. We achieve phononic comb excitation from 250 MHz to 900 MHz and compare the electrical and laser Doppler vibrometer (LDV) measurements at 277 MHz. We then show the low-frequency spectrum of the devices, highlighting mechanical motion at the comb's spacing and demonstrating energy transfer from 277 MHz to 21 kHz.

eess.SP↗

arXiv2026

FASHION-RQ: Mining Hierarchical Semantic Structure for Automated Evaluation of Fashion Retrieval

Evaluating fashion retrieval systems remains challenging due to the limited availability of benchmarks that capture the fine-grained, open-ended queries encountered in real-world search and recommendation. Existing benchmarks often rely on manual curation, predefined taxonomies, or synthetic prompts, limiting scalability and semantic coverage. We introduce FASHION-RQ: Mining Hierarchical Semantic Structure for Automated Evaluation of Fashion Retrieval, an automated framework that derives user-type queries and relevance sets directly from catalog structure. Our key insight is that hierarchical discrete representations learned by Residual Quantized Variational Autoencoders (RQ-VAE) organize products into semantically coherent clusters at progressively finer granularities. We leverage this structure to construct FASHION-RQBENCH, a scalable benchmark without manual query annotation or predefined taxonomies. We propose four complementary tasks for evaluating ranking, relevance classification, fine-grained sibling discrimination, and paraphrase robustness, alongside query- and attribute-level relevance metrics. Experiments across recent retrieval models demonstrate that FASHION-RQBENCH differentiates model capabilities across query types and attributes. A human study further shows that benchmark queries achieve comparable naturalness and higher intent clarity than real user queries, supporting their validity for real-world evaluation. The code and FASHION-RQBENCH dataset will be publicly released upon acceptance.

cs.IR↗

arXiv2026

HASTE: Hierarchical and Attribute-aware Supervision for Generative Recommendation

Generative recommendation models have shown promising results by representing items as semantic IDs and generating these IDs autoregressively. We introduce an approach showing that explicitly incorporating hierarchical and attribute-level supervision into generative recommendation can simultaneously improve training efficiency and long-tail recommendation performance. Existing approaches typically optimize semantic ID prediction with a standard causal cross-entropy objective, which does not explicitly exploit the hierarchical structure of semantic IDs and can require substantial training to learn effective item representations. Moreover, data-sparse tail items often suffer from poor representations due to limited supervision, resulting in weaker long-tail recommendation performance. We address these challenges with HASTE (Hierarchical and Attribute-aware Supervision for generaTive rEcommendation), a unified training framework that introduces hierarchical and attribute-specific supervision. HASTE's Hierarchical Loss explicitly exploits the multi-level structure of semantic IDs, providing supervision at each level of the item hierarchy and substantially accelerating training convergence. Its Attribute-Specific Losses encourage the model to preserve fine-grained item attributes, leveraging the language model's inherent semantic knowledge to improve representations and recommendations for tail items. We extensively evaluate HASTE on a fashion recommendation benchmark and across multiple domains of the Amazon dataset. HASTE improves recommendation performance across datasets and item-frequency regimes. Notably, the Hierarchical Loss achieves approximately 2x faster convergence than the standard causal cross-entropy objective, substantially improving training efficiency while maintaining strong recommendation quality.

cs.IR↗

arXiv2026

In-Plane Q Anisotropy of Higher-Order XBARs in 128°Y-Cut Lithium Niobate

128$^\circ$Y-cut lithium niobate (LN) laterally field-excited higher-order antisymmetric bulk acoustic resonators (XBARs) have attracted interest for high-frequency acoustic devices thanks to their high electromechanical coupling coefficient ($k^2$), high quality factor ($Q$) from low metal coverage ratio, and thickness-defined resonant frequency. So far, the in-plane orientation of these resonators is commonly chosen to maximize $k^2$, thereby maximizing bandwidth. More recently, in-plane-rotated XBARs in 128$^\circ$Y-cut LN have been built to provide greater design flexibility in filter synthesis. However, the in-plane anisotropy of $Q$ has been far less explored. This leaves an important gap in understanding whether the propagation direction that determines $k^2$ also affects $Q$. In this work, we investigate the anisotropic $Q$ of higher-order antisymmetric modes (namely, A$_3$, A$_5$, and A$_7$) in 500-nm-thick 128$^\circ$Y-cut LN on Si. By characterizing resonator performance in various in-plane orientations, we observe that both Bode $Q$ and $Q_{\mathrm{3dB}, f_p}$ show minimum values at 90$^\circ$ to the material x-axis and maximum values around 0$^\circ$, following a trend similar to $k^2$. The A$_3$, A$_5$, and A$_7$ modes around 10.4, 17, and 24 GHz exhibit averaged Bode $Q$/$Q_{\mathrm{3dB}, f_p}$ values of 735/556, 204/149, and 59/37, respectively. At 90$^\circ$, the average Bode $Q$ values are reduced to 66, 9, and 12. Finite element analysis (FEA) results suggest that the orientation-dependent degradation of $Q$ near 90$^\circ$ is associated with stronger transverse displacement near the inactive and anchor regions, resulting in enhanced energy leakage. These results reveal an orientation-dependent loss pathway in 128$^\circ$Y-cut LN XBARs and provide design guidance for jointly optimizing $k^2$ and $Q$.

physics.app-ph↗

arXiv2026

Bimorph Lithium Niobate Thickness-Shear Overtone Film Bulk Acoustic Resonator

High quality factor ($Q$) and overtone operation enable narrow-linewidth acoustic devices with multiple discrete frequencies in a single cavity. Maintaining both high $Q$ and sufficient electromechanical coupling at higher mode orders remains challenging. Here, we demonstrate a bimorph periodically poled piezoelectric film (P3F) lithium niobate (LN) platform for high-order thickness-shear (TS) overtone excitation. The device comprises a bonded 80-$μ$m-thick single-crystal X-cut LN bimorph with opposite polarizations, patterned top and floating bottom electrodes, and a suspended air cavity. The P3F configuration mitigates charge cancellation from the alternating stress distribution of higher-order TS modes, enabling measurable coupling across a broad sequence of overtones. The thick LN acoustic cavity and increasingly confined high-order mode profiles support low-loss operation. Measured TS overtones extend to 1.75 GHz. At room temperature, representative overtones at 0.77 and 0.89 GHz exhibit 3-dB $Q$ values of 11,338 and 11,917, corresponding to $fQ$ products of $8.74\times10^{12}$ and $1.06\times10^{13}$ Hz, respectively. Cooling from 297 to 12 K systematically enhances $Q$, yielding a peak 3-dB $Q$ of 20,507 at 779 MHz and a maximum $fQ$ product of $1.98\times10^{13}$ Hz at 1.379 GHz. These results establish bimorph P3F LN as a promising platform for high-$Q$, frequency-scalable micro-acoustic resonators in the sub-GHz and low-GHz regimes.

physics.app-ph↗

arXiv2026

Gradient Residual Stress in Transferred Thin-Film Lithium Niobate and Its Compensation Using Periodically Poled Piezoelectric Bilayers

In this work, we experimentally investigate the gradient stress (sigma1) in 128 deg Y-cut transferred thin film lithium niobate (TFLN) films with thicknesses from 100 to 460 nm using cantilever curvature analysis. The results reveal a strong dependence of sigma1 on both crystallographic orientation and film thickness, with stress-free orientations at approximately 55 deg and 125 deg for 220-460 nm films, shifting to approximately 20 deg and 160 deg for 100 nm films. The extracted normalized sigma1 ranges from -0.1 to 3.4 MPa/nm (100 nm), -0.8 to 0.34 MPa/nm (220 nm), and -0.12 to 0.08 MPa/nm (460 nm), indicating a pronounced thickness-dependent through-thickness stress gradient. Finite element simulations show excellent agreement with the measurements, validating the curvature-based extraction method and confirming that sigma1 originates from an orientation-dependent residual stress gradient. To mitigate this effect, a bilayer TFLN structure with opposite crystallographic orientations, forming a periodically poled piezoelectric film (P3F), is investigated, enabling partial cancellation of sigma1. A 90/110 nm P3F bilayer reduces the equivalent normalized sigma1 to -0.4 to -0.04 MPa/nm, resulting in significantly reduced deformation. These results establish gradient stress engineering through orientation, thickness, and bilayer design as an effective strategy for achieving mechanically stable and scalable TFLN microelectromechanical systems (MEMS) devices.

physics.app-ph↗

arXiv2026

Thin Film AlN Microbolometer for Very Long-Wave Infrared Detection

We demonstrate a suspended thin-film aluminum nitride (AlN) microbolometer for narrowband very long-wave infrared detection. The device uses a 100-nm-thick AlN membrane suspended above a Pt back reflector by a 1-um air gap. Resonant absorption is set by the AlN transverse optical phonon near 15.4 um and is strengthened by suspension above the reflector. A periodic perforation pattern reduces membrane thermal mass and enhances absorption without further thinning the film. DC resistance measurements under tunable infrared illumination verify bolometric operation, and the measured spectral response follows the absorption profile expected from spectroscopic measurement of passive devices. Narrowband response is observed in the 14--18 um range, with peak responsivity of 920.8 ppm/mW at 15.48 um. This platform can enable compact wavelength-selective thermal detectors for multispectral imaging, on-chip infrared spectroscopy, and chemical sensing.

physics.optics↗

arXiv2026

Nonlinear Characterization of Thin-Film LiNbO3 Acoustic Filters

Compact, high-performance components in millimeter-wave (mmWave) communication systems demand new acoustic filter technology at increasingly higher frequencies. Among various promising mmWave platforms, first-order antisymmetric (A1) mode laterally excited bulk acoustic resonators (XBARs) in thin-film lithium niobate (LiNbO3) have perhaps the most impressive linear performance. Despite these advances, there are few reports of nonlinear characterization of LiNbO3 filters at mmWaves. Here, we address this gap by developing a new nonlinear methodology for high-frequency filters. The result is a methodology for performing power-dependent S-parameters and third-order intermodulation (IMD3) measurements. To test our methodology, we fabricated filters on transferred single-crystal LiNbO3 films on sapphire (Al2O3) and silicon (Si) substrates with amorphous silicon (aSi) sacrificial layer. At 21.8 GHz, the filters on Al2O3 demonstrated an insertion loss of 1.48 dB, a 3 dB fractional bandwidth (FBW) of 17.7%, and in-band third-order input intercept points (IIP3) of 50.8 dBm. At 21.6 GHz, the filters on silicon demonstrated an insertion loss of 2.47 dB, a 3 dB FBW of 18.6%, and in-band IIP3 of 46.5 dBm. The nonlinear results conclusively show that thermal stability and passband distortion improved on the Al2O3 substrate, confirming that substrate selection plays a pivotal role in mitigating nonlinearity in acoustic front-end modules.

eess.SP↗

arXiv2026

High Coupling Tunable Acoustic Resonators in Monolithic Barium Titanate

The growing number of wireless communication bands has driven demand for compact, low-loss, and frequency adjustable RF filtering. Tunable acoustic resonators are well suited to address these needs, offering a path toward reconfigurable front ends with reduced component count. In this work, we extend upon previous conference results to investigate epitaxial barium titanate (BTO) grown on silicon as a platform for tunable acoustic resonators. We demonstrate lateral excitation of symmetric Lamb (S0) modes in 120 nm X-cut BTO membranes using a multi-cell electrode architecture that simultaneously achieves high electromechanical coupling and practical impedance levels. Devices are fabricated with laterally patterned electrodes on released BTO membranes. Under applied DC bias, ferroelectric domains align, allowing electrical excitation, frequency tuning, and quality-factor enhancement of acoustic modes. The primary resonance near 700 MHz exhibits a Bode quality factor of 175, electromechanical coupling up to 25.1%, and series and parallel resonance tunability of 2.3% and 5.6%, respectively. Voltage-dependent material parameters, including permittivity, stiffness, and piezoelectric coefficients, are extracted through a combination of modified Butterworth-Van Dyke modeling and finite-element simulation to explain the observed trends. These results highlight monolithic BTO on silicon as a promising material system for laterally excited, tunable acoustic resonators for reconfigurable RF applications.

eess.SP↗

arXiv2026

Phononic Combs in Lithium Niobate Acoustic Resonators

Frequency combs consist of a spectrum of evenly spaced spectral lines. Optical frequency combs enable technologies ranging from timing, LiDAR, and ultra-stable signal sources. Microwave frequency combs are analogous to optical frequency combs, but often leverage electronic nonlinearity for comb generation. Generating microwave frequency combs using piezoelectric mechanical resonators would enable this behavior in a more compact form factor, thanks to the shorter acoustic wavelengths. In this work, we demonstrate a microwave frequency comb leveraging thermal nonlinearity in high quality factor ($Q$) overmoded acoustic resonators in thin film lithium niobate. By providing input power at 257 MHz, which is the sum frequency of two acoustic modes at 86 MHz and 171 MHz, we generate parametric down conversion and comb generation. We explore the nonlinear mixing regimes and the associated conditions for comb generation. Comb spacing is observed to vary significantly with drive frequency and power, and its general behavior is found to rely heavily on initial conditions. This demonstration showcases the potential for further improvement in compact and efficient microwave frequency combs, leveraging nonlinear acoustic resonators.

physics.app-ph↗

arXiv2026

Tunable Ferroelectric Acoustic Resonators in Monolithic Thin-Film Barium Titanate

The increasing development of wireless communication bands has motivated the development of compact, low-loss, and frequency adjustable RF filtering technologies. Acoustic resonators are the ideal solution to these requirements, and tunable implementations offer a path toward reconfigurable front ends. In this work, we investigate epitaxial barium titanate (BTO) grown on silicon as a platform for tunable acoustic resonators operating in the sub-GHz regime. We demonstrate lateral excitation of symmetric lamb (S0) modes in X-cut BTO membranes, in contrast to prior thickness-defined ferroelectric resonators. Devices are designed using finite-element simulations and fabricated with laterally patterned electrodes that enable overtone coupling to multiple resonant modes. Under applied DC bias, ferroelectric domains align, allowing electrical excitation, frequency tuning, and quality-factor enhancement of acoustic modes. Resonances near 300 MHz and 700 MHz exhibit electromechanical coupling up to 8% and bias-dependent frequency tuning, with a distinct transition in behavior near 20 V. These results highlight monolithic BTO on silicon as a promising material system for laterally excited, tunable acoustic resonators for reconfigurable RF applications.

eess.SY↗

arXiv2026

Lattice XBAR Filters in Thin-Film Lithium Niobate

This work presents the demonstration of lattice filters based on laterally excited bulk acoustic resonators (XBARs). Two filter implementations, namely direct lattice and layout-balanced lattice topologies, are designed and fabricated in periodically poled piezoelectric film (P3F) thin-film lithium niobate (TFLN). By leveraging the strong electromechanical coupling of XBARs in P3F TFLN together with the inherently wideband nature of the lattice topology, 3-dB fractional bandwidths (FBWs) of 27.42\% and 39.11\% and low insertion losses (ILs) of 0.88 dB and 0.96 dB are achieved at approximately 20 GHz for the direct and layout-balanced lattice filters, respectively, under conjugate matching. Notably, all prototypes feature compact footprints smaller than 1.3 mm\textsuperscript{2}. These results highlight the potential of XBAR-based lattice architectures to enable low-loss, wideband acoustic filters for compact, high-performance RF front ends in next-generation wireless communication and sensing systems, while also identifying key challenges and directions for further optimization.

eess.SP↗

arXiv2026

62.6 GHz ScAlN Solidly Mounted Acoustic Resonators

We demonstrate a record-high 62.6 GHz solidly mounted acoustic resonator (SMR) incorporating a 67.6 nm scandium aluminum nitride (Sc0.3Al0.7N) piezoelectric layer on a 40 nm buried platinum (Pt) bottom electrode, positioned above an acoustic Bragg reflector composed of alternating SiO2 (28.2 nm) and Ta2O5 (24.3 nm) layers in 8.5 pairs. The Bragg reflector and piezoelectric stack above are designed to confine a third-order thickness-extensional (TE) bulk acoustic wave (BAW) mode, while efficiently transducing with thickness-field excitation. The fabricated SMR exhibits an extracted piezoelectric coupling coefficient (k2) of 0.8% and a maximum Bode quality factor (Q) of 51 at 63 GHz, representing the highest operating frequency reported for an SMR to date. These results establish a pathway toward mmWave SMR devices for filters and resonators in next-generation RF front ends.

eess.SP↗

arXiv2026

Uncooled low-noise thin-film optomechanical resonator for thermal sensing on lithium niobate

Optomechanical transduction harnesses the interaction between optical fields and mechanical motion to achieve sensitive measurement of weak mechanical quantities with inherently low noise. Lithium niobate combines low optical loss, strong piezoelectricity, high intrinsic fQ_m factor, and low thermal conductivity, making it promising for exploring optomechanical platforms targeting thermal sensing applications. Here, we developed an integrated optomechanical platform on thin-film lithium niobate with precisely engineered optical, mechanical, and thermal fields within a compact 40 μm by 40 μm footprint. The platform integrates suspended microring resonators with ultrathin central membranes, reducing mechanical stiffness and effective mass while maintaining a high optical factor Q_o of 1e6 and mechanical quality factor Q_m of 1117, which increases to 5.1e4 after oscillation. The design suppresses thermal dissipation into the silicon substrate and enhances thermal sensitivity, achieving a temperature coefficient of frequency of -124 ppm/K and a noise-equivalent power of 6.2 nW/sqrt(Hz) at 10 kHz at room temperature. This compact and scalable platform opens up new opportunities for high-sensitivity thermal sensing, supports heterogeneous integration with infrared absorbers for uncooled infrared detection, and enables fully integrated, all-optical on-chip readout, paving the way toward large-format, low-noise infrared sensing arrays.

physics.optics↗

arXiv2025

Valuation Measure of the Stock Market using Stochastic Volatility and Stock Earnings

We create a time series model for annual returns of three asset classes: the USA Standard & Poor (S&P) stock index, the international stock index, and the USA Bank of America investment-grade corporate bond index. Using this, we made an online financial app simulating wealth process. This includes options for regular withdrawals and contributions. Four factors are: S&P volatility and earnings, corporate BAA rate, and long-short Treasury bond spread. Our valuation measure is an improvement of Shiller's cyclically adjusted price-earnings ratio. We use classic linear regression models, and make residuals white noise by dividing by annual volatility. We use multivariate kernel density estimation for residuals. We state and prove long-term stability results.

q-fin.RM↗

arXiv2025

Residual Stress Anisotropy In Thin-Film Lithium Niobate For Stress-Managed MEMS

In this work, we present the first experimental study of residual stress and post-release beam deflection in 128-degree Y-cut thin-film lithium niobate (TFLN) on Si, revealing pronounced stress anisotropy with in-plane orientation. Using optical profilometry with curvature fitting, we extract the stress gradient (sigma1) and generate orientation-resolved stress maps across multiple film thicknesses (100 nm, 220 nm, and 460 nm). For films in the 220 to 460 nm range, we identify stress-free in-plane orientations near approximately 55 degrees and 125 degrees, enabling extremely flat suspended beams. In contrast, ultra-thin 100 nm films exhibit shifted stress-free orientations near approximately 20 degrees and 160 degrees. Leveraging these orientations, we demonstrate very long suspended beams up to 2 cm in length, 10 micrometers in width, and 460 nm in thickness without collapse. These results establish in-plane stress anisotropy and thickness selection in TFLN as practical design levers for mechanically stable, scalable, and stress-managed microelectromechanical systems (MEMS).

physics.app-ph↗

arXiv2025

LookSync: Large-Scale Visual Product Search System for AI-Generated Fashion Looks

Generative AI is reshaping fashion by enabling virtual looks and avatars making it essential to find real products that best match AI-generated styles. We propose an end-to-end product search system that has been deployed in a real-world, internet scale which ensures that AI-generated looks presented to users are matched with the most visually and semantically similar products from the indexed vector space. The search pipeline is composed of four key components: query generation, vectorization, candidate retrieval, and reranking based on AI-generated looks. Recommendation quality is evaluated using human-judged accuracy scores. The system currently serves more than 350,000 AI Looks in production per day, covering diverse product categories across global markets of over 12 million products. In our experiments, we observed that across multiple annotators and categories, CLIP outperformed alternative models by a small relative margin of 3--7\% in mean opinion scores. These improvements, though modest in absolute numbers, resulted in noticeably better user perception matches, establishing CLIP as the most reliable backbone for production deployment.

cs.IR↗

arXiv2025

Practical Demonstrations of FR3-Band Thin-Film Lithium Niobate Acoustic Filter Design

This article presents an approach to control the operating frequency and fractional bandwidth (FBW) of miniature acoustic filters in thin-film lithium niobate (TFLN). More specifically, we used first-order antisymmetric (A1) mode lateral-field-excited bulk acoustic wave resonators (XBARs) to achieve efficient operation at 20.5 GHz. Our technique leverages the thickness-dependent resonant frequency of A1 XBARs, combined with the in-plane anisotropic properties of 128$^\circ$ Y-cut TFLN, to customize filter characteristics. The implemented three-element ladder filter prototype achieves an insertion loss (IL) of only 1.79 dB and a controlled 3-dB FBW of 8.58% at 20.5 GHz, with an out-of-band (OoB) rejection greater than 14.9 dB across the entire FR3 band, while featuring a compact footprint of 0.90 $\times$ 0.74 mm2. Moreover, an eight-element filter prototype shows an IL of 3.80 dB, an FBW of 6.12% at 22.0 GHz, and a high OoB rejection of 22.97 dB, demonstrating the potential for expanding to higher-order filters. As frequency allocation requirements become more stringent in future FR3 bands, our technique showcases promising capability in enabling compact and monolithic filter banks toward next-generation acoustic filters for 6G and beyond.

eess.SP↗