About

Cristian Cassella is an Associate Professor of Electrical and Computer Engineering at Northeastern University College of Engineering. His research focuses on acoustic resonators, nonreciprocal components, zero-power sensors for the Internet of Things (IoT), nonlinear dynamics, and ultrasonic transducers. He is affiliated with the Microsystems Radio Frequency Laboratory, where his goal is to explore fundamental physics in micro and nano devices to surpass the performance limitations of current communication and sensing systems. Throughout his career, Cassella has contributed to the development of innovative technologies such as reprogrammable wireless systems, high-performance sensors capable of detecting single cancer cells, and advanced filter technologies. His work has earned him several awards, including the 2025 European Frequency and Time Forum Young Scientist Award, the 2024 Søren Buus Outstanding Research Award, and the National Science Foundation CAREER Award. He has also been recognized for his patents related to low-power Ising systems and ultra-high-frequency subharmonic tags for passive identification. Cassella's research has significant implications for the advancement of RF microacoustics, wireless sensing, and quantum computing, making him a prominent figure in his field.

Research topics

• Computer Science
• Telecommunications
• Electrical engineering
• Engineering
• Physics
• Electronic engineering
• Acoustics
• Computer network
• Embedded system

Selected publications

• Bulge Test for Direct Mechanical Characterization of ALN and Scaln Thin Films

  2026-01-25

  article

  This study presents the mechanical characterization of AlN and 30%-ScAlN thin-film membranes using a bulgetest setup developed for rectangular geometries. A controlled air-pressure system and digital holographic microscopy were used to measure pressure-deflection behavior and extract the in-plane biaxial modulus. Both materials showed reversible deformation with minimal hysteresis, as loading and unloading curves almost overlapped. The extracted biaxial modulus was about 320 GPa for AlN and 200 GPa for 30%-ScAlN, consistent with the softening effect of Sc incorporation. Size-dependent deflection trends were also observed. The method enables a reliable comparison of material and geometric effects in nitride-based MEMS membranes.

  PublisherDOI

• Monolithic Integration of a Dual-Mode On-Chip Antenna with a Ferroelectric Hafnium Zirconium Oxide Varactor for Reprogrammable Radio-Frequency Front Ends

  Preprints.org · 2026-01-08

  preprintOpen accessSenior author

  In this work, we report a dual-mode ferroelectrically programmable on-chip antenna. The antenna is built on a silicon wafer using Complementary Metal-Oxide-Semiconductor (CMOS) processes and exhibits two programmable resonant modes: one in the super high frequency (SHF) range and one in the extremely high frequency (EHF) range. The SHF mode resonates at 8.5 GHz and exhibits ultrawideband (UWB) behavior, while the EHF mode resonates at 36.6 GHz. Both resonance frequencies can be tuned in a non-volatile fashion by controlling the ferroelectric polarization state of a Hafnium Zirconium Oxide (HZO) varactor monolithically integrated into the feed line. This programmability arises from the ferroelectric switching of the embedded HZO film, which results in a non-volatile variation of its permittivity upon application of a voltage pulse. Ferroelectric switching occurs at approximately ±3 V and induces maximum resonance frequency shifts of 381 MHz for the SHF mode and 3 GHz for the EHF mode, corresponding to fractional frequency changes of 4.5% and 8.3%, respectively. Unlike previously reported ferroelectrically tunable antennas, our reported antenna combines full integration, CMOS compatibility, higher operating frequency, compact footprint, and non-volatile programmability.

  PublisherOA PDFDOI

• Monolithic Integration of a Dual-Mode On-Chip Antenna with a Ferroelectric Hafnium Zirconium Oxide Varactor for Reprogrammable Radio-Frequency Front Ends

  Electronics · 2026-02-12

  articleOpen accessSenior authorCorresponding

  In this work, we report a dual-mode ferroelectrically programmable on-chip antenna. The antenna is built on a silicon wafer using complementary metal-oxide semiconductor (CMOS) processes and exhibits two programmable resonant modes: one in the super high frequency (SHF) range and one in the extremely high frequency (EHF) range. The SHF mode resonates at 8.5 GHz and exhibits ultrawideband (UWB) behavior, while the EHF mode resonates at 36.6 GHz. Both resonance frequencies can be tuned in a non-volatile fashion by controlling the ferroelectric polarization state of a Hafnium Zirconium Oxide (HZO) varactor monolithically integrated into the feed line. This programmability arises from the ferroelectric switching of the embedded HZO film, which results in a non-volatile variation of its permittivity upon application of a voltage pulse. Ferroelectric switching occurs at approximately ±3 V and induces maximum resonance frequency shifts of 381 MHz for the SHF mode and 3 GHz for the EHF mode, corresponding to fractional frequency changes of 4.5% and 8.3%, respectively. Unlike previously reported ferroelectrically tunable antennas, our reported antenna combines full integration, CMOS compatibility, higher operating frequency, compact footprint, and non-volatile programmability.

  PublisherDOI

• Design, Multiphysics Modeling and Experimental Characterization of RF AlScN Magnetoelectric Antennas

  Preprints.org · 2026-05-11

  preprintOpen accessSenior author

  Over the past decade, acoustically-actuated magnetoelectric (ME) antennas have been proposed as chip scale radiofrequency (RF) antennas compatible with post Complementary Metal Oxide Semiconductor (CMOS) fabrication processes. These devices have been reported to exhibit antenna gains far exceeding those of conventional electromagnetic (EM) antennas with comparable footprint. However, recent studies have challenged whether this enhanced gain originates from magnetoelastic coupling or from stray radiation sources, like the electric dipole moment in the piezoelectric film or currents in the probing pads. We resolve this controversy through a combined analytical, numerical, and experimental investigation. We model and quantify the radiated power and corresponding gain contributions from (I) magnetoelastic coupling; (II) the strain driven, time-varying electric dipole moment in the piezoelectric layer; and (III) the currents in the probing pads. Our results confirm that the radiation from magnetoelastic coupling exceeds that of the other sources by several orders of magnitude. In addition, we explain how to optimize the return loss and the radiated power of ME antennas when connected to a 50 Ω source, showing that the optimal operating point is the anti-resonance frequency. Based on this finding, we investigate the impact of the electromechanical coupling (kt2) on gain and-10 dB fractional bandwidth. To corroborate our simulation results, we design, fabricate, and characterize the first two Aluminum Scandium Nitride (AlScN) magnetoelectric Bulk Acoustic Wave (BAW) antennas operating beyond 1.1 GHz. The two prototypes integrate different magnetostrictive materials (FeGaB and FeCoSiB) and exhibit measured realized gains of-31.8 dB and-29.7 dB, with-10 dB fractional bandwidths of 1.28% and 1.27% at 2.62 and 3.08 GHz, respectively. The achieved bandwidths are the highest reported for radiofrequency (RF) ME antennas, owing primarily to the enhanced piezoelectric coefficients of the AlScN. Benchmarking against control structures (unreleased FeGaB and FeCoSiB devices) confirms substantially degraded radiation performance in the absence of a strong magnetoelastic coupling. These results elucidate the working principle of ME antennas and provide RF designers with a rigorous framework for the design and modeling of acoustically actuated ME antennas for wireless communication and sensing.

  PublisherDOI

• Synchronization Dynamics of MEMS Oscillators With Sub-Harmonic Injection Locking (SHIL) for Emulating Artificial Ising Spins

  Journal of Microelectromechanical Systems · 2026-01-01

  article

  This paper reports on synchronization dynamics in coupled self-sustaining oscillators referenced to bulk acoustic wave (BAW) resonant microelectromechanical systems (MEMS), for emulating artificial Ising spins. Bistable phase states are created by applying a sub-harmonic injection locking (SHIL) signal to a piezoelectric aluminum nitride-on-silicon (AlN-on-Si or AlN/Si) length-extensional (LE) mode MEMS feedback oscillator, which is the first realization of emulating spin up and down states of the Ising model using BAW MEMS self-sustaining oscillators. The oscillator performance specifications, including phase noise and frequency stability (Allan deviation), are characterized prior to initiation of coupling and synchronization. The probabilities of obtaining bistable phase states are then determined as a function of SHIL amplitude. Detailed theoretical and experimental analyses of the stable operation of AlN/Si MEMS oscillators in the nonlinear regime and the dynamics of a single BAW MEMS oscillator synchronized to SHIL are presented. The initial experimental realization of two coupled MEMS oscillators allows for careful calibration of the parameters governing synchronization dynamics, including amplitude-frequency dependency via the resonance backbone curve, frequency detuning, and coupling between oscillators. The measured results show that the synchronization bandwidth can be varied by increasing the SHIL amplitude at a fixed coupling strength, which provides flexibility in synchronizing multiple oscillators for building MEMS oscillator Ising machines. Finally, the probability of obtaining an out-of-phase state (for reactive coupling) and an in-phase state (for dissipative coupling) is studied as a function of the coupling coefficient, thus enabling its optimal value to be found. [2024-0161]

  PublisherDOI

• Floquet-Based Ising Machines Escape Local Minima in QUBO Problems

  Research Square · 2025-06-16

  preprintOpen access1st authorCorresponding
  PublisherOA PDFDOI

• Programmable threshold sensing in wireless devices using Ising dynamics

  Nature Electronics · 2025-06-02

  articleSenior author
  PublisherDOI

• A Hafnium Zirconium Oxide-Based Reconfigurable Reflectarray for THz Communications

  2025-05-18 · 1 citations

  article

  This study presents the design and simulation of a reconfigurable reflectarray (RRA) utilizing a Hafnium Zirconium Oxide (HZO)-based varactor for terahertz (THz) communication systems. A unit cell analysis investigates the influence of varactor capacitance on reflection magnitude and phase variation, while full-wave simulations of a 10×10 reflectarray array validate its beam-scanning capabilities. The findings indicate that despite a limited phase tuning range and row-wise element control, the design achieves competitive gain performance due to its high aperture efficiency. This work establishes a foundation for advancing THz wireless communication systems using CMOS-compatible ferroelectric materials.

  PublisherDOI

• A design and simulation methodology for radio frequency receiver front-ends with frequency selective limiting devices

  Analog Integrated Circuits and Signal Processing · 2025-10-09

  articleOpen access

  Abstract It has recently been shown that emerging frequency selective limiter (FSL) devices allow to suppress interference with high power levels in the same frequency band as desired signals. This paper introduces an FSL model for circuit simulations that was validated with measurement results of a prototype FSL device. An RF front-end was constructed with this FSL model and a transistor-level CMOS low-noise amplifier (LNA) design. A co-simulation methodology has been developed under large-signal interference considerations using the Bluetooth Low-Energy (BLE) standard as a representative example. Results from simulations with a two-tone signal confirm that the modeled FSL can provide a 9.4 dB reduction of the third-order intermodulation distortion (IMD3) components, which benefits resilience to interference.

  PublisherOA PDFDOI

• Topologically enhanced guided acoustic wave sensors

  Physical Review Applied · 2025-10-08

  articleOpen accessSenior author

  Piezoelectric microelectromechanical guided acoustic wave (GAW) sensors are widely used across a range of applications, from inertial sensing to environmental and chemical sensing. These devices typically rely on the resonance frequency of a Lamb mode as readout parameter, making them well suited for detecting parameters of interest (PoIs) that act over their entire vibrating structure. However, this approach is less effective for monitoring localized PoIs. To address this limitation, prior efforts have focused on miniaturizing GAW sensors. While this miniaturization strategy permits us to enhance responsivity to localized PoIs, it also causes a degradation of the limit of detection (LoD). In this paper, we present a GAW sensor for localized PoIs that overcomes the trade-off between responsivity and limit of detection by leveraging topological interface states (ISs). We demonstrate the effectiveness of our approach by sensing the infrared (IR) power emitted by a laser with a 5-$\text{\ensuremath{\mu}}\mathrm{m}$-diameter beam size, focused on the interface at which the IS is transduced. Our results show that harnessing ISs yields significantly higher responsivity to IR power ($R=835\phantom{\rule{0.1em}{0ex}}\mathrm{Hz}/\text{\ensuremath{\mu}}\mathrm{W}$) and a 2 orders of magnitude better limit of detection (${\mathrm{LoD}}_{\mathrm{tm}}=79\phantom{\rule{0.2em}{0ex}}\mathrm{fW}/\sqrt{\mathrm{Hz}}$) compared to conventional Lamb modes. Our findings pave the way for deploying GAW sensors in emerging applications that require monitoring localized parameters, such as proteomics, spintronics, mass spectroscopy, and more.

  PublisherOA PDFDOI

Recent grants

• Boosting the Cold Chain Efficiency through Integrated, Magnetoelectric, Piezoelectric and Ferroelectric devices in pAssive on-Chip Tags (IMPACT)

  NSF · $500k · 2024–2027

• Fully Integrated Parametric Filters for Extensive Phase-Noise Reduction in Low-Power RF Front-Ends and Resonant Sensing Platforms

  NSF · $437k · 2019–2023

• Collaborative Research: FET: Small: Massive Scale Computing and Optimization through On-chip ParameTric Ising MAchines (OPTIMA)

  NSF · $278k · 2021–2025

• CAREER: Giant Tunability through Piezoelectric Resonant Acoustic Metamaterials for Radio Frequency Adaptive Integrated Electronics

  NSF · $500k · 2021–2027

Frequent coauthors

• Matteo Rinaldi

  Scuola Normale Superiore

  88 shared

• Michele Pirro

  Northeastern University

  22 shared

• Giuseppe Michetti

  Northeastern University

  21 shared

• Gianluca Piazza

  University of Cambridge

  21 shared

• Bernard Herrera

  Northeastern University

  21 shared

• Flavius Pop

  Northeastern University

  20 shared

• Luca Colombo

  Telecom Italia (Italy)

  20 shared

• Hussein M. E. Hussein

  Northeastern University

  20 shared

Labs

• Microsystems Radio Frequency LaboratoryPI

Awards & honors

• 2025 European Frequency and Time Forum (EFTF) Young Scientis…
• 2024 Søren Buus Outstanding Research Award
• National Science Foundation CAREER Award
• Marie Skłodowska-Curie Individual Fellowship
• IEEE Outstanding Paper Award (2024 UFFC)