Georgios C. Trichopoulos

• Electrical and Computer Engineering, PhD
• Professor (Associate) at Arizona State University

We propose a high spatial resolution fingerprint scanning method that utilizes sub-terahertz (THz) waves to image the finger skin surface and sub-surface. The fingerprint is a biomarker widely used as an identifier in security applications. However, current popular fingerprint scanners mostly detect skin surface undulation and hence are vulnerable...

In this work, we show how active terahertz (THz) imaging systems can exploit the unique propagation properties of THz waves to reconstruct images of non-line-of-sight (NLoS) scenes. Most building surfaces' material properties and roughness allow for a unique combination of diffuse and strong specular scattering. As a result, most surfaces behave as...

There exist scientifically interesting molecular lines, such as the ground state transitions of water, that cannot be observed except from space. Observations of these lines can be made more cost-effective by lightweighting observation components, such as the primary optical aperture. This is particularly important for SmallSats and CubeSats which...

We present a 1-bit reconfigurable intelligent surface (RIS) operating at millimeter-wave frequencies that suppresses the undesired grating lobes encountered in binary phase modulation schemes and achieves high resolution beam steering. We incorporate fixed, random phase delays at each unit cell of the surface which breaks the periodicity of the pha...

We investigate the effect of side lobe level (SLL) and multipath propagation in millimeter-wave(mmWave) and terahertz (THz) imaging systems for various transceiver array topologies. This work considers practical limitations in high-resolution active imaging systems and focuses on electrically large, planar antenna array topologies. As such, we inve...

Traditional imaging systems, such as the eye or cameras, image scenes that lie in the direct line-of-sight (LoS). Most objects are opaque in the optical and infrared regimes and can limit dramatically the field of view (FoV). Current approaches to see around occlusions exploit the multireflection propagation of signals from neighboring surfaces eit...

This study presents findings in the terahertz (THz) frequency spectrum for non-contact cardiac sensing applications. Cardiac pulse information is simultaneously extracted using THz waves based on the established principles in electronics and optics. The first fundamental principle is micro-Doppler motion effect. This motion based method, primarily...

This paper presents a novel compact unit-cell design for 1-bit reconfigurable intelligent surfaces (RISs) with mitigated quantization lobes. The suppression of the quantization lobes is achieved by introducing a random pre-phasing over the RIS utilizing multiple delay lines within the confined space of the unit-cell. To retain a compact topology an...

Reconfigurable intelligent surfaces (RISs) have promising coverage and data-rate gains for wireless communication systems in 5G and beyond. Prior work has mainly focused on analyzing the performance of these surfaces using simulations or lab-level prototypes. To draw accurate insights about the actual performance of these systems, this paper develo...

This study presents findings at Terahertz (THz) frequency band for non-contact cardiac sensing application. For the first time, cardiac pulse information is simultaneously extracted using THz waves based on the two established principles in electronics and optics. The first fundamental principle is micro-Doppler (mD) motion effect, initially introd...

In this work, we present a rigorous full-wave eigenanalysis for the study of nanoantennas operating at both terahertz (THz) (0.1–10 THz), and infrared/optical (10–750 THz) frequency spectrums. The key idea behind this effort is to reveal the physical characteristics of nanoantennas such that we can transfer and apply the state-of-the-art antenna de...

Reconfigurable intelligent surfaces (RISs) have promising coverage and data rate gains for wireless communication systems in 5G and beyond. Prior work has mainly focused on analyzing the performance of these surfaces using computer simulations or lab-level prototypes. To draw accurate insights about the actual performance of these systems, this pap...

Due to a production error, in the original article [1] , Fig. 5 was incorrectly published. We apologize for this error. The correct figure, with the corresponding caption, is shown below.

We present a method for the mitigation of quantization lobes in single-bit reconfigurable reflective surfaces (RRSs). Typically, RRSs are planar beamforming structures consisting of hundreds or thousands of antennas with integrated tunable switches. Under plane-wave illumination, single-bit RRSs suffer from undesired side lobes or quantization lobe...

We present a method for the mitigation of quantization lobes in single-bit reconfigurable reflective surfaces (RRSs). Typically, RRSs are planar beamforming structures consisting of hundreds or thousands of antennas with integrated tunable switches. Under plane-wave illumination, single-bit RRSs suffer from undesired side lobes or quantization lobe...

We present an analysis of graphene-loaded transmission line switches for sub-millimeter wave and terahertz applications. As such, we propose equivalent circuit models for graphene-loaded coplanar waveguides and striplines and examine the switching performance under certain parameters. Specifically, we identify the optimum design of graphene switche...

We present an analysis of graphene loaded transmission line switches. Namely, we propose equivalent circuit models for graphene loaded coplanar waveguides and striplines and examine the switching performance under certain design parameters. As such, the models account for the distributed effects of electrically-large shunt switches in coplanar wave...

We present an analysis of graphene loaded transmission line switches. Namely, we propose equivalent circuit models for graphene loaded coplanar waveguides and striplines and examine the switching performance under certain design parameters. As such, the models account for the distributed effects of electrically-large shunt switches in coplanar wave...

We present a method for the mitigation of quantization lobes in single-bit reconfigurable reflective surfaces (RRSs). Typically, RRSs are planar beamforming structures consisting of hundreds or thousands of antennas with integrated tunable switches. Under plane-wave illumination, single-bit RRSs suffer from undesired side lobes or quantization lobe...

We present a novel non-contact probing approach for on-wafer metrology of high-speed devices and integrated circuits. The new method has been developed under the ONR DATE MURI and enables, for the first time, contact-free multi-port S-parameter measurements on-wafer. The main motivation to develop this new method was the inherent issues in the stat...

The authors present a fabrication process for the development of high-frequency (>30 GHz) on-wafer graphene devices with the use of titanium sacrificial layers. Graphene patterning requires chemical processes that have deleterious effects on graphene resulting in very low yield. The authors prevent delamination of the delicate graphene from the sub...

We propose a novel quasi-optical topology to enable ultra-wideband on-wafer characterization in the THz regime. Using quasi-optical components, we implement a highperformance directional coupler and a non-contact probing scheme, to interrogate on-wafer devices and circuits. The use of quasi-optics allows superior signal isolation and wideband opera...

We present a novel imaging method for compact, low-profile imagers in millimeter wave (mmW) and terahertz (THz) frequencies. The method borrows the principles of computerized tomography (CT) to generate 2D or 3D high-resolution images using simplified RF-front-ends. To perform imaging the proposed scheme implements the projection-slice theorem. Spe...

At mmW and THz band, on-wafer testing is very critical for on-wafer electronics devices and circuits as well as spectroscopy. Nevertheless, current measurement capabilities are limited by contact probe technology and vector network analyzers (VNAs). Recently, we proposed a non-contact method to tackle the issue of using expensive and brittle contac...

Frequencies from 100 GHz to 3 THz are promising bands for the next generation of wireless communication systems because of the wide swaths of unused and unexplored spectrum. These frequencies also offer the potential for revolutionary applications that will be made possible by new thinking, and advances in devices, circuits, software, signal proces...

In this work, we propose a novel approach for high accuracy user localization by merging tools from both millimeter wave (mmWave) imaging and communications. The key idea of the proposed solution is to leverage mmWave imaging to construct a high-resolution 3D image of the line-of-sight (LOS) and non-line-of-sight (NLOS) objects in the environment a...

A hybrid full-wave/quasi-optical electromagnetic model for the design of lens-integrated THz antennas for high frequency non-contact device characterization (30 GHz – 3 THz) is presented. Experimental validation of the antenna properties (input impedance and radiation pattern) is also provided to demonstrate the accuracy of the proposed model.

We propose a novel technique for efficient and robust modeling of multistatic, multi-dimensional, large-format millimeter-wave/terahertz (mmW/THz) imaging systems. The proposed method significantly reduces the necessary computational resources for the design of electrically large systems of multiple sensors that acquire multi-frequency images, such...

The W-Band ($75-110\; \mathrm{GHz}$) sky contains a plethora of information about star formation, galaxy evolution and the cosmic microwave background. We have designed and fabricated a dual-purpose superconducting circuit to facilitate the next generation of astronomical observations in this regime by providing proof-of-concept for both a millimet...

In this study a novel THz system is presented for 2D or 3D radar imaging. The system implements a Computerized Tomography's (CT's) algorithm that records the Radon Transform (RT) of an object and reconstructs the image using the Inverse Radon Transform (IRT). As such, the imaging system is comprised of a simple linear antenna that significantly sim...

The aim of this paper is the investigation of nonreciprocal phenomena in anisotropically loaded 2-D periodic structures. For this purpose, our well-established 2-D curvilinear finite difference frequency domain method is combined with periodic boundary conditions and extended toward the eigenanalysis of periodic structures loaded with both isotropi...

We propose a compact, low profile imaging array for active imaging applications and focused illumination capability. As such, the object scene is illuminated and imaged by the same array. The new topology allows for the implementation of densely packed, large-format sensors that operate in the millimeter (mmW) and sub-mmW region. RF sources, antenn...

We present a broadband lumped-element parasitic equivalent circuit to accurately capture the frequency response of electromagnetic (EM) interactions inside the structure and surrounding environment of high electron-mobility transistors (HEMTs). A new mutual inductance term is included to account for the high-frequency magnetic field coupling betwee...

We present a novel THz computed tomography system that enables fast 3-dimensional imaging and spectroscopy in the 0.6-1.2 THz band. The system is based on a new real-time broadband THz camera that enables rapid acquisition of multiple cross-sectional images required in computed tomography. Tomographic reconstruction is achieved using digital images...

We present a broadband lumped-element parasitic equivalent circuit extraction procedure based on full-wave modeling of electromagnetic interactions within the pad layout of millimeter-wave high electron mobility transistors (HEMTs). The proposed method is illustrated using a conventional two-finger HEMT topology within a coplanar waveguide environm...

We propose a compact endoscopic probe for tissue margin detection through reflection measurements in the terahertz band (0.1 – 3 THz). Compared to scalar reflectivity measurements, a fully polarimetric characterization of tissue and malignancy margins provides order-of-magnitude better differentiation, facilitating medical diagnosis of internal org...

We present significant performance improvements of non-contact probes for the mmW and sub-mmW device characterization. Repeatability and accuracy of the measurement setup is studied using an automated non-contact probe system and compared with conventional contact-probes. Owing to the planar, non-contact nature of the new setup, only 2-axis automat...

This paper reports on the design and performance of a terahertz (THz) linear camera with 50 pW/√Hz noise-equivalent power (NEP). This camera is sensitive to four bands of vertically and horizontally polarized THz radiation (0.22, 0.32, 0.42, and 0.52 THz). The heart of the camera is a diode-based focal plane array (FPA) that has a 10 nV thermal noi...

We present a novel non-contact metrology approach for on-wafer characterization of sub-millimeter-wave devices, components, and integrated circuits. Unlike existing contact probes that rely on small metallic tips that make physical contact with the device on the chip, the new non-contact probes are based on electromagnetic coupling of vector networ...

We demonstrate, for the first time, on-wafer 2-port characterization of passive millimeter wave components using a novel, non-contact measurement probe technique in the G-band (140-220 GHz). This new non-contact approach enables fast, repeatable, low-cost, wear&tear-free, robust, and large-scale evaluation of integrated circuits (IC) and devices. O...

We develop a new terahertz (THz) imaging approach with 90 μm image resolution at 750 GHz using an inverse-microscope quasi-optical setup with an extended hemispherical high-resistivity silicon lens and a vector network analyzer frequency extender with horn-antenna output port. Owing to the large refractive index of silicon lens (n∼3.5), the achieve...

We present a novel, non-contact, on-wafer device characterization method covering both THz (300 GHz-3 THz) and mmW bands (60-300 GHz). Unlike existing contact probes which rely on fragile tips and physical contact with the device on the chip, the new non-contact probe setup is based on radiative coupling of vector network analyzer test ports into t...

We have developed a cost-effective, quad-frequency band THz imager for real-time THz imaging applications operating at 220GHz, 320GHz, 420GHz, and 520GHz frequency bands. The new sensor is based on antimonide-based heterostructure backward diodes impedance matched and monolithically integrated with high-gain, narrowband planar antennas. The antenna...

Due to the low penetration depth of THz waves, research in biomedical THz imaging has been primarily focused on the reflection-mode spectroscopy for the diagnosis of various types of cancer (breast, skin, cervical and colon) as well as the classification of skin burns. However, alternative techniques have been around for many decades. For instance,...

We present a non-contact, on-wafer, broadband device and component testing methodology scalable to the THz band. The “contactless” probe setup is based on radiative coupling of vector network analyzer test ports onto the coplanar waveguide environment of monolithic devices and integrated circuits. Efficient power coupling is achieved via planar, br...

We present a hybrid full-wave/quasi-optical electromagnetic model for the design of lens-integrated THz antennas for high frequency non-contact device characterization (0.1-3 THz). The new non-contact probe setup consists of on-chip receiving and transmitting THz antennas in a co-planar waveguide environment. Commercially available THz-frequency ex...

We present a novel approach for on-wafer device characterization in the THz band. A non-contact method eliminating the need for physical contact with test wafer is proposed. Non-contact method is based on radiative coupling of Network Analyzer's test ports into coplanar environment of monolithic device (DUT) through integrated planar THz antennas....

We present a large-format focal plane array sensor for THz imaging. Each pixel of the sensor array consists of an 85μm×92μm lithographically fabricated wideband dual-slot antenna, monolithically integrated with an ultra-fast diode tuned for the 0.6-1.2 THz band. The small antenna footprint enables a densely packed THz imaging array. Concurrently, o...

We present a large-format, sub-millimeter-resolution, focal plane array sensor for THz imaging. Each pixel in the sensor array consists of broadband THz antennas monolithically integrated with ultra-fast heterostructure backward diodes for THz sensing. With the aid of in-house hybrid electromagnetic modeling tools, the focal plane array is optimize...

Sub-millimeter scale image resolution afforded by the THz frequency band, coupled with the ability of THz waves to penetrate through packaging materials have sparked significant interest in THz frequencies for security screening. Conventionally, large-format THz images have been solely acquired using a raster scan of a single pixel, taking several...

We develop a simple and robust impedance characterization method for planar THz antennas with micron- and submicron-size port geometries. Such antennas are often encountered in THz sensing applications where an ultrafast electronic device, such as a Schottky junction or a heterostructure backward diode, is integrated with a planar antenna structure...

We propose a contactless characterization approach for evaluating semiconductor devices and integrated circuits that operate in the THz regime (0.1-3 THz). The non-contact probe consists of on-chip receiving and transmitting THz antennas in a co-planar waveguide environment. Commercially available frequency extension modules with horn antennas are...