Maria S. Papadopoulou

• Physicist (B.Sc.)-Electronic Engineer (M.Sc., Ph.D.)
• Professor (Assistant) at International Hellenic University

As the energy crisis is leading to energy shortages and constant increases in prices, green energy and renewable energy sources are trending as a viable solution to this problem. One of the most rapidly expanding green energy methods is RF (RadioFrequency) energy harvesting, as RF energy and its corresponding technologies are constantly progressing...

In this work, a novel quad-band rectifier circuit is introduced for RF energy harvesting and Internet of Things (IoT) applications. The proposed rectifier operates in the Wi-Fi frequency band and can supply low-power sensors and systems used in IoT services. The circuit operates at 2.4, 3.5, 5, and 5.8 GHz. The proposed RF-to-DC rectifier is design...

The necessity for permanent use of electrical and electronic devices has generated a greater demand for electricity along with more efficient transmission techniques. Energy from the environment can be radio frequency (RF) signals, friction, solar, thermal, or vibration. The increase in autonomous energy devices and sensors depends on the evolution...

Over the past few decades, manufacturers of freezer units such as fridges and refrigerators have been focusing on improving the performance of their products. These devices are typically large and consume a significant amount of electricity, leaving behind a considerable carbon footprint and requiring high maintenance and operating costs. In recent...

In-vitro fertilization (IVF) is an assisted reproductive technology (ART) and is regarded as one of the most successful. The embryo quality is determined by the Gardner system which quantifies three characteristics of embryo morphology: expansion, inner cell mass (ICM), and trophectoderm quality (TE). However, several complex and expensive procedur...

This paper describes a system that is developed to solve a problem related to the packaging of chemical liquids. The problem arises in small chemical production plants where container packaging is done slowly, manually and with free-flowing methods. The user is selecting the chemical liquid type and the weight of the container. In a computer there...

Advanced driver assistance systems (ADAS) technology has been developed to improve driver safety and is a major part of today's autonomous vehicle functionalities. Automotive radars operate as core sensors in modern ADAS systems since they can detect the speed and range of objects near the vehicle. This work uses a recent variant of the Runge-Kutta...

This work presents the performance changes of a function generator, during its warm-up time. An automated measurement and performance verification system is implemented for this generator, according to manufacturer’s instructions. Due to the automated procedure, which is controlled by a computer application, the performance test is executed in only...

This paper provides a technical report on the Smart Embryo project. The Smart Embryo project (Project code: KP6-0079459) combines computer vision, image processing, and artificial intelligence methodologies to classify and characterize fetal images for assisted reproduction applications.

In this paper a technical report of the Smart Fridge project is presented. The Smart Fridge project (Project code: KMP6-0078831) combines Internet of Things technologies, wireless sensor networking, and artificial intelligence to reduce the energy footprint of companies involved in the retail food industry.

In this work a technical report of the Ymnodos project is presented. The Ymnodos project (Project code: KMP6-0078938) combines artificial intelligence methodologies, audio signal processing, and computer vision techniques to provide automatic identification and characterization of cultural items especially Greek Orthodox Church hymns.

This paper presents a plant growth chamber that gives agriculture researchers theability to monitor and control many specialized parameters, measure plant growth rate and setoptimum conditions. A climate chamber is insufficient for modern agriculture research because itcontrols only air temperature and air relative humidity. An agriculture research...

The rapid emergence of the 5G networks has posed a number of new planning problems, which should be carefully analyzed to optimize the installation of the new technologies and to integrate them into the existing mobile network. The main planning objectives are to build up a network satisfying the expected traffic demands in its various sections, in...

Energy consumption is a key factor in environmental sustainability and the economy. In the next 30 years, global food production will need to increase rapidly and, in this context, refrigeration will play a pivotal role. In the SmartFridge project, several aspects of the operating cycle of refrigeration equipment are explored. Energy consumption re...

Deep learning techniques have found numerous applications in the sector of cultural and religious heritage. Greek Orthodox Church hymns are examples of Byzantine religious tradition. Their performance is governed by stringent rules not observed in other cultures. This work trains a novel shallow convolutional neural network to identify Greek Orthod...

In-vitro fertilization (IVF) is considered one of the most effective assisted reproductive approaches. However, it involves a series of complex and expensive procedures, that result in approximately 30% success rate. New technological concepts, like deep learning (DL), are required to increase the success rate while simplifying the procedure. DL te...

Numerous applications for music listeners, educators, DJs, and musicians have been created over the past decade as the field of Music Deep Learning has expanded. Evidently, the majority of works rely on training their architectures using well-established databases, which consist primarily of Western popular music genres. This creates a deficiency i...

This work presents a study comparing two control methods used in IPMC actuators. The position of the free end of the actuator is extracted using low-frequency signals, and the driving voltage is limited to ±3 V. This paper also proposes a new image sensor-based method for measuring displacement, which uses the actuator's route and applied current t...

Watering plants is a crucial task in agriculture, while at the same time, its manual management can be laborious and time-consuming [Aher, et. al, 2020]. To address this challenge, the present project focuses on the development of an automated plant irrigation system using an Arduino microcontroller [Badamasi et al., 2014] and a humidity sensor. Th...

During the last decades, the term “remote laboratory” was rarely heard and more rarely implemented because it was immature and the technology was not able to offer the necessary connectivity. Before the pandemic of covid-19, many universities have already used the remote or virtual laboratories to offer the distance learning. Nowadays, after the pa...

Sine wave is a periodic waveform used by physicists and mathematicians for several applications. It has the unique property of retaining its wave shape when added to another sine wave of the same frequency and arbitrary phase and magnitude. This property is significant in Fourier analysis while making it acoustically unique In this paper: ✓We study...

Micromechanical actuators are commonly utilized in biomedical engineering, robotics, and microelectromechanical systems (MEMS). To effectively define the electromechanical properties of these devices, a comprehensive knowledge of their motion parameters, especially the actuator position, is required (Shahinpoor & Kim, 2001). Due to its unique prope...

The advent of the Internet of Things has allowed the re-usability of established techniques combined with emerging technologies. In the TERMINET project, several key-enabling technologies in an IoT ecosystem are explored. The smart farming paradigm is one of the realistic use cases of the project, in which Wireless Power Transfer, assisted by an Un...

This paper describes a proposed method for optimizing the parameters of a Model Reference Adaptive Control (MRAC) system. The MRAC system uses a reference model to control a plant with unknown dynamics and continuously updates its parameters to improve control accuracy. The system requires an adjustment of parameter γ, which participates in the fee...

Radio-frequency (RF) energy harvesting (EH) is emerging as a reliable and constantly available free energy source. The primary factor determining whether this energy can be utilized is how efficiently it can be collected. In this work, an RF EH system is presented. More particularly, we designed a dual-band RF to DC rectifier circuit at sub-6 GHz i...

The discipline of Deep Learning has been recognized for its strong computational tools, which have been extensively used in data and signal processing, with innumerable promising results. Among the many commercial applications of Deep Learning, Music Signal Processing has received an increasing amount of attention over the last decade. This work re...

This paper presents the upgrade of a climate chamber to a plant growth chamber. Initially, the capabilities of a simple climate chamber are presented. Next, the needs of plant growth are analyzed and the conversion procedure is shown. The plants, in order to grow, have more needs than a controlled temperature and humidity. So, the upgraded chamber,...

During the last decades, the number of people visiting religious destinations has considerably increased. These visits are so often that there is a new trend on the global tourist map, that of religious tourism. The noteworthy difference from the other tourism trends is that the participants in this phenomenon do not treat their experience in a typ...

It is common knowledge that the fertility of couples declines dramatically over time worldwide. The World Health Organization (WHO) has classified infertility as a "disease" of the reproductive system. Infertile couples resort to assisted reproduction treatments to find a solution to their problem. The science of assisted reproduction is relatively...

Refrigeration of food requires significant electricity amounts, equivalent to 50% of the consumption of food retail businesses. International Institute of Refrigeration estimates that the proportion of electricity consumed only for cooling is 17% in a worldwide scale and, taking into consideration that the concentration of population in urban cente...

The need for electronic devices usage has risen significantly over the years. This has in turn generated greater demands for electricity and in addition for green energy sources. These include Radio-Frequency (RF) energy harvesting. In this concept we design a rectifier circuit for RF to DC conversion suitable for operation at sub-6 GHz 5G bands. S...

In developed countries, companies active in the food retail sector consume about 20% of the total power required for cooling and are therefore ranked among them with the largest energy footprint after the industries. For this reason, refrigeration equipment manufacturers are increasingly focusing on methods that will reduce the power consumption re...

Internet of Things (IoT) and Unmanned Aerial Vehicles (UAVs) are two hot technologies utilized in cultivation fields, which transform traditional farming practices into a new era of precision agriculture. In this paper, we perform a survey of the last research on IoT and UAV technology applied in agriculture. We describe the main principles of IoT...

In this paper, we study a three-dimensional Lorenz system that demonstrates chaotic behavior. We present the state equations and mathematical analysis of the system. We use a system-design platform, like LabView, to study and analyze main information properties, such as chaotic attractors, time series, bifurcation diagram, and dynamic behavior of t...

The exigency for continuous use of electrical devices has created greater demands for electricity along with more efficient transmission techniques. Energy from natural resources can be solar, thermal, vibration, friction, or Radio Frequencies (RF) signals. This state-of-the-art work provides a summary of RF energy harvesting techniques and can be...

Frequency Selective Surfaces (FSSs) have become increasingly popular during the last years due to their combined characteristics, which meet, in general, the requirements of the next-generation wireless communication networks. In this work, a cross-platform design framework for FSS structures is presented and evaluated by utilizing a recently intro...

Swarm Intelligence (SI) Algorithms imitate the collective behavior of various swarms or groups in nature. In this work, three representative examples of SI algorithms have been selected and thoroughly described, namely the Grey Wolf Optimizer (GWO), the Whale Optimization Algorithm (WOA), and the Salp Swarm Algorithm (SSA). Firstly, the selected SI...

Agriculture 4.0, as the future of farming technology, includes several key enabling technologies towards sustainable agriculture. The use of state-of-the-art technologies, such as the Internet of Things, transform traditional cultivation practices, like irrigation, to modern solutions of precision agriculture. In this paper, we present in detail th...

Radio Frequency (RF) energy harvesting has been emerged as a potentially reliable method to replace the costly and difficult to maintain source of low-power wireless sensor networks. A plethora of dual-band rectifier designs has been proposed in the literature operating in various frequency bands. In this paper, a triple-band RF-to-DC rectifier tha...

A triple-band single-layer rectenna for outdoor RF energy applications is introduced in this paper. The proposed rectenna operates in the frequency bands of LoRa, GSM-1800, and UMTS-2100 networks. To obtain a triple-band operation, a modified E-shaped patch antenna is used. The receiving module (antenna) of the rectenna system is optimized in terms...

Radio frequency energy harvesting has attracted considerable interest as a technique of enabling self-powered wireless networks. This technique faces several challenges, such as the receiving and the rectifying modules of a rectenna system. Multiband antennas provide several comparative advantages against the goal of maximizing the amount of energy...

Nowadays electricity is undoubtedly one of the most important goods. Over the years, the dependence of people on electrical devices has sharply increased. The need for continuous use of these devices has created greater demand for electricity as well as more efficient transmission techniques. Environmental energy scavenging, as well as wireless tra...

Grey wolf optimizer (GWO) is a nature inspired stochastic meta-heuristic that mimics the hunting behavior of grey wolves. Differential evolution (DE) is a popular stochastic algorithm that is well suited for global optimization. In this digest, we propose a new algorithm based on hybridization of GWO and two DE variants, namely the GWO-DE algorithm...

The design of a wireless sensor network (WSN) has several key points to consider. Power management and battery charging, especially when is applied in a harsh environment, are crucial parameters. In this paper, we present an RF energy harvesting system that converts ambient AC electromagnetic energy into DC voltage, which is applicable to supply lo...

As the power requirements of electronic systems in wireless sensor networks are progressively reducing, radio frequency (RF) energy harvesting (EH) technique is becoming increasingly interesting during the last years. In this paper, we design and optimize a modified printed bow-tie antenna, operating in the frequency band of 5G NR mobile communicat...

Radio Frequency Energy Harvesting (RF EH) is an alternative, yet well-promising technique to deliver power in electronic circuits of wireless sensor networks that require small amounts of energy. The design of the receiving module (antenna) in RF EH systems is a demanding and, in most cases, a complex task. As a result, an optimization method is of...

Radio Frequency (RF) energy harvesting is emerging as a potentially reliable method to replace the costly and, difficult to maintain, source of low-power wireless sensors networks. In this paper, a dual-band RF-to-DC rectifier, that operates at LoRaWAN and GSM-900 cellular communication frequency bands, is presented. The system is composed of an im...

Radio Frequency (RF) energy harvesting is emerging as a potentially reliable method to replace the costly and, difficult to maintain, source of low-power wireless sensors networks. In this paper, a dual-band RF-to-DC rectifier, that operates at LoRaWAN and GSM-900 cellular communication frequency bands, is presented. The system is composed of an im...

Radio Frequency Energy Harvesting (RF EH) is an alternative, yet well-promising technique to deliver power in electronic circuits of wireless sensor networks that require small amounts of energy. The design of the receiving module (antenna) in RF EH systems is a demanding and, in most cases, a complex task. As a result, an optimization method is of...

Radio frequency energy harvesting is a relatively recent and quite interesting technique for delivering adequate amounts of energy in low power consumption wireless networks. This technique faces several challenges, with most of them are related to the antenna design of the harvesting system. In this paper, we address to these challenges by designi...

Water scarcity and desertification are considered to be among the greatest challenges of humanity over the coming decades. Worldwide, agriculture accounts to 69% of total water usage, while industry accounts for 23%, and urban use to 8%. In Greece, a rural development model and poor farming practices have resulted in an overwhelming 83% of total wa...

In this thesis, both theoretically and experimentally, the dynamic behaviour of unidirectional and bidirectional coupled non-linear, high order circuits is studied. Firstly, we presented the dynamics of a 4th order nonlinear, autonomous circuit with two active elements, one nonlinear resistor RN and one linear negative conductance Gn. Using the cap...

It is generally difficult to synchronize a ring network that features chaotic behaviour, especially if the system's order is too large. In this paper, we consider a ring network of three identical nonlinear and non-autonomous circuits of fourth order, which are bidirectionally coupled through three coupling linear resistances R C . We present simul...

In this paper, theoretical and experimental investigations of chaos synchronization and its application to chaotic data transmission in a communication scheme with two identical nonlinear circuits are presented. The conditions for chaos synchronization and its application as a secure communication system based on two 4th order non-autonomous chaoti...

The experimental study of in-out intermittency during the incomplete synchronization of two coupled, nonlinear, autonomous, fourth-order, chaotic, circuits is reported. The two circuits are unidirectionally coupled via a linear resistor. The dependence of laminar lengths, on the deviation of the control parameter from its critical value, and the me...

Chaos synchronization of two identical, bidirectionally and unidirectionally coupled, non-autonomous circuits are presented. A secure communication scheme based on two unidirectionally coupled circuits is proposed. Information is embedded in a chaotic carrier by using chaotic masking technique [1].

We study the case of hyperchaotic synchronization of two identical, linearly coupled, four-dimensional chaotic systems. Individual system contains one nonlinear element, with a double-break, piecewise-linear and symmetrical v-i characteristic, and one negative conductance. Using the capacitance C 1 as the control parameter, we have observed periodi...

We study the complex dynamics of an autonomous, nonlinear circuit. The system consists of a nonlinear element, with a double-break, piecewiselinear and symmetrical v-i characteristic, a negative conductance, two capacitances, two inductances and two resistances. Using the capacitances C 1 , and C 2 as the control parameters, we have observed variou...

This paper studies and compares two non-adaptive synchronization methods of identical chaotic circuits, both theoretically and experimentally. More particularly, bidirectional and unidirectional synchronization of two autonomous nonlinear circuits are studied. Each circuit is described by a set of four first order differential equations, while the...

Τα ηλεκτρονικά κυκλώματα αποτελούν ένα ιδανικό εργαλείο για τη μελέτη της θεωρίας του χάους και των φαινομένων της μη-γραμμικής δυναμικής. Έχουν αποδειχθεί μείζονος σημασίας στην κατανόηση της χαοτικής δυναμικής και στη μελέτη των ιδιοτήτων των δυναμικών συστημάτων. Μια ποικιλία ηλεκτρονικών κυκλωμάτων έχουν χρησιμοποιηθεί γι’ αυτόν τον σκοπό, πολλ...

In this paper a novel non-autonomous 4 th order chaotic oscillator was investigated. This oscillator consists of a nonlinear resistance R N and a negative conductance G n . We have studied the dynamics of the circuit for various values of the input sinusoidal signal v s (t) in the low frequency area, both theoretically and experimentally. We have d...

In this paper the dynamic behavior of a fourth order nonlinear circuit has been studied. The circuit consists of a N-type nonlinear resistor RN, a negative conductance Gn and a sinusoidal generator vs (t). The theoretical and experimental phase portraits and spectrums are been presented, for various values of the amplitude of the input signal, in t...

In this paper a 4 th order, nonlinear and non-autonomous electric circuit has been studied. We have investigated the low frequency response of the circuit, both theoretically and experimentally. The circuit is based on the 3 rd order Chua's canonical circuit and is driven by a sinusoidal voltage source. We have studied the dynamics of the circuit f...

In this paper we have studied the case of chaotic synchronization of two identical, mutually coupled, non linear, 4 th order autonomous electric circuits. Each circuit contains one linear negative conductance G and one non linear resistor R N with a symmetrical piecewise-linear υ-i characteristic. Using the capacitances C 1 and C 2 as the control p...

In this paper we have studied an autonomous circuit. It is a fourth order circuit with a nonlinear resistor of N-type v-i characteristic. The control parameters are the capacitance C1, which is parallel to the nonlinear element, and the resistor R1, which couples the linear conductance with the nonlinear resistor. We have observed the system's depe...

In this paper we have studied a nonlinear electric circuit. It is a fourth-order, non driven circuit, which contains two active elements, one linear negative conductance and one non linear resistor. The coupling resistor between the negative conductance and the nonlinear element serves as the control parameter. We have observed that depending on th...

We have studied an autonomous 4th order circuit, which exhibits sensitive dependence on initial conditions. The circuit contains a non linear resistor RN of N-type. We have observed the dynamics of the non linear circuit for various values of its parameters. A diversity of phenomena has been detected, such as antimonotonicity, period doubling route...

In this paper we have studied the dynamics of a non driven circuit of fourth-order. The circuit constitutes of two active elements, one linear negative conductance and one non linear resistor exhibiting a symmetrical piecewise linear v-i characteristic. The resistor R1, which couples the negative conductance and the nonlinear element, serves as the...

We have studied the case of chaotic synchronization of two identical nonlinear autonomous electric circuits, which are mutually (bidirectionally) coupled via a linear resistor RC. The two circuits can be either υC1-coupled or υC2-coupled. Both, experimental and simulation results, have shown that chaotic synchronization is possible only in the case...

In this paper, we have studied the dynamics of two identical resistively coupled Chua's canonical circuits and have found that it is strongly affected by initial conditions, coupling strength and the presence of coexisting attractors. Depending on the coupling variable, chaotic synchronization has been observed both numerically and experimentally....

In this paper we have studied the dynamics of a 4th order, non driven electric circuit and the bidirectional coupling of two identical circuits. Primarily, we have observed the dynamic behavior of each autonomous circuit. The regions where it exhibits periodic and chaotic phase trajectories were found by investigating the bifurcations diagrams. The...

In this paper the synchronization of two similar, mutually coupled, non-linear circuits, through linear coupling resistance R C is studied. The possibility of chaos synchronization is demonstrated. The basic parameter is the linear coupling resistance, through which we control the current flowing through the branch coupling. Both theoretical and ex...

In this paper we have studied the case of chaotic synchronization of two identical, bidirectional coupled, nonlinear, 4th order autonomous electric circuits. Each circuit contains one linear negative conductance G and one nonlinear resistor RN with a piecewise-linear υ-i characteristic. Using the capacitance C1 and C2 as the control parameters, we...

Στην εργασία αυτή μελετήθηκε ένα αυτόνομο κύκλωμα τέταρτης τάξης ιδιαίτερα ευαίσθητο στις αρχικές συνθήκες με μη γραμμικό αντιστάτη RN χαρακτηριστικής τύπου Ν με μονό σπάσιμο. Ερευνήθηκε για διάφορες τιμές των παραμέτρων του κυκλώματος η δυναμική συμπεριφορά του και επεξεργάσθηκαν περιοχές όπου εμφανίζονται συμπεριφορές αντιμονοτονικότητας, διακλαδ...

Τα μη-γραμμικά κυκλώματα εμφανίζουν πολύπλοκη συμπεριφορά, από περιοδική μέχρι χαοτική. Στην παρούσα εργασία μελετούμε τη δυνατότητα συγχρονισμού δύο όμοιων, αμοιβαία συζευγμένων, μη-γραμμικών κυκλωμάτων 4ης τάξης, τα οποία δεν περιλαμβάνουν εξωτερική πηγή διέγερσης (αυτόνομα κυκλώματα). Μελετώνται οι τρόποι αλληλεπίδρασης των κυκλωμάτων ως προς τι...

We study the case of chaotic synchronization of two identical nonlinear autonomous electric circuits, which are mutually (bidirectionally) coupled via a linear resistor Rc. The two circuits can be either υC1-coupled or υC2-coupled. Chaotic synchronization is observed only in the case of υC2-coupling.