Gerhard Schmidt

Christian-Albrechts-Universität zu Kiel | CAU · Digital Signal Processing and System Theory

Conventional active SONAR systems often use beamformers and matched filters separately to extract bearing and range information from the received signal and offer a straightforward way of creating a two‐dimensional map of the environment. In SONAR systems the minimum‐variance‐distortionless‐response beamformer (MVDR beamformer) is a commonly used t...

In the development of any type of magnetic field sensor based on magnetic films, special consideration must be given to the magnetic layer component. The presented work investigates the use of scalable flux closing magnetostrictive multilayers for inverse magnetoelectric sensors. In such a type of magnetic field sensor, highly sensitive AC and DC f...

Accurate tremor classification is crucial for effective patient management and treatment. However, clinical diagnoses are often hindered by misdiagnoses, necessitating the development of robust technical methods. Here, we present a two-stage convolutional neural network (CNN)-based system for classifying physiological tremor, essential tremor (ET),...

Electroanatomical mapping is a method for creating a model of the electrophysiology of the human heart. Medical professionals routinely locate and ablate the site of origin of cardiac arrhythmias with invasive catheterization. Non-invasive localization takes the form of electrocardiographic (ECG) or magnetocardiographic (MCG) imaging, where the goa...

Modulating a speaker’s auditory feedback is a valuable technique for investigating vocal motor control. In auditory feedback alteration (AFA) experiments, participants receive real-time perturbed feedback of their voice through earphones while producing vocalizations into a microphone. Previous studies primarily focused on pitch and amplitude alter...

Introduction The clinical assessment of mobility, and walking specifically, is still mainly based on functional tests that lack ecological validity. Thanks to inertial measurement units (IMUs), gait analysis is shifting to unsupervised monitoring in naturalistic and unconstrained settings. However, the extraction of clinically relevant gait paramet...

In this paper we present a novel noninvasive approach to estimate current densities in the heart from magnetocardiography. The proposed algorithm uses nested optimization to model current densities in equally-sized voxels of myocardial tissue. First-order Thiran all-pass filters are used to describe the propagation between voxels.We demonstrate fea...

Accurate calibration is key for any reliable sensor system. Magnetoelectric (ME) sensors, in particular, are influenced in their operating point by external parameters such as the Earth’s magnetic field or the ambient temperature. In this paper, we introduce a new planar coil design for the generation of a magnetic test field within the plane of th...

While mechanical tracking is commonly seen in robot-assisted surgery, contactless gesture control leads to a more intuitive approach. Magnetic localization systems might be able to provide an untethered access to the necessary hand movement data. A model-based system exploiting a priori knowledge to improve the accuracy and robustness can be benefi...

Magnetic motion sensing enables non-contact tracking of relative position and orientation in 3D space. With recent advances in sensor and actuator devices, applications in human movement analysis seem feasible. However, establishing a setup from scratch in terms of hardware and software is challenging. Therefore, we introduce a comprehensive simula...

Characterising underwater acoustic transducers is essential to optimal signal processing in sound navigation and ranging systems. Precise characterisation allows for equalisation of the input and output hardware, resulting in improved performance of the overall system. A critical quantity of the characterisation is the impulse response of the under...

The swallowing process involves complex muscle coordination mechanisms. When alterations in such mechanisms are produced by neurological conditions or diseases, a swallowing disorder known as dysphagia occurs. The instrumental evaluation of dysphagia is currently performed by inva-sive and experience-dependent techniques. Otherwise, non-invasive ma...

In principle, electrode-based bioelectrical signal acquisition can be complemented by biomagnetic sensing and therefore requires a more detailed assessment, especially because of the availability of novel noncryogenic sensor technologies. The current development of thin film magnetoelectric (ME) sensors ensures that the ME technology is becoming a...

In today’s world, conference calls are becoming more and more important. It is possible to talk to participants from different countries anytime and anywhere. The disadvantage of such meetings is that it is sometimes incredibly difficult to identify talkers by voice alone. This is even more noticeable in meetings with many participants. One solutio...

Installing spatial telephony systems inside vehicles provides the advantage that different communication partners from the same downlink can be spatially separated during playback. A spatial separation of talkers may decrease the effort required from the listener to follow the conversation and may, therefore, also increase driving safety. This chap...

Active magnetic motion sensing relies on a combination of magnetic sensors and actuators to indirectly sense a time-varying change in position and orientation. Based on our previous work on a 1D setup with magnetoelectric (ME) sensors, we introduce a concept for a full 6D sensing system, which is positioned as a modular setup for human movement pat...

Some magnetoelectric sensors require predefined external magnetic fields to satisfy optimal operation depending on their resonance frequency. While coils commonly generate this external magnetic field, a microelectromechanical systems (MEMS) resonator integrated with permanent magnets could be a possible replacement. In this proof-of-concept study,...

Ultrasound measurements are a widely used instrument in clinical practice. For later traceability of the images, the position (and orientation) of the ultrasound probe must be recorded during the measurement. Until now this has to be done manually by the physician. An easier and more accurate approach would be the automatic tracking of the ultrasou...

Many algorithms use 3D accelerometer and/or gyroscope data from inertial measurement unit (IMU) sensors to detect gait events (i.e., initial and final foot contact). However, these algorithms often require knowledge about sensor orientation and use empirically derived thresholds. As alignment cannot always be controlled for in ambulatory assessment...

The process of diagnosing tremor patients often leads to misdiagnoses. Therefore, existing technical methods for analysing tremor are needed to more effectively distinguish between different diseases. For this purpose, a system has been developed that classifies measured tremor signals in real time. To achieve this, the hand tremor of 561 subjects...

Dedicated research is currently being conducted on novel thin film magnetoelectric (ME) sensor concepts for medical applications. These concepts enable a contactless magnetic signal acquisition in the presence of large interference fields such as the magnetic field of the Earth and are operational at room temperature. As more and more different ME...

Magnetoelectric (ME) sensors with a form factor of a few millimeters offer a comparatively low magnetic noise density of a few pT/Hz−−−√ in a narrow frequency band near the first bending mode. While a high resonance frequency (kHz range) and limited bandwidth present a challenge to biomagnetic measurements, they can potentially be exploited in indi...

A major challenge in modern society is the need to increase awareness and excitement with regard to science, technology, engineering and mathematics (STEM) and related careers directly or among peers and parents in order to attract future generations of scientists and engineers. The numbers of students aiming for an engineering degree are low compa...

The evidence of the responsiveness of dopaminergic medication on gait in patients with Parkinson’s disease is contradicting. This could be due to differences in complexity of the context gait was in performed. This study analysed the effect of dopaminergic medication on arm swing, an important movement during walking, in different contexts. Forty-f...

The knowledge of the exact position and orientation of a sensor with respect to a source (distribution) is essential for the correct solution of inverse problems. Especially when measuring with magnetic field sensors, the positions and orientations of the sensors are not always fixed during measurements. In this study, we present a processing chain...

When designing closed-loop electro-acoustic systems, which can commonly be found in hearing aids or public address systems, the most challenging task is canceling and/or suppressing the feedback caused by the acoustic coupling of the transducers of such systems. In many applications, feedback cancelation based on adaptive filters is used for this p...

Abstract In recent years, significant effort has been allocated to research on multiple‐input–multiple‐output (MIMO) sound navigation and ranging (SONAR) and RADAR systems. Most work has been conducted on the general theoretical functionality of such systems. Less effort has been applied to considerations of the real‐time MIMO capability, although...

Delta-E effect sensors are based on magnetoelectric resonators that detune in a magnetic field due to the delta-E effect of the magnetostrictive material. In recent years, such sensors have shown the potential to detect small amplitude and low-frequency magnetic fields. Yet, they all require external magnetic bias fields for optimal operation, whic...

Wie sieht die Medizin von morgen aus? Mit Magnetfeldsensoren lassen sich Herzaktivitäten sehr genau analysieren, noch sind solche Messungen aber aufwendig und teuer. Der Kieler Sonderforschungsbereich 1261 „Biomagnetic Sensing“ arbeitet an der Weiterentwicklung dieser Messtechnologien. In einer Unterrichtseinheit für die Sekundarstufe II lernen Sch...

Background Identification of individual gait events is essential for clinical gait analysis, because it can be used for diagnostic purposes or tracking disease progression in neurological diseases such as Parkinson’s disease. Previous research has shown that gait events can be detected from a shank-mounted inertial measurement unit (IMU), however d...

Neurological pathologies can alter the swinging movement of the arms during walking. The quantification of arm swings has therefore a high clinical relevance. This study developed and validated a wearable sensor-based arm swing algorithm for healthy adults and patients with Parkinson's disease (PwP). Arm swings of 15 healthy adults and 13 PwP were...

Background: Identication of individual gait events is essential for clinical gait analysis, because it can be used for diagnostic purposes or tracking disease progression in neurological diseases such as Parkinson's disease. Previous research has shown that gait events can be detected from a shank-mounted inertial measurement unit (IMU), however de...

Background: Identification of individual gait events is essential for clinical gait analysis, because it can be used for diagnostic purposes or tracking disease progression in neurological diseases such as Parkinson's disease. Previous research has shown that gait events can be detected from a shank-mounted inertial measurement unit (IMU), however...

Mobile health technologies (wearable, portable, body-fixed sensors, or domestic-integrated devices) that quantify mobility in unsupervised, daily living environments are emerging as complementary clinical assessments. Data collected in these ecologically valid, patient-relevant settings can overcome limitations of conventional clinical assessments,...

Objective: Electroneurography has been an essential method for assessing peripheral nerve disorders for decades. During this procedure, a nerve is briefly electrically excited, and nerve conduction properties are identified by indirect means from the behavior of the innervated muscle. The magnetic field of the resulting muscle response can also be...

So-called full-face masks are essential for fire fighters to ensure respiratory protection in smoke diving incidents. While such masks are absolutely necessary for protection purposes on one hand, they impair the voice communication of fire fighters drastically on the other hand. For this reason communication systems should be used to amplify the s...

Objective: Electroneurography is a wellestablished diagnostic test for supporting the diagnosis of disorders ofmyelinated peripheral nerves. Neurophysiological quantities are automatically calculated and are used to determine the pathology of the nerve (axonal damage) or its sheath (myelin damage). Specific differential diagnostic criteria are der...

Recently, there has been much interest in magnetoelectric magnetic field sensors utilizing the delta-E effect. Such sensors are fully integrable and combine the advantages of high sensitivity at low frequencies with broad bandwidth. Here, we report the influence of the quality factor Q on the signal-to-noise ratio of magnetoelectric magnetic field...

Despite obvious advantages over their electric counterparts, magnetic measurements are still performed very rarely for medical diagnosis. The high operating costs of established systems with a sufficient limit of detection, mainly based on superconducting quantum interference devices, prevent the spread of magnetic diagnostic procedures. Consequent...

Background: Hypokinetic dysarthria is highly prevalent in idiopathic Parkinson’s disease (PD) and effectivity of high intensity voice treatment is well established. However, the neural correlates remain largely unknown. Objective: We aimed to specify cerebral pathophysiology of hypokinetic dysarthria and treatment induced changes using functional m...

For further development and optimization of novel uncooled magnetoelectric (ME) sensors, a better understanding of spectral power distribution and signal strength of nerve signals is of high interest. For obtaining information on these signal properties, Superconducting Quantum Interference Device (SQUID) measurements were performed at the Physikal...

Artificial bandwidth extension reconstructs a 16 kHz wideband signal from a given 8 kHz narrowband signal. Stateof-the-art approaches use regression deep neural networks (DNNs) for extending the spectral envelope. As a cost function during training, they use the mean squared error (MSE) between true and estimated wideband spectral envelopes. With p...

Introduction: Impaired sit-to-stand and stand-to-sit movements (postural transitions, PTs) in patients with Parkinson's disease (PD) and older adults (OA) are associated with risk of falling and reduced quality of life. Inertial measurement units (IMUs, also called “wearables”) are powerful tools to monitor PT kinematics. The purpose of this study...

Objective Clinical electroneurography, the diagnostic standard for the assessment of thickly myelinated peripheral nerves, is of limited spatial resolution since it provides only average data (nerve conduction velocity [NCV], nerve or muscle action potential amplitude) on relatively large nerve segments. Accordingly, different distribution patterns...

Objective Sustained neuronal activity can be localized with functional magnetic resonance imaging (fMRI). Signal analysis of the time series within and across brain voxels reveal state specific characteristics enriching our understanding of, e.g., different states of consciousness (Tagliazucchi et al., 2015, Tagliazucchi et al., 2014, Tagliazucchi...

Artificial bandwidth extension (BWE) is still an important topic, especially in the automotive domain where consumers experience a dramatic degradation in voice quality when a wideband call suddenly falls back to 8-kHz GSM. This happens e.g. due to poor network coverage in the countryside. The aim of BWE is to bridge the perceived voice quality gap...

Artificial bandwidth extension (ABWE) for speech signals is still an important topic in mobile telephony, especially when a 16 kHz wideband (WB) call suddenly falls back to an 8 kHz GSM connection. The aim of ABWE is to bridge the arising voice quality gap by reconstructing the WB signal. In order to achieve this, the speech signal is typically dec...

We present a comprehensive study of a magnetic sensor system that benefits from a new technique to substantially increase the magnetoelastic coupling of surface acoustic waves (SAW). The device uses shear horizontal acoustic surface waves that are guided by a fused silica layer with an amorphous magnetostrictive FeCoSiB thin film on top. The veloci...

Thin-film magnetoelectric sensors are able to measure very low magnetic fields. As a consequence the hypothesis that magnetoelectric sensors could be used for biomagnetic measurements was often mentioned but never proven. In this contribution the first proof of this hypothesis will be given by the measurement of the (well-known) R-wave of the human...

Introduction Inertial measurement units (IMUs) positioned on various body locations allow detailed gait analysis even under unconstrained conditions. From a medical perspective, the assessment of vulnerable populations is of particular relevance, especially in the daily-life environment. Gait analysis algorithms need thorough validation, as many ch...

We present a comprehensive noise model for an electromechanical resonator that is utilized as a magnetic field sensor. The cantilever-type sensor is coated with a magnetostrictive film that exhibits a change in elastic modulus E with a magnetic field and therefore detunes the resonator--the so-called delta-E effect. The noise model contains all rel...

Thin-film magnetoelectric sensors reach a sensitivity in the picotesla range around the resonance frequency of the mechanical structure. Using magnetic frequency conversion a magnetic low-frequency signal can be transferred to the sensor’s resonance frequency. However, the required additional large carrier signal leaks to the sensor’s output with a...

Neuartige, auf dem magnetoelektrischen Effekt basierende Sensoren haben das Potential, biomagnetische Signale messen zu können. Allerdings koppeln aufgrund ihrer Struktur auch akustische Störungen mit in den Sensor ein, die das gesuchte magnetische Nutzsignal uberlagern. Abhilfe schafft eine Kompensation der Störung mit Hilfe akustischer Referenzse...

Thin-film magnetoelectric sensors, i.e. composites of magnetostrictive and piezoelectric materials, are able to measure very low magnetic flux densities in the picotesla range. In order to further improve the limit of detection it is of high importance to understand and quantify the relevant noise sources. In this paper a common model for the defle...

Composite magnetoelectrics implemented as thin film heterostructures are discussed in view of their applicability as highly sensitive magnetic field sensors. Here, either PZT or AlN served as piezoelectric component. The magnetostrictive phase consisted of layer systems based on FeCo or (Fe 90 Co 10 ) 78 Si 12 B 10 . All functional layers were depo...

Microphones placed on the seat belts of an automobile (in the following called beltmics for short) are an interesting alternative compared to other sensor positions. Because of the small distance to the speaker’s mouth, usually a good signal quality (e. g., measured in terms of high signal-to-noise ratio) can be achieved. However, the signalsmay al...

The Lombard effect is a phenomenon of increasing the vocal effort that people develop due to, amongst others, the presence of background noise. For example, if the background noise level rises, both pitch and loudness of the voice usually increase, but also the duration of individual speech sounds and the diction may change. In order to investigate...

Thin-film magnetoelectric (ME) sensors offer a promising potential to measure biomagnetic signals in the near future. Unfortunately, this sensor type shows usually a large cross-sensitivity to all kinds of mechanic distortion due to the resonant structure. In order to overcome this problem several sensor designs have been proposed. Beside these app...

One of the most commonly used therapy to treat patients with Parkinson's disease (PD) is deep brain stimulation (DBS) of the subthalamic nucleus (STN). Identifying the most optimal target area for the placement of the DBS electrodes have become one of the intensive research area. In this study, the first aim is to investigate the capabilities of di...

Monitoring driver's intentions beforehand is an ambitious aim, which will bring a huge impact on the society by preventing traffic accidents. Hence, in this preliminary study we recorded high resolution electroencephalography (EEG) from 5 subjects while driving a car under real conditions along with an accelerometer which detects the onset of steer...

Thin-film magnetoelectric sensors, i.e., composites of magnetostrictive and piezoelectric materials, are able to measure very low magnetic fields. As a consequence, an application of such sensors could be, e.g., the measurement of biomagnetic fields in the near future. To measure these signals, typically characterized by low-frequency components, t...

We present an analytical and experimental study on low-noise piezoelectric thin film resonators that utilize the delta-E effect of a magnetostrictive layer to measure magnetic fields at low frequencies. Calculations from a physical model of the electromechanical resonator enable electrode designs to efficiently operate in the first and second tran...

This study aimed to evaluate an In-Car Communication system (ICC), which was developed to improve the communication between passengers inside a driving car. The evaluation was conducted by assessing parameters involved in the Lombard effect, i.e. modifications of speech production in the presence of loud noises. Speech recordings were made inside a...

Magnetoelectric thin film composites have demonstrated their potential to detect sub-pT magnetic fields if mechanical resonances (typically few hundred Hz to a few kHz) are utilized. At low frequencies (1–100 Hz), magnetic field-induced frequency conversion has enabled wideband measurements with resonance-enhanced sensitivities by using the nonline...

Microphones integrated on a seat belt are an interesting alternative to conventional sensor positions used for hands-free telephony or speech dialog systems in automobile environments. In the setup presented in this contribution, the seat belt consists of three microphones which usually lay around the shoulder and chest of a sitting passenger. The...

This study aimed to evaluate an In-Car Communication system (ICC), which was developed to improve the communication between passengers inside a driving car. The evaluation was conducted by assessing parameters involved in the Lombard effect, i.e. modifications of speech production in the presence of loud noises. Speech recordings were made inside a...

Recently, magnetoelectric sensors have gained importance in medical applications. Among several sensor types microelectromechanical magnetic field sensors are a promising option since they can be manufactured in a very small fashion and can operate at room temperature. In this contribution we present a new readout scheme for such sensors that simul...

Multiple sclerosis (MS) is a progressive neurological disorder that affects the central nervous system. Functional magnetic resonance imaging (fMRI) has been employed to track the course and disease progression in patients with MS. The two main aims of this study were to apply in a data-driven approach the independent component analysis (ICA) in th...

In many speech signal processing applications, voice activity detection (VAD) plays an essential role for separating an audio stream into time intervals that contain speech activity and time intervals where speech is absent. Many features that reflect the presence of speech were introduced in literature. However, to our knowledge, no extensive comp...

Sensors based on the magnetoelectric (ME) effect have the potential to be genuine alternatives for measuring bio-magnetic signals. Unfortunately, the sensor structure usually inhibits the problem that several non-magnetic types of noise couple mechanically into the sensor: in this contribution, we will focus on undesired acoustic coupling. Therefor...

Cognitive signal processing has been intensively studied over the past years. Nevertheless, cognitive sonar systems only draw little attention in the research community. In this paper the signal processing of a cognitive sonar system for diver detection is shown in detail. It is inspired by the target-detection system of a bat and thus able to adap...

Essential tremor follows an autosomal dominant type of inheritance in the majority of patients, yet its genetic basis has not been identified. The age of onset in this tremor is bimodal, one in young age and another when they are old. The old onset is referred to as senile tremor in this study. The precise pathology is still not completely understo...

Voxel based morphometry (VBM) is an automated analysis technique which allows voxel-wise comparison of mainly grey-matter volumes between two magnetic resonance images (MRI). Two main analysis processes in VBM are possible. One is cross-sectional data analysis, where one group is compared with another to depict see the regions in the brain, which s...

Lautsprachliche Kommunikation im Auto wird durch die Geräuschbelastung unterschiedlicher Geschwindigkeiten stark beeinflusst. Dabei spielt vor allem der Lombard-Effekt eine entscheidende Rolle, der die Veränderungen der Sprachproduktion bei Lärm beschreibt. Um festzustellen, ob die im Fahrzeug entstehende Lombard-Sprache unter kontrollierten Laborb...

The invention provides a method for estimating a fundamental frequency of a speech signal comprising the steps of receiving a signal spectrum of the speech signal, filtering the signal spectrum to obtain a refined signal spectrum, determining a cross-power spectral density using the refined signal spectrum and the signal spectrum, transforming the...

A method for detecting barge-in in a speech dialog system comprising determining whether a speech prompt is output by the speech dialog system, and detecting whether speech activity is present in an input signal based on a time-varying sensitivity threshold of a speech activity detector and/or based on speaker information, where the sensitivity thr...

A communication system enhances communications in a noisy environment. Multiple input arrays convert a voiced or unvoiced signal into an analog signal. A converter receives the analog signal and generates digital signals. A digital signal processor determines temporal and spatial information from the digital signals. The processed signals are then...

Research into speech communication was until recently solely concerned with basic issues of sound-segment interaction and tune structure. Many issues are still far from being fully understood, even for Western European languages, but we have gained enough knowledge to start digging deeper into the social and interactional aspects of speech that act...

Lautsprachliche Kommunikation im Auto wird durch die Geräuschbelastung unterschiedlicher Geschwindigkeiten stark beeinflusst. Dabei spielt vor allem der Lombard-Effekt eine entscheidende Rolle, der die Veränderungen der Sprachproduktion bei Lärm beschreibt. Um festzustellen, ob die im Fahrzeug entstehende Lombard-Sprache unter kontrollierten Laborb...

Subthalamic nucleus deep brain stimulation (STN-DBS) therapy is an effective treatment for the motor symptoms of advanced Parkinson’s disease (PD). However, the underlying neurophysio- logical mechanisms for the motor improvement are uncertain. We utilised a simultaneous functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG)...

Communicating inside a car can be difficult because there is usually a high level of background noise and also the talking and the listening passengers do not necessarily face each other as they would do in a natural conversation. In-car communication (ICC) systems are a solution to this problem. They record the talkers’ speech signal by means of m...

In this contribution, methods for spectral refinement (SR) and spectral interpolation (SI) are presented. These methods can be implemented as a post-processing stage after conventional frequency analyses such as overlap add-based decomposition schemes. The principle idea of SR is to individually refine each subband signal after frequency decomposit...

A system enhances speech by detecting a speaker's utterance through a first microphone positioned a first distance from a source of interference. A second microphone may detect the speaker's utterance at a different position. A monitoring device may estimate the power level of a first microphone signal. A synthesizer may synthesize part of the firs...

In this paper a simple yet robust noise power spectral density estimation algorithm is presented. The motivation for the algorithm developed here is the harsh noise environment present in automobiles along with the need to keep the complexity low for real-time implementations. The scheme is based on a multiplicative estimator in which multiple incr...

In-car communication systems aim at improving the speech communication inside a vehicle by picking up the talking passenger's voice by means of microphones and playing it back over loudspeakers that are located close to the listening passengers. Because of this closed-loop operation, system instability caused by acoustical feedback is a limiting fa...

The signal quality at different microphone locations varies for distributed microphone arrays. Such microphone constellations require a suitable beamformer design that considers these differences in the input signal conditions. In this paper a frequency domain minimum variance (MV) beamforming approach is presented that uses a soft reference select...

The present invention relates to a method for processing sound signals in a vehicle multimedia system. A sound signal is recorded by a microphone. A voice signal component resulting from reproducing a voice signal and an audio signal component resulting from reproducing an audio signal are compensated in the recorded sound signal. The invention fur...