Measured Frequency Response Research Articles

Stability properties of regenerative cutting processes, based on impulse response functions expressed in the impulse dynamic subspace

An extensive study on the implementation of the convolution based impulse dynamic subspace (IDS) concept for machining applications is presented in this paper. The suggested method is adequate to avoid modeling based on modal parameters. Instead of parameter driven dynamical modeling, the impulse response functions (IRFs) are used for the IDS decomposition and for constructing the corresponding delayed and, on occasion, time periodic equations of motion of regenerative cutting processes. This approach makes possible to use measured frequency response functions (FRFs) in time domain based methods. This is achieved by establishing the connection between the IRF and the fundamental matrix of the corresponding linearized generally time periodic delayed system. It is shown that the concept provides the well-known analytic solution of the orthogonal turning model, demonstrating the applicability of the proposed methodology, while a specially tailored high-order semidiscretization scheme is tested on milling models.

Vibrotactile rendering on a touch surface with reduced sound radiation

Vibrotactile feedback has been utilized in various electronic devices with interactive touch surfaces to improve the tactile interaction between the user and the touch surface. Recent studies have proposed vibration rendering methods that enable specific vibration patterns to be generated at desired positions on a touch surface. However, the vibration rendering causes the surface to radiate considerable acoustic noise, which can deteriorate the overall quality of the haptic interaction. This paper proposes a vibration rendering method that reduces the sound radiation from vibrating touch surfaces. In the proposed method, a vibroacoustic model of a touch surface system, combined with measured frequency response functions, is utilized to predict the vibration responses and sound radiation generated by actuator driving signals. Subsequently, a constrained optimization problem is formulated to obtain the optimal driving signals that minimize the estimated sound radiation while rendering a target vibration pattern at desired positions. To validate the proposed method, vibration rendering experiments were conducted on an experimental touch surface system. The driving signals obtained through the proposed method accurately rendered a complex target vibration pattern at the desired positions on the touch surface. Compared to an existing vibration rendering method, the proposed method reduced the estimated sound radiation by 5.1 to 12.3 dB, without structural modifications and hardware additions.

Structural Modifications of Headphone Front Chamber for Better Frequency Response: Experimental and Simulation Studies

The supra-aural headphone concentrates the sound in the listener’s ears, so the loudspeaker sound is confined to the cavity between the pinna and the headphone casing. It is then directed toward the tympanic membrane through the ear-canal. The high-quality sound requirement of supra-aural headphone on one side and space limitation on the other prompted this research. Similarly, inherent sound leakages from headphone on one side and a need for loud sound on the other also impelled this research. This research proposes headphone design modifications for interaction between sound from the diaphragm’s rear and front side for improved frequency response. The changes attempt to stop the sound from the diaphragm’s rear side to leak to the external surrounding, and it is routed to interact with the sound from the front side of the diaphragm in two distinct ways due to the geometrical/structural modifications of the headphone front cover. Prototypes of three headphones (one traditional and two modified) have been modeled by computer-aided drafting software and fabricated by 3D printing. In parallel, equivalent circuits have been formed for the simulation as per the proposed headphone testing setup. The frequency response measurements of headphones have been done in an anechoic chamber using B&K HATS Type 4128. The simulated and measured responses of headphones demand modification of the equivalent circuit by adding the current-controlled voltage source. The optimum simulated performances of all three headphones with a modified equivalent circuit show an improved agreement with respective measured performances.

Thin-film lithium niobate modulators for non-invasive sensing of high-frequency electric fields

We propose a non-invasive, large-bandwidth electro-optic (EO) detection scheme for high-frequency electric fields using thin-film lithium niobate Mach–Zehnder interferometers. Our proof-of-concept device is capable of detecting high-strength electric fields, such as those present in x-ray free electron lasers and linear accelerators. The proposed detection scheme utilizes an off-the-shelf C-band fiber optic continuous-wave laser and optical spectrum analyzer, which has a lower system cost and footprint compared to bulk-crystal-based schemes. Towards this objective, fabricated devices are characterized in the 1–40 GHz frequency range to estimate the detection threshold, detection bandwidth, and EO modulation strength. The characterized device exhibits a 0.13 V ⋅ m − 1 ⋅ H z − 1 / 2 normalized electric field sensitivity. By extrapolating the measured frequency response, it is expected that the characterized device will be able to detect free-space electric fields up to 150 GHz.

Микрополосковые фильтры с широкими полосами пропускания

New microstrip designs of bandpass filters based on a low-pass filter was developed. Several or all the sections of high-impedance microstrip lines of the designed filters were connected to the ground by stubs. The filters have high frequency-selective properties, and their fractional bandwidths are in the range of 30 % –150 %. An experimental sample of a filter with a 2 GHz central frequency of the passband and 70% fractional bandwidth was made on an alumina substrate 1 mm thick. The filter has a substrate area of 46 × 21 mm2. Good agreement of the measured frequency response of the filter with the characteristics calculated by the numerical electrodynamic analysis of its 3D model was shown.

Frequency-Agile WLAN Notch UWB Antenna for URLLC Applications

This paper introduces a compact dual notched UWB antenna with an independently controllable WLAN notched band integrated with fixed WiMAX band-notch. The proposed antenna utilizes a slot resonator placed in the main radiator of the antenna for fixed WiMAX band notch, while an inverted L-shaped resonator in the partial ground plane for achieving frequency agility within WLAN notched band. The inverted L-shaped resonator is also loaded with fixed and variable capacitors to control and adjust the WLAN notch. The WLAN notched band can be controlled independently with a wide range of tunability without disturbing the WiMAX band-notch performance. Step by step design approach of the proposed antenna is discussed and the corresponding mathematical analysis of the proposed resonators are provided in both cases. Simulation of the proposed antenna is performed utilizing commercially available 3D-EM simulator, Ansoft High Frequency Structure Simulator (HFSS). The proposed antenna has high selectivity with experimental validation in terms of reflection coefficient, radiation characteristics, antenna gain, and percentage radiation efficiency. The corresponding measured frequency response of the input port corresponds quite well with the calculations and simulations in both cases. The proposed antenna is advantageous and can adjust according to the device requirements and be one of the attractive candidates for overlay cognitive radio UWB applications and URLLC service in 5G tactile internet. The proposed multi-functional antenna can also be used for wireless vital signs monitoring, sensing applications, and microwave imaging techniques.

Estimation of Humidity Sensor Equivalent Circuit Parameters Utilizing Frequency Response Measurements Combined With Subspace Identification and Similarity Transformations

This article presents an algorithm to estimate the impedance parameters of a humidity sensor from the measured frequency response data. The sensor is modeled as a multielement two-terminal network. The procedure accurately identifies the impedance parameters using a noniterative algorithm. Traditional nonlinear least-squares procedures rely on having initial parameter values close to the actual values for converging. We approach the problem in two steps: a black-box system identification and a physical parameter extraction step. Based on the first principles, a physical state-space model is developed, where the system matrices contain the impedance parameters in very complicated ways. By strategically introducing extra variables that are a function of these problematic parameters, the state-space model is converted into an observable canonical form. Using frequency response data, a subspace algorithm identifies a model of the same order as the physical model. An unknown similarity transformation matrix is then used to establish the relationship between the identified model and the canonical model. In the first step, we determine the additional variables and the transforming matrix. The impedance parameters are obtained from the relationship between the additional variables and the physical parameters. Simulations and experiments validate the proposed algorithm.

Broadband Optoelectronic Frequency Response Measurement Utilizing Frequency Conversion

A broadband optoelectronic (O/E) frequency response measurement method utilizing photonics-based frequency conversion is proposed and experimentally demonstrated. It is characterized by a sub-kilohertz frequency resolution and a doubled measurement bandwidth compared with the RF frequency sweeping range and the working bandwidth. A carrier-frequency-shifted optical double-sideband (ODSB) signal is produced by employing a dual-drive Mach-Zehnder modulator (DD-MZM) and stimulated Brillouin scattering (SBS). Then, a photodetector (PD) under test receives and converts the optical signal into a photocurrent. By detecting the frequency up- and down-conversion components generated by the two first-order sidebands and the optical carrier, the O/E frequency responses in the low- and high-frequency regions are achieved. After stitching the two measured responses together, an O/E frequency response with a frequency range that is twice the bandwidth of the input microwave signal is obtained. In an experiment, the O/E frequency response of a commercial high-speed PD is precisely characterized with a frequency resolution up to 5.55 MHz. A frequency bandwidth of 66.8 GHz (0.1–66.9 GHz) is achieved by using a 25-GHz DD-MZM. The measured O/E frequency response is coincident with that measured by a commercial instrument.

Frequency Response Analysis Interpretation Using Numerical Indices and Machine Learning: A Case Study Based on a Laboratory Model

Frequency response analysis is a powerful tool for mechanical fault diagnostics in power transformers. However, interpretation schemes still today depend on expert analyses, mainly because of the complex structure of power transformers. One of the fundamental shortcomings of experimental investigations is that mechanical deformations cannot be managed on real transformers to obtain data for different scenarios because they are too destructive. To address this issue in a systematic way, the current research used a specially designed laboratory transformer model that allows mechanical defects to be introduced so its frequency response can be evaluated under different conditions. The key feature of this model is the non-destructive interchangeability of its winding sections, allowing reproducibility and repeatability of frequency response measurements. Numerical indices were compared over key performance indicators (linearity, sensitivity and monotonicity). The analysis indicated that comparative standard deviation offered promising results for evaluation of mechanical deformations on the laboratory winding model given its monotonic behaviour, sensitivity and linear increase with fault severity. Additionally, support vector machine learning, radial basis function neural network and the statistical k-nearest neighbour method were used for fault classification with different strategies and configurations. While limited data from different transformers are used in the available literature, the approach discussed here considers 371 measurements from the same transformer model. The test results are supportive and demonstrate great accuracy when machine learning is used for winding fault classification.

A method for the experimental identification of equivalent viscoelastic models from vibration of thin plates

Aim of the present study is the identification of equivalent viscoelastic models for layered thin walled structures, obtained from vibration measurement only, able to fit the experimental data on a relatively wide frequency range by means of a minimum number of parameters. A novel approach is proposed, based on a definition of an equivalent modal damping ratio applied to the circle-fit technique, to overcome the difficulties related to the identification of modal parameters when adopting non-conventional viscoelastic models. When the structural internal dissipative effects are dominant, this procedure identifies the parameters of an equivalent Young’s modulus in the frequency domain, representing the viscoelastic properties of a homogenized structure as a scalar function with frequency-dependent real and imaginary parts. The proposed procedure is applied to the analysis of Aluminum plates coated by damping pads and of plates made by Quiet Aluminum. To fit the experimentally found equivalent modal damping ratios, several viscoelastic models are adopted and compared (viscous, hysteretic, generalized Maxwell, fractional derivative damping, and in particular the Fractional Kelvin-Voigt model), assessing the accuracy of the identified parameters by comparison of numerically simulated with experimentally measured frequency response functions.

Validation of a Coupled Simulation for Machine Tool Dynamics Using a Linear Drive Actuator

In order to ensure high productivity capabilities of machine tools at a low cost but at increased geometric accuracy, modeling of their static and dynamic behavior is a crucial task in structure optimization. The drive control and the frictional forces acting in feed axes significantly determine the machine’s response in the frequency domain. The aim of this study was the accurate modeling and the experimental investigation of dynamic damping effects using a machine tool test rig with three-axis kinematics. For this purpose, an order-reduced finite element model of the mechanical structure was coupled with models of the drive control and of the non-linear friction behavior. In order to validate the individual models, a new actuator system based on a tubular linear drive was used for frequency response measurements during uniaxial carriage movements. A comparison of the dynamic measurements with the simulation results revealed a good match of amplitudes in the frequency domain by considering dynamic damping. Accordingly, the overall dynamic behavior of machine tool structures can be predicted and thus optimized by a coupled simulation at higher level of detail and by considering the damping effects of friction. Dynamic testing with the newly designed actuator is a prerequisite for model validation and control drive parameterization.

Size selective particle filtering on centimeter scale by frequency sweep type dynamic acoustic field

The objective of the study was to investigate and demonstrate the application of frequency-sweep dynamic acoustic fields for size-selective particle filtration on centimeter scale in a regulated continuous flow. The 3D-printed prototype of the acoustic separator has two inlets and two outlets, whereas the dynamic acoustic field is generated between a transducer, operating in the MHz range, and a reflector. The measured frequency response of the prototype was input to computer models, and simulations were carried out to explore the effects of the sweep period and the flow parameters on the filtration performance. A design-of-experiments study showed that the filtration performance is largely affected by the sweep period and the outlet flow rate. Lab experiments with model particle mixtures demonstrated the size selective filtration performance of the prototype with a total flow rate of 1Lh-1. A mixture with unknown properties was also used to demonstrate the selective filtration performance of the prototype.

Fast and robust identification of railway track stiffness from simple field measurement

We propose to combine a physics-based finite element (FE) track model and a data-driven Gaussian process regression (GPR) model to directly infer railpad and ballast stiffness from measured frequency response functions (FRF) by field hammer tests. Conventionally, only the rail resonance and full track resonance are used as the FRF features to identify track stiffness. In this paper, eleven features, including sleeper resonances, from a single FRF curve are selected as the predictors of the GPR. To deal with incomplete measurements and uncertainties in the FRF features, we train multiple candidate GPR models with different features, kernels and training sets. Predictions by the candidate models are fused using a weighted Product of Experts method that automatically filters out unreliable predictions. We compare the performance of the proposed method with a model updating method using the particle swam optimization (PSO) on two synthesis datasets in a wide range of scenarios. The results show that the enriched features and the proposed fusion strategy can effectively reduce prediction errors. In the worst-case scenario with only three features and 5% injected noise, the average prediction errors for the railpad and ballast stiffness are approximately 12% and 6%, outperforming the PSO by about 6% and 3%, respectively. Moreover, the method enables fast predictions for large datasets. The predictions for 400 samples takes only approximately 10 s compared with 40 min using the PSO. Finally, a field application example shows that the proposed method is capable of extracting the stiffness values using a simple setup, i.e., with only one accelerometer and one impact location.

High-sensitivity optical fiber temperature sensor based on a dual-loop optoelectronic oscillator with the Vernier effect.

In this paper, a high-sensitivity optical fiber temperature sensor based on a dual-loop optoelectronic oscillator (OEO) with the Vernier effect has been proposed and experimentally demonstrated. Different from the traditional dual-loop OEOs which comprise a very long loop and a short loop to achieve low-phase noise and single-mode selection, the proposed OEO scheme has two loops with slightly different lengths and does not use any RF filters. A part of the fiber in one of the loops is used as a temperature sensing element as well as the delaying component. An obvious Vernier effect has been generated in the frequency response of the OEO. By detecting the frequency shift of the envelope peak of the measured frequency response curve, the temperature sensing interrogation of the dual-loop OEO based sensor is conducted. The experimental results show that the sensitivity of the proposed dual-loop OEO based temperature sensor can be improved from 6.625 KHz/°C for a single-loop OEO to 210.25KHz/°C by employing the Vernier effect.

Discrete Lissajous and Recton Functions: A New Method for Frequency Response Measurements

An innovative and completely new technique so called discrete Lissajous functions and recton functions for signal analysis and measurement is explained. The contribution of the study is that it is a new digital method of obtaining information on frequency, change of frequency, phase and phase shift as well as auto-correlation, cross-correlation and energy functions of signals in digital form on-line that may be difficult to be provided in analog form and available for measurement and control applications at each sampling instance directly. The discrete Lissajous figures and recton functions can also be sketched in digital image form for further analysis of signals and systems. They are based on an algorithm utilizing discrete convolutions of discrete time signals. They can be depicted in 3D form. They give more information than classical analog Lissajous figures obtained on an oscilloscope screen. They can be used for several applications from chaotic systems to biomedical applications requiring to finding correlations, energies as well as frequency and phase information of the signals and controlling such systems. In this study, the application of them to systems steady-state, mainly frequency response analysis is explained after giving basic definitions.

Balanced dual-band superconducting filter using square ring loaded resonators with ultra-low insertion loss and common-mode noise suppression

In this paper, a multi-mode square ring loaded resonator (SRLR) comprising a full-wavelength ring resonator and six open stubs is introduced. The resonant characteristics are discussed and analyzed using differential-mode (DM) and common-mode (CM) equivalent circuits. Compared to the conventional design, the proposed SRLR involves two advantageous modifications for high-order balanced structure. First, two pairs of open stubs on the four corners of the ring resonator provide more flexible control of the internal coupling between two SRLR units under DM excitation. In addition, the shorted H-shaped resonator is compact, which makes proposed structure suitable for high-order filter design with desired operating frequency and bandwidth. Second, one pair of open stubs is added to the ring resonator along the horizontally symmetric plane. We found that the proposed SRLR provides more design freedom for CM noise suppression without extra components or defected ground structure. In addition, the proposed SRLR topology structure is folded to avoid large circuit occupation. Based on our analyses, a fourth-order balanced dual-band bandpass filter was designed with two passbands operating at 2.2 GHz and 3.5 GHz with corresponding in-band insertion loss of 0.1 dB and 0.12 dB, respectively. The filter was fabricated using high-temperature superconductor (HTS) YBCO thin films on an MgO substrate. Good agreement between simulated and measured frequency responses was observed, which verifies the proposed structure and design method.

Correction to: Displacement and frequency response measurements of a ship using GPS and fibre optic-based sensors

Correction to: Displacement and frequency response measurements of a ship using GPS and fibre optic-based sensors

Displacement and frequency response measurements of a ship using GPS and fibre optic-based sensors

GPS and more recently multi-GNSS carrier phase measurements have been used to measure the dynamic displacements of large structures, such as long-span bridges, in both the time and frequency domains. Such measurements can be used as part of a structural health monitoring system. Additionally, fibre optic-based systems have been used to measure long-term deformations of structures, such as tunnels and roads. The research presented in this paper brings together the ideas and technologies in the two aforementioned areas of research, resulting in dynamic displacement measurements of the hull of a ship at high frequencies, and indoor environments. Field trials using kinematic GPS and FBG sensors on the 138-m long Smyril passenger and vehicle ferry operating in the North Atlantic Ocean on the Faroe Islands are presented. FBG sensors were in the bow and engine room of the ship, gathering data at 1 kHz. The configuration of the surveys and the results from the FBG and GPS sensors are presented, in both the time and frequency domains. Various frequencies were measured, due to the movements of the ship in the ocean as well as the vibrations caused through the ship mainly due to the engine. One dominant frequency was of 12.25 Hz, measured at all the FBG locations, due to the engines’ operating speed of 735 RPM. Common frequencies were evident for both the FBG and GPS results for lower frequency displacement, caused by the movements in the sea. Such measurements could be used to monitor the long-term displacement characteristics and changes, in both the time and frequency domains, and used to help understand the health characteristics of the ship. Further, such measurements could be used to analyse the noise characteristics of the ship for both operational and environmental reasons.

Designing Power Module Health Monitoring Systems Based on Converter Load Profile

This article presents a method for designing converter systems embedding power modules for a specified degradation monitoring performance in real-time applications. It builds upon prior work which identified specific variations in three-dimensional transient heat transfer with interface and interconnect state-of-health. This article contributes a joint, module-converter concurrent design method to quantify opportunities and limits in using chip-based temperature sensing to integrate electrothermal impedance spectroscopy in situ . Challenges intrinsic to modules, such as many, closely packed heat sources, are quantified. This article also examines spatial degrees-of-freedom for placing additional degradation sensing temperature detectors. Experimental measurements of transient thermal frequency response show trends that can be exploited to push temperature sensors against their signal-to-noise ratio limits. Overall, the design method relies on circuit topology and modulation details; it is directed toward early-stage converter development. To that end, an included harmonic loss modeling step immediately provides a designer with feedback about the feasibility of a degradation sensing concept.

FRA lookup charts for the quantitative determination of winding axial displacement fault in power transformers

Frequency response analysis (FRA) has gained attention as a reliable diagnostic tool, to assess the mechanical integrity of power transformers, due to standardised FRA measurement methods. However, the assessment of FRA results is still a challenge as it demands skilful personnel for diagnosis. Since there is no definitive and reliable code available for FRA interpretation. In this study, the three-dimensional (3D) finite integration technique is used to simulate the physical geometrical dimensions of a three-phase transformer which emulate the behaviour of real transformer and frequency response measurements. This novel method eliminates the need for lumped parameter circuit models, as it provides the ability to extract the FRA signatures directly from the 3D winding model. Axial displacement of different levels is simulated in several connection schemes. It was found that variation of the inter-winding capacitance due to the axial displacement possesses a linear relationship with the degree of axial displacement fault. This provides the possibility for the quantitative determination of winding axial displacement fault using FRA. A simple mathematical relation is derived for calculating the variation of inter-winding capacitance and a geometrical factor is introduced to generalise the method. Finally, lookup charts are introduced to diagnose axial displacement fault in different transformers.