Energy Density Sensor Research Articles

Electromagnetic energy harvesting and density sensor application based on perfect metamaterial absorber

The proposed study presents an electromagnetic (EM) energy harvesting and density sensor application based on a perfect metamaterial absorber (MA) in microwave frequency regime. In order to verify the absorption behavior of the structure, its absorption behavior is experimentally tested along with the energy harvesting and sensing abilities. The absorption value is experimentally found 0.9 at the resonance frequency of 4.75 GHz. In order to harvest the EM energy, chips resistors are used. In addition, the suggested model is analyzed for its dependency on polarization angles. The results show that the perfect MA can be easily and efficiently used for EM energy harvesting applications. Moreover, as an additional feature of the model, we also realized a density sensor application. It can be seen that this structure can be used as a multi-functional device and configured for many other sensing applications.

Determination of bone density distribution in proximal femur by using the 3D orthotropic bone adaptation model

Most of the models developed and presented in the literature about bone remodelling assume bone as isotropic material. During this study, a structural model which has orthotropic bone properties is developed to simulate bone behaviour under mechanical loads. For a three-dimensional finite element modelling of proximal femoral bone, a computer code was written to investigate bone property changes owing to mechanical loads. The bone density distribution was determined after stress analysis was carried out in an iterative method. At every time step the bone properties were calculated depending on density change. Additionally, the effects of the bone remodelling parameters and sensors on numerical results were investigated. The most realistic bone density distribution in the proximal femur is obtained with strain energy density sensor. Generally initial bone density values do not have any effect on density distribution but at the low iteration numbers they may have some effects. Lastly, the density distribution of proximal femoral bone is more realistic for the dead zone size less than 0.35 and the stimulus value less than 2500.

Active noise control in a pure tone diffuse sound field using virtual sensing

Local active noise control systems generate a zone of quiet at the physical error sensor using one or more secondary sources to cancel acoustic pressure and its spatial derivatives at the sensor location. The resulting zone of quiet is generally limited in size and as such, placement of the error sensor at the location of desired attenuation is required, which is often inconvenient. Virtual acoustic sensors overcome this by projecting the zone of quiet away from the physical sensor to a remote location. The work described here investigates the effectiveness of using virtual sensors in a pure tone diffuse sound field. Stochastically optimal virtual microphones and virtual energy density sensors are developed for use in diffuse sound fields. Analytical expressions for the controlled sound field generated with a number of control strategies are presented. These expressions allow the optimal control performance to be predicted. Results of numerical simulations and experimental measurements made in a reverberation chamber are also presented and compared.

Free field reconstruction using energy density measurements

Forward wave propagation to the farfield using nearfield pressure measurements has undergone extensive development. Up until now, discrete pressure measurements are typically made using a conformal array of microphones. However, complex acoustic fields require large microphone arrays in order to accomplish accurate field reconstruction. The use of energy density sensors has indicated several advantages over conventional pressure microphones in active noise control applications. This study examines possible benefits of energy-based measurements in free field reconstruction. To determine and quantify the possible advantages of energy density measurements, an analytical model was built to evaluate the performance. The error in acoustic fields reconstructed using energy density sensors is compared with conventional pressure microphone reconstruction accuracy. A number of analytical studies will be presented showing the benefits of using energy-based measurements in free field reconstruction.

Energy density and intensity measurements in a reverberant sound field

The measurement of reverberant fields using an acoustic energy density sensor has been investigated over the years but has not seen general use. The energy density sensor can also measure acoustic intensity, which is a more commonly used technique in noise control. Measuring three-dimensional acoustic intensity with the energy density sensor shows that the techniques of energy density are complementary to intensity measurement and worthy of broader use Statistical measurements of kinetic and potential energy density were taken using a rotating boom in a reverberation room. Vector intensity was simultaneously measured in three orthogonal directions along with the total intensity. The measurements show that while the vector intensity components were significant, their sum was zero within the limits of the measurement system.

Active Control of Enclosed Sound Fields Using Three-axis Energy Density Sensors: Rigid Walled Enclosures

Active Control of Enclosed Sound Fields Using Three-axis Energy Density Sensors: Rigid Walled Enclosures

Active minimization of acoustic energy density in enclosed sound fields

Minimization of acoustic energy density has been investigated for active noise control applications for enclosed sound fields. The standard approach of minimizing the squared acoustic pressure has been shown to often lead to localized control of the sound field, which may be undesirable. It has been shown that minimizing the energy density often leads to improved global attenuation of the field, since quantities dependent on both the pressure and particle velocity are minimized. This penalizes active control solutions in which the pressure is minimized and the particle velocity is increased, as often occurs when simply minimizing the squared pressure. Minimizing the acoustic energy density also requires multiple microphones to be integrated as part of the error sensor. However, in many cases the number of microphones can be reduced by strategically placing the sensor in a location where one component of the particle velocity is assumed to be negligible. Active control results will be shown for an enclosed sound field to compare the reduction obtained using energy density with that obtained for minimizing squared pressure. In addition, the attenuation obtained using a full three-dimensional energy density sensor will be compared with the control achieved using an error sensor with fewer microphones.

Active noise control in a free field with virtual sensors.

The zone of local control around a "virtual energy density sensor" is compared with that offered by an actual energy density sensor, a single microphone, and a virtual microphone. Intended as an introduction to the concept of forward difference prediction and a precursor to evaluating the virtual sensor control algorithms in damped enclosures, this paper investigates an idealized scenario of a single primary sound source in a free-field environment. An analytical model is used to predict the performance of the virtual error sensors and compare their control performance with their physical counterparts. The model is then experimentally validated. The model shows that in general the virtual energy density sensor outperforms the actual energy density sensor, the actual microphone, and the virtual microphone in terms of centering a practically sized zone of local control around an observer who is remotely located from any physical sensors. However, in practice, the virtual sensor algorithms are shown to be sensitive (by varying degrees) to short wavelength spatial pressure variations of the primary and secondary sound fields.

ERRORS ARISING FROM THREE-DIMENSIONAL ENERGY DENSITY SENSING IN ONE-DIMENSIONAL SOUND FIELDS

The performance of four different configurations of three-dimensional acoustic energy density sensors are evaluated for two idealized one-dimensional sound field: a reactive single mode and a propagating plane wave. The 4 configurations of sensors are; two types of 4-microphone arrangements, a 6-microphone arrangement and a 7-microphone arrangement. Like the companion paper for one-dimensional sensors by the same authors this paper investigates the bias errors arising from four error types: inherent, phase mismatch, sensitivity mismatch and spatial errors. It is shown that for plane wave conditions a 4-microphone arrangement is more accurate than the “standard” 6-microphone arrangement.

Error analysis of a practical energy density sensor

The investigation of an active control system based on acoustic energy density has led to the analysis and development of an inexpensive three-axes energy density sensor. The energy density sensor comprises six electret microphones mounted on the surface of a 0.025-m (1 in.) radius sphere. The bias errors for the potential, kinetic, and total energy density as well as the magnitude of intensity of a spherical sensor are compared to a sensor comprising six microphones suspended in space. Analytical, computer-modeled, and experimental data are presented for both sensor configurations in the case of traveling and standing wave fields, for an arbitrary incidence angle. It is shown that the energy density measurement is the most nearly accurate measurement of the four for the conditions presented. Experimentally, it is found that the spherical energy density sensor is within +/- 1.75 dB compared to reference measurements in the 110-400 Hz frequency range in a reverberant enclosure. The diffraction effects from the hard sphere enable the sensor to be made more compact by a factor of 3 compared to the sensor with suspended microphones.

A proposal to adopt Maxwell distribution as a measure of acoustic field diffuseness in a reverberation room

The existence of an acoustic velocity vector resultant field which follows Maxwell distribution in a reverberation room indicates 3-D diffuseness of the field. Therefore, Maxwell distribution is a better measure for the sound-field diffuseness than Gaussian distribution given by the acoustic pressure in the same room that does not have a directional information. A Gaussian distributed pressure field does not always give a satisfactory diffuseness. The acoustic velocity vector resultant was measured using total energy density sensor. Theoretical and experimental investigations are given to support this proposal.

Narrow-band and broadband active control in an enclosure using energy density sensors

An active control system has been constructed based on the minimization of the energy density at discrete points within an enclosure. Though most control systems for use in enclosures are based on squared pressure as a cost function, a system based on energy density is more capable of sensing modes contributing to the acoustic field. The enclosure used is lightly damped and measures 1.5×2.4×1.9 m. A measurement system within the enclosure is capable of spatially sampling the pressure field and decomposing the field into complex modal amplitudes, which yield insight into the control phenomena. The control system can use squared pressure as well as energy density as a cost function for comparisons of the two methods. The squared pressure and energy density control are consistent with predictions of active control performance in the case of single-frequency multiple sensor/source configurations. Global control of up to 18 dB is achieved. Broadband control results using a single sensor and control source are also presented.

Acoustic velocity related distributions

The acoustic velocity x, y, z components and its resultant amplitudes, the kinetic and total energy density distributions in a reverberation space, were measured using an energy density sensor consisting of four microphones. The space is a 225-m3 with average reverberation time of 6 s at 1 kHz. The room was excited with pure-tone, narrow- or wide-band noise. The result of the measurements showed that the acoustic velocity x, y, z component amplitudes were Gaussian-distributed, its resultant amplitude was Maxwell-distributed. The kinetic and total energy densities were gamma-distributed with three and four degrees of freedom, respectively. In agreement with published literature, the measurement also showed that acoustic pressure was Gaussian and the potential energy density was exponentially distributed, however, the other distributions have not been reported. Theoretical background and measured data will be presented.

One-dimensional sound field control by sound pressure and energy-density sensor

The use of an energy density error quantity for adaptive filtered-x active noise control has been demonstrated to provide advantages over pressure squared control in a one-dimensional experiment [S. D. Sommerfeldt and P. J. Nashif, ‘‘An Adaptive Filtered-X Algorithm for Energy-Based Active Control,’’ J. Acoust. Soc. Am. 96, 300–306 (1994)]. The performance of energy-density-based control was further explored in comparison to pressure-squared control. By using two small microphones, the pressure and energy-density sensor was moved through regions of the upstream and downstream of the secondary source in a one-dimensional low-frequency harmonic sound field. Extensive data were collected for various sensor locations to demonstrate that the pressure-based control strongly depends on sensor location, while the energy-density-based control is more sensor location-independent.

Glass solid electrolytes: Past, present and near future — the year 2004

Glasses have been known to be solid electrolytes as early as 1884 and have been used over the years in a variety of thermochemical probes. Recent advances in the development of fast ion conducting glasses has opened up many new potential applications including high energy density batteries, electrochromic displays and sensors. We review the additional constraints of chemical and electrolytic stability imposed on glasses considered in these applications and present some novel electrochemical approaches for characterizing stability. Future applications for glass solid electrolytes are considered as well as novel means for forming them.