Array Optimization Techniques Research Articles

Novel Method to Improve the Uniformity of 7T Body MR Images

When using ultrahigh-field MR systems (7T), the variations in the RF magnetic field can lead to significant loss in image uniformity. To optimize the overall MR image quality, the image region is divided into multiple smaller regions of interest (the ROIs), which can be independently optimized using transmit array optimization techniques including RF shimming, to improve RF magnetic fields and image intensity. Electromagnetic numerical simulations and corresponding transverse magnetization (|Mt|) acquired using the Bloch equation-based MRI simulator are used to evaluate the proposed method. Compared to the simulation results of quadrature driving method, mean and standard deviation (SD) of |Mt| in the full image (an inner diameter of 500 mm) were improved 47% (mean) and 48% (SD), whereas 94% (max) and 97% (mean) improved in the unaveraged SAR using the proposed method. The uniformity of |Mt| acquired using the method was especially improved in the peripheral region of the selected phantom image compared to that of other methods. The proposed method using multiple independently optimized ROIs and numerical simulations significantly improved the uniformity of |Mt| body images at 7T. This technique would be generally applicable to any high-field strength MR systems, which generate short RF wavelengths compared to the field of view.

E-Nose Sensor Array Optimization Based on Volatile Compound Concentration Data

Currently, most e-nose studies are for lab-based applications, the e-nose does not provide access from other places. To be able to implement the internet of things (IoT) technology that is gaining momentum, the e-nose device must be efficient. This study proposes a sensor array optimization technique. If in previous studies using electrical signal data, our study used volatile organic compounds concentration data to minimize the use of sensors. From 10 initial sensors used in the e-nose prototype, only 4 sensors remained. The experimental results showed that by using the KNN algorithm, these 4 sensors were able to predict banana samples with an 80% accuracy rate. When applied to the final e-nose product, the prediction accuracy was 78%.

Sensor array optimization techniques for exhaled breath analysis to discriminate diabetics using an electronic nose

Sensor array optimization techniques for exhaled breath analysis to discriminate diabetics using an electronic nose

Optimizing the alkaline oxidation pretreatment of a refractory gold ore using taguchi orthogonal array method

This study investigates the alkaline oxidation pretreatment process of Zarshuran refractory gold ore. Taguchi method-orthogonal array design (OAD) is applied to evaluate and optimize the influence of five main factors including solution pH, aeration rate, agitation speed, temperature, and oxidation time. In order to establish relationship between the gold dissolution rate and influential factors, a linear regression model with R2 of 0.9706 is fitted to experimental data. The results indicated that in the range studied, the agitation speed does not have any significant impact on the gold recovery, while oxidation time and temperature were the most significant factors. Au recovery increased with increasing the aeration rate, pretreatment time, and temperature as well as decreasing the solution pH. Using Taguchi orthogonal array optimization technique (OAOT), the maximum gold recovery was about 96.72%. Also, the optimal conditions were 11 for solution pH, 150 ml min−1 for aeration rate, 240 rpm for agitation rate, 50 °C for temperature, and 24 h for oxidation time.

Optimizing Arrays of Randomly Placed Wireless Transmitters for Receivers Located Within the Array Volume

We investigate the potential of using arbitrarily placed wireless transceivers to increase the probability of maintaining a communication link in an electrically harsh environment. Specifically, we adapt a well-known matrix-based array optimization technique to the case when the transmitting elements exist in a complex environment and the receiver is not in the far-field of the array. Study of array performance in a non-ideal setting represents an important step in determining the feasibility of using this optimization technique for ad hoc wireless arrays within a building. Measures of array performance consist of median values for the directivity or gain, the total power at the receiver location, and the power per transmitter. The simulation results include array performance in the presence of a lossy dielectric corner to study the effects of building floors and walls. Our results show the median of the optimized directivity or gain for the frequencies of interest with simple boundaries is within 3 dB of that for the optimized configuration in free space

Application of near-field optimum microphone arrays to hands-free mobile telephony

This paper discusses the application of fixed microphone arrays to speech pickup in mobile telephone applications. Array optimization techniques are used to design two broad-band beamformers for speech pickup in the near field. The first beamformer provides optimum gain for spatially incoherent noise while the second beamformer provides optimum gain in spherically isotropic noise. Array performance was measured using vehicular noise recorded under realistic driving conditions. Results obtained are in agreement with theoretical predictions for a spherically isotropic noise field and are comparable to previously reported results obtained using adaptive beamforming algorithms.

Application of near-field optimum microphone arrays to hands-free mobile telephony

This paper discusses the application of fixed microphone arrays to speech pickup in mobile telephone applications. Array optimization techniques are used to design two broad-band beamformers for speech pickup in the near field. The first beamformer provides optimum gain for spatially incoherent noise while the second beamformer provides optimum gain in spherically isotropic noise. Array performance was measured using vehicular noise recorded under realistic driving conditions. Results obtained are in agreement with theoretical predictions for a spherically isotropic noise field and are comparable to previously reported results obtained using adaptive beamforming algorithms.

Array optimization applied in the near field of a microphone array

This paper describes the application of array optimization techniques in the near-field of a microphone array. It is shown that the optimum weights obtained for microphone spacing equal to a half wavelength are real, aside from the propagation delay, and inversely proportional to the distance from each microphone to the focal point. When the microphone spacing is less than a half wavelength, the optimum weights are super-directive requiring both an amplitude and phase adjustment in addition to delay-and-sum beamforming. In the super directive regime, the maximum array gain increases as the distance to the focal points decreases. The technique is suitable for applications where the source of interest is located in the near-field region but interfering sources are located farther from the array.

Comparisons of Streit's array optimization technique with other methods

A general array optimization technique developed by Streit [“Optimization of Discrete Arrays of Arbitrary Geometry,” J. Acoust. Soc. Am. (to be published)] is reviewed briefly. Several examples which have been studied in the literature by a variety of other methods are re-examined using this new and more general technique. In each of these examples, the earlier results are shown to be nearly optimum in the sense defined by Streit. Therefore, this new optimization technique not only yields results comparable to earlier methods, but is applicable in many situations where earlier methods do not apply. Arrays with nearly 500 directional elements have been successfully treated using this technique.

Optimization of gain of a conformal array for torpedo sonar

A conformal array designed for torpedo sonar has been analytically investigated using several array optimization techniques. In particular, the complex as well as the real weights which maximize the (receive) gain of this array have been computed. The incident signal is assumed to be a narrowband, plane wave; however, the noise field is assumed to be torpedo flow noise radiated within the near field of the array. A theoretical model of the covariance matrix of this noise field has been determined. A comparison is made with the (similarly optimized) planar arrays conventionally used in torpedo sonars. The results indicate that a more comprehensive criterion than array gain is required for the torpedo sonar application. Several alternative criterion are discussed.