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Transducers and beam forming
Published in Peter R Hoskins, Kevin Martin, Abigail Thrush, Diagnostic Ultrasound, 2019
Tony Whittingham, Kevin Martin
As mentioned when discussing the piezoelectric plate, one of the limitations of the ceramic piezoelectric material PZT is that during polarization, the granular structure limits the alignment of piezoelectric domains that can be achieved and hence the piezoelectric efficiency of the device (Figure 3.9a). Transducers are now commercially available which use alternative piezoelectric materials, grown as single crystals (Chen et al. 2006; Zhou et al. 2014). These include lead titanate (PT) doped with various other elements, such as lead, magnesium and niobium (PMN–PT) or lead, zinc and niobium (PZN–PT). The single crystal is produced by melting the constituent materials and drawing out a seed crystal very slowly under careful temperature control. The resultant crystal does not have any grain structure, so that when it is sliced into multiple wafers, these can be poled to have almost uniform polarization, i.e. all the electric dipoles in line with the poling electric field (Figure 3.9b). These single-crystal wafers are much more efficient at converting the electrical energy supplied to the transducer into mechanical energy of vibration, and have a much larger response in terms of thickness change for a given applied voltage. They also lead to transducers with wider bandwidths since their greater efficiency means that they retain less unconverted energy and therefore ring for less time. This greater bandwidth improves axial resolution as well as being necessary for multi-frequency operation and harmonic imaging (see Chapter 4).
Preliminaries and Review
Published in Brijesh Iyer, Nagendra Prasad Pathak, Multiband Non-Invasive Microwave Sensor, 2018
Brijesh Iyer, Nagendra Prasad Pathak
The performance of the existing single-band NIVSD sensors can be improved by using multiband operation. A higher frequency allows signal detection even with very minute variations, but at the cost of increased noise whereas lower frequencies minimize noise but with decreased detection sensitivity. Multiband systems can reap the advantage of increased detection sensitivity with lower noise interference. A multiband architecture can be achieved by parallel, switchable, or concurrent arrangement of transceiver building blocks. The use of parallel system architecture for concurrent operation at individual frequency bands is less attractive due to the requirements for high power consumption, large hardware, and its bulky nature. Detection from either side of the human body by two separate transceivers is unappealing due to its hardware requirements [55]. A switched mode multiband system has the drawback of inconsistent measurement conditions for the same human subject due to switching delay [58]. Further, multifrequency interferometric radar is used for this purpose where selection of frequency is incorporated by means of an RF switch. Similar methodologies were proposed by Fletcher and Han and Oum et al. for random body moment cancellation so as to achieve fair detection of the required signals [59,60].
Reverse time migration for inverse obstacle scattering with a generalized impedance boundary condition
Published in Applicable Analysis, 2022
The purpose of this example is to consider the dependence of the RTM algorithm on the wave number κ. The obstacle of this example is a kite which is described by And the coefficients are given by In this example, we consider two cases. For the first case, we consider the RTM algorithm employing single-frequency data where we set . The numerical results from noisy data are demonstrated in the right column of Figure 3. It is easily seen that the imaging quality can be improved with the increase of the wave number. For the second case, we consider the performance of the RTM algorithm with multi-frequency data. To this end, we write for to show the dependence of on the wave number κ. For multi-frequency case , one can define the new functional as the sum of , more precisely, and plot the mapping against z. We illustrate the recover results from noisy in the left column of Figure 3 when , and . We observe from these figures that employing multi-frequency data can greatly improved the imaging results.
Design of a dual-band filter with high selectivity and wide stopband
Published in Electromagnetics, 2023
Li-Qin Liu, Min-Hang Weng, Wen-Yen Hsu, Huang-Sheng Lai, Ru-Yuan Yang
With the development of communication technology, multi-frequency transceiver technology is more and more favored. Therefore, a filter is desirable to work in multiple frequency bands at the same time, which can effectively reduce the size and cost, and realize the miniaturization and low cost of the microwave system (Hong and Lancaster 2001). In recent years, the design of dual-band bandpass filter (BPF) has attracted the attention of many researchers, and many design methods have been reported. Generally, dual-band BPFs are designed by multi-mode resonators, such as step-impedance resonator (SIR) (Kuo, Yeh, and Yeh 2005; Shi et al. 2018) or stub-loaded resonator (SLR) (Mondal and Mandal 2008; Sheng and Zhu 2005; Zhang et al. 2007). In order to meet the wide stopband requirements, the design of dual-band BPFs with a wide stopband has also been popular. In past, a dual-band BPF with high selectivity and wide stopband was designed by using a spiral SIR loaded with stubs (Liu, Li, and Ren 2013). In another, symmetrical stubs loaded open-circuited resonator was used to a dual-band BPF with wide stopband by adjusting the electrical length ratio and impedance ratio (Singh, Killamsetty, and Mukherjee 2016). In order to achieve a wide stop band, a defective ground structure (DGS) was added to the dual-band BPF (Challal, Hocine, and Mermoul 2019; Shi, Zhao, and Zhang 2020; Xie, Chen, and Li 2017). But the DGS structure would make the component incomplete. Recently, a dual-band BPF with simultaneous narrow- and wide-bandwidth and a wide stopband was designed by using the stepped-impedance ring loaded resonator (SIRLR), and a bandstop filter was loaded at the input and output ends to suppress the upper sideband and achieve a wide stopband (Weng et al. 2019). Moreover, stub-loaded square ring resonator (SLSRR) was reported to achieve dual-wide band responses (Zhang et al. 2020).
Asymmetrical mirror imaged monopole antenna with modified ground structure for DBDP radiations
Published in International Journal of Electronics, 2020
Yatendra Kumar, Ravi Kumar Gangwar, Binod Kumar Kanaujia
With the rapid growth in wireless communication technology, there are never-ending demands for such devices that can be operated at multi frequency bands simultaneously. The progress of such antennas has been acknowledged extensive consideration from several communication systems. For such antennas, the design challenges have been raised by the further requirements such as specific polarisation characteristic at different frequency bands and low profile with less fabrication cost. An antenna with dual polarisation is advantageous for base stations in mobile communication systems. Since polarisation diversity is common method to address the issue of multipath fading. Dual polarised (DP) microstrip antennas are very much capable of both types of radiation characteristics i.e. linear as well as circular polarisations (CPs). Nowadays, multi-band linear (LP) and CP features adapted in a single antenna have turn out to be popular (Bao & Ammann, 2011; Falade, Gao, & Chen et al., 2013; Mathew et al., 2015). In Falade et al., (2013), a stacked triple-band patch antenna having linear and CP characteristics was proposed. A broadband dual-band dual-polarised printed dipole-like antenna was presented in (Bao & Ammann, 2011). A sectorial patch antenna with truncated corner was employed to produce triple-band and dual-polarised features (Mathew et al., 2015). However, most of the above-cited antennas feature broadside radiation characteristics. Such antennas are potentially useful for handheld devices which are very much needed in terrestrial and satellite communication network systems. In addition to this, multi-band microstrip antennas have given enormous consideration for the cause of the distinctive progress in the area of wireless communication and satellite navigation systems (Chang & Lin, 2014; Kaboli, Abrishamian, & Mirtaheri, 2012; Liang, Jiao, & Luan, 2015; Mak, Gao, & Lai, 2014). Most of the dual band antennas can be extended as dual polarised antennas by modifying their structure in such a way to excite two orthogonal resonant modes with quad feed, dual feed points or single feed points (Maci & BifJi Gentili, 1997). The multi--band operation can be achieved either with multi-resonator patches (Ferrero, Luxey, & Jacquemod, 2005) or antenna structure loaded with reactive lumped or distributed elements (Richards, Davidson, & Long, 1985). In past two decades, several studies have been reported for dual band dual polarised (DBDP) microstrip antennas. These DBDP antenna structures with dual orthogonal ports were implemented with intention of reducing equipment and installation cost. A combination of quad port dual polarised antenna was analysed (Chiou & Wong, 2003; Sharma, Kulshrestha, & Chakrabarty, 2013). In this design, a bigger size antenna patch is realised with two orthogonal ports for lower frequency band; while a smaller antenna consisting another pair of orthogonal ports for higher frequency band. In the above antenna design, four ports are the major concern. In order to overcome the problem of a number of ports, some sizeable antenna designs having dual feeding port for dual band operation have been proposed (Lai & Chen, 2007; Li, Yang, & Li, 2014).