High-permittivity Ceramics Research Articles

High-permittivity ceramics enabled highly homogeneous zero-index metamaterials for high-directivity antennas and beyond

Zero-index metamaterials (ZIMs) can support uniform electromagnetic field distributions at any frequency, but their applications are hampered by the ZIM’s homogenization level—only 3 unit cells per free-space wavelength, which is fundamentally limited by the low-permittivity inclusions (εr ≈ 12) and background matrix (εr ≈ 1). Here, by filling high-permittivity SrTiO3 ceramic (εr ≈ 294) pillars in BaTiO3 (εr ≈ 25) background matrix, we demonstrate a highly homogeneous microwave ZIM with an over threefold increase in the homogenization level. Leveraging such a ZIM, we achieve not only an antenna, approaching the fundamental limit in the directivity with outstanding scalability, but also a concave lens with a focal length of as short as 1λ0. Our highly homogeneous ZIM has profound implications in ceramics, ZIM-based waveguides and cavities, free-space wavefront manipulation, and microwave quantum optics, and opens up enormous possibilities in wireless communications, remote sensing, global positioning satellites, etc.

All-dielectric polarization conversion metasurface achieved by high-permittivity ceramics

In this letter, we propose the design and manufacture of an all-dielectric metasurface using high-permittivity ceramics. The unit structure consists of a rectangular ceramic, which is asymmetric in the x and y direction. Electric and magnetic resonances are generated to form cross-polarization reflection. As an example, cross-polarization reflection is demonstrated both numerically and experimentally. This work not only gives the designing method but also discusses how to manufacture a large sample and the difference between ideal simulation and the practical sample. After a large number of simulations and experiments, the feasible design methods and problems needing attention in design are given. The experiment result is according to the adjusted simulated result. The result confirms the feasibility of the design and processing of an all-dielectric metasurface in the microwave band. If we can find a suitable material preparation process or optimize the unit structure that is easy to process, the all-dielectric polarization conversion metasurface can realize a maximum conversion efficiency of nearly 100% and form a broadband working band. Since such metasurfaces are made of low-loss high-permittivity ceramics, they are of important value especially in high temperature or high-power applications. This method can also be used to design all-dielectric metasurfaces in other frequencies by changing the geometry parameters.

Improving detection of fMRI activation at 1.5 T using high permittivity ceramics

In this work, we propose an application of high permittivity materials (HPMs) to improve functional magnetic resonance imaging (fMRI) at 1.5 T, increasing the receive (Rx) sensitivity of a commercial multi-channel head coil. To evaluate the transmit efficiency, specific absorption rate (SAR), and the signal-to-noise ratio (SNR) changes introduced by the HPMs with relative permittivity of 4500, we considered the following configurations in simulation: a whole-body birdcage coil and an Rx-only multi-channel head coil with and without the HPM blocks in the presence of a homogeneous head phantom or a human body model. Experimental studies were also performed with a phantom and with volunteers. Seven healthy volunteers enrolled in a prospective study of fMRI activation in the motor cortex with and without HPMs. fMRI data were analyzed using group-level paired T-tests between acquisitions with and without HPM blocks. Both electromagnetic simulations and experimental measurements showed ∼25% improvement in the Rx sensitivity of a commercial head coil in the areas of interest when HPM blocks were placed in close proximity. It increased the detected motor cortex fMRI activation volume by an average of 56%, thus resulting in more sensitive functional imaging at 1.5 T.

High dielectric permittivity and ultralow dielectric loss in Nb-doped SrTiO3 ceramics

In this study, we prepared a series of Nb-doped SrTiO3 ceramics sintered in both air and N2 atmospheres. The X-ray diffraction (XRD) analysis indicated that all samples had a pure cubic phase perovskite structure with no secondary phase. The dielectric test showed that the Nb-doped SrTiO3 ceramics had a high dielectric permittivity (>3 × 104) and low dielectric loss (<0.004) over a broad temperature range from −100 to 300 °C with a breakdown strength over 20 kV/cm. The dielectric performance is attributed to the designated TiTi′−VO··−TiTi′ deep-lattice-defect states localising weak-hopping electrons to generate high defect-dipole concentrations, as verified by systematic X-ray photoelectron spectroscopy (XPS) experiments. This study offers a route for designing other types of high dielectric permittivity ceramics.

Circular Polarization Antenna-Filter

A two-function filtering antenna device in the 1-2 GHz band is investigated. The device radiates or receives electromagnetic waves of circular polarization and simultaneously performs the function of a second-order bandpass filter. The considered design consists of a dual-mode printed antenna-resonator coupled with two non-radiating resonators which are fed by a quadrature balanced power divider. Using the model in the form of an equivalent circuit the main features of the structure synthesis and its tuning are analyzed including potentially achievable characteristics. The results of the numerical simulations using electromagnetic software are presented in comparison with the experimental characteristics for the prototype made of high-permittivity high-quality ceramics. It is found that the proposed design is characterized by an almost two-fold increase of the operating frequency band compared to the resonant antenna itself while maintaining a low level of cross-polarization within the passband. It is also shown that the design has the frequency response of the second-order bandpass filter.

EWideband transmission enhancement of electromagnetic waves through high-permittivity ceramics via magnetic metamaterial films

To achieve wideband high-efficiency transmission of EM waves through high-permittivity ceramics (HPC), we propose to improve the impedance matching on the interface using magnetic metamaterial antireflection (AR) film. To facilitate practical applications, the magnetic metamaterial is integrated within the supporting dielectric substrate, which enables strong magnetic responses under normal incidence. The AR film is attached onto the interior wall of a HPC plate. Due to strong magnetic resonance of the metamaterial, the effective permeability on the interface is increased to match the high permittivity of the ceramic plate, leading to near-unity relative impedance in a wide band. In this way, the reflection is reduced and hence the transmission is enhanced. We demonstrated a prototype for enhancing the transmission of a 3mm-thick alumina plate at X band. Both the simulated and measured results verify our design. This work provides a new route to the design of AR structures for HPC radomes.

High permittivity ceramics improve the transmit field and receive efficiency of a commercial extremity coil at 1.5 Tesla.

The purpose of this work is to investigate the use of ceramic materials (based on BaTiO3 with ZrO2 and CeO2-additives) with very high relative permittivity (εr ∼ 4500) to increase the local transmit field and signal-to-noise ratio (SNR) for commercial extremity coils on a clinical 1.5 T MRI system. Electromagnetic simulations of transmit efficiency and specific absorption rate (SAR) were performed using four ferroelectric ceramic blocks placed around a cylindrical phantom, as well as placing these ceramics around the wrist of a human body model. Results were compared with experimental scans using the transmit body coil of the 1.5 T MRI system and an eight-element extremity receive array designed for the wrist. SNR measurements were also performed for both phantom and in vivo scans. Electromagnetic simulations and phantom/in vivo experiments showed an increased in the local transmit efficiency from the body coil of ∼20-30%, resulting in an ∼50% lower transmit power level and a significant reduction in local and global SAR throughout the body. For in vivo wrist experiments, the SNR of a commercial eight-channel receive array, integrated over the entire volume, was improved by ∼45% with the ceramic. The local transmit efficiency as well as the SNR can be increased for 1.5 T extremity MRI with commercial array coils by using materials with very high permittivity.

High permittivity ceramics loaded silicone elastomer composites for flexible electronics applications

The dielectric properties of silicone elastomer composites are important in designing flexible electronic devices. The recent explosive growth in wireless communication, automotive and biomedical applications increases the demand for flexible dielectric materials. However, it is very difficult to identify a homogeneous material which possesses these desired properties. Flexible silicone rubber- ceramic composites based BaTiO3 (BT), SrTiO3 (ST) and Ca(1−x)Nd(2x/3)TiO3 (CNT) ceramic fillers have been prepared. The relative permittivity, thermal conductivity and water absorption increase whereas the coefficient of linear thermal expansion decrease as the volume fraction of filler increases. In the case of dielectric loss; a decreasing trend is shown by SR-ST and SR-CNT composites with filler volume fraction whereas SR-BT composites show a reverse trend since BT is a lossy material. The composites have εr in the range 3–14 in the microwave frequency range. The composites with high filler loading are suitable candidates for core of flexible dielectric waveguide and embedded capacitor applications and the composites with ST and CNT are suitable for cladding of flexible dielectric waveguide and also for microwave substrate applications

Temperature Tuning Mie Resonance-Based All-Dielectric Metamaterial

In this paper, a tunable all-dielectric left-handed metamaterial was studied by employing two types of high permittivity ceramics. The two kinds of ceramics were 0.8Ba0.45Sr0.55TiO3 + 0.2MgO (BST–MgO) and 0.65Ba0.6Sr0.4TiO3 + 0.35La (Mg0.5Ti0.5)O3 (BST–LMT), which were cut to cubes and rods to compose the metamaterial. In the X-band, the BST–LMT rods could provide a stable, wide negative permittivity band. On the other hand, the BST–MgO cubes produced tunable negative effective permeability based on Mie resonance theory. With this cubes/rods configuration, the transmission properties are tunable via different temperatures. Simulations and experiments show that the double-negative frequency range could move from 8.4 GHz to 10.2 GHz by changing temperature from 20°C to 80°C. The fabricated all-dielectric metamaterial can provide tunable operating frequencies in a large frequency range.

Reconfigurable all-dielectric metamaterial frequency selective surface based on high-permittivity ceramics.

Based on effective medium theory and dielectric resonator theory, we propose the design of reconfigurable all-dielectric metamaterial frequency selective surfaces (FSSs) using high-permittivity ceramics. The FSS is composed of ceramic resonators with different band stop responses under front and side incidences. By mechanically tuning the orientation of the ceramic resonators, reconfigurable electromagnetic (EM) responses between two adjacent stopbands can be achieved. The two broad stopbands originate from the first two resonant modes of the ceramic resonators. As an example, a reconfigurable FSS composed of cross-shaped ceramic resonators is demonstrated. Both numerical and experimental results show that the FSS can switch between two consecutive stopbands in 3.55–4.60 GHz and 4.54–4.94 GHz. The design method can be readily extended to the design of FSSs in other frequencies for high-power applications.

Achieving all-dielectric metamaterial band-pass frequency selective surface via high-permittivity ceramics

In this paper, we propose the design of all-dielectric metamaterial band-pass frequency selective surfaces (FSSs) using high-permittivity ceramics based on effective medium theory and dielectric resonator theory. The band-pass response can be determined by the permittivity of the dielectric material, the periodicity, and geometrical shape of the dielectric unit cell. As an example, a band-pass FSS composed of H shaped ceramic resonators is demonstrated. Both the simulation and experiment results show that the FSS can achieve a pass band in X-band. Since such FSSs are made of low-loss high-permittivity ceramics, they are of important application values, especially in high-temperature, high-power environments. The design method can be readily extended to the design of FSSs in other frequencies.

All-dielectric metamaterial frequency selective surfaces based on high-permittivity ceramic resonators

In this letter, we propose the design of all-dielectric metamaterial frequency selective surface (FSS) using high-permittivity ceramics. The FSS is composed of 2D arrays of rectangular ceramic resonators. By adjusting the geometrical parameters of the ceramic resonator, the first two resonant modes are merged to achieve broadband band-stop property. As an example, a nearly 1.5 GHz wide stop-band is demonstrated both numerically and experimentally in X band. Since such FSSs are made of low-loss high-permittivity ceramics, they are of important values especially in high-temperature or high-power applications. The method can also be used to design all-dielectric FSS in other frequencies by simply scaling the geometry parameters.

Miniaturized C-Band SIW Filters Using High-Permittivity Ceramic Substrates

This paper introduces an effective way to build efficient miniature C-band filters using high-permittivity ceramics. The objective was to evaluate the feasibility of such filters using commercial electromagnetic simulators and a conventional fabrication process. For the demonstration, the substrate integrated waveguide (SIW) technology was chosen. Compared with planar solutions, this configuration offers good quality factors and good electrical performances as a consequence. However, its dimensions are large, leading to unacceptably large footprints for many applications. The solution proposed in this paper is based on a ceramic substrate with a permittivity of 90, which allowed us to work with shorter wavelengths. In comparison with a standard alumina substrate (permittivity $\varepsilon _{r}= 9.9$ ), this approach makes it possible to reduce the footprint up to nine times. Two prototypes were realized on a Trans-Tech ceramic substrate ( ${\rm thickness}=635~\mu \text{m}$ , $\varepsilon _{r} = 90$ , and tan $\delta = 9\cdot 10^{-4})$ . The first prototype is a folded sixth-order SIW filter including a cross coupling combining coplanar waveguide probes and a thin microstrip line on an InterVia substrate. The second one is a folded eighth-order SIW filter without cross couplings. Here, we compare the sixth-order prototype with an identical one built on alumina. The eighth-order filter, which had no alumina counterpart, is a potentially useful alternative for situations where complex technological steps must be avoided.

Electrostatic Thermal Energy Harvester Using Unsteady Temperature Change

A model electrostatic thermal generator using unsteady temperature change is proposed. The device consists of a capacitor based on high-permittivity ceramics, and an electret layer serving as a permanent voltage source. Connecting them in series, permittivity change by temporal temperature change alters the amount of induced charges on the electrode thereby produces electric current in the external circuit. Optimum design parameters of the system have been obtained using a simplified circuit model. An early prototype using BaTiO3 ceramic as the dielectric and SiO2 as the electret is microfabricated, and its response is compared with the model prediction.

Dielectric Grain-Size Effect in High-Permittivity Ceramics

On the basis of existing experiments, the grain-size effect on the permittivity and dielectric function in the case of ferroelectric and relaxor ferroelectric dense single-phase ceramics is reviewed and critically discussed. Relevant data exist for BaTiO3 (BTO), SrTiO3 (STO), Pb(Zr,Ti)O3 (PZT), Pb(Mg1/3Nb2/3)O3 (PMN) and Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT). In the case of displacive ferroelectrics, the grain-size effect (decrease of the permittivity with decreasing grain size) can be attributed to a narrow low-permittivity grain-boundary layer (dead layer), whose effect can be modeled as a core-shell composite using an effective-medium approach. The strongest size effect was observed for STO, for which a model of two dead layers with a microscopic meaning was suggested. In the case of relaxor ferroelectrics it appears that rather thick layers near grain boundaries are influenced in such a way that the slow relaxation dispersion is there missing, which could be interpreted as pinning of the polar nano-regions by the grain boundaries, which prevents their flipping. In the ferroelectric phases, the grain-size effect is dominated by the domain structure (domain-wall contribution), which is processing and grain-size dependent and is present even in nano-grain ceramics.

Band-pass filters using high-permittivity ceramics substrate

The miniaturization of ring band-pass filters by employing high-permittivity ceramic substrates (with respective dielectric constants of 9.7 and 23.5) are investigated. Microwave dielectric ceramics with high-permittivity are commonly applied in several microwave communication components. With the advantages of compact size, high-permittivity ceramics can be used as the substrate for band-pass filters. Moreover, the fundamental characteristics of newly developed compact ring resonators have also been described and applied to the design of band-pass filters. In this article, the designed ring resonators structures are simulated using an HFSS simulator. The responses of the fabricated band-pass filters using Al2O3 (εr = 9.7, tanδ = 0.0001) and 0.875Mg0.95Zn0.05TiO3-0.125Ca0.8Sm0.4/3TiO3 (εr = 23.5, tanδ = 0.000083) ceramic substrates are designed at the center frequency of 2.4 GHz. This compact size, low loss band-pass filter should be useful in many wireless communication systems. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2344–2347, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25439

Doping and Atomic Site Substitution in the Dielectric Ceramics Ti(Al)O2 Rutile and (1−x)Ca2/5Sm2/5TiO3–xLi1/2Sm1/2TiO3 Perovskite

Temperature‐stable, high‐permittivity (high‐dielectric constant) ceramics are used as resonators for microwave telecommunications. Research and development in this area is aimed at increasing the dielectric constant (in order to reduce component size) while maintaining very high quality factor (low dielectric loss). This present work is a synchrotron X‐ray powder diffraction study of high quality factor, high permittivity ceramics of the Ti(Al)O2 and (1−x)Ca2/5Sm2/5TiO3–xLi1/2Sm1/2TiO3 families. The synchrotron powder diffraction was used to investigate doping of Al onto the Ti site in Ti(Al)O2. It was found that the lattice parameters in Ti(Al)O2 are not affected by the Al doping. Although this null result does not give any evidence for substitution of Al on the Ti site, it does not exclude the possibility that a small proportion of the Al ions do substitute for Ti in Ti(Al)O2. In (1−x)Ca2/5Sm2/5TiO3–xLi1/2Sm1/2TiO3 the variation of lattice parameters and crystal structure versus x, and the possibility of substitution of Li onto the Ti site were investigated. Single phase samples with the orthorhombic CaTiO3 perovskite structure were obtained for 0.20&lt;x&lt;0.50. It was found that the unit cell volume increased in an inverse linear relationship with the (decreasing) vacancy concentration. Rietveld analysis of the powder diffraction data shows that there is no substitution of Li on the Ti site in (1−x)Ca2/5Sm2/5TiO3–xLi1/2Sm1/2TiO3.

Pulsed Electric Field inactivation of microbial cells: the use of ceramic layers to increase the efficiency of treatment

The impact of Pulsed Electric Fields (PEF) on bacteria and plant or animal cells has been investigated since the early 1960s. High electric fields pulses (20–70 kV/cm, 1–10 μs) are reported to cause rupture of the cellular lipid membrane, through the mechanism of irreversible electroporation. Quantitative description of cell inactivation kinetics is based on the analysis of stability of lipid bilayers under electric fields and the thermal fluctuations associated with the production of pores. PEF has been successfully applied to inactivation of both Gram-positive and Gram-negative bacteria in many sorts of liquids, such as milk, fruit juices and liquid eggs. In all these media, the level of inactivation could reach the 5 Logs for an approximate range of pulses of 100–200, and an energy consumption of ∼ 10–100 kJ/kg. The advantages of PEF are the superior maintenance of functional and nutritional levels (if compared to traditional thermal treatment), continuous treatment and short processing times, while the current high costs of this technique make it more suitable for treatment of expensive media. We present a solution to the problem of volumes in PEF treatment through the use of high permittivity ceramics, while retaining the same inactivation efficiency and improving the duration of the electrodes.

Microstrip ring resonator bandpass filters using ceramic substrate

AbstractThe miniaturization of ring bandpass filters by employing high‐permittivity ceramic substrates (with respective dielectric constants of 9.7 and 23.5) are investigated. Microwave dielectric ceramics with high permittivity are commonly applied in several microwave communication components. With the advantages of compact size, high‐permittivity ceramics can be used as the substrate for bandpass filters. Moreover, the fundamental characteristics of newly developed compact square‐ring resonators have also been described and applied to the design of bandpass filters. In this paper, the designed square‐ring resonators structures are simulated using an IE3D simulator. The responses of the fabricated bandpass filters using Al2O3 (εr = 9.7, tan δ = 0.000036) and 0.875Mg0.95Zn0.05TiO3‐0.125Ca0.8Sm0.4/3TiO3 (εr = 23.5, tan δ = 0.000021) ceramic substrates are designed at the center frequency of 2.4 GHz. This compact size, low loss bandpass filter should be useful in many wireless communication systems. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 218–220, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24847

Dielectric properties of high permittivity ceramics based on Dy2/3CuTa4O12

Abstract The paper reports on the dielectric properties of Dy 2/3 CuTa 4 O 12 ceramic—a new material exhibiting very high permittivity exceeding 10 4 at low frequencies and broad steps in the permittivity versus temperature plots. Impedance spectroscopy studies performed in a frequency range 10 Hz to 2 MHz and within a temperature range from −160 to 650 °C revealed two distinct contributions in impedance and electric modulus formalisms, which were attributed to semiconducting grains and more resistive grain boundaries. Two plateaus of about 40,000 and 50 were found in the real part of the permittivity versus frequency plots. Resistances and capacitances of grains, estimated on the basis of the impedance data, are 1.5–2 orders and about 400 times, respectively, lower than those of grain boundaries. The influence of sintering temperature within a range 1180–1250 °C on the dielectric properties and the microstructure of the ceramics was also investigated. The permittivity values were found to increase significantly with increasing sintering temperature. The observed high dielectric constant behavior was explained in terms of Maxwell–Wagner polarization related to internal (grain boundary) barrier layer capacitance effects.