The research and development works directed to a creation of solid state coolers and refrigerators based on the electrocaloric effect have been initiated in various countries, mainly in USA and USSR, in the 70s of the last century The goal of these works was formed as a creation of microcryogenic cooling systems for infrared radiation receivers for space optoelectronic systems.

A method is proposed for studying the dynamics of the electrocaloric response of a ferroelectric capacitor to the pulsed action of the electric field, and the results of measurements are reported. The temperature of the capacitor was measured with the help of a ferromagnetic film resonator. The sensitivity of temperature measurements was ∼10 −4 K/kHz. The recalculated temperature dependence of the resonance frequency showed that the ferroelectric ceramic sample was heated by 0.065 K and was cooled by 0.041 K relative to the thermostat temperature under the action of high-voltage pulses. The relaxation time of the electrocaloric effect of the 0.87PMN-0.13PT relaxor ferroelectric ceramic is 4.5 μs.

The influence of applied electric field, temperature variation rate, and free charge carrier density on the hysteresis of C(T) dependence is investigated on ferroelectric ceramic capacitors. The measurements were performed on the ceramic capacitors of Ba0.55Sr0.45TiO3 containing 12 wt % of Mg complex additive and the 0.87Pb(Mg1/3Nb2/3)O-3-0.13PbTiO(3) ceramics. The investigations were directed to study of electrocaloric response of ferroelectric ceramics. Various mechanisms of temperature hysteresis are discussed. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3532944]

A thermodynamic cycle in a solid-state cooling line including two ferroelectric capacitors which exhibit the electrocaloric (EC) effect is considered. Expressions are derived for determining the cooling factor and the efficiency of the EC cooling line in terms of the Carnot cycle. Numerical estimates obtained for barium-strontium titanate ferroelectric capacitors make it possible to determine the cooling efficiency upon a change in temperature by ΔT = 2 K. At the initial temperature of 272 K, the efficiency is 0.6 Carnot, which considerably exceeds the efficiency of vapor-compression refrigerators.

The dynamics of change in temperature at the edges of a layered structure consisting of one or more electrocaloric and heat-conducting elements in response to pulses of a periodic electric field has been studied with the use of the finite-element method. The possibility of using ceramic materials and (Ba,Sr)TiO 3 films as electrocaloric and heat-conducting elements of linear and radial cooling structures is considered. The difference between the temperatures at the center and periphery of the radial film microstructure with two interdigital circular electrode lines is 2.5 K. An increase in the number of lines and the electric field frequency leads to an increase of the thermal effect.

The principle of the design of devices with the double electrical and magnetic control that are based on a ferromagnetic resonator structure coupled with a slotline containing a ferroelectric film is considered. The effective hybridization of the magnetostatic surface wave and the slot mode is demonstrated.

The electrocaloric response of a ferroelectric capacitor to a periodic electric field has been analyzed in terms of the nonstationary heat conduction equation. A linear physical model is considered for an electrocaloric element in which one end ( x = 0) is thermally insulated and a constant temperature T 0 is maintained at the boundary x = l . The effect of a periodic electric field on the capacitor gives rise to temperature oscillations about a decreasing average value that reaches saturation. A relatively simple analytic expression is derived for the temperature distribution along the electrocaloric element and the heat flux density under stationary conditions. The calculations are carried out using the results obtained from measurements performed for a PMN-PT relaxor ferroelectric in the temperature range of the phase transition. A temperature gradient and a heat flux of ∼150 W/cm 2 are observed in an electric field of 2.4 V/μm at a frequency of 10 Hz.

ABSTRACT Microwave slot and coplanar transmission lines formed on a surface of ferroelectric films grown on dielectric substrates are used for various microwave devices with electrically tunable amplitude and phase frequency characteristics. The electric field intensity, which is required for the effective modulation of dielectric permittivity of the ferroelectric film is varied between 10 and 15 V/micron. Therefore rather narrow gaps with width no more than 10 microns can provide necessary electric field at bias voltage no more than 100 V. In this case the attenuation of the electromagnetic slot mode is considerably increased, so the implementation of such devices has no a sense.

A novel microwave resonator of yttrium iron garnet and ferroelectric barium strontium titanate films in a slotline structure is proposed. The resonator is electric field tunable, by 75 MHz for E 5 V/mu m applied to the slotline electrodes, and has several advantages: (i) a low cutoff frequency of a few megahertz compared with several gigahertz for open-dielectric waveguides, and (ii) a high degree of hybridisation of magnetostatic surface spin waves and electromagnetic modes that results in excellent tunability.

The temperature response in the solid state cooling line composed of electrocaloric (EC) and thermoconductive elements was investigated using analytical approach and computational experiment. A periodical bias electric field applied to ferroelectric capacitor caused their heating and cooling, however, alternative adiabatic and isothermal switching of the EC elements allowed to generate the directed heat flux and the temperature decrease ΔT at one edge of the solid state structure. Thin film topologies are expediently to be used because thin electrocaloric elements are most appropriate to enhance switching frequency and increase ΔT. The temperature decrease ∼20° was obtained at one edge of the cooling line with (Ba,Sr)TiO3 EC elements. The serial connection of the EC lines can give a considerable cooling effect.

The novel design of microwave slot transmission line comprising inner electrodes - multislot line (MSL) was used for formation of transmitting phase shifter. The planar MSL topology was combined with the Vivaldi irradiator patterned on the edges of the substrate. The phase transmission characteristics and the diagram pattern of the single irradiator were measured and presented in the paper.

Novel design of microwave four-pole band-pass filter based on the tunable waveguide dielectric resonators with the embedded planar (Ba,Sr)TiO3 film ferroelectric varactors is presented. The following operational parameters were obtained after the experimental test in Ka-band: the bandwidth at 1 dB level is about 350 MHz (1.2 %), the range of tuning is 570 MHz (1.9 %) and insertion losses are no more than 5.0 dB.

ABSTRACT Novel design of microwave four-pole band-pass filter based on the tunable waveguide dielectric resonators with the embedded planar (Ba,Sr)TiO3 film ferroelectric varactors is presented. The following operational parameters were obtained after the experomental test in Ka-band: the bandwidth at 1 dB level is about 350 MHz (1.2%), the range of tuning is 570 MHz (1.9%) and insertion losses are no more than 5.0 dB.

The local nonlinear microwave response of YBa 2 Cu 3 O 7 − x films was measured by near-zone field microscopy with a spatial resolution of 50 μm, and YBa 2 Cu 3 O 7 − x film microbridges were locally studied by low-temperature scanning microscopy with a spatial resolution of 4 μm. The microstructure of epitaxial YBa 2 Cu 3 O 7 − x films was examined using x-ray diffraction and electron microscopy. A correlation is detected between the average crystallite size and the half-widths of the temperature dependences of the third-harmonic power ( W TH ) and the electron-beam-induced voltage ( W EBIV ). The experimental results are described in terms of a model of a two-phase medium taking into account the nonlinear I-V characteristic of the superconductor. For large crystallites, the nonlinear microwave response is shown to be caused by intracrystallite vortex pinning. As the average crystallite size decreases, an additional contribution to the nonlinear response appears due to the pinning of a magnetic flux by the Josephson network of crystallite boundaries. Calculations show that a three-fold increase in the crystallite size decreases the nonlinearity coefficient of YBa 2 Cu 3 O 7 − x films by two orders of magnitude.

It is demonstrated experimentally that a layered structure consisting of ferrite and ferroelectric thin films can be used as an electrically and magnetically tunable microwave resonator. The dual tunability is realized through the application of a bias electric field to the ferroelectric layer (thus changing its dielectric constant), and a bias magnetic field to the ferrite layer. The resonator having central frequency f0≅5GHz and bandwidth Δf=3.5MHz demonstrated a broadband (∼300Δf) tunability through the variation of the bias magnetic field, and a narrow-band (∼2Δf) tunability through the variation of the bias electric field.

The electric field tuning characteristics of a combined microwave resonator based on ferrite-ferroelectric layered structure have been studied in a wide range of bias magnetic fields. The combined ferrite-ferroelectric resonator was composed of two rectangular resonators fabricated from a ceramic barium strontium titanate (BST) slab and a single-crystal yttrium iron garnet (YIG) film. The in-plane dimensions for the YIG and BST resonators were chosen to be equal in order to maximize the electromagnetic coupling between their main modes and reduce spurious influence of their higher order modes. A tuning range of 100MHz for the resonator frequency was realized at 5GHz through the variation of magnetic permeability and dielectric permittivity of the YIG-BST structure. A theory for the hybrid wave excitations, based on a coupled-mode approach, has been developed and provides good description of the data.

Microwave multislot transmission lines formed on (Ba,Sr)TiO3–BST ferroelectric films were studied using full-wave analysis and resonator measurements. The BST films were grown on sapphire, MgO and alumina substrates in the process of RF sputtering. The multislot resonators formed on different types of BST films were measured at frequency ∼30 GHz. The slot and multislot resonator topologies measured in rectangular waveguide had similar quality factor (100–120). The BST film dielectric characteristics were obtained: ϵ = 1100–1800; tan δ = 0.02–0.03. The coupled multislot structures were simulated to realize tunable band-pass filters of various tunability range, pass band and microwave losses in the band.

The properties of ferroelectric ceramics based on barium strontium titanate and doped by admixtures with low permittivity and dielectric loss tangent are studied experimentally. These ceramics are viewed as a promising material for microwave devices applied in the acceleration technology. Ceramic samples the I-V characteristics of which contain long horizontal segments are found to have good insulating properties. Various conductivity mechanisms in these ceramics are discussed, and their effect on the amount and character of dielectric hysteresis in these samples is considered.

Recent results on development of BST (barium strontium titanium oxide composition) ferroelectric materials are presented to be used as the basis for new advanced technology components suitable for high-gradient accelerators. The ferroelectric ceramic has an electric field-dependent dielectric permittivity that can be altered by applying a bias voltage. Ferroelectric materials offer significant benefits for linear collider applications, in particular, for switching and control elements where a very short response time of 10 ns can be potentially achieved. The BSM ceramic exhibits a high tunability factor: a bias voltage of 50 kV/cm reduces the permittivity from 500 to 400. The applications include: fast active Xband and Ka-band high-power ferroelectric switches, high-power X-band, and L-band ferroelectric-based phase-shifters. The recently developed large diameter (11 cm) BST-based ferroelectric rings will be used at high pulse power (tens of megawatts) for the X-band components as well as at high average power (in the range of a few kilowatts) for the L-band phase-shifters which are suitable for ILC applications.

The modifications of microwave slot transmission lines formed on the (Ba,Sr)TiO 3 ferroelectric films were investigated to realize high quality factor millimeter-wavelength devices tunable by low bias voltages. The narrow inner electrodes inserted to a slot line form the novel type of the transmission lines, which was called multislot line (MSL). The MSL short-circuited and tunable resonators were tested at frequency ∼30 GHz. The MSL phase shifter merit factor was evaluated higher than 100 degree/dB at bias voltage lower 100 V. The comparatively high quality factors of tunable MSL resonators and phase shifters evidence on real prospects of novel topology approach to the development of such microwave devices as tunable band-pass filters and electronically steerable antennas.