Pyroelectric Signal Research Articles

Pyrooptic converter, a new device for wavelength conversion of electromagnetic radiation

Abstract The operation of a “pyrooptic” converter based on the combined utilization of a pyroelectric detector and an electrooptic light modulator is demonstrated. In the device investigated the intensity changes of an electromagnetic radiation incident to a triglycine sulphate pyroelectric detector induce a pyroelectric signal, and this signal controls the intensity of a light beam passing through a liquid crystal light modulator, i.e. a modulated radiation is converted into modulated light. With impedance matching between the two elements of the converter but without amplifying the pyroelectric voltage a minimum detectable intensity of radiation of 0.3–0.6 W/m2, and an intensity required for total opening of the light modulator of 17–47 W/m2 is found in the chopper frequency range of 5–20 Hz.

Pyroelectric imaging on gash

Abstract Ferroelectric domain patterns of GASH crystals were examined by a pyroelectric probe technique. The pyroelectric signals from the sample capacitor were stored in computer memeorics and read out to display pyroelectric images in desirable modes. The experimental results of the pyroelectric imaging are in good agreement with the patterns revealed by a powder deposition technique. The center segment of the crystal is uni-polar, and the pyroelectric signal intensity level is comparable with that of the outer segment. The statistical variance of the signal intensity spectrum in the center segment is larger than that in the outer segment.

Thermal hysteresis of pyroelectric signal of LATGS crystals

Abstract The pyroelectric coefficient and the dielectric susceptibility of a LATGS crystal are measured. The existence of thermal hysteresis is shown. From the data of the pyroelectric coefficient, the polarization and the dielectric susceptibility we obtain the behaviour of the internal bias field. This is found to be dependent on the temperature near the transition point.

Pyroelectric Imaging on the Ferroelectric GASH[C(NH2)3Al(SO4)2·6H2O

Ferroelectric domain patterms of guanidine aluminum sulfate hexahydrate (GASH) were examined by a pyroelectric probe technique, in which the laser beam scanning and data storing were controlled by a microcomputer. It was confirmed that the averaged polarity and the magnitude of pyroelectric signal on the (0001) growth region are equal to those of either (10\bar10) or (01\bar10) growth regions, which are connected by 3-fold inversion symmetry of the crystal. The standard deviation of the pyroelectric signal intensity spectrum in the (0001) region is larger than that in the other regions. The spatial fluctuation of the pyroelectric constant in the (0001) region is larger than 25 µm, which is consistent with the inhomogeneous distribution of the polar region on the spiral patterns revealed by the powder deposition technique.

NaNO2thin films for pyroelectric detector arrays

Abstract Integrated NaNO2 pyroelectric radiation detectors have been made by growing NaNO2-films from the melt directly on silicon. The pyroelectric signal is read out by an integrated circuit in the Si-substrate. The detectors, single element or arrays, can be coupled to the electronics in two ways, either by the ferroelectric field effect at the NaNO2-Si contact, or by separate MOS-FETs. The performance of the electrical coupling by the ferroelectric field effect is strongly limited by the trapping of charge in interface states. The performance of signal transfer to a MOS-FET is more efficient, but suffers from a large capacitive load, if the gate of the MOS-FET is connected to the lower detector electrode formed by metallization on the silicon chip. Impedance matching therefore requires a small thickness of the NaNO2-film. A small thickness, on the other hand, favors the penetration of the temperature wave into the substrate with the accompanying heat loss. Electrical and thermal optimization are thus ...

Analog technique for the analysis of pyroelectric optical-detection signals

An experimental technique has been specifically developed for the determination of heating inequivalence errors in the use of electrically calibrated pyroelectric optical detectors. The technique is based upon an analog simulation of detector response. A null balance current detection method is used to eliminate preamplifier distortion errors. The technique is similar to thermal pulse methods used in the study of electret materials and may, therefore, find further application in this area. In addition, the technique may be adapted to allow investigation of thermally stimulated relaxation effects in the audiofrequency range.

Ferroelectric field effect of a thin NaNO2-layer on a Si-substrate

Ferroelectric single crystalline NaNO2-layers are grown from the melt onto Si-FET substrates. The pyroelectric signal appearing across the NaNO2-Layer upon a temperature change of the NaNO2 is observed to induce a change in conductance of the source-drain channel in the adjacent Si-FET. The deposition of the NaNO2-layer on the Si-FET constitutes the integration of the pyroelectric NaNO2 radiation sensor with an impedance transformer. This appears as an important step towards the realization of a pyroelectric sensor array integrated into circuits on a Si-substrate for processing the sensor signals.

Theory of photopyroelectric spectroscopy of solids

Light absorption by a solid material and conversion of part, or all, of the optical energy into heat due to nonradiative deexcitation processes within the solid can give rise to an electrical signal in a pyroelectric thin film in contact with the sample. This effect forms the basis of a new spectroscopic technique for the study of condensed phase matter. A one-dimensional theory is presented, which describes the dependence of the pyroelectric signal on the optical, thermal, and geometric parameters of the solid/pyroelectric system. Specifically, the theory examines the conditions under which the photopyroelectric signal exhibits a linear dependence on the optical absorption coefficient of the solid. Thus a theoretical basis for the technique of photopyroelectric spectroscopy is established. Qualitative comparisons between predictions of the theory and preliminary experimental observations are used to test the applicability of the theory to experimental configurations of practical interest.

Measurement of thermal diffusivity using a pyroelectric detector

A new method of measuring the thermal diffusivity of thin layers has been developed and applied to the characterization of laminated structures. The thermal diffusivity is measured using pyroelectric detection of a laser generated thermal pulse propagating through the sample. The shape of this pulse is governed by the thermal properties of both the sample and the detector. However, the thermal diffusivity of the sample can be determined from the position of the peak in the pyroelectric signal and the sample thickness. This method can be applied to thermal diffusivity measurements of thin or thick films, laminates, and thermal greases.

Reversible pyroelectric effect in Pb(Sc1/2Ta1/2)03ceramics under DC bias

Abstract It has been shown that quenched Pb(Scl/2Ta1/2)03 (PST) disordered ceramics and crystals show diffuse dispersive dielectric properties, while well annealed ordered materials exhibit normal sharp first order transition. The pyroelectric depolarization measurements taken using a Hewlett Packard Model 4140B picoammeter/DC Source under computer controlled heating cycle also have shown different behaviors between disordered and ordered materials In this work pyroelectric measurements by Chynoweth method under DC bias up to 1.8 KV/mm within a temperature range of 70°C around the temperature of maximum dielectric constant have been studied. A very significant enhancement of the pyroelectric signal under DC bias is observed in thermally quenched disordered samples. The largest enhancement of the signal appears at temperatures some degrees below the temperature of maximum dielectric constant The existence of microdomains in disordered materials is believed to be responsible for this new extrinsic component...

Electrically balanced pyroelectric radiometer

A TGS Pyroelcctric detector has been used for absolute measurements of low level optical radiation. The front electrode of the detector is used as: (i) a high efficiency radiation absorption film: (ii) an electrode for the pyroelectric condenser; and (iii) as an electric heater for producing heating pulses. Radiation is chopped by a 20% open mechanical chopper. The pyroelectric signal of the detector contains pulses due to radiation and electric heating. These two pulses are balanced by a null detection method in a lock-in amplifier. Thus electrical power is matched with radiation power for the absolute measurement of the latter. The operating frequency of the detector lies between the thermal relaxation frequency and the electrical cut-off frequency. Applications of this radiometer include absolute measurements of black body radiation and spectral radiation.

Pyroelectric Infrared Sensor Using PbTO3 Thin Film

A pyroelectric infrared sensor made of PbTiO3 ferroelectric thin film constructed on Si wafer has been developed. Pyroelectric output signal is amplified in current mode by a bipolar transistor which is devised on the same Si wafer. The device performance is much improved in high frequency region as compared with that of previous FET mode monolithic sensors, and it can be operated up to a few tens kHz region. Current responsivity of the PbTiO3 film has been also increased by reducing a heat capacity of the sensitive area and the output voltage of the device is 1.1 mV under the illumination of 120 mW/cm2 at 1 kHz which is one order of magnitude larger than that of the previous FET mode structure attached directly to Si wafer. The detectivity is ∼105 cm √Hz/W with bandwidth of 1 Hz at chopping frequency of 1 kHz. The rise time of the response measured under CO2 laser pulse irradiation is about 2.5 µs.

Evidence for pyroelectric and piezoelectric sensory mechanisms in the insect integument

Quantitative pyroelectric (PE) and piezoelectric (PZE) measurements were carried out on the insect integument of live Blaberus giganteus (cockroach) and on dry integument preparations of the same species. Voltage responses to optical pulses of 10--500 ms, absorbed in the live integument, were PE: interference filter measurements showed the responses to be proportional to the absorbed thermal radiation flux and independent of the wavelength. The voltage/time-course of the responses was in agreement with theoretically calculated PE signals. Voltage responses to mechanical pulses were PZE. The responses of the inner and outer integument surfaces always had opposite electric signs. The polar character of the integument was confirmed by means of a separate dielectric heating method. To explain these results, we hypothesize that the PE properties are for the most part localized in the two outermost layers (outer and inner epicuticle) of the integument, which consists mainly of polar lipids and proteins. Parallel alignment of these polar molecules perpendicular to the integument surface is very likely. PE and PZE responses, therefore, will not only occur in live insects but will also be measurable in dead, dry integument preparations as long as the polar tissue texture remains intact. Due to its polar texture, the insect integument will react to rapid changes in temperature, illumination, or uniaxial pressure in the same way as nonbiological PE materials, where the voltage responses depend on dX/dt (X, pressure or temperature). It seems clear, therefore, that the well-known physiological reactions of various arthropods to such physical outside influences may be related to the PE property of their integument.

Pyroelectric glass-ceramics

Highly oriented surface layers of lithium disilicate crystals were grown by crystallizing glasses of composition Li2Si2O5 in a temperature gradient. The polar c axes of the crystallites were oriented parallel to the temperature gradient and perpendicular to the sample surface. The pyroelectric response of the glass-ceramic crystallized in a thermal gradient was approximately four times larger than that of a touramaline crystal of similar dimensions. The time dependence of the pyroelectric signal obeys the thin-film equivalent circuit model developed by Chynoweth.

Phase transition induced changes of some properties of CsCuCl3

Abstract Changes of refractive indices induced by the phase transition in CsCuCl3 at Ttr=148°C are reported. Electrooptic coefficient has been measured and found to increase when Ttr is approached, contrary to expectation. Pyroelectric signal has been detected at Ttr. NQR data show no evidence for a further phase transition up to 260°C.

A clue to the origin of pyroelectricity in PVF2from the low temperature behavior

Abstract Since the discovery of pyroelectricity in the polymer polyvlnylidene fluoride (PVF2), there has been a continuing effort to identify the origin of the effect and to determine whether the material is best classified as an electret or ferroelectric. A recent study of the pyroelectric signal following pulsed heating provided fairly strong evidence that the primary pyroelectricity contributes at most a very small fraction of the total effect: the dominant contribution coming from thermal expansion of the piezoelectric polymer (secondary pyroelectricity). We report additional evidence from low temperature pyroelectric measurements that there is no significant contribution to the pyroelectric effect from low lying optic modes.

Major noise sources in pyroelectric imaging devices

Abstract The only good pyroelectric imaging device which eiists at present that is capable of producing a good quality video image with relatively good thermal sensitivity is the pyroelectric vidicon. Nevertheless, in the recent past there have been reports of linear imaging arrays of about 30 pyroelectric elements and several laboratories are currently involved in programs to build prototype arrays with as many as 1000 picture elements. These arrays usually consist of pyroelectric material (the thermal sensor) which is electrically coupled to an array of silicon transducers. These are used to multiplex and amplify the pyroelectric signal.

The pyroelectric signal from triglycine sulphate

The pyroelectric signal from triglycine sulphate has been studied by a focussed He-Ne laser beam and a phase sensitive detection method. It is observed that anti-parallel domains give rise to pyroelectric signals of opposite polarity. The pyroelectric signal is zero when the laser spot is in between anti-parallel domains. The intensity of the pyroelectric signal is recorded and the domain structure is determined.

Domain pattern in ferroelectric triglycine sulphate using pyroelectric effect

A method to study domain structure in ferroelectrics, using pyroelectric effect is described. Variation of pyroelectric signal from the surface of a triglycine sulphate crystal plate has been studied by scanning the surface of the crystal with a low wattage He-Ne laser beam. The integrated pyroelectric signal is due to two components, namely, (1) the primary component arising out of the change in spontaneous polarization with temperature and (2) the delayed component arising out of the possible polarization reversal. The component of an electric field along the ferroelectric axis due to thermal hemisphere within the crystal plate formed by the laser beam has been calculated and shown to exceed coercive field, making polarization reversal possible. The delayed pyroelectric signal is a measure of polarization reversal within the patch illuminated and its observed variation over the surface yields information of the domain structure.

Laser scanning microscope for pyroelectric display in real time

The pyroelectric probe technique is now capable of inspecting a 100 x 100-microm TGS area in a few seconds with a 2-microm limit of resolution. The method is described in detail, and a calculation of the pyroelectric signal is presented. The longitudinal growth of a cylindrical domain is mathematically simulated and also the variation of pyroelectric signal at domain boundary. These calculations are in good accordance with experiment. With a 200-kHz chopping frequency only a thin layer of the crystal surface is inspected (thermal diffusion length l = 0.64 microm), while the lateral limit of resolution is given by the laser spot radius (R(1) = 1 microm). It is possible to decrease this limit by using a smaller laser spot, but the chopping frequency ought to be increased.