JPS63273020A - Infrared detector - Google Patents

Abstract

PURPOSE:To obtain a highly sensitive detector with few noises by using specific frequency bands and combining an amplifier circuit for the frequency bands and a composite pyroelectric element with each other. CONSTITUTION:Lead titanate ceramic powder is arranged on a polyamide imide varnish sheet in single scattering and, after the solvent of the varnish is removed, applied with a pressure and heated to obtain a sheet. After both surfaces of the sheet are polished to expose the ceramic powder on both the surfaces, copper is formed by sputtering to make an electrode. One surface of the electrode is blackened as a light receiving surface to make a composite pyroelectric element. The element is connected to an FET and accommodated in a stainless steel casing together with a signal take-out resistor. A polyethylene foam with an independent bubble structure is adhered to the wall surfaces of the casing except an infrared transmission window to perform a thermal insulation. In this case, signals have a frequency band from 0.01Hz-0.5Hz to be amplified and the signals are led to an amplifier circuit having an amplification factor of 40dB or above in afore-mentioned region. The amplifier circuit constitutes a detector.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an infrared detector that can reliably detect even slow movements, and more particularly to an infrared detector for people.

[Prior art]

Conventionally, interpersonal infrared detectors using pyroelectric elements have to remove as much as possible the infrared energy (noise) generated by nature other than the human body, and also capture the weak infrared energy generated by the human body. Therefore, a concave mirror is used for the infrared sensing part, and the amplifier circuit is designed to
Those having an amplification factor of about 40 dll to 80 dB for the Hz frequency band were used.

However, such an amplifier circuit is not sensitive to extremely slow changes in the infrared energy source, which has been the biggest drawback of conventional infrared detectors using pyroelectric elements.

In other words, the fact that the pyroelectric element senses infrared energy and emits a signal is governed by the amount of time it takes for the infrared energy source to cross the beam diameter of the concave mirror, and in order to sufficiently follow the slow motion, the amplification factor of the circuit is 0.5 Hz. Although it is necessary to maintain a high level in the following low frequency ranges, these low frequency bands have been completely ignored due to noise etc. No infrared detector with high band amplification was found.

[Purpose of the invention]

As a result of extensive research into an infrared detector capable of capturing the slow motion of infrared energy sources that could not be detected in the past, the present invention was developed by increasing the amplification factor in the low frequency band to a high level, which was previously unthinkable. After gaining the knowledge that it was possible to extract a large signal for slow movements, we conducted various studies and completed the process. The object of the present invention is to obtain an infrared detector with less noise.

[Structure of the Invention] The present invention provides an infrared detector system consisting of an infrared sensing element and an amplifier circuit, in which the amplification factor of the circuit is from 0.01Hz to 0.511Hz.
an amplifier circuit having an output of 40 dB or more in the frequency band of No. 2;
The present invention relates to an infrared detector characterized in that the infrared sensing element is composed of a composite pyroelectric element.

In conventional infrared detectors, the output of the pyroelectric element is determined by the amount of time the infrared energy source traverses the field of view of the pyroelectric element.

On the other hand, the walking speed of a human body crossing this field of view is 0.1 m1s
ec to l m/sec, the change in infrared energy received by the pyroelectric element can be estimated to be 0.511 z or more in frequency, and the amplification factor of the amplifier circuit is 0.5 Hz or more in the frequency band. It was designed to maintain a high standard.

Therefore, even with conventional infrared detectors, the walking speed is 0.1 m+
Sufficient output can be obtained if the walking speed is 0.1 ec or more, but for slow movements where the walking speed is 0.1 ec or less, the amplification factor of the circuit is insufficient and almost no output can be obtained.

In contrast, the circuit of the present invention ranges from 0.01112 to 0.0.
It is necessary to have an amplification factor of 40 dB or more in the 58Z frequency band.

In the circuit of the present invention, it is preferable that the lower frequency side of the frequency band of the amplifier circuit is closer to direct current, as it can follow even extremely slow movements that are close to stationary.However, since the pyroelectric element outputs a signal in response to temperature changes, Normally, the operating point (bias voltage) when there is no signal is determined, and the design must be such that the signal can be output up and down around this bias voltage value. The output of the circuit becomes saturated, which is undesirable.Therefore, it is necessary to cut the amplification factor very close to DC, but from the perspective of the slope characteristics of practical electrical filters and the stability of the circuit, it is not desirable to cut the amplification factor to 0.0.
1Hz is the limit. Furthermore, it is sufficient to keep the frequency band of the amplifier circuit up to 0.5 Hz, and even if the frequency band is extended further to the high frequency side, not only will it hardly contribute to the output for slow operation, Gradually, the influence of hum starts to become noticeable, which is not desirable.

The amplified signal is normally guided to a threshold circuit and subjected to signal processing, but when carrying out signal processing, the amplified signal must be 0.0.
Since the signal of the pyroelectric element by receiving infrared energy, which is preferably maintained at a level of 5 volts or more, is extremely small, the amplifier circuit of the present invention requires an amplification factor of at least 40 dB. An amplification factor lower than this is not preferable because the S/N ratio decreases and reliability becomes poor.

The composite pyroelectric element used in the present invention is a composite of ferroelectric ceramic powder and polymer resin, and can be processed to be thinner than pyroelectric elements such as single ceramic or single crystal. It becomes possible to suppress the heat capacity of the element and improve the sensitivity. In particular, a structure in which ceramic powder is arranged in a monodisperse manner in the thickness direction of a polymer resin, exposed on both sides without intervening resin, and in direct contact with electrodes formed in the thickness direction, is a pyroelectric This is preferable in order to further improve the sensitivity of the body element.

In addition, in the infrared detector according to the present invention, the amplification factor of the amplifier circuit is maintained at a high level in the low frequency band, so if there is a slow temperature fluctuation in the environment in which the detector is placed, it will be sensitive to this and the S/N will increase. 0 Normally, in a detector, if the S/N ratio is not 3 or higher, there are many malfunctions and the reliability is poor.
/N is effective for the infrared detector of the present invention, by insulating the area around the pyroelectric element from the outside world,
It is more preferable to suppress temperature fluctuations from the viewpoint of improving reliability.

As a heat insulation method, it is desirable to embed the casing containing the pyroelectric element in a system with low thermal conductivity. Effective methods include casting embedding, or a method in which the housing is made into a double structure and the space between the housings is evacuated and maintained.

〔Effect of the invention〕

The present invention utilizes a frequency band that has not been considered in the past, and by combining these amplifier circuits and a composite pyroelectric element, it can also capture the slow motion of infrared energy sources that has not been able to be detected until now. Furthermore, by using it as a human body detector, it is an infrared detector that can be extremely effective in the crime prevention field.

(Example〕 Examples of the infrared detector according to the present invention are shown below.

Lead titanate ceramic powder (average particle size 100μ) with a dielectric constant of 200 was arranged in a monodisperse state on a polyamide-imide varnish sheet, and after removing the solvent from the face, the sheet was obtained by applying pressure and heating. . Both sides of this sheet were polished to expose the ceramic powder on both sides of the sheet, and then copper was formed by sputtering to form electrodes.
Polarization was performed for 15 minutes. Thereafter, one side of the electrode was blackened to serve as a light-receiving surface, and the electrode was cut into four square pieces to obtain a composite pyroelectric element having a thickness of 50 μm. The device was wired to a field effect transistor (hereinafter abbreviated as FET) and housed in a stainless steel casing together with a signal extraction resistor. The housing formed a window for transmitting infrared rays, and a 6μ cut-on interference filter was attached to the window.

A closed-cell polyethylene foam having a thickness of 3ffIg+ and a thermal conductivity of 0.04 cal/+*,hr,"C was attached to the wall surface of this housing other than the transparent window to provide heat insulation.

The signal is amplified in a frequency band of 0.0IHz to 0.5IHz.
11z, and an infrared detector was constructed by introducing an amplifier circuit with an amplification factor of 80 dB and an fIi attenuation characteristic of 24 dB10 ct in this region. The distance 3m in front of this detector is determined by walking speed 0.
．． The output signal of the detector was measured when a human body crossed at a speed of 0.05 m/sec.

The results are shown in Table 1.

11) The same measurements as in Example 1 were carried out using the same detector as in Example 1 except that the main insulation was not applied.

The results are shown in Table 1.

11. The same measurements as in Example 1 were carried out on the same detector as in Example 1 except that the amplification factor of the engineering amplifier circuit was 45 dll.

The results are shown in Table 1.

, ratio "L doctor" - lead titanate ceramics (dielectric constant 200, thickness 0.1
Form copper electrodes on m+a) by sputtering and heat at 180°C.
, 8KV/M T215 minutes Fi:
: 0) Blacken one side of the rear electrode as a light-receiving surface, and
It was cut out to make a pyroelectric element. The element, FET, and signal extraction resistor are wired together, and the whole is housed in a stainless steel housing with an infrared transmission window equipped with a 6μ steel cut-on interference filter.
IIIlφ) was placed and fixed so that its focal point coincided with the position of the pyroelectric element.

The signal was guided to an amplification circuit similar to that of Example 1, except that the frequency band to be amplified was from 0.5 Hz to 5 Hz, to form an infrared detector. The same measurements as in Example 1 were performed on this detector.

The results are shown in Table 1.

, ``Philippine Doctor'' - Example 1 except that the amplification factor of the amplifier circuit is 35 dB
The same measurements as in Example 1 were carried out using a detector similar to the above.

The results are shown in Table 1.

From these facts, it can be seen that the infrared detector according to the present invention can reliably detect even slow movements that could not be detected conventionally.

Table 1; Examples and comparative examples

Claims (1)

[Claims] In an infrared detection system consisting of an infrared sensing element and an amplifier circuit, the amplifier circuit has an amplification rate of 40 dB or more in the frequency band from 0.01 Hz to 0.5 Hz, and the infrared sensing element is comprised of a composite pyroelectric element. An infrared detector featuring