Passive infrared human body detection sensor

Abstract

The utility model provides a passive infrared human body detection sensor. The passive infrared human body detection sensor comprises a shell which plays a role in protection and fixation; the Fresnel lens is assembled at the opening end of the shell and is used for converging external infrared radiation and segmenting a sensor detection area; the MEMS galvanometer is assembled at the focus of the Fresnel lens and is fixed on the shell through a bracket structure; the control circuit board is fixed on the mounting supporting column of the shell through screws, a pyroelectric sensing unit, an AD conversion circuit and a microcontroller MCU unit are assembled on the control circuit board, and the pyroelectric sensing unit comprises two pyroelectric sensing units, an induction window covering the pyroelectric sensing units and a signal amplification and filter circuit; a sensing window of the pyroelectric sensing unit faces the MEMS galvanometer, and the normal direction of the pyroelectric sensing unit is perpendicular to the central axis of the Fresnel lens. According to the utility model, static human bodies in a detection area can be effectively detected, environmental noise interference can be effectively overcome, and high detection sensitivity is also provided for human bodies moving in the radial direction and in the horizontal direction.

Description

TECHNICAL FIELD

[0001] The utility model relates to passive infrared sensor especially relates to passive infrared sensor of static human body can be detected. BACKGROUND

[0002] Passive Infrared Sensor (PIR Sensor) is a commonly used motion detection sensor, widely used in security systems, automatic lighting, automatic doors, toys and other fields. Since it does not emit any energy (such as infrared light), but works by detecting changes in infrared radiation in the environment, it is called "passive" infrared sensor. All objects in nature with a temperature above absolute zero will continue to radiate infrared energy. Warm-blooded organisms such as humans and animals are typical sources of infrared radiation, with body temperatures (about 37°C) producing infrared radiation wavelengths mainly concentrated in the 9-10 micron range. The core of the PIR sensor is a pyroelectric detection element, usually containing two or more rectangular pyroelectric detection units connected in a differential manner. This element is made of a specific crystal material (such as lithium tantalate LiTaO3, lead zirconate titanate PZT, etc.) sensitive to infrared radiation. When the temperature of this material changes, an electric charge (voltage signal) is generated on its surface, i.e. the pyroelectric effect. The front of the sensor is usually covered with a specially designed plastic lens - a Fresnel lens, which serves to: focus the infrared radiation from the detection area onto the internal pyroelectric detection element, improving detection sensitivity; divide the detection area into multiple alternating sensitive (detection) and non-sensitive (transition) zones. When there is no moving heat source, the two sensitive units receive essentially the same and stable environmental infrared radiation, or the change is very slow, and the electric signals they generate cancel each other out (or change very little), and the sensor does not output a signal; when a moving infrared radiation source (such as a person) enters the detection area, it will pass through the different sensitive zones divided by the Fresnel lens in turn, causing the infrared radiation to be focused on the two detection units alternately and sequentially, causing their temperatures to change alternately, thereby generating a varying differential voltage signal. This weak differential voltage signal is amplified and filtered (to filter out interference and select a specific frequency range, such as the typical frequency of human movement 0.1-10 Hz) by the internal circuit, compared with the set threshold value, and an output decision signal is output; or after AD conversion, it is sent to the MCU unit for more complex decision making.

[0003] Although this passive infrared sensor has the advantages of low cost and low power consumption, it is widely used in security systems and automatic lighting energy-saving systems, but such sensors also have obvious defects: they cannot detect stationary human bodies; they are also susceptible to environmental temperature changes, heat source interference and other factors, which may cause false positives; and they are not sensitive enough to detect radial human movement. These defects greatly affect its application effect and promotion.

[0004] To address these shortcomings, Chinese patents CN201234378 and CN201696320U propose an improvement by adding a chopper between the pyroelectric sensing unit and the Fresnel lens. The chopper is driven to rotate by a motor or piezoelectric ceramic to simulate infrared temperature measurement. However, its output voltage is related to the average indoor temperature and the emissivity of objects, making it unable to accurately distinguish human signals, resulting in a high false detection rate and difficulty in distinguishing background noise from human signals. Patents CN202025401U, CN201707454U, and CN201766566U propose solutions that use a motor to drive the Fresnel lens or sensor to simulate human movement between the lens's field of view and blind spot. However, this solution has many mechanical parts, a high failure rate, and high power consumption. Furthermore, it suffers from severe background noise interference, easily drowning out human signals.

[0005] This invention addresses the aforementioned technical deficiencies and market demands by proposing a passive infrared human body detection sensor. By introducing a MEMS galvanometer into the incident optical path, the reciprocating motion of the MEMS galvanometer near its equilibrium position enables the sensing unit to scan the detection area and transition area, thereby achieving effective detection of stationary human bodies. Simultaneously, this sensor effectively overcomes environmental noise interference and also exhibits high detection sensitivity for radially moving human bodies. Utility Model Content

[0006] This invention proposes a passive infrared human body detection sensor, comprising a housing that protects and secures internal components; a Fresnel lens mounted at the opening of the housing for focusing external infrared radiation and dividing the detection area of ​​the passive infrared human body detection sensor; a MEMS galvanometer mounted at the focal point of the Fresnel lens and fixed to the housing by a bracket structure; and a control circuit board fixed to the mounting support of the housing by screws, on which a pyroelectric sensing unit, an AD conversion circuit, and a microcontroller (MCU) unit are mounted. The pyroelectric sensing unit includes two pyroelectric sensing elements, a sensing window covering the pyroelectric sensing elements, and signal amplification and filtering circuits. The sensing window of the pyroelectric sensing unit faces the MEMS galvanometer, and its normal direction is perpendicular to the central axis of the Fresnel lens.

[0007] The sensor window is a layer of silicone protective film.

[0008] The MEMS galvanometer includes a wavelength-selective reflector that can reciprocate around its equilibrium position along its axis of symmetry under the drive of a control signal.

[0009] When the wavelength-selective mirror is in its equilibrium position, the angle between its mirror surface and the central axis of the Fresnel lens is 45 degrees.

[0010] The wavelength-selective mirror includes a highly reflective substrate layer and a wavelength modulation layer composed of multiple dielectric thin films superimposed thereon.

[0011] The substrate is made of aluminum metal, and the multilayer dielectric film is composed of alternating and periodically stacked high and low refractive index dielectric materials, with each dielectric film having a thickness of 2.5 micrometers.

[0012] The analog signal output by the pyroelectric sensing unit is connected to the input terminal of the AD conversion circuit via PCB traces. The output of the latter is connected to the microcontroller (MCU) unit via a data bus interface. The MCU unit runs an intelligent judgment algorithm and connects to the MEMS galvanometer via a control interface to control the rotation of its reflector, thereby realizing the scanning and judgment of the detection area.

[0013] The passive infrared human body detection sensor proposed in this invention introduces a MEMS galvanometer in the incident optical path. Through the reciprocating motion of the MEMS galvanometer near its equilibrium position, the sensing unit scans the detection area and transition area, thereby achieving effective detection of stationary human bodies. Simultaneously, this sensor effectively overcomes environmental noise interference and also exhibits high detection sensitivity for radially moving human bodies.

[0014] Other features and advantages of this utility model will become clearer after reading the detailed description of the embodiments of this utility model in conjunction with the accompanying drawings. Attached Figure Description

[0015] To clearly illustrate the technical solution and embodiments of this utility model, the accompanying drawings are briefly described below. It should be noted that the drawings are primarily intended to explain the interconnections, structural features, and advantages of the various components of the device, and are not drawn to scale according to the actual dimensions of the device. Obviously, the drawings only relate to a limited set of embodiments and should not be construed as limiting the present utility model. Those skilled in the art can easily obtain new embodiments through formal variations based on these drawings.

[0016] Figure 1 This is a schematic diagram of the structure and working principle of a traditional passive infrared sensor;

[0017] Figure 2 This is a schematic diagram of the structure of one embodiment of the present utility model;

[0018] Figure 3 This is a schematic diagram of the reciprocating deflection of a MEMS galvanometer in one embodiment of this utility model;

[0019] Figure 4 This is a schematic diagram of the reflection coefficient spectrum of a MEMS galvanometer embodiment in one embodiment of the present invention;

[0020] Figure 5 This is a functional module block diagram of one embodiment of the present invention. Detailed Implementation

[0021] The specific embodiments of this utility model are described in detail below with reference to the accompanying drawings.

[0022] This invention proposes a passive infrared human body detection sensor, which aims to overcome the shortcomings of existing technologies, such as the inability to detect stationary human bodies, weak resistance to environmental interference, and weak sensitivity in detecting radially moving human bodies. Figure 1 A typical structure of a passive infrared sensor typically includes: a pyroelectric sensing unit, the core detection element of the sensor, encapsulated in a metal housing, containing two differentially connected pyroelectric sensing units S1 and S2; a Fresnel lens F, a plastic lens covering the front of the sensor, used to focus infrared light and divide the detection area into multiple alternating sensitive areas (detection areas) A and B, and a non-sensitive area C (transition area), focusing infrared radiation from detection area A onto pyroelectric sensing unit S1, and infrared radiation from detection area B onto pyroelectric sensing unit S2; a signal amplification and filtering circuit, which amplifies the weak signal from the pyroelectric element using an operational amplifier (Op-Amp) and filters out interference signals using a bandpass filter; and a comparator / trigger circuit, which compares the processed signal with a reference threshold, generating a logic level output (e.g., a high level indicating motion detection) when the signal exceeds the threshold as a subsequent control signal. Some sensors also integrate delay circuits to maintain output for a period of time after detecting movement, as well as photoresistors that trigger only in low light conditions. When a person moves laterally within the detection range, they continuously enter and leave areas focused on two different pyroelectric sensitive units. Each crossing of the boundary of the "non-sensitive zone" causes a significant change in the distribution of infrared radiation on the two units, thus continuously generating an effective differential signal. The amplified and filtered signal waveform is shown in Figure S3. When the human body is stationary, the infrared radiation focused on pyroelectric sensitive units S1 and S2 remains unchanged, and no pyroelectric phenomenon occurs, thus the presence of a stationary human body cannot be detected. Figure 1 It can also be seen that the infrared radiation converged by the Fresnel lens facing the pyroelectric sensitive unit is incident on the detection surface of the pyroelectric sensitive unit approximately perpendicularly, while in other areas it is incident at an angle. The closer to the edge of the lens, the larger the incident angle. This means that the sensor has different detection sensitivities for different areas, and the detection sensitivity at the edge of the detection area is significantly lower than that in the central area.

[0023] The passive infrared human body detection sensor proposed in this invention has made improvements in this regard, such as... Figure 2As shown, a MEMS galvanometer S4 is placed at the focal point of the infrared light rays behind the Fresnel lens F, reflecting the incident infrared light to a pyroelectric sensing unit located above the MEMS galvanometer. This pyroelectric sensing unit includes two differentially connected pyroelectric sensing elements S1 and S2, a sensing window covering the pyroelectric sensing elements S1 and S2, and signal amplification and filtering circuitry. The sensing window is a silicone protective film. The MEMS galvanometer S4 includes a wavelength-selective reflector capable of reciprocating around its equilibrium position along its axis of symmetry under control signal drive. Figure 3 As shown. The wavelength-selective mirror includes a highly reflective substrate layer and a wavelength modulation layer composed of multiple dielectric thin films superimposed thereon. Figure 4 The reflection coefficient spectrum of the wavelength-selective reflector used in the MEMS galvanometer is presented. This reflector consists of an aluminum substrate with multiple periodically distributed dielectric films. The dielectric films are formed by alternating periodic stacking of high and low refractive index materials to create a high-reflectivity distributed Bragg reflector structure. Each dielectric film is 2.5 micrometers thick, and the two dielectric materials used are germanium (Ge) and zinc sulfide (ZnS). As shown in the figure, the reflector exhibits nearly 100% emissivity for infrared light with wavelengths around 10 micrometers, which is the primary infrared radiation band emitted by the human body. For infrared light outside this band, the reflectivity decreases rapidly. The design of the wavelength-selective reflector helps filter out interference from environmental thermal noise.

[0024] When the MEMS galvanometer is in a certain position, it reflects only a portion of the infrared radiation from the detection area segmented by the Fresnel lens to the pyroelectric sensing unit. When it is in an equilibrium position, its reflective surface forms a 45-degree angle with the central axis of the Fresnel lens, at which point the central detection area segmented by the Fresnel lens becomes the effective detection area. Through its reciprocating rotation, it completes the scanning of all detection areas. It is worth noting that, through this scanning method, the infrared radiation from each detection area is incident on the pyroelectric sensing unit at a near-vertical angle, which further optimizes the sensor's detection sensitivity in all directions. When the human body is stationary, during the MEMS galvanometer scanning process, the human body will appear and disappear from the sensor's field of view intermittently, thus generating an output signal similar to that of a traditional passive infrared sensor when the human body is moving, thereby achieving the detection of stationary human bodies. When the human body is moving, it is only necessary to control the MEMS galvanometer to change its scanning speed. Only when the speed at which the human body switches detection areas due to movement is exactly synchronized with the scanning speed of the MEMS galvanometer (both speed and direction are the same) will the moving human body be undetectable; otherwise, it can be successfully detected. The greater the speed difference, the higher the detection sensitivity. When the human body moves radially, because this invention uses a scanning scheme, the human body will also appear and disappear in the sensor's field of view at intervals, thereby achieving effective detection.

[0025] Figure 5 The functional block diagram of the passive infrared human body detection sensor is further provided. Besides the Fresnel lens, MEMS galvanometer, and pyroelectric sensing unit mentioned above, it also includes an AD conversion circuit and a microcontroller (MCU) unit. The analog signal output from the pyroelectric sensing unit is connected to the input terminal of the AD conversion circuit via PCB traces. After being converted into a digital signal by the AD conversion circuit, it is sent to the microcontroller (MCU) unit through a data bus interface. The MCU unit runs an intelligent judgment algorithm and connects to the MEMS galvanometer through a control interface to control the rotation of its reflector, thereby achieving scanning and judgment of the detection area. All functional modules are assembled in a housing. The Fresnel lens is mounted at one end of the housing opening. The MEMS galvanometer is installed at the focal point of the Fresnel lens and fixed to the housing by a bracket structure. The pyroelectric sensing unit, AD conversion circuit, and microcontroller (MCU) unit are assembled on a control circuit board, which is fixed to the housing by mounting supports and screws. The sensing window of the pyroelectric sensing unit faces the MEMS galvanometer, and its normal direction is perpendicular to the central axis of the Fresnel lens.

[0026] The description of this utility model is given for illustrative purposes only and is not intended to be exhaustive or to limit the utility model to the disclosed forms. The embodiments were chosen and described to better illustrate the principles and practical applications of this utility model, and to enable those skilled in the art to understand this utility model and design various embodiments with various modifications suitable for specific applications. All new embodiments implemented through simple variations, modifications, equivalent substitutions, or improvements within the basic concept, construction principles, and spirit of this utility model should be included within the scope of protection of this utility model. For example, the present utility model uses a MEMS galvanometer to achieve one-dimensional scanning of the infrared detection area, which is sufficient for detecting both stationary and moving objects in most application scenarios. However, based on the concept of this utility model, a second MEMS galvanometer can be added above the existing MEMS galvanometer to achieve two-dimensional scanning. The scope of this utility model is defined by the appended claims.

Claims

1. A passive infrared human body detection sensor, characterized by, The passive infrared human body detection sensor comprises a shell for protecting and fixing internal components; a Fresnel lens assembled at the open end of the shell for converging external infrared radiation and dividing the detection area of the passive infrared human body detection sensor; a MEMS scanning mirror assembled at the focal point of the Fresnel lens and fixed on the shell through a support structure; a control circuit board fixed on the mounting pillar of the shell by screws, on which a pyroelectric sensing unit, an AD conversion circuit and a microcontroller MCU unit are assembled, wherein the pyroelectric sensing unit comprises two pyroelectric sensitive units, an induction window covering the pyroelectric sensitive units, and a signal amplification and filtering circuit; the induction window of the pyroelectric sensing unit faces the MEMS scanning mirror, and the normal direction thereof is perpendicular to the central axis of the Fresnel lens.

2. The passive infrared human detection sensor of claim 1, wherein, The induction window is a layer of silica gel protective film.

3. The passive infrared human detection sensor of claim 1, wherein, The MEMS scanning mirror comprises a wavelength-selective mirror capable of reciprocating rotation around its symmetric axis near its equilibrium position under the driving of a control signal.

4. The passive infrared human detection sensor of claim 3, wherein, The angle between the mirror surface of the wavelength-selective mirror at its equilibrium position and the central axis of the Fresnel lens is 45 degrees.

5. The passive infrared human detection sensor of claim 3, wherein, The wavelength-selective mirror comprises a high-reflectivity base layer and a wavelength-modulating layer composed of a plurality of dielectric thin films stacked thereon.

6. The passive infrared human detection sensor of claim 5, wherein, The base layer is composed of aluminum metal, and the plurality of dielectric thin films are composed of high and low refractive index dielectric materials stacked alternately and periodically, and the thickness of each dielectric film is 2.5 microns.

7. The passive infrared human detection sensor according to any one of claims 1 to 6, characterized in that The analog signal output by the pyroelectric sensing unit is connected to the input end of the AD conversion circuit through PCB wiring, and the output of the AD conversion circuit is connected to the microcontroller MCU unit through a data bus interface; the microcontroller MCU unit runs an intelligent decision algorithm, controls the rotation of the mirror of the MEMS scanning mirror through a control interface, and realizes the scanning and decision of the detection area.

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