The principle and application of sound sensor

A sound sensor is a device that can convert sound signals into electrical signals or vice versa. In the former case, they are called input sound sensors, and microphones are an example of this. In the latter case, they are called output sound sensors, speakers being an example. As a sensor that can detect, measure and display sound waveforms, sound sensors are widely used in daily life, military, medical, industry, territorial waters, aerospace, etc., and have become an indispensable part of the development of modern society.

composition

The sensor is a built-in condenser electret microphone sensitive to sound. The electret microphone is mainly composed of two parts - the acoustic-electric conversion part and the impedance part. The key element of acoustic-electric conversion is the electret diaphragm. It is an extremely thin plastic film on which a thin film of pure gold is evaporated on one side. Then after passing through the high-voltage electric field electret, opposite charges are stationed on both sides. The steamed gold surface of the diaphragm is outward and communicates with the metal shell.

The other side of the diaphragm is separated from the metal plate by a thin insulating gasket. In this way, a capacitor is formed between the evaporated gold film and the metal pole plate. When the electret diaphragm encounters sound wave vibration, it causes the electric field at both ends of the capacitor to change, thus generating an alternating voltage that changes with the sound wave. The capacitance between the electret diaphragm and the metal plate is relatively small. Therefore, its output impedance value is very high, about tens of megohms or more. Such a high impedance cannot be directly matched with an audio amplifier. Therefore, a junction field effect transistor transistor is connected to the microphone for impedance transformation.

Field effect transistors are characterized by extremely high input impedance and low noise figure. Ordinary field effect transistors have three poles: source (S), gate (G) and drain (D). What is used here is a special field effect transistor that combines a diode between the internal source and the gate. The purpose of connecting the diode is to protect the FET when it is impacted by a strong signal. The gate of the field effect transistor is connected to the metal plate. In this way, there are two output lines of the electret microphone. That is, the source S generally uses a blue plastic wire, and the drain D generally uses a red plastic wire and a braided shielding wire connected to the metal case.

principle

The transducer incorporates a sound-sensitive condenser electret microphone. Sound waves vibrate the electret membrane inside the microphone, causing a change in capacitance, which produces a corresponding change in tiny voltage. This voltage is then converted into a voltage of 0-5V, which is accepted by the data collector through A/D conversion and sent to the computer.

Model and its technical indicators

BR-ZS1 sound sensor is an integrated noise monitor with industrial standard output (4~20mA), which complies with noise monitoring standards such as GB3785 and GB/T17181. BR-ZS1 sound sensor is designed for noise testing requirements and supports on-site noise decibel values Real-time display, compatible with the user's monitoring system, fixed-point all-weather monitoring of noise, and alarm limit can be set to alarm if the environmental noise exceeds the standard. The monitor has high precision, strong versatility, and high cost performance.

Technical parameters of BR-ZS1 sound sensor:

Measuring range: 30 ~ 120dB (A)

Frequency range: 20Hz～8kHz

Frequency weighting: A (weighting)

Time Weighting: F (Fast)

Output interface: 4~20mA/RS232 Sensitivity:

Voltage 41.5mV/dB;

Current 0.133mA/dB

Maximum error: 0.5dB

Power supply: 220V mains or 24VDC

Size: 200mm&TImes;104mm&TImes;50mm

application

With the rapid development of sensors, sound sensors have also risen rapidly, and have been applied to daily life, military, medical, industry, territorial waters, aerospace, etc., and have become an indispensable part of the development of modern society.

• Daily life: The sound sensor samples the sound signal and applies it to devices such as microphones, recorders, and mobile phones. There is an audio sensor in the sound-activated lighting lamp. As long as someone makes a friction sound for 1 second, the lighting lamp on the wall will automatically light up for about ten seconds; the voice-activated TV can store the voices of two people.

• Industry: The acoustic wave sensor uses the direct and inverse piezoelectric effects of lead zirconate titanate PZT piezoelectric ceramics to convert between electrical energy and mechanical energy. When an electrical signal is added to the piezoelectric ceramics, mechanical vibrations are generated and ultrasonic waves are emitted. When an obstacle is encountered during air transmission, it is immediately reflected back, and when it acts on its ceramics, an electrical signal will be output, and the distance between the vehicle and the obstacle will be calculated and displayed through the data processing time difference. This sensor is used as a car reversing anti-collision alarm device; most sewing equipment manufacturers have used electronic testing instruments to test where the largest sound source of the machine is generated, and measure the force and vibration of parts.

• Military: Acoustic sensors use sound waves to determine the chemical composition of materials in closed containers to enhance port security; to defend against sniper attacks, the acoustic sensor system can locate and classify sniper firepower and provide the azimuth angle of sniper firepower , elevation angle, range, caliber and error distance.

• Medical: The fiber optic microphone has natural anti-interference ability to the magnetic field and can be used in MRI communication. It is the only microphone that can communicate between the patient and the doctor during the MRI scan. Hearing aids, stethoscopes, measuring pulse, blood pressure, etc.

• Territorial sea:

① US MAVS-3 deep water 3-axis acoustic multi-parameter current measuring instrument

MAVS-3 is a 3-axis acoustic multi-parameter flowmeter using time-differential measurement technology. The 4 acoustic probes of the flow meter provide the average velocity vector value. Programmable segmented recording and triggered recording modes give the flow meter great flexibility. Due to the small geometric size of the probe and the application of time difference measurement technology, the resolution and accuracy of MAVS-3 are unmatched by other flow meters. Therefore, no matter in the range of 2m/s or 10cm/s, the resolution of 0.03cm/s can be guaranteed, and the accuracy can reach 0.3cm/s. In addition, the instrument can also provide parameters such as temperature, conductance, and depth, and the working depth can reach 6000M.

②UK AQUA Deepwater CTD

Using metal titanium as the shell, it can measure conductance, temperature and depth within a depth range of 6000m. The instrument can be installed on underwater towing tools, buoys and anchor equipment, and can also be used for vertical profile measurement. Data recording can adopt self-contained recording or real-time data collection, and the data can also be transmitted to a PC for editing and storage.

summary

The sound sensor can be used to receive sound waves and display the vibration image of the sound, but it cannot measure the intensity of the noise. The sound sensor has a built-in capacitive electret microphone sensitive to sound. The sound wave makes the electret film in the microphone vibrate, causing The change of capacitance produces a corresponding change of tiny voltage, which is then converted into a voltage of 0-5V, accepted by the collector through A/D conversion, and sent to the computer.

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