For underwater inspection cameras to work stably in complex underwater environments, the core prerequisite is to overcome the two major technical challenges of "waterproofing" and "pressure resistance". From daily inspections in shallow waters to extreme exploration in thousand-meter-deep seas, every increase in water depth imposes higher requirements on the camera's structural design. Waterproof design must prevent any water molecules from penetrating into the camera's interior to avoid short circuits and component damage; pressure-resistant design must resist the compression and deformation of the camera body caused by high pressure in deep water, ensuring the stability of the optical system and mechanical structure. These two functions work in synergy to jointly build a "survival defense line" for underwater inspection cameras, and their technical details can be analyzed from the following five core dimensions:
1. Waterproof Sealing Design: Multi-Layer Protection to Create a "Water-Free Zone"
Waterproof sealing is the basic guarantee for underwater inspection cameras. It is necessary to adopt differentiated sealing solutions according to the structural characteristics of different parts of the camera body, forming a sealing system of "multi-layer protection and no dead-angle blocking".
(1) Overall Shell Sealing: Dual Control from Material to Process
The camera shell is the first line of defense against water. Mainstream designs use high-strength engineering plastics (such as PC/ABS alloy) or corrosion-resistant metal alloys (such as titanium alloy, 316L stainless steel). These materials not only have excellent impact resistance but also can be seamlessly formed through precision injection molding or CNC machining, reducing sealing risks caused by splicing gaps. Taking deep-sea inspection cameras as an example, the shell adopts an integrated titanium alloy forging process, with only necessary openings such as lens windows and data interfaces retained, and the rest of the parts are complete metal structures, reducing the risk of water leakage from the source.
At the same time, the surface of the shell will undergo special coating treatment, such as polytetrafluoroethylene (PTFE) coating or ceramic coating. On the one hand, it enhances the seawater corrosion resistance of the material, avoiding shell aging and reduced sealing performance due to long-term immersion; on the other hand, it improves surface smoothness, reduces water resistance, and facilitates the camera's flexible movement underwater.
(2) Key Interface Sealing: Dual Protection of "Dynamic + Static"
The camera's data interfaces (such as HDMI, USB), charging interfaces, etc., are weak points in waterproofing and need to cope with both "static sealing" (long-term waterproofing when not plugged in) and "dynamic sealing" (temporary waterproofing during plugging and unplugging).
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Static Sealing: Dual O-ring rubber seals (mostly made of oil and water-resistant nitrile rubber or fluororubber) are used to form two annular sealing belts on the fitting surface of the interface and the shell. The compression amount of the seal ring is controlled between 20%-30%, which not only ensures tight fitting but also avoids accelerated aging caused by excessive compression. Some high-end cameras also fill waterproof glue (such as epoxy resin glue) on the outside of the seal ring, forming a dual static protection of "seal ring + waterproof glue". The waterproof level can reach IP68 and above, and it can be soaked in 1.5 meters of water for a long time without leakage.
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Dynamic Sealing: For interfaces that need frequent plugging and unplugging, a self-sealing valve structure is designed. A spring-loaded sealing plug is built into the interface. When the plug is not inserted, the sealing plug fits tightly against the inner wall of the interface under the action of spring force to block water flow; when the plug is inserted, the plug pushes the sealing plug to compress the spring, and at the same time, the seal ring between the outer wall of the plug and the inner wall of the interface forms a real-time seal, maintaining a waterproof state during the plugging and unplugging process. This design is common in shallow-water inspection cameras that require real-time data transmission, meeting the demand for high-frequency data export.
(3) Lens Window Sealing: Balancing Light Transmittance and Sealing Performance
The lens window must not only ensure high transmittance of optical signals but also achieve strict sealing, and its design needs to balance "light transmittance" and "sealing performance". The mainstream solution uses high-transmittance quartz glass as the window material. Quartz glass has a light transmittance of more than 92%, high hardness, and wear resistance, which can maintain stable optical performance for a long time.
In terms of sealing method, a vacuum welding + silicone seal ring composite process is adopted: first, the quartz glass and the metal flange are vacuum-welded to form a high-strength, gap-free connection; then the welded flange is connected to the camera shell through a silicone seal ring. The fitting surface of the flange and the shell is precision-ground, with a flatness error controlled within 0.005mm, ensuring uniform pressure on the seal ring and achieving dual protection of "welding leak-proof + seal ring leak-proof". This design can avoid the problem of glue aging and falling off caused by long-term immersion in traditional glue bonding, and is suitable for long-term inspection in deep-sea high-pressure environments.
2. Pressure-Resistant Structural Design: A "Rigid Frame" to Resist High Pressure
For every 10 meters increase in water depth underwater, the pressure increases by 1 standard atmosphere (about 0.1MPa). The pressure in the thousand-meter-deep sea can reach more than 100MPa, which is equivalent to applying a weight of 10 kilograms on an area of 1 square centimeter. If the pressure-resistant design is insufficient, the camera will experience problems such as shell deformation, lens extrusion and deviation, and internal component damage. Therefore, it is necessary to build a "rigid frame" that can resist high pressure through "structural optimization + material strengthening".
(1) Body Structure: Combining Bionic Design and Mechanical Optimization
Some cameras draw on the pressure-resistant structure of deep-sea organisms (such as the skeletal structure of deep-sea snailfish) and adopt a sandwich design of "hard outside and soft inside": the outer layer is a high-strength metal shell that bears the main water pressure; the inner layer is an elastic buffer layer (such as silicone foam) that wraps the internal circuits and optical components. When the outer shell is squeezed by high pressure, the buffer layer can absorb the pressure through slight deformation, preventing the internal components from directly bearing high-pressure impact.
At the same time, reinforcing ribs are set inside the body. Finite element analysis software is used to simulate the pressure distribution under different water depths, and cross-shaped or grid-shaped reinforcing ribs are added to the weak parts of the body (such as around the lens window and battery compartment) to enhance the local structural strength. Taking a 500-meter water depth inspection camera as an example, through the reinforcing rib design, the thickness of the body shell is reduced from 15mm to 10mm, which ensures the pressure-resistant performance while reducing the body weight and improving underwater flexibility.
(2) Optical System Pressure Resistance: Dual Protection of Fixation and Buffering
The lens and image sensor are the core of the optical system. Even slight deviations under high pressure can lead to blurred imaging, so it is necessary to design a pressure-resistant fixing structure for them.
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Lens Fixation: A metal lens barrel + thread locking method is adopted. The lens assembly and the lens barrel are connected through precision threads, and the thread gap is controlled between 0.001-0.003mm to prevent the lens from loosening under high pressure; the lens barrel is fixed to the camera shell through a rigid bracket, and the bracket material is titanium alloy to ensure that the lens always maintains coaxiality with the image sensor under high pressure, with a deviation of no more than 0.005mm.
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Image Sensor Buffering: The image sensor is connected to the main board through a flexible printed circuit (FPC), and an ultra-thin silicone buffer pad (thickness 0.5-1mm) is pasted on the bottom of the sensor. When the body is slightly deformed by high pressure, the buffer pad can absorb the stress, avoiding damage to the sensor caused by rigid connection; at the same time, a metal protective cover is set around the sensor to prevent external impurities from squeezing the sensor surface.
(3) Internal Cavity Pressure Resistance: Synergy of "Active Balance" and "Passive Pressure Bearing"
The camera has internal cavities such as battery compartments and circuit compartments. If the cavity is in a sealed state, high pressure will cause excessive pressure difference between the inside and outside, leading to shell deformation. Therefore, it is necessary to adopt a cavity treatment scheme of "active balance" or "passive pressure bearing":
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Active Balance: Suitable for cameras with a water depth of more than 300 meters. A pressure balancer (such as an elastic capsule filled with hydraulic oil) is placed in the internal cavity. When the external water pressure increases, the capsule is compressed, the volume of hydraulic oil decreases, and the pressure in the internal cavity increases accordingly, maintaining balance with the external water pressure and avoiding the extrusion of the body by the internal and external pressure difference. This design is common in inspection cameras equipped with deep-sea ROVs and can achieve real-time pressure balance at a water depth of 1000 meters.
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Passive Pressure Bearing: Suitable for shallow-water cameras (water depth within 100 meters). The internal cavity is designed to be "semi-open" and connected to the outside through a waterproof and breathable membrane. The breathable membrane allows air molecules to pass through but blocks water molecules. When the pressure difference between the inside and outside changes, air can enter and exit the cavity through the breathable membrane to achieve pressure balance while preventing water ingress. This design has low cost and simple structure, and is suitable for daily shallow-water inspection scenarios.
3. Special Environment Adaptation: Enhanced Design to Cope with Extreme Underwater Conditions
In addition to conventional waterproof and pressure-resistant requirements, some underwater inspection scenarios also face extreme conditions such as low temperature, corrosive liquids, and sediment impact. It is necessary to carry out targeted strengthening on the basis of the basic design to ensure the camera's adaptability.
(1) Low-Temperature Environment Protection: Combination of Anti-Freezing Materials and Heating Systems
In polar scientific expeditions or high-latitude deep-sea inspections, the water temperature can be as low as -2℃. Ordinary rubber seals will become hard and lose elasticity due to low temperature, leading to seal failure; battery capacity will also decrease significantly due to low temperature. To address this problem, low-temperature resistant materials are used in the design: the seal ring is made of ethylene propylene diene monomer (EPDM), which has a minimum service temperature of -40℃ and can still maintain good elasticity; a flexible heating sheet (such as a polyimide heating sheet) is pasted inside the shell, and the internal temperature is monitored in real time through a temperature sensor. When the temperature is lower than 5℃, the heating sheet starts automatically, maintaining the internal temperature between 10-20℃ to ensure the normal operation of the battery and circuit.
(2) Corrosive Environment Protection: Full-Body Anti-Corrosion Treatment
In environments with strong corrosion such as industrial wastewater pipelines and mariculture areas, the camera needs to resist the erosion of acid-base liquids and microbial adhesion. A "full-body anti-corrosion" solution is adopted in the design: the shell is made of 316L stainless steel (which has better acid and alkali corrosion resistance than ordinary stainless steel), and the surface is subjected to passivation treatment or polyurea coating spraying to enhance corrosion resistance; internal circuit components are subjected to anti-corrosion packaging, such as immersing the PCB board in epoxy resin to form a sealed protective layer; the interface seal ring is made of fluororubber, which has much better chemical corrosion resistance than ordinary rubber and can be used in liquids with a pH value of 1-14 for a long time.
(3) Sediment Impact Protection: Wear-Resistant Structure and Diversion Design
In water areas with high sediment content such as rivers and ports, the camera is easily impacted by sediment, resulting in lens wear and shell scratches. In the design, the lens window uses sapphire glass (with a hardness second only to diamond), and the surface hardness can reach Mohs level 9, which can resist the friction and wear of sediment; a streamlined deflector is set at the front of the body to guide water flow and sediment to flow from both sides of the body, reducing direct impact; ceramic wear-resistant patches are pasted on the easily worn parts of the shell (such as the bottom and sides) to further improve the impact resistance and extend the service life of the camera.
4. Waterproof and Pressure-Resistant Performance Testing: "Strict Assessment" to Simulate Real Scenarios
Any waterproof and pressure-resistant design needs to be verified through strict performance testing to ensure reliable operation in practical applications. The testing process covers two major stages: "laboratory simulation testing" and "field scenario testing", covering all scenarios from shallow waters to deep seas.
(1) Laboratory Simulation Testing: Precise Control of Environmental Parameters
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Waterproof Performance Testing: Using IP waterproof level testing equipment, the camera is placed in a pressure chamber with different water depths to simulate a pressure of 1.5 times the design water depth (for example, a camera with a design water depth of 100 meters has a test water depth of 150 meters), soaked continuously for 24-72 hours, and after being taken out, check whether there is water inside, and at the same time test whether the circuit function and imaging quality are normal. Some high-end cameras also conduct "thermal cycle waterproof testing" to maintain a waterproof state in a temperature cycle of -20℃ to 60℃ to verify the impact of temperature changes on sealing performance.
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Pressure-Resistant Performance Testing: A high-pressure pressure chamber is used to gradually increase the pressure inside the chamber to 1.2 times the design pressure (for example, a camera with a design pressure of 10MPa has a test pressure of 12MPa), maintain the pressure for 1 hour, and monitor the body deformation through a high-precision displacement sensor (the deformation is required to be no more than 0.1mm), and at the same time check whether the lens is offset and whether the internal components are damaged. After the test, a "repeated pressure test" is also required to simulate the pressure changes during the camera's multiple diving and ascending processes to ensure the stability of the sealing and pressure-resistant performance.
(2) Field Scenario Testing: Verifying the Reliability of Practical Applications
After passing the laboratory test, field tests need to be conducted in real underwater environments: shallow-water tests select scenarios such as rivers and lakes to verify the camera's waterproof performance under turbid water and water flow impact; deep-water tests are conducted by carrying ROVs or human-occupied vehicles (HOVs) to conduct actual inspections in the deep sea of 500 meters to 1000 meters, recording the camera's imaging quality, data transmission stability, and sealing status after long-term immersion. For example, a deep-sea inspection camera conducted a field test at 10,900 meters in the Mariana Trench, working continuously for 72 hours with no abnormalities in waterproof and pressure-resistant performance and clear imaging, verifying its reliability in extreme environments.
5. Technology Development Trend: Lighter, Thinner, and More Intelligent Waterproof and Pressure-Resistant Design
With the upgrading of underwater inspection needs, the waterproof and pressure-resistant design is developing towards the direction of "lightweight, integrated, and intelligent". In the future, new composite materials (such as carbon fiber-reinforced composite materials) will gradually replace traditional metal shells. While ensuring pressure-resistant performance, the body weight will be reduced by more than 30%, improving the camera's portability and underwater flexibility; intelligent sealing monitoring technology will be applied, with humidity sensors and pressure sensors installed inside the camera to monitor the sealing status and internal and external pressure differences in real time. Once signs of seal failure (such as increased humidity and abnormal pressure difference) appear, early warning signals will be sent to the ground terminal in time to facilitate timely equipment recovery and reduce losses; in addition, modular waterproof design will become mainstream. The camera's lens module, battery module, and data module can be independently disassembled and replaced, and each module has independent waterproof and pressure-resistant capabilities, which not only reduces maintenance costs but also flexibly combines modules according to different inspection needs, improving the versatility of the equipment.
