Annular magnetic device

Abstract

An annular magnetic device is characterized in that the annular magnetic device is provided with a first shell and a magnet module; the first shell is in a closed ring shape or a ring shape with a notch and is provided with a first side face and a second side face, and the first side face is exposed. The first shell is made of a conductor, and the resistivity rho of the first shell is not less than 9.5 * 10 <-8 > omega.m < 2 > / m; and the magnet module is arranged in an area close to the second side surface.

Description

Technical Field

[0001] The present invention relates to a shell implementation method for a magnetic attraction device in a wireless charging system for magnetic attraction positioning with an annular magnetic field, and in particular to solving the problem that a shell made of a conductor will become seriously hot during wireless charging, solving the problem that only a low-power wireless charging mode can be entered but not a high-power wireless charging mode, and solving the problem that the mechanical strength of the existing shell using a notched ring-shaped conductor as the shell is weak, resulting in easy deformation of the shell. Background Art

[0002] The MagSafe wireless charging system released by Apple Inc. in the United States, by setting a ring-shaped magnet module outside the coil of the wireless charging device, can achieve precise alignment and temporary fixation between wireless charging devices, solving the most common consumer complaints in wireless charging applications, "misalignment, failure to charge, and slow charging", at the lowest cost. Therefore, there are hundreds of millions of users worldwide, almost all of whom use mobile phone cases with MagSafe-type ring-shaped magnet functions to protect MagSafe-type mobile phones. It also further leads other brand mobile phone companies and other consumer and civilian product companies to launch products compatible with the MagSafe wireless charging system. For example, China's OPPO company launched a mobile phone case with a ring-shaped magnet module for its FindX series of mobile phones, which enables the FindX series of mobile phones to support the MagSafe wireless charging function after wearing this case.

[0003] Some MagSafe protective cases or MagSafe product shells have two parts, namely a first shell and a second shell, wherein the first shell is a closed or notched ring-shaped metal, which serves as a partially exposed surface of the mobile phone protective shell to cover and protect the fragile magnet module. In the following text, the metal shell specifically refers to the first shell made of metal material.

[0004] There are two reasons why metal is used as the first shell: the first reason is that the metal shell can be made thinner than the plastic shell, so that when a thinner magnet module is used, the same magnetic field adsorption force as when a thicker plastic shell plus a thicker magnet module is used, thereby significantly reducing the thickness of the protective shell and reducing material costs; the second reason is that some metal shells will be installed with hinges next to them, and the other side of the hinge is fixed to the main shell of the protective cover or product shell. When the metal shell is flipped outward, it can be formed as a support frame to support the smartphone or related products on the desktop in a posture similar to a desktop photo frame, which is convenient for consumers to watch the screen or do other things. The metal shells used in mobile phone protective cases and other products currently sold on the market are basically made of aluminum alloy. The reason is that aluminum alloy is easy to process, low cost, and has a rich selection of external surface processes. In addition, some grades of aluminum alloy have the hardness and toughness that meet application requirements.

[0005] Because the outer diameter of the wireless charging coil of the MagSafe wireless charging system is about 41 mm, and the inner diameter of the magnet module is about 46 mm, the inner diameter D of the metal shell will be slightly smaller than 46 mm and larger than 42 mm, protecting the magnet module while reducing interference with the wireless charging magnetic field. However, during the wireless charging process, a certain proportion of the alternating magnetic field flux generated by the wireless charging transmitting coil will inevitably pass through the inner ring area of ​​the metal shell, thereby generating an induced current on the metal shell, and then generating a certain amount of heat.

[0006] According to actual tests, the induced heat on the closed-loop metal shell made of aluminum alloy is about 1w, which produces a temperature rise of about 15℃ on the mobile phone case made of PC as the main material. If the temperature of the mobile phone itself is 35℃, then the temperature of the metal shell is 50℃, and the user will feel a little hot and uncomfortable.

[0007] Therefore, in recent years, the metal shells of some new products have been changed to a C-shaped ring structure with a gap, which reduces the induced heat and the resulting temperature rise by almost doubling the channel resistance of the induced current, but there will still be 0.5W of induced heat and a temperature rise of about 9°C. Moreover, the mechanical strength of the ring structure with a gap as a bracket will be significantly weaker than that of the closed ring structure, so it will deform after a period of use, affecting the appearance and user experience, and even the speed of its own damage will be significantly faster than that of the closed ring structure, increasing user costs.

[0008] Using aluminum alloy as the material for the metal shell has another adverse effect: it interferes with the communication between Apple's MagSafe wireless charger and MagSafe mobile devices, causing Apple's MagSafe wireless charger to be unable to accurately determine whether there are metal foreign objects between it and the MagSafe mobile device, or the mobile device protective cover is very thick, so it can only enter low-power wireless charging mode to charge the MagSafe mobile device, resulting in slow charging speed and poor user experience.

[0009] Therefore, it is necessary to select a material that is easy to mass-produce at low cost, has high hardness and toughness, does not generate obvious induced heat, and does not interfere with communications to replace the aluminum alloy metal shell to make a new shell. Summary of the invention

[0010] The present invention discloses a ring-shaped magnetic device, which is characterized by comprising a first shell and a magnet module; the first shell is a closed ring or a ring with a gap, and has a first side surface and a second side surface, and generally, the first side surface is exposed; the material of the first shell is a conductor and the resistivity ρ is not less than 9.5X10 -8Ω·m2 / m; the magnet module is arranged in an area close to the second side surface.

[0011] Make sure the first shell is a conductor and the resistivity is not less than 9.5X10 -8 The reasoning, practical testing and theoretical calculation of Ω·m2 / m are divided into the following steps: First of all, among the existing civilian materials, only metal materials meet the requirements of low cost, high hardness, high toughness, easy processing, and rich external surface processing. Metal materials are bound to be conductive, and under the same magnetic field environment, the higher the resistivity, the smaller the induced current and thus the less induced heat.

[0012] Then, it is necessary to calculate the appropriate lower limit of the resistivity of metal materials based on the principles of physiology, thermodynamics, electromagnetic induction, electrical principles, etc.: The first step is to set the target temperature rise T, and then calculate the surface area S according to the size of the metal shell, as well as the thermal conductivity λ of the material around the metal shell, the average thickness L of the material around the metal shell and the ambient temperature t, and substitute them into the formula of conduction heat dissipation to obtain the heat J generated by the first shell.

[0013] According to the statistical data of human temperature perception in physiology, when a person touches a metal object over 45°C, he or she will feel hot and have psychological discomfort. The actual ambient temperature range is generally 10~40°C. The higher value of 40°C is taken as the ambient temperature t, and the value of T is recommended to be less than 5°C. Of course, the lower the temperature rise, the better the user experience.

[0014] The metal shell inner diameter D = 45mm, outer diameter = 55mm, thickness = 1.5mm, and the surface area of ​​the metal shell that contacts the main body of the mobile phone case is 12.5cm 2 .

[0015] The material of the main part such as the mobile phone protective case is a polymer material, and its thermal conductivity λ is 0.1-0.4W / (m·K). The λ in this paper is 0.2W / (m·K) of the PC material commonly used in the main part of the mobile phone protective case.

[0016] The material thickness of the main parts such as the mobile phone protective shell and the thickness L of the PC material equivalent to the combination of the mobile phone glass shell and the internal battery is about 4mm.

[0017] Therefore, applying the heat conduction formula J=λ×S×T / L, we can see that J must be less than 0.25W to achieve a temperature rise T of 5°C.

[0018] The second step is to cut a tiny opening in the closed-loop metal shell on the existing mobile phone case to make it a C-shape that is close to a closed loop, and retain the original magnet module. The modified mobile phone case is then put on a suitable mobile phone and then attached to the MagSafe wireless charger for charging. The effective value V of the AC voltage at both ends of the C-shape is detected by an oscilloscope, and V is 55mV when the MagSafe power is 15W.

[0019] The third step is to substitute the heat J and voltage V into the heat formula related to Ohm’s law, J=V 2 / R, the resistance R on the induced current path in the first shell is obtained to be 0.0121Ω.

[0020] The fourth step is to substitute the resistance R and the inner diameter D of the first shell into the resistance and resistivity conversion formula R=ρ*D*π (closed-loop metal shell) or R=ρ*D*π*2 (ring-shaped metal shell with a gap), and the resistivity ρ=9.5X10 -8 Ω·m2 / m (closed-loop metal housing) or ρ=4.25X10 -8 Ω·m2 / m (ring-shaped metal shell with a gap). Considering that the ring-shaped metal shell with a gap has obvious defects in aesthetics and mechanics compared with the closed-loop metal shell, ρ=9.5X10 -8 Ω·m2 / m.

[0021] The following is a comparison table of the heat generated and temperature rise of three materials suitable for metal shells: Metal material Resistivity (Ω·m2 / m) HV / HB hardness Heat generated (W) Temperature rise (℃) Metal shell temperature at 40℃ (℃) 7025 Aluminum Alloy <![CDATA[2.86x10 -8 ]]> HB180 1.02 16.3 56.3 304 Stainless Steel <![CDATA[7.3x10 -7 ]]> HV220 0.04 0.64 40.64 Zirconium-based amorphous metal <![CDATA[2.2x10 -6 ]]> HV520 0.013 0.21 40.21 As can be seen from the above table, 304 stainless steel and zirconium-based amorphous alloy can both meet the requirements, and the material of the first shell can be selected from 304 stainless steel, amorphous metal, especially zirconium-based amorphous alloy.

[0022] However, 304 stainless steel is not suitable for use because of the following problems: Some users will have an immune reaction to nickel metal, and 304 stainless steel has had a large number of nickel immune events in history. Only by performing secondary processing on the stainless steel surface can the probability of nickel immune events be reduced, which will also increase costs.

[0023] Making metal shells with 304 stainless steel requires a finishing process involving precision casting + CNC, which is inefficient and costly, and is not suitable for use in hundreds of millions of consumer products each year.

[0024] There are very few optional surface treatment processes for 304 stainless steel, only polishing, sandblasting, brushing and overall electroplating, which is not suitable for the increasingly common social demand for personalization.

[0025] On the other hand, zirconium-based amorphous alloys do not have the above problems: Medically proven, zirconium-based amorphous alloys are friendly to the human body and will not cause immune response.

[0026] The BMG process can produce zirconium-based amorphous alloys by one-step injection molding, which is highly efficient and low-cost.

[0027] There are many optional surface treatment processes for zirconium-based amorphous alloys, which are basically the same as those for aluminum alloys.

[0028] Furthermore, because the resistivity of zirconium-based amorphous alloy is three times that of 304 stainless steel, its shielding, interference, and attenuation effects on communications are also much weaker. According to actual tests, zirconium-based amorphous alloy will not interfere with the communication between Apple's MagSafe wireless chargers and MagSafe mobile devices, and can achieve the MagSafe wireless chargers produced by Apple smoothly entering the high-power wireless charging mode when the thickness of the metal shell using zirconium-based amorphous alloy is reasonable.

[0029] Therefore, although the first shell of the annular magnetic device disclosed in the present invention can be made of 304 stainless steel, from the perspective of practical feasibility, zirconium-based amorphous alloy is a better choice.

[0030] Since the magnet module of the MagSafe system has an inner diameter of about 46 mm and an outer diameter of about 54 mm, and there is a non-magnetic area near the circumference of about 50 mm in diameter, and the magnetic field directions inside and outside the circumference are perpendicular to the circumferential plane and opposite, the magnet module in the annular magnetic device disclosed in the present invention has two optional solutions: The inner diameter is about 50 mm, the outer diameter is about 54 mm, and the magnetic field direction is perpendicular to the plane of the ring.

[0031] It is basically the same as the magnet module of the MagSafe system: the inner diameter is not less than 46mm, the outer diameter is approximately 54mm, there is a non-magnetic area near the circumference of approximately 50mm in diameter, and the direction of the magnetic field on both sides of the circumference is perpendicular to the plane of the circumference and opposite.

[0032] Both of the above solutions can use the magnetic field to adsorb MagSafe system devices and basically do not interfere with wireless charging. However, the magnetic field adsorption force of the first one is far inferior to that of the second one.

[0033] Therefore, in order to protect the fragile magnet module by surrounding it, the inner diameter of the first shell of a ring-shaped magnetic device disclosed by the present invention is not greater than 49 mm. Furthermore, in order to minimize the magnetic flux of the alternating magnetic field passing through the first shell during wireless charging, the inner diameter of the first shell should be as large as possible. Therefore, it has been experimentally verified that the optimal choice for the inner diameter of the first shell is 44.5~46.5 mm.

[0034] In summary, the annular magnetic device disclosed in the present invention uses a zirconium-based amorphous alloy instead of aluminum alloy to make the first shell, thereby achieving the beneficial effect of reducing the induced heat generated by the first shell during wireless charging from any to almost no heat, and then the user's body sensation from feeling hot to not feeling it. Instruction Manual

[0035] Figure 1 It is a schematic structural diagram of the first embodiment of the present invention when used in a mobile phone protective cover.

[0036] Figure 2 It is a schematic diagram of the magnetic flux and induced current of the magnetic field passing through the first shell when the MagSafe system is wirelessly charging according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention and do not limit the scope of application of the present invention. For ordinary technicians in the field, the present invention can be applied to other similar scenarios based on these drawings without creative work; as shown in this specification and claims, unless the context clearly indicates an exception, the words "one", "a", "a kind" and / or "the" do not specifically refer to the singular, but may also include the plural. In general, the terms "including" or "comprising" only indicate that the steps and elements that have been clearly identified are included, and these steps and elements do not constitute an exclusive list, and the method or device may also include other steps or elements. The term "based on" means "based at least in part". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment".

[0038] exist Figure 1 In the embodiment, the first shell 1 is fixed to the outside of the mobile phone protective shell 3 whose basic structure is a polymer material, and the first shell 1 and the mobile phone protective shell 3 wrap the magnet module 2. Figure 2 In the wireless charging transmitting coil 41 of the MagSafe system, an alternating magnetic field 51 is generated to induce the receiving coil 42. A part of the magnetic flux of the alternating magnetic field 51 passes through the first shell 1, so the first shell 1 generates an induced alternating current 52, thereby Q=V 2 t / R generates heat, where Q is heat, t is time, and R is the annular resistance value of the first shell 1. When the relative magnetic permeability of the first shell 1 is about 1, the magnetic flux of the alternating magnetic field 51 passing through the first shell 1 made of different materials is basically the same, so when the frequency of the alternating magnetic field 51 is also unchanged, the value of Q is inversely proportional to the resistance value R, so the Q value can be reduced by simply increasing the R value.

Claims

1. A ring-shaped magnetic device, characterized in that: It has a first shell and a magnet module; The first shell is a closed ring or a ring with a gap, and has a first side surface and a second side surface, and the first side surface is exposed; The material of the first shell is a conductor and the resistivity ρ is not less than 9.5X10 -8 Ω·m2 / m; The magnet module is arranged in a region close to the second side surface.

2. The annular magnetic device according to claim 1, characterized in that: The conductor is made of stainless steel.

3. The annular magnetic device according to claim 1, characterized in that: The conductor is an amorphous metal.

4. The annular magnetic device according to claim 2, characterized in that: The amorphous metal is a zirconium-based amorphous alloy.

5. A ring-shaped magnetic device according to claims 1-4, characterized in that: The inner diameter D of the first shell is not greater than 49 mm.

6. The annular magnetic device according to claim 5, characterized in that: The inner diameter D of the first shell is in the range of 44.5 to 46.5 mm.

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