105 lines
4.0 KiB
Markdown
105 lines
4.0 KiB
Markdown
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$\require{physics}$
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# Abstract
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声表面波就是在表面传播、波矢在面内的波。
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通常使用两个叉指电极(interdigitated electrodes,IDT),通过正向和逆向的压电效应,在一个电极上产生声表面波,经过介质传播,另一个电极上产生电压信号。
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一些需要测量的属性(例如温度)会影响声表面波的性质,从而被检测出来。
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图片来自维基百科。
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![undefined](assets/SAW_device.png)
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# Introduction
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这些微型的传感器(sensor)和执行器(actuator)被称为微机电系统(Microelectromechanical Systems, MEMS)。
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对于生物传感的方面,The devices have the potential to transform a complete wet laboratory into a tiny, miniaturized chip.
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One of the major limitations comes from the requirements of simultaneous sensing and the actuation in an environment
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while engaging with mutually exclusive physics and mechanisms.
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为了解决这些问题,基于声表面波的传感器被提出来了,它们可以同时进行传感和执行。
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这些器件通常被称为 SAW sensors 或者 SAW devices,但它的功能不局限于传感和执行,还包括 filters, oscillators, transformers, etc.
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电到声的转换叫 actuation,声到电的转换叫 sensing。
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SAW sensor 用到了非常多的领域。
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The acoustic devices are responsive to the physical parameters of the species
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that interact with the mechanical properties of the guided waves in the SAW sensors.
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总结来说,要探测的物理参数包括:mass, density, viscosity, elastic modulus, conductivity, temperature, and pressure.
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通常来说,可以通过检测波的传播速度来检测需要的物理参数。按照线性近似可以得到:
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$$
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\dd{V} = \pdv{V}{m}\dd{m} + \pdv{V}{E}\dd{E} + \pdv{V}{M_i}\dd{M_i} + \pdv{V}{e_v}\dd{e_v}
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$$
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但仅仅通过速度,是无法区分这些量导致的变化的,因此需要更多的信息,常用的包括:
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* the change in amplitude of the central frequency
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* the frequency shift of the given frequency input,
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* kurtosis
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* change in phase
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* higher-order frequency peaks to measure nonlinearity
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SAW sensor 的质量可以通过 sensitivity 和 selectivity 来衡量。
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Sensitivity 是指对于某个物理参数的响应程度(而不是直接对测得的电流或电压等的响应程度)。
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以受主和受体的结合为例子,sensitivity 是指多少受主被结合就可以检测出来,而 selectivity 是指其它不是目标的受主的出现是否会影响检测结果。
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# Types of Waves in SAW Devices
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## Rayleigh Waves
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瑞丽波的波矢在面内,由纵波和 shear vertical 模式组成,原子运动轨迹是椭圆形的。仅仅存在于表面,有效深度通常小于波长。
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地震波在远离震源的地表传播时,就是瑞丽波。
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![image-20240104230226306](assets/image-20240104230226306.png)
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#TODO: 更详细的性质
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## Shear Horizontal Waves
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波矢量在面内,原子运动轨迹垂直于波矢且在面内。
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可以深入材料大约几个波长的深度,在生物化学传感中有广泛应用,特别适合用于液体中。还有许多其它优点。
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#TODO: 更多优点
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通常会使用一个 guiding layer 来优化器件的性能,这个 guiding layer 可以使用 SiO2, Si3N4, 和其它多晶材料。
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#TODO: 更多理论
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![image-20240105112520807](assets/image-20240105112520807.png)
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## Lamb Waves
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兰姆波穿透整个材料,相当于将薄膜层作为了一个波导。它分为对称和反对称两种,乍一看有点类似光学的平板波导,只不过这个是机械波。
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![image-20240105113056845](assets/image-20240105113056845.png)
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#TODO: 更详细的理论
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## Love Waves
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在一种介质(薄膜)中传播时可以穿透整个材料(类似于 SH 波),而在另一种介质中传播时只能在表面传播(类似于瑞利波)。
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![image-20240105113614509](assets/image-20240105113614509.png)
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#TODO: 更详细的理论
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# Materials for the SAW Devices
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#TODO
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# Configuration of the Interdigitated Electrodes in the SAW Devices
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#TODO
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# SAW Applications
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#TODO
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# Conclusions
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#TODO
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