案例分析
时间晶体的量子物理视图：用于稳定 the 的 OAV 空气轴承电动式 Shaker 对液滴非平衡物理实验的共振
澳大利亚墨尔本斯威本科技大学的光学科学中心旨在更好地了解液滴在表面弹跳的行为液体浴的脸 通过量子物理透镜.当飞沫受到影响时 到周期性强迫，它们可能开始在流体表面“行走”， ar液滴与流体表面的每次碰撞触发毛细管波的结果,和e 流体表面中的后续梯度驱动液滴的平面运动。该团队将这些液滴描述为“液滴时间晶体”(DTC)，它们是周期性驱动的系统，表现出驱动周期整数倍的持续振荡响应。实验的主要组成部分包括d 电动振动器，OAV 空气轴承 [OAVBX5050]，用于观察和处理实验信息的液槽、液滴打印机和光学成像系统。
使用固定在被动隔振腿上的定制光学平台来消除外部噪音，驱动力由螺栓固定在层饼结构上的电动振动器提供，该结构固定在机器支架上。振动台通过驱动杆连接到 OAV 空气轴承，空气轴承安装在光学平台顶部的铝板上，连接到高纯度压缩空气供应。在将空气轴承滑杆连接到驱动杆之前，将流体槽调平，并将空气轴承组件夹紧到位。设计组件可以在下图中看到。
The Optical Sciences Centre at the Swinburne University of Technology in Melbourne, Australia aimed to better understand the behavior of liquid droplets bouncing on the surface of a fluid bath through a quantum physical lens. When droplets are subject to periodic forcing, they may begin to "walk" on the surface of the fluid, a result of each impact of the droplet with the fluid surface triggering a capillary wave, and the subsequent gradients in the fluid surface driving the planar motion of the droplets. The team characterized these droplets as "droplet time crystals" (DTC), which are periodically driven systems that exhibit a persistent oscillatory response with an integer multiple of the driving period. The main components of the experiment included the electrodynamic shaker, the OAV Air Bearing [OAVBX5050], the fluid bath, the droplet printer, and the optical imaging system used to observe and process the information from the experiments.
Using a custom optical table that rested on passive vibration isolation legs for elimination of external noise, the driving force was provided by an electrodynamic shaker bolted onto a layer cake structure, which rested on machine mounts. The shaker was connected to the OAV Air Bearing through a drive rod, and the air bearing was mounted on an aluminum plate on top of the optical table, connected to a high-purity compressed air supply. The fluid bath was leveled, and the air bearing assembly was clamped in place before the air bearing slider bar was connected to the drive rod. The design assembly can be seen in the below graphic.
The OAV Air Bearing was a crucial component in the assembly. Indeed, the OAVBX5050 was used to reduce the transverse vibrations through stabilization of the entire system due its smooth and ultra-precise frictionless motion. Frictionless motion in the axial direction prevented adverse motion in the transverse plane. The team chose an air bearing with a large enough surface area to maintain the total payload to a minimum, reducing the shaker resonances.
The fluid bath had a fluid containing diameter of 100 mm, with mass totaling to 570 g. It was mounted on an air bearing slider bar and was precisely aligned by tilting the whole optical table using a two-axis digital level. Vibrations of the bath were measured using two piezoelectric single-axis accelerometers. Droplets were introduced onto the fluid bath surface using a droplet printer consisting of a computer-controlled two-axis linear translation stage and a piezoelectric droplet generator. The droplet generator utilized a 35 mm diameter piezoelectric buzzer disk and M6 threaded brass nozzle with 0.1-1.0 mm nozzle size. The fluid was pumped into the generator by a peristaltic pump, and the fluid level was set using a micrometer translation stage. The droplets' motion was tracked via a top view camera and a side view camera.
In the experiment, multiple subsystems were used to control the data acquisition and measurement. A computer was used to generate the driving signal for the shaker and read the accelerometer data, both at a 32 kHz sampling rate. The signals were monitored using a digital storage oscilloscope and a software feedback loop maintained a fixed driving amplitude. A droplet printer was used to deposit droplets onto the fluid surface and two microcontrollers were used to monitor temperature probes and the droplet printer. The cameras were triggered manually and the images were processed manually. However, all subsystems were integrated and controlled by a single workstation. Baseline measurements were performed to characterize the mechanical resonance properties of the shaker and study its dependence on payload. The shaker resonances were found to conform to the expectations and were in good agreement with previous studies.
The laboratory had air conditioning system to maintain 0.5 °C temperature stability, monitored by two PT100 platinum RTD probes and a microcontroller. Calibration was done relative to each other at 21 °C ambient temperature. The fluid used for the experiments was silicone oil with density of 950 kg/m3 and viscosity of 20 cSt at 25 °C. The thermal characterization depicted that the temperature of the fluid and the air remained within the air conditioning system specifications. However, the high-speed imaging light (135 W LED) could generate turbulent air currents and affect the droplet dynamics, so it should only be turned on when necessary. These adverse effects can be eliminated by protecting the fluid bath with enclosures. Continuous measurement of fluid temperature is not necessary unless extreme precision is required.
When the fluid bath vibrated above a certain frequency-dependent amplitude, called the Faraday threshold, Faraday waves emerged on the fluid surface. The authors observed Faraday patterns with square and triangular unit cells that repeated at a lower frequency than the driving frequency of the fluid bath. The authors also introduced droplets onto the fluid surface and observed that they stably bounced in a (2,1) mode, where their center of mass undergoes vertical periodic oscillations at half the driving frequency of the fluid bath. The droplets also supported internal vibrational modes in free space. The authors fixed the driving frequency and amplitude and studied the effect of varying the droplet size on the droplet's bouncing dynamics.
OAV 空气轴承是装配中的关键部件。事实上，OAVBX5050 由于其平滑和超精确的无摩擦运动而被用于通过稳定整个系统来减少横向振动。轴向上的无摩擦运动防止了横向平面上的不利运动。该团队选择了具有足够大表面积的空气轴承，以将总有效载荷保持在最低水平，从而减少振动台共振。
流体浴具有包含直径为100mm的流体，总质量为570g。它安装在空气轴承滑杆上，并通过使用两轴数字水平仪倾斜整个光学平台来精确对齐。使用两个压电单轴加速度计测量浴的振动。使用由计算机控制的两轴线性平移台和压电液滴发生器组成的液滴打印机将液滴引入到流体浴表面上。液滴发生器使用直径为 35 毫米的压电蜂鸣器盘和喷嘴尺寸为 0.1-1.0 毫米的 M6 螺纹黄铜喷嘴。流体通过蠕动泵泵入发生器，并使用千分尺平移台设置液位。通过顶视摄像机和侧视摄像机跟踪液滴的运动。
在实验中，多个子系统被用来控制数据采集和测量。使用计算机生成振动器的驱动信号并读取加速度计数据，两者均以 32 kHz 采样率进行。使用数字存储示波器监测信号，软件反馈回路保持固定的驱动幅度。液滴打印机用于将液滴沉积到流体表面上，两个微控制器用于监控温度探头和液滴打印机。相机是手动触发的，图像是手动处理的。但是，所有子系统都由一个工作站集成和控制。执行基线测量以表征振动器的机械共振特性并研究其对有效载荷的依赖性。发现激振器共振符合预期，与之前的研究非常吻合。
实验室有空调系统以保持 0.5 °C 的温度稳定性，由两个 PT100 铂 RTD 探头和一个微控制器监控。在 21 °C 环境温度下相对于彼此进行校准。用于实验的流体是硅油，其密度为 950 kg/m3，粘度为 20 cSt (25 °C)。热特性描述了流体和空气的温度保持在空调系统规格范围内。然而，高速成像灯（135 W LED）会产生湍流气流并影响液滴动力学，因此只应在必要时打开。这些不利影响可以通过用外壳保护流体浴来消除。除非需要极高的精度，否则无需连续测量流体温度。
当流体浴振动超过特定的频率相关振幅（称为法拉第阈值）时，法拉第波出现在流体表面。作者观察到具有方形和三角形晶胞的法拉第图案，其重复频率低于流体浴的驱动频率。作者还将液滴引入流体表面并观察到它们以 (2,1) 模式稳定地弹跳，其中它们的质心以液浴驱动频率的一半进行垂直周期性振荡。液滴还支持自由空间中的内部振动模式。作者固定了驱动频率和振幅，并研究了改变液滴尺寸对液滴弹跳动力学的影响。
液滴打印机发生器在浴缸上产生任意二维图案的液滴。所得结构由液滴-液滴相互作用确定。这方面的一个例子是液滴的方形格子，5 分钟后，它会转变为三角形格子。这是一个非常重要的现象，因为系统远离法拉第阈值，并且不能仅通过能量守恒或更高的填充率来解释三角形晶格优于正方形晶格的偏好。观察到的行为是由于波介导的液滴之间的多体相互作用和微妙的边界效应之间复杂的、自洽的相互作用。
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TP Simula 2023物理层秒。屏幕截图.水滴时间晶体
本材料基于澳大利亚墨尔本斯威本科技大学光学科学中心支持的工作。