Solutions and Approaches to Enhance Vibration Isolation Strategies for Biophysics

Ambient vibration limits the resolution for all types of microscopes. The vibration diminishes the localizability of features in noticeable ways - an increasing issue for the long acquisition times and reducing scale of current imaging applications.

What is not obvious is the interplay of seismic, cable-borne, mechanical, and acoustic stimuli. Bolting equipment to a generic air-table may not be enough to realize nanoscale stabilities that are required today.

This article provides a review of isolation methods, which range from the classical to the most recent. It also spotlights the under-appreciated factors contributing to system instabilities, and provides suggestions for productive strategies for mitigation.

Conventional Air Isolators

Since the 1970s, the air table has remained a common tool for improving stability. Here, a pressurized diaphragm provides support to the table-top, while also offering a low-friction, weak-spring support that attenuates the high-frequency vibration originating from the floor.

The resulting spring-mass system presents a transmissibility curve with a characteristic resonant frequency (F_res) of 1 - 3 Hz, and amplifying the spectral components near to these frequencies (Figure 1).

Figure 1.Conventional air isolator transmissibility curve

Piezo Technology Addresses Low-Frequency Transmissibility and Amplification

空气隔离器可很好地衰减高频地板振动组件。隔离器在F处的低频传输和放大_resin the 1 - 3 Hz band is problematic for use in advanced imaging techniques.

Piezoelectric technology provides responsive nano-actuation and long-term positional stability of objectives, sample positioners, and scanning probes^[1]. This feature has been utilized in novel isolators that cancel out low-frequency transmitted floor excitation.

In such主动振动取消系统，传感器连续监视和测量地板振动，压电设备会在数字控制下实时实时提供无效力量的扩展和收缩^[2].

Figure 2.High-force piezo stacks

In a unique hybrid technique of particular interest for advanced microscopies, pneumatic isolation elements are combined with high-reliabilitypiezoelectric active nullification technologyto provide better combined isolation.

The strengths of both technologies are utilized in this approach. The piezoelectric active isolation handles the issue of the transmissibility and amplification of the pneumatic component at low frequencies. The pneumatic element takes care of the inevitably finite bandwidth of the active isolation technology (Figure 3).

Figure 3.Comparative transmissibilities for passive vs. hybrid isolation

The Floor Is Only One Source

表是谐音结构。更好的模型将阻尼元素集成到它们中，以减少其对刺激的反应。刺激可能是通过隔离器，电缆，声音或船上来源（包括变压器和风扇）的底层振动的残留物。缓解技术包括：

• Leverage structural nodes
  Mounting isolators on the node-lines of the lowest-order resonant mode can reduce the excitation. (As per Chladni analysis, the node-lines are located approximately at 20% of a rectangular leaf’s length from the short sides of the leaf.) This can also be the location to wrap cables that transmit vibration.
• Reduce coupling of acoustic room-modes
  A box on the table isolates optics from obvious air currents, but acoustic disturbances have to be dealt with differently. A helium-filled covering can reduce the noise spectral density through reduced path fluctuations^[3]. In contrast, airborne disturbances are coupled directly to the isolated platform. For a typical laboratory measuring 10 meters in length, the least longitudinal room mode frequency is f = c / 2L. Taking the speed of sound c to be 340 m/sec, f is approximately 17 Hz. Although this is in subaudible range, it can cause problems for sensitive equipment. Mitigation strategies include usage of separate frames for covering boxes and decreasing their surface area as shown in Figure 4. In addition, “bass traps” from recording-studio engineering can also be helpful.

图4。Before/after quiescent spectra of an advanced microscopy apparatus with “isolation box” attached or removed from the table-top^[4]. Top: accelerometer data. Bottom: Data observed at AFM tip. [Courtesy Thomas Perkins, JILA, National Institute of Standards and Technology and University of Colorado, Boulder].

Additional Application Photos of LaserTable-Base™

图片由IBM Corporation提供

图片由乌普萨拉大学（Uppsala University）提供

参考

[1]Jordan, S. and Anthony, P., Curr. Pharm. Biotechnology, 2009, 10, 515-521

[2] Yuan Shen等人，2013年，高级材料研究，706-708，亚博网站下载1423

[3] Abbondazieri et al, Nature, Nov. 24, 2005, 438(7067): 460–465.

[4] The authors thank Thomas Perkins for contributing this vivid before/after data.

This information has been sourced, reviewed and adapted from materials provided by TMC.

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