Insertion loss

I oise Transmission Reduction in HVACSystems. One common use of sound-absorbing treatment is to reduce noise transmission in heating, ventilating, and air-conditioning (HVAC) systems (6). The treatments ate used to reduce the transmission of fan noise and air turbulence noise through ducts into occupied spaces. Noise transmission reduction in duct systems is described in terms of insertion loss, the difference in sound power level or sound pressure level measured at a given location before and after installation of the treatment or sound attenuation, the reduction in sound power between two locations affected by a sound source. The units ate decibels. 

Acoustical Louvers. Acoustical louvers are used in building mechanical systems when exterior walls are penetrated for fresh air intake, exhaust, or rehef air, in situations where the impact of HVAC noise is of concern in the surrounding environment. The louvers consist of a series of hoUow sheet metal blades. The bottom faces of the louver blades are perforated and the blades are filled with fibrous sound-absorbing material. Typical acoustical louvers are 20 cm (8 in.) to 30 cm (12 in.) in depth. The amount of insertion loss they provide is limited. 

Another measure of vibration isolation is isolation efficiency, which is one minus transmissibihty and is usually defined as the percent of force transmitted through the isolator. Thus an isolator with a transmissibihty of 0.75 has an isolation efficiency of 25%. A third measure of vibration isolation is insertion loss, which is the difference between the transmitted vibration with the isolators in place and with no isolators. 

Test Methods. There is no standard test method for measuring transmissibihty or isolation efficiency of vibration isolation devices. The most common procedure is to measure the vibration transmitted to the supporting stmcture with the isolators in place and with the equipment supported on rigid blocking. From these measurements the insertion loss in dB is deterrnined by the following where T is the transmitted vibration with isolators in place and is the transmitted vibration with rigid supports. 

Insertion loss, weather louver The difference in simulated rain penetration between the test specimen and the calibration plate at the same test conditions. 

A hollow waveguide (HWG) is essentially a hollow tube that transports light from one end to the other either by multiple mirror reflection or by total internal reflection. The hollow structure gives them several advantages (i) a high power threshold, (ii) low insertion losses, (iii) no end reflections, (iv) a small beam divergence, (v) robustness and - especially important for sensor applications - (vi) a wide spectral transmission range. 

Figure 20. Calculated insertion loss for an SOI slab waveguide with surface roughness parameterized by cjms = 10 nm and = 500 nm.

Having dynamic insertion loss in dB. Forward (+) and reverse (—) flow. 

While propagation loss in electro-optically active waveguides remains a great concern, typically the greatest contribution to device insertion loss comes from mode mismatch between silica fibers and electro-optic waveguides. At... 

Fig. 29. Low insertion loss electro-optic modulator structure...

Of course the details of device and system performance will depend on the particular device or system under consideration. Our discussion will, however, focus primarily on limitations to system performance associated with material limitations rather than that of a particular device configuration. Parameters of particular interest include drive (Vjj) voltage, bandwidth, waveguide propagation loss, total device insertion loss, drive voltage stability, bias voltage stability, and optical power handling capability. 

Propagation losses through active materials are a serious concern however, these typically contribute only a small fraction to the total insertion loss. The most serious problem relating to minimization of optical loss with use of electro-optic modulators is that of loss associated with mode mismatch between passive and active optical circuitry. When tapered transitions and other device structures discussed in this review are used to reduce optical loss associated with mode mismatch, total device insertion losses in the order of 4-6 dB are obtained. Without such adequate attention to coupling losses, insertion loss can be 10 dB or greater. 

Figure 1.4 Measurement schemes used with the acoustic sensors illustrated in Figure 1.2.1.L. = insertion loss, fres = resonant frequency, Q = quality factor, and Zin = input impedance.

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