Piezo buzzer structure and theory introduction
Piezoelectoric ceramic buzzer element have a simple structure in which piezoceramic element is glued to vibration plate. When alternating voltage is applied to piezoceramic element, the element expands or shrinks diametrically. This characteristic is utilized to make vibration plated bend to generate sounds.
The acoustic generating method can be roughly divided into self-drive oscillation method and external-drive oscillation method. The former shows the lowest impedance on the acoustic generator, and produces the sound by the positive feedback oscillation circuit to make resonance. Thereby, big sound pressure can be obtained by a simple circuit. While the latter selects an optional frequency and makes sound by the nonstable multivibrator, and it is used for the case having the oscillation circuit
There are 2 support methods for piezoelectric ceramic buzzers products:
A
Circumference Fixing Method - This method is to fix the outside circumference of the buzzer element to the supporting ring of the plate. Considerable sound pressure can be obtained covering a wide frequency range around the resonant frequency.
B
Nodal Mounting Method - This Method is to fix the nodal diameter of the buzzer element to the supporting ring of the plate. Loud sound pressure can be obtained. Flexible adhesives, such as silicon rubber, should be used between the buzzer element and the support ring.
RoHS, WEEE
The amount of waste electrical and electronic equipment (widely known as WEEE or e-waste) generated every year in the EU is increasing rapidly. It is now one of the fastest growing waste streams.
EU rules on WEEE aim to contribute to sustainable production and consumption. They address environmental and other issues caused by the growing number of discarded electronics in the EU.
The EU has introduced the WEEE Directive and the RoHS Directive to tackle the issue of the growing amount of WEEE.
RoHS
The Restriction of Hazardous Substances Directive (RoHS), which bans the use of certain hazardous substances (such as lead, mercury, cadmium, hexavalent chromium and some polybrominated flame retardants) in EEE.
RoHS is the EU Directive that restricts the use of certain hazardous substances in electrical and electronic products (EEE products). ROHS II, adopted in 2011, is an “open scope” directive which means that by July 22, 2019 it will apply to all EEE products that are “dependent on electric current or electromagnetic fields for at least one intended function. The current list of restricted substances is found in Annex II of the directive and currently includes: llead, lmercury, lcadmium, lhexavalent chromium, lpolybrominated biphenyls (PBB), lpolybrominated diphenyl ethers (PBDE), lbis(2-ethylhexyl) phthalate (DEHP), lbutyl benzyl phthalate (BBP), ldibutyl phthalate (DBP), and ldiisobutyl (DIBP).
RoHS mandates that EEE products must not contain more than 0.1% weight by weight of homogenous material of any listed substance. Cadmium is an exception to this rule where the EU prohibits products from containing more than 0.01% of this substance. Homogenous material means a material that cannot be mechanically disjointed into different materials.
WEEE
The Waste Electrical and Electronic Equipment Directive (WEEE), which sets out the responsibilities of EEE producers for the collection and recycling of their products at the end of their lifecycle.