主题：请帮忙介绍蜂鸣器原理

小弟愚笨，请各位高手帮忙介绍一下压电蜂鸣器的工作原理？据我所知压电式片是靠压电陶瓷在电场下变形产生振动。但我发现如果把蜂鸣片的一面贴在腔体内壁上（这样并不影响压电陶瓷变形，应该说其中一面固定后，更利于另一面产生较大形变），声音会变小。蜂鸣器是否利用了铜基片产生谐振来提高灵敏度？

各位是否有办法将压电陶瓷片的灵敏度提高10dB？或是否知道有原理类似，但灵敏度更高的替代品？谢谢！

记得很久以前农村用的有线广播就是用压电陶瓷加全纸振膜来提高灵敏度的。

先分分类吧,

1.压垫式

2.电磁式

最常见.

邀请常州一带的高手来谈谈了!

INTRODUCTION TO PIEZO TRANSDUCERS

Transducers convert one form of energy to another. Piezo actuators convert electrical energy to mechanical energy. This is why they are referred to as "motors" (often linear motors). Piezo sensors convert mechanical energy into electrical energy. This is why they are referred to as "generators". In most cases, the same element can be used to perform either task.

Single sheets: can be energized to produce motion in the thickness, length, and width directions. They may be stretched or compressed to generate electrical output.

Thin 2-layer elements are the most versatile configuration of all. They may be used like single sheets (made up of 2 layers), they can be used to bend, or they can be used to extend. "Benders" achieve large deflections relative to other piezo transducers. "Extenders", being much stiffer, produce smaller deflections but higher forces.

Multilayered piezo stacks can deliver and support high force loads with minimal compliance, but they deliver small motions.

SINGLE-LAYER MOTORS (Sheets & Plates) When an electric field having the same polarity and orientation as the original polarization field is placed across the thickness of a single sheet of piezoceramic, the piece expands in the thickness or "longitudinal" direction (i.e. along the axis of polarization) as shown in Figure-1. At the same time, the sheet contracts in the "transverse" direction (i.e. perpendicular to the axis of polarization) as shown in Figure-2. When the field is reversed, the motions are reversed. Sheets and plates utilize this effect. The motion of a sheet in the thickness direction is extremely small (on the order of tens of nanometers). On the other hand, since the length dimension is often substantially greater than the thickness dimension, the transverse motion is generally larger (on the order of microns to tens of microns) . The transverse motion of a sheet laminated to the surface of a structure can induce it to stretch or bend, a feature often exploited in structural control systems.

Figure-1: Single Layer Longitudinal (d33) Motor Getting Thicker Figure-2: Single Layer Transverse (d31) Motor With Sides Contracting

2-LAYER MOTORS (Benders & Extenders) 2 -layer elements can be made to elongate, bend, or twist depending on the polarization and wiring configuration of the layers. A center shim laminated between the two piezo layers adds mechanical strength and stiffness, but reduces motion. "2-layer" refers to the number of piezo layers. A "2-layer" element actually has nine layers, consisting of: four electrode layers, two piezoceramic layers, two adhesive layers, and a center shim. The two layers offer the opportunity to reduce drive voltage by half when configured for parallel operation. Extension Motors: A 2-layer element behaves like a single layer when both layers expand (or contract) together. If an electric field is applied which makes the element thinner, extension along the length and width results. Typically, only motion along one axis is utilized, as demonstrated in Figure-3. Extender motion on the order of microns to tens of microns, and force from tens to hundreds of Newtons is typical. Bending Motors: A 2-layer element produces curvature when one layer expands while the other layer contracts. These transducers are often referred to as benders, bimorphs, or flexural elements. Bender motion on the order of hundreds to thousands of microns, and bender force from tens to hundreds of grams, is typical. Figures-4, 5 and 6 show several common bending configurations. The variety of mounting and motion options make benders a popular choice of design engineers.

Figure-3: 2-Layer Extension (d31) Motor With sides Extending For extension motors of the same thickness: Free Deflection (Xf) L Blocked Force (Fb) W Resonant Frequency (Fr) I / L Capacitance (C) L x W Figure-4: 2-Layer Bending Motor Mounted as a Cantilever For standard cantilevered benders of the same thickness: Free Deflection (Xf) L2 Blocked Force (Fb) W / L Resonant Frequency (Fr) I / L2 Capacitance (C) L x W Characteristics: End takes on an angle. Easy to mount. Figure-5: 2-Layer "S" Bending Motor Mounted as a Cantilever To convert standard cantilever performance to "S" bender performance: Free Deflection (Xf) = 1 / 2 x cantilever motion Blocked Force (Fb) = 1 / 2 x cantilever force Resonant Frequency (Fr) = same as cantilever frequency Capacitance (C) = same as cantilever capacitance Characteristics: end moves up and down in a parallel plane Figure-6: 2-Layer Bending Motor Mounted as a Simple Beam To convert cantilever performance to simple beam performance: Free Deflection (Xf) = 1 / 4 X cantilever motion Blocked Force (Fb) = 4 X cantilever force Resonant Frequency (Fr) = 3 X cantilever frequency Capacitance (C) = same as cantilever capacitance Characteristics: center moves up and down in a parallel plane.

MULTI-LAYER MOTORS (Stacks) Any number of piezo layers may be stacked on top of one another. Increasing the volume of piezoceramic increases the energy that may be delivered to a load. As the number of layers grows, so does the difficulty of accessing and wiring all the layers. Stack Motors: The co-fired stack shown in Figure-7 is a practical way to assemble and wire a large number of piezo layers into one monolithic structure. The tiny motions of each layer contribute to the overall displacement. Stack motion on the order of microns to tens of microns, and force from hundreds to thousands of Newtons is typical.

Figure-7: Co-fired Multi-Layer Stack Motor

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MOTOR PERFORMACE Piezoelectric actuators are usually specified in terms of their free deflection and blocked force. Free deflection (Xf) refers to displacement attained at the maximum recommended voltage level when the actuator is completely free to move and is not asked to exert any force. Blocked force (Fb) refers to the force exerted at the maximum recommended voltage level when the actuator is totally blocked and not allowed to move. Deflection is at a maximum when the force is zero, and force is at a maximum when the deflection is zero. All other values of simultaneous displacement and force are determined by a line drawn between these two points on a force versus deflection line, as shown in Figure-8. Generally, a piezo motor must move a specified amount and exert a specified force, which determines its operating point on the force vs. deflection line. An actuator is considered optimized for a particular application if it delivers the required force at one half its free deflection. All other actuators satisfying the design criteria will be larger, heavier, and consume more power.

Figure-8: Piezo Motor Performance (Force versus Deflection Diagram)

Making a 2-layer piezo element either bend or extend is determined by how it is polarized and wired. SERIES AND PARALLEL OPERATION Series Operation: Series operation refers to the case where supply voltage is applied across all piezo layers at once. The voltage on any individual layer is the supply voltage divided by the total number of layers. A 2-layer device wired for series operation uses only two wires (one attached to each outside electrode), as shown in Figure-17. Parallel Operation: Parallel operation refers to the case where the supply voltage is applied to each layer individually. This means accessing and attaching wires to each layer. A 2-layer bending element wired for parallel operation requires three wires (one attached to each outside electrode and one attached to the center shim), as shown in Figure-18. For the same motion, a 2-layer element poled for parallel operation needs only half the voltage required for series operation.

Figure-17: 2-Layer Bending Element Poled for Series Operation (2-wire) Figure-18: 2-Layer Bending Element Poled for Parallel Operation (3-wire)

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"X" AND "Y" POLING CONFIGURATIONS X-Poled: refers to the case where the polarization vectors for each of the 2 layers point in opposite directions, generally, towards each other. Y-Poled: refers to the case where the polarization vectors for each of the 2 layers point in the same direction.

Figure-19: X-Poled Element Figure-20: Y-Poled Element

ltem	Symbol(Unit)	P-1	P-2	P-3	P-4
Relative Dielectric Constant	ε11T/ε0	1490	1670	1930	3200
	ε33T/ε0	1510	1780	2100	4720
Loss Coefficient	tanδ (%)	0.4	1.2	1.4	2.2
Electro-mechanical Coupling Factor	Kp Radial (%)	56	57	65	65
	K31 Length (%)	32	32	38	36
	K33 Longitudinal (%)	62	65	71	68
	Kt Thickness (%)	45	48	51	47
	K15 Shear (%)	60	61	66	57
Piezoelectric Constant	d31 (10-12m/V)	-131	-148	-207	-303
	d33 (10-12m/V)	271	311	410	603
	d15 (10-12m/V)	400	431	550	592
	g31 (10-3V.m/N)	-10	-9	-11	-7
	g33 (10-3V.m/N)	20	20	22	14
	g15 (10-3V.m/N)	30	29	32	21
"Frequency Constant"	Np Radial (%)	2250	2210	2050	1960
	N31 Length (%)	1610	1540	1430	1370
	N33 Longitudinal (%)	1550	1540	1400	1350
	Nt Thickness (%)	2060	2060	2000	1970
	N15 Shear (%)	1010	1000	930	930
		1010
Mechanical Q	Qm	970	110	80	70
"Elastic Constant"	S11E (10-12m2/N)	12.4	13.4	15.8	16.7
	S12E (10-12m2/N)	-4.1	-4.8	-5.7	-5.9
	S13E (10-12m2/N)	-5.2	-5.4	-7.0	-7.5
	S33E (10-12m2/N)	14.3	14.5	18.1	18.8
	S44E (10-12m2/N)	34.0	34.2	40.6	38.8
	S66E (10-12m2/N)	33.0	36.5	43.0	45.4
	Y11E (1010N/m2)	8.1	7.5	6.3	6.7
Poisson's Ratio	σ E	0.33	0.36	0.36	0.36
Density	ρ (103Kg/m3)	7.8	7.9	7.8	8.0
"Temperature Coefficient"	TK(fr) (ppm/℃）	115	38	59	336
	TK(cf) (ppm/℃）	3500	-	4500	13500
Curie Temperature	TC (℃）	280	280	300	180
Linear Expansion Ratio	α (10-6/℃）	4	4	2	2
Bending Strength	τ (106N/m2)	113	103	99	85
Compressive Strength	K1c (106N/m1.5)	1.1	0.9	0.8	0.9
Applications		Ultrasonic cleaners for high power"	Sensors	Ultrasonic- sensors pickups Actuators Acoustic- application	Actuators Acoustic- application
Note:This table shows typical values measured on standard test piece.Qm,TK(fr) and TK(Cf) are measured for radial vibration mode.

　可惜是英文的．很多同行看不懂啊

压电材料本身特性比较复杂，是各向异性的。光Piezoelectric Constant(压电常数）就有几种模式。

是比较复杂。

搞超声换能器的对压电材料研究较多

比较复杂!
楼主所说的方式已经改变了震动模式.

压电陶瓷主要性能及参数




















































　　对于径向和横向长度伸缩振动模式，其频率常数为串联谐振频率与决定此频率的振子尺寸（直径或长度）的乘积。对于纵向长度厚度和伸缩切变振动模式，其频率常数为并联谐振频率与决定此频率的振子尺寸（长度或厚度）的乘积，其单位：HZ.M 

123学习中

专业的很啊！！！

太专业了。